RU2559336C1 - Method of micro-profiling of silicon structures - Google Patents

Abstract

FIELD: instrument engineering.

SUBSTANCE: method of micro-profiling of silicon structures comprises applying a protective film on the plate of single-crystal silicon, the formation from the protective film of the local mask in the area of microprofile formation, anisotropic etching of the plate of single-crystal silicon, applying the protective film, applying the layer of polycrystalline silicon, anisotropic etching of polycrystalline silicon, oxidation of polycrystalline silicon, etching of silicon dioxide with the newly applied protective film, etching the protective film to the surface of the plate, and anisotropic etching in the resulting window of the plate of single-crystal silicon. These processes are alternately repeated as many times as may be necessary until obtaining the desired microprofile followed by smoothing the resulting surface in the isotropic or anisotropic etching agent or anisotropic and isotropic etching agents.

EFFECT: reduction of labour intensity of manufacturing, and increase in quality of the structures.

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Description

The invention relates to instrumentation and can be used for the manufacture of structural elements of micromechanical devices on silicon single-crystal substrates, namely, elastic suspensions and the entire sensitive element as a whole, for example, for micromechanical accelerometers and gyroscopes.

A known method of manufacturing deeply profiled silicon structures by isotropic etching of the original plate of single-crystal silicon [1].

The disadvantage of this method is the inaccuracy of the manufacture of structural elements for microdevices, due to the dependence of the etching rate on temperature and the concentration of the etchant, as well as the difficulty of providing local protection from prolonged exposure to the etchant. Another disadvantage of this method is the significant lateral melt single crystal silicon, because with isotropic etching, the speed in all directions is the same.

A known method of manufacturing a sensitive element of a micromechanical device, which consists in applying a protective mask to the plate, forming a window and local anisotropic etching of silicon in the window of this mask [2].

However, the known method has the following disadvantages. As a result of anisotropic etching, a profile is obtained in the form of a trapezoid in cross section, on the tops of which concentrators of mechanical stress arise at the points of abrupt transition and, in the presence of microcracks, it is destroyed during operation. In addition, in micromechanical devices, this also leads to a failure of the entire device, therefore, to a decrease in reliability. In addition, in micromechanical devices, an elastic suspension made in this way has a low resistance to longitudinal compressive action. When the measured value is exposed, the elastic element obtained in this way experiences distributed bending, which reduces the accuracy of the transducer.

The problem to which the invention is directed, is to reduce the complexity of manufacturing and improve the quality of structures. To achieve this, the method of microprofiling silicon structures includes applying a protective film to a single-crystal silicon wafer, forming a local mask from the protective film in the area of microprofile formation and further anisotropic etching of a single-crystal silicon wafer, after anisotropic etching of a single-crystal silicon wafer, a protective film is applied, a layer of polycrystalline silicon is applied, conduct anisotropic etching of polycrystalline silicon, conduct oxidation of the floor crystalline silicon, etch silicon dioxide from the newly applied protective film, etch the protective film to the wafer surface, conduct anisotropic etching in the resulting window of a single-crystal silicon wafer, then apply a protective film, a layer of polycrystalline silicon, conduct anisotropic etching of polycrystalline silicon, oxidize polycrystalline silicon , etching of silicon dioxide, etching of the protective film to the surface of the plate and anisotropic etching of neo the required number of times until the desired microprofile is obtained, followed by smoothing in the isotropic or anisotropic etch or anisotropic and isotropic etch of the resulting surface.

Distinctive features of the claimed method is that after anisotropic etching of a single-crystal silicon wafer, a protective film is applied, a layer of polycrystalline silicon is applied, anisotropic etching of polycrystalline silicon is carried out, polycrystalline silicon is oxidized, silicon dioxide is etched from the newly applied protective film, and the protective film is etched to the surface plates, conduct anisotropic etching in the resulting window of the plate of a single-crystal cream They then apply a protective film again, a layer of polycrystalline silicon, conduct anisotropic etching of polycrystalline silicon, oxidize polycrystalline silicon, etch silicon dioxide, etch the protective film to the wafer surface and anisotropic etch as many times as necessary to obtain the desired microprofile, followed by smoothing in an isotropic or anisotropic etch or anisotropic and isotropic etch the resulting surface. The repetition of the sequence of the technological cycle and technological operations, as well as the number of cycles is determined by the complexity of the designed profile and its purpose, respectively, by the specific application of the final obtained profile, for example, for sensitive elements of pressure sensors, or linear, angular acceleration sensors, or angular velocity sensors, or force sensors , or displacement sensors. Thus, obtaining a specific profile is determined by the specific purpose of the devices in which the microprofile will be used, for example, its elastic elements, which determine its basic accuracy and strength characteristics. Accordingly, for each specific microprofile as intended, the number of cycles is determined for each individual microprofile separately for its intended purpose. The proposed method allows to make the profile of the elastic elements of micromechanical devices smooth. This increases reliability compared to the prototype, in which stress concentrators appear on bends, leading to the destruction of the device.

The invention is illustrated by the drawings of FIG. 1, FIG. 2.

