JP6645652B2 - Method for manufacturing MEMS device - Google Patents

Description

The present invention relates to a method of manufacturing a MEMS device, in particular a microphone, various sensors, a method of manufacturing a capacitance type MEMS device used as a switch or the like.

  2. Description of the Related Art Conventionally, a MEMS (Micro Electro Mechanical Systems) element using a semiconductor process has a structure in which a fixed electrode, a sacrifice layer (insulating film) and a movable electrode are formed on a semiconductor substrate, and a part of the sacrifice layer is removed to form a spacer. An air gap (hollow) structure is formed between the fixed electrode and the movable electrode which are fixed through the gap.

  For example, in a condenser microphone which is a capacitive MEMS element, a fixed electrode having a plurality of through holes through which sound pressure passes, and a movable electrode (diaphragm film) that vibrates in response to sound pressure are arranged facing each other. The displacement of the movable electrode that vibrates in response to sound pressure is detected as a change in capacitance between the electrodes.

  A MEMS device having such a structure is generally formed as follows. First. A silicon substrate 1 having a (100) crystal orientation on the surface is prepared, and an insulating film 2a having a thickness of 0.2 to 1.0 μm is formed on the surface by thermal oxidation. Further, a polysilicon film having a thickness of 0.2 to 1.0 μm is formed on the insulating film 2a by a CVD (Chemical Vaper Deposition) method, and is patterned by a usual photolithography method to form a diaphragm film 3 serving as a movable electrode. (FIG. 3a).

  Thereafter, a USG (Undoped Silicate Glass) film 4 having a thickness of 2 to 4 μm is laminated on the entire surface. This USG film is a film constituting a sacrificial layer. Further, after forming a polysilicon film 5 having a thickness of 0.1 to 1.0 μm as a fixed electrode on the USG film 4, a silicon nitride film 6 having a thickness of 0.1 to 2.0 μm is deposited and formed on the entire surface. (FIG. 3b).

  Next, in order to remove the previously formed USG film 4 in a later step, a plurality of through holes 7 are formed by etching away a part of the silicon nitride film 6 and the polysilicon film 5 serving as a fixed electrode. 4 is exposed (FIG. 3c).

  A wiring portion 8 is formed to be in contact with each of the diaphragm film 3 serving as a movable electrode and the polysilicon film 5 serving as a fixed electrode (FIG. 3D). Thereafter, the silicon substrate 1 is removed until the insulating film 2a is exposed from the back side of the silicon substrate 1, and a back chamber 9 is formed as shown in FIG.

  After that, the USG film 4 is etched from the through hole 7 in order to form a hollow structure between the movable electrode and the fixed electrode. The etchant used here is a hydrofluoric acid-based mixed acid aqueous solution having a high etching selectivity with respect to the wiring material forming the wiring portion 8 and capable of performing isotropic etching. Specifically, a mixed solution of hydrofluoric acid, ammonium fluoride, and acetic acid is used.

  As a result, as shown in FIG. 3 (f), an air gap 10 is formed between the diaphragm film 3 serving as a movable electrode and the polysilicon film 5 serving as a fixed electrode, and a part of the USG film 4 becomes the first. At the same time as remaining as the spacer 11, the insulating film 2a formed between the silicon substrate 1 and the diaphragm film 3 serving as the movable electrode is also etched, and a part of the insulating film 2a remains as the second spacer 12a. An example in which the first spacer 11 and the second spacer 12a are formed by etching is described in Patent Document 1, for example.

JP 2014-233059 A

  In the conventionally proposed MEMS element, when pressure is applied to the diaphragm film 3 constituting the movable electrode, as shown in FIG. 4, a stress is applied to the connection point 13 between the second spacer 12a and the diaphragm film 3 constituting the movable electrode. Is concentrated, and in this portion, there is a problem that the diaphragm film 3 constituting the movable electrode is easily broken.

  Further, when such stress concentration occurs, the diaphragm film 3 is deformed and displaced in an attempt to alleviate the stress at the contact portion between the second spacer 12a and the diaphragm film 3 constituting the movable electrode, and the sensitivity of the MEMS element decreases. In addition, the problem of fluctuation or fluctuation occurs.

The present invention is to solve the above problems, it is possible to prevent the destruction of the MEMS element, and an object thereof is to provide a method for manufacturing a MEMS device which can suppress a decrease or fluctuation in sensitivity.

