Mirror device production method and mirror device

Abstract

A mirror device production method according to the present disclosure comprises: a structure formation step for processing a first silicon substrate so as to form, on a first surface side of the first silicon substrate, a structure that includes a mirror part which reflects light and a support part which swingably supports the mirror part; a smoothing step for smoothing a processing surface of the structure; a cap layer formation step for forming a cap layer which covers the structure on the first surface side of the first silicon substrate; and a piezoelectric film formation step for forming a first electrode layer on the cap layer and forming a piezoelectric film on the first electrode layer.

Description

Mirror device manufacturing method and mirror device

[0001] The technology of the present disclosure relates to a method for manufacturing a mirror device and a mirror device.

[0002] Micromirror devices (also known as optical scanners) are known as one type of microelectromechanical systems (MEMS) device fabricated using silicon (Si) microfabrication technology. Because of their small size and low power consumption, micromirror devices are expected to be widely used in laser displays, laser projectors, optical coherence tomography, and other applications.

[0003] These applications require micromirror devices with a large optical scanning angle to obtain a wide projection field or a wide sensing field. To achieve this, it is important to achieve both a large driving force and the ability to withstand stress caused by large displacements. In terms of driving force, piezoelectric driving methods are advantageous because they generate a higher torque than other driving methods. On the other hand, in terms of stress resistance, it is necessary to suppress damage caused by distortion of the silicon structure due to displacement, and to achieve this, it is necessary to suppress defects that occur during the manufacturing process. A micromirror device with a large scanning angle can be obtained by combining the above technologies.

[0004] Micromirror devices can be mass-produced from a single wafer at low cost using deep silicon etching technology. However, the sidewalls of the silicon structure formed by deep etching are roughened to a scalloped shape, which causes stress to concentrate on the scalloped sidewalls when the device is driven. Because it is necessary to prevent damage caused by this stress concentration, micromirror devices have the problem of being unable to achieve a large scan angle due to the deep etching process.

[0005] To address this problem, for example, Japanese Patent Application Laid-Open No. 2013-35081 proposes smoothing the scalloped sidewall surface by performing a hydrogen annealing process or a process of repeatedly forming and removing a thermal oxide film after deep trenching of the silicon substrate. Also, Japanese Patent No. 6899974 proposes forming a protective film on the scalloped sidewall surface, or forming a protective film after smoothing the sidewall surface.

[0006] The manufacturing method described in JP 2013-35081 A relates to an electromagnetically driven micromirror device, and therefore presents several problems when applied to a piezoelectrically driven micromirror device. When manufacturing a piezoelectrically driven micromirror device using the manufacturing method described in JP 2013-35081 A, it is necessary to smooth the sidewall surface of the silicon structure formed by deep trenching and then form the piezoelectric element on the silicon structure. Because the silicon structure on which the piezoelectric film is formed is not flat, lithography cannot be used to form the pattern of the piezoelectric film and metal wiring, and mask evaporation is required. Mask evaporation is a method in which material is evaporated through a patterned mask. However, forming a pattern of the piezoelectric film using mask evaporation can result in poor step coverage and cracks. Furthermore, mask evaporation cannot form piezoelectric elements containing a large number of highly precise wiring, making it difficult to achieve high performance and miniaturization.

[0007] The method of forming a protective film on the sidewall surface described in Japanese Patent No. 6899974 can be applied to the manufacture of piezoelectrically driven micromirror devices, but its purpose is to improve moisture resistance. When manufacturing a piezoelectrically driven micromirror device using the manufacturing method described in Japanese Patent No. 6899974, it is also necessary to form a pattern of the piezoelectric film using a mask vapor deposition method, so there are similar issues as when using the manufacturing method described in Japanese Patent Laid-Open No. 2013-35081.

[0008] The technique of the present disclosure aims to provide a mirror device and a manufacturing method thereof that can obtain a large scan angle and enable miniaturization.

[0009] The manufacturing method of the mirror device of the present disclosure includes a structure forming step of processing a first silicon substrate to form a structure on a first surface side of the first silicon substrate, the structure including a mirror portion that reflects light and a support portion that supports the mirror portion so that it can oscillate; a smoothing step of smoothing the processed surface of the structure; a cap layer forming step of forming a cap layer that covers the structure on the first surface side of the first silicon substrate; and a piezoelectric film forming step of forming a first electrode layer on the cap layer and forming a piezoelectric film on the first electrode layer.

