CN1240995C - Microcantilever sensor and its making method - Google Patents

Abstract

The invention relates to a micro-cantilever beam sensor and a manufacturing method thereof. It comprises a chip, on which at least one group of sensing units is arranged, and the sensing unit consists of four completely identical force sensors forming a Wheatstone bridge. The two force-sensitive resistors are located on the substrate of the chip, and the other two resistors are respectively located on the two cantilever beams, and one of the cantilever beams is used as a measuring cantilever beam. Another described cantilever beam is used as a reference cantilever beam, and it is characterized in that: a microgroove is set on the chip, the cantilever beam is arranged in the microgroove, and the material of the force sensitive resistor adopts single crystal silicon or polycrystalline silicon , boron ions are doped on the front surface of the single crystal silicon or polycrystalline silicon, and silicon nitride or silicon oxide protective layers are arranged on the upper and lower surfaces of the force sensitive resistor to form the cantilever beam together, and the surface of the measuring cantilever beam There are sensitive layers set. The invention has wide application prospects in the fields of environment monitoring, clinical diagnosis and treatment, new drug development, food safety, industrial process control, military affairs and the like.

Description

Micro-cantilever beam sensor and manufacturing method thereof

technical field

The invention relates to a sensor and a manufacturing method thereof, in particular to a micro-cantilever sensor with a rectangular cantilever beam used in biological and chemical sensing and a manufacturing method thereof.

Background technique

One of the most significant advances in microelectronics over the past 20 years has been the development of new test techniques. Scanning probe microscopy is one of the well-known detection techniques, among which scanning tunneling microscope and scanning force microscope are the two most representative high-sensitivity detection instruments. The working principle of the scanning force microscope is to fix the probe on a micro-cantilever beam that is very sensitive to weak force, and make it interact with the surface atoms of the sample to be tested, and the force between the probe and the sample The force causes the cantilever to deform and is recorded. Since the microcantilever is very sensitive to weak force changes, it can image the surface topography of the material with high resolution and study the surface properties.

The tiny bending of a cantilever is usually recorded optically or electrically. The optical detection method can obtain a vertical resolution as small as 0.01 Å. Although it has high sensitivity, the huge optical measurement system and the precise calibration of the laser limit its wide application: such as ultra-high vacuum, low temperature, liquid conditions and array cantilever beam measurements. The way to get rid of this problem is to integrate capacitance, piezoelectric, and force-sensitive elements into the electrical detection method of the cantilever beam, because the electrical detection method is easier to operate than the optical method, and it is easy to turn to practical use. Among the electrical detection methods, the piezoresistive in-situ readout method is easier to implement than other detection techniques.

In recent years, the application of high-sensitivity micro-cantilever technology to biological and chemical sensors has become a research hotspot in the field of sensors. This type of sensor can detect the existence of trace biochemical molecules under gaseous or liquid conditions, such as organic gases, harmful gases, aromatics in the air, DNA and proteins in liquids, etc. Although the research work of the cantilever beam biochemical sensor has achieved some results, it still has a certain distance from wide application, especially in the field of liquid biosensor research. At the same time, there are still problems in the manufacturing process of the cantilever beam microsensor that the manufacturing process is relatively complicated and the yield is low.

Contents of the invention

The object of the present invention is to provide a micro-cantilever sensor and a manufacturing method thereof that are applied in biological and chemical sensing with higher measurement sensitivity and simpler manufacturing process on the basis of the prior art.

In order to achieve the above object, the present invention adopts the following technical solutions: a micro-cantilever beam sensor, which includes a chip, on which at least one group of sensing units is arranged, and the sensing units are composed of four Wheatstone bridges. Two identical force-sensitive resistors and two cantilever beams, wherein two force-sensitive resistors are located on the substrate of the chip, and the other two are respectively located on the two cantilever beams, and one of the cantilever beams is used as Measuring the cantilever beam, the other as a reference cantilever beam, is characterized in that: a microgroove is arranged on the chip, the cantilever beam is arranged in the microgroove, and the material of the force sensitive resistor adopts single crystal silicon or polycrystalline silicon , boron ions are doped on the front surface of the single crystal silicon or polycrystalline silicon, and silicon nitride or silicon oxide protective layers are arranged on the upper and lower surfaces of the force sensitive resistor to form the cantilever beam together, and the surface of the measuring cantilever beam There are sensitive layers set.

