Method for manufacturing mirror device

Abstract

To provide a method for manufacturing a mirror device, by which the mirror device having a movable portion can be favorably manufactured.SOLUTION: A method for manufacturing a mirror device includes: a first forming step of forming, on a SOI wafer 80, a plurality of parts S, each corresponding to a structural body 50, such that a part of each of the plurality of parts S corresponding to a first movable portion 3 is swingable or movable to a part of each of the plurality of parts S corresponding to a support portion 2; a second forming step of forming a mirror layer 7 on the part corresponding to the first movable portion 3; a heating step of heating the part corresponding to the first movable portion 3, in a state where the part corresponding to the first movable portion 3 is swingable or movable to the part corresponding to the support portion 2, after the first forming step and the second forming step; and a cutting step of cutting the SOI wafer 80 so as to separate the plurality of parts S from one another, in a state where the part corresponding to the first movable portion 3 is swingable or movable to the part corresponding to the support portion 2, after the heating step.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a mirror device having a movable part.

Background Art

[0002] Patent Document 1 describes a method for manufacturing a mirror device having a movable part. In the manufacturing method described in Patent Document 1, after forming a plurality of micro-mechanical structures having a movable structure on a semiconductor substrate, dicing is performed to separate the plurality of micro-mechanical structures from each other. At this point, the movable structure is curved. Subsequently, after forming a metal layer that functions as a mirror on the movable structure, the entire micro-mechanical structure is heated. By this heat treatment, the movable structure is flattened.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the method for manufacturing a mirror device as described above, it is required to manufacture the mirror device better. Therefore, an object of the present invention is to provide a method for manufacturing a mirror device that can manufacture a mirror device having a movable part well.

Means for Solving the Problems

[0005] The manufacturing method of the mirror device of the present invention is a manufacturing method of a mirror device including a support part, a movable part, and a structure having a connecting part that connects the movable part to the support part so that the movable part can swing or move, and a mirror layer provided on the movable part, the method including: a first forming step of forming a plurality of parts each corresponding to the structure on a wafer; a second forming step of forming a mirror layer on a part corresponding to the movable part in each of the plurality of parts; a heating step of heating a part corresponding to the movable part in each of the plurality of parts after the first forming step and the second forming step; and a cutting step of cutting the wafer so that the plurality of parts are separated from each other after the heating step.

[0006] When forming the mirror layer, residual stress may occur in the mirror layer, and warping may occur in the mirror layer due to the residual stress. If the mirror device is shipped in this state, there is a concern that the amount of warping of the mirror layer may change when the residual stress is relaxed due to the environmental temperature or self-heating during use. On the other hand, in this method of manufacturing a mirror device, a plurality of portions each corresponding to a structure are formed on a wafer, and after a mirror layer is formed on a portion corresponding to a movable portion in each of the plurality of portions, the portion corresponding to the movable portion in each of the plurality of portions is heated. Thereby, the residual stress existing in the mirror layer can be relaxed, and it is possible to suppress a change in the amount of warping of the mirror layer when the mirror device is used. Further, in this method of manufacturing a mirror device, the wafer is cut after the heating. Thereby, compared with the case where a heat treatment is performed after cutting the wafer, the temperature of the mirror layer during heating can be made uniform among the plurality of portions. As a result, variations in the quality of the mirror device can be suppressed. Further, by heating in the wafer state, for example, a large number of mirror devices can be arranged in a constant temperature bath used for heating. As a result, the manufacturing efficiency of the mirror device can be improved. Further, for example, when measuring the amount of warping of the mirror layer after heating, the amount of warping can be measured in the wafer state. In this case, since it is easy to accurately grasp the position of the mirror layer, the measurement efficiency can be improved. Further, for example, when cleaning the mirror layer after heating, it can be cleaned in the wafer state, and the workability of cleaning can be improved. Further, when a heat treatment is performed after cutting the wafer, fragments of the wafer generated during cutting may adhere to the mirror layer. In this case, there is a concern that the semiconductor material constituting the fragment diffuses into the mirror layer when the fragment is heated during the heat treatment, resulting in a decrease in the reflectance of the mirror layer. On the other hand, in this method of manufacturing a mirror device, since the wafer is cut after heating in the wafer state, such a situation can be suppressed. As a result, the quality of the mirror device can be ensured. As described above, according to this method of manufacturing a mirror device, a mirror device having a movable portion can be manufactured favorably.

