KR20020016117A - The Fabrication Process For Microphone Using The MEMS - Google Patents

Abstract

PURPOSE: A method for fabricating microphone using mems(micro electro mechanical systems) process is provided to fabricate a compact microphone with a simple and standard fabrication process using a MEMS(Micro Electro Mechanical Systems) process. CONSTITUTION: A diaphragm(30) is supported by an anchor part(31), and a gap(32) is formed around the diaphragm by a bulk etching process. Sound through the gap is vibrated in a space surrounded by the diaphragm and a bottom Al electrode and a space formed during etching a bottom bulk. These air vibration is transferred to the external through an external withdrawal electrode connected with a top Al electrode and the bottom Al electrode.

Description

The fabrication process for microphone using the MEMS

The present invention relates to a method of fabricating a micro microphone using a MEMS process technology on a silicon wafer.

Currently used microphones are mainly used in medical devices such as hearing aids or miniaturized multifunctional smart sensors or small precision devices. Such compact microphones have a problem that their size is limited because they are manufactured through mechanical processing. In particular, in the case of various miniaturized devices, the electronic circuit unit is generally manufactured in the form of an integrated IC, and such integration enables production of a very small product.

On the other hand, since the part containing the mechanical moving parts such as the microphone has a physical limit that is hard to shrink any more than the minimum size, the degree of integration is determined by the size of the part including the mechanical moving part and the size of the final product is Is determined.

Recently, as a method used for the integration of micro devices, there is a semiconductor processing technology using micromachining. This technology, called MEMS, is developing the two-dimensional silicon process technology, which has been represented by the planner technology, into an area capable of processing three-dimensional solid structures.

MEMS (Micro Electro Mechanical Systems) is a field for fabricating and experimenting microscopic sensors, actuators, and electromechanical structures in micrometers using micromachining technology using semiconductor processes, particularly integrated circuit technology. Micromachines manufactured by micromachining techniques can realize sizes of mm or less and precision of μm or less.

The advantages of micromachining technology are miniaturization, high performance, multifunctionality and integration through ultra-precision micromachining, and stability and reliability can be improved. In addition, as the integrated integrated system can be implemented, the necessity of assembly is reduced, and the mass production is possible because it is manufactured in a batch process.

The micromachining technology used in MEMS is largely bulk bulk micromachining by bulk etching silicon and deposit polycrystalline silicon, silicon nitride film, oxide film, and metal film on silicon, and etch the structure according to the designed shape. It can be divided into surface micromachining (surface micromachining) to be produced.

In the bulk micromachining, an alkaline solution may etch a silicon single crystal wafer according to a crystal direction to realize a desired three-dimensional structure, and precise etching depth and shape control are key.

The surface micromachining forms a microstructure through a process of depositing and etching a structural layer and a sacrificial layer on a silicon substrate. That is, the sacrificial layer and the structure layer is formed on the substrate and then the sacrificial layer is etched so that only the structure layer remains. At present, surface micromachining techniques include the production of highly integrated circuits such as a thermal oxidation technique for forming a silicon oxide film, an ion implantation technique for injecting impurities into silicon, a metal process for forming a metal thin film, and chemical vapor deposition for forming a nitride film or polycrystalline silicon. The advanced semiconductor processing technology used is applied.

Such MEMS technology is gradually expanding its use in all fields of machinery, metals, semiconductors, automobiles, etc., but the standard process for applying this technology to manufacture micro microphones has not been put to practical use.

The present invention provides a manufacturing process of a capacitive micro microphone that can be manufactured in a simpler and more standardized manufacturing process using MEMS technology.

1 is a flow chart of a manufacturing process of a microphone according to the present invention;

2A-2H are cross-sectional schematics of microphone manufacturing process steps in accordance with the present invention; And

3 is a shape of a final microphone obtained by a microphone manufacturing process according to the present invention.

* Brief description of the main parts of the drawing

30: diaphragm 31: anchor

32: gab

According to the method of manufacturing a microphone using the MEMS process according to the present invention, a diaphragm of a predetermined shape is formed on a center portion of a wafer by bulk etching the upper and lower portions of a wafer on which a SiO ₂ layer and an SOI layer are stacked on a Si substrate with a predetermined thickness. Mechanical structure forming process; A first vacuum deposition step of forming an upper Al electrode on the diaphragm; A second vacuum deposition step of forming a lower Al electrode corresponding to the upper Al electrode on the tempered glass; And an anode bonding process for bonding the tempered glass and the mechanical structure such that the upper and lower Al electrodes face each other.

Hereinafter, with reference to the accompanying drawings, it will be described a preferred embodiment of the present invention.

One example of a microphone manufacturing process using the MEMS process according to the present invention is as follows.

First, as shown in FIG. 2A, a wafer having a thickness of about 10 μm in which SiO ₂ and SOI layers are stacked on a Si substrate to a predetermined thickness is prepared. The wafer thus prepared is subjected to an oxidation process as shown in FIG. 2B to form an SiO ₂ film having a thickness of about 1 μm to serve as a bulk etching mask above and below the wafer. In order to obtain an excellent and thick SiO ₂ thin film, the oxidation process is first performed by dry oxidation to form a film having a thickness of about 0.1 to 0.2 μm, followed by a wet oxidation process to form a film having a thickness of about 0.8 to 1 μm. And, it is preferably carried out by forming a SiO ₂ film of about 0.1㎛ through a dry oxidation process. The SiO ₂ thin film obtained at this time does not react with TMAH, KOH, or the like, which is a solution for etching the wafer, and thus may have a sufficient mask function even in a bulk etching process for a long time.

Next, SiO ₂ around the diaphragm is removed to form an island-like diaphragm (see “30” in FIG. 3) on the wafer, and the p + doping region for external electrode withdrawal is diffused using a photomask. . In this case, as shown in FIG. 3, SiO ₂ is removed to form p + diffusion so that a plurality of anchors (see “31” in FIG. 3) are formed to support the diaphragm.

Then, an emulsion mask was used to remove the SiO ₂ films of the portions to be etched from the upper and lower portions of the wafer (FIG. 2C), and then a bulk etching process was performed using TMAH as an etching solution (FIG. 2D). The diaphragm 30 is formed. Although the upper and lower portions of the wafer may be bulk etched in separate processes, it is preferable to simultaneously etch the upper and lower portions to simplify the manufacturing process. When the TMAH solution is used as the etching solution, the difference in etching rate and the etching rate difference of Si and SiO ₂ are almost 1000: 1 according to the direction, so that even if the upper thickness is smaller than the lower thickness, specifically, according to FIG. 2. In an embodiment the top thickness is about 10-15 μm and the bottom thickness is about 400-500 μm, but the first etched top etch portion is not overetched while the bottom etch finishes.

On the other hand, during the upper bulk etching, the anchor portion 31 supporting the diaphragm to be formed is not removed. Since the anchor portion becomes a portion responding to sound waves applied from the outside according to the size and shape of the diaphragm to be formed, the response characteristics according to the shape ratio and mass composition and area according to each is variable. The size of the diaphragm formed in one embodiment of the present invention shown in FIG. 2 was about 300 × 300 μm, and the anchor portion was about 30 μm wide and about 50 μm long.

Once the bulk etch to the desired depth is complete, the SiO ₂ film used as a mask is etched away (FIG. 2E). As shown in FIG. 2E, an island-like diaphragm floats in the air on the wafer, and the anchor 31 is not shown in view of the viewing angle. Next, Al is vacuum-deposited in the direction of the arrow on the drawing using a shadow mask to form an Al upper electrode of a desired thickness (FIG. 2F). The Al upper electrode is connected to a p + doped diffusion region previously formed for external electrode withdrawal.

The same shadow mask was used to perform Al vacuum deposition to form an Al bottom electrode on pyrex glass (FIG. 2E). In the manufacturing method according to the invention, the size of the tempered glass sheet is preferably slightly larger than the wafer. Since the same shadow mask and process used for forming the upper Al electrode were used, the Al lower electrode deposited on the tempered glass was formed in the same size and thickness as the upper Al electrode.

Finally, since the operation of the microphone is enabled by using the capacity change between the upper and lower Al films, Al vacuum deposition of these two parts should be done carefully.

On the other hand, in the structure of the microphone manufactured according to the present invention, the lead line of the upper electrode portion and the lower electrode portion should be formed on the outer portion of the diaphragm. In order to form such a structure, in the case of the upper electrode, as described above, the anchor portion is doped with p + to be used as the electrode lead-out portion, that is, the anchor portion which is a path connected to the outside from the diaphragm floating in the air It will act as an electrode.

In the case of the lower electrode, according to a preferred embodiment of the present invention, as mentioned above, a tempered glass plate slightly larger than the upper structure is used, and an Al pattern is connected to the lower electrode part of the tempered glass plate to draw out the wire to the outside. Do it.

Finally, the diaphragm portion on the wafer, which is the upper structure, and the tempered glass portion, which is the lower structure, are attached by using anodic bonding to finish the entire manufacturing process (FIG. 2H).

3 is a plan view and a cross-sectional side view of a small microphone using MEMS technology according to the present application. Referring to FIG. 3, the gap 32 is supported by the anchor portion 31 and the bulk etching process is formed around the diaphragm 30. The sound coming through the gap 32 is ringed in the interior surrounded by the diaphragm 30, the lower Al electrode, and the space formed during lower bulk etching, and the amount of air vibration is applied to the external drawing electrode connected to the upper and lower Al electrodes. It is passed to the outside.

So far, the manufacturing process of the microphone using MEMS technology has been described as a preferred embodiment, but the present invention is not limited thereto, but only by the appended claims, and those skilled in the art have the above patents It will be apparent that various modifications and variations can be made without departing from the scope and spirit of the claims. For example, although the diaphragm and wafer shapes are shown in a quadrangular shape in the drawings, the shapes may be manufactured in sufficiently different shapes according to the intention of the manufacturer, such as a circular shape.

According to the manufacturing process of the microphone according to the present invention, by using MEMS technology more simply and simply, the size can be reduced to several tens of micrometers, it is possible to produce a more compact product than conventional mechanical products In addition, there is an advantage in that integration is possible when configuring an integrated circuit together with a peripheral circuit.

Claims (4)

In the method of manufacturing a micro microphone using MEMS, A mechanical structure forming step of forming a diaphragm of a predetermined type on the center of the wafer by bulk etching the upper and lower portions of the wafer on which the SiO ₂ layer and the SOI layer are laminated on the Si substrate to a predetermined thickness; A first vacuum deposition step of forming an upper Al electrode on the diaphragm; A second vacuum deposition step of forming a lower Al electrode corresponding to the upper Al electrode on the tempered glass; And And an anode bonding process for bonding the tempered glass and the mechanical structure such that the upper and lower Al electrodes face each other. The method of claim 1, The mechanical structure forming process is: An oxidation process of growing a SiO ₂ film, which is a bulk etching mask, on the upper and lower portions of the wafer to a predetermined thickness; Diffusing a p + doping region for an external electrode leader line of the diaphragm on the wafer; Removing the upper and lower SiO ₂ films by a predetermined range and then bulk etching the SiO ₂ layer of the wafer to form a diaphragm; And And an etching process for removing upper and lower SiO ₂ films not removed after the bulk etching. The method of claim 2, An oxidation process for forming the SiO ₂ film as the bulk etching mask is: Dry oxidation to form a SiO ₂ film having a thickness of about 0.1 to 0.2 μm; A wet oxidation process for forming a SiO ₂ film about 0.8-1 μm thick; And A method of manufacturing a micro microphone using MEMS, characterized in that it is carried out by a dry oxidation process to form a SiO ₂ film having a thickness of about 0.1 μm. The method according to any one of claims 1 to 3, The first vacuum deposition process and the second vacuum deposition process is a method of manufacturing a micro microphone using a MEMS, characterized in that using the same shadow mask.