KR19980050175A - How to make a micro gyroscope - Google Patents

Abstract

1. TECHNICAL FIELD OF THE INVENTION

The present invention relates to a material and a manufacturing method of a micro gyroscope sensor using surface micromachining technology.

2. Technical problem to be solved by the invention

The stress of the polysilicon, which is a conventional structure material, is solved to prevent the structure from being deformed, and also the compatibility of thermal processes that can occur during the fabrication of semiconductor IC circuits for driving and sensing sensors. To solve problems, metal wiring difficulties and the complexity of vacuum seals.

3. Summary of the Solution of the Invention

As a stress-free structure, instead of conventional polycrystalline silicon, single crystal silicon on top of SOI (Silicon On Insulator) is used, and a semiconductor IC circuit for driving and sensing is manufactured on a separate wafer and then bonded onto the structure. solves thermal process compatibility, metal wiring and vacuum sealing issues.

4. Important uses of the invention

Fabrication of MEMS (micro eletro mechanical system)

Description

How to make a micro gyroscope

The present invention relates to a material and a manufacturing method of a micro gyroscope sensor using surface microfabrication technology.

Gyroscopes are well known for angular velocity measuring devices used in navigation and inertial guidance devices such as aircraft, ships and automobiles. However, conventional rotary gyroscopes have a problem that they are bulky, expensive to maintain high precision, and are easily damaged by shock and vibration. Gyroscopes using fiber optics, lasers, etc. have excellent sensitivity, but they have not overcome the disadvantages of complicated manufacturing process and high price.

Recently, in order to satisfy the miniaturization requirement for a gyroscope, a sensor having another type of driving principle has been developed. Systeron, USA, manufactures a product that processes piezoelectric quartz (quArtz) in the form of a tuning fork type beam and detects deformation due to Coriolis force.

In addition, the research results of the micro gyroscope that can achieve miniaturization, high sensitivity, and low cost using silicon surface micromachining technology were published in the IEEE micro electro mechanical system (MEMS) conference in 1995 (K.Tanaka etal). , IEEE / ASME MEMS Workshop, 1995, pp. 278-282). In this gyroscope (angular velocity sensor), as shown in Fig. 1, a mechanical structure capable of two degrees of freedom of x and y motion is driven in an electrostatic force in the left and right directions (x directions) and up and down directions ( When a rotation around the y axis is applied, a Coriolis force in the vertical direction (z direction) acts on the structure. This force vibrates the structure in the vertical direction (z direction), and the sensor circuit detects the magnitude of the vibration changed by the capacitance. In order to drive the structure at a low voltage, the environment in which the structure vibrates must be made in a vacuum state. For this purpose, a small vacuum chamber into which a sensor can be inserted must be manufactured.

The above surface microfabrication technology is based on a semiconductor integrated circuit fabrication process that processes thin film material on a silicon substrate. By using this technology, a microstructure is fabricated on a silicon substrate and bonded to a semiconductor circuit, such as a micro sensor. High-performance MEMS devices can be made. The microstructure, which is the main component of MEMS, is generally composed of a cantilever in which one part stands out from the substrate, and a bridge in which a center part is lifted from the substrate to form a space. A sacrificial layer etching method is used to form the microstructure, and an oxide film having a large etching selectivity with silicon is used as the sacrificial layer etching method.

Here, the problems of the material and manufacturing method of the gyroscope manufactured by the surface micromachining technology are as follows.

One serious limiting factor in the fabrication of microstructures by surface micromachining is the residual strees of thin films with thicknesses of 1-10 um. The residual stress of the thin film causes a large deformation in the bridge and cantilever, which is the main form of the structure, when the structure is removed from the substrate by removing the sacrificial layer, thereby obtaining a device having a designed characteristic. In other words, the presence of an average internal stress with respect to the thickness of the thin film causes buckling in the bridge, and the stress gradient due to uneven stress causes bending of the cantilever and results in severe up and down direction. Cause deformation. This residual stress arises from the internal stresses formed in the crystal structure as the polycrystalline silicon grows and from the uneven concentration distribution caused by the addition of impurities to the polycrystalline silicon to fabricate the conductive structure. .

Next, we look at the compatibility issue of the fabrication process for micro gyroscopes. The following problems can be expected in the conventional method of fabricating a polycrystalline silicon microstructure and a peripheral circuit on the same wafer. In the case of fabricating a circuit first and then fabricating a polycrystalline silicon structure later, during the polycrystalline silicon process and the annealing process of 900 ° C. or more, aluminum wiring, which is widely used in recent years due to low temperature processability and material stability, is later deposited at a temperature of 600 ° C. Melting results in poor device characteristics. If the polycrystalline silicon structure is fabricated first and the circuit is fabricated later, the wiring metal problem is not serious. However, as shown in FIG. 2, since the surface roughness is usually 5 μm or more due to the height of the polysilicon structure, a problem such as uneven photo resist coating is generated in the fabrication of the peripheral circuit, which is the next process, resulting in a circuit pattern. Becomes difficult to make.

In the method for making the structure in which the structure vibrates in a vacuum state, it is cumbersome to manufacture a separate small vacuum chamber, which makes it difficult to realize miniaturization of the sensor. At present, the vacuum sealing method of the sensor is attempted using the deposition method during the semiconductor manufacturing process, but it is still in the early research stage.

As described above, in the conventional micro gyroscope, the structure is deformed by the stresses appearing in the polycrystalline silicon structure, and the compatibility of the thermal process, the metal wiring, and the vacuum sealing in the fabrication of the semiconductor IC circuit for driving and sensing the sensor are described. there is a problem.