[0007] The manufacturing method of the mirror device of the present invention may further include a measurement step of measuring the amount of warpage of the mirror layer between the heating step and the cutting step. In this case, the amount of warpage of the mirror layer can be measured in the wafer state, and the measurement efficiency can be improved.

[0008] In the cutting step, a modified region may be formed inside the wafer by irradiating a laser beam, and the wafer may be cut by extending cracks in the thickness direction of the wafer from the modified region. In this case, the stress acting on the wafer during cutting can be reduced, and deformation of the mirror layer and the movable part due to the stress can be suppressed. Further, it is possible to suppress a change in the amount of warpage of the mirror layer during cutting.

[0009] The second forming step may be performed after the first forming step. In this case, it is possible to suppress a situation where the quality of the mirror layer deteriorates due to heat when forming a plurality of parts.

[0010] In the heating step, the amount of warpage of the mirror layer may be decreased by heating the portion corresponding to the movable part in each of the plurality of parts. Alternatively, the amount of warpage of the mirror layer may be increased by heating the portion corresponding to the movable part in each of the plurality of parts. In either case, the residual stress present in the mirror layer can be relaxed, and a change in the amount of warpage of the mirror layer during use of the mirror device can be suppressed.

[0011] In the second forming step, the mirror layer may be formed by sputtering. In this case, the mirror layer can be formed well.

[0012] The mirror device may further include a coil or a piezoelectric element for applying a driving force to the movable part. In this case, heat is likely to be generated during use of the mirror device, but according to the manufacturing method of this mirror device, even in such a case, a change in the amount of warpage of the mirror layer during use of the mirror device can be suppressed.

[0013] In the heating process, the portion corresponding to the movable part in each of the plurality of portions may be heated to 60°C or higher and 300°C or lower. In this case, the residual stress present in the mirror layer can be effectively relaxed.

[0014] The maximum width of the mirror layer may be 0.5 mm or more and 30 mm or less. In this case, the amount of warping of the mirror layer is likely to change during the use of the mirror device. However, according to the manufacturing method of this mirror device, even in such a case, it is possible to suppress the change in the amount of warping of the mirror layer during the use of the mirror device.

[0015] The mirror layer may include an adhesion layer, a diffusion prevention layer, and a reflection layer formed in this order on the movable part. In this case, by including the adhesion layer, the mirror layer can be stably formed on the movable part. Further, by including the diffusion prevention layer, it is possible to suppress the occurrence of metal diffusion between the reflection layer and the adhesion layer during heating.

[0016] The mirror layer includes a plurality of layers including a reflection layer, and the plurality of layers may include a layer in which compressive stress remains at the completion of the second forming process and a layer in which tensile stress remains at the completion of the second forming process. In this case, the amount of warping of the mirror layer before the heating process can be reduced. Further, the change in the amount of warping of the mirror layer in the heating process can be reduced. As a result, the heating time can be shortened and the amount of warping of the mirror layer can be easily controlled.

[0017] In the heating process, the entire wafer may be heated. In this case, the temperature of the mirror layer during heating can be made uniform among the plurality of portions.

[0018] In the heating process, without heating the entire wafer, the portion corresponding to the movable part in each of the plurality of portions may be heated. Also in this case, even if there are variations in the position and output of the heat source used in the heating process, the temperature of the mirror layer can be made uniform among the plurality of portions by heat conduction within the wafer.

Advantages of the Invention

[0019] According to the present invention, it becomes possible to provide a method for manufacturing a mirror device capable of favorably manufacturing a mirror device having a movable part.

Brief Description of the Drawings

[0020]

Figure 1

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Figure 11

Embodiments for Carrying Out the Invention

[0021] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In the following description, the same or corresponding elements are denoted by the same reference numerals, and redundant descriptions are omitted. [Mirror Device]

[0022] As shown in FIGS. 1 and 2, the mirror device 1 has a support portion 2 and a movable mirror portion 10. The movable mirror portion 10 has a first movable portion 3, a second movable portion 4, a pair of first connecting portions 5, a pair of second connecting portions 6, and a mirror layer 7. The support portion 2, the first movable portion 3, the second movable portion 4, the pair of first connecting portions 5, and the pair of second connecting portions 6 constitute a structure 50. In other words, the mirror device 1 includes the structure 50 and the mirror layer 7.

