CN1159208C - Fabrication Method of Movable Silicon Micromechanical Structure Integration on Glass Substrate - Google Patents

Abstract

The present invention relates to a manufacturing method for integrating a micro mechanical structure of movable silicon on a monocrystal glass substrate. In the method, a silicon-glass electrostatic bonding technique is used for manufacturing a sensitive monocrystal silicon structure on a glass substrate, a movable structure corresponding to a pre-etching shallow pit at the bottom of the movable structure at one side of a bonding surface of a silicon chip is suspended, a deep reactive ion etching technique of monocrystal silicon is introduced for etching and molding a micro structure, and the monocrystal silicon can be used as a structural material to manufacture a plane-movable micro structure having a high depth ratio from surface micro mechanical dimensional thickness to body micro mechanical dimensional thickness; the present invention is suitable for manufacturing various plane-movable micro structures, such as accelerated sensors, gyroes, resonators, etc.

Description

Fabrication Method of Movable Silicon Micromechanical Structure Integration on Glass Substrate

technical field

The invention relates to microelectronic machining, in particular to a manufacturing method for the integration of movable silicon micromechanical structures on a glass substrate.

Background technique

Since the 1980s, micromachining technology has emerged and made great progress, and many mechanical components on a macro scale, such as motors, gears, cranks, springs, etc., have been realized on a micro scale of tens of microns. Based on this, people organically combine micromechanics and microelectronic components to form a system with specific functions, thus creating a new discipline of microelectromechanical system (MicroElectro Mechanical System, referred to as MEMS). Compared with conventional systems, integrated MEMS has significant advantages such as small size, light weight, low cost, compatibility with large-scale integrated circuit manufacturing processes, and easy mass production. It is widely used in military, communication, automotive electronics, biomedical engineering, etc. There are broad application prospects in these fields. Micromachining technology can be roughly divided into two categories: surface micromachining and bulk micromachining. Surface micromachining deposits or grows thin film materials, such as polysilicon, silicon nitride, etc., on a single crystal silicon substrate, processes these thin film materials, and stacks the required microstructure. The suspension of its movable structure is generally realized by the method of sacrificial layer corrosion release. Bulk micromachining directly processes bulk materials (usually monocrystalline silicon substrates) to produce quasi-three-dimensional microstructures, and various etching techniques for bulk materials are mostly used. In recent years, deep reactive ion etching technology (Deep Reactive Ion Etching, referred to as DRIE) has made great breakthroughs, and has been able to achieve silicon etching with a depth of hundreds of microns in a relatively short period of time, and obtain very high depth The width ratio and the steepness of the side wall provide a powerful technical means for the micromachining of single crystal silicon. Using micro-machining technology, people have realized the fabrication of various movable micro-structures such as micro-acceleration sensors, micro-gyroscopes, micro-resonators, and micro-motors.

The production of planar movable microstructures can be made by using monocrystalline silicon as a substrate and micromachining on the surface of polycrystalline silicon. The suspension of movable microstructures adopts sacrificial layer technology, such as the micro accelerometer developed by Analog Devices in the United States. ADXL50. However, the thickness of the polysilicon structure layer deposited by this production method is generally not more than a few microns due to the process limitation, so the sensitive capacitance of the sensor is very small. Detection brings difficulties, and the stress introduced during the deposition of polysilicon, the device structure material, also affects the device behavior to a certain extent. From then on, people began to try to use glass as a substrate to fabricate silicon-glass composite movable microstructures through micromachining of single crystal silicon. The micromachining of single crystal silicon body can greatly increase the thickness of the device, and at the same time, the use of glass as the substrate can avoid the parasitic capacitance between the device and the substrate. Using monocrystalline silicon as the device structure material does not have the internal stress problem of polysilicon, and the suspension of the movable structure is realized by pre-etching shallow pits before silicon-glass bonding, which can avoid the problems of movable structures and surface micromachining sacrificial layer release technology. The "adhesion" problem of the substrate, thus the movable silicon microstructure structure on the glass substrate has begun to receive widespread attention. In 1995, the Proceedings of Micro Electro Mechanical Systems reported that the Japanese K. Ohwads et al. used (110) index crystal surface silicon wafer anisotropic wet etching combined with silicon-glass electrostatic bonding technology to obtain the following Glass is the substrate, and the single crystal silicon comb-shaped capacitive acceleration sensor structure with a thickness of 58 μm, however, the comb-shaped acceleration sensor structure etches shallow pits on the glass to realize the suspension of the movable structure. Since the glass is isotropically etched, the corroded area It is difficult to control precisely, and only a large square shallow pit can be corroded, and the bottom of the fixed finger of the device is also suspended, and the fixed fork is also deflected under the action of acceleration, which will bring errors to the acceleration measurement. In addition, due to the use of wet etching, after the device is formed, the corrosive liquid will penetrate into the gap between the fingers and cause over-corrosion on the bottom of the suspended structure, and it is also difficult to clean the corrosive liquid that has penetrated into the gap between the fingers.

