MEMS sensor and method for manufacturing a MEMS sensor

Abstract

To improve bonding strength between a first substrate and a second substrate in addition to suppressing adhesion of an electrode on a stopper part.SOLUTION: A MEMS sensor includes a first substrate 10 with a cavity 12, and a second substrate 20 bonded to the first substrate 10. On the first substrate 10, an electrode 13 that is disposed movably in the cavity 12 and a sealed part 17 that is bonded to the second substrate 20 are provided. On the second substrate 20, a stopper part 23 that restricts a movement of the electrode 13 and a sealing part 27 that is bonded to the sealed part 17 are provided. The sealed part 17 is formed of a first metal layer 19 on the first substrate 10, and the sealing part 27 is formed of a second metal layer 29 on the second substrate 20. On the stopper part 23, a polycrystalline layer 25 is formed and the polycrystalline layer 25 is formed between the second substrate 20 and the second metal layer 29.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a MEMS sensor and a method for manufacturing the MEMS sensor.

Background Art

[0002] MEMS (Micro Electro Mechanical System) sensors manufactured using semiconductor microfabrication technology are known. Patent Document 1 discloses a MEMS sensor in which a device-side substrate and a lid-side substrate are bonded by glass frit, and electrodes of a sensor element provided on the device-side substrate are sealed.

[0003] As a bonding technique that can be adopted for bonding the device-side substrate and the lid-side substrate, metal bonding for bonding metal films respectively formed on the device-side substrate and the lid-side substrate is also known. Metal bonding enables the MEMS sensor to be made more compact compared to bonding using glass frit.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In MEMS sensors such as MEMS acceleration sensors in which the electrodes of the sensor element are arranged to be movable, the second substrate is bonded to the first substrate provided with the electrodes by metal bonding, and a stopper portion that restricts the movement of the electrodes may be provided on the second substrate so as to prevent the electrodes from being excessively deflected and displaced toward the second substrate side.

[0006] When a stopper portion is provided on the second substrate to restrict the movement of electrodes, there is a risk that the electrodes provided on the first substrate may stick to the stopper portion when they bend toward the second substrate and come into contact with the stopper portion on the second substrate, thereby reducing the reliability of the sensor element. Therefore, it is desirable to suppress the electrodes from sticking to the stopper portion.

[0007] Furthermore, when joining a first metal layer formed on a first substrate and a second metal layer formed on a second substrate by metal bonding, it is desirable to improve the bonding strength between the first substrate and the second substrate.

[0008] This disclosure relates to a MEMS sensor in which a second substrate is bonded to a first substrate having electrodes, and a stopper portion is provided on the second substrate to restrict the movement of the electrodes. The objective is to suppress the electrodes from sticking to the stopper portion and to improve the bonding strength between the first substrate and the second substrate. [Means for solving the problem]

[0009] This disclosure provides a MEMS sensor comprising: a first substrate having a cavity on its surface in which a portion of the cavity is exposed; and a second substrate bonded to the first substrate so as to cover the cavity, wherein the first substrate is provided with electrodes of a sensor element movably disposed within the cavity and a sealed portion bonded to the second substrate; the second substrate is provided with a stopper portion that restricts the movement of the electrodes toward the second substrate and a sealing portion bonded to the sealed portion, the sealed portion is formed by a first metal layer on the first substrate, the sealing portion is formed by a second metal layer on the second substrate, a polycrystalline layer is formed on the stopper portion and a polycrystalline layer is formed between the second substrate and the second metal layer.

[0010] According to this disclosure, electrodes are movably provided on a first substrate, a stopper portion is provided on a second substrate bonded to the first substrate, and a polycrystalline layer is formed on the stopper portion. This makes it possible to increase the surface roughness and reduce the contact area when the electrodes come into contact with the stopper portion, compared to the case where a polycrystalline layer is not formed on the stopper portion, thereby suppressing the electrodes from sticking to the stopper portion. Even when it is not possible to use a non-adhesive fluororesin coating or the like on the stopper portion, it is possible to suppress the adhesion between the electrodes and the stopper portion.

[0011] The portion to be sealed is formed by a first metal layer on a first substrate, and the sealing portion to be joined to the portion to be sealed is formed by a second metal layer on a second substrate, with a polycrystalline layer formed between the second substrate and the second metal layer. As a result, when the first metal layer and the second metal layer are joined by metal, the surface roughness can be increased to improve adhesion and improve the bonding strength between the first substrate and the second substrate compared to when a polycrystalline layer is not formed between the second substrate and the second metal layer.

[0012] Therefore, in a MEMS sensor in which a second substrate is bonded to a first substrate having electrodes, and a stopper portion is provided on the second substrate to restrict the movement of the electrodes, it is possible to suppress the electrodes from sticking to the stopper portion and to improve the bonding strength between the first substrate and the second substrate.

[0013] Furthermore, this disclosure provides a method for manufacturing a MEMS sensor, comprising: forming a cavity on the surface of a first substrate in which a portion of the cavity is exposed; forming electrodes for a sensor element that is movable within the cavity on the first substrate; forming a stopper portion on a second substrate that is bonded to the first substrate so as to cover the cavity and restricting the movement of the electrodes toward the second substrate; forming a first metal layer on the first substrate that forms a sealed portion to be bonded to the second substrate; forming a second metal layer on the second substrate that forms a sealing portion to be bonded to the sealed portion; forming a polycrystalline layer on the stopper portion and forming a polycrystalline layer between the second substrate and the second metal layer; and bonding the sealing portion to the sealed portion to bond the second substrate to the first substrate.

[0014] According to this disclosure, electrodes are movably formed on a first substrate, a stopper portion is formed on a second substrate bonded to the first substrate, and a polycrystalline layer is formed on the stopper portion. This increases the surface roughness compared to the case where no polycrystalline layer is formed on the stopper portion, thereby reducing the contact area when the electrodes contact the stopper portion and suppressing the electrodes from sticking to the stopper portion. Even when it is not possible to use a non-adhesive fluororesin coating or the like on the stopper portion, adhesion between the electrodes and the stopper portion can be suppressed.