It prevents the structure from deforming by relieving the stresses in the polycrystalline silicon, which is the existing structure material, and also the compatibility problem of thermal process that can occur in the process of manufacturing semiconductor IC circuits for driving and sensing the sensor, metal wiring And to solve the difficulty of vacuum sealing.

1 is a plan view of a conventional micro gyroscope

2 is a cross-sectional structural view of a conventional micro gyroscope

3 is a cross-sectional structural view of a micro gyroscope of the present invention

4 is a manufacturing process chart of the micro gyroscope of the present invention

* Explanation of symbols for main parts of the drawings

11 polycrystalline silicon structure 12 polycrystalline silicon spring

14 polycrystalline silicon electrode 15 anchor

16: vacuum sealing part 21: polycrystalline silicon structure

22 polycrystalline silicon spring 24 polycrystalline silicon electrode

25: anchor 26: lower electrode

27: peripheral circuit 28: metal wiring

30 silicon wafer 31 single crystal silicon structure

32: single crystal silicon spring 33: thermal oxide film

34: nitride film 35: sacrificial layer oxide film

36: lower electrode 37: peripheral circuit

38: wiring for circuit connection 39: wiring for vacuum sealing

40 silicon wafer 41 SOI substrate

The micro gyroscope sensor in the present invention uses a silicon crystal on top of a silicon on insulator (SOI) as a structure material, as shown in FIG. Since the silicon single crystal has a small residual stress, the strain due to the stress can be reduced. Even in the life of the structure, single crystal silicon has a high fatigue fracture strength against vibration, thus making it possible to manufacture a longer life micro gyroscope.

A peripheral circuit for driving and detecting a micro gyroscope is manufactured on a separate wafer, not a wafer on which the structure is manufactured, and then bonded to the structure. Such a method can solve the compatibility problem of the thermal process, the difficulty of the metal wiring due to the step, and the complexity of the vacuum sealing process at the same time.

Based on the above description, an embodiment of the present invention will be described in detail with reference to FIG. 4.

First, an oxide film serving as an etching mask is deposited to fabricate single crystal silicon of the SOI wafer 41 into the structure 31 as shown in A1 of FIG. 4, and then a structure pattern is formed by a lithography process as shown in B1 of FIG. 4. Remove the photoresist (not shown) formed by the lithographic process. Subsequently, as shown in 3C of FIG. 4, a structure is formed on the silicon crystal by using a reactive ion etching process, and then etched to the oxide layer 35 under the SOI. In D1 of FIG. 4, an exposed oxide layer of SOI is removed by a gas phase etching method including anhydrous hydrofluoric acid (HF) and methanol to form a space at the bottom. In the removal of the sacrificial layer oxide film by HF vapor phase etching, no sticking phenomenon and no etching residue occur, and thus a fine structure having a desired shape can be formed well.

Next, as shown in A2 of FIG. 4, the oxide film 33 and the nitride film 34 are deposited on a separate silicon substrate 40 for electrical insulation, and then, as shown in B2 of FIG. 4, the lower electrode of the micro gyroscope ( 36), a polycrystalline silicon film is deposited. Subsequently, as in C2 of FIG. 4, a peripheral circuit 37 for driving the structure and processing the signal is fabricated on the same wafer 40. In step D2 of FIG. 4, the wiring 38 necessary for the electrical connection between the structure and the peripheral circuit 37 and the wiring 39 in the closed form 16 surrounding the sensor for vacuum sealing are performed.

As described above, the silicon structure fabricated from the SOI substrate and the peripheral circuit fabricated from a separate general wafer are aligned with electrode patterns as shown in E of FIG. 4, and then the electrodes wired to connect and seal the circuits as shown in FIG. Glue.

The present invention described above is not limited to the above-described embodiments and the accompanying drawings, and various substitutions, modifications, and changes are possible in the art without departing from the technical spirit of the present invention. It will be apparent to those of ordinary knowledge.

In a micro gyroscope sensor using surface micromachining technology, a structure is fabricated using silicon crystals on top of a silicon on insulator (SOI), and thus a device having no deformation and a long lifetime can be manufactured.

In addition, semiconductor IC circuits for driving and sensing are fabricated on separate wafers, and then bonded to the structures to solve the compatibility problem of thermal processes in the fabrication of the structures and circuits. Difficulty in electrical wiring and vacuum sealing due to the step can be solved at the same time.

The present invention aims to prevent the structure from being changed by eliminating the internal stress present in the polycrystalline silicon, which is a conventional structure material, in a micro gyroscope sensor using surface micromachining technology. In addition, thermal process compatibility problems in manufacturing semiconductor IC circuits for driving and sensing sensors, metal wiring processes are difficult due to wafer steps during the process, and vacuum sealing seal) to solve the complexity of the process.

Claims (4)

In the manufacturing process of micro gymscope sensor using surface micromachining technology, single crystal silicon on top of SOI (Silicon On Insulator) is used to fabricate long-life structure with low strain due to residual stress. Manufacturing process of a micro gyroscope, characterized in that using. The method of claim 1, wherein the microstructure is fabricated by using reactive ion etching having anisotropic etching characteristics, and the lower sacrificial layer oxide film is formed using a gas phase etching process using hydrofluoric anhydride and methanol. Micro gyroscope fabrication process, characterized in that the removal without. The method of claim 1, in order to simultaneously solve the difficulty of the compatibility of the thermal process and the metal wiring due to the step, after fabricating the structure and the peripheral circuit on a separate wafer, respectively, and then bonded the fabricated peripheral circuit on the structure A manufacturing process of a micro gyroscope, characterized in that the (bonding). 4. The micro gyroscope according to claim 3, comprising a closed wiring process and a bonding process in which the sensor is wound for vacuum sealing when performing the bonding process necessary for the electrical connection between the structure and the peripheral circuit. Production process.