CN115676770A - Silicon nanowire gyroscope with adjustable working state and preparation method thereof - Google Patents

Abstract

The invention belongs to the technical field of gyroscope design, and particularly relates to a silicon nanowire gyroscope with an adjustable working state and a preparation method thereof. The silicon nanowire gyroscope adopts a silicon nitride film, a grid and a silicon nanowire to jointly support a mass block, and adopts a monocrystalline silicon nanowire to replace a traditional piezoresistor as a detection mode of angular acceleration. The gate skillfully prepared on the silicon nitride film can effectively modulate a silicon nanowire channel so as to find out the optimal working point of the device, and can effectively protect the silicon nanowire from being broken due to various reasons, thereby greatly improving the long-term stability of the silicon nanowire device.

Description

Silicon nanowire gyroscope with adjustable working state and preparation method thereof

Technical Field

The invention belongs to the technical field of gyroscope design, and particularly relates to a silicon nanowire gyroscope with an adjustable working state and a preparation method thereof.

Background

A micromechanical gyroscope, i.e., a MEMS gyroscope, is a typical angular velocity microsensor, and has a very wide application in the consumer electronics market due to its advantages of small size, low power consumption, and convenient processing. With the gradual improvement of performance in recent years, MEMS gyroscopes are widely used in the fields of industry, automobiles, virtual reality, and the like.

With the development of scientific technology, the demand for microminiaturization and integration of sensor devices is becoming stronger, and the size of the traditional capacitance detection and piezoresistance detection-based gyroscope is difficult to be greatly reduced under the condition of ensuring the accuracy and the resolution of the gyroscope to be unchanged, so that the existing gyroscope has larger volume.

The silicon nanowire is a novel one-dimensional nano material, and the property of the material can be changed violently due to subtle changes of external environments, so that the silicon nanowire can be used for replacing a traditional piezoresistor to be used as a detection mode of a gyroscope, microminiaturization of a device can be realized, and the silicon nanowire has a great application prospect. However, after the structure of the silicon nanowire is determined, the concentration of the channel carrier of the silicon nanowire cannot be adjusted, so that the working state of the gyroscope cannot be adjusted to be optimal according to the actual application scene.

Disclosure of Invention

The invention aims to solve the problems and provides a silicon nanowire gyroscope with adjustable working state and a preparation method thereof.

In order to realize the purpose of the invention, the invention adopts the following technical scheme:

a preparation method of a silicon nanowire gyroscope with an adjustable working state comprises the following steps:

s1, preparing a silicon nitride film on the top silicon surface of an SOI silicon chip to form a dielectric mask layer;

s2, transferring the small triangular patterns on the medium mask layer through a photoetching process, and etching silicon nitride at the small triangular patterns to form small triangular windows; then, dry etching is carried out on the silicon at the triangular window until an oxide layer is formed, a small vertical triangular groove is formed, and then the photoresist is removed;

s3, oxidizing the small vertical triangular groove by using a self-limiting thermal oxidation process;

s4, transferring three large triangular patterns distributed along the circumferential direction of the small vertical triangular grooves on the medium mask layer through a photoetching process, and etching silicon nitride at the large triangular patterns to form large triangular windows; then, dry etching is carried out on the silicon at the three large triangular windows until an oxide layer is formed, three vertical large triangular grooves with the same depth are formed, and then photoresist is removed;

s5, carrying out anisotropic wet etching on the large vertical triangular groove to form hexagonal etching grooves with side walls belonging to a {111} crystal face group, forming a monocrystalline silicon thin-wall structure between every two adjacent hexagonal etching grooves, and forming opposite cone-like structures among the three hexagonal etching grooves;

s6, oxidizing the silicon wafer by using a self-limiting thermal oxidation process to form a monocrystalline silicon nanowire at the center of the top of the monocrystalline silicon thin-wall structure;

s7, etching silicon nitride at a proper position of the silicon wafer to form a square window, injecting boron ions into the square window, then annealing, and then manufacturing a positive electrode and a negative electrode;

s8, manufacturing a grid electrode on the suspended silicon nitride film;

s9, manufacturing an isolation channel at a proper position of the silicon wafer to realize physical isolation of the positive electrode and the negative electrode;

and S10, removing the oxidized monocrystalline silicon thin-wall structure and releasing the whole structure.

Preferably, the thickness of the silicon nitride film is 50nm-5 μm.

Preferably, the side length of the small triangular window is 1-50 μm.

Preferably, the small triangular window is replaced by a circle or a square.

Preferably, the depth of the small vertical triangular groove is 1-100 μm.

Preferably, the oxidation depth in the step S3 is 100nm-20 μm.

Preferably, the depth of the large vertical triangular groove is 1-100 μm.

Preferably, the width of the monocrystalline silicon nanowire is 10-800nm.

Preferably, the gate is positioned right above the silicon nanowires, and each silicon nanowire is covered by the gate.

The invention also provides a silicon nanowire gyroscope with adjustable working state, which is prepared by the preparation method of any one scheme.

