CN111204701B - Micro-mirror with fully symmetrical differential capacitance angle feedback - Google Patents
Micro-mirror with fully symmetrical differential capacitance angle feedback Download PDFInfo
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B81—MICROSTRUCTURAL TECHNOLOGY
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- B81B7/00—Microstructural systems; Auxiliary parts of microstructural devices or systems
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B81—MICROSTRUCTURAL TECHNOLOGY
- B81B—MICROSTRUCTURAL DEVICES OR SYSTEMS, e.g. MICROMECHANICAL DEVICES
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- B81B7/0032—Packages or encapsulation
- B81B7/007—Interconnections between the MEMS and external electrical signals
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B81—MICROSTRUCTURAL TECHNOLOGY
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- B81C1/00015—Manufacture or treatment of devices or systems in or on a substrate for manufacturing microsystems
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- G—PHYSICS
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- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B26/00—Optical devices or arrangements for the control of light using movable or deformable optical elements
- G02B26/08—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light
- G02B26/0816—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light by means of one or more reflecting elements
- G02B26/0833—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light by means of one or more reflecting elements the reflecting element being a micromechanical device, e.g. a MEMS mirror, DMD
- G02B26/0841—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light by means of one or more reflecting elements the reflecting element being a micromechanical device, e.g. a MEMS mirror, DMD the reflecting element being moved or deformed by electrostatic means
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B81—MICROSTRUCTURAL TECHNOLOGY
- B81B—MICROSTRUCTURAL DEVICES OR SYSTEMS, e.g. MICROMECHANICAL DEVICES
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Abstract
The invention relates to the field of micro-nano optical devices, in particular to a micro-mirror with fully symmetrical differential capacitance angle feedback, which comprises a base, wherein a first insulating layer is arranged on the upper surface of the base, a first fixing layer is arranged on the upper surface of the first insulating layer, a second insulating layer is arranged on the upper surface of the first fixing layer, a reflecting element layer is arranged on the upper surface of the second insulating layer, a third insulating layer is arranged on the upper surface of the reflecting element layer, a second fixing layer is arranged on the upper surface of the third insulating layer, a fourth insulating layer is arranged on the upper surface of the second fixing layer, and a bonding pad is arranged on the fourth insulating layer. The angle sensor is integrated in the micro mirror, so that the micro mirror has compact structure, low power consumption and high process compatibility; the structure has vertical and plane symmetry, the driving is reliable and easy, the detection signal-to-noise ratio is high, and the complexity of the detection signal processing circuit is obviously reduced; can be applied to the application requirements from low frequency to high frequency.
Description
Technical Field
The invention relates to the field of micro-nano optical devices, in particular to a micro-mirror with fully symmetrical differential capacitance angle feedback.
Background
The micro-mirrors are micro-nano chips capable of effectively realizing light path regulation and control, and are widely applied to the fields of projection, imaging, laser navigation and the like. The most widely used micromirrors at present include electrostatic, electromagnetic, piezoelectric, and electrothermal micromirrors. Most of the micromirrors used at present adopt an open-loop control mode without angle feedback, and one serious disadvantage of the micromirrors is that the micromirrors lack effective angle feedback, which causes inaccurate control, and thus causes problems such as projection and imaging drift and navigation deviation. Some micromirrors still have more problems due to the angular feedback.
The currently applied micromirror, an angle feedback mode, is to set an angle detection device outside the micromirror for measuring the rotation angle of the micromirror, so that the angle feedback of the micromirror can be realized to a certain extent. For example, patent No. ZL 200410085274.1 discloses a micromirror solution for angle measurement using an optical assembly. However, the detection device of the method needs to add components such as a laser light source, a light path, a position sensor and the like into the micro-mirror module, so that the volume, the power consumption and the system complexity of the micro-mirror module are greatly increased. More importantly, due to factors such as installation errors, accurate angle feedback is difficult to achieve in the detection mode, and consistency of each micromirror module is poor.
There are also proposals for angle detection using an angle sensor integrated in a micromirror, for example, a micromirror using plate capacitance detection is designed for electrothermal driving in the published patent application No. CN109814251 a. According to the scheme, the capacitive plate is arranged on the substrate, and the relation between the capacitance value on the capacitive plate and the actual torsion angle of the micro-lens is used as a feedback value to perform signal feedback on the controller. The proposal reduces the components of the light path and the position sensor in the micro-mirror module, and reduces the complexity of the micro-mirror module to a certain extent. However, the scheme adopts the flat electrode element as the angle feedback capacitor, the feedback capacitor has a nonlinear relation between output and the corner of the micromirror, the corresponding relation is complex, the output conversion speed is slow, the solving and discarding error of the nonlinear relation is large, the flat electrode has small capacitance, the output signal is weak, the requirement on a processing circuit is high, and the signal to noise ratio is low. The scheme adopts an electrothermal driving mode, has low working frequency of the micromirror and is difficult to be suitable for high-frequency scanning.
A piezoelectric driven micro mirror integrated with a piezoelectric angle sensor is disclosed in paper "A Piezoelectrically Actuated Scaning Micromirror Integrated with Angle Sensors" (Key Engineering Materials 2011, 483:437-442). However, the piezoelectric driving and piezoelectric sensor are made of PZT materials, so that the process compatibility is poor, the processing difficulty is high, and the pollution to a chip production line is easy to generate. Meanwhile, the piezoelectric sensor has extremely high input impedance requirement on a processing circuit, and is complex in circuit and high in cost. Piezoelectric sensors have poor performance at low frequencies and are difficult to apply to low frequency scanning of micromirrors.
The comparison document 4-CN107976871A, a mirror surface comb tooth structure of a dynamic deformation controllable micro mirror and a processing method thereof, discloses a micro mirror comb tooth processing method and a corresponding comb tooth structure electrostatic driving micro mirror, and can realize integrated micro mirror angle detection, but the driving structure in the scheme does not have symmetry, so that the electrostatic driving control difficulty is high, and the control precision is easy to be low; more importantly, the detection structure does not have symmetry, cannot realize the detection output of complete difference, has low signal-to-noise ratio of detection signals and low sensitivity, has high requirements on a processing circuit, and is not beneficial to the improvement of control precision. Meanwhile, the micro-mirror comb structure processing method provided by the document needs to carry out photoetching after etching the deep groove structure, namely high-quality glue homogenizing is needed on the surface of the deep groove structure, and the complete equal-thickness coverage of the glue layer is ensured, so that the method is extremely difficult to realize in terms of technology.
In summary, the micromirror with no feedback has poor control accuracy, and the conventional angle measurement scheme of the micromirror with angle feedback has the problems of complex system, low signal to noise ratio, incapability of being simultaneously applicable to high frequency and low frequency, incapability of realizing static scanning, poor process compatibility and the like.
Disclosure of Invention
Aiming at the problems that the existing micromirror with no feedback has poor control precision, the angle measurement scheme of the micromirror with angle feedback has complex system, low signal to noise ratio, incapability of being simultaneously applicable to high frequency and low frequency, poor process compatibility and the like, the invention provides the micromirror with fully symmetrical differential capacitance angle feedback.
The implementation process of the invention is as follows:
the utility model provides a possess micro mirror of complete symmetry formula differential capacitance angle feedback, includes the base, the base upper surface is provided with first insulating layer, the upper surface of first insulating layer is provided with first fixed layer, the upper surface of first fixed layer is provided with the second insulating layer, the upper surface of second insulating layer is provided with the reflecting element layer, the upper surface of reflecting element layer is provided with the third insulating layer, the upper surface of third insulating layer is provided with the second fixed layer, the upper surface of second fixed layer is provided with the fourth insulating layer, be provided with the pad on the fourth insulating layer.
Further, the base is a hollow frame-shaped structure surrounded by surrounding frames, and the first insulating layer, the first fixing layer, the second insulating layer, the reflecting element layer, the third insulating layer, the second fixing layer and the fourth insulating layer are all overlapped and fixed on the hollow frame-shaped structure of the base in sequence.
Further, the first insulating layer, the second insulating layer, the reflecting element layer, the third insulating layer and the fourth insulating layer are all planar structures; the first fixing layer and the second fixing layer are of a ladder-shaped structure.
Further, the first insulating layer is formed by a plurality of insulating thin layers arranged on the upper surfaces around the hollow frame-shaped structure of the base; the first fixed layer comprises a first peripheral fixed structure, a first fixed capacitor, a second fixed capacitor, a third fixed capacitor, a fourth fixed capacitor, a first fixed driving element and a second fixed driving element; the inner sides of the two axial ends of the first peripheral fixed structure are provided with a first fixed capacitor, a second fixed capacitor, a third fixed capacitor and a fourth fixed capacitor; a first fixed driving element and a second fixed driving element are arranged on the inner sides of the two radial ends of the first peripheral fixed structure; the first fixed capacitor, the second fixed capacitor, the third fixed capacitor, the fourth fixed capacitor, the first fixed driving element and the second fixed driving element are all suspended comb tooth structures, and the root parts of the comb tooth structures are all connected with the first peripheral fixed structure; the lower surface of the comb tooth part is flush with the lower surface of the first peripheral fixing structure, and the upper surface of the comb tooth part exceeds the upper surface of the first peripheral fixing structure to form a stepped structure; the first peripheral fixing structure is connected with the first insulating layer.