The sensitive layer is polymer sensitive material.

The sensitive layer is bioactive molecules.

The cantilever beam is rectangular with a length of 50-500 μm, a width of 10-100 μm, and a thickness of 100-5000 nm.

The size of the force sensitive resistor is 20-200 μm in length and 5-50 μm in width.

A method for making a micro-cantilever beam sensor is characterized in that it comprises the following steps:

1. Use an SOI silicon wafer with an oxide layer and a single crystal silicon device layer, and thin the device layer as the chip substrate; or use a single-sided polished p-type silicon wafer. After conventional cleaning, plasma-enhanced chemical Vapor deposition of silicon nitride, and then low-pressure chemical vapor deposition of polysilicon on the surface of silicon nitride as the chip substrate;

2. Doping boron ion implantation on the front side of monocrystalline silicon or polycrystalline silicon;

3. Carry out photolithography for the first time on the chip after step 2 with a mask plate, and form a force sensitive resistor after etching;

4. Deposit silicon nitride on the chip surface through step 3 by plasma enhanced chemical vapor deposition, and anneal in nitrogen;

5. Carry out photolithography for the second time on the chip after step 4 with a mask plate, and form force sensitive resistor contact holes and cantilever beams through etching;

6. Pass the electron beam through the chip surface through step 5, and sputter the chromium/gold bimetallic film;

7. Carry out photolithography for the third time on the chip after step 6 with a mask plate, and corrode to form metal lines connecting each force sensitive resistor;

8. Scribe a single sensor on the entire chip;

9. Corrode the chip through step 8 with potassium hydroxide to release the cantilever beam;

10. Alloying the metal wire in the contact hole of the force sensitive resistor on the chip and the chip substrate;

11. Split the entire chip into a single sensor;

12. A sensitive layer is set on the surface of one cantilever beam in every two cantilever beams.

In step 5, the microgroove on the chip is formed at the same time as the force sensitive resistor contact hole and the cantilever beam are formed.

Wherein step 1, the thickness of the oxide layer of the SOI silicon wafer is 200-800nm, and the thickness of the device layer is 100-500nm.

Wherein step 1, when plasma-enhanced chemical vapor deposition of silicon nitride is performed on the surface of the silicon wafer, the thickness of the silicon nitride is 100-1000 nm.

Wherein step 1, when polysilicon is deposited by low pressure chemical vapor phase, the thickness of polysilicon is 100-500nm.

Wherein step 2, when doping the boron ion implantation on the front side of monocrystalline silicon or polycrystalline silicon, the concentration of implanted boron ions is 5×10 ¹³ cm ⁻² ~5×10 ¹⁵ cm ⁻² , and the implantation energy is 30keV～80keV.

Wherein step 4, when plasma-enhanced chemical vapor deposition of silicon nitride, the thickness of silicon nitride is 100-1000nm, and then annealed in nitrogen at 900-1100°C for 20-30 minutes.