[0015] A first metal layer is formed on the first substrate to form the portion to be sealed, a second metal layer is formed on the second substrate to form the sealing portion to be joined to the portion to be sealed, and a polycrystalline layer is formed between the second substrate and the second metal layer. As a result, when the first metal layer and the second metal layer are joined by metal, the surface roughness can be increased to improve adhesion and improve the bonding strength between the first substrate and the second substrate compared to when no polycrystalline layer is formed between the second substrate and the second metal layer.

[0016] Therefore, in a MEMS sensor in which a second substrate is bonded to a first substrate having electrodes, and a stopper portion is provided on the second substrate to restrict the movement of the electrodes, it is possible to suppress the electrodes from sticking to the stopper portion and to improve the bonding strength between the first substrate and the second substrate. [Brief explanation of the drawing]

[0017] [Figure 1] Figure 1 is a plan view of a MEMS sensor according to the first embodiment of this disclosure. [Figure 2] Figure 2 is a plan view of the first substrate assembly. [Figure 3] Figure 3 is an enlarged view of the main parts of the first substrate assembly shown in Figure 2. [Figure 4] Figure 4 is a cross-sectional view of the MEMS sensor along the line IV-IV in Figure 3. [Figure 5] Figure 5 is a cross-sectional view of the MEMS sensor along the VV line in Figure 1. [Figure 6]Figure 6 is a diagram showing the first substrate assembly and the second substrate assembly before bonding. [Figure 7] Figure 7 is a diagram illustrating the method for manufacturing the first substrate assembly. [Figure 8] Figure 8 is a diagram illustrating the method for manufacturing the first substrate assembly. [Figure 9] Figure 9 is a diagram illustrating the method for manufacturing the first substrate assembly. [Figure 10] Figure 10 is a diagram illustrating the method for manufacturing the second substrate assembly. [Figure 11] Figure 11 is a diagram showing the MEMS sensor according to the second embodiment of the present disclosure. [Figure 12] Figure 12 is a cross-sectional view of a conventional MEMS sensor. DETAILED DESCRIPTION OF EMBODIMENTS

[0018] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[0019] Figure 1 is a plan view of the MEMS sensor according to the first embodiment of the present disclosure. As shown in Figure 1, the MEMS sensor 1 according to the first embodiment of the present disclosure is a capacitive acceleration sensor having a capacitive acceleration sensor element as the sensor element 2. The MEMS sensor 1 includes a first substrate assembly 11 having a first substrate 10 as a device-side substrate including the sensor element 2, and a second substrate assembly 21 having a second substrate 20 as a lid-side substrate bonded to the first substrate 10. The MEMS sensor 1 is manufactured by processing the first substrate 10 and the second substrate 20 using semiconductor micromachining technology.

[0020] In the following description, a predetermined direction along the surfaces of the first substrate 10 and the second substrate 20 is defined as the X direction, a direction orthogonal to the X direction is defined as the Y direction, and the thickness direction of the first substrate 10 and the second substrate 20 orthogonal to the X direction and the Y direction is defined as the Z direction. Figure 1 shows the MEMS sensor 1 in which the second substrate 20 is bonded to the upper side of the first substrate 10 in the Z direction. In Figure 1, the wiring formed on the first substrate 10 is omitted from illustration.

[0021] Sensor element 2 is a sensor element that detects acceleration acting in the X direction. The sensor element is not limited to this, and may also be a sensor element that detects acceleration acting in the Y direction, or a sensor element that detects acceleration acting in the Z direction.

[0022] The sensor element 2 is covered and sealed by the second substrate 20, which is bonded to the first substrate 10. The first substrate 10 has multiple pad portions 3, specifically five, spaced apart from each other in the X direction. The pad portions 3 are connected to external electronic components, etc. The pad portions 3 are configured to input electrical signals to the sensor element 2 or to output electrical signals from the sensor element 2.

[0023] Figure 2 is a plan view of the first substrate assembly. Figure 3 is an enlarged view of the main part of the first substrate assembly shown in Figure 2, showing an enlarged view of part A1 in Figure 2. Figure 4 is a cross-sectional view of the MEMS sensor along the line IV-IV in Figure 3. Figure 5 is a cross-sectional view of the MEMS sensor along the line VV in Figure 1.

[0024] As shown in Figures 4 and 5, the first substrate assembly 11 comprises a first substrate 10 having a first main surface 10a which is the front surface and a second main surface 10b which is the back surface opposite to the first main surface 10a. In plan view, the first substrate 10 is formed in a rectangular shape with two sides extending in the X direction and two sides extending in the Y direction. As the first substrate 10, a conductive single-crystal silicon substrate having a resistivity of, for example, 1 Ω·m to 5 Ω·m, which has been doped with impurities to impart conductivity, is used. The first main surface 10a of the first substrate 10 is formed with a surface roughness Sa (arithmetic mean roughness) of 1 nm or less.

[0025] As shown in Figure 2, the first substrate 10 has a cavity 12 on its central side that corresponds to the sensor element 2 and is partially exposed on the first main surface 10a. As shown in Figure 5, the cavity 12 is formed as a recess in the thickness direction of the first substrate 10 from the first main surface 10a and has a bottom wall portion 12a and a side wall portion 12b that extends from the bottom wall portion 12a in the thickness direction of the first substrate 10.

[0026] As shown in Figures 3 and 4, the first substrate 10 has a beam portion 14 that forms the electrodes 13 of the sensor element 2, and a support portion 15 that supports the beam portion 14. The beam portion 14 is placed inside the cavity 12 of the first substrate 10 and is supported by the support portion 15 in a floating state within the cavity 12. The beam portion 14 is formed from a part of the first substrate 10. As shown in Figure 2, the support portion 15 is formed in an annular shape that is approximately rectangular in plan view, surrounding the sensor element 2. The inner circumferential surface of the support portion 15 constitutes the side wall portion 12b of the cavity 12.

[0027] The electrode 13 formed by the beam portion 14 is movably positioned within the cavity 12 while being supported by the support portion 15. The electrode 13 comprises a fixed electrode 30 and a movable electrode 40 that is movable relative to the fixed electrode 30 in the X direction. The fixed electrode 30 and the movable electrode 40 are formed with the same thickness in the thickness direction of the first substrate 10. As shown in Figure 3, the beam portion 14 comprises a support beam portion 14a connected to the support portion 15, a beam portion 14b for the fixed electrode, and a beam portion 14c for the movable electrode.