Further, the second insulating layer is formed by a plurality of insulating thin layers arranged on the upper surface of the first peripheral fixing structure; the reflecting element layer comprises a reflecting mirror peripheral fixed structure, a mirror body, a first rotating capacitor, a second rotating capacitor, a third rotating capacitor, a fourth rotating capacitor, a first rotating driving element and a second rotating driving element; the first rotating capacitor, the second rotating capacitor, the third rotating capacitor, the fourth rotating capacitor, the first rotating driving element and the second rotating driving element are all of suspended comb tooth structures; the axial both sides limit of the mirror body is connected with the inside of the peripheral fixed knot of speculum structure axial both sides limit through first pivot, second pivot, the radial both sides limit of the mirror body is connected with the broach root of first rotation driving element, second rotation driving element respectively, first pivot both sides limit is connected with the broach root of first rotation electric capacity, second rotation electric capacity respectively, second pivot both sides limit is connected with the broach root of third rotation electric capacity, fourth rotation electric capacity respectively, the peripheral fixed knot of speculum constructs and is connected with the second insulating layer.
Further, the third insulating layer is formed by a plurality of insulating thin layers arranged on the upper surface of the reflector peripheral fixing structure; the second fixed layer comprises a second peripheral fixed structure, a fifth fixed capacitor, a sixth fixed capacitor, a seventh fixed capacitor, an eighth fixed capacitor, a third fixed driving element and a fourth fixed driving element; the inner sides of the two axial ends of the second peripheral fixed structure are provided with a fifth fixed capacitor, a sixth fixed capacitor, a seventh fixed capacitor and an eighth fixed capacitor; the inner sides of the two radial ends of the second peripheral fixed structure are provided with a third fixed driving element and a fourth fixed driving element; the fifth fixed capacitor, the sixth fixed capacitor, the seventh fixed capacitor, the eighth fixed capacitor, the third fixed driving element and the fourth fixed driving element are all suspended comb tooth structures, and the root parts of the comb tooth structures are all connected with the second peripheral fixed structure; the upper surface of the comb tooth part is flush with the upper surface of the second peripheral fixed structure, and the lower surface of the comb tooth part exceeds the lower surface of the second peripheral fixed structure to form a stepped structure; the second peripheral fixed structure is connected with the third insulating layer; the fourth insulating layer is composed of a plurality of insulating thin layers arranged on the upper surface of the second peripheral fixing structure.
Further, the first fixed driving element, the first rotating driving element and the third fixed driving element form a group of comb tooth driving capacitors; the second fixed driving element, the second rotating driving element and the fourth fixed driving element form a group of comb tooth driving capacitors; the first fixed capacitor and the first rotating capacitor form a group of comb tooth detection capacitors, and the fifth fixed capacitor and the first rotating capacitor form a group of comb tooth detection capacitors; the second fixed capacitor and the second rotating capacitor form a group of comb tooth detection capacitors, and the sixth fixed capacitor and the second rotating capacitor form a group of comb tooth detection capacitors; the third fixed capacitor and the third rotating capacitor form a group of comb tooth detection capacitors, and the seventh fixed capacitor and the third rotating capacitor form a group of comb tooth detection capacitors; the fourth fixed capacitor and the fourth rotating capacitor form a group of comb tooth detection capacitors, and the eighth fixed capacitor and the fourth rotating capacitor form a group of comb tooth detection capacitors; the comb tooth driving capacitor sets are symmetrically arranged; the comb tooth detection capacitor sets are symmetrically arranged.
Further, the base is connected with the first insulating layer, the first insulating layer and the first fixing layer, the first fixing layer and the second insulating layer, the second insulating layer and the reflecting element layer, the reflecting element layer and the third insulating layer, the third insulating layer and the second fixing layer, and the second fixing layer and the fourth insulating layer in a bonding mode; the base may be a hollow frame-like structure of circular, oval, diamond, rectangular or square shape.
Further, the material of the base, the first fixing layer and the second fixing layer is any one of monocrystalline silicon, polycrystalline silicon or amorphous silicon; the material of the reflecting element layer is any one of monocrystalline silicon, polycrystalline silicon, amorphous silicon or high molecular polymer; the resistivity of the first fixed layer, the reflective element layer and the second fixed layer is less than 1Ω cm; the first insulating layer, the second insulating layer, the third insulating layer and the fourth insulating layer are made of any one of silicon oxide, silicon nitride, silicon carbide or high-molecular polymer; the resistivity of the first insulating layer, the second insulating layer, the third insulating layer and the fourth insulating layer is larger than 10Ω & cm.
Further, the high molecular polymer is selected from any one of polydimethylsiloxane, SU8 glue, epoxy resin, polyamide, polyimide, polypropylene, polyethylene, polyvinyl chloride, polystyrene, polyethylene terephthalate and polymethyl methacrylate.
The manufacturing method of the micro-mirror with the complete symmetrical differential capacitance angle feedback comprises the following steps: (1) preparing a silicon wafer; (2) front side first lithography; (3) first dry etching of the front surface; (4) back side first lithography; (5) back surface first dry etching; (6) front side oxygen ion implantation; (7) backside oxygen ion implantation; (8) front thinning and polishing; (9) back thinning and polishing; (10) front side second lithography; (11) front side second dry etching; (12) backside second lithography; (13) second dry etching of the back surface; (14) preparing a base; (15) Bonding the base with the silicon wafer subjected to the second dry etching on the back surface in the step 13; (16) structural release; (17) preparing a front-side oxide layer; and (18) manufacturing a bonding pad.
The manufacturing method of the micromirror with the completely symmetrical differential capacitance angle feedback comprises the following steps:
(1) Preparing a silicon wafer which is monocrystalline silicon or polycrystalline silicon, and polishing the two sides, wherein the thickness of the silicon wafer is 50-300 mu m, and the resistivity is less than 0.01 omega-cm;
(2) First photoetching on the front side, and defining a corresponding pattern of changing the position of the front side oxygen ion implantation area in the vertical direction;
(3) The front surface is etched for the first time by a dry method, and a groove-shaped structure is etched on the front surface of the silicon wafer and used for subsequent oxygen ion implantation, so that the position change of the oxygen ion implantation in the vertical direction is realized; removing photoresist on the front surface of the silicon wafer after the dry etching is finished; the depth of the groove-shaped structure realized in the step is 10nm-10 mu m;
(4) Performing first photoetching on the back, reversing the silicon wafer, performing photoetching on the back, wherein the mask pattern is a mirror image of the mask pattern used in the first photoetching on the front, and defining a corresponding pattern with the position change of the oxygen ion implantation area on the back in the vertical direction;
(5) The back surface is etched for the first time by a dry method, and a groove-shaped structure is etched on the back surface of the silicon wafer and used for subsequent oxygen ion implantation, so that the position change of the oxygen ion implantation in the vertical direction is realized; removing photoresist on the back of the silicon wafer after the dry etching is finished, wherein the back groove-shaped structure realized in the step is symmetrical to the front groove-shaped structure realized in the step (3) with respect to the neutral layer of the silicon wafer; the depth of the groove-shaped structure on the back surface realized by the step is 10nm-10 mu m;
(6) Performing front oxygen ion implantation, namely performing integral oxygen ion implantation on the front of the silicon wafer, and selecting proper implantation energy according to the depth of the oxygen ions; forming an oxide layer at a position which is a certain distance away from the front surface of the silicon wafer after oxygen ion implantation; the different implantation energies, the different distances between the oxide layer and the front surface of the silicon wafer, the lower the energy, the smaller the distance, the larger the energy, and the larger the distance; because the dry etching is performed in the step (3), the front surface of the silicon wafer forms a groove-shaped structure before oxygen ion implantation, namely, the front surface of the silicon wafer is not a plane but has high and low fluctuation, so that in the same oxygen ion implantation, the distance between an oxide layer and the front surface of the silicon wafer is the same although the implantation energy is fixed, and the front surface of the silicon wafer has high and low fluctuation, so that the oxide layer formed by implantation is not a plane, but has fluctuation in the vertical direction corresponding to the fluctuation of the front surface of the silicon wafer; the front oxygen ion implantation depth is 5 μm-100 μm;
(7) Performing back oxygen ion implantation, namely performing overall oxygen ion implantation on the back of the silicon wafer, and selecting proper implantation energy according to the depth of the oxygen ions; forming an oxide layer at a position which is a certain distance away from the back surface of the silicon wafer after oxygen ion implantation; the different implantation energies, the different distances between the oxide layer and the back surface of the silicon wafer, the lower the energy, the smaller the distance, the larger the energy, and the larger the distance; since the dry etching is performed in the step (3), the back surface of the silicon wafer is formed into a groove-like structure before the oxygen ion implantation, that is, the back surface of the silicon wafer is not flat but has high and low fluctuation, so that in the same oxygen ion implantation, the distance between the oxide layer and the back surface of the silicon wafer is the same although the implantation energy is constant, and the oxide layer formed by the implantation is not a flat surface but has fluctuation in the vertical direction corresponding to the fluctuation of the back surface of the silicon wafer because the back surface of the silicon wafer has high and low fluctuation. The depth of the back oxygen ion implantation is equal to that of the front oxygen ion implantation in the step (6);