The present invention has the following advantages due to the adoption of the above technical scheme: 1, the present invention is due to two resistors in the Wheatstone bridge being respectively arranged on two cantilever beams, one is used as a measurement resistor, and the other is used as a reference resistor instead of using the reference resistor The resistance is set on the substrate of the chip, so when the external environment noise deforms the cantilever beam during measurement, this additional signal can be filtered out through the reference cantilever beam to make the measurement result more accurate. 2. The cantilever beams of the present invention are arranged in an array, and two adjacent cantilever beams are used as a group. Therefore, different polymer sensitive layers and bioactive molecules can be coated on the cantilever beams to make each pair of cantilever beams A measurement function can be completed through the sensitive layer, and then the simultaneous measurement of various characteristic indicators of different substances can be realized. 3. In the manufacturing process of the cantilever beam of the present invention, the contact hole, the cantilever beam and the microgroove on the chip that are connected to the metal lead wire and the force sensitive resistor are defined by the same mask plate, that is, only three masks are used in the present invention. mask plate, compared with the prior art, the present invention effectively simplifies the process flow. 4. Since the present invention uses gold as the metal lead, it can resist long-term KOH corrosion. At the same time, due to the method of scribing first and then KOH corrosion, it effectively avoids the damage of the cantilever beam caused by scribing after releasing the cantilever beam. Thus, the yield rate is effectively improved. 5. In the present invention, the cantilever beam can be designed and prepared in the liquid-flowable microgroove through front-side etching technology and silicon-glass (polymer) bonding technology, so that it can be directly used for the detection of liquid biomolecules.

Description of drawings

Fig. 1 is a structural representation of the present invention

Fig. 2 is the schematic diagram of Wheatstone bridge of the present invention

Fig. 3 is the enlarged schematic diagram of the micro-cantilever beam of the present invention arranged on one side of the chip

Fig. 4a～4j is the schematic diagram of technological process of the present invention

Detailed ways

As shown in Fig. 1, Fig. 2, Fig. 3, the present invention belongs to piezoresistive microsensor, and it comprises a chip 1, is provided with a microgroove 2 on it, is provided with four groups of sensing units 3 symmetrically on both sides of microgroove 2, Each set of sensing units 3 includes two cantilever beams 4 and a set of Wheatstone bridges 5 . Each group of Wheatstone bridge 5 is made up of four completely identical force sensitive resistors R1, R2, R3, R4, wherein two resistors R1, R4 are respectively connected on the two cantilever beams 4, and one is used as the measuring cantilever beam 4', The other is used as a reference cantilever beam 4". Then connect the other two resistors R2 and R3 to the substrate of chip 1 respectively. Design the reference resistor R4 on the reference cantilever beam 4" instead of setting it on the substrate of chip 1 It is to consider that when the external environmental noise and thermal mechanical vibration noise cause the cantilever beam 4 to deform, this additional signal can be filtered out by referring to the cantilever beam 4". According to the different needs of the measured material on the surface of the cantilever beam 4', the cantilever beam can be measured The surface of 4' is coated with polymer sensitive material, bioactive molecule or metal as a sensitive layer (not shown in the figure).

For example, bioactive molecules such as DNA and protein are immobilized on the surface of the cantilever beam 4', and the recognition of trace biomolecules such as DNA and protein is realized through the hybridization reaction between DNA molecules or the specific binding reaction between proteins. The sensor for measuring DNA immobilizes a single-stranded DNA molecule of known sequence (also called ssDNA probe) on the surface of the cantilever beam. The detected biomolecule is a complementary ssDNA molecule (also called target DNA), and the hybridization reaction between the two As a result of the formation of double-stranded DNA, the force during the reaction makes the cantilever bend, showing a certain change in the output signal. The sensor for measuring protein usually immobilizes the antibody on the surface of the cantilever. Based on the structural complementarity and affinity between the two molecules, an antigen-antibody complex is formed. force) to bend the cantilever beam. The slight bending of the cantilever beam 4 changes the resistance value of the force sensitive resistor R1, and the differential voltage signal records the reaction between the detected biomolecules and the molecules of the sensitive layer.