In order to achieve the above object, the invention according to claim 1 of the present application is directed to a method for manufacturing a MEMS element in which a fixed electrode and a movable electrode are arranged on a substrate having a back chamber with a first spacer interposed therebetween. After thermally oxidizing the insulating film forming the second spacer, the substrate is thermally oxidized, and impurities are ion-implanted and thermally oxidized into the substrate, so that the etching rate at the time of forming the second spacer is in contact with the substrate. The etching rate of the insulating film forming the second spacer on the side to be formed is higher than the etching rate of the insulating film forming the second spacer on the side in contact with the movable electrode formed in a later step. Forming the movable electrode on the insulating film constituting the second spacer; and forming the first spacer on the movable electrode. Forming an insulating film, forming the fixed electrode on the insulating film forming the first spacer, forming a through hole in the fixed electrode, and removing a part of the substrate. Forming the back chamber, and etching away a part of the insulating film forming the first spacer from the through hole to form the first spacer, and forming the first electrode and the movable electrode. An air gap is formed therebetween, and a part of the insulating film constituting the second spacer is removed by etching. The contact portion between the insulating film constituting the second spacer and the substrate is formed by the back chamber from the back chamber. The contact portion between the movable film and the insulating film constituting the second spacer recedes in the direction opposite to the center direction of the movable electrode. Forming a second spacer that is the placed than the contact portion toward the center of the movable electrode structure, characterized in that it comprises a.

In the MEMS element according to the present invention, the stress generated when pressure is applied to the movable electrode is not concentrated only at the connection point between the spacer and the movable electrode formed between the substrate and the movable electrode, but is applied to the movable electrode. Since the structure is such that the movable electrodes are dispersed, it is possible to prevent the movable electrode from being broken. In addition, since excessive stress is not concentrated on the contact portion between the movable electrode and the spacer formed between the substrate and the movable electrode, the movable electrode is not deformed or displaced, and a decrease in sensitivity and fluctuation are suppressed. There is an advantage that can be.

  In addition, the method of manufacturing a MEMS element according to the present invention is an ordinary semiconductor device manufacturing process, and includes only generally used steps. Therefore, the MEMS element can be formed very stably and inexpensively. There is an advantage that can be. In particular, the second spacer is very thin and is excellent in that a desired shape can be stably formed.

It is an explanatory view of the manufacturing process of the MEMS element of the present invention. (A) is an explanatory view of a MEMS device according to the present invention. (B) is an enlarged view of A part shown in (a). It is explanatory drawing of the manufacturing process of the conventional MEMS element. (A) is an explanatory view of a conventional MEMS element. (B) is an enlarged view of the part A shown in (a).

  The MEMS element according to the present invention is configured such that the spacer formed between the substrate and the movable electrode has a predetermined structure. That is, the contact portion with the substrate retreats from the back chamber to the opposite side to the center direction of the air gap (the center direction of the fixed electrode or the center direction of the movable electrode), and the contact portion with the movable electrode is compared with the contact portion with the substrate. Therefore, it is configured to be arranged in the center direction of the air gap.

  With this configuration, the cross-sectional shape of the end of the spacer formed between the substrate and the movable electrode has an inversely tapered shape, and the stress concentration generated at the connection point between the spacer and the movable electrode is dispersed to the movable electrode. I will be. As a result, the movable electrode is not damaged, or the movable electrode is not deformed or displaced, and it is possible to prevent the sensitivity and the fluctuation of the MEMS element from being lowered or changed. Hereinafter, examples of the present invention will be described according to the method of manufacturing the MEMS device of the present invention.

An embodiment of the present invention will be described. First, a thermal oxide film having a thickness of about 0.01 to 0.1 μm is formed on a silicon substrate 1 having a crystal orientation (100) plane. Then, boron ions are implanted under the conditions of an implantation energy of 30 to 100 eV and a dose of 1 × 10 ¹⁴ to 1 × 10 ¹⁶ cm ^{−2, and} a 0.1 to 1.0 μm insulating film 2 is formed by thermal oxidation. . The impurity concentration of the insulating film 2 thus formed becomes higher as it is closer to the silicon substrate 1.

  Next, a conductive polysilicon film having a thickness of 0.5 to 1.0 μm is formed on the insulating film 2 by a CVD (Chemical Vapor Deposition) method. Next, patterning is performed by a normal photolithography method to form a diaphragm film 3 serving as a movable electrode (FIG. 1A).

  Thereafter, a USG (Undoped Silicate Glass) film 4 having a thickness of 2.0 to 4.0 μm is laminated on the front surface of the front surface, as in the conventional case. This USG film is a film constituting a sacrificial layer. Further, a conductive polysilicon film 5 having a thickness of about 0.1 to 1.0 μm serving as a fixed electrode is formed on the USG film 4 and a silicon nitride film 6 having a thickness of 0.2 μm is formed on the front surface ( FIG. 1b).

  Next, in order to remove the previously formed USG film 4 in a later step, a plurality of through holes 7 are formed by etching away a part of the silicon nitride film 6 and the polysilicon film 5 serving as a fixed electrode. Part of the surface of 4 is exposed. Further, a part of the silicon nitride film 6 in a region where the wiring film is to be formed, which is in contact with the fixed electrode or the movable electrode, is also removed by etching (FIG. 1C).