Compared with the prior art, the invention has the beneficial effects that:

according to the invention, the silicon nitride film and the three silicon nanowires jointly support the conical mass block as a core structure of the gyroscope, so that the sensitivity of the gyroscope is effectively improved; in addition, the silicon nitride film is skillfully reserved, and the silicon nitride film is used as an insulating layer to manufacture the grid electrode on the silicon nitride film, so that the silicon nanowire can be effectively protected from being broken due to various reasons. In addition, the concentration of the carrier of the silicon nanowire channel is adjusted through the grid electrode, so that the optimal working point of the gyroscope can be found.

Due to the special design of the silicon nanowire and the mass block, the silicon nanowire gyroscope can still normally work under the condition of a large angular acceleration value, and the preparation of the gyroscope with an ultra-large range can be realized.

The invention has simple process, all process flows belong to the traditional micro-processing process, the cost is low, and the large-scale industrial production can be realized.

Drawings

FIG. 1 is a schematic diagram of the fabrication of a silicon nitride film on top silicon according to example 1 of the present invention;

FIG. 2 is a schematic diagram of a triangular etching trench fabricated on a silicon wafer according to example 1 of the present invention;

FIG. 3 is a schematic diagram of a wet etching process for forming triangular grooves with inclined hexagonal etching grooves according to example 1 of the present invention;

FIG. 4 is a schematic diagram of the formation of silicon nanowires by thermal oxidation of thin silicon nano-walls in example 1 of the present invention;

FIG. 5 is a schematic diagram of the fabrication of gold electrodes and isolation trenches on a silicon wafer according to embodiment 1 of the present invention;

FIG. 6 is a schematic illustration of a silicon nanowire proof-mass after releasing the entire structure of example 1 of the present invention;

fig. 7 is a schematic structural view of a silicon nanowire gyroscope according to embodiment 1 of the present invention;

FIG. 8 is a photograph of the wet-etched triangular groove of example 1 of the present invention;

FIG. 9 is a photograph showing wet etching of triangular grooves in example 2 of the present invention.

Detailed Description

In order to more clearly illustrate the embodiments of the present invention, the following description will explain the embodiments of the present invention with reference to the accompanying drawings. It is obvious that the drawings in the following description are only some examples of the invention, and that for a person skilled in the art, without inventive effort, other drawings and embodiments can be derived from them.

Example 1:

as shown in fig. 1 to 7, the silicon nanowire gyroscope of the present embodiment mainly includes a silicon nanowire 8, a silicon nitride film 1, a mass block 9, a gold electrode 12, a gate 13, and an SOI silicon wafer.

When the gyroscope is subjected to the action of external angular acceleration, the mass block 9 rotates along with the direction of the angular acceleration, so that the silicon nanowire 8 supporting the mass block is deformed, the deformation causes the conductivity change of the silicon nanowire, and then a changed signal is output. Meanwhile, the gate 13 of the gyroscope of the embodiment can adjust the carrier concentration of the silicon nanowire channel, so as to find the optimal working point of the gyroscope.

Specifically, the preparation method of the silicon nanowire gyroscope of the embodiment includes the following steps:

1. firstly, a (111) type SOI silicon wafer with 100 type bottom silicon is selected, a silicon nitride film 1 with the thickness of 50nm-5 mu m is prepared on the surface of the substrate top silicon 2 by using a low-stress CVD film growth technology, and a compact dielectric mask layer is formed, as shown in figure 1.

Then, transferring the triangular pattern through a photoetching process, and simultaneously performing an RIE (reactive ion etching) process to etch silicon nitride at the triangular pattern to form a triangular window 14; the side length of the triangular window 14 is 1-50 mu m, and silicon at the triangular window 14 is subjected to dry etching to prepare a vertical triangular groove with the depth of 1-100 mu m; the photoresist is then removed and the vertical triangular grooves are oxidized 100nm-20 μm based on a self-limiting thermal oxidation process, as shown in fig. 2.

2. Three triangular windows 5 are formed in the silicon nitride layer 1 through a photoetching process, dry etching is carried out on the three windows until the oxide layer 3 of the silicon wafer is etched, vertical triangular grooves with the depth of 1-100 mu m are prepared, and photoresist is removed, as shown in figure 2.

3. Performing anisotropic wet etching on the silicon wafer in 10-100 ℃ KOH solution with the weight percent of 10-80, wherein the wet etching time is 5 minutes to 10 hours, and then three triangular grooves in the step 2 are etched into hexagonal etching grooves with side walls belonging to a {111} crystal face family, as shown in FIGS. 3 and 8; and a monocrystalline silicon thin-wall structure 7 with the preset width smaller than 1 μm is formed between two adjacent hexagonal corrosion grooves, a relative quasi-triangular cone structure appears in the middle of three hexagonal corrosion grooves, and the quasi-cone positioned above the three hexagonal corrosion grooves is the mass block 9 of the gyroscope (wherein, the suspension of the mass block needs two processes, one is the breaking of a small triangle, and the other is the complete breaking of the subsequent removal of oxidized monocrystalline silicon thin-wall structure by BOE, so as to realize the suspension of the mass block), as shown in FIG. 3 and FIG. 6.