(8) The front surface is thinned and polished, a groove-shaped structure of the front surface for assisting oxygen ion implantation is removed, and the polished surface of the front surface is restored;
(9) Thinning and polishing the back surface, removing a groove-shaped structure of the back surface for assisting oxygen ion implantation, and recovering the polished surface of the back surface; after the process is completed, the silicon wafer forms a five-layer structure, namely a first fixed layer, a second insulating layer, a reflector element layer, a third insulating layer and a second fixed layer from bottom to top; wherein the reflector element layer has a planar structure with a thickness of 5-100 μm, the first and second fixing layers have a stepped structure with a thickness of 5-100 μm; the first fixed layer and the second fixed layer are symmetrical about the mirror element layer center plane; the thickness of the second insulating layer is 0.2-5 μm, and the second insulating layer and the third insulating layer are symmetrical about the central plane of the reflector element layer;
(10) A third fixed driving element, a fourth fixed driving element, a fifth fixed capacitor, a sixth fixed capacitor, a seventh fixed capacitor and a pattern corresponding to the eighth fixed capacitor are defined by front second photoetching;
(11) Etching the front surface for the second time by dry etching to form a third fixed driving element, a fourth fixed driving element, a fifth fixed capacitor, a sixth fixed capacitor, a seventh fixed capacitor and an eighth fixed capacitor structure; removing photoresist on the front surface of the silicon wafer after etching is completed; the etching depth is equal to the front oxygen ion implantation depth in the step (6);
(12) Performing second photoetching on the back, namely reversing the silicon wafer, and performing photoetching on the back of the silicon wafer to define patterns corresponding to a first fixed driving element, a second fixed driving element, a first fixed capacitor, a second fixed capacitor, a third fixed capacitor and a fourth fixed capacitor;
(13) Etching the back surface for the second time by dry method to etch out a first fixed driving element, a second fixed driving element, a first fixed capacitor, a second fixed capacitor, a third fixed capacitor and a fourth fixed capacitor structure; removing photoresist on the back of the silicon wafer after etching is completed; the etching depth is equal to the back oxygen ion implantation depth in the step 7;
(14) Preparing a base, wherein a monocrystalline silicon wafer or a polycrystalline silicon wafer is adopted, the resistivity is larger than 0.1 omega-cm, and the thickness is 100-800 mu m; firstly, depositing or thermally oxidizing a layer of oxide layer on the surface of a monocrystalline silicon wafer or a polycrystalline silicon wafer used for preparing a base, wherein the oxide layer is used as a first insulating layer, and the thickness of the oxide layer is 0.2-5 mu m; manufacturing a base with a frame-shaped structure by adopting a dry etching or wet etching method;
(15) Bonding the base with the silicon wafer finished in the step 13 (back surface second dry etching); the upper surface of the base contacts with the lower surface of the silicon wafer finished in the step 13 during bonding, the hollow area of the frame-shaped structure of the base is larger than the area of the first fixed driving element, the second fixed driving element, the first fixed capacitor, the second fixed capacitor, the third fixed capacitor and the fourth fixed capacitor corresponding to the silicon wafer finished in the step 13, so that the bonding alignment requirement is low, only the alignment tolerance of plus or minus 1-50 mu m is ensured, and the specific tolerance is determined according to the specific device size;
(16) The structure is released, the bonded silicon wafer is put into a hydrofluoric acid wet etching tank or a hydrogen fluoride dry etching device, and the two oxide layers formed in the step (6) and the step (7) are removed by etching, so that the release of the structures contained in the first fixed layer, the reflector element layer and the second fixed layer is realized;
(17) Preparing a front oxide layer, namely depositing a silicon oxide layer on the upper surface of the silicon wafer after the structure release in the step (16) is completed, or preparing the oxide layer by a thermal oxidation method to serve as a fourth insulating layer; the thickness of the fourth insulating layer is 0.2-5 mu m;
(18) And after the structure is manufactured, manufacturing the bonding pad by adopting a sputtering or vapor plating mode, wherein the mask is a hard mask.
The alternating driving signal used by the micro mirror with the fully symmetrical differential capacitance angle feedback is selected from square waves, sawtooth waves, triangular waves, sine waves or cosine waves.
The driving structure of the micromirror with the completely symmetrical differential capacitance angle feedback has the symmetry in the vertical direction, and the height difference exists between the comb teeth of the fixed driving element and the comb teeth of the rotary driving element in the vertical direction, so that torque can be generated after the driving voltage is applied, and parameter excitation is not needed; the driving structure has plane symmetry at the same time, so that the driving force is symmetrical, and the micro-mirror vibration control precision is high. The detection structure has vertical and plane symmetry, the detection signals are in differential output, the detection output signals are strong, the signal to noise ratio is high, and the requirements of a processing circuit following the detection signals are low. The specific driving and detecting principle is as follows:
The first and fourth fixed driving elements apply a driving voltage Vd1, the second and third fixed driving elements apply a driving voltage Vd2, and the first and second rotary driving elements are grounded. The fourth rotating capacitor, the second rotating capacitor, the third rotating capacitor and the fourth rotating capacitor are all grounded. The mirror element generates rotational vibration about the rotational axis under the influence of electrostatic forces. Wherein Vd1 and Vd2 are square wave signals which are mutually opposite in phase, the minimum value of the two is 0, and the amplitude is Vd. When vd1=vd, the mirror element rotation direction is defined as the forward direction, and the output values δc1, δc3, δc6 and δc8 of the first, third, sixth and eighth fixed capacitances increase, and the output values δc2, δc4, δc5 and δc7 of the second, fourth, fifth and seventh fixed capacitances decrease. Due to structural symmetry, δc1=δc3=δc6=δc8= - δc2= - δc4= - δc5= - δc7=δc, and the total detected capacitance change amount Δc= (δc1+δc3+δc6+δc8) - (- δc2- δc4- δc5- δc7) =8δc=f (θ) using a differential output method. When vd2=vd, the mirror element rotation direction is defined as negative, and the output values δc1, δc3, δc6 and δc8 of the first, third, sixth and eighth fixed capacitances decrease, and the output values δc2, δc4, δc5 and δc7 of the second, fourth, fifth and seventh fixed capacitances increase. Due to structural symmetry, - δc1= - δc3= - δc6= - δc8=δc2=δc4=δc5=δc7=δc, and the total detected capacitance change amount Δc= (δc2+δc4+δc5+δc7) - (- δc1- δc3- δc6- δc8) =8δc=f (θ) is also applied by the differential output method.
The total detected capacitance change ΔC is a function of the mirror element rotation angle θ, and ΔC is introduced as real-time angle feedback to the drive signals Vd1 and Vd2, which are adjusted in real-time.
The micro mirror is driven by static electricity, and the capacitive sensor performs angle feedback to form closed-loop control, so that the control precision of the micro mirror is improved. The micro mirror provided by the invention is integrated with the angle sensor, so that the micro mirror has the advantages of compact structure, low power consumption and high process compatibility; the structure has vertical and plane symmetry, the driving is reliable and easy, the detection signal-to-noise ratio is high, and the complexity of the detection signal processing circuit is obviously reduced; can be applied to the application requirements from low frequency to high frequency.
The bonding connection mode adopts normal temperature bonding (Wang Chenxi, king, xu Jikai, wang Yuan, tian Yangong. Wafer direct bonding and room temperature bonding technology research progress [ J ]. Precision forming engineering 2018.10 (1): 67-73) if the used material is a high molecular material; in the case of inorganic materials, all bonding methods and anodic bonding methods (Chen Daming, hu Lifang, fang Rong, meng Qingsen. Si-glass-Si anodic bonding mechanism and mechanical properties [ J ]. Welding journal, 2019,40 (02): 123-127+166.) were employed in reference (Wang Chenxi, king, xu Jikai, wang Yuan, tian Yangong. Wafer direct bonding and room temperature bonding techniques research progress [ J ]. Precision forming engineering, 2018.10 (1): 67-73).
The invention has the positive effects that:
(1) And an angle sensor is integrated in the micromirror to perform real-time angle detection of the micromirror, so that the control precision of the micromirror is effectively improved.
(2) The integrated design of the micro-mirror and the angle sensor is that one chip contains the micro-mirror and the sensor, and the structure is compact, the volume is small, and the power consumption is low.
(3) The chip containing the micro-mirror and the sensor is manufactured by adopting a micro-nano manufacturing process once flow sheet, the process compatibility is high, the structural and functional consistency and stability of the micro-mirror are high, and the subsequent packaging is simple.
(4) The angle sensor adopts a fully symmetrical capacitive sensor design, so that differential output of the sensor is realized, an output signal is large, noise is effectively restrained, the angle detection sensitivity is high, and the requirement on a subsequent processing circuit is low.
(5) The micro-mirror driving structure adopts a completely symmetrical design, and the initial vertical position difference exists between the rotating capacitor and the static capacitor, so that the problem that the driving of the planar micro-mirror structure is difficult to start is avoided, the micro-mirror driving structure can be suitable for static scanning and dynamic scanning, and has the advantages of wide application range and high control precision.
(6) The design of the electrostatic driving and capacitive detection sensor ensures that the micro-mirror can meet the scanning requirement from low frequency to high frequency.
(7) The micro-mirror manufacturing method provided by the invention only needs one-time bonding, and the bonding function is to connect the base and the upper structure, the alignment precision requirement is low, the alignment precision of 1-50 mu m is only required to be met, and the micro-mirror manufacturing method is easy to realize in the prior art.