[0028] The fixed electrode beam section 14b and the movable electrode beam section 14c are each connected to the support beam section 14a via a separation section 16. The separation section 16 electrically separates the fixed electrode beam section 14b and the movable electrode beam section 14c from the support beam section 14a and mechanically connects them. The separation section 16 has silicon oxide and is formed of silicon oxide, which is an insulating film.

[0029] As shown in Figures 2 and 3, the fixed electrode 30 has a connecting portion 31 connected to the support beam portion 14a via a separating portion 16, a base portion 32 connected to the connecting portion 31, and a plurality of electrode portions 33 connected to the base portion 32 and formed in a comb-like shape so as to extend in the Y direction. The connecting portion 31 is provided in a grid pattern in plan view, and the base portion 32 is provided in a ladder-like shape in plan view. The plurality of electrode portions 33 extend linearly from the base portion 32 in the Y direction and are arranged in a comb-like shape at equal intervals in the X direction.

[0030] The movable electrode 40 has a connecting portion 41 connected to the support beam portion 14a via a separating portion 16, a spring portion 44 connected to the connecting portion 41 and extending in the Y direction, a base portion 42 connected to the connecting portion 41 via the spring portion 44, and a plurality of electrode portions 43 connected to the base portion 42 and formed in a comb-like shape so as to extend in the Y direction.

[0031] The connection portion 41 includes a first connection portion 45 located on one side in the X direction and a second connection portion 46 located on the other side in the X direction. The first connection portion 45 and the second connection portion 46 each have a first transverse linear portion 41a (see Figure 3) extending linearly in the X direction to the inside of the sensor element 2 in the X direction, a second transverse linear portion 41b (see Figure 2) extending linearly in the X direction to the outside of the sensor element 2 in the X direction, and a plurality of vertical linear portions 41c (see Figure 2) extending linearly in the Y direction to one side in the Y direction of the sensor element 2.

[0032] The first connection section 45 and the second connection section 46 each have a first transverse straight section 41a connected to the support beam section 14a via a separation section 16. The first connection section 45 and the second connection section 46 each have multiple vertical straight sections 41c connected to the base section 32 of the fixed electrode 30 via a separation section 16, and the second transverse straight section 41b connected to the spring section 44. The separation section 16 electrically separates and mechanically connects two adjacent regions. The separation section 16 has silicon oxide and is formed of silicon oxide, which is an insulating film.

[0033] As shown in Figure 2, the spring portion 44 includes a first spring portion 47 connected to the first connecting portion 45 and a second spring portion 48 connected to the second connecting portion 46. The first spring portion 47 and the second spring portion 48 are arranged on both sides of the sensor element 2 in the X direction and extend in the Y direction, and are configured to be movable in the X direction in response to acceleration acting in the X direction.

[0034] The base portion 42 has a plurality of first vertical linear portions 42a and second vertical linear portions 42b that extend linearly in the Y direction in a plan view, and a plurality of horizontal linear portions 42c that extend linearly in the X direction in a plan view, and is arranged in a grid pattern. The first vertical linear portions 42a and the second vertical linear portions 42b are arranged alternately in the X direction, a first spring portion 47 is connected to one side in the Y direction of the first vertical linear portion 42a on one side in the X direction, and a second spring portion 48 is connected to one side in the Y direction of the second vertical linear portion 42b on the other side in the X direction.

[0035] The first vertical straight section 42a and the second vertical straight section 42b are electrically separated by a separation section 16 provided on the horizontal straight section 42c. The multiple first vertical straight sections 42a are electrically connected via multiple contacts and wiring provided on the horizontal straight section 42c. The multiple second vertical straight sections 42b are electrically connected via multiple contacts and wiring provided on the horizontal straight section 42c.

[0036] The multiple electrode portions 43 extend linearly from the base portion 42 to the other side in the Y direction and are arranged in a comb-like manner at equal intervals in the X direction. The multiple electrode portions 43 include a plurality of first electrode portions 43a extending linearly in the Y direction from a first longitudinal linear portion 42a, and a plurality of second electrode portions 43b extending linearly in the Y direction from a second longitudinal linear portion 42b.

[0037] The first electrode portion 43a and the second electrode portion 43b are arranged as a pair between the electrode portions 33 of the fixed electrode 30, and the first electrode portion 43a and the second electrode portion 43b are positioned so as not to come into contact with the opposing electrode portion 33 of the fixed electrode 30. The pair of first electrode portions 43a and second electrode portions 43b are connected by a plurality of transverse linear portions 43c that extend linearly in the X direction and are electrically separated by a separation portion 16.

[0038] The movable electrode 40 has a first movable electrode 40a having a first electrode portion 43a and a second movable electrode 40b having a second electrode portion 43b. The first movable electrode 40a includes a first electrode portion 43a, a first vertical straight portion 42a of the base portion 42, a first spring portion 47 and a first connecting portion 45, and the second movable electrode 40b includes a second electrode portion 43b, a second vertical straight portion 42b of the base portion 42, a second spring portion 48 and a second connecting portion 46.

[0039] When acceleration in the X direction acts on the sensor element 2, the electrode portion 43 of the movable electrode 40 moves relative to the electrode portion 33 of the fixed electrode 30 in accordance with the acceleration, changing the distance between the electrode portions 33 and 43, and thus changing the capacitance between the fixed electrode 30 and the movable electrode 40, specifically the capacitance between the fixed electrode 30 and the first movable electrode 40a and the capacitance between the fixed electrode 30 and the second movable electrode 40b. The MEMS sensor 1 is capable of detecting acceleration by extracting the change in capacitance between the fixed electrode 30 and the movable electrode 40 as an electrical signal.

[0040] In the MEMS sensor 1, as shown in Figure 3, the fixed electrode 30 is connected to the fixed electrode via a contact 5 for the fixed electrode, the first movable electrode 40a is connected to the first movable electrode via a contact 6 for the first movable electrode, and the second movable electrode 40b is connected to the first movable electrode via a contact 7 for the second movable electrode. The first substrate 10 is connected to the first substrate via a contact 7 for the substrate, which connects to the pad portion 3.

