CN1631764A - Electrochemical deep etching method and device thereof - Google Patents

Abstract

The invention relates to a produce method of a micro-electromechanical system device, especially electrochemistry deep etching, also to the processing device of the electrochemistry deep etching, belongs to the micro-electronics and micro-electromechanical system techs fields. Above method is adding magnetic field perpendicular to the sample's surface to the classic electrochemistry deep etching device, or the process takes place in a circumstance at -10 deg C up to 15 deg C. the transverse current is limited due to the effect of magnetic field so to avoid the transverse encroachment in the anodizing and collapse on the edge of some certain structure. Controlling the temperature lowers the crystal lattice scattering rate of the dispersing stream particles which makes the etching much more remarkable.

Description

Electrochemical deep etching method and device thereof

Technical field

The invention relates to a manufacturing method of a microelectromechanical system device, in particular to an electrochemical deep etching method and a device for the electrochemical deep etching method, belonging to the technical fields of microelectronics and microelectromechanical systems.

Background technique

In microelectromechanical systems (collectively referred to as "MEMS" hereinafter), the deep etching technology of silicon is of great significance. Usually, sensors of mechanical quantities such as gyroscopes, acceleration sensors, and pressure sensors can be made by deep etching of silicon, and deep holes or trenches that can be used for through-hole interconnection of RF MEMS can also be made by using deep etching technology, or used to make micro-electromechanical systems. fluid structure.

At present, the main method for deep etching of silicon is deep reactive ion etching, also known as plasma coupled reactive ion etching. Deep etching of silicon is one of the key technologies in the field of integrated circuits and micro-electromechanical systems. Due to the limitations of the characteristics of the mask layer and lateral erosion in the deep reactive ion etching method, it is very difficult for the aspect ratio to break through 50. That is to say, if you want to etch a structure with a well width of 2 microns and a depth of 100 microns on a silicon wafer, it is almost impossible to use deep reactive ion etching. At the same time, deep reactive ion etching equipment is very expensive, and its maintenance and use costs are also very high. This limits the fabrication of some MEMS devices.

In recent years, on the basis of porous silicon technology, people have developed a macroporous silicon technology. Its working principle is to take advantage of the fact that holes are mainly involved in the anodic oxidation of porous silicon, use the MEMS process to define the position of the well or hole through the mask, and use the anisotropic etching of silicon to form inverted pyramid-shaped pits. Due to the tip discharge, the bottom of the pit is the place with the highest hole density, so it is also the place where corrosion is most likely to occur. The holes can be generated by means of light or electrical injection. By this method, the directional etching of the controlled hole along the substrate can be achieved. It can reach a very high aspect ratio, and this method has been used to make photonic crystal structures arranged in microscopic order and has been used to study the fabrication of gyroscopes and other structures. However, because electrochemical corrosion is closely related to the microscopic distribution of current, the uniform distribution of design patterns is often the key to the smooth progress of etching. When the distribution of design patterns is dense, that is, the distance between patterns is smaller than the size of the pattern itself, and When uniformly distributed, such as photonic crystals, the requirements for mask materials are not high at this time, and it can be successfully etched even without mask materials. However, in most cases, the fabrication of devices often only requires deep etching at a specific position and it is hoped that the etching process will be carried out according to the design requirements, which requires that the mask material can effectively protect the underlying silicon during the etching process. The choice of mask material is mainly based on the fact that its corrosion rate during the etching process is much lower than that of silicon itself, that is, its protective function will not be lost before the etching is completed. Generally, SiN, SiC and some metal alloys can be selected as the mask layer.

In addition, the direct anodic oxidation method can only obtain a pore or groove structure with a single pore size less than 5 microns, and, due to the scattering of carriers, there is lateral erosion during the anodic oxidation process when the current density is high, and in some The edge of the structure collapses and so on. As a result, there are problems in making microsensors by using this method instead of deep reactive ion etching. The present invention solves the above-mentioned problems by modifying the design and process flow, and can use this wet deep etching technology to manufacture precision gyroscopes, acceleration sensors, microfluidic channels, micro-nano nozzles, and field emission and scanning probe arrays.

Contents of the invention

The object of the present invention is to provide a low-cost electrochemical deep etching method capable of achieving a very high aspect ratio, and provide a device for the electrochemical deep etching method.

The present invention realizes the object of the present invention through the following technical approaches.