In FIG. 1 (a, b, c, d, e) and FIG. 2 (a, b, c) shows the sequence of microprofiling of silicon structures,

Where:

1 - single crystal silicon wafer;

2 - a protective film of silicon dioxide;

3 - a protective film of silicon nitride;

4 - layer of polycrystalline silicon.

The method is implemented as follows. A protective film of silicon dioxide 2 is applied to the single-crystal silicon plate 1 (Fig. 1a), exposure is performed to open the windows in the protective film of silicon dioxide 2 (Fig. 1b). Anisotropic etching of a single-crystal silicon wafer 1 is carried out in the resulting window (Fig. 1c). Again, a protective film of silicon nitride 3 is applied (Fig. 1d). Polycrystalline silicon 4 is applied (FIG. 1 d). Anisotropic etching of polycrystalline silicon 4 is carried out (Fig. 1e). The oxidation of polycrystalline silicon 4 is carried out (Fig. 2A). The protective film of silicon nitride 3 is etched to the surface of the plate 1 (Fig. 2b). Anisotropic etching of a single-crystal silicon wafer 1 is carried out in the resulting window (Fig. 2c). Repeat the required number of times until the desired microprofile is obtained, followed by smoothing in the isotropic or anisotropic etchant or anisotropic and isotropic etch the resulting surface. Obtaining a specific profile is determined by the specific purpose of the devices in which the microprofile will be used, for example, its elastic elements, which determine its basic accuracy and strength characteristics. Accordingly, for each specific microprofile as intended, the number of cycles is determined for each individual microprofile separately for its intended purpose.

Example.

On a single-crystal silicon wafer of orientation (100), during thermal oxidation at a temperature of 1100 ° C for 65 min in water vapor, a silicon dioxide film 0.4 μm thick is formed on the surface of single-crystal silicon at normal atmospheric pressure. Then apply photoresist FP-383. Photolithography is carried out. Plasma-chemical etching (vertical) of SiO _{2 is} carried out. Next, plasma-chemical etching of silicon to a depth of 2 μm is carried out. After that, the deposition of Si ₃ N ₄ (100 nm). The deposition process of Si ₃ N _{4 is} carried out from the gas phase (monosilane and ammonia) for 60 min, at a temperature of 850-870 ° C, operating pressure of 30 Pa. Then, polycrystalline silicon is deposited (1 μm = 2 times 60 min) from the gas phase (monosilane) for 120 min, at a temperature of 850-870 ° C, and a working pressure of 30 Pa. Plasma-chemical etching (vertical) of polysilicon to a depth of 1 μm is carried out. Then polycrystalline silicon is oxidized at a partial pressure of H ₂ O of 0.6 atm for 600 min, a temperature of 1150 ° C, and a working pressure of 1 atm. Plasma-chemical etching (vertical) of Si ₃ N _{4 is} carried out to the plate surface. Plasma-chemical etching of silicon to a depth of 2 μm is carried out. Operations are repeated starting from the deposition of Si ₃ N _{4 the} required number of times until the desired microprofile is obtained, followed by smoothing in the isotropic or anisotropic etchant or anisotropic and isotropic etch of the resulting surface. Moreover, the process of microprofiling silicon structures is carried out with one photomask. In this case, by varying the thickness of the deposited polycrystalline silicon and the depth of anisotropic etching in the resulting window of the single-crystal silicon wafer of each formation stage, the desired microprofile shape is obtained. It is possible to obtain various profile shapes of silicon structures: both oval and broken.

Thus, the proposed method reduces the complexity of manufacturing sensitive elements, increasing the efficiency of the Converter by increasing the mechanical strength of the suspension. In this case, the concentration of mechanical stresses at the junctions of the elastic elements is significantly reduced.

In the case of microcracks in the body of the suspension element in comparison with the prototype reduces the likelihood of failure of the Converter.

Information sources

1. Etching of semiconductors [collection of articles]. Per. from English S.N. Gorina. M.: Mir, 1965.

2. Vaganov V.I. Integrated strain gauges. - M .: Energoatomizdat, 1983. - prototype.

Claims (1)

A method of microprofiling silicon structures, including applying a protective film to a single-crystal silicon wafer, forming a local mask from the protective film in the area of forming the microprofile and further anisotropic etching of the single-crystal silicon wafer, characterized in that after the anisotropic etching of the single-crystal silicon wafer, a protective film is applied, a polycrystalline layer is applied silicon, conduct anisotropic etching of polycrystalline silicon, conduct oxidation polycrystalline silicon, etching silicon dioxide from a newly applied protective film, etching the protective film to the wafer surface, conducting anisotropic etching in the resulting window of a single crystal silicon wafer, then applying a protective film again, a layer of polycrystalline silicon, conducting anisotropic etching of polycrystalline silicon, oxidizing polycrystalline silicon , etching of silicon dioxide, etching of the protective film to the surface of the plate and anisotropic etching the required number of times until the desired microprofile is obtained, followed by smoothing in the isotropic or anisotropic etch or anisotropic and isotropic etch of the resulting surface.

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