(8) The invention realizes the manufacture of the oxide layer in the silicon wafer by adopting the mode of oxygen ion implantation after etching, the manufactured oxide layer undulates along with the undulation of the surface structure of the silicon wafer in the vertical direction, and realizes the manufacture of the bonding-free vertical staggered structure by the subsequent oxide layer release process, thereby completely eliminating the alignment error caused by the bonding process adopted by the traditional vertical staggered structure manufacture. Avoiding the problems of uneven bonding, fragments and the like which are easy to occur in bonding.
Drawings
FIG. 1 is an overall isometric view of a micromirror;
FIG. 2 is a general left side view and a partial enlarged view of a micromirror;
FIG. 3 is a top view of the micromirror as a whole;
FIG. 4 is a general back view of a micromirror;
FIG. 5 is an isometric view of a base;
FIG. 6 is an isometric view of a first insulating layer;
FIG. 7 is an isometric view of a first fixed layer;
FIG. 8 is an isometric view of a second insulating layer;
FIG. 9 is an isometric view of a mirror element layer;
FIG. 10 is an isometric view of a third insulating layer;
FIG. 11 is an isometric view of a second fixed layer;
FIG. 12 is an isometric view of a fourth insulating layer;
FIG. 13 is a comb drive capacitor formed by a fixed drive element and a rotary drive element;
fig. 14 is a timing chart of the driving voltages Vd1 and Vd 2;
fig. 15 is a forward rotation state of the micromirror at the driving voltage vd1=vd;
fig. 16 is a negative rotation state of the micromirror at the driving voltage vd2=vd;
FIG. 17 is a comb detection capacitor formed by a fixed capacitor and a rotating capacitor;
FIG. 18 shows the detected capacitance state when the micromirror is rotated in the forward direction;
FIG. 19 shows the detected capacitance state during negative rotation of the micromirror;
FIG. 20 (1) is a schematic diagram of a silicon wafer prepared in example 3; FIG. 20 (2) is a schematic view of the front side first lithography of example 3; FIG. 20 (3) is a schematic view of the first etching of the front surface of example 3; FIG. 20 (4) is a schematic view of the first lithography on the back side of example 3; FIG. 20 (5) is a schematic view of the first etching of the back surface of example 3; FIG. 20 (6) is a schematic view of the front side oxygen ion implantation of example 3; FIG. 20 (7) is a schematic view of the back side oxygen ion implantation of example 3; FIG. 20 (8) is a schematic view of the front surface thinning polishing of example 3; FIG. 20 (9) is a schematic view of the back surface thinning polishing of example 3; FIG. 20 (10) is a schematic view of the front side second lithography of example 3; FIG. 20 (11) is a schematic view of the second etching of the front surface of example 3; FIG. 20 (12) is a schematic diagram of the second lithography on the back side of example 3; FIG. 20 (13) is a schematic view of the second etching of the back surface of example 3; FIG. 20 (14) is a schematic view of the preparation base of example 3; FIG. 20 (15) is a schematic illustration of the bonding of example 3; FIG. 20 (16) is a schematic view showing the release of the structure of example 3; FIG. 20 (17) is a schematic illustration of the front side oxide layer preparation of example 3; FIG. 20 (18) is a schematic diagram of a bonding pad fabrication according to embodiment 3;
FIG. 21 is a schematic view of a micromirror fabricated in example 4;
FIG. 22 is a schematic diagram of a micromirror fabricated in example 5;
in the figure, 1 pedestal, 2 first insulating layers, 3 first fixed layers, 31 first peripheral fixed structures, 301 first fixed capacitances, 302 second fixed capacitances, 303 third fixed capacitances, 304 fourth fixed capacitances, 311 first fixed driving elements, 312 second fixed driving elements, 4 second insulating layers, 5 reflecting element layers, 51 mirror peripheral fixed structures, 530 mirror bodies, 501 first rotating capacitances, 502 second rotating capacitances, 503 third rotating capacitances, 504 fourth rotating capacitances, 511 first rotating driving elements, 512 second rotating driving elements, 521 first rotating shafts, 522 second rotating shafts, 6 third insulating layers, 7 second fixed layers, 71 second peripheral fixed structures, 705 fifth fixed capacitances, 706 sixth fixed capacitances, 707 seventh fixed capacitances, 708 eighth fixed capacitances, 713 third fixed driving elements, 714 fourth fixed driving elements, 8 fourth insulating layers, 9 pads.
Detailed Description
The invention is further illustrated below with reference to examples.
Aiming at the problems that the existing micromirror with no feedback has poor control precision, the angle measurement scheme of the micromirror with angle feedback has complex system, low signal to noise ratio, incapability of being simultaneously applicable to high frequency and low frequency, poor process compatibility and the like, the invention provides the micromirror with fully symmetrical differential capacitance angle feedback. The micromirror provided by the invention is integrated with the angle detection sensor, the signal to noise ratio of the angle detection sensor is high, the angle of the micromirror can be effectively detected in real time, and the control precision of the micromirror is improved; meanwhile, due to the adoption of an integrated angle detection sensor design, the micro-mirror chip comprises an angle sensor, and the micro-mirror has the advantages of compact structure, small volume and low power consumption; the micro-mirror chip is formed by adopting a micro-nano processing technology and is formed by one-time flow sheet, the micro-mirror structure and function are high in consistency and stability, and the subsequent packaging is simple; meanwhile, the micro-mirror processing technology and the micro-mirror material are conventional micro-nano processing technology and micro-nano processing material, and are high in process compatibility. The angle detection sensor adopts a symmetrical capacitive sensor design, so that the sensitivity is high and the requirement on a subsequent processing circuit is low. The micro mirror of the invention can be suitable for the requirement from low frequency to high frequency by adopting an electrostatic driving and capacitive detection sensor.
Example 1
The micro mirror with fully symmetrical differential capacitance angle feedback, see fig. 1-3, comprises a base 1, wherein a first insulating layer 2 is arranged on the upper surface of the base 1, a first fixing layer 3 is arranged on the upper surface of the first insulating layer 2, a second insulating layer 4 is arranged on the upper surface of the first fixing layer 3, a reflecting element layer 5 is arranged on the upper surface of the second insulating layer 4, a third insulating layer 6 is arranged on the upper surface of the reflecting element layer 5, a second fixing layer 7 is arranged on the upper surface of the third insulating layer 6, a fourth insulating layer 8 is arranged on the upper surface of the second fixing layer 7, and a bonding pad 9 is arranged on the fourth insulating layer 8. The number of bonding pads is 13. The bonding pads are electrically communicated with each structural layer through TSV (through hole communication) mode (TSV technology is a common technology, see in detail: hu Zhenggao, cap UK, xu Gaowei, luo Le. TSV technology research [ J ] sensing technology report applied to MOEMS integration, 2019,32 (05): 649-653).
Further, the base 1 is a hollow frame structure surrounded by peripheral frames, as shown in fig. 4-5, and the first insulating layer 2, the first fixing layer 3, the second insulating layer 4, the reflecting element layer 5, the third insulating layer 6, the second fixing layer 7, and the fourth insulating layer 8 are all stacked and fixed on the hollow frame structure of the base 1 in order.
Further, the first insulating layer 2, the second insulating layer 4, the reflective element layer 5, the third insulating layer 6, and the fourth insulating layer 8 are all planar structures; the first fixing layer 3 and the second fixing layer 7 have a stepped structure.
Further, as shown in fig. 6, the first insulating layer 2 is formed of a plurality of insulating thin layers disposed on the upper surface of the periphery of the hollow frame-like structure of the base 1; which serves to interrupt the electrical connection between the base 1 and the first fixing layer 3. The material of the insulating thin layer is high-resistance materials such as silicon oxide, silicon nitride and the like.
As shown in fig. 7, the first fixed layer 3 includes a first peripheral fixed structure 31, a first fixed capacitor 301, a second fixed capacitor 302, a third fixed capacitor 303, a fourth fixed capacitor 304, a first fixed driving element 311, and a second fixed driving element 312; a first fixed capacitor 301, a second fixed capacitor 302, a third fixed capacitor 303 and a fourth fixed capacitor 304 are arranged on the inner sides of the two axial ends of the first peripheral fixed structure 31; the inner sides of the two radial ends of the first peripheral fixed structure 31 are provided with a first fixed driving element 311 and a second fixed driving element 312; the first fixed capacitor 301, the second fixed capacitor 302, the third fixed capacitor 303, the fourth fixed capacitor 304, the first fixed driving element 311 and the second fixed driving element 312 are all suspended comb structures, and the root parts of the comb structures are all connected with the first peripheral fixed structure 31; the lower surface of the comb teeth part is flush with the lower surface of the first peripheral fixing structure 31, and the upper surface of the comb teeth part exceeds the upper surface of the first peripheral fixing structure 31 to form a stepped structure; the first peripheral fixing structure 31 is connected to the first insulating layer 2.
Further, as shown in fig. 8, the second insulating layer 4 is composed of a plurality of insulating thin layers provided on the upper surface of the first peripheral fixing structure 31; which serves to break the electrical connection between the first fixing layer 3 and the mirror element layer 5. The material of the insulating thin layer is high-resistance materials such as silicon oxide, silicon nitride and the like.