[0010] The smoothing step is preferably a step of smoothing the processed surface by hydrogen annealing.

[0011] The smoothing step is preferably a step of smoothing the processed surface by repeating a thermal oxide film formation process for forming a thermal oxide film on the processed surface and a thermal oxide film removal process for removing the thermal oxide film formed on the processed surface one or more times.

[0012] The cap layer formation step is preferably a step of forming a cap layer by bonding a second silicon substrate to the first surface side of the first silicon substrate and performing a thinning process on the second silicon substrate including grinding and polishing.

[0013] The second silicon substrate is preferably formed by forming a thermal oxide film on the surface of a silicon layer, and the thermal oxide film is bonded to the first surface of the first silicon substrate.

[0014] The cap layer preferably includes a portion of the silicon layer and a thermal oxide film.

[0015] It is preferable to include a piezoelectric element formation step of forming a piezoelectric element that constitutes an actuator that drives the mirror portion by depositing a second electrode layer on the piezoelectric film and processing the first electrode layer, the piezoelectric film, and the second electrode layer.

[0016] It is preferable to include a structure exposing step of exposing the structure by processing the cap layer.

[0017] It is preferable to include an opening forming step of processing the first silicon substrate from a second surface side opposite to the first surface to form an opening that exposes the structure from the second surface side.

[0018] The first silicon substrate is preferably an SOI substrate.

[0019] The mirror device of the present disclosure is a mirror device comprising a structure including a mirror portion that reflects light and a support portion that supports the mirror portion so that it can oscillate, both formed by processing a silicon substrate, and an actuator composed of a portion of a cap layer formed on the silicon substrate and a piezoelectric element formed on the portion of the cap layer, wherein the cap layer includes silicon and a thermal oxide film.

[0020] The silicon contained in the cap layer is preferably single crystal silicon.

[0021] According to the technology of the present disclosure, it is possible to provide a manufacturing method for a mirror device that can obtain a large scan angle and enable miniaturization, and a mirror device.

[0022] 1. A schematic diagram of an optical scanning device. 2. A plan view of a micromirror device as viewed from the light incident side. 3. A perspective view of the appearance of a micromirror device. 4. A view showing a state in which a mirror portion has oscillated around a first axis. 5. A view showing a state in which a mirror portion has oscillated around a second axis. 6. A cross-sectional view taken along line A-A in FIG. 3. 7. A view showing a manufacturing procedure for a micromirror device. 8. A view showing a continuation of the manufacturing procedure shown in FIG. 9. 9. A view showing a continuation of the manufacturing procedure shown in FIG. 10. 11. A view showing a continuation of the manufacturing procedure shown in FIG. 12. 13. A view showing experimental results.

[0023] An example of an embodiment of the technology of the present disclosure will be described with reference to the accompanying drawings.

[0024] 1 is a schematic diagram of an optical scanning device 10 according to one embodiment. The optical scanning device 10 includes a micro mirror device (MMD) 2, a light source 3, and a drive controller 4. The optical scanning device 10 optically scans a surface 5 to be scanned by reflecting a light beam L emitted from the light source 3 by the MMD 2 under the control of the drive controller 4. The surface 5 to be scanned is, for example, a screen or the retina of a human eye.

[0025] The light source 3 is a laser device that emits, for example, laser light as the light beam L. The light beam L is an example of "light" according to the technology of the present disclosure.

[0026] MMD2 is the first axis a １ and the first axis a １ A second axis a perpendicular to ２ The micromirror device is a piezoelectric drive type that can oscillate the mirror portion 20 (see FIG. 2) around the first axis a. １ The direction parallel to this is the X direction, and the second axis a ２ The direction parallel to the axis a is the Y direction. １ and the second axis a ２ The direction perpendicular to the mirror axis is referred to as the Z direction. The MMD 2 is an example of a "mirror device" according to the technology of the present disclosure.

[0027] The drive control unit 4 outputs drive signals to the light source 3 and the MMD 2 based on the optical scanning information. The light source 3 generates a light beam L based on the input drive signal and irradiates the MMD 2 with the light beam L. The MMD 2 rotates the mirror unit 20 along the first axis a based on the input drive signal. １ and the second axis a ２ Rock it around.