Contents of the invention

The object of the present invention is to completely solve the shortcomings in the above-mentioned process, and propose a manufacturing method for the integration of movable silicon micro-mechanical structures on a glass substrate.

The technical solution of the present invention is: a manufacturing method for the integration of movable silicon micromechanical structures on a glass substrate, which is characterized in that silicon-glass electrostatic bonding technology and single crystal silicon deep reactive ion etching technology are used in the method , and make the suspended shallow pits on the silicon wafer to realize the movable needs.

A manufacturing method for the integration of movable silicon micromechanical structures on a glass substrate, specifically, it is characterized in that it includes the following steps:

①Silicon wafer double-sided polishing;

②At 1050°C, wet oxygen thermally oxidizes both sides of the above-mentioned silicon wafer to form silicon dioxide with a certain thickness;

③ Photolithography is carried out on the silicon dioxide, and the shallow pit pattern corresponding to the suspended movable structure is photolithography;

④ Use silicon dioxide as a mask to etch shallow pits of several microns to more than ten microns with single crystal silicon anisotropic wet etchant;

⑤Remove the double-sided silica and clean it;

⑥ Electrostatically bond the shallow pit surface of the silicon wafer to the glass, the diameter or side length of the glass is about 2-3 mm smaller than that of the silicon wafer, and seal the periphery of the silicon-glass bonding interface with epoxy resin;

⑦Use an anisotropic etchant to wet-etch silicon wafers to uniformly thin the entire silicon wafer to the required thickness of the device and ensure good flatness of the etched surface of the silicon wafer;

⑧Remove the epoxy resin by heating with concentrated sulfuric acid, clean it, and deposit aluminum with a thickness of about 0.2 μm on the silicon surface of the silicon-glass composite material;

⑨ Photoetching a planar movable microstructure pattern on the aluminum layer;

⑩Using aluminum as a mask, deep reactive ion etching single crystal silicon until the silicon in the field area is completely removed, the movable structure is suspended, and the device is formed;

The aluminum mask is removed, and the movable silicon micromechanical structure on the glass substrate is completed.

In the above step ②, the wet oxygen is 1050°C, and double-sided thermal oxidation grows silicon dioxide with a thickness of about 0.1 μm. The thermal oxidation conditions here can be changed, the oxidation temperature can be increased or decreased, and the thickness of the grown silicon dioxide can also be increased. Or reduce, silicon dioxide is used as a mask for KOH wet etching of single crystal silicon 10μm deep shallow pits, although the etching rate of KOH to silicon dioxide is much lower than that of single crystal silicon, but KOH has a low corrosion rate of 2 There is still a slight corrosion of silicon oxide, and the thickness of the grown silicon dioxide only needs to ensure that the silicon dioxide is not corroded after the shallow pit is made.

In the above-mentioned ④ and ⑦ step, said etchant can adopt potassium hydroxide (KOH), also can adopt other single crystal silicon anisotropic wet etching agent, as tetramethylammonium hydroxide (TMAH), ethylenediamine For the catechol and water system (EPW system), the depth of the shallow pit is about 10 μm.

It is best to use 50% KOH and corrode at a temperature of 60°C, so that a smooth and even corroded surface can be obtained, and at the same time, it has a relatively fast corrosion rate.

Said glass is preferably selected from Pyrex (Pyrex) #7740 glass, because the thermal expansion coefficient of Pyrex #7740 glass is the closest to silicon, and the size of the glass radius smaller than the silicon wafer does not necessarily have to be 2 to 3 mm, as long as It is enough to ensure that the effective area of the silicon wafer is lost as little as possible under the premise of coating the epoxy resin on the periphery.

The manufacturing method of the integrated movable silicon micromechanical structure on the glass substrate of the present invention adopts silicon-glass electrostatic bonding technology, combined with single crystal silicon deep reactive ion etching technology, and single crystal silicon can be used as the structural material to produce microstructures from the surface. High-aspect-ratio planar movable microstructures with arbitrary thickness from mechanical to bulk micromechanical scales are suitable for the fabrication of various planar movable microstructures such as acceleration sensors, gyroscopes, and resonators. The introduction of deep reactive ion etching technology can increase the thickness of the device to hundreds of microns, and obtain very smooth and steep side walls. Compared with anisotropic wet etching, deep reactive ion etching technology is dry etching, which will not cause No corrosive liquid contamination, no need to clean the device after molding, the etched shape is not limited by crystal orientation, and microstructures of any shape can be processed. The present invention realizes the suspension of the movable structure by pre-etching shallow pits in the area corresponding to the movable structure on the bonding surface of the silicon wafer, that is, the shallow pits for the suspension of the movable structure are opened on the silicon wafer instead of the glass, which can be selectively and accurately Distinguish between the movable structure and the fixed structure area, and ensure the anchoring of the fixed structure while realizing the suspension of the movable structure. The present invention uses potassium hydroxide wet etching to thin the silicon wafer to the required thickness. In order to prevent the undercutting of the bonding surface of the silicon wafer due to potassium hydroxide wet etching, the radius of the silicon wafer is 2 to 3 smaller than that of the silicon wafer during electrostatic bonding. mm glass slides, and seal the perimeter of the silicon-glass bonding interface with epoxy. After the silicon film is prepared, the epoxy resin can be removed by heating and carbonizing with concentrated sulfuric acid, which is the advantage of the present invention.