[0041] As shown in Figures 4 and 5, the second substrate assembly 21 comprises a second substrate 20 having a first main surface 20a which is the front surface and a second main surface 20b which is the back surface opposite to the first main surface 20a. In plan view, the second substrate 20 is formed in a rectangular shape with two sides extending in the X direction and two sides extending in the Y direction. As the second substrate 20, a conductive single-crystal silicon substrate having a resistivity of, for example, 1 Ω·m to 5 Ω·m, which has been doped with impurities to impart conductivity, is used. The first main surface 20a of the second substrate 20 is formed to have a surface roughness Sa (arithmetic mean roughness) of 1 nm or less, similar to the first main surface 10a of the first substrate 10.

[0042] The second substrate 20 is bonded to the first substrate 10 so as to cover the cavity 12. A sealed portion 17 is formed on the first substrate 10 to be bonded to the second substrate 20, and a sealing portion 27 is formed on the second substrate 20 to be bonded to the sealed portion 17.

[0043] As shown in Figure 2, the sealed portion 17 is arranged around the cavity 12 and is formed in an annular shape in a roughly rectangular frame when viewed from above. As shown in Figure 5, the sealed portion 17 is formed by an Al layer 19 as a first metal layer formed by sputtering on the first main surface 10a of the first substrate 10.

[0044] As shown in Figure 1, the sealing portion 27 is formed in an annular shape in a roughly rectangular frame in a plan view, corresponding to the portion to be sealed 17, and as shown in Figure 5, it is formed by a Ge layer 29 as a second metal layer formed by vapor deposition on the first main surface 20a of the second substrate 20.

[0045] The Ge layer 29 is formed on a polycrystalline silicon layer 25, which is a polycrystalline layer formed on the second substrate 20 by the CVD method. The Al layer 19 is formed on the first substrate 10 without providing a polycrystalline silicon layer. The Ge layer 29 is formed to be thinner than the Al layer 19. For example, the Al layer 19 is formed to a thickness of 1000 nm, and the Ge layer 29 is formed to a thickness of 400 nm. For example, the polycrystalline silicon layer 25 is formed to a thickness of 100 nm. The polycrystalline silicon layer 25 is formed to have a surface roughness greater than the first main surface 10a of the first substrate 10 and the first main surface 20a of the second substrate 20. The polycrystalline silicon layer 25 has a surface roughness Sa (arithmetic mean roughness) of 10 nm to 20 nm.

[0046] The sealing portion 27 formed on the second substrate 20 is joined to the sealed portion 17 formed on the first substrate 10. As a result, the cavity 12 provided in the first substrate 10 is covered and sealed by the second substrate 20. The sealing portion 27 of the second substrate 20 and the sealed portion 17 of the first substrate 10 are joined by metal bonding. When the first substrate 10 and the second substrate 20 are superimposed and a predetermined pressure is applied, and then heated to a predetermined temperature such as 430 degrees, the Al layer 19 and the Ge layer 29 are joined by metal bonding, specifically eutectic bonding.

[0047] As shown in Figure 5, the second substrate 20 has a cavity 22 that is recessed in a substantially rectangular shape in the thickness direction of the second substrate 20 from the first main surface 20a. The cavity 22 has a bottom wall portion 22a and a side wall portion 22b that extends from the bottom wall portion 22a in the thickness direction of the second substrate 20.

[0048] The second substrate 20 is provided with a stopper portion 23 that restricts the movement of the electrode 13 of the sensor element 2 toward the second substrate. The stopper portion 23 is formed to extend from the bottom wall portion 22a of the cavity 22 to the first main surface 20a of the second substrate 20 in the thickness direction of the second substrate 20. The stopper portion 23 may also be provided on the side of the bottom wall portion 22a from the first main surface 20a of the second substrate 20.

[0049] As shown in Figure 1, the stopper portion 23 comprises two linear portions 24 that are spaced apart in the Y direction and extend linearly and parallel to each other in the X direction. The stopper portion 23 is formed to face the electrode 13, and the two linear portions 24 are spaced apart above the spring portion 44 extending in the Y direction, the multiple electrode portions 33 of the fixed electrode 30, and the multiple electrode portions 43 of the movable electrode 40.

[0050] A polycrystalline silicon layer 25, which is a polycrystalline layer, is formed on the stopper portion 23. In the MEMS sensor 1, the opposing surface of the stopper portion 23 that faces the electrode 13 is the opposing surface 25a of the polycrystalline silicon layer 25 that faces the electrode 13. When the electrode 13 provided on the first substrate 10 bends excessively toward the second substrate and contacts the stopper portion 23 of the second substrate 20, the electrode 13 contacts the polycrystalline silicon layer 25 formed on the stopper portion 23.

[0051] In this way, by positioning the stopper portion 23 that restricts the movement of the electrode 13 above the electrode 13 on the second substrate 20, it is possible to suppress the electrode 13 from bending excessively towards the second substrate, and thus prevent the electrode 13 from breaking.

[0052] In the MEMS sensor 1, a second substrate 20 is bonded to a first substrate 10 having electrodes 13, and a stopper portion 23 is provided on the second substrate 20 to restrict the movement of the electrodes 13. The sealed portion 17 of the first substrate 10 is formed by an Al layer 19, the sealed portion 27 of the second substrate 20 is formed by a Ge layer 29, a polycrystalline silicon layer 25 is formed on the stopper portion 23 of the second substrate 20, and a polycrystalline silicon layer 25 is formed between the second substrate 20 and the Ge layer 29.

[0053] Figure 6 shows the first and second substrate assemblies before bonding. As shown in Figure 6, the Ge layer 29 that forms the seal portion 27 of the second substrate 20 is formed on a polycrystalline silicon layer 25 formed on the second substrate 20. Compared to the case where no polycrystalline silicon layer is formed on the second substrate 20, the polycrystalline silicon layer 25 creates a larger surface roughness Sa on the facing surface of the first substrate 10 that faces the sealed portion 17.