[0023] The structure 50 is integrally formed by, for example, an SOI (Silicon on Insulator) substrate 8. That is, the mirror device 1 is configured as a MEMS (Micro Electro Mechanical Systems) device. The SOI substrate 8 has a support layer 81, a device layer 82, and an intermediate layer 83. The support layer 81 and the device layer 82 are semiconductor layers made of, for example, silicon. The intermediate layer 83 is an insulating layer made of, for example, silicon oxide and is disposed between the support layer 81 and the device layer 82.

[0024] The first movable portion 3 is formed, for example, in a rectangular plate shape. The second movable portion 4 is formed, for example, in a rectangular ring shape and surrounds the first movable portion 3 when viewed from the optical axis direction A. The support portion 2 is formed, for example, in a rectangular frame shape and surrounds the second movable portion 4 when viewed from the optical axis direction A. That is, the support portion 2 surrounds the first movable portion 3 and the second movable portion 4 when viewed from the optical axis direction A. The optical axis direction A is a direction perpendicular to the plane in which the support portion 2, the first movable portion 3, the second movable portion 4, the pair of first connecting portions 5, and the pair of second connecting portions 6 are arranged, and is a direction intersecting the mirror layer 7.

[0025] The first movable part 3 has a first part 31 and a second part 32. The first part 31 is formed, for example, in a circular shape when viewed in the optical axis direction A. The second part 32 is formed, for example, in a rectangular ring shape when viewed in the optical axis direction A. The second part 32 surrounds the first part 31 when viewed in the optical axis direction A and is connected to the first part 31 via a pair of connection parts 33. In this example, the pair of connection parts 33 are arranged on the second axis X2, which will be described later, so as to sandwich the first part 31. In FIG. 2, the illustration of the second part 32 and the connection part 33, etc. is omitted. The first movable part 3 may not have the second part 32 and the connection part 33.

[0026] The pair of first connecting parts 5 are arranged on the first axis X1 so as to sandwich the first movable part 3 in the gap between the second part 32 of the first movable part 3 and the second movable part 4. Each first connecting part 5 functions as a torsion bar. Each first connecting part 5 connects the first movable part 3 to the second movable part 4 so that the first movable part 3 can swing around the first axis X1. Each first connecting part 5 can also be regarded as connecting the first movable part 3 to the support part 2 via the second movable part 4 and the second connecting part 6 so that the first movable part 3 can swing around the first axis X1.

[0027] The pair of second connecting parts 6 are arranged on the second axis X2 so as to sandwich the second movable part 4 in the gap between the second movable part 4 and the support part 2. Each second connecting part 6 functions as a torsion bar. Each second connecting part 6 connects the second movable part 4 to the support part 2 so that the second movable part 4 can swing around the second axis X2. When the second movable part 4 swings around the second axis X2, the first movable part 3 also swings around the second axis X2 together with the second movable part 4. Thus, the first movable part 3 can swing around each of the first axis X1 and the second axis X2. The first axis X1 and the second axis X2 are perpendicular to the optical axis direction A and intersect each other (perpendicular to each other in this example).

[0028] The support part 2, the first movable part 3, and the second movable part 4 are composed of a support layer 81, a device layer 82, and an intermediate layer 83. The first connecting part 5 and the second connecting part 6 are composed of the device layer 82. The thickness of the support layer 81 (the thickness along the optical axis direction A) that constitutes the first movable part 3 and the second movable part 4 is thinner than the thickness of the support layer 81 that constitutes the support part 2. The support layer 81 that constitutes the first movable part 3 functions as a beam part that suppresses the warpage of the first movable part 3 and the mirror layer 7. The first movable part 3 and the second movable part 4 may be composed only of the device layer 82.