The electrochemical deep etching method described in the present invention is to carry out homogeneous ion implantation and annealing activation on the back of the sample, deposit a mask layer on the front surface, open the etching window by photolithography and etching the mask layer, and use anisotropic etching solution to form The inverted pyramid structure is put into the electrochemical reaction tank for anodic oxidation. The corrosion process adopts two modes: constant light, automatic adjustment of input voltage with corrosion current and constant input voltage, automatic adjustment of light with corrosion current. The corrosion current density is controlled at 0.1-20mA/cm ² , characterized in that the corrosion system is placed in a magnetic field with a magnetic induction intensity between 0.01T-2T, and the direction of the magnetic field is perpendicular to the surface of the sample. Due to the increase of the effect of the magnetic field in the electrochemical deep etching process, the lateral current is limited, and the phenomenon of lateral erosion in the anodic oxidation process and collapse at the edge of some structures is overcome.

If the electrochemical deep etching method of the present invention does not add a magnetic field, but adds a temperature control device, the reaction temperature is controlled within the range of -10°C to 15°C, which reduces the lattice scattering probability of stray particles, and can also achieve effective. Of course, the addition of a magnetic field can also be carried out at a low temperature, and the effect is better at this time.

When the electrochemical deep etching method described in the present invention is used to design small structures, the shape of the etching window is a rectangle or a line with a width of 0.1 μm to 3 μm.

When the electrochemical deep etching method described in the present invention is used to design large structures, the way to make them is to decompose the large structures into arrays of small structures that are closely arranged. Arrays of deep wells or tips on the micro or nano scale are formed. Then use methods such as applying pulse current to make the isolation layer between the small structures fall off, so that the small structures can be merged into the required large structures.

The present invention proposes to adopt anti-HF thin film material as mask layer such as silicon nitride, silicon carbide and some alloys. It is reported that as long as there is a sharp structure on the silicon surface, deep etching of silicon can be realized. For the production of some dense arrays It is possible, but for device fabrication mainly based on isolated structures, the etching of the isolated area needs to have sufficient protection for other adjacent areas.

The device of the electrochemical deep etching method of the present invention comprises cathode 1, anode 2, electrochemical reaction tank 3, system control device 4, adjustable light source (for generating minority carriers such as holes) 5, magnetic field generating device 6. Sample 7 to be etched. The electrodes 1 and 2 are respectively connected to the positive and negative poles of the system control device 4 , and the adjustable light source 5 is also connected to the system control device 4 .

The device of the electrochemical deep etching method of the present invention can also be equipped with a temperature control device to control the ambient temperature to the required temperature, so that the reaction ambient temperature can be controlled between -10°C and 15°C.

The cathode used for corrosion is made of metal or silicon resistant to hydrofluoric acid corrosion, and the material usually used is platinum wire. A structure similar to a capacitor is formed on the silicon surface of the anode, and the back of the silicon chip is connected to the anode of the power supply. The corroded silicon wafer needs to form a low-resistance layer on the back to control the uniformity of the current. This low-resistance layer can be obtained by ion implantation. On this basis, metal aluminum can be deposited and then fabricated by photolithography. Out of the window structure for lighting needs. This improves contact performance across the back of the wafer.

The electrochemical deep etching provided by the present invention can be carried out in a magnetic field environment. Due to the effect of the magnetic field, the lateral current of carriers can be limited, thereby reducing lateral erosion and edge collapse phenomenon is also controlled, and because of lateral erosion and remote collapse phenomenon is avoided, so it is possible to use this etching technique for the fabrication of isolated structures.

In addition, the traditional N-type silicon electrochemical etching realizes the constant current by adjusting the light intensity under the condition of light. The present invention provides constant control of the current by voltage regulation, so that very fine micropores or Groove structure. And can solve the edge effect problem.

Most of the components of the device provided by the present invention are relatively cheap, so the price of the whole device is cheap, and the amount of chemical reagents used in the electrochemical deep etching process is very small, not only the operating cost is low, but also the surrounding environment will not be damaged.

Description of drawings

Figure 1: Diagram of electrochemical deep etching device

Specific embodiments

Below in conjunction with the manufacturing method of specific MEMS device, and contact the device provided by the present invention, the present invention is clearly and completely explained:

Example 1: Fabrication of Silicon Precision Interdigital Capacitors

Silicon interdigitated capacitors are an important part of silicon inertial gyroscopes. Using high aspect ratio deep etching technology can shorten interdigital spacing, increase effective capacitance, and improve resolution. Here is an electrochemical deep etching method to make this kind of interdigitated capacitor. The layout design of the device needs to consider the size of the interdigitated capacitor. If the spacing is greater than 2 microns, it is recommended to use a method of combining small structures. In this embodiment, the spacing is 1 micron, the process steps are as follows:

The sample used in this embodiment is a silicon wafer, and the silicon wafer is an n-type <100> silicon wafer with a resistivity of 1-5Ω·cm.

1. First, As ions are used to implant the back surface, the dose is 5×10 ¹⁵ /cm ² , and the energy can be selected as 150keV, and then annealed and activated in nitrogen at a temperature of 1000°C.