[0054] Figure 6 shows the Al oxide film 8 formed on the Al layer 19 that forms the sealed portion 17 of the first substrate 10. As shown in Figure 6, the Al oxide film 8, which is a native oxide film, is formed on the Al layer 19, and the Al oxide film 8 is formed to a thickness of, for example, about 5 nm. The surface roughness Sa of the Ge layer 29 is formed to 10 nm to 20 nm by the polycrystalline silicon layer 25 so that Ge can pass through the Al oxide film 8. As a result, even when the Al oxide film 8 is formed on the sealed portion 17, metal bonding can be achieved by penetrating the Al oxide film 8 and bringing Al and Ge into contact.

[0055] When the Al layer 19 and the Ge layer 29 are metallically bonded, specifically eutectic bonded, the adhesion between the polycrystalline silicon layer 25 between the second substrate 20 and the Ge layer 29 and the eutectic particles generated by the eutectic reaction can be improved compared to the case where the polycrystalline silicon layer 25 is not formed between the second substrate 20 and the Ge layer 29, thereby improving the bonding strength between the first substrate 10 and the second substrate 20.

[0056] As mentioned above, the Ge layer 29 is formed with a thinner thickness than the Al layer 19. As a result, when the Al layer 19 and the Ge layer 29 are eutectic bonded, the Al layer 19 can undergo a eutectic reaction only on the Ge layer side, without the anti-Ge layer side undergoing a eutectic reaction. Therefore, the bonding strength between the first substrate 10 and the second substrate 20 can be improved without forming a polycrystalline silicon layer 25 between the first substrate 10 and the Al layer 19.

[0057] The polycrystalline silicon layer 25 is also formed on the stopper portion 23. The polycrystalline silicon layer 25 on the stopper portion 23 results in a larger surface roughness Sa on the opposing surface 25a facing the electrode 13 compared to the case where the polycrystalline silicon layer 25 is not formed. This increases the surface roughness Sa on the stopper portion 23 compared to the case where the polycrystalline silicon layer is not formed on the stopper portion 23, reducing the contact area when the electrode 13 contacts the stopper portion 23 and preventing the electrode 13 from sticking to the stopper portion 23.

[0058] Figure 12 is a cross-sectional view of a conventional MEMS sensor. In Figure 12, the same cross-section as the MEMS sensor 1 shown in Figure 5 is shown. In the MEMS sensor 101 shown in Figure 12, the sealing portion 127 of the second substrate 20 is formed by an Al layer 129 formed on the second substrate 20, the sealed portion 117 of the first substrate 10 is formed by an Al layer 119 formed on the first substrate 10, and the first substrate 10 and the second substrate 20 are joined and sealed by a glass frit 102 placed between the sealing portion 127 and the sealed portion 117.

[0059] In the MEMS sensor 101 shown in Figure 12, a water-repellent coating layer 103, such as a non-adhesive fluororesin coating, is formed on the first substrate 10 and the second substrate 20, respectively, before bonding the first substrate 10 and the second substrate 20 with glass frit 102. The water-repellent coating layer 103 is also formed on the electrode 13 and the stopper portion 23. In the MEMS sensor 101, the water-repellent coating layer 103 suppresses the adhesion of the electrode 13 to the stopper portion 23, and the first substrate 10 and the second substrate 20 are bonded together by glass frit 102.

[0060] In the MEMS sensor 1, the first substrate 10 and the second substrate 20 are joined by metal bonding, which allows for a more compact design compared to bonding with glass frit. Furthermore, the formation of a polycrystalline silicon layer 25 on the stopper portion 23 of the second substrate 20 prevents the electrode 13 from sticking to the stopper portion 23. Even when it is not possible to use a non-adhesive fluororesin coating on the stopper portion 23, such as when the first substrate 10 and the second substrate 20 are joined by metal bonding, adhesion between the electrode 13 and the stopper portion 23 can be suppressed.

[0061] Next, we will describe the manufacturing method of the MEMS sensor 1. Figures 7 to 9 illustrate the manufacturing method of the first substrate assembly. Figures 7 and 8 show a cross-section of the first substrate assembly along the line IV-IV in Figure 3, and Figure 9 shows a cross-section of the first substrate assembly along the line VV in Figure 2. In the manufacturing of the MEMS sensor 1, a first substrate 10 and a second substrate 20, which are single-crystal silicon substrates, are prepared.

[0062] As shown in Figure 7, a trench 18 is formed in the first substrate 10 by removing the portion corresponding to the separation portion 16. After the trench is formed, the trench 18 and the entire first main surface 10a of the first substrate 10 are thermally oxidized, forming the separation portion 16 with a silicon oxide film, and a silicon oxide film is also formed on the first main surface 10a of the first substrate 10. Once the separation portion 16 is formed, the silicon oxide film on the first main surface 10a of the first substrate 10 is removed.

[0063] Next, an Al layer 19 is formed on the portion of the first substrate 10 corresponding to the sealed portion 17 by sputtering. Pad portions 3, contacts, and wiring are also formed on the first substrate 10. Subsequently, the first substrate 10 is patterned by photolithography and anisotropic etching to form trenches that leave electrodes 13. Then, the trenches are deepened by isotropic etching and etched in a direction parallel to the first main surface 10a of the first substrate 10, forming cavities 12 that are partially exposed on the first main surface 10a, as shown in Figures 8 and 9, and beam portions 14 that form electrodes 13 are placed in a floating state within the cavities 12, thereby manufacturing the first substrate assembly 11.

[0064] Figure 10 illustrates a method for manufacturing the second substrate assembly. As shown in Figure 10, a polycrystalline silicon layer 25 is formed on the second substrate 20 by CVD in the portions corresponding to the seal portion 27 and the stopper portion 23 of the second substrate 20. It is preferable that the polycrystalline silicon layer 25 formed on the portion corresponding to the seal portion 27 of the second substrate 20 and the polycrystalline silicon layer 25 formed on the portion corresponding to the stopper portion 23 of the second substrate 20 be formed at the same time, but they do not have to be formed at the same time.

[0065] Next, a Ge layer 29 is formed on the portion of the second substrate 20 corresponding to the seal portion 27 by a vapor deposition method. The Ge layer 29 is formed on a polycrystalline silicon layer 25 formed on the second substrate 20.

[0066] Then, the seal portion 27 and the stopper portion 23 are patterned by photolithography and etching, forming a cavity 22 in the second substrate 20, along with the seal portion 27 and the stopper portion 23, and the second substrate assembly 21 is manufactured.

[0067] In this way, a first substrate assembly 11 is manufactured in which an electrode 13 is formed on the first substrate 10 so as to be movable within the cavity 12 and a sealed portion 17 is formed thereon, and a second substrate assembly 21 is manufactured in which a stopper portion 23 is formed on the second substrate 20 so as to face the electrode 13 and a sealed portion 27 is formed thereon.

[0068] After the manufacturing of the first substrate assembly 11 and the second substrate assembly 21, the sealing portion 27 of the second substrate 20 is superimposed on the sealing portion 17 of the first substrate 10 and bonded, and the second substrate 20 is bonded to the first substrate 10 so as to cover the cavity 12. The bonding of the first substrate assembly 11 and the second substrate assembly 21 is performed by eutectic bonding, for example, by heating to a predetermined temperature such as 430 degrees.

[0069] As described above, in the manufacturing method of the MEMS sensor 1 according to this embodiment, a cavity 12 is formed in the first substrate 10 and an electrode 13 is formed to be movable within the cavity 12, a stopper portion 23 is formed on the second substrate 20 to restrict the movement of the electrode 13 toward the second substrate side, a first metal layer 19 is formed on the first substrate 10 to form a sealed portion 17, a second metal layer 29 is formed on the second substrate 20 to form a seal portion 27, a polycrystalline silicon layer 25 is formed on the stopper portion 23 and a polycrystalline silicon layer 25 is formed between the second substrate 20 and the second metal layer 29, and the seal portion 27 is joined to the sealed portion 17 so that the second substrate 20 is joined to the first substrate 10.

[0070] As a result, an electrode 13 is formed on the first substrate 10 so as to be movable within the cavity 12, a stopper portion 23 is formed on the second substrate 20 which is bonded to the first substrate 10, and a polycrystalline silicon layer 25 is formed on the stopper portion 23. Compared to the case where a polycrystalline silicon layer is not formed on the stopper portion 23, the surface roughness is increased, reducing the contact area when the electrode 13 contacts the stopper portion 23, and preventing the electrode 13 from sticking to the stopper portion 23.

[0071] Furthermore, when the first metal layer 19 that forms the sealed portion 17 is formed on the first substrate 10, and the second metal layer 29 that forms the sealing portion 27 that is joined to the sealed portion 17 is formed on the second substrate 20, and a polycrystalline silicon layer 25 is formed between the second substrate 20 and the second metal layer 29, when the first metal layer 19 and the second metal layer 29 are metal-bonded, the surface roughness can be increased to improve adhesion and improve the bonding strength between the first substrate 10 and the second substrate 20 compared to when a polycrystalline silicon layer is not formed between the second substrate 20 and the second metal layer 29. When the first metal layer 19 and the second metal layer 29 are eutectic-bonded, the adhesion between the polycrystalline silicon layer 25 formed between the second substrate 20 and the second metal layer 29 and the eutectic particles generated by the eutectic reaction can be improved, and the bonding strength between the first substrate 10 and the second substrate 20 can be improved.

[0072] In the MEMS sensor 1, the beam portion 14 is equipped with a support beam portion 14a, and the fixed electrode beam portion 14b and the movable electrode beam portion 14c are connected to the support beam portion 14a via separation portions 16. However, the support beam portion 14a may be omitted, and the separation portion 16 may be provided on the support portion 15.

[0073] Figure 11 shows a MEMS sensor according to a second embodiment of the present disclosure, and Figure 11 shows the first substrate assembly 11 and the second substrate assembly 21 before bonding. The MEMS sensor 61 according to the second embodiment is formed by creating a first metal layer 19 with the same thickness as the second metal layer 29 in addition to the MEMS sensor 1 according to the first embodiment, and forming a polycrystalline layer between the first substrate 10 and the first metal layer 19. A description of similar configurations will be omitted.

[0074] In the MEMS sensor 61 according to the second embodiment, similar to the MEMS sensor 1 according to the first embodiment, a second substrate 20 is bonded to a first substrate 10 having electrodes 13, and a stopper portion 23 that restricts the movement of electrodes 13 is provided on the second substrate 20. The sealed portion 17 of the first substrate 10 is formed by an Al layer 19, the sealed portion 27 of the second substrate 20 is formed by a Ge layer 29, a polycrystalline silicon layer 25 is formed on the stopper portion 23 of the second substrate 20, and a polycrystalline silicon layer 25 is formed between the second substrate 20 and the Ge layer 29.

[0075] In the MEMS sensor 61, the Al layer 19 forming the sealed portion 17 and the Ge layer 29 forming the sealing portion 27 are formed to the same thickness, and a polycrystalline silicon layer 35 is formed between the first substrate 10 and the Al layer 19. The Al layer 19 is formed on the polycrystalline silicon layer 35 formed on the first substrate 10 by the CVD method. The Al layer 19 and the Ge layer 29 are each formed to a thickness of, for example, 500 nm. The polycrystalline silicon layers 25 and 35 are formed to a thickness of, for example, 100 nm.

[0076] In the MEMS sensor 61, the Al layer 19 forming the sealed portion 17 and the Ge layer 29 forming the sealing portion 27 are formed to the same thickness, a polycrystalline silicon layer 25 is formed between the second substrate 20 and the Ge layer 29, and a polycrystalline silicon layer 35 is formed between the first substrate 10 and the Al layer 19.

[0077] When the Al layer 19 forming the sealed portion 17 and the Ge layer 29 forming the sealed portion 27 are formed to the same thickness, and the Al layer 19 and the Ge layer 29 are eutectic bonded, the adhesion between the polycrystalline silicon layer 25 and the eutectic particles generated from the liquid phase by the eutectic reaction is improved, as is the adhesion between the polycrystalline silicon layer 35 and the eutectic particles generated from the liquid phase by the eutectic reaction, thereby improving the bonding strength between the first substrate 10 and the second substrate 20.

[0078] In the MEMS sensor 1,61, an Al layer 19 is used as the first metal layer forming the sealed portion 17, and a Ge layer 29 is used as the second metal layer forming the sealed portion 27. However, the first and second metal layers may be made of a different metal that undergoes a eutectic reaction than Al and Ge.

