MEMS device and method for manufacturing MEMS device

Abstract

To improve sensitivity in a MEMS device.SOLUTION: A MEMS device comprises: a substrate that has a first main surface and a second main surface facing the first main surface and in which a cavity recessed from the first main surface is disposed; and a MEMS electrode disposed and spaced apart toward the first main surface with respect to a bottom surface of the cavity. The MEMS electrode includes: a movable electrode finger that is relatively movable with respect to the substrate; a fixed electrode finger disposed at an interval from the movable electrode finger so as to face the movable electrode finger; and a beam portion that is cantilevered on the substrate and connects the fixed electrode finger to the substrate. The beam portion includes a first portion that has a first thermal expansion coefficient and a second portion that is disposed adjacent to the first portion and has a second thermal expansion coefficient different from the first thermal expansion coefficient. The beam portion is deformed due to a difference between the thermal stress generated in the first portion and the thermal stress generated in the second portion, and the interval between the fixed electrode finger and the movable electrode finger is narrowed due to the deformation of the beam portion as compared with an interval formed before the deformation of the beam portion.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] FIELD OF THE DISCLOSURE This disclosure relates to MEMS devices and methods for manufacturing MEMS devices. [Background technology]

[0002] Patent Document 1 discloses a capacitive MEMS (Micro Electro Mechanical System) sensor having fixed and movable electrodes that face each other and mesh with each other like comb teeth. The fixed and movable electrodes described in Patent Document 1 are formed by etching a semiconductor substrate. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2023-020325

[0004] [overview] In general, in a capacitance-type MEMS sensor, the narrower the gap between the movable electrode and the fixed electrode, the higher the sensitivity. However, since there is a limit to the aspect ratio of etching, the deeper the etching, the wider the gap between the movable electrode and the fixed electrode. In other words, when etching the gap between the movable electrode and the fixed electrode to a predetermined depth, it is difficult to make the gap between the fixed electrode and the movable electrode narrower than a certain gap. Patent Document 1 does not describe the gap between the fixed electrode and the movable electrode, and there is room for improvement in terms of improving sensitivity.

[0005] The present disclosure aims to improve the sensitivity of MEMS devices.

[0006] One aspect of the present disclosure is a substrate having a first main surface and a second main surface opposite to the first main surface, and a cavity recessed from the first main surface side to the second main surface side; a MEMS electrode disposed within the cavity and spaced apart from a bottom surface of the cavity toward the first principal surface; Equipped with The MEMS electrode is a movable electrode finger connected to the substrate so as to be movable relative to the substrate; fixed electrode fingers arranged to face the movable electrode fingers and spaced apart from the movable electrode fingers; a beam portion that is cantilevered on the substrate and connects the fixed electrode finger to the substrate; Equipped with The beam portion is a first portion having a first coefficient of thermal expansion; a second portion disposed adjacent to the first portion and having a second coefficient of thermal expansion different from the first coefficient of thermal expansion; having The beam portion is deformed due to the difference between thermal stress generated in the first portion and thermal stress generated in the second portion, and the deformation of the beam portion narrows the distance between the fixed electrode finger and the movable electrode finger compared to before the deformation of the beam portion. [Brief description of the drawings]

[0007] [Figure 1] FIG. 1 is a plan view of an acceleration sensor according to an embodiment of the present disclosure. [Diagram 2] FIG. 2 is a cross-sectional view taken along line II-II in FIG. [Diagram 3] FIG. 3 is a flowchart illustrating a manufacturing process of the acceleration sensor according to the embodiment of the present disclosure. [Figure 4] FIG. 4 is a diagram for explaining a manufacturing process of the acceleration sensor according to the embodiment of the present disclosure. [Diagram 5] FIG. 5 is a diagram for explaining a manufacturing process of the acceleration sensor according to the embodiment of the present disclosure. [Figure 6] FIG. 6 is a diagram for explaining a manufacturing process of the acceleration sensor according to the embodiment of the present disclosure. [Figure 7] FIG. 7 is a diagram for explaining a manufacturing process of the acceleration sensor according to the embodiment of the present disclosure. [Figure 8]FIG. 8 is a diagram for explaining a manufacturing process of the acceleration sensor according to the embodiment of the present disclosure. [Figure 9] FIG. 9 is a diagram for explaining a manufacturing process of the acceleration sensor according to the embodiment of the present disclosure. [Figure 10] FIG. 10 is a diagram for explaining a manufacturing process of the acceleration sensor according to the embodiment of the present disclosure. [Figure 11] FIG. 11 is a cross-sectional view similar to FIG. 2 according to a modification of an embodiment of the present disclosure.

[0008] [Detailed Description] Hereinafter, a MEMS device and a method for manufacturing a MEMS device according to an embodiment of the present disclosure will be described with reference to the accompanying drawings. Note that the following description is essentially merely illustrative and is not intended to limit the present disclosure, its applications, or its uses. Also, the drawings are schematic, and the ratios of dimensions, etc. differ from the actual ones.