2. Deposit low-stress silicon nitride on the silicon wafer with a thickness of 500nm.

3. Coating glue on the front side of the silicon wafer, photolithography, using reactive ion etching to etch away the SiN, and etching in 85C, 25wt% tetramethylammonium hydroxide for 1 to 2 minutes.

4. Reverse photolithography, open an etching window with a width of 1 micron, and use reactive ion etching to etch away the SiN on the back window.

5. The electrochemical deep etching reaction is carried out in the electrochemical deep etching device provided by the present invention, the corrosion current is 10mA/cm ² during the reaction, the constant input voltage mode is adopted, the current is controlled by adjusting the light on the back, and the reaction temperature is 0°C , The magnetic induction is 0.2T.

6. Oxidize the surface for surface protection.

7. Etch silicon from the back window until reaching the etched hole, and remove SiO ₂ .

Through the above process, the precision interdigitated capacitor can be manufactured successfully.

Example 2: Silicon micro-nano channel

Making micro-nano channels through up and down on silicon wafers has many uses. It can be made into micro-channel photomultiplier devices, and can also be made into filters specially used in nanobiology, such as DNA filters. In addition, it can also be As the central channel of the micro-nano needle, it is similar to Example 1. Note that if the channel density is relatively large, the requirements for the mask layer are not high, and ordinary materials such as silicon nitride, silicon carbide, and gold-chromium alloy can be used. Specifically, In terms of the fabrication of the silicon micro-nano channel in this embodiment, the silicon micro-nano channel is 0.5 μm, and the sample is also a silicon chip, and the sample silicon in Example 1 is an n-type <100> silicon chip, and its resistivity is 1-5Ω cm, the process steps are as follows:

1. First, As or P ions are used to implant the back surface with a dose of 5×10 ¹⁵ /cm ² , and then activated by annealing in nitrogen at a temperature of 1000°C;

2. Deposit silicon nitride on the silicon wafer with a thickness of 200nm;

3. Apply glue on the front side of the silicon wafer, perform photolithography, and use reactive ion etching to etch away SiN, at 85C, 25wt% tetramethylammonium hydroxide for 1 to 2 minutes;

4. Reverse photolithography, open the window, and use reactive ion etching to etch away the SiN on the back window;

5. Perform deep etching in the electrochemical deep etching system provided by the present invention. According to the size of the hole, the current density is set to be very small if the size of the channel is required. This embodiment adopts the constant illumination mode and utilizes the adjustment of the input voltage Control the corrosion current, the current is 5mA/cm ² , and the temperature of the electrochemical deep etching process is 15°C;

6. The inner surface is treated and protected to delay the erosion of tetramethylammonium hydroxide.

7. Etch silicon from the back window until reaching the etched hole.

Claims (7)

1, a kind of electrochemical deep etching method, at first, to the sample back side carry out that the homotype ion injects and annealing activates, at positive deposit mask layer, open corrosion window, utilize anisotropic etchant to form inverted pyramid structure by the chemical wet etching mask layer, put into again and carry out anodic oxidation in the electrochemical reaction groove, it is characterized in that: the electrochemical deep etching process is carried out in magnetic field, and the direction in magnetic field is vertical with sample surfaces.

2, a kind of electrochemical deep etching method, at first, to the sample back side carry out that the homotype ion injects and annealing activates, at positive deposit mask layer, open corrosion window, utilize anisotropic etchant to form inverted pyramid structure by the chemical wet etching mask layer, put into and carry out anodic oxidation in the electrochemical reaction groove, it is characterized in that: the electrochemical deep etching process is carried out in temperature is-10 ℃～15 ℃ environment.

3, electrochemical deep etching method as claimed in claim 1 is characterized in that magnetic field intensity is between 0.01T～2T.

4, as claim 1,2 or 3 described electrochemical deep etching methods, corrosion window is shaped as rectangle or the lines that width is 0.1 μ m～3 μ m when it is characterized in that carrying out the minor structure design.

5, as claim 1,2 or 3 described electrochemical deep etching methods, when it is characterized in that carrying out the macrostructure design, being shaped as of corrosion window by the compact arranged array of minor structure, these arrays are at deep hole or most advanced and sophisticated array through forming micron or nanoscale behind the electrochemical deep etching, adopt again to apply pulse current and make between the minor structure to such an extent that separation layer comes off, thereby make minor structure merge into macrostructure.

6, a kind of electrochemical deep etching device, by negative electrode 1, anode 2, electrochemical reaction groove 3, system control device 4, tunable light source 5, sample 7 is formed, electrode 1 is connected with the both positive and negative polarity of system control device 4 respectively with electrode 2, and tunable light source 5 also is connected with system control device 4, it is characterized in that comprising field generator for magnetic 6.

7, as claim 1,2 described electrochemical deep etching devices is characterized in that comprising temperature control equipment.

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