In the above embodiment, the designed dimensions of the cantilever beam 4 may be: length 50-500 μm, width 10-100 μm, thickness 100-5000 nm. The dimensions of the four identical force-sensitive resistors forming the symmetrical Wheatstone bridge 5 may be: 20-200 μm in length and 5-50 μm in width. After the cantilever beam is stressed, the stress distribution depends on the moment M and the moment of inertia I of the cantilever beam. It can be proved that the maximum stress usually occurs on the surface of the cantilever beam. It is theoretically deduced that the longitudinal stress σ on the cantilever beam arm and the cantilever beam end point The relationship between force F and vertical displacement Δz is:

${\mathrm{<span\; class="notranslate">\; \&sigma;</span>}}_{\mathrm{<span\; class="notranslate">\; l</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 6</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; wt</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 3</span>}\mathrm{<span\; class="notranslate">\; E.</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; <figure-callout\; id="3"\; label="l"\; filenames="C0310949200111.png"\; state="\{\{state\}\}">l</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 3</span>}}}\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\text{<span class="notranslate"> z----</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

Where l, w and t are the length of the cantilever, L, width and thickness L is the length of the force sensitive resistor, t is the thickness of the cantilever, E is Young's modulus, Δz is the vertical displacement of the cantilever end.

If only the longitudinal stress is considered, the relative change rate ΔR/R of the force sensitive resistor can be given by the following formula:

$\frac{\mathrm{<span\; class="notranslate">\; \&Delta;R</span>}}{\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; \&sigma;\&pi;</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

where π is the longitudinal piezoresistive coefficient. When measuring the deformation of the cantilever beam due to the action of force, the resistance value change of the cantilever beam force-sensitive resistor is ΔR. When the bias voltage V acts on the Wheatstone bridge, the output signal of the Wheatstone bridge is:

${\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="4"\; label="V\; bias"\; filenames="C0310949200111.png,C0310949200121.png"\; state="\{\{state\}\}">V</figure-callout></span><figure-callout\; id="4"\; label="V\; bias"\; filenames="C0310949200111.png,C0310949200121.png"\; state="\{\{state\}\}">\; </figure-callout>}}_{\mathrm{<span\; class="notranslate">\; </span>}}}{\mathrm{<span\; class="notranslate">\; 4</span>}}\frac{\mathrm{<span\; class="notranslate">\; \&Delta;R</span>}}{\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

The measurement sensitivity of a cantilever is defined as the ratio of the relative change in resistance to the offset of the cantilever's endpoints. Substituting the stress result calculated by formula (1) into formula (2), the relationship between the relative change of resistance and the change of force can be obtained, and according to Hooke's law (Hook's) and the definition of elastic coefficient, the measurement sensitivity of the cantilever beam can be expressed as :

$\frac{\mathrm{<span\; class="notranslate">\; \&Delta;R</span>}}{\mathrm{<span\; class="notranslate">\; R</span>}}\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; z</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 3</span>}{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}_{\mathrm{<span\; class="notranslate">\; l</span>}}\mathrm{<span\; class="notranslate">\; Et</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="3"\; label="l"\; filenames="C0310949200111.png"\; state="\{\{state\}\}">l</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 3</span>}}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 3</span>}\mathrm{<span\; class="notranslate">\; Kt</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; l</span>}}^{\mathrm{<span\; class="notranslate">\; 3</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

Where K = Eπ _l is the strain sensitivity coefficient,.

The minimum detectable displacement (MDD) of the force-sensitive cantilever is defined as the vertical displacement of the cantilever under the condition that the signal-to-noise ratio of the cantilever is 1:1. It not only depends on the detection sensitivity of the cantilever, but also is affected by the noise of the force-sensitive resistor constraints. Let the Wheatston bridge output voltage signal V _o equal to the total noise, the MDD of the cantilever beam can be expressed as:

$\mathrm{<span\; class="notranslate">\; MDD</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 4</span>}}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; bias</span>}}}{<span\; class="notranslate">\; [</span>\frac{\mathrm{<span\; class="notranslate">\; a</span>}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; bias</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; N</span>}}\mathrm{<span\; class="notranslate">\; ln</span>}\frac{{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; max</span>}}}{{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; min</span>}}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 4</span>}{\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; B</span>}}\mathrm{<span\; class="notranslate">\; TR</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; max</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; min</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span>}^{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; K</span>}\frac{\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; t</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; l</span>}}^{\mathrm{<span\; class="notranslate">\; 3</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; )</span>$

In the above formula, the first term in the brackets corresponds to the 1/f noise of the force sensitive resistor, and the second term corresponds to the Johnson noise of the force sensitive resistor.