As shown in fig. 9, the reflective element layer 5 includes a mirror peripheral fixing structure 51, a mirror body 530, a first rotary capacitor 501, a second rotary capacitor 502, a third rotary capacitor 503, a fourth rotary capacitor 504, a first rotary driving element 511, and a second rotary driving element 512; the first rotary capacitor 501, the second rotary capacitor 502, the third rotary capacitor 503, the fourth rotary capacitor 504, the first rotary driving element 511 and the second rotary driving element 512 are all suspended comb structures; the two axial sides of the mirror body 530 are connected to the inner sides of the two axial sides of the peripheral fixing structure 51 of the mirror through the first rotating shaft 521 and the second rotating shaft 522, the two radial sides of the mirror body 530 are respectively connected to the roots of the teeth of the first rotating driving element 511 and the second rotating driving element 512, the two sides of the first rotating shaft 521 are respectively connected to the roots of the teeth of the first rotating capacitor 501 and the second rotating capacitor 502, the two sides of the second rotating shaft 522 are respectively connected to the roots of the teeth of the third rotating capacitor 503 and the fourth rotating capacitor 504, and the peripheral fixing structure 51 of the mirror is connected to the second insulating layer 4.
Further, as shown in fig. 10, the third insulating layer 6 is composed of a plurality of insulating thin layers provided on the upper surface of the mirror peripheral fixing structure 51; which serves to break the electrical connection between the mirror element layer 5 and the second fixing layer 7. The material of the insulating thin layer is high-resistance materials such as silicon oxide, silicon nitride and the like.
As shown in fig. 11, the second fixed layer 7 includes a second peripheral fixed structure 71, a fifth fixed capacitor 705, a sixth fixed capacitor 706, a seventh fixed capacitor 707, an eighth fixed capacitor 708, a third fixed driving element 713, and a fourth fixed driving element 714; a fifth fixed capacitor 705, a sixth fixed capacitor 706, a seventh fixed capacitor 707 and an eighth fixed capacitor 708 are arranged on the inner sides of the two axial ends of the second peripheral fixed structure 71; the second peripheral fixed structure 71 is provided inside of both radial ends thereof with a third fixed driving element 713 and a fourth fixed driving element 714; the fifth fixed capacitor 705, the sixth fixed capacitor 706, the seventh fixed capacitor 707, the eighth fixed capacitor 708, the third fixed driving element 713 and the fourth fixed driving element 714 are all suspended comb structures, and the root parts of the comb structures are all connected with the second peripheral fixed structure 71; the upper surface of the comb tooth part is flush with the upper surface of the second peripheral fixing structure 71, and the lower surface of the comb tooth part exceeds the lower surface of the second peripheral fixing structure 71 to form a stepped structure; the second peripheral fixing structure 71 is connected to the third insulating layer 6;
As shown in fig. 12, the fourth insulating layer 8 is formed of a plurality of insulating thin layers provided on the upper surface of the second peripheral fixing structure 71; the function of the micro-mirror chip is to provide the required electrical isolation for the lead connection of the micro-mirror chip and the peripheral circuit. The material of the insulating thin layer is high-resistance materials such as silicon oxide, silicon nitride and the like.
Further, as shown in fig. 13, the first fixed driving element 311, the first rotating driving element 511 and the third fixed driving element 713 form a group of differential comb-tooth driving capacitors; the second fixed driving element 312, the second rotary driving element 512 and the fourth fixed driving element 714 form a set of differential comb-tooth driving capacitors;
the first and fourth fixed driving elements 311 and 714 apply a driving voltage Vd1, the second and third fixed driving elements 312 and 713 apply a driving voltage Vd2, and the first and second rotary driving elements 511 and 512 are grounded. Where Vd1 and Vd2 are square wave signals that are mutually inverted, the minimum value of which is 0, the amplitude of which is Vd, and the timings of driving voltages Vd1 and Vd2 are as shown in fig. 14.
When vd1=vd, the mirror element rotation direction is defined as the forward direction, as shown in fig. 15; when vd2=vd, the mirror element rotation direction is defined as negative, as shown in fig. 16.
As shown in fig. 17, the first fixed capacitor 301 and the first rotating capacitor 501 form a set of comb-teeth detecting capacitors, and the fifth fixed capacitor 705 and the first rotating capacitor 501 form a set of comb-teeth detecting capacitors; the second fixed capacitor 302 and the second rotating capacitor 502 form a group of comb tooth detection capacitors, and the sixth fixed capacitor 706 and the second rotating capacitor 502 form a group of comb tooth detection capacitors; the third fixed capacitor 303 and the third rotating capacitor 503 form a group of comb tooth detection capacitors, and the seventh fixed capacitor 707 and the third rotating capacitor 503 form a group of comb tooth detection capacitors; the fourth fixed capacitor 304 and the fourth rotating capacitor 504 form a set of comb detection capacitors, and the eighth fixed capacitor 708 and the fourth rotating capacitor 504 form a set of comb detection capacitors; the comb tooth driving capacitor sets are symmetrically arranged; the comb tooth detection capacitor sets are symmetrically arranged.
The first rotary capacitor 501, the second rotary capacitor 502, the third rotary capacitor 503 and the fourth rotary capacitor 504 are all grounded. The mirror element generates rotation vibration around the rotating shaft under the action of electrostatic force, and the output of the corresponding comb tooth detection capacitor group is changed.
When the micromirror rotates in the forward direction, as shown in fig. 18, the output values δc1, δc3, δc6 and δc8 of the first, third, sixth and eighth fixed capacitances 301, 303, 706 and 708 increase; the output values δc2, δc4, δc5 and δc7 of the second, fourth, fifth and seventh fixed capacitances 302, 304, 705 and 707 decrease. Due to structural symmetry, δc1=δc3=δc6=δc8= - δc2= - δc4= - δc5= - δc7=δc, and the total detected capacitance change amount Δc= (δc1+δc3+δc6+δc8) - (- δc2- δc4- δc5- δc7) =8δc=f (θ) using a differential output method.
When the micromirror rotates negatively, as shown in fig. 19, the output values δc1, δc3, δc6 and δc8 of the first, third, sixth and eighth fixed capacitances 301, 303, 706 and 708 decrease; the output values δc2, δc4, δc5 and δc7 of the second, fourth, fifth and seventh fixed capacitances 302, 304, 705 and 707 increase. Due to structural symmetry, - δc1= - δc3= - δc6= - δc8=δc2=δc4=δc5=δc7=δc, and the total detected capacitance change amount Δc= (δc2+δc4+δc5+δc7) - (- δc1- δc3- δc6- δc8) =8δc=f (θ) is also applied by the differential output method.
The total detected capacitance change delta C is a function of the rotation angle theta of the reflector element, delta C is used as real-time angle feedback to be introduced into the driving signals Vd1 and Vd2, and the driving signals are adjusted according to the real-time angle feedback, so that the driving control precision can be effectively improved.
Further, the base 1 is connected with the first insulating layer 2, the first insulating layer 2 is connected with the first fixing layer 3, the first fixing layer 3 is connected with the second insulating layer 4, the second insulating layer 4 is connected with the reflecting element layer 5, the reflecting element layer 5 is connected with the third insulating layer 6, the third insulating layer 6 is connected with the second fixing layer 7, and the second fixing layer 7 is connected with the fourth insulating layer 8 in a bonding mode; the base 1 may be a hollow frame-like structure of a circle, an ellipse, a diamond, a rectangle or a square.
Example 2
The micro mirror with fully symmetrical differential capacitance angle feedback comprises a base 1, wherein a first insulating layer 2 is arranged on the upper surface of the base 1, a first fixing layer 3 is arranged on the upper surface of the first insulating layer 2, a second insulating layer 4 is arranged on the upper surface of the first fixing layer 3, a reflecting element layer 5 is arranged on the upper surface of the second insulating layer 4, a third insulating layer 6 is arranged on the upper surface of the reflecting element layer 5, a second fixing layer 7 is arranged on the upper surface of the third insulating layer 6, a fourth insulating layer 8 is arranged on the upper surface of the second fixing layer 7, and a bonding pad 9 is arranged on the fourth insulating layer 8. The base 1 is a hollow frame structure surrounded by peripheral frames, as shown in fig. 4-5, and the first insulating layer 2, the first fixing layer 3, the second insulating layer 4, the reflecting element layer 5, the third insulating layer 6, the second fixing layer 7 and the fourth insulating layer 8 are all stacked and fixed on the hollow frame structure of the base 1 in sequence.
Example 3 concrete production method
In order to better explain the method for manufacturing the micromirror with fully symmetrical differential capacitance angle feedback according to embodiment 1, the method for manufacturing will be described with reference to fig. 20 (1) to 20 (18).
The manufacturing method of the micromirror with symmetrical differential capacitance angle feedback comprises the following steps:
(1) Preparing a silicon wafer. The silicon wafer is monocrystalline silicon or polycrystalline silicon, the thickness of the silicon wafer is 150 mu m, and the resistivity is 0.01 omega-cm. See fig. 20 (1).
(2) And (3) carrying out front first photoetching, and defining a corresponding pattern of vertical direction position change of the front oxygen ion implantation area. See fig. 20 (2).
(3) And carrying out dry etching on the front surface for the first time, and etching a groove-shaped structure on the front surface of the silicon wafer for subsequent oxygen ion implantation to realize the change of the position of the oxygen ion implantation in the vertical direction. And removing the photoresist on the front surface of the silicon wafer after the dry etching is finished. The depth of the etched trench structure was 25 μm. See fig. 20 (3).