[0029] The mirror layer 7 is formed in a circular shape on the surface 31a of the first portion 31 in the first movable part 3. The surface 31a is constituted by the surface on the opposite side of the intermediate layer 83 in the device layer 82 and extends so as to intersect the optical axis direction A. The mirror layer 7 is formed in a region including the intersection point of the first axis X1 and the second axis X2. The center (geometric center) of the mirror layer 7 when viewed from the optical axis direction A coincides with the intersection point of the first axis X1 and the second axis X2. The outer edge of the mirror layer 7 extends at a certain interval from the outer edge of the first portion 31. The diameter of the mirror layer 7 (the maximum width when viewed from the optical axis direction A) is 0.5 mm or more and 30 mm or less. In this example, the diameter of the mirror layer 7 is about 2 mm. The mirror layer 7 may be formed in any shape such as an elliptical shape, a rectangular shape, or a polygonal shape. Similarly, the first portion 31 may be formed in any shape such as an elliptical shape, a rectangular shape, or a polygonal shape. The second portion 32 of the first movable part 3 and the second movable part 4 may be formed in any shape such as an annular shape, an elliptical annular shape, or a polygonal annular shape.

[0030] The mirror layer 7 includes an adhesion layer 71, an anti-diffusion layer (intermediate layer) 72, and a reflective layer 73. The adhesion layer 71, the anti-diffusion layer 72, and the reflective layer 73 are laminated in this order on the surface 31a of the first portion 31. The adhesion layer 71 has a high adhesion to the first portion 31 (silicon) compared to the anti-diffusion layer 72 and the reflective layer 73. The anti-diffusion layer 72 suppresses the occurrence of metal diffusion between the adhesion layer 71 and the reflective layer 73 during heating. The surface of the reflective layer 73 on the side opposite to the first portion 31 constitutes a mirror surface 73a extending so as to intersect the optical axis direction A. Each of the adhesion layer 71, the anti-diffusion layer 72, and the reflective layer 73 is formed of a metal material. For example, the adhesion layer 71 is made of titanium, the anti-diffusion layer 72 is made of platinum, and the reflective layer 73 is made of gold. The thickness of each of the adhesion layer 71 and the anti-diffusion layer 72 is, for example, about 50 nm to 300 nm, preferably about 100 nm. The thickness of the reflective layer 73 is, for example, about 50 nm to 300 nm, preferably about 200 nm. When the thickness of the adhesion layer 71 or the anti-diffusion layer 72 is 50 nm or more, the adhesion function of the adhesion layer 71 or the anti-diffusion function of the anti-diffusion layer 72 can be effectively exerted. When the thickness of the reflective layer 73 is 50 nm or more, the reflectivity of the reflective layer 73 can be increased. When the thickness of the adhesion layer 71, the anti-diffusion layer 72, or the reflective layer 73 is 300 nm or less, the stress generated in the adhesion layer 71, the anti-diffusion layer 72, or the reflective layer 73 can be reduced, the warpage amount of the mirror layer 7 before the heating process described later can be reduced, and the change in the warpage amount of the mirror layer 7 in the heating process can be reduced. The anti-diffusion layer 72 may be formed of tungsten. The reflective layer 73 may be formed of aluminum. When the reflective layer 73 is made of gold, the reflectivity with respect to light in the near-infrared region can be increased compared to the case where it is made of aluminum.

[0031] In each of the adhesion layer 71, the anti-reflection layer 72, and the reflection layer 73 that constitute the mirror layer 7, as will be described later, a compressive stress (a force in the direction of convex warping) or a tensile stress (a force in the direction of concave warping) is generated as a residual stress. The type (compressive or tensile) and magnitude of the stress are determined by manufacturing conditions such as the material, thickness, area, and film formation temperature of each layer. By adjusting the material, thickness, area, film formation temperature, etc., it is possible to adjust the type and magnitude of the stress in the state before the heating process described later, as well as the amount of change in warping during the heating process. As an example, in the present embodiment, the adhesion layer 71 and the anti-reflection layer 72 are formed so that a compressive stress remains in the state before the heating process (at the completion of the second formation process described later), and the reflection layer 73 is formed so that a tensile stress remains in the state before the heating process (at the completion of the second formation process). By combining a layer having a compressive stress and a layer having a tensile stress, the amount of warping of the mirror layer 7 and the first movable portion 3 before the heating process can be reduced. Also, when formed of the same material, a larger stress is generated as the layer thickness is thicker. Therefore, from the viewpoint of reducing the amount of warping before the heating process and the change in the amount of warping during the heating process, it is preferable that the thickness of each layer is thin.