[0028] The drive control unit 4 rotates the mirror unit 20 along the first axis a １ and the second axis a ２ , and the light beam L reflected by the mirror portion 20 is scanned so as to trace a Lissajous waveform, for example, on the surface to be scanned 5. This optical scanning method is called a Lissajous scanning method.

[0029] The optical scanning device 10 is applicable to, for example, a Lissajous scanning laser display. Specifically, the optical scanning device 10 is applicable to laser scanning displays such as AR (Augmented Reality) glasses and VR (Virtual Reality) glasses.

[0030] Next, an example of the configuration of the MMD 2 will be described with reference to Figures 2 to 6. Figure 2 is a plan view showing an outline of the MMD 2, and Figure 3 is a perspective view showing the appearance of the MMD 2. Figures 4 and 5 are views showing the state in which the mirror section 20 oscillates. Figure 6 is a diagram schematically showing a cross section taken along line A-A in Figure 3.

[0031] As shown in FIGS. 2 and 3, the MMD 2 has a mirror section 20 , a first actuator 21 , a second actuator 22 , a first support section 24 , a second support section 25 , a connection section 26 , and a fixing frame 27 .

[0032] The mirror section 20 has a reflective surface 20A that reflects incident light. The reflective surface 20A is formed of a thin metal film such as gold (Au) or aluminum (Al) provided on one surface of the mirror section 20. The reflective surface 20A is, for example, circular.

[0033] The first actuator 21 is disposed around the mirror section 20, has a ring-shaped planar shape when viewed in the XY plane, and surrounds the mirror section 20. The second actuator 22 is disposed around the mirror section 20 and the first actuator 21, has a ring-shaped planar shape, and surrounds the mirror section 20 and the first actuator 21. The second actuator 22 has a larger planar size than the first actuator 21.

[0034] The first support portion 24 supports the mirror portion 20 along the first axis a １ and the mirror part 20 is connected to the first axis a １ The first axis a is supported so as to be swingable around the first axis a. １ is in a plane including the reflecting surface 20A when the mirror unit 20 is stationary. For example, the first support unit 24 is １ The first support portion 24 is a torsion bar extending along the mirror portion 22. The first support portion 24 is an example of a "support portion that supports the mirror portion so that it can swing" according to the technology of the present disclosure.

[0035] The second support portion 25 connects the first actuator 21 and the second actuator 22 to the second axis a ２ The mirror part 20 and the first actuator 21 are connected to each other on the second axis a ２ The second axis a is supported so as to be swingable around the second axis a.２ is the angle of the first axis a in a plane including the reflecting surface 20A when the mirror unit 20 is stationary. １ For example, the second support portion 25 is perpendicular to the second axis a ２ The second support portion 25 is a torsion bar extending along the mirror portion 21. The second support portion 25 is an example of a "support portion that supports the mirror portion so that it can swing" according to the technology of the present disclosure.

[0036] The fixed frame 27 has, for example, a rectangular frame shape and surrounds the second actuator 22. The lengths of the fixed frame 27 in the X and Y directions are, for example, about 1 mm to 10 mm, and the thickness of the fixed frame 27 in the Z direction is, for example, about 5 μm to 0.2 mm.

[0037] The first actuator 21 and the second actuator 22 are piezoelectric actuators each having a piezoelectric element 40 (see FIG. 6). The first actuator 21 is attached to the mirror section 20 along a first axis a １ The second actuator 22 applies a rotation torque around the second axis a ２ As a result, the mirror part 20 rotates about the first axis a １ Around and second axis a ２ Swinging around.

[0038] The first actuator 21 is an annular thin plate member surrounding the mirror section 20, and is composed of a pair of first and second movable sections 21A and 21B, each of which is provided with a piezoelectric element 40. The first and second movable sections 21A and 21B are each semi-annular. The first and second movable sections 21A and 21B are connected to each other by a first axis a. １ The shape is symmetrical with respect to the first axis a １ Connected above.

[0039] The second actuator 22 is an annular thin plate member that surrounds the mirror section 20 and the first actuator 21, and is composed of a pair of first and second movable sections 22A and 22B that are provided with a piezoelectric element 40. The first and second movable sections 22A and 22B are each semi-annular. The first and second movable sections 22A and 22B are connected to each other by a second axis a. ２ The shape is symmetrical with respect to the second axis a ２Connected above.

[0040] In the first actuator 21, the first movable portion 21A and the second movable portion 21B are each provided with a piezoelectric element 40. In the second actuator 22, the first movable portion 22A and the second movable portion 22B are each provided with a piezoelectric element 40.

[0041] The drive control unit 4 rotates the mirror unit 20 relative to the first actuator 21 along the first axis a １ and supplies a drive signal to the second actuator 22 to swing the mirror unit 20 about the second axis a ２ The drive control unit 4 supplies a drive signal to resonate the mirror unit 20 by supplying a drive signal with a resonance frequency corresponding to a natural frequency determined by the shapes of the mirror unit 20, the first actuator 21, and the second actuator 22, etc. This makes it possible to increase the deflection angle when the mirror unit 20 swings. The larger the deflection angle, the larger the scan angle, which is the angular range that can be scanned by the light beam L reflected by the mirror unit 20. The scan angle refers to the total angle of the optical deflection angle.

[0042] 4 and 5 specifically show the state in which the mirror section 20 is oscillating. As shown in FIG. 4, the mirror section 20 is oscillated along the first axis a １ 5, the second axis a ２ When driving the mirror section 20, the first actuators 21 and second actuators 22 arranged around the mirror section 20 deform in the same phase or in the opposite phase to the mirror section 20 in accordance with the deformation of the piezoelectric element 40, and oscillate together with the mirror section 20.

[0043] As shown in Fig. 6, the MMD 2 is formed by processing, for example, an SOI (Silicon On Insulator) substrate 30 using lithography technology. The SOI substrate 30 is configured by sequentially stacking a handle layer 31, a BOX (Buried Oxide) layer 32, and a device layer 33. The handle layer 31 and the device layer 33 are made of single crystal silicon. The BOX layer 32 is made of silicon oxide. The SOI substrate 30 is an example of a "first silicon substrate" according to the technology of the present disclosure.

[0044] The mirror portion 20, the first movable portion 21A, the second movable portion 21B, the first movable portion 22A, the second movable portion 22B, the first support portion 24, the second support portion 25, and the connection portion 26 are formed by a silicon structure 35 obtained by processing the SOI substrate 30. The silicon structure 35 is a device layer 33 that remains after anisotropic etching is performed on the SOI substrate 30. The silicon structure 35 is an example of a "structure including a mirror portion and a support portion" according to the technology of the present disclosure.

[0045] The fixed frame 27 is formed of three layers: a handle layer 31, a BOX layer 32, and a device layer 33. That is, the fixed frame 27 is thicker than the silicon structure 35. In the present disclosure, the thickness refers to the length in the Z direction.

[0046] The piezoelectric element 40 is formed on the device layer 33 via a part of a cap layer 50 described below. The piezoelectric element 40 has a layered structure in which a lower electrode layer 41, a piezoelectric film 42, and an upper electrode layer 43 are stacked in this order. The lower electrode layer 41 is an example of a "first electrode layer" according to the technology of the present disclosure. The upper electrode layer 43 is an example of a "second electrode layer" according to the technology of the present disclosure.

[0047] The lower electrode layer 41 and the upper electrode layer 43 are formed of a metal such as gold (Au) or platinum (Pt). The piezoelectric film 42 is formed of a piezoelectric material such as PZT (lead zirconate titanate). The lower electrode layer 41 and the upper electrode layer 43 are electrically connected to the drive control unit 4 via wiring and electrode pads (not shown).

[0048] The lower electrode layer 41 is connected to the drive control unit 4 via wiring and electrode pads, and is supplied with a ground potential. A drive voltage is applied to the upper electrode layer 43 from the drive control unit 4.

[0049] When a positive or negative voltage is applied in the polarization direction, the piezoelectric film 42 undergoes deformation (e.g., expansion and contraction) proportional to the applied voltage. That is, the piezoelectric film 42 exhibits a so-called inverse piezoelectric effect. When a drive voltage is applied to the upper electrode from the drive control unit 4, the piezoelectric film 42 exhibits the inverse piezoelectric effect, displacing the first actuator 21 and the second actuator 22.

[0050] Next, an example of a method for manufacturing an MMD 2 will be described with reference to Figures 7 to 13. First, an SOI substrate 30 is prepared as shown in Figure 7(A). Here, the SOI substrate 30 is in wafer form. A plurality of MMDs 2 are manufactured simultaneously by processing the wafer-like SOI substrate 30, but the following description will focus on an area where one MMD 2 is manufactured.