(4) And reversing the silicon wafer by first photoetching on the back surface, photoetching the back surface, wherein the mask pattern is the mirror image of the mask pattern used by the first photoetching on the front surface, and defining a corresponding pattern with the position change of the oxygen ion implantation area on the back surface in the vertical direction. See fig. 20 (4).
(5) And etching the back surface by a dry method for the first time, and etching the back surface of the silicon wafer to form a groove-shaped structure for subsequent oxygen ion implantation to realize the change of the position of the oxygen ion implantation in the vertical direction. And removing the photoresist on the back of the silicon wafer after the dry etching is finished. The depth of the etched trench structure was 25 μm. See fig. 20 (5).
(6) Performing front oxygen ion implantation, namely performing integral oxygen ion implantation on the front of the silicon wafer, and selecting proper implantation energy according to the depth of the oxygen ions; and forming an oxide layer at a position which is a certain distance away from the front surface of the silicon wafer after oxygen ion implantation. The different implantation energies, the different distances between the oxide layer and the front surface of the silicon wafer, the lower the energy, the smaller the distance, the larger the energy, and the larger the distance; because the dry etching is performed in the step 3, the front surface of the silicon wafer forms a groove-shaped structure before oxygen ion implantation, namely, the front surface of the silicon wafer is not a plane but has high and low fluctuation, so that in the same oxygen ion implantation, the distance between an oxide layer and the front surface of the silicon wafer is the same although the implantation energy is fixed, and the front surface of the silicon wafer has high and low fluctuation, so that the oxide layer formed by implantation is not a plane, but has fluctuation in the vertical direction corresponding to the fluctuation of the front surface of the silicon wafer. The oxygen ion implantation depth was 50 μm. See fig. 20 (6).
(7) Performing back oxygen ion implantation, namely performing overall oxygen ion implantation on the back of the silicon wafer, and selecting proper implantation energy according to the depth of the oxygen ions; and forming an oxide layer at a position which is a certain distance away from the back surface of the silicon wafer after oxygen ion implantation. The different implantation energies, the different distances between the oxide layer and the back surface of the silicon wafer, the lower the energy, the smaller the distance, the larger the energy, and the larger the distance; since the dry etching is performed in step 3, the back surface of the silicon wafer is formed into a groove-like structure before oxygen ion implantation, that is, the back surface of the silicon wafer is not flat but has high and low fluctuation, so that in the same oxygen ion implantation, the distance between the oxide layer and the back surface of the silicon wafer is the same although the implantation energy is constant, and the oxide layer formed by implantation is not a flat surface but has fluctuation in the vertical direction corresponding to the fluctuation of the back surface of the silicon wafer because the back surface of the silicon wafer has high and low fluctuation. The depth of the oxygen ion implantation is 50 μm, which is the same as that in the step 6. See fig. 20 (7).
(8) And (3) thinning and polishing the front surface, removing the groove-shaped structure of the front surface for assisting oxygen ion implantation, and recovering the polished surface of the front surface. See fig. 20 (8).
(9) And thinning and polishing the back surface, removing the groove-shaped structure of the back surface for assisting oxygen ion implantation, and recovering the polished surface of the back surface. After the process is completed, the silicon wafer forms a five-layer structure, namely a first fixed layer, a second insulating layer, a reflector element layer, a third insulating layer and a second fixed layer from bottom to top; wherein the reflector element layer has a planar structure with a thickness of 50 μm, the first and second fixing layers have a stepped structure with a thickness of 50 μm; the first and second anchor layers are symmetrical about a mirror element layer center plane. The second insulating layer and the third insulating layer are equal in thickness and are 1 μm in thickness, and the two insulating layers are symmetrical about the center plane of the mirror element layer. See fig. 20 (9).
(10) And photoetching the front surface for the second time, and defining patterns corresponding to the third fixed driving element, the fourth fixed driving element, the fifth fixed capacitor, the sixth fixed capacitor, the seventh fixed capacitor and the eighth fixed capacitor of the second fixed layer. See fig. 20 (10).
(11) And etching the front surface for the second time by dry etching to form a third fixed driving element, a fourth fixed driving element, a fifth fixed capacitor, a sixth fixed capacitor, a seventh fixed capacitor and an eighth fixed capacitor structure. And removing the photoresist on the front surface of the silicon wafer after etching is finished. This etching depth is equal to the depth of the oxygen ion implantation in step 6 and is 50 μm. See fig. 20 (11).
(12) And reversing the silicon wafer for the second photoetching on the back surface, and photoetching the back surface of the silicon wafer to define patterns corresponding to the first fixed driving element, the second fixed driving element, the first fixed capacitor, the second fixed capacitor, the third fixed capacitor and the fourth fixed capacitor. See fig. 20 (12).
(13) And etching the back surface for the second time by dry etching to obtain a first fixed driving element, a second fixed driving element, a first fixed capacitor, a second fixed capacitor, a third fixed capacitor and a fourth fixed capacitor structure. And removing the photoresist on the back of the silicon wafer after etching is finished. This etching depth is equal to the oxygen ion implantation depth in step 7 and is 50 μm. See fig. 20 (13).
(14) Preparing a base, wherein a monocrystalline silicon wafer or a polycrystalline silicon wafer is adopted, the resistivity is 1000 omega-cm, and the thickness is 400 mu m. Firstly, an oxide layer is deposited or thermally oxidized on the surface of a monocrystalline silicon wafer or a polycrystalline silicon wafer used for preparing a base, and is used as a first insulating layer, and the thickness of the oxide layer is 1 mu m. And manufacturing the base with the frame-shaped structure by adopting a dry etching method. See fig. 20 (14).
(15) The submount is bonded to the wafer completed in step 13 (second dry etching of the back side). The upper surface of the base contacts with the lower surface of the silicon wafer finished in the step 13 during bonding, and the hollow area of the frame-shaped structure of the base is larger than the area of the first fixed driving element, the second fixed driving element, the first fixed capacitor, the second fixed capacitor, the third fixed capacitor and the fourth fixed capacitor corresponding to the silicon wafer finished in the step 13, so that the bonding alignment requirement is low, and only the alignment tolerance of plus or minus 50 mu m is ensured, as shown in the figure 20 (15).
(16) And (3) releasing the structure, namely placing the bonded silicon wafer into a hydrofluoric acid wet etching tank or a hydrogen fluoride dry etching device, and etching and removing the two oxide layers formed in the step (6) and the step (7), so as to release the structures contained in the first fixed layer, the reflector element layer and the second fixed layer. See fig. 20 (16).
(17) And (3) preparing a front-side oxide layer, and depositing a silicon oxide layer on the upper surface of the silicon wafer after the release in the step (16) (structure release) is completed, or preparing an oxide layer by a thermal oxidation method to serve as a fourth insulating layer. The fourth insulating layer had a thickness of 1. Mu.m. See fig. 20 (17).
(18) And after the structure is manufactured, manufacturing the bonding pad by adopting a sputtering or vapor plating mode, wherein the mask is a hard mask. See fig. 20 (18).
The method for manufacturing the micro-mirror with the symmetrical differential capacitance angle feedback is a preferred embodiment, wherein some steps can be adjusted according to specific structures and process conditions, for example, front side photoetching and etching can be replaced sequentially with back side photoetching and etching, front side oxygen ion implantation and back side oxygen ion implantation can be replaced sequentially, and structure release and bonding can be replaced sequentially according to requirements.
In the embodiment, a five-layer structure is realized on an initial monocrystalline silicon wafer or polycrystalline silicon wafer through oxygen ion implantation, and three-layer, seven-layer or even more-layer structures can be realized by adopting an oxygen ion implantation mode according to requirements.
It is within the scope of the present method to simply change some of the process sequences of the present method, or to change the number of layers implemented.
Example 4 micromirror fabrication method
As shown in FIG. 21, the difference from example 3 is that the base thickness is 400. Mu.m, the first and second anchor layers are 25. Mu.m, the mirror element layer thickness is 100. Mu.m, and the oxygen ion implantation depth is 25. Mu.m. The depth of the groove-shaped structure formed by the first dry etching of the front side and the back side is 10nm. The thickness of each oxide layer was 0.2. Mu.m. The resistivity of the base is 1 omega. A first fixing layerResistivity of the second pinned layer and mirror element layer 10 -4 Omega. Cm. (the dimensions in the figures are not to scale)
Example 5 micromirror fabrication method
As shown in fig. 22, the difference from example 3 is that the susceptor thickness is 100 μm. The thickness of the first fixing layer and the second fixing layer is 60 μm, the thickness of the reflector element layer is 60 μm, and the oxygen ion implantation depth is 60 μm. The depth of the groove-shaped structure formed by the first dry etching of the front side and the back side is 1 mu m. The thickness of each oxide layer was 5. Mu.m. Base resistivity 10 4 Omega. Cm. First fixed layer, second fixed layer, and mirror element layer resistivity 10 -4 Ω·㎝。
The specific structure, parameters and manufacturing method shown in fig. 21 and 22 are all preferred embodiments, and are not limited to the parameters of the invention, and simple changes of the structure shape, number, process parameters or process sequence based on the above are still within the scope of the invention.