It can be seen from formula 5 that noise and sensitivity are a balanced process, and the actual design size should be selected in combination with process conditions. The size of the force sensitive resistor first affects the noise of the force sensitive resistor, the larger the size, the smaller the noise. The cantilever size also affects the sensitivity and noise of the cantilever,

In the present invention, by optimizing the design of the technological process, only three mask plates are used in the manufacture of the micro-cantilever beam, which greatly simplifies the technological process compared with other manufacturing methods. The following is the making of the present invention

Example:

1. Make the chip substrate, which can be made of single crystal silicon or polycrystalline silicon.

(1) When making a polysilicon cantilever beam, it can be a single-sided polished p-type silicon wafer 10. After the silicon wafer 10 is routinely cleaned, plasma-enhanced chemical vapor deposition (PECVD) silicon nitride (Si ₃ N ₄ ) 11 (as shown in Figure 4a), used to seal the bottom layer of the force sensitive resistor, with a thickness of 150nm; then low-pressure chemical vapor deposition (LPCVD) polysilicon 12 (as shown in Figure 4b), with a thickness of 200nm, A polysilicon force sensitive resistor layer is formed.

(2) When making a single crystal silicon cantilever beam, it can be an SOI (silicon structure on insulator) silicon wafer, and its surface is treated to thin the device layer. The thickness of the oxide layer is: 400nm, and the thickness of the device layer is: 200nm. Layer is the single crystal silicon force sensitive resistor layer.

2. Use the monocrystalline silicon or polycrystalline silicon wafer treated in step 1 as the chip substrate, and dope 13 boron ion implantation on the front side (as shown in Figure 4c), and the implanted boron ion concentration is 5×10 ¹³ or 5× 10 ¹⁵ cm ^-2 , the injection energy is 30keV.

3. Use a mask plate to convert the pattern of the force sensitive resistor, and perform SF ₆ (sulfur hexafluoride) reactive ion etching (RIE) on the doped single crystal silicon or polycrystalline silicon to form a force sensitive resistor R (as shown in Figure 4d shown).

4. To completely seal the force-sensitive resistor R, plasma-enhanced chemical vapor deposition of silicon nitride 11 (as shown in FIG. 4e ) with a thickness of 150 nm, and then annealing in N ₂ at 1050° C. for 20 minutes.

5. Use a mask plate integrating microgrooves, contact holes, and cantilever beams for photolithography (as shown in Figure 4f). If the cantilever beam 4 is set on one side of the chip 1, microgrooves may not be provided. For Si ₃ N ₄ Perform CHF ₃ +SF ₆ (trifluoromethane+sulfur hexafluoride) reactive ion etching to etch away the Si ₃ N ₄ on the microgroove 14 and the contact hole 15 of the force sensitive resistor, and simultaneously etch away the surrounding area of the cantilever beam arm Si ₃ N ₄ ;

6. By electron beam sputtering chromium/gold (Cr/Au) bimetallic film 16 (as shown in Figure 4g), the thickness of chromium is 40nm, which is used to make gold better adhere to the chip substrate, the thickness of gold is 400nm, Gold is used instead of aluminum because gold is resistant to corrosion by potassium hydroxide (KOH).

7. Using a metal mask (as shown in FIG. 4h ), after photolithography, corrode the metal to complete the forming of the metal wire 17;

8. Carry out scribing of a single sensor on the entire chip 1 (as shown in FIG. 4i ), and scribing is performed before potassium hydroxide etching to ensure that the cantilever beam is not damaged during the slicing process.

9. Carry out potassium hydroxide corrosion silicon, release cantilever beam (as shown in Figure 4j), utilize potassium hydroxide to the character of the anisotropic salient corner corrosion of silicon, under long enough corrosion time, the silicon below the cantilever beam can be It is completely etched clean, and the depth of the etched groove is about 60 μm.