[0009] [Accelerometer] Fig. 1 is a plan view that shows a schematic diagram of an acceleration sensor 1 according to an embodiment of the present disclosure. Fig. 2 is a cross-sectional view taken along line II-II in Fig. 1. The acceleration sensor 1 according to this embodiment is a capacitance type acceleration sensor manufactured using semiconductor microfabrication technology. The acceleration sensor 1 according to this embodiment is an example of a MEMS (Micro Electro Mechanical System) device according to the present disclosure.

[0010] In the following description, for convenience, among the directions along each side of the acceleration sensor 1 in the plan view shown in Fig. 1, the left-right direction in Fig. 1 is referred to as the X direction, the up-down direction in Fig. 1 is referred to as the Y direction, and the thickness direction of the acceleration sensor 1 in the cross-sectional view shown in Fig. 2 (the up-down direction in Fig. 2) is referred to as the Z direction. In particular, the right side in Fig. 1 may be referred to as the +X direction, the left side as the -X direction, the upper side as the +Y direction, and the lower side as the -Y direction. In Fig. 2, the upper side may be referred to as the +Z direction, and the lower side as the -Z direction. In this embodiment, the X direction, the Y direction, and the Z direction are perpendicular to each other.

[0011] 1 and 2, the acceleration sensor 1 includes a substrate 10 and a MEMS electrode 20 provided in the substrate 10. As shown in FIG.

[0012] The substrate 10 has a rectangular shape in plan view. The substrate 10 has a first main surface 10a located on the +Z side and a second main surface 10b located on the -Z side and facing the first main surface 10a. The substrate 10 is a conductive silicon (Si) substrate. The substrate 10 of this embodiment is made of only a single silicon layer. The first main surface 10a and the second main surface 10b extend parallel to the X direction and the Y direction. An insulating layer 11 is disposed on the first main surface 10a of the substrate 10. The substrate 10 has a cavity 12 formed therein that is rectangular in plan view and recessed from the first main surface 10a toward the -Z side.

[0013] The MEMS electrode 20 includes a movable electrode 30 and a fixed electrode 40. The movable electrode 30 and the fixed electrode 40 are disposed within the cavity 12.

[0014] The movable electrode 30 is spaced from the bottom surface 12a of the cavity 12 on the +Z side. The movable electrode 30 includes movable electrode fingers 31 extending in the Y direction, a base 32 to which +Y side ends of the movable electrode fingers 31 are connected, and two spring portions 33A and 33B that connect the base 32 to the substrate 10. In the following description, when there is no need to particularly distinguish between the spring portions 33A and 33B, one of the two spring portions 33A and 33B may be simply referred to as the spring portion 33.

[0015] The movable electrode finger 31 includes a conductive silicon (Si) layer. The movable electrode finger 31 is connected to the substrate 10 so as to be movable in the X direction relative to the substrate 10.

[0016] The base 32 includes a conductive silicon (Si) layer. The base 32 functions as a proof mass of the acceleration sensor 1. The base 32 is connected to the substrate 10 so as to be movable relative to the substrate 10 in the X direction.

[0017] The spring portion 33 includes a conductive silicon (Si) layer. The spring portion 33 is cantilevered on the side surfaces of the substrate 10 extending in the Y and Z directions. The spring portion 33 protrudes into the cavity 12 from the side surfaces of the substrate 10 extending in the Y and Z directions. The spring portions 33A and 33B are disposed on the -X and +X sides of the base portion 32, respectively. The spring portion 33 is configured to be expandable and contractable in the X direction. When acceleration in the X direction acts on the base portion 32, the spring portions 33A and 33B are elastically deformed, displacing the movable electrode finger 31 in the X direction.

[0018] The movable electrode 30 has an isolation joint 34 that crosses the spring portion 33 in the Y and Z directions and divides it in the X direction. The isolation joint 34 mechanically connects both sides of the spring portion 33 divided in the X direction by the isolation joint 34, while electrically insulating them. The isolation joint 34 electrically insulates the movable electrode finger 31 from the substrate 10. The isolation joint 34 in this embodiment is made of silicon oxide (SiO2).

[0019] The fixed electrode 40 is spaced from the bottom surface 12a of the cavity 12 on the +Z side. The fixed electrode 40 includes two fixed electrode fingers 41A, 41B extending in the Y direction, and two beam portions 42A, 42B connecting the two fixed electrode fingers 41A, 41B to the substrate 10, respectively. In the following description, when there is no need to particularly distinguish between the two fixed electrode fingers 41A, 41B, one of the two fixed electrode fingers 41A, 41B may be simply referred to as the fixed electrode finger 41. Similarly, in the following description, when there is no need to particularly distinguish between the two beam portions 42A, 42B, one of the two beam portions 42A, 42B may be simply referred to as the beam portion 42.