[0032] Furthermore, the mirror device 1 includes a first driving coil 11, a second driving coil 12, wirings 15a, 15b, wirings 16a, 16b, electrode pads 21a, 21b, and electrode pads 22a, 22b. In FIG. 1, the first driving coil 11 and the second driving coil 12 are indicated by a one-dot chain line, and the wirings 15a, 15b and the wirings 16a, 16b are indicated by solid lines. The first driving coil 11, the second driving coil 12, etc. are actually covered by an insulating layer 42 described later.

[0033] The first driving coil 11 is provided on the second portion 32 of the first movable portion 3. The first driving coil 11 is wound a plurality of times in a spiral (spiral) shape. A magnetic field generated by a magnetic field generation unit (not shown) acts on the first driving coil 11. The magnetic field generation unit is configured to include, for example, a permanent magnet having a Halbach array.

[0034] The first driving coil 11 is disposed in a groove formed on the surface of the second portion 32. That is, the first driving coil 11 is embedded in the first movable portion 3. The first driving coil 11 is disposed in the groove via an insulating layer 41. The insulating layer 41 is, for example, a silicon nitride film. The insulating layer 41 is formed over the surfaces of the support portion 2, the first movable portion 3, the second movable portion 4, the pair of first connecting portions 5, and the pair of second connecting portions 6, but is not formed on the first portion 31 of the first movable portion 3. An insulating layer 42 made of, for example, silicon nitride is formed on the insulating layer 41.

[0035] One end of the first driving coil 11 is connected to the electrode pad 21a via the wiring 15a. The wiring 15a extends from the first movable portion 3, through one of the first connecting portions 5, the second movable portion 4, and one of the second connecting portions 6, to the support portion 2. The wiring 15a and the electrode pad 21a are integrally formed of a metal material such as tungsten, aluminum, gold, silver, copper, or an aluminum-based alloy. The wiring 15a is provided as a surface wiring on the surfaces of one of the first connecting portions 5, the second movable portion 4, and one of the second connecting portions 6. The wirings 15b, 16a, and 16b described later are provided as surface wirings in the same manner as the wiring 15a.

[0036] The other end of the first driving coil 11 is connected to the electrode pad 21b via the wiring 15b. The wiring 15b extends from the first movable portion 3, through the other of the first connecting portions 5, the second movable portion 4, and the other of the second connecting portions 6, to the support portion 2. The wiring 15b and the electrode pad 21b are integrally formed of the same metal material as the wiring 15a.

[0037] The second driving coil 12 is provided on the second movable part 4. The second driving coil 12 is wound a plurality of times in a spiral (spiral) shape on the second movable part 4. A magnetic field generated by the magnetic field generating part acts on the second driving coil 12. The second driving coil 12 is disposed in a groove 4b formed on the surface 4a of the second movable part 4. That is, the second driving coil 12 is embedded in the second movable part 4. The second driving coil 12 is disposed in the groove via an insulating layer 41.

[0038] One end of the second driving coil 12 is connected to the electrode pad 22a via the wiring 16a. The wiring 16a extends from the second movable part 4 through one of the second connecting parts 6 to the support part 2. The wiring 16a and the electrode pad 22a are integrally formed of the same metal material as the wiring 15a.

[0039] The other end of the second driving coil 12 is connected to the electrode pad 22b via the wiring 16b. The wiring 16b extends from the second movable part 4 through the other second connecting part 6 to the support part 2. The wiring 16b and the electrode pad 22b are integrally formed of the same metal material as the wiring 15a.

[0040] Hereinafter, as examples of the operation of the movable mirror unit 10 in the mirror device 1, the first example to the fifth example will be described. In the first example, a high-frequency driving current is applied to the first driving coil 11. At this time, since a magnetic field generated by the magnetic field generating part acts on the first driving coil 11, a Lorentz force is generated in the first driving coil 11. By this Lorentz force acting as a driving force, the first movable part 3 is swung around the first axis X1 at, for example, the resonance frequency level.