  Next, a part of the diaphragm film 3 is exposed, and a wiring film 8 in contact with the exposed diaphragm film 3 and a wiring film 8 in contact with the polysilicon film 5 serving as a fixed electrode are formed (FIG. 1D). This wiring film 8 is made of a conductive film such as aluminum.

  Thereafter, the silicon substrate 1 is removed until the insulating film 2 is exposed from the back surface side of the silicon substrate 1, and a back chamber 9 is formed (FIG. 1e).

  After that, the USG film 4 is etched from the through hole 7 in order to form a hollow structure between the movable electrode and the fixed electrode. The etchant used here is a hydrofluoric acid-based mixed acid aqueous solution having a high etching selectivity with respect to the wiring material forming the wiring portion 8 and capable of performing isotropic etching. Specifically, a mixed solution of hydrofluoric acid, ammonium fluoride, and acetic acid is used. When there is a difference in the impurity concentration of this etching solution, the etching rate (speed) also changes. That is, an etching solution in which the etching rate becomes higher as the impurity concentration becomes higher is used.

  When etching is performed using such an etchant, an air gap 10 is formed between the diaphragm film 3 serving as a movable electrode and the polysilicon film 5 serving as a fixed electrode, and a part of the USG film 4 becomes the first film. At the same time as the spacer 11, the insulating film 2 formed between the substrate 1 and the diaphragm film 3 is also etched, and a part of the insulating film 2 remains as the second spacer 12.

  Particularly, in the present invention, as described above, the insulating film 2 is formed so that the impurity concentration becomes higher as it is closer to the silicon substrate 1. Be faster. As a result, as shown in FIG. 2, the cross-sectional shape of the end of the second spacer 12 can be formed in an inversely tapered shape (FIG. 1f).

  With such a structure, when pressure is applied to the diaphragm film 3 constituting the movable electrode, in the conventional structure, the stress concentrated at the connection point between the second spacer 12a and the diaphragm film 3 constituting the movable electrode is increased. Are dispersed in the diaphragm film 3 which constitutes the above, and the destruction can be prevented. Further, the diaphragm film 3 constituting the movable electrode is not deformed or displaced, so that it is possible to prevent the sensitivity and the fluctuation of the MEMS element from being lowered or changed.

  Although the embodiment of the present invention has been described above, the method of changing the etching rate for etching by imparting an impurity concentration to the insulating film is not limited to the ion implantation method. Thermal oxidation using a high-concentration substrate. In addition, the angle of the inverse tapered shape of the cross-sectional shape of the spacer can be variously changed, and the wet etching method can use a desired etching solution.

  In addition, the insulating film serving as a spacer formed between the substrate and the movable electrode is not limited to a single-layer structure, but is formed of a plurality of layers having different etching rates. What is necessary is just to laminate | stack so that the etching rate of an upper layer may become the slowest.

1: Silicon substrate, 2a: insulating film, 3: diaphragm film, 4: USG film, 5: polysilicon film, 6: silicon nitride film, 7: through hole, 8: wiring portion, 9: back chamber, 10 : Air gap, 11: first spacer, 12, 12a: second spacer, 13: connection point

Claims (1)

In a method for manufacturing a MEMS device in which a fixed electrode and a movable electrode are arranged on a substrate having a back chamber with a first spacer interposed therebetween,
After thermally oxidizing the insulating film forming the second spacer on the substrate, the substrate is thermally oxidized, and then impurities are ion-implanted and thermally oxidized to the substrate, so that the etching rate at the time of forming the second spacer is reduced. A film in which the etching rate of the insulating film forming the second spacer on the side contacting the substrate is higher than the etching rate of the insulating film forming the second spacer on the side contacting the movable electrode formed in a later step. A step of forming so that
Forming the movable electrode on an insulating film constituting the second spacer;
Forming an insulating film constituting the first spacer on the movable electrode;
Forming the fixed electrode on an insulating film constituting the first spacer;
Forming a through hole in the fixed electrode;
Removing a portion of the substrate to form the back chamber;
A part of the insulating film constituting the first spacer is removed by etching from the through hole, the first spacer is formed, and an air gap is formed between the fixed electrode and the movable electrode. A part of the insulating film forming the second spacer is removed by etching, and the contact portion between the insulating film forming the second spacer and the substrate recedes from the back chamber in a direction opposite to the center direction of the movable electrode. The contact portion between the insulating film forming the second spacer and the movable electrode has a structure arranged closer to the center of the movable electrode than the contact portion between the insulating film forming the second spacer and the substrate. Forming a second spacer.

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