[0079] In the MEMS sensors 1 and 61, the first metal layer 19, the second metal layer 29, and the polycrystalline silicon layers 25 and 35 are formed by sputtering, vapor deposition, and CVD, respectively, but they may be formed by other methods. The MEMS sensor 1 and 61 is a capacitive acceleration sensor, but it can also be applied to other sensors in which electrodes are movably arranged.

[0080] As described above, in the MEMS sensor 1,61 according to this embodiment, an electrode 13 is movably provided on a first substrate 10, a stopper portion 23 is provided on a second substrate 20 bonded to the first substrate 10, and a polycrystalline layer 25 is formed on the stopper portion 23. This increases the surface roughness compared to the case where a polycrystalline layer is not formed on the stopper portion 23, thereby reducing the contact area when the electrode 13 contacts the stopper portion 23 and suppressing the electrode 13 from sticking to the stopper portion 23. Even when it is not possible to use a non-adhesive fluororesin coating or the like on the stopper portion 23, the sticking between the electrode 13 and the stopper portion 23 can be suppressed.

[0081] Furthermore, the sealed portion 17 is formed by the first metal layer 19 on the first substrate 10, the sealing portion 27 that is joined to the sealed portion 17 is formed by the second metal layer 29 on the second substrate 20, and a polycrystalline layer 25 is formed between the second substrate 20 and the second metal layer 29. As a result, when the first metal layer 19 and the second metal layer 29 are joined by metal, the surface roughness can be increased to improve adhesion and improve the bonding strength between the first substrate 10 and the second substrate 20, compared to the case where a polycrystalline layer is not formed between the second substrate 20 and the second metal layer 29.

[0082] Therefore, in a MEMS sensor 1,61 in which a second substrate 20 is bonded to a first substrate 10 having an electrode 13, and a stopper portion 23 that restricts the movement of the electrode 13 is provided on the second substrate 20, it is possible to suppress the electrode 13 from sticking to the stopper portion 23 and to improve the bonding strength between the first substrate 10 and the second substrate 20.

[0083] Furthermore, the second substrate 20 is a single-crystal silicon substrate, and the polycrystalline layer 25 is a polycrystalline silicon layer. As a result, in the MEMS sensor 1,61 in which the polycrystalline silicon layer 25 is formed on the stopper portion 23 of the second substrate 20 which is a single-crystal silicon substrate, and the polycrystalline silicon layer 25 is formed between the second substrate 20 which is a single-crystal silicon substrate and the second metal layer 29 which forms the seal portion 27, it is possible to suppress the electrode 13 from sticking to the stopper portion 23 and to improve the bonding strength between the first substrate 10 and the second substrate 20.

[0084] Furthermore, the sealed portion 17 and the sealed portion 27 are joined by eutectic bonding between the first metal layer 19 and the second metal layer 29. As a result, when the first metal layer 19 and the second metal layer 29 are eutectic bonded, the adhesion between the polycrystalline layer 25 formed between the second substrate 20 and the second metal layer 29 and the eutectic particles generated by the eutectic reaction can be improved compared to the case where no polycrystalline layer is formed between the second substrate 20 and the second metal layer 29, thereby improving the bonding strength between the first substrate 10 and the second substrate 20.

[0085] Furthermore, the second metal layer 29 is formed with a thinner thickness than the first metal layer 19. As a result, when the first metal layer 19 and the second metal layer 29 are eutectic bonded, the first metal layer 19 undergoes a eutectic reaction only on the side facing the second metal layer, without the side facing the second metal layer undergoing a eutectic reaction. This prevents the formation of a polycrystalline layer between the first substrate 10 and the first metal layer 19, thereby improving the bonding strength between the first substrate 10 and the second substrate 20.

[0086] Furthermore, the first metal layer 19 is an Al layer 19, and the second metal layer 29 is a Ge layer 29. This makes it possible to improve the bonding strength between the first substrate 10 and the second substrate 20 in the MEMS sensor 1,61, in which the Al layer 19 and the Ge layer 29 are eutectic bonded together to bond the first substrate 10 and the second substrate 20.

[0087] Furthermore, the sensor element 2 is a capacitive acceleration sensor element 2. This makes it possible to suppress the electrode 13 from sticking to the stopper portion 23 in the MEMS sensor 1,61 having the capacitive acceleration sensor element 2, and to improve the bonding strength between the first substrate 10 and the second substrate 20.

[0088] Furthermore, in the manufacturing method of the MEMS sensor 1,61 according to this embodiment, an electrode 13 is formed on the first substrate 10 so as to be movable within a cavity 12, a stopper portion 23 is formed on the second substrate 20 which is bonded to the first substrate 10 so as to cover the cavity 12, and a polycrystalline layer 25 is formed on the stopper portion 23. As a result, compared to the case in which the polycrystalline layer 25 is not formed on the stopper portion 23, the surface roughness is increased, the contact area when the electrode 13 contacts the stopper portion 23 is reduced, and the electrode 13 can be prevented from sticking to the stopper portion 23. Even when it is not possible to use a non-adhesive fluororesin coating or the like on the stopper portion 23, the sticking between the electrode 13 and the stopper portion 23 can be prevented.

[0089] Furthermore, a first metal layer 19 is formed on the first substrate 10 to form the sealed portion 17, a second metal layer 29 is formed on the second substrate 20 to form a sealing portion 27 that is joined to the sealed portion 17, and a polycrystalline layer 25 is formed between the second substrate 20 and the second metal layer 29. As a result, when the first metal layer 19 and the second metal layer 29 are joined by metal, the surface roughness can be increased to improve adhesion and improve the bonding strength between the first substrate 10 and the second substrate 20 compared to when a polycrystalline layer is not formed between the second substrate 20 and the second metal layer 29.

[0090] Therefore, in a MEMS sensor 1,61 in which a second substrate 20 is bonded to a first substrate 10 having an electrode 13, and a stopper portion 23 that restricts the movement of the electrode 13 is provided on the second substrate 20, it is possible to suppress the electrode 13 from sticking to the stopper portion 23 and to improve the bonding strength between the first substrate 10 and the second substrate 20.

[0091] The present invention is not limited to the embodiments described herein, and various improvements and design modifications are possible without departing from the spirit of the invention.