10. Alloy the metal and silicon in the contact hole of the force sensitive resistor to form an ohmic contact. Alloy conditions: 320°C, 20 minutes.

11. Split the entire chip into individual sensors from the above-mentioned dicing place.

12. Coating a sensitive layer on the surface of one of the two cantilever beams, i.e. the measuring cantilever beam 4'.

In the above method,

In step 1, when plasma-enhanced chemical vapor deposition of silicon nitride is performed on the surface of the silicon wafer, its thickness may be 100-1000 nm; the thickness of the oxide layer of the SOI silicon wafer may be 200-800 nm, and the thickness of the device layer may be 100-500 nm.

Step 1, when polysilicon is deposited by low-pressure chemical vapor phase as the force-sensitive resistor layer, its thickness can be 100-500 nm; the thickness of the silicon nitride or silicon oxide protective layer determines the thickness of the cantilever beam, and the thickness of the cantilever beam determines Its sensitivity can be seen from formula (4).

Step 2, when doping boron ion implantation on the front side of monocrystalline silicon or polycrystalline silicon, the concentration of implanted boron ions can be 5×10 ¹³ cm ^-2 to 5×10 ¹⁵ cm ^-2 , and the energy is 30keV to 80keV; the higher the doping concentration The higher the value, the lower the noise of the cantilever beam, but the sensitivity decreases at the same time. The ion implantation energy determines the depth of boron ion diffusion in the resistive layer, thus affecting the sensitivity of the cantilever beam.

Step 4, when plasma-enhanced chemical vapor deposition of silicon nitride, the deposition thickness can be 100-1000nm, and then annealed in nitrogen at 900-1100°C for 20-30 minutes, the deposition thickness determines the thickness of the cantilever beam, and the cantilever The thickness of the beam determines its sensitivity, which can be seen from formula (4).

Step 5, the thickness of the chromium/gold bimetallic film can be adjusted appropriately.

In the above manufacturing method, after the chip is photolithographically etched, whether it is etched in gas or etched in liquid, the gas or liquid used can be changed as required.

In the above-described embodiment, the quantity of the cantilever beam 4 can be set according to the needs of the measurement item, but its quantity should be an even number, that is, two cantilever beams are a group, and four force-sensitive beams arranged on the two cantilever beams and the chip substrate The resistance forms an independent sensing unit to complete a measurement item. Therefore, a chip with two cantilever beams can form a sensor; if multiple sets of cantilever beams are set, an array sensor is formed, and the sensor does not need to be equipped with microgrooves. , so that the cantilever beam is located on one side of the chip (as shown in Figure 3), and the microgroove can also be set so that the cantilever beam is located on both sides of the microgroove (as shown in Figure 1).

In the present invention, the cantilever beam can be designed and prepared in the liquid-flowable microgroove through the front-side etching technology and the silicon-glass (polymer) bonding technology, so that it can be directly used for the detection of liquid biomolecules.

Whether the unit type or array type piezoresistive cantilever beam of the present invention is applied to a gas sensor or a biosensor, it will play an important role in reducing the size of the device, improving the sensitivity of the device and realizing the multifunctionality of the sensor. Cantilever beam sensors have broad application prospects in environmental monitoring, clinical diagnosis and treatment, new drug development, food safety, industrial process control, military and other fields.

Claims (13)