4. After the silicon wafer is oxidized by the self-limiting thermal oxidation process, a monocrystalline silicon nanowire 8 is formed at the center of the top of the monocrystalline silicon nanowall 7, as shown in fig. 4.

5. Respectively etching silicon nitride at the upper left corner and the lower right corner of the silicon wafer to form a square window, implanting boron ions into the square window, annealing, wherein the ion implantation energy is 5-100KeV, and the ion implantation dosage is 0.1E15cm ^-2 -10E15cm ^-2 Annealing at 200-4000 deg.c for 5 min-10 hr, and making gold electrode 12 as positive and negative electrodes in the area;

then preparing a grid 13 on the suspended silicon nitride film, wherein the grid is positioned right above the silicon nanowires, each silicon nanowire is covered by the grid, and the width of the grid is 1-100 mu m;

the silicon wafer is also etched to the oxide layer at the proper position of the silicon wafer to make the isolation channel 11 of the device, so as to realize the physical isolation of the positive electrode and the negative electrode of the device, as shown in fig. 5.

6. And (4) removing the oxidized monocrystalline silicon thin-wall structure in the step (4) by using BOE (buffer oxide etching solution) to release the whole structure.

After the above steps are completed, the silicon nanowire gyroscope shown in fig. 7 can be prepared.

The grid of the silicon nanowire gyroscope of the embodiment can effectively modulate a silicon nanowire channel, so that the optimal working point of a device is found, and the silicon nanowire can be effectively protected.

Example 2:

the present embodiment is different from the silicon nanowire gyroscope of embodiment 1 in that:

as shown in fig. 9, the arrangement positions of the three triangular windows are different, and the structures related to the three triangular windows are adjusted correspondingly; other structures can refer to embodiment 1;

the processing technology of the silicon nanowire gyroscope is adaptively adjusted according to different arrangement positions of the three triangular windows, and the specific steps can refer to embodiment 1.

The foregoing has outlined rather broadly the preferred embodiments and principles of the present invention and it will be appreciated that those skilled in the art may devise variations of the present invention that are within the spirit and scope of the appended claims.

Claims (10)

1. A preparation method of a silicon nanowire gyroscope with an adjustable working state is characterized by comprising the following steps:

s1, preparing a silicon nitride film on the surface of top silicon of an SOI silicon wafer to form a dielectric mask layer;

s2, transferring the small triangular patterns on the medium mask layer through a photoetching process, and etching silicon nitride at the small triangular patterns to form small triangular windows; then, dry etching is carried out on the silicon at the triangular window until an oxide layer is formed, a small vertical triangular groove is formed, and then the photoresist is removed;

s3, oxidizing the small vertical triangular groove by using a self-limiting thermal oxidation process;

s4, transferring three large triangular patterns distributed along the circumferential direction of the small vertical triangular grooves on the medium mask layer through a photoetching process, and etching silicon nitride at the large triangular patterns to form large triangular windows; then, dry etching is carried out on silicon at the three large triangular windows until an oxide layer is formed, three vertical large triangular grooves with the same depth are obtained, and then photoresist is removed;

s5, performing anisotropic wet etching on the large vertical triangular grooves to form hexagonal etching grooves with side walls belonging to a {111} crystal face family, forming a monocrystalline silicon thin-wall structure between every two adjacent hexagonal etching grooves, and forming a relative cone-like structure among the three hexagonal etching grooves;

s6, oxidizing the silicon wafer by using a self-limiting thermal oxidation process to form a monocrystalline silicon nanowire at the center of the top of the monocrystalline silicon thin-wall structure;

s7, etching silicon nitride at a proper position of the silicon wafer to form a square window, implanting boron ions into the square window, annealing, and then manufacturing a positive electrode and a negative electrode;

s8, manufacturing a grid electrode on the suspended silicon nitride film;

s9, manufacturing an isolation channel at a proper position of the silicon wafer to realize physical isolation of the positive electrode and the negative electrode;

and S10, removing the oxidized monocrystalline silicon thin-wall structure and releasing the whole structure.

2. The method according to claim 1, wherein the silicon nitride film has a thickness of 50nm to 5 μm.

3. The method of claim 1, wherein the small triangular window has a side length of 1 to 50 μm.

4. The method of claim 1, wherein the small vertical triangular grooves have a depth of 1 to 100 μm.

5. The method according to claim 5, wherein the oxidation depth in the step S3 is 100nm to 20 μm.

6. The method of claim 1, wherein the large vertical triangular grooves have a depth of 1-100 μm.

7. The method of claim 1, wherein the single-crystal silicon nanowires have a width of 10 to 800nm.

8. The method of claim 1, wherein the gate is directly over the silicon nanowires and each silicon nanowire is covered by the gate.

9. The silicon nanowire gyroscope with adjustable working state manufactured by the manufacturing method according to any one of claims 1 to 9.

10. The silicon nanowire gyroscope of claim 9, wherein the core structure of the gyroscope is formed by a silicon nitride film and a conical mass supported by three silicon nanowires.

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