[0092] [Note 1] A first substrate having a cavity in which part of the cavity is exposed on the surface, A second substrate is bonded to the first substrate so as to cover the cavity, Equipped with, The first substrate is provided with electrodes for a sensor element that is movably arranged within the cavity and a sealed portion that is joined to the second substrate. The second substrate is provided with a stopper portion that restricts the movement of the electrode toward the second substrate and a sealing portion that is joined to the sealed portion. The sealed portion is formed by the first metal layer on the first substrate, The sealing portion is formed by the second metal layer on the second substrate, A polycrystalline layer is formed on the stopper portion, and a polycrystalline layer is formed between the second substrate and the second metal layer. MEMS sensor. [Note 2] The second substrate is a single-crystal silicon substrate, The aforementioned polycrystalline layer is a polycrystalline silicon layer. The MEMS sensor described in Appendix 1. [Note 3] The sealed portion and the sealed portion are joined by a eutectic bonding between the first metal layer and the second metal layer. A MEMS sensor as described in Appendix 1 or Appendix 2. [Note 4] The second metal layer is formed to be thinner than the first metal layer. A MEMS sensor as described in any of the appendices 1 through 3. [Note 5] The first metal layer is an Al layer, and the second metal layer is a Ge layer. A MEMS sensor as described in any of the appendices 1 through 4. [Note 6] The aforementioned sensor element is a capacitive acceleration sensor element. A MEMS sensor as described in any of the appendices 1 through 5. [Note 7] A cavity is formed on the surface of the first substrate in which a portion of the cavity is exposed, and electrodes for a sensor element that is movable within the cavity are formed on the first substrate. A stopper portion is formed on the second substrate, which is bonded to the first substrate so as to cover the cavity, to restrict the movement of the electrode toward the second substrate. A first metal layer is formed on the first substrate to form a sealed portion that will be bonded to the second substrate. A second metal layer is formed on the second substrate to form a sealing portion that is joined to the portion to be sealed. A polycrystalline layer is formed on the stopper portion, and a polycrystalline layer is formed between the second substrate and the second metal layer. The sealing portion is joined to the sealed portion, and the second substrate is joined to the first substrate. Manufacturing method for MEMS sensors. [Note 8] The second substrate is a single-crystal silicon substrate, The aforementioned polycrystalline layer is a polycrystalline silicon layer. A method for manufacturing the MEMS sensor described in Appendix 7. [Note 9] The sealed portion and the sealed portion are joined by a eutectic bonding between the first metal layer and the second metal layer. A method for manufacturing a MEMS sensor as described in Appendix 7 or Appendix 8. [Note 10] The second metal layer is formed to be thinner than the first metal layer. A method for manufacturing a MEMS sensor as described in any one of the items 7 to 9 of the appendix. [Note 11] The first metal layer is an Al layer, and the second metal layer is a Ge layer. A method for manufacturing a MEMS sensor as described in any of the appendices 7 to 10. [Note 12] The aforementioned sensor element is a capacitive acceleration sensor element. A method for manufacturing a MEMS sensor as described in any of the appendices 7 to 11. [Explanation of Symbols]

[0093] 1,61,101 MEMS sensors 2 Sensor elements 10. First board 12 Cavity 13 electrodes 17,117 Sealed portion 19 1st metal layer 20 Second board 23 Stopper section 25,35 polycrystalline layer 27,127 seal section 29 Second metal layer

Claims

1. A first substrate having a cavity in which part of the cavity is exposed on the surface, A second substrate is bonded to the first substrate so as to cover the cavity, Equipped with, The first substrate is provided with an electrode of a sensor element, which is formed by a beam portion supported by a support portion of the first substrate and is placed in the cavity while being supported by the support portion, and a sealed portion that is joined to the second substrate. The second substrate is provided with a stopper portion that restricts the movement of the electrode toward the second substrate and a sealing portion that is joined to the sealed portion. The sealed portion is formed by the first metal layer on the first substrate, The sealing portion is formed by the second metal layer on the second substrate. A polycrystalline layer is formed on the stopper portion, and a polycrystalline layer is formed between the second substrate and the second metal layer. MEMS sensor.

2. The second substrate is a single-crystal silicon substrate, The aforementioned polycrystalline layer is a polycrystalline silicon layer. The MEMS sensor according to claim 1.

3. The sealed portion and the sealed portion are joined by a eutectic bonding between the first metal layer and the second metal layer. The MEMS sensor according to claim 1.

4. The second metal layer is formed to be thinner than the first metal layer. The MEMS sensor according to claim 1.

5. The first metal layer is an Al layer, and the second metal layer is a Ge layer. The MEMS sensor according to claim 1.

6. The aforementioned sensor element is a capacitive acceleration sensor element. The MEMS sensor according to claim 1.

7. A cavity is formed on the surface of the first substrate in which a portion of the cavity is exposed, and electrodes for a sensor element are formed on the first substrate by beam portions supported by a support portion of the first substrate, and are placed in the cavity while being supported by the support portion. A stopper portion is formed on the second substrate, which is bonded to the first substrate so as to cover the cavity, to restrict the movement of the electrode toward the second substrate. A first metal layer is formed on the first substrate to form a sealed portion that will be bonded to the second substrate. A second metal layer is formed on the second substrate to form a sealing portion that is joined to the portion to be sealed. A polycrystalline layer is formed on the stopper portion, and a polycrystalline layer is formed between the second substrate and the second metal layer. The sealing portion is joined to the sealed portion, and the second substrate is joined to the first substrate. A method for manufacturing MEMS sensors.

8. The second substrate is a single-crystal silicon substrate, The aforementioned polycrystalline layer is a polycrystalline silicon layer. A method for manufacturing a MEMS sensor according to claim 7.

9. The sealed portion and the sealed portion are joined by a eutectic bonding between the first metal layer and the second metal layer. A method for manufacturing a MEMS sensor according to claim 7.

10. The second metal layer is formed to be thinner than the first metal layer. A method for manufacturing a MEMS sensor according to claim 7.

11. The first metal layer is an Al layer, and the second metal layer is a Ge layer. A method for manufacturing a MEMS sensor according to claim 7.

12. The aforementioned sensor element is a capacitive acceleration sensor element. A method for manufacturing a MEMS sensor according to claim 7.

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