[0051] As shown in FIG. 7B , a structure formation step is performed in which the SOI substrate 30 is processed from the first surface side by lithography to form a silicon structure 35 on the first surface side of the SOI substrate 30. Here, the first surface refers to the surface of the device layer 33 opposite the BOX layer 32. The first surface side refers to the device layer 33 side of the SOI substrate 30. Specifically, a resist pattern is formed on the first surface of the SOI substrate 30, and anisotropic etching is performed on the device layer 33 based on the formed resist pattern, thereby forming the silicon structure 35. At this time, a fine wavy shape called a scallop is generated on the processed surface 36 of the silicon structure 35. The processed surface 36 is the sidewall surface of the mirror portion 20, the first support portion 24, the second support portion 25, etc.

[0052] Next, as shown in FIG. 8, a smoothing step is performed to smooth the processed surface 36 of the silicon structure 35. Examples of the smoothing step include hydrogen annealing, which is a high-temperature heat treatment performed in an atmosphere containing hydrogen gas. Specifically, the hydrogen annealing is a heat treatment performed at approximately 900 to 1300°C in an Ar atmosphere containing 2% or more hydrogen at a pressure ranging from a few torr to atmospheric pressure. This smooths the scalloped processed surface 36. Furthermore, the corners of the processed surface 36 are rounded.

[0053] In addition, instead of hydrogen annealing, the smoothing step can use a thermal oxide film formation / removal process in which a thermal oxide film formation process for forming a thermal oxide film on the processing surface 36 and a thermal oxide film removal process for removing the thermal oxide film formed on the processing surface 36 are repeated one or more times. The thermal oxide film is a silicon oxide film. For example, the thermal oxide film formation process is a method for forming a thermal oxide film by thermal oxidation. For example, the thermal oxide film removal process is a cleaning process using hydrofluoric acid (HF).

[0054] Next, a cap layer formation process is performed to form a cap layer 50 that covers the silicon structure 35 on the first surface side of the SOI substrate 30. First, as shown in FIG. 9 , a silicon substrate 53 for forming the cap layer 50 is prepared. The silicon substrate 53 is made of a silicon layer 51 and a thermal oxide film 52 formed on the surface of the silicon layer 51. The silicon layer 51 is made of single crystal silicon. The thermal oxide film 52 is a silicon oxide film. The silicon substrate 53 is in the form of a wafer having the same size as the SOI substrate 30. The silicon substrate 53 is an example of a "second silicon substrate" according to the technology of the present disclosure.

[0055] Next, a silicon substrate 53 is bonded to the first surface side of the SOI substrate 30. The thermal oxide film 52 of the silicon substrate 53 is bonded to the first surface of the SOI substrate 30. The SOI substrate 30 and the silicon substrate 53 can be bonded by a method such as plasma assisted bonding or diffusion bonding.

[0056] Next, as shown in FIGS. 10 and 11A, a cap layer 50 is formed by thinning the silicon substrate 53. The cap layer 50 includes a portion of the silicon layer 51 and a thermal oxide film 52. In the thinning process, the thickness of the cap layer 50 is adjusted by grinding and polishing. The polishing can be performed using a chemical mechanical polishing (CMP) method. The thickness of the cap layer 50 is selected so that it can be easily removed later and has little deflection directly above the cavity of the silicon structure 35, resulting in a flat surface. For example, the thickness of the cap layer 50 is preferably set to a value within the range of 5 μm to 50 μm.

[0057] 11B, a lower electrode layer 41 is formed on the cap layer 50, a piezoelectric film 42 is formed on the lower electrode layer 41, and an upper electrode layer 43 is formed on the piezoelectric film 42. For example, a sputtering method can be used to form the lower electrode layer 41 and the upper electrode layer 43. For example, a sputtering method, a Sol-gel method, or the like can be used to form the piezoelectric film 42.

[0058] 12A , a piezoelectric element formation process is performed in which the lower electrode layer 41, the piezoelectric film 42, and the upper electrode layer 43 are processed by lithography to form the piezoelectric elements 40. Specifically, a resist pattern is formed on the upper electrode layer 43, and at least the piezoelectric film 42 and the upper electrode layer 43 are etched based on the formed resist pattern to form the piezoelectric elements 40. The piezoelectric elements 40 are formed in regions corresponding to the first movable portion 21A, the second movable portion 21B, the first movable portion 22A, and the second movable portion 22B, respectively. Note that the lower electrode layer 41 may be patterned in a separate process from the piezoelectric film 42 and the upper electrode layer 43.