[0041] In addition, a driving current of a certain magnitude is applied to the second driving coil 12. At this time, since the magnetic field generated by the magnetic field generating unit acts on the second driving coil 12, a Lorentz force is generated in the second driving coil 12. By this Lorentz force acting as a driving force, the second movable part 4 is rotated around the second axis X2 according to, for example, the magnitude of the driving current, and is stopped in that state. Thereby, according to the mirror device 1, the light from the light source incident along the optical axis direction A can be reflected by the mirror surface 73a and scanned. In the first example, the first movable part 3 is oscillated at the resonance frequency and the second movable part 4 is used statically.

[0042] In the second example, similar to the operation of the first movable part 3 in the first example, a high-frequency driving current is applied to the first driving coil 11, so that the first movable part 3 is oscillated according to the resonance frequency, and a high-frequency driving current is applied to the second driving coil 12, so that the second movable part 4 is oscillated according to the resonance frequency. Thus, in the second example, both the first movable part 3 and the second movable part 4 are oscillated at the resonance frequency.

[0043] In the third example, similar to the operation of the second movable part 4 in the first example, a driving current of a certain magnitude is applied to the first driving coil 11, so that the first movable part 3 is rotated around the first axis X1 according to the magnitude of the driving current and stopped, and a driving current of a certain magnitude is applied to the second driving coil 12, so that the second movable part 4 is rotated around the second axis X2 according to the magnitude of the driving current and stopped. Thus, in the third example, both the first movable part 3 and the second movable part 4 are used statically.

[0044] In the fourth and fifth examples, only the first movable part 3 is driven. In the fourth example, by applying a high-frequency drive current to the first drive coil 11, the first movable part 3 is oscillated according to the resonance frequency. In the fifth example, by applying a drive current of a certain magnitude to the first drive coil 11, the first movable part 3 is rotated and stopped around the first axis X1 according to the magnitude of the drive current. The fourth and fifth examples can be used, for example, when the second movable part 4 is not provided. [Method of manufacturing mirror device]

[0045] While referring to FIGS. 3 to 8, a method of manufacturing the mirror device 1 will be described. First, a pre-processed SOI wafer 80 is prepared (preparation step, FIG. 3(a)). The SOI wafer 80 has a support layer 81, a device layer 82, and an intermediate layer 83. The SOI wafer 80 has a plurality of regions R. Each of the plurality of regions R will become the SOI substrate 8 of the mirror device 1 after the dicing step described later. The plurality of regions R are set to be arranged in a lattice pattern, for example, and a dicing line L is set at the boundary between adjacent regions R. The SOI wafer 80 is diced along the dicing line L in the dicing step.

[0046] Subsequently, a plurality of parts S each corresponding to the structure 50 are formed on the SOI wafer 80 (first formation step, FIG. 3(b)). The "part corresponding to the structure 50" means the part that will become the structure 50 after the dicing step. In the first formation step, the structure 50 is formed in each of the plurality of regions R. The structure 50 is composed of the support part 2, the first movable part 3, the second movable part 4, a pair of first connecting parts 5, and a pair of second connecting parts 6 as described above. The structure 50 (part S) is formed using MEMS technology (patterning, etching, etc.). Also, in the first formation step, the first drive coil 11, the second drive coil 12, etc. are formed in each of the plurality of regions R. In the first formation step, the first movable part 3 can oscillate around the first axis X1 with respect to the second movable part 4 and can oscillate around the first axis X1 and the second axis X2 with respect to the support part 2, and the second movable part 4 can oscillate around the second axis X2 with respect to the support part 2.

[0047] In the first forming step, for example, first, the first drive coil 11, the second drive coil 12, the wirings 15a, 15b, 16a, 16b, and the electrode pads 21a, 21b, 22a, 22b are formed in each region R (wiring forming step). Subsequently, the support portion 2, the first movable portion 3, the second movable portion 4, the pair of first connecting portions 5, and the pair of second connecting portions 6 are formed in each region R (structural body forming step). The structural body forming step may be carried out before the wiring forming step.

[0048] Subsequently, a mirror layer 7 is formed on the portion corresponding to the first movable portion 3 in each of the plurality of portions S (second forming step, Fig. 4(a)). More specifically, a mirror layer 7 including an adhesion layer 71, a diffusion prevention layer 72, and a reflection layer 73 is formed on the surface 31a of the first portion 31 in the first movable portion 3. In this example, the mirror layer 7 is formed by sputtering (sputtering method), but the mirror layer 7 may be formed by vapor deposition (vapor deposition method).

[0049] Figs. 5(a) and 5(b) are diagrams for explaining the second forming step. As shown in Fig. 5(a), first, a shadow mask 91 made of silicon is disposed on the plurality of portions S. The shadow mask 91 is formed with an opening 91a for exposing the formation planned region of the mirror layer 7. Subsequently, as shown in Fig. 5(b), the mirror layer 7 is formed by sputtering. After the formation of the mirror layer 7, the shadow mask 91 is removed. As shown in Fig. 5(b), in the mirror layer 7 formed by sputtering, the central portion is thicker than the edge portion. Note that the opening 91a of the shadow mask 91 may be larger than the mirror layer 7. In this case, a mirror layer 7 having a uniform thickness can be formed.

[0050] When the mirror layer 7 is formed by sputtering or vapor deposition in this way, the temperature of the SOI wafer 80 rises to nearly 100°C, for example, during processing. When the temperature of the SOI wafer 80 drops from this state, residual stress may occur in the mirror layer 7 due to the difference in the coefficient of thermal expansion between the mirror layer 7 and the SOI wafer 80, etc. In this case, warping may occur in the mirror layer 7 and the first movable portion 3 due to the residual stress.

[0051] More specifically, it is considered that residual stress is generated in the mirror layer 7 for the following three reasons. (1) Difference in coefficient of thermal expansion between the mirror layer 7 and the SOI wafer 80 (2) Difference in lattice constant between the mirror layer 7 and the SOI wafer 80 (3) Argon atom trapping in the SOI wafer 80 and the mirror layer 7 due to sputtering

[0052] Regarding (1), during the formation of the mirror layer 7, the temperature of the SOI wafer 80 may be increased. When returning to room temperature from this state, the mirror layer 7 and the SOI wafer 80 contract. The degree of contraction differs depending on the coefficient of thermal expansion. When the coefficient of thermal expansion of the mirror layer 7 is smaller than that of the SOI wafer 80, compressive stress is generated in the mirror layer 7 so that the mirror layer 7 warps convexly. When the coefficient of thermal expansion of the mirror layer 7 is larger than that of the SOI wafer 80, tensile stress is generated in the mirror layer 7 so that the mirror layer 7 warps concavely. Also, not only the difference in coefficient of thermal expansion between the mirror layer 7 and the SOI wafer 80, but also the difference in coefficient of thermal expansion between the plurality of layers (adhesion layer 71, diffusion prevention layer 72, and reflection layer 73) constituting the mirror layer 7 causes residual stress to be generated in the mirror layer 7.

[0053] Regarding (2), the lattice constant of the mirror layer 7 is different from that of the SOI wafer 80. In the vicinity of the interface between the mirror layer 7 and the SOI wafer 80, the lattice constant of the mirror layer 7 tends to approach that of the SOI wafer 80. On the other hand, as the distance from the interface increases, the lattice constant of the mirror layer 7 approaches the value inherent to the substance. Therefore, distortion occurs in the mirror layer 7 in the vicinity of the interface, and stress is generated accordingly. Also, not only the difference in lattice constant between the mirror layer 7 and the SOI wafer 80, but also the difference in lattice constant between the plurality of layers (adhesion layer 71, diffusion prevention layer 72, and reflection layer 73) constituting the mirror layer 7 causes residual stress to be generated in the mirror layer 7.

[0054] (3) Regarding this, in sputtering, sputtered atoms emitted from the target enter the SOI wafer 80 to form a thin film. At the same time, argon cations that have collided with the target are neutralized at a certain rate and enter the SOI wafer 80 and the mirror layer 7 being formed with high kinetic energy. By the argon atoms entering into the interstices of the crystal lattice within the mirror layer 7 and expanding the lattice spacing, compressive stress is generated in the mirror layer 7 such that the mirror layer 7 warps convexly.

[0055] The direction and magnitude of the warpage generated in the mirror layer 7 and the first movable part 3 vary depending on the material, thickness, area, formation method, etc. of the mirror layer 7. For example, in the present embodiment, as shown in FIG. 4(a), the mirror layer 7 curves convexly, but there may also be a case where the mirror layer 7 curves concavely as shown in FIG. 9(a) described later. The larger the area (diameter) of the mirror layer 7, the greater the amount of warpage of the mirror layer 7. As described above, at the completion of the second formation step, compressive stress remains in the adhesion layer 71 and the diffusion prevention layer 72, and tensile stress remains in the reflection layer 73. These stresses may also remain after the heating step. That is, at least at the completion of the second formation step, it is sufficient that compressive stress remains in the adhesion layer 71 and the diffusion prevention layer 72 and tensile stress remains in the reflection layer 73.

[0056] Subsequently, the SOI wafer 80 is heated (heating step, FIG. 4(b)). In this example, the entire SOI wafer 80 is heated. By heating the SOI wafer 80, the residual stress present in the mirror layer 7 is relaxed (annealing treatment). In the present embodiment, by relaxing the residual stress, the amount of warpage of the mirror layer 7 decreases and the mirror layer 7 is flattened. After the heating step, a cleaning step of cleaning the SOI wafer 80 is performed. The cleaning step may be performed when foreign matter adheres to the mirror layer 7 in the heating step, may be always performed, or may be omitted.

[0057] In the heating process, it is considered that the residual stress is relaxed for the following reasons. First, the formation of a stress relaxation layer (alloy layer) between the mirror layer 7 and the SOI wafer 80 can be mentioned. In the heating process, a part of the atoms constituting the mirror layer 7 diffuses. Due to this diffusion of atoms, a stress relaxation layer (alloy layer) is formed between the mirror layer 7 and the SOI wafer 80, or between the adhesion layer 71, the diffusion prevention layer 72, and the reflection layer 73 constituting the mirror layer 7 so as to reduce the difference in lattice constants. As a result, it is considered that the residual stress is relaxed. As another reason, in the heating process, as described in (3) above, the argon atoms trapped between the crystal lattices in the mirror layer 7 are released into the atmosphere. As a result, it is considered that the residual stress is relaxed.

[0058] Figure 6 is a graph showing an example of the change in the warpage amount of the mirror layer 7 in the heating process. The horizontal axis represents the elapsed time (unit: hour) from the start of heating, and the vertical axis represents the warpage amount (unit: nm) of the mirror layer 7. In this example, the SOI wafer 80 was heated at 150°C for 30 hours. As shown in Figure 6, the warpage amount at the start of heating was about 300 nm, but it can be seen that the mirror layer 7 became substantially flat by the heating process, and the change in the warpage amount became smaller with the passage of time. The warpage amount of the mirror layer 7 is a value measured by the same method as the measurement process described later.

[0059] In the heating process, the heating temperature for heating the SOI wafer 80 is set, for example, to be 60°C or higher and 300°C or lower. The higher the heating temperature, the shorter the heating time can be. However, if the heating temperature is too high, problems such as cracks and metal diffusion may occur. The heating temperature of 150°C in the embodiment is a value obtained by adding 70°C, which is assumed to be the maximum value of the ambient temperature of the mirror device 1, 70°C, which is assumed to be the self-heating temperature, and 10°C of the margin temperature. The heating time is set to be equal to or longer than the time until the change in the warpage amount saturates and becomes small based on the relationship between the time and the warpage amount obtained in advance. For example, in the case of FIG. 6, since the change in the warpage amount reaches saturation in about 5 hours, the heating time may be 5 hours or longer. By setting the heating time to be about the time until the change in the warpage amount reaches saturation, the energy for heating can be reduced. The heating temperature is preferably set to be higher than at least the self-heating temperature of the mirror device 1 (the temperature of the mirror device 1 during driving) in order to surely suppress the change in the warpage amount at the customer site.

[0060] During heating, the SOI wafer 80 is placed in a constant temperature bath (oven). Thereby, the entire SOI wafer 80 is heated, and thus the portions corresponding to the first movable portions 3 in each of the plurality of portions S are heated simultaneously. One SOI wafer 80 may be placed in the constant temperature bath, or a plurality of SOI wafers 80 (for example, 2, 6, or 12) may be placed. The SOI wafer 80 may be placed horizontally or vertically (along the vertical direction) in the constant temperature bath. From the viewpoint of preventing foreign matter from adhering to the mirror layer 7, the oven is preferably a clean oven.

[0061] The warpage amount of the mirror layer 7 may decrease or increase depending on the heating process as in this embodiment. Whether the warpage amount increases or decreases depends on the material, thickