JP2018058150A - Mems element and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a MEMS element improved in sensitivity by large displacement of a movable electrode without reducing intensity, and having increased sensitivity with area efficiency.SOLUTION: In a MEMS element, a fixed electrode 5 is disposed on a substrate 1 having a back chamber 10, and a displaceable movable electrode 3 is disposed almost in parallel on the fixed electrode 5 via an air gap G. In the MEMS element, support columns 7 that penetrate a hole h formed from an insulator film 6 to the fixed electrode 5 and reach the movable electrode 3 are arranged in matrix on a surface of the movable electrode. Accordingly, a narrow air gap G is realized with the thin movable electrode 3 so that sensitivity is increased.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a MEMS element and a manufacturing method thereof, and more particularly to a MEMS element used as various sensors such as a transducer and a manufacturing method thereof.

  Conventionally, MEMS (Micro Electro Mechanical System) elements are used for transducers, sensors, actuators, electronic circuits, and the like.

  FIG. 4 shows an example of a transducer (microphone) which is a conventional MEMS element. In this microphone, a movable electrode having a thickness of about 0.2 to 2.0 μm is formed on a semiconductor substrate 11 with an insulating film 12 interposed therebetween. 13 is formed, and a fixed electrode 15 is provided via a support layer 14. The fixed electrode 15 and the movable electrode 13 are arranged so as to be parallel via an air gap G of about 2.0 to 5.0 μm, and a large number of sound holes are formed in the fixed electrode 15 and the insulating film 16 thereon. 18 is formed. The support layer 14 is a part of a sacrificial layer formed on the movable electrode 13, and an air gap (hollow) is formed between the movable electrode 13 and the fixed electrode 15 by removing a part of the sacrificial layer. ) G is formed. In addition, 19 is an electrode connected to the fixed electrode 15, 20 is a back chamber, and an electrode connected to the movable electrode 13 is not shown.

  In such a microphone, the movable electrode 13 and the fixed electrode 15 formed on the substrate 11 form a parallel plate type capacitor, and the displacement of the electrostatic capacitance caused by the vibration of the movable electrode due to sound pressure is detected. The voice is converted into an electrical signal.

JP, 2014-233059, A

By the way, as described above, the sensitivity of the microphone detects the change in the electrostatic capacitance caused by the displacement of the movable electrode 13 that has received the sound pressure from the sound hole 18. It is necessary to increase the displacement.
Therefore, in order to increase the sensitivity, a method of weakening the spring of the movable electrode 13 is generally performed. However, this method causes the strength of the movable electrode 13 to decrease, and at the same time, weakens the spring of the movable electrode 13 and at the same time. It was a difficult problem to maintain the strength.

Such a problem is not limited to the above-described microphone, and is similarly a problem to be solved for other MEMS elements that convert displacement and vibration into an electric quantity.
Further, in the MEMS element, if the area efficiency of the sensitivity region can be increased, not only the sensitivity can be improved, but also the element can be miniaturized.

  The present invention has been made in view of the above problems, and its object is to provide a MEMS element that does not decrease in strength, improves sensitivity by a large displacement of the movable electrode, and can increase sensitivity efficiently in an area. Is to provide.

In order to achieve the above object, a MEMS device according to the invention of claim 1 is a displaceable movable device in which a fixed electrode is disposed on a substrate having a back chamber and substantially parallel to the fixed electrode via an air gap. In a MEMS device including an electrode, a support column that extends through the hole formed in the fixed electrode and extends to the movable electrode to support the movable electrode is provided, and is supported on the movable electrode by the support column. The movable small area is arranged.
The invention of claim 2 is characterized in that the support pillar is integrally coupled to an insulating film formed on the opposite side of the fixed electrode to the air gap.
The invention of claim 3 is characterized in that the support columns are arranged in a matrix with respect to the movable electrode surface.

According to a fourth aspect of the present invention, there is provided a method of manufacturing a MEMS element comprising: forming a movable electrode, a sacrificial layer for forming an air gap and a fixed electrode on a substrate; and forming the movable electrode on the fixed electrode and the sacrificial layer. A step of forming a reaching through hole, and a support column forming step of forming a support column for supporting the movable electrode by reaching the movable electrode through the through hole from the opposite side of the air gap of the fixed electrode And a step of forming an air gap by removing a part of the sacrificial layer, and a step of forming a back chamber on the substrate.
According to a fifth aspect of the present invention, in the support pillar forming step, an insulating material is deposited on the surface of the fixed electrode on which the through hole is formed, thereby embedding the insulating material in the through hole to form the support pillar. It is characterized by.

  According to the above configuration, the movable electrode is supported by, for example, a plurality of support pillars, so that the movable electrode is provided with a plurality of movable small regions, and the movable electrode is made thinner than the conventional one, so that the necessary displacement is maintained. A plurality of movable small regions are arranged in parallel. This movable electrode has physical properties similar to those of a fixed electrode in a macro and behaves like a parallel plate type capacitor, which can contribute to an improvement in SNR.

According to the present invention, since the movable electrode is supported by the support column and provided with a plurality of movable small regions, even if the movable electrode is made thinner than the conventional one, the strength is not lowered and the interval of the air gap G can be narrowed. Therefore, the sensitivity can be improved by sufficient displacement of the movable electrode.
In addition, the movable electrode is not limited to a circle as in the prior art, but can be a shape close to a quadrangle, so a large sensitivity area can be set in the same element area as in the past, and the area efficiency is increased. This has the advantage that it can contribute to downsizing.

The structure of the microphone which is a MEMS element of the Example of this invention is shown, A figure (A) is sectional drawing, A figure (B) is a top view. It is the figure which expanded a part of microphone of FIG. It is sectional drawing which shows the manufacturing process of the microphone of an Example. The structure of the microphone of a prior art example is shown, FIG. (A) is sectional drawing and FIG. (B) is a plane.

  1 and 2 show the configuration of a microphone that is a MEMS element (transducer) of the embodiment. In FIG. 1, 1 is a silicon substrate, 2 is an insulating film, and 3 is formed on the insulating film 2. 4 is a support layer, 5 is a support electrode supported by the support layer 4 and is arranged parallel to the movable electrode 3, 6 is an insulating film, and 7 is a plurality of support pillars. The pillar 7 is integral with the insulating film 6, extends into the air gap G, is coupled to the movable electrode 3, and serves as a pillar that supports the movable electrode 3 at a plurality of points. Therefore, the area surrounded by the support pillar 7 becomes a movable small area, and this constitutes one small movable electrode. 8 is a sound hole penetrating the insulating film 6 and the fixed electrode 5, G is an air gap between the movable electrode 3 and the fixed electrode 5, 10 is a back chamber, and 19 is an electrode connected to the fixed electrode 5. Note that the electrodes connected to the movable electrode 3 are not shown.

Next, a manufacturing process of the microphone of the embodiment will be described with reference to FIG.
First, in the process of FIG. 3A (electrode formation process), a thermal oxide film 2a having a thickness of about 1 μm (becomes an insulating film 2) is formed on a silicon substrate 1 having a crystal orientation (100) plane of 420 μm. A very thin conductive polysilicon film (3) having a thickness of about 0.01 to 0.10 μm is laminated on the thermal oxide film 2a by a CVD (Chemical Vapor Deposition) method. The movable electrode 3 is formed by patterning the conductive polysilicon film by the photolithographic method.

  The thickness of the polysilicon film (3) at this time is set to a desired thickness in consideration of the size of the movable small region of the movable electrode 3 and the breaking strength. That is, the thickness of the conventional movable electrode is about 0.2 to 2.0 μm. In the embodiment, the movable small area is set by the support pillar 7 as described above. In consideration of the size, the thickness is reduced to about 1/20 of the conventional one. As the movable electrode 3, in addition to the polysilicon (polycrystalline silicon) film, a silicon single crystal, amorphous silicon, or the like to which impurities are added can be used.

  Next, a sacrificial layer 4 a (to be a support layer 4) made of a thin USG (Undoped Silicate Glass) film having a thickness of about 0.5 to 1.0 μm is stacked on the movable electrode 3. By laminating and forming a conductive polysilicon film (5) having a thickness of about 0.1 to 1.0 μm on the sacrificial layer 4a, and patterning the conductive polysilicon film (5) by a photolithography method, A fixed electrode 5 is formed. The central side of the sacrificial layer 4a is finally removed to form an air gap G between the movable electrode and the fixed electrode. The air gap G is also narrower than in the prior art. That is, the interval of the conventional air gap G is about 2 to 5 μm, but in the embodiment, it is narrowed to about 0.1 to 1.0 μm in consideration of the size of the movable small region.

  In the step of FIG. 3B (through-hole forming step), the fixed electrode 5 and the sacrificial layer 4a are formed in a matrix by a normal photolithography method as shown by the support pillars 7 in FIG. A plurality of holes h are formed. The hole h is formed so as to penetrate the fixed electrode 5 and the sacrificial layer 4a and reach the movable electrode 3. In order to determine the size of the movable small region set by the movable electrode 3, the matrix-shaped holes h are formed at a desired interval in consideration of the strength and strength of the spring of the movable electrode 3. Become.

  In the step of FIG. 3C (support column forming step), a nitride film 6a having a thickness of about 0.2 μm to 2.0 μm is deposited on the entire upper surface of the element provided with the fixed electrode 5, and simultaneously A nitride film 6a to be the support pillar 7 is embedded in the matrix-shaped holes h. The nitride film 6a forms an insulating film 6 on the fixed electrode 5 and a support column 7 coupled from the insulating film 6 to the movable electrode 3 through the through hole h. Instead of the nitride film (silicon nitride) 6a, an insulating material such as oxygen-doped polycrystalline silicon or oxide film may be used.

  In the step of FIG. 3D (sound hole forming step), the wiring pattern and the electrode 19 respectively connected to the movable electrode 3 and the fixed electrode 5 are 1.0 to 3.0 μm in thickness by a normal photolithographic method. It is formed by an AlCu film. In the figure, the wiring portion formed on the movable electrode is omitted. In addition, a sound hole 8 that penetrates the insulating film 6 and the fixed electrode 5 and exposes a part of the sacrificial layer 4a is formed.

In the step of FIG. 3E (back chamber and air gap forming step), the silicon substrate 1 is removed from the back surface side of the silicon substrate 1 until the thermal oxide film 2a below the movable electrode 3 is exposed. 10 is formed.
Next, as in the general manufacturing process of the capacitive MEMS element, a part of the sacrificial layer 4 a is removed through the sound hole 8 formed in the fixed electrode 5, and the air gap G between the movable electrode 3 and the fixed electrode 5 is removed. Is formed. At this time, the thermal oxide film 2a under the movable electrode 3 is also removed. Since there is a support column 7 between the fixed electrode 5 and the movable electrode 3, sticking does not occur even if the air gap G is narrower than before.

  The microphone manufactured as described above is configured as shown in FIGS. 1A and 1B. However, according to the embodiment, the movable electrode 3 is formed very thin, and then the microphone shown in FIG. As shown in FIG. 2, when the sound pressure is received from the sound hole 8 as shown in FIG. 2, the movable electrode 3 has a plurality of small movable regions set in the movable electrode 3 by the support columns 7 arranged in a matrix. Each movable small area between the support columns is displaced and vibrated, and the movable small area is greatly displaced and vibrated. Since the fixed electrode 5 facing the movable electrode 3 is arranged at a position closer to that of the conventional art, it is possible to improve the sensitivity.

  Further, in the present invention, as shown in FIG. 1B, the arrangement area of the movable electrode 3 and the fixed electrode 5 and the opening of the back chamber 10 are not a circle but a square or an ellipse, which is wider than before. In addition, the area efficiency of the sensitivity region (vibration membrane) in the element can be increased. That is, in the related art, as shown in FIG. 4B, the sensitivity region (or the opening of the back chamber 20) is circular. You can freely choose the shape. In the case of a rectangular element, the area becomes larger when the sensitivity region is closer to a rectangle than a circle, and in the embodiment, the regions of the movable electrode 3 and the fixed electrode 5 and the back chamber opening are closer to a rectangle. The area efficiency of the sensitivity region is increased. On the other hand, when the sensitivity is sufficient, the element can be downsized.

1, 11 ... silicon substrate, 2, 12 ... insulating film,
2a ... thermal oxide film 3,13 ... movable electrode,
4,14 ... support layer, 4a ... sacrificial layer,
5, 15 ... fixed electrode, 6, 16 ... insulating film,
6a ... nitride film, 7 ... support pillar,
8, 18 ... sound holes, 10, 20 ... back chamber,
h: Hole (through hole), G: Air gap.

Claims (5)

In a MEMS element comprising a fixed electrode on a substrate having a back chamber, and a movable movable electrode disposed substantially parallel to the fixed electrode via an air gap,
A support column that extends through the hole formed in the fixed electrode and extends to the movable electrode to support the movable electrode is provided, and a movable small region supported by the support column is arranged on the movable electrode. MEMS element.   The MEMS element according to claim 1, wherein the support pillar is integrally coupled to an insulating film formed on a side opposite to the air gap of the fixed electrode.   3. The MEMS element according to claim 1, wherein the support columns are arranged in a matrix with respect to the movable electrode surface. Forming a movable electrode, a sacrificial layer for forming an air gap, and a fixed electrode on the substrate;
Forming a through hole reaching the movable electrode to the fixed electrode and the sacrificial layer;
A support column forming step of forming a support column for supporting the movable electrode by reaching the movable electrode through the through hole from the opposite side of the air gap of the fixed electrode;
Removing a portion of the sacrificial layer to form an air gap;
Forming a back chamber on the substrate.   5. The support pillar forming step includes depositing an insulating material on the surface of the fixed electrode in which the through hole is formed, thereby embedding the insulating material in the through hole to form the support pillar. The manufacturing method of the MEMS element of description.

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