According to the invention, the materials of the base 1, the first fixing layer 3 and the second fixing layer 7 are any one of monocrystalline silicon, polycrystalline silicon or amorphous silicon; the material of the reflecting element layer 5 is any one of monocrystalline silicon, polycrystalline silicon, amorphous silicon or high molecular polymer; the resistivity of the first fixed layer 3, the reflective element layer 5 and the second fixed layer 7 is less than 1Ω·cm; the materials of the first insulating layer 2, the second insulating layer 4, the third insulating layer 6 and the fourth insulating layer 8 are selected from any one of silicon oxide, silicon nitride, silicon carbide or high molecular polymer; the resistivity of the first insulating layer 2, the second insulating layer 4, the third insulating layer 6 and the fourth insulating layer 8 is larger than 10Ω·cm. The high polymer is selected from any one of polydimethylsiloxane, SU8 glue, epoxy resin, polyamide, polyimide, polypropylene, polyethylene, polyvinyl chloride, polystyrene, polyethylene terephthalate and polymethyl methacrylate.
The foregoing is a further detailed description of the invention in connection with specific preferred embodiments, and it is not intended that the invention be limited to such description. It will be apparent to those skilled in the art that several simple deductions or substitutions can be made without departing from the spirit of the invention, and these should be considered to be within the scope of the invention.
Claims (10)
1. A micromirror with fully symmetrical differential capacitive angle feedback, characterized in that: the novel light-emitting diode comprises a base (1), wherein a first insulating layer (2) is arranged on the upper surface of the base (1), a first fixing layer (3) is arranged on the upper surface of the first insulating layer (2), a second insulating layer (4) is arranged on the upper surface of the first fixing layer (3), a reflecting element layer (5) is arranged on the upper surface of the second insulating layer (4), a third insulating layer (6) is arranged on the upper surface of the reflecting element layer (5), a second fixing layer (7) is arranged on the upper surface of the third insulating layer (6), a fourth insulating layer (8) is arranged on the upper surface of the second fixing layer (7), and a bonding pad (9) is arranged on the fourth insulating layer (8);
the base (1) is a hollow frame-shaped structure surrounded by peripheral frames, and the first insulating layer (2), the first fixing layer (3), the second insulating layer (4), the reflecting element layer (5), the third insulating layer (6), the second fixing layer (7) and the fourth insulating layer (8) are all overlapped and fixed on the hollow frame-shaped structure of the base (1) in sequence;
The first insulating layer (2), the second insulating layer (4), the reflecting element layer (5), the third insulating layer (6) and the fourth insulating layer (8) are all planar structures; the first fixing layer (3) and the second fixing layer (7) are of a ladder-shaped structure.
2. The micromirror with fully symmetrical differential capacitive angle feedback according to claim 1, wherein: the first insulating layer (2) is formed by a plurality of insulating thin layers arranged on the upper surfaces around the hollow frame-shaped structure of the base (1); the first fixed layer (3) comprises a first peripheral fixed structure (31), a first fixed capacitor (301), a second fixed capacitor (302), a third fixed capacitor (303), a fourth fixed capacitor (304), a first fixed driving element (311) and a second fixed driving element (312); a first fixed capacitor (301), a second fixed capacitor (302), a third fixed capacitor (303) and a fourth fixed capacitor (304) are arranged on the inner sides of the two axial ends of the first peripheral fixed structure (31); a first fixed driving element (311) and a second fixed driving element (312) are arranged on the inner sides of the two radial ends of the first peripheral fixed structure (31); the first fixed capacitor (301), the second fixed capacitor (302), the third fixed capacitor (303), the fourth fixed capacitor (304), the first fixed driving element (311) and the second fixed driving element (312) are all suspended comb structures, and the root parts of the comb structures are all connected with the first peripheral fixed structure (31); the lower surface of the comb tooth part is flush with the lower surface of the first peripheral fixing structure (31), and the upper surface of the comb tooth part exceeds the upper surface of the first peripheral fixing structure (31) to form a stepped structure; the first peripheral fixing structure (31) is connected to the first insulating layer (2).
3. The micromirror with fully symmetrical differential capacitive angle feedback according to claim 2, wherein: the second insulating layer (4) is formed by a plurality of insulating thin layers arranged on the upper surface of the first peripheral fixing structure (31); the reflecting element layer (5) comprises a reflecting mirror peripheral fixed structure (51), a mirror body (530), a first rotating capacitor (501), a second rotating capacitor (502), a third rotating capacitor (503), a fourth rotating capacitor (504), a first rotating driving element (511) and a second rotating driving element (512); the first rotating capacitor (501), the second rotating capacitor (502), the third rotating capacitor (503), the fourth rotating capacitor (504), the first rotating driving element (511) and the second rotating driving element (512) are all of suspended comb structures; the mirror body (530) is axially connected with the inner sides of the two side edges of the mirror peripheral fixing structure (51) through a first rotating shaft (521) and a second rotating shaft (522), the radial two side edges of the mirror body (530) are respectively connected with the root parts of the comb teeth of the first rotating driving element (511) and the second rotating driving element (512), the two side edges of the first rotating shaft (521) are respectively connected with the root parts of the comb teeth of the first rotating capacitor (501) and the second rotating capacitor (502), the two side edges of the second rotating shaft (522) are respectively connected with the root parts of the comb teeth of the third rotating capacitor (503) and the fourth rotating capacitor (504), and the mirror peripheral fixing structure (51) is connected with the second insulating layer (4).
4. A micromirror with fully symmetric differential capacitive angle feedback according to claim 3, characterized in that: the third insulating layer (6) is formed by a plurality of insulating thin layers arranged on the upper surface of the reflector peripheral fixing structure (51); the second fixed layer (7) comprises a second peripheral fixed structure (71), a fifth fixed capacitor (705), a sixth fixed capacitor (706), a seventh fixed capacitor (707), an eighth fixed capacitor (708), a third fixed driving element (713) and a fourth fixed driving element (714); a fifth fixed capacitor (705), a sixth fixed capacitor (706), a seventh fixed capacitor (707) and an eighth fixed capacitor (708) are arranged on the inner sides of the two axial ends of the second peripheral fixed structure (71); a third fixed driving element (713) and a fourth fixed driving element (714) are arranged on the inner sides of the two radial ends of the second peripheral fixed structure (71); the fifth fixed capacitor (705), the sixth fixed capacitor (706), the seventh fixed capacitor (707), the eighth fixed capacitor (708), the third fixed driving element (713) and the fourth fixed driving element (714) are all suspended comb structures, and the root parts of the comb structures are all connected with the second peripheral fixed structure (71); the upper surface of the comb tooth part is flush with the upper surface of the second peripheral fixing structure (71), and the lower surface of the comb tooth part exceeds the lower surface of the second peripheral fixing structure (71) to form a stepped structure; the second peripheral fixing structure (71) is connected with the third insulating layer (6); the fourth insulating layer (8) is composed of a plurality of insulating thin layers arranged on the upper surface of the second peripheral fixing structure (71).
5. The micromirror with fully symmetrical differential capacitive angle feedback according to claim 4, wherein: the first fixed driving element (311), the first rotating driving element (511) and the third fixed driving element (713) form a group of comb tooth driving capacitors; the second fixed drive element (312), the second rotary drive element (512) and the fourth fixed drive element (714) form a set of comb drive capacitors; the first fixed capacitor (301) and the first rotating capacitor (501) form a group of comb tooth detection capacitors, and the fifth fixed capacitor (705) and the first rotating capacitor (501) form a group of comb tooth detection capacitors; the second fixed capacitor (302) and the second rotating capacitor (502) form a group of comb tooth detection capacitors, and the sixth fixed capacitor (706) and the second rotating capacitor (502) form a group of comb tooth detection capacitors; the third fixed capacitor (303) and the third rotating capacitor (503) form a group of comb tooth detection capacitors, and the seventh fixed capacitor (707) and the third rotating capacitor (503) form a group of comb tooth detection capacitors; the fourth fixed capacitor (304) and the fourth rotating capacitor (504) form a group of comb tooth detection capacitors, and the eighth fixed capacitor (708) and the fourth rotating capacitor (504) form a group of comb tooth detection capacitors; the comb tooth driving capacitor sets are symmetrically arranged; the comb tooth detection capacitor sets are symmetrically arranged.
6. The micromirror with fully symmetrical differential capacitive angle feedback according to any of claims 1 to 4, characterized in that: the base (1) is connected with the first insulating layer (2), the first insulating layer (2) is connected with the first fixing layer (3), the first fixing layer (3) is connected with the second insulating layer (4), the second insulating layer (4) is connected with the reflecting element layer (5), the reflecting element layer (5) is connected with the third insulating layer (6), the third insulating layer (6) is connected with the second fixing layer (7) and the second fixing layer (7) is connected with the fourth insulating layer (8) in a bonding mode; the base (1) is of a hollow frame-shaped structure with a round shape, an oval shape, a diamond shape, a rectangle shape or a square shape.
7. The micromirror with fully symmetrical differential capacitive angle feedback according to claim 1, wherein: the base (1), the first fixing layer (3) and the second fixing layer (7) are made of any one of monocrystalline silicon, polycrystalline silicon or amorphous silicon; the material of the reflecting element layer (5) is any one of monocrystalline silicon, polycrystalline silicon, amorphous silicon or high molecular polymer; the resistivity of the first fixed layer (3), the reflective element layer (5) and the second fixed layer (7) is smaller than 1 omega cm; the materials of the first insulating layer (2), the second insulating layer (4), the third insulating layer (6) and the fourth insulating layer (8) are selected from any one of silicon oxide, silicon nitride, silicon carbide or high-molecular polymer; the resistivity of the first insulating layer (2), the second insulating layer (4), the third insulating layer (6) and the fourth insulating layer (8) is larger than 10Ω & cm.
8. The micromirror with fully symmetrical differential capacitive angle feedback according to claim 7, wherein: the high polymer is selected from any one of polydimethylsiloxane, SU8 glue, epoxy resin, polyamide, polyimide, polypropylene, polyethylene, polyvinyl chloride, polystyrene, polyethylene terephthalate and polymethyl methacrylate.
9. A method for fabricating a micromirror with fully symmetrical differential capacitive angular feedback according to any one of claims 1 to 5, comprising the steps of: (1) preparing a silicon wafer; (2) front side first lithography; (3) first dry etching of the front surface; (4) back side first lithography; (5) back surface first dry etching; (6) front side oxygen ion implantation; (7) backside oxygen ion implantation; (8) front thinning and polishing; (9) back thinning and polishing; (10) front side second lithography; (11) front side second dry etching; (12) backside second lithography; (13) second dry etching of the back surface; (14) preparing a base; (15) Bonding the base with the silicon wafer subjected to the second dry etching on the back surface in the step 13; (16) structural release; (17) preparing a front-side oxide layer; and (18) manufacturing a bonding pad.
10. The method of fabricating a micromirror with fully symmetrical differential capacitive angle feedback according to claim 9, comprising the steps of:
(1) Preparing a silicon wafer which is monocrystalline silicon or polycrystalline silicon, and polishing the two sides, wherein the thickness of the silicon wafer is 50-300 mu m, and the resistivity is less than 0.01 omega-cm;
(2) First photoetching on the front side, and defining a corresponding pattern of changing the position of the front side oxygen ion implantation area in the vertical direction;
(3) The front surface is etched for the first time by a dry method, and a groove-shaped structure is etched on the front surface of the silicon wafer and used for subsequent oxygen ion implantation, so that the position change of the oxygen ion implantation in the vertical direction is realized; removing photoresist on the front surface of the silicon wafer after the dry etching is finished; the depth of the groove-shaped structure realized in the step is 10nm-10 mu m;
(4) Performing first photoetching on the back, reversing the silicon wafer, performing photoetching on the back, wherein the mask pattern is a mirror image of the mask pattern used in the first photoetching on the front, and defining a corresponding pattern with the position change of the oxygen ion implantation area on the back in the vertical direction;
(5) The back surface is etched for the first time by a dry method, and a groove-shaped structure is etched on the back surface of the silicon wafer and used for subsequent oxygen ion implantation, so that the position change of the oxygen ion implantation in the vertical direction is realized; removing photoresist on the back of the silicon wafer after the dry etching is finished, wherein the back groove-shaped structure realized in the step is symmetrical to the front groove-shaped structure realized in the step (3) with respect to the neutral layer of the silicon wafer; the depth of the groove-shaped structure on the back surface realized by the step is 10nm-10 mu m;
(6) Performing front oxygen ion implantation, namely performing integral oxygen ion implantation on the front of the silicon wafer, and selecting proper implantation energy according to the depth of the oxygen ions; forming an oxide layer at a position which is a certain distance away from the front surface of the silicon wafer after oxygen ion implantation; the different implantation energies, the different distances between the oxide layer and the front surface of the silicon wafer, the lower the energy, the smaller the distance, the larger the energy, and the larger the distance; because the dry etching is performed in the step (3), the front surface of the silicon wafer forms a groove-shaped structure before oxygen ion implantation, namely, the front surface of the silicon wafer is not a plane but has high and low fluctuation, so that in the same oxygen ion implantation, the distance between an oxide layer and the front surface of the silicon wafer is the same although the implantation energy is fixed, and the front surface of the silicon wafer has high and low fluctuation, so that the oxide layer formed by implantation is not a plane, but has fluctuation in the vertical direction corresponding to the fluctuation of the front surface of the silicon wafer; the front oxygen ion implantation depth is 5 μm-100 μm;
(7) Performing back oxygen ion implantation, namely performing overall oxygen ion implantation on the back of the silicon wafer, and selecting proper implantation energy according to the depth of the oxygen ions; forming an oxide layer at a position which is a certain distance away from the back surface of the silicon wafer after oxygen ion implantation; the different implantation energies, the different distances between the oxide layer and the back surface of the silicon wafer, the lower the energy, the smaller the distance, the larger the energy, and the larger the distance; because the dry etching is carried out in the step (3), the back surface of the silicon wafer forms a groove-shaped structure before oxygen ion implantation, namely the back surface of the silicon wafer is not a plane but has high and low fluctuation, so that in the same oxygen ion implantation, the distance between an oxide layer and the back surface of the silicon wafer is the same although the implantation energy is fixed, the oxide layer formed by implantation is not a plane but has fluctuation in the vertical direction corresponding to the fluctuation of the back surface of the silicon wafer because the back surface of the silicon wafer has high and low fluctuation, and the back oxygen ion implantation depth is equal to the depth of front oxygen ion implantation in the step (6);
(8) The front surface is thinned and polished, a groove-shaped structure of the front surface for assisting oxygen ion implantation is removed, and the polished surface of the front surface is restored;
(9) Thinning and polishing the back surface, removing a groove-shaped structure of the back surface for assisting oxygen ion implantation, and recovering the polished surface of the back surface; after the process is completed, the silicon wafer forms a five-layer structure, namely a first fixed layer, a second insulating layer, a reflector element layer, a third insulating layer and a second fixed layer from bottom to top; wherein the reflector element layer has a planar structure with a thickness of 5-100 μm, the first and second fixing layers have a stepped structure with a thickness of 5-100 μm; the first fixed layer and the second fixed layer are symmetrical about the mirror element layer center plane; the thickness of the second insulating layer is 0.2-5 μm, and the second insulating layer and the third insulating layer are symmetrical about the central plane of the reflector element layer;
(10) A third fixed driving element, a fourth fixed driving element, a fifth fixed capacitor, a sixth fixed capacitor, a seventh fixed capacitor and a pattern corresponding to the eighth fixed capacitor are defined by front second photoetching;
(11) Etching the front surface for the second time by dry etching to form a third fixed driving element, a fourth fixed driving element, a fifth fixed capacitor, a sixth fixed capacitor, a seventh fixed capacitor and an eighth fixed capacitor structure; removing photoresist on the front surface of the silicon wafer after etching is completed; the etching depth is equal to the front oxygen ion implantation depth in the step (6);
(12) Performing second photoetching on the back, namely reversing the silicon wafer, and performing photoetching on the back of the silicon wafer to define patterns corresponding to a first fixed driving element, a second fixed driving element, a first fixed capacitor, a second fixed capacitor, a third fixed capacitor and a fourth fixed capacitor;
(13) Etching the back surface for the second time by dry method to etch out a first fixed driving element, a second fixed driving element, a first fixed capacitor, a second fixed capacitor, a third fixed capacitor and a fourth fixed capacitor structure; removing photoresist on the back of the silicon wafer after etching is completed; the etching depth is equal to the back oxygen ion implantation depth in the step 7;
(14) Preparing a base, wherein a monocrystalline silicon wafer or a polycrystalline silicon wafer is adopted, the resistivity is larger than 0.1 omega-cm, and the thickness is 100-800 mu m; firstly, depositing or thermally oxidizing a layer of oxide layer on the surface of a monocrystalline silicon wafer or a polycrystalline silicon wafer used for preparing a base, wherein the oxide layer is used as a first insulating layer, and the thickness of the oxide layer is 0.2-5 mu m; manufacturing a base with a frame-shaped structure by adopting a dry etching or wet etching method;
(15) Bonding the base with the silicon wafer subjected to the second dry etching on the back surface in the step 13; the upper surface of the base contacts with the lower surface of the silicon wafer finished in the step 13 during bonding, the hollow area of the frame-shaped structure of the base is larger than the area of the first fixed driving element, the second fixed driving element, the first fixed capacitor, the second fixed capacitor, the third fixed capacitor and the fourth fixed capacitor corresponding to the silicon wafer finished in the step 13, so that the bonding alignment requirement is low, only the alignment tolerance of plus or minus 1-50 mu m is ensured, and the specific tolerance is determined according to the specific device size;
(16) The structure is released, the bonded silicon wafer is put into a hydrofluoric acid wet etching tank or a hydrogen fluoride dry etching device, and the two oxide layers formed in the step (6) and the step (7) are removed by etching, so that the release of the structures contained in the first fixed layer, the reflector element layer and the second fixed layer is realized;
(17) Preparing a front oxide layer, namely depositing a silicon oxide layer on the upper surface of the silicon wafer after the structure release in the step (16) is completed, or preparing the oxide layer by a thermal oxidation method to serve as a fourth insulating layer; the thickness of the fourth insulating layer is 0.2-5 mu m;
(18) And after the structure is manufactured, manufacturing the bonding pad by adopting a sputtering or vapor plating mode, wherein the mask is a hard mask.
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| CN113072033B (en) * | 2021-03-26 | 2023-04-21 | 华南农业大学 | Longitudinal double-side multi-group differential capacitive micro-mechanical structure and preparation method thereof |
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