[0059] Thereafter, although not shown in the drawings, an insulating film is formed to cover the piezoelectric element 40, and then wiring is patterned to supply a drive voltage to the piezoelectric element 40. The insulating film is a protective film that protects the piezoelectric element 40 from humidity and electric fields. In addition, a metal thin film is formed on the surface of the region of the silicon structure 35 that corresponds to the mirror portion 20 to form the reflective surface 20A. This metal thin film may be formed in the same process as the wiring. Furthermore, because the mirror portion 20 has a large diameter, the metal thin film can also be formed by a mask vapor deposition method, not limited to lithography.

[0060] 12B, a structure exposing step is performed in which the cap layer 50 is processed by lithography to expose the silicon structure 35. This lithography step includes forming a resist pattern and anisotropic etching.

[0061] 13, an opening formation step is performed in which the SOI substrate 30 is processed from the second surface side opposite the first surface side by lithography to form an opening 60 that exposes the silicon structure 35 from the second surface side. This lithography method includes the formation of a resist pattern and anisotropic etching. As a result, a fixing frame 27 is formed around the opening 60, completing the MMD 2.

[0062] Since a plurality of MMDs 2 are simultaneously manufactured from one SOI substrate 30, a dicing process is carried out to separate the MMDs 2 into individual pieces.

[0063] As described above, in the manufacturing method of the MMD 2 according to this embodiment, after smoothing the processed surface 36 of the silicon structure 35, the cap layer 50 covering the silicon structure 35 is formed on the first surface side of the SOI substrate 30. This allows the piezoelectric film 42 and other films to be formed on the flat cap layer 50. In other words, the piezoelectric film 42 and other films can be patterned by lithography without using a mask vapor deposition method. Therefore, according to the manufacturing method of the MMD 2 according to this embodiment, the processed surface 36 of the silicon structure 35 can be smoothed and a high-definition piezoelectric film 42 can be formed, thereby achieving a large scan angle and enabling miniaturization. Furthermore, since lithography can also be used to form the wiring, a high-precision MMD 2 can be manufactured.

[0064] FIG. 14 shows an example of the experimental results of the maximum scan angle. Example 1 shows the maximum scan angle of an MMD2 manufactured using a hydrogen annealing process as the smoothing process. Example 2 shows the maximum scan angle of an MMD2 manufactured using a thermal oxide film formation and removal process as the smoothing process. Comparative Example shows the maximum scan angle of an MMD2 manufactured without smoothing. The maximum scan angle is the maximum scan angle that can be driven without causing damage. For example, 75° x 50° is the maximum scan angle of the first axis a １ The maximum scan angle around the second axis a is 75°. ２ The maximum scan angle around the periphery is shown to be 50°.

[0065] As shown in FIG. 14, the smoothing process reduces scallops, thereby improving the maximum scan angle.

[0066] It should be noted that various modifications are possible to the configuration of the MMD 2. In the above embodiment, the MMD 2 is a two-axis mirror device in which the mirror section 20 oscillates around two intersecting axes, but the MMD 2 may also be a one-axis mirror device in which the mirror section 20 oscillates around one axis.

[0067] Furthermore, from the above description, the techniques described in the following supplementary paragraphs can be understood.