The present invention will be further described below in conjunction with the preferred embodiment and accompanying drawings.

Description of drawings

Fig. 1 is a process flow chart of the best embodiment of the manufacturing method of the integrated movable silicon micromechanical structure on the glass substrate of the present invention.

In the picture:

1-Silicon Wafer 2-Silicon Dioxide

3-glass 4-epoxy resin

5- Aluminum

Detailed ways

The preferred embodiment of the present invention is as shown in the figure, comprises the following steps:

(1) Double-sided polished silicon wafer (as shown in Figure 1-1);

(2) Double-sided wet oxygen thermal oxidation, wet oxidation is carried out at 1050 ° C, and double-sided oxidation produces silicon dioxide of about 0.1 μm (as shown in Figure 1-2);

(3) The shallow pit pattern of the suspended movable structure by photolithography (as shown in Figure 1-3);

(4) Using silicon dioxide as a mask, KOH wet etch shallow pits with a depth of about 10 μm (as shown in Figure 1-4);

(5) Remove the double-sided silicon dioxide and clean it (as shown in Figure 1-5);

(6) Electrostatically bond the shallow pit surface of the silicon wafer with Pyrex#7740 glass, the glass radius is 2 to 3 mm smaller than the silicon wafer, and seal it around the silicon-glass bonding surface with epoxy resin (as shown in Figure 1-6)

(7) Use 50% KOH at 60°C to wet-etch the entire silicon wafer and evenly thin it to the required thickness of the device to ensure good flatness of the silicon wafer corrosion surface (as shown in Figure 1-7);

(8) Remove the epoxy resin by heating with concentrated sulfuric acid, clean it, and deposit aluminum with a thickness of about 0.2 μm on the corroded and thinned surface of the silicon wafer (as shown in Figure 1-8);

(9) The aluminum layer is photoetched to form a planar movable microstructure pattern (as shown in Figure 1-9);

(10) Using aluminum as a mask, deep reactive ion etching single crystal silicon until the silicon in the field area is completely removed, the movable structure is suspended, and the device is formed (as shown in Figure 1-10);

(11) Remove the aluminum mask (as shown in Figure 1-11), and the movable silicon micromechanical structure on the glass substrate is completed.

Claims (5)

1, the integrated manufacture method of movable silicon micro mechanical structure on a kind of glass substrate comprises the following steps:

1. silicon chip twin polishing;

2. under 1050 ℃, wet oxygen forms certain thickness silicon dioxide to the two-sided thermal oxidation of above-mentioned silicon chip;

3. silicon dioxide is carried out photoetching, the shallow hole figure of photoetching suspending movable structure;

4. be mask with silicon dioxide, erode away several microns to tens microns shallow hole with the moist corrosive agent of monocrystalline silicon anisotropy;

5. remove two-sided silicon dioxide, clean up;

6. with silicon chip shallow hole face and glass electrostatic bonding, the size of glass is than the little about 2-3 millimeter of size of silicon chip, with epoxy sealing silicon-glass bonded interface periphery;

7. use anisotropic etchant wet etching silicon chip, make the full wafer silicon chip be thinned to the device desired thickness equably, and guarantee the good evenness in silicon slice corrosion surface;

8. add heat abstraction epoxy resin with the concentrated sulfuric acid, clean up, at the thick aluminium of the about 0.2 μ m of silicon slice corrosion attenuate face coating by vaporization;

9. aluminium lamination makes plane movable structure figure by lithography;

10. be mask with aluminium, deep reaction ion etching monocrystalline silicon is removed fully to place silicon, and movable structure is unsettled, the device moulding;

(11) remove the aluminium mould that salts down, complete.

2, the integrated manufacture method of movable silicon micro mechanical structure on the glass substrate according to claim 1 is characterized in that the said the 2. about 0.1 μ m of thickness of silicon dioxide in the step.

3, the integrated manufacture method of movable silicon micro mechanical structure on the glass substrate according to claim 1, it is characterized in that said, 4. to go on foot employed anisotropic etchant be potassium hydroxide, erodes away the shallow hole of 10 μ m.

4, the integrated manufacture method of movable silicon micro mechanical structure on the glass substrate according to claim 1 is characterized in that 7. said the go on foot employed anisotropic etchant and adopt 50% KOH, carries out corrosion thinning when 60 ℃ of temperature.

5, the integrated manufacture method of movable silicon micro mechanical structure on the glass substrate according to claim 1 is characterized in that said glass is pyrex 7740 glass.

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