1. A micro-cantilever beam sensor, which comprises a chip, on which at least one group of sensing units is arranged, and the sensing units are composed of four identical force-sensitive resistors and two Cantilever beams, wherein two force-sensitive resistors are located on the substrate of the chip, and the other two are respectively located on the two cantilever beams, wherein one of the cantilever beams is used as a measuring cantilever beam, and the other is used as a reference cantilever beam , characterized in that: a microgroove is arranged on the chip, the cantilever beam is arranged in the microgroove, the material of the force sensitive resistor is monocrystalline silicon or polycrystalline silicon, and the front surface of the monocrystalline silicon or polycrystalline silicon Doped with boron ions, silicon nitride or silicon oxide protective layers are arranged on the upper and lower surfaces of the force sensitive resistor to form the cantilever beam together, and a sensitive layer is arranged on the surface of the measuring cantilever beam. 2. The micro-cantilever sensor according to claim 1, characterized in that: the sensitive layer is a polymer sensitive material. 3. The micro-cantilever sensor according to claim 1, wherein the sensitive layer is bioactive molecules. 4. The micro-cantilever sensor according to claim 1, 2 or 3, characterized in that: the cantilever is a rectangle with a length of 50-500 μm, a width of 10-100 μm, and a thickness of 100-5000 nm. 5. The micro-cantilever sensor according to claim 1, 2 or 3, wherein the size of the force sensitive resistor is 20-200 μm in length and 5-50 μm in width. 6. The micro-cantilever sensor according to claim 4, wherein the size of the force sensitive resistor is 20-200 μm in length and 5-50 μm in width. 7. A method for making a micro-cantilever beam sensor, characterized in that it comprises the following steps: (1) Use an SOI silicon wafer with an oxide layer and a single crystal silicon device layer, and thin the device layer as the chip substrate; or use a single-sided polished p-type silicon wafer, and after conventional cleaning, plasmon enhancement on the surface of the silicon wafer Chemical vapor deposition of silicon nitride, and then low-pressure chemical vapor deposition of polysilicon on the surface of silicon nitride as the chip substrate; (2) Doping boron ion implantation on the front side of monocrystalline silicon or polycrystalline silicon; (3) carry out photolithography for the first time to the chip through step (2) with mask plate, through etching, form force sensitive resistor; (4) Deposit silicon nitride on the surface of the chip through step (3) by plasma enhanced chemical vapor deposition, and anneal in nitrogen; (5) carry out photolithography for the second time to the chip through step (4) with mask plate, through etching, form force sensitive resistance contact hole and cantilever beam; (6) through the chip surface of step (5) by electron beam, sputtering chromium/gold bimetallic film; (7) carry out photolithography for the third time to the chip through step (6) with mask plate, through corrosion, form the metal wire that connects each force sensitive resistor; (8) Scribing a single sensor on the entire chip; (9) Corroding the chip through step (8) with potassium hydroxide, releasing the cantilever beam; (10) Alloying the metal wire in the contact hole of the force sensitive resistor on the chip and the chip substrate; (11) Splitting the entire chip into a single sensor; (12) A sensitive layer is provided on the surface of one cantilever beam in every two cantilever beams. 8. A method for manufacturing a micro-cantilever sensor according to claim 7, wherein in step (5), the microgroove on the chip is formed at the same time as the force-sensitive resistor contact hole and the cantilever are formed. 9. The manufacturing method of a micro-cantilever beam sensor according to claim 7, characterized in that in step (1), the thickness of the oxide layer of the SOI silicon wafer is 200-800 nm, and the thickness of the device layer is 100-500 nm. 10. The manufacturing method of a micro-cantilever beam sensor according to claim 7, wherein in step (1), when performing plasma-enhanced chemical vapor deposition of silicon nitride on the surface of the silicon wafer, the silicon nitride The thickness is 100-1000nm. 11. A method for manufacturing a micro-cantilever beam sensor as claimed in claim 7, characterized in that in step (1), when polysilicon is deposited by low pressure chemical vapor phase, the thickness of polysilicon is 100-500nm. 12. The manufacturing method of a micro-cantilever sensor as claimed in claim 7, characterized in that: in step (2), when doping the front side of monocrystalline silicon or polycrystalline silicon with boron ion implantation, the concentration of implanted boron ions is 5×10 ¹³ cm ^-2 to 5×10 ¹⁵ cm ^-2 , and the injection energy is 30keV to 80keV. 13. A method for manufacturing a micro-cantilever sensor as claimed in claim 7, wherein in step (4), when plasma-enhanced chemical vapor deposition of silicon nitride, the thickness of silicon nitride is 100-1000 nm, Then anneal at 900-1100° C. for 20-30 minutes in nitrogen.

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