[0068] [Supplementary Item 1] A method for manufacturing a mirror device, comprising: a structure forming step of processing a first silicon substrate to form a structure on a first surface side of the first silicon substrate, the structure including a mirror portion that reflects light and a support portion that supports the mirror portion so that it can oscillate; a smoothing step of smoothing the processed surface of the structure; a cap layer forming step of forming a cap layer on the first surface side of the first silicon substrate to cover the structure; and a piezoelectric film forming step of forming a first electrode layer on the cap layer and forming a piezoelectric film on the first electrode layer. [Supplementary Item 2] A method for manufacturing a mirror device according to Supplementary Item 1, wherein the smoothing step is a step of smoothing the processed surface by a hydrogen annealing treatment. [Supplementary Item 3] A method for manufacturing a mirror device according to Supplementary Item 1, wherein the smoothing step is a step of smoothing the processed surface by repeating, one or more times, a thermal oxide film formation process of forming a thermal oxide film on the processed surface and a thermal oxide film removal process of removing the thermal oxide film formed on the processed surface. [Supplementary Item 4] The method for manufacturing a mirror device according to any one of Supplementary Items 1 to 3, wherein the cap layer forming step is a step of bonding a second silicon substrate to the first surface side of the first silicon substrate and performing a thinning process including grinding and polishing on the second silicon substrate to form the cap layer. [Supplementary Item 5] The method for manufacturing a mirror device according to Supplementary Item 4, wherein the second silicon substrate is formed by forming a thermal oxide film on a surface of a silicon layer, and the thermal oxide film is bonded to the first surface of the first silicon substrate. [Supplementary Item 6] The method for manufacturing a mirror device according to Supplementary Item 5, wherein the cap layer includes a part of the silicon layer and the thermal oxide film. [Supplementary Item 7] The method for manufacturing a mirror device according to any one of Supplementary Items 1 to 6, comprising a piezoelectric element forming step of forming a second electrode layer on the piezoelectric film, and processing the first electrode layer, the piezoelectric film, and the second electrode layer to form a piezoelectric element that constitutes an actuator that drives the mirror portion. [Supplementary Item 8] The method for manufacturing a mirror device according to any one of Supplementary Items 1 to 7, further comprising a structure exposing step of processing the cap layer to expose the structure.[Supplementary Item 9] The method for manufacturing a mirror device according to Supplementary Item 8, including an opening forming step of forming an opening that exposes the structure from the second surface side by processing the first silicon substrate from a second surface side opposite to the first surface. [Supplementary Item 10] The method for manufacturing a mirror device according to any one of Supplementary Items 1 to 9, wherein the first silicon substrate is an SOI substrate.

Claims

1. A method for manufacturing a mirror device, comprising: a structure forming step of forming, by processing a first silicon substrate, a structure including a mirror portion that reflects light and a support portion that swingably supports the mirror portion on a first surface side of the first silicon substrate; a smoothing step of smoothing a processed surface of the structure; a cap layer forming step of forming a cap layer that covers the structure on the first surface side of the first silicon substrate; and a piezoelectric film forming step of forming a first electrode layer on the cap layer and forming a piezoelectric film on the first electrode layer.

2. The method for manufacturing a mirror device according to claim 1, wherein the smoothing step is a step of smoothing the processed surface by hydrogen annealing treatment.

3. The method for manufacturing a mirror device according to claim 1, wherein the smoothing step is a step of smoothing the processed surface by repeating, one or more times, a thermal oxide film forming treatment of forming a thermal oxide film on the processed surface and a thermal oxide film removing treatment of removing the thermal oxide film formed on the processed surface.

4. The method for manufacturing a mirror device according to any one of claims 1 to 3, wherein the cap layer forming step is a step of forming the cap layer by bonding a second silicon substrate to the first surface side of the first silicon substrate and performing a thinning treatment including grinding and polishing on the second silicon substrate.

5. The method for manufacturing a mirror device according to claim 4, wherein the second silicon substrate has a thermal oxide film formed on a surface of a silicon layer, and the thermal oxide film is bonded to the first surface of the first silicon substrate.

6. The method for manufacturing a mirror device according to claim 5, wherein the cap layer includes a part of the silicon layer and the thermal oxide film.

7. The method for manufacturing a mirror device according to claim 1, further comprising a piezoelectric element forming step of forming a piezoelectric element that constitutes an actuator for driving the mirror portion by forming a second electrode layer on the piezoelectric film and processing the first electrode layer, the piezoelectric film, and the second electrode layer.

8. The method for manufacturing a mirror device according to claim 7, further comprising a structure exposing step of exposing the structure by processing the cap layer.

9. The method for manufacturing a mirror device according to claim 8, further comprising an opening forming step of forming an opening for exposing the structure from a second surface side opposite to the first surface by processing the first silicon substrate from the second surface side.

10. The method for manufacturing a mirror device according to claim 9, wherein the first silicon substrate is a SOI substrate.

11. A mirror device comprising: a structure including a mirror portion that reflects light and a support portion that swingably supports the mirror portion, the structure being formed by processing a silicon substrate; a part of a cap layer formed on the silicon substrate; and an actuator constituted by a piezoelectric element formed on a part of the cap layer, wherein the cap layer includes silicon and a thermal oxide film.

12. The mirror device according to claim 11, wherein the silicon included in the cap layer is single crystal silicon.

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