[0020] The fixed electrode finger 41 includes a conductive silicon (Si) layer. The two fixed electrode fingers 41A, 41B extend in the Y direction and are arranged side by side in the X direction. The two fixed electrode fingers 41A, 41B are arranged with the movable electrode finger 31 sandwiched between them in the X direction. The fixed electrode finger 41 is arranged facing the movable electrode finger 31 in the X direction. The fixed electrode finger 41 is arranged with a gap G1 between it and the movable electrode finger 31 in the X direction. In this embodiment, the aspect ratio of the space between the movable electrode finger 31 and the fixed electrode finger 41, that is, the ratio D / G1 of the depth D of the movable electrode finger 31 and the fixed electrode finger 41 to the gap G1 in the X direction between the movable electrode finger 31 and the fixed electrode finger 41, that is, the dimension in the Z direction, is, for example, 100 or more.

[0021] The beam portion 42 is cantilevered by the substrate 10. The beam portion 42 extends from the side surfaces of the substrate 10 extending in the X and Z directions into the cavity 12. The beam portion 42 includes a first end portion 42a connected to the substrate 10 and a second end portion 42b connected to the +Y side end portion of the fixed electrode finger 41. In plan view, the beam portion 42 includes a first beam 43 curved from the first end portion 42a toward the movable electrode finger 31 in the X direction toward the +Y side, and a second beam 44 extending from the +Y side end portion of the first beam 43 toward the movable electrode finger 31 in the X direction. That is, the beam portion 42 of this embodiment is substantially L-shaped in plan view.

[0022] The first beam 43 is arranged side by side with the fixed electrode finger 41 in the X direction. Specifically, in the beam portion 42A, the first beam 43 is arranged on the -X side of the fixed electrode finger 41A, and in the beam portion 42B, the first beam 43 is arranged on the +X side of the fixed electrode finger 41B. The first beam 43 in this embodiment is curved from the first end portion 42a toward the +Y side toward the fixed electrode finger 41 in the X direction. Specifically, the first beam 43 of the beam portion 42A in this embodiment is curved from the first end portion 42a toward the +Y side toward the fixed electrode finger 41A side, that is, toward the +X side, and the first beam 43 of the beam portion 42B is curved from the first end portion 42a toward the +Y side toward the fixed electrode finger 41B side, that is, toward the -X side.

[0023] The first beam 43 has a first portion 43a having a first thermal expansion coefficient, and a second portion 43b arranged adjacent to the first portion 43a in the X direction and having a second thermal expansion coefficient different from the first thermal expansion coefficient. Here, the first thermal expansion coefficient and the second thermal expansion coefficient are linear thermal expansion coefficients in the Y direction. In this embodiment, the first thermal expansion coefficient is larger than the second thermal expansion coefficient.

[0024] The first portion 43a includes a conductive silicon (Si) layer. The first portion 43a extends in a curved manner toward the movable electrode finger 31 in the X direction toward the +Y side.

[0025] The second portion 43b in this embodiment is made of silicon oxide (SiO2) formed by thermally oxidizing the substrate 10. The second thermal expansion coefficient of the second portion 43b is smaller than the first thermal expansion coefficient of the first portion 43a. The second portion 43b is curved and extends toward the movable electrode finger 31 in the X direction toward the +Y side. That is, the second portion 43b extends along the first portion 43a. The second portion 43b is disposed on the opposite side of the fixed electrode finger 41 with respect to the first portion 43a in the X direction. In the beam portion 42A, the second portion 43b is disposed adjacent to the -X side of the first portion 43a. In the beam portion 42B, the second portion 43b is disposed adjacent to the +X side of the first portion 43a.

[0026] The second beam 44 includes a conductive silicon (Si) layer. The second beam 44 extends in the X direction so as to connect the +Y side end of the first beam 43 and the +Y side end of the fixed electrode finger 41.

[0027] Beam portion 42 is deformed due to the difference in thermal stress generated between first portion 43a and second portion 43b in the step of forming second portion 43b in the manufacturing method of acceleration sensor 1. Specifically, first beam 43, which extends linearly in the Y direction in beam portion 42 before deformation, is deformed so as to curve toward the +Y side toward movable electrode finger 31 in the X direction due to the difference in thermal stress generated between first portion 43a and second portion 43b. As a result, gap G1 in the X direction between movable electrode finger 31 and fixed electrode finger 41 is narrower than gap G2 (shown in FIG. 9) before deformation.

[0028] Beam portion 42 has an isolation joint 45 that crosses first beam 43 in the X and Z directions and divides it in the Y direction. Isolation joint 45 mechanically connects both sides of beam portion 42 divided in the Y direction by isolation joint 45, while electrically insulating them. Fixed electrode finger 41 and substrate 10 are electrically insulated by isolation joint 45. Isolation joint 45 in this embodiment is made of silicon oxide (SiO2).

[0029] The acceleration sensor 1 includes a restricting portion 50 connected to the substrate 10. When the beam portions 42 of the fixed electrode 40 are deformed due to thermal stress and the fixed electrode fingers 41 are displaced toward the movable electrode fingers 31 by a predetermined distance or more, the restricting portion 50 comes into contact with the fixed electrode fingers 41 to restrict the displacement of the fixed electrode fingers 41. In this way, the restricting portion 50 maintains the gap G between the movable electrode fingers 31 and the fixed electrode fingers 41 at a predetermined gap G1.

[0030] The restricting portion 50 includes a main body 51 extending in the Y direction, and two protruding portions 52A, 52B protruding from the main body 51 on both sides in the X direction. When there is no need to particularly distinguish between the two protruding portions 52A, 52B, one of the two protruding portions 52A, 52B may be simply referred to as a protruding portion 52.

[0031] The main body 51 includes a conductive silicon (Si) layer. The main body 51 protrudes into the cavity 12 from the side surfaces of the substrate 10 extending in the X and Z directions.

[0032] The protruding portion 52 includes a conductive silicon (Si) layer. The protruding portion 52A protrudes from the +Y side end of the main body 51 to the -X side, and the protruding portion 52B protrudes from the +Y side end of the main body 51 to the +X side.

[0033] The restricting portion 50 has an isolation joint 53 that crosses the protruding portion 52 in the Y and Z directions and divides it in the X direction. The isolation joint 53 mechanically connects both sides of the protruding portion 52 divided in the X direction by the isolation joint 53, while electrically insulating them. The isolation joint 53 electrically insulates the portion of the protruding portion 52 facing the fixed electrode finger 41 from the substrate 10. The isolation joint 53 in this embodiment is made of silicon oxide (SiO2).

[0034] The acceleration sensor 1 includes electrode pads 60 to 63 through which electrical signals (voltages) are input and output to and from the MEMS electrode 20. Different voltages are applied to the electrode pads 60 to 63. The electrode pads 60 to 63 are disposed on an insulating layer 11.

[0035] The electrode pad 60 is electrically connected to the movable electrode 30 via a wiring layer 70. The wiring layer 70 is electrically insulated from the substrate 10 by an insulating layer 11.

[0036] Electrode pad 61 is electrically connected to fixed electrode finger 41A via wiring layer 71, and is electrically connected to a portion of protrusion 52A of restrictor 50 facing fixed electrode finger 41A via wiring layer 72. As a result, fixed electrode finger 41A and a portion of protrusion 52A in contact with fixed electrode finger 41A are connected to the same potential. In addition, wiring layers 71 and 72 are electrically insulated from substrate 10 by insulating layer 11.

[0037] Electrode pad 62 is electrically connected to fixed electrode finger 41B via wiring layer 73, and is electrically connected to a portion of protrusion 52B of restrictor 50 that faces fixed electrode finger 41B via wiring layer 74. As a result, fixed electrode finger 41B and the portion of protrusion 52B in contact with fixed electrode finger 41B are connected to the same potential. In addition, wiring layers 73 and 74 are electrically insulated from substrate 10 by insulating layer 11.

[0038] The electrode pad 63 is electrically connected to the substrate 10 via a wiring layer 75 .

[0039] In the acceleration sensor 1 of this embodiment, a first capacitor C1 is formed by the movable electrode finger 31 and the fixed electrode finger 41A arranged adjacent to the movable electrode finger 31 on the -X side. A second capacitor C2 is formed by the movable electrode finger 31 and the fixed electrode finger 41B arranged adjacent to the movable electrode finger 31 on the +X side.

[0040] When acceleration in the X direction acts on the acceleration sensor 1, the movable electrode finger 31 moves in the X direction relative to the fixed electrode 40. The acceleration sensor 1 is configured to be capable of detecting acceleration by detecting changes in the electrostatic capacitance of each of the first capacitor C1 and the second capacitor C2 that accompany the displacement of the movable electrode 30 in the X direction when acceleration acts on the sensor.

[0041] [Manufacturing method of acceleration sensor] A method for manufacturing the acceleration sensor 1, particularly a method for manufacturing the structure around the fixed electrode 40, will be described with reference to Figs. 3 to 10. Fig. 3 is a flowchart for explaining the method for manufacturing the acceleration sensor 1 according to this embodiment. Figs. 4 to 10 are views for explaining the method for manufacturing the acceleration sensor 1 according to this embodiment. Figs. 4 to 8 and Fig. 10 show cross-sectional views similar to Fig. 2, and Fig. 9 shows a plan view similar to Fig. 1.

[0042] In step S1, as shown in Fig. 4, a substrate 10 including a silicon (Si) layer is prepared. The substrate 10 of this embodiment is made of only a single silicon layer. The substrate 10 has a first main surface 10a located on the +Z side and a second main surface 10b located on the Z side and facing the first main surface 10a.

[0043] Next, in step S2, as shown in FIG. 5, a first trench T1 is formed extending from the first main surface 10a of the substrate 10 to the second main surface 10b. Specifically, a first silicon oxide (SiO2) layer L1 is formed on the first main surface 10a of the substrate 10, with a part of the first main surface 10a exposed in order to form the second portion 43b (shown in FIG. 1). Next, the first silicon oxide layer L1 is used as a hard mask to dig down the substrate 10 from the first main surface 10a to the -Z side by anisotropic etching, thereby forming the first trench T1. In this embodiment, the first trench T1 extends linearly in the Y direction in plan view. Although not shown, in step S2, trenches for forming the isolation joints 34, 45, and 53 may be formed in the substrate 10.

[0044] Next, in step S3, as shown in FIG. 6, a vertical structure B having a second thermal expansion coefficient different from the first thermal expansion coefficient of the substrate 10 is formed in the first trench T1. In this embodiment, the vertical structure B is formed by thermally oxidizing the wall surface of the first trench T1. Specifically, after removing the first silicon oxide layer L1 (shown in FIG. 5) from the substrate 10, the substrate 10 is thermally oxidized from the +Z side to form a thermal oxide film of thermally oxidized silicon on the inner wall surface of the first trench T1. The thermal oxide film formed on the inner wall surface of the first trench T1 fills the inside of the first trench T1 to form the vertical structure B. That is, in this embodiment, the vertical structure B is a structure made of silicon oxide (SiO2) obtained by thermally oxidizing the substrate 10. In this embodiment, the vertical structure B extends linearly in the Y direction in a plan view. The second portion 43b of the beam portion 42 is formed by the vertical structure B. Although not shown in the figure, in step S3, the wall surfaces of the trenches for forming the isolation joints 34, 45, 53 formed in step S2 may be thermally oxidized to form the isolation joints 34, 45, 53 by the same mechanism as that for forming the vertical structure B.

[0045] In this embodiment, the vertical structures B have a second thermal expansion coefficient lower than the first thermal expansion coefficient of the substrate 10. The thermal oxidation of the first trench T1 is performed at a high temperature (for example, 800 to 1200°C). When the vertical structures B formed at a high temperature are cooled, the contraction of the vertical structures B due to cooling is restricted by the portion of the substrate 10 arranged around the vertical structures B, so that distortion remains inside the vertical structures B and thermal stress occurs. Similarly, distortion remains inside the portion of the substrate 10 arranged around the vertical structures B and thermal stress occurs.

[0046] In step S4, as shown in Fig. 6, a thermally oxidized film M is formed on the first main surface 10a of the substrate 10. In this embodiment, the formation of the thermally oxidized film M in step S4 is performed in the same process as the formation of the vertical structures B in the first trenches T1 in step S3. Specifically, after removing the first silicon oxide layer L1 (shown in Fig. 5) from the substrate 10, the substrate 10 is thermally oxidized from the +Z side to form the thermally oxidized film M, which is thermally oxidized silicon, on the first main surface 10a. The thermally oxidized film M formed on the first main surface 10a constitutes the insulating layer 11 (shown in Fig. 1).

[0047] Next, in step S5, as shown in FIG. 7, of the thermally oxidized film M formed on the first main surface 10a of the substrate 10, a portion corresponding to the cavity 12 (shown in FIG. 1) is partially removed.

[0048] Next, in step S6, although not shown, the wiring layers 70 to 75 (shown in FIG. 1) are formed in a predetermined pattern.

[0049] Next, in step S7, as shown in FIG. 8 and FIG. 9, a second trench T2 is formed extending from the first main surface 10a to the second main surface 10b of the substrate 10. Specifically, a second silicon oxide layer L2 is formed on the +X side of the first main surface 10a of the substrate 10 in a portion corresponding to the MEMS electrode 20. Next, the second silicon oxide layer L2 is used as a hard mask to dig down the substrate 10 from the first main surface 10a to the -Z side by anisotropic etching, thereby forming the second trench T2. As shown in FIG. 9, the second trench T2 defines the MEMS electrode 20 in the substrate 10. Specifically, the second trench T2 defines the movable electrode fingers 31, the fixed electrode fingers 41, and the beam portion 42 in the substrate 10.

[0050] In a state in which MEMS electrode 20 is partitioned on substrate 10, first beam 43 extends linearly in the Y direction, as shown in Fig. 9. In the state shown in Fig. 8 and Fig. 9, distance G2 in the X direction between movable electrode finger 31 and fixed electrode finger 41 is wider than distance G1 in the X direction between movable electrode finger 31 and fixed electrode finger 41 in the state shown in Fig. 1. In the state shown in Fig. 8 and Fig. 9, the movement of partitioned fixed electrode finger 41 and beam portion 42 is restricted by a portion of substrate 10 located on the -Z side of fixed electrode finger 41 and beam portion 42.

[0051] Next, in step S8, the cavity 12 is formed. Specifically, as shown in Fig. 10, a third silicon oxide layer L3 is formed on the inner wall surface of the second trench T2, and the third silicon oxide layer L3 is removed at the bottom of the second trench T2. Thereafter, the bottom of the second trench T2 is removed by isotropic etching, thereby removing a portion of the substrate 10 located on the -Z side of the MEMS electrode 20. As a result, the bottoms of adjacent second trenches T2 are connected to each other, thereby forming the cavity 12, and the MEMS electrode 20 is formed so as to be separated (also referred to as released) from the bottom surface 12a of the cavity 12 to the +Z side.

[0052] Finally, although not shown, the second silicon oxide layer L2 and the third silicon oxide layer L3 are removed, thereby completing the acceleration sensor 1.

[0053] After the MEMS electrode 20 moves away from the bottom surface 12a of the cavity 12, the first beam 43 is deformed so as to be curved due to the difference between the thermal stress generated in the first portion 43a and the thermal stress generated in the second portion 43b (vertical structure B), as described in detail below.

[0054] When the MEMS electrode 20 is released from the bottom surface 12a of the cavity 12, a thermal stress that tries to compress the first portion 43a in the Y direction is generated in the first portion 43a that extends linearly in the Y direction in a plan view. Similarly, when the MEMS electrode 20 is released from the bottom surface 12a of the cavity 12, a thermal stress that tries to compress the second portion 43b in the Y direction is generated in the second portion 43b that extends linearly in the Y direction in a plan view. Here, since the first thermal expansion coefficient of the first portion 43a is larger than the second thermal expansion coefficient of the second portion 43b, the thermal stress that tries to compress the first portion 43a in the Y direction is larger than the thermal stress that tries to compress the second portion 43b in the Y direction. Therefore, the contraction amount in the Y direction of the first portion 43a of the first beam 43 arranged on the side of the fixed electrode finger 41 in the X direction becomes larger than the contraction amount in the Y direction of the second portion 43b of the first beam 43 arranged on the opposite side of the fixed electrode finger 41 with respect to the first portion 43a in the X direction, so that the first beam 43 is curved toward the fixed electrode finger 41 toward the +Y side. This deformation of the first beam 43 displaces the fixed electrode finger 41 so as to approach the movable electrode finger 31. As a result, the distance between the movable electrode finger 31 and the fixed electrode finger 41 becomes narrower than the distance G2 when etching is performed to separate the movable electrode finger 31 and the fixed electrode finger 41. In this embodiment, when the fixed electrode finger 41 is displaced by a predetermined distance or more due to the deformation of the beam portion 42, it comes into contact with the protrusion 52 of the restriction portion 50, and the displacement of the fixed electrode finger 41 is restricted. As a result, the distance G1 between the movable electrode finger 31 and the fixed electrode finger 41 is maintained at a predetermined distance.

[0055] [effect] When etching between the movable electrode finger 31 and the fixed electrode finger 41, the aspect ratio of the etching is limited, so the interval between the movable electrode finger 31 and the fixed electrode finger 41 becomes wider depending on the depth of the etching. In other words, when etching between the movable electrode finger 31 and the fixed electrode finger 41 to a predetermined depth, it is difficult to narrow the interval between the fixed electrode finger 41 and the movable electrode finger 31 below a certain interval. In contrast, with this configuration, the beam portion 42 is deformed due to the difference between the thermal stress generated in the first portion 43a and the thermal stress generated in the second portion 43b, and the deformation of the beam portion 42 can make the interval between the movable electrode finger 31 and the fixed electrode finger 41 narrower than the interval G2 before the beam portion 42 is deformed. As a result, for example, the interval G1 between the movable electrode finger 31 and the fixed electrode finger 41 can be made narrower than the interval G2 when the fixed electrode finger 41 and the beam portion 42 are separated from the bottom surface 12a of the cavity 12. That is, the gap G1 between the movable electrode fingers 31 and the fixed electrode fingers 41 can be made narrower than the gap G2 formed between the fixed electrode fingers 41 and the movable electrode fingers 31 by etching for forming the fixed electrode fingers 41 and the movable electrode fingers 31. As a result, regardless of the limit of the aspect ratio of the etching, the gap between the fixed electrode fingers 41 and the movable electrode fingers 31 can be narrowed, and therefore the sensitivity of the MEMS device can be improved.

[0056] According to the acceleration sensor 1 of this embodiment, the displacement of the fixed electrode fingers 41 in the X direction is restricted by the restricting portion 50, so that the distance G1 between the movable electrode fingers 31 and the fixed electrode fingers 41 can be maintained at a predetermined distance regardless of manufacturing errors or temperature changes.

[0057] According to the acceleration sensor 1 of this embodiment, the portion of the restricting portion 50 that contacts the fixed electrode fingers 41 is connected to the same potential as the fixed electrode fingers 41, so that when the fixed electrode fingers 41 contact the restricting portion 50, no current flows from the fixed electrode fingers 41 to the restricting portion 50. As a result, it is possible to suppress a decrease in the sensitivity of the MEMS device.

[0058] The MEMS device according to the present disclosure is not limited to the configuration of the above embodiment, and various modifications are possible.

[0059] In the above embodiment, the acceleration sensor 1 has been described as an example of the MEMS device, but the present disclosure can be applied to various MEMS devices having MEMS electrodes. For example, the MEMS device according to the present disclosure may be a MEMS oscillator or an acceleration sensor.

[0060] In the above embodiment, the acceleration sensor 1 has the restricting portion 50, but the present invention is not limited to this.

[0061] In the above embodiment, fixed electrode finger 41 and the portion of restricting portion 50 that contacts fixed electrode finger 41 are electrically connected to the same potential, but this is not limited to this. In other words, fixed electrode finger 41 and the portion of restricting portion 50 that contacts fixed electrode finger 41 may be electrically connected to different potentials.

[0062] The shape and structure of beam portion 42 are not limited to those exemplified in the above embodiment. As long as beam portion 42 has a function of deforming due to thermal stress and making gap G1 between movable electrode finger 31 and fixed electrode finger 41 after deformation narrower than gap G2 between movable electrode finger 31 and fixed electrode finger 41 before deformation, the shape and structure of beam portion 42 can be changed.

[0063] The position, size, range, material, etc. of the first portion 43a and the second portion 43b are not limited to those exemplified in the above embodiment. As long as the beam portion 42 has a function of deforming due to thermal stress and making the gap G1 between the movable electrode finger 31 and the fixed electrode finger 41 after deformation narrower than the gap G2 between the movable electrode finger 31 and the fixed electrode finger 41 before deformation, the position, size, range, material, etc. of the first portion 43a and the second portion 43b can be changed. For example, in the above embodiment, the first portion 43a is made of silicon (Si) and the second portion 43b is made of silicon oxide (SiO2), but this is not limited thereto. The first portion 43a may be made of a material different from that of the substrate 10.

[0064] In the above embodiment, the substrate 10 is described as being made of only a single silicon layer, but the substrate according to the present disclosure may have other layers such as a silicon oxide (SiO2) layer or silicon carbide (SiC) layer in addition to the silicon layer. For example, the substrate according to the present disclosure may be a silicon on insulator (SOI) substrate. Specifically, as in the modified example shown in FIG. 11, the substrate 10 may include a support layer 10c made of silicon, an insulating layer 10d made of silicon oxide and stacked on the +Z side of the support layer 10c, and an active layer 10e made of silicon and stacked on the +Z side of the insulating layer 10d.

[0065] [Note] The MEMS device and the method for manufacturing the MEMS device according to the present disclosure provide the following aspects.

[0066] [Aspect 1] a substrate having a first main surface and a second main surface opposite to the first main surface, and a cavity recessed from the first main surface side to the second main surface side; a MEMS electrode disposed within the cavity and spaced apart from a bottom surface of the cavity toward the first principal surface; Equipped with The MEMS electrode is a movable electrode finger connected to the substrate so as to be movable relative to the substrate; fixed electrode fingers arranged to face the movable electrode fingers and spaced apart from the movable electrode fingers; a beam portion that is cantilevered on the substrate and connects the fixed electrode finger to the substrate; Equipped with The beam portion is a first portion having a first coefficient of thermal expansion; a second portion disposed adjacent to the first portion and having a second coefficient of thermal expansion different from the first coefficient of thermal expansion; having The beam portion is deformed due to the difference between thermal stress generated in the first portion and thermal stress generated in the second portion, and the deformation of the beam portion narrows the distance between the fixed electrode finger and the movable electrode finger compared to before the deformation of the beam portion.

[0067] When etching between the movable electrode fingers and the fixed electrode fingers, the aspect ratio of the etching is limited, so the interval between the movable electrode fingers and the fixed electrode fingers becomes wider depending on the depth of the etching. In other words, when etching between the movable electrode fingers and the fixed electrode fingers to a predetermined depth, it is difficult to narrow the interval between the fixed electrode fingers and the movable electrode fingers below a certain interval. In contrast, according to the MEMS device of the first aspect, the beam portion is deformed due to the difference between the thermal stress generated in the first portion and the thermal stress generated in the second portion, and the deformation of the beam portion can make the interval between the movable electrode fingers and the fixed electrode fingers narrower than the interval before the beam portion is deformed. This makes it possible to make the interval between the movable electrode fingers and the fixed electrode fingers narrower than the interval when the fixed electrode fingers and the beam portion are separated from the bottom surface of the cavity, for example. In other words, the interval between the movable electrode fingers and the fixed electrode fingers can be narrower than the interval formed between the fixed electrode fingers and the movable electrode fingers by etching for forming the fixed electrode fingers and the movable electrode fingers. As a result, the distance between the fixed electrode fingers and the movable electrode fingers can be narrowed regardless of the limit of the aspect ratio of etching, thereby improving the sensitivity of the MEMS device.

[0068] [Aspect 2] The MEMS device of aspect 1 is provided, wherein the substrate has a regulating portion that regulates displacement of the fixed electrode finger by coming into contact with the fixed electrode finger when the fixed electrode finger is displaced toward the movable electrode finger by more than a predetermined distance due to deformation of the beam portion.

[0069] [Aspect 3] In the MEMS device according to aspect 2, a portion of the restricting portion that comes into contact with the fixed electrode finger is connected to the same potential as the fixed electrode finger.

[0070] [Aspect 4] providing a substrate having a first main surface and a second main surface opposite to the first main surface; forming a first trench extending from the first major surface of the substrate toward the second major surface; forming a vertical structure in the first trench having a thermal expansion coefficient different from a thermal expansion coefficient of the substrate by thermally oxidizing a wall surface of the first trench; a second trench is formed by anisotropic etching, the second trench extending from the first main surface of the substrate toward the second main surface, the second trench defines movable electrode fingers, fixed electrode fingers, and a beam portion in the substrate, the vertical structure being included in the beam portion; A cavity is formed by at least partially removing the substrate located on the second main surface side of the partitioned movable electrode fingers, the fixed electrode fingers, and the beam portion, and the fixed electrode fingers, the movable electrode fingers, and the beam portion are formed apart from a bottom surface of the cavity. Including, The present invention provides a manufacturing method for a MEMS device, in which, after the beam portion moves away from the bottom surface of the cavity, the beam portion is deformed by thermal stress generated in the beam portion due to the difference between thermal stress generated in the portion of the beam portion adjacent to the vertical structure and thermal stress generated in the vertical structure, and the deformation of the beam portion narrows the distance between the fixed electrode finger and the movable electrode finger compared to before the deformation of the beam portion. [Explanation of symbols]

[0071] 1. Acceleration sensor (MEMS device) 10 Substrate 10a First main surface 10b Second main surface 11 Insulating layer 12 Cavity 12a Bottom 20 MEMS electrodes 30 Movable electrode 31 Movable electrode finger 32 Base 33 Spring section 34 Isolation joint 40 Fixed electrode 41 Fixed electrode finger 42 Beam section 42a First end 42b Second end 43 1st beam 43a Part 1 43b Part 2 44 2nd beam 45 Isolation joint 50 Regulatory Department 51 Main unit 52 Protrusion 53 Isolation joint 60 Electrode Pads 61 Electrode Pads 62 Electrode Pads 63 Electrode Pads 70 wiring layer 71 Wiring layer 72 wiring layer 73 Wiring layer 74 Wiring layer 75 Wiring layer

Claims

1. a substrate having a first main surface and a second main surface opposite to the first main surface, and a cavity recessed from the first main surface side to the second main surface side; a MEMS electrode disposed in the cavity and spaced apart from a bottom surface of the cavity toward the first principal surface; Equipped with The MEMS electrode is a movable electrode finger connected to the substrate so as to be movable relative to the substrate; fixed electrode fingers arranged to face the movable electrode fingers and spaced apart from the movable electrode fingers; a beam portion that is cantilevered on the substrate and connects the fixed electrode finger to the substrate; Equipped with The beam portion is a first portion having a first coefficient of thermal expansion; a second portion disposed adjacent to the first portion and having a second coefficient of thermal expansion different from the first coefficient of thermal expansion; having The beam portion is deformed due to the difference between the thermal stress generated in the first portion and the thermal stress generated in the second portion, and the deformation of the beam portion causes the distance between the fixed electrode finger and the movable electrode finger to become narrower than before the deformation of the beam portion.

2. The MEMS device according to claim 1 , wherein the substrate has a regulating portion that regulates displacement of the fixed electrode finger by contacting the fixed electrode finger when the fixed electrode finger is displaced toward the movable electrode finger by more than a predetermined distance due to deformation of the beam portion.

3. The MEMS device according to claim 2 , wherein a portion of the restricting portion that comes into contact with the fixed electrode finger is connected to the same potential as the fixed electrode finger.

4. providing a substrate having a first main surface and a second main surface opposite to the first main surface; forming a first trench extending from the first major surface of the substrate toward the second major surface; forming a vertical structure in the first trench having a thermal expansion coefficient different from a thermal expansion coefficient of the substrate by thermally oxidizing a wall surface of the first trench; a second trench is formed by anisotropic etching, the second trench extending from the first main surface of the substrate toward the second main surface, the second trench defines movable electrode fingers, fixed electrode fingers, and a beam portion in the substrate, the vertical structure being included in the beam portion; A cavity is formed by at least partially removing the substrate located on the second main surface side of the partitioned movable electrode fingers, the fixed electrode fingers, and the beam portion, and the fixed electrode fingers, the movable electrode fingers, and the beam portion are formed apart from a bottom surface of the cavity. Including, A manufacturing method for a MEMS device, wherein after the beam portion moves away from the bottom surface of the cavity, the beam portion is deformed by thermal stress generated in the beam portion due to the difference between thermal stress generated in the part of the beam portion adjacent to the vertical structure and thermal stress generated in the vertical structure, and the deformation of the beam portion causes the distance between the fixed electrode finger and the movable electrode finger to become narrower than before the deformation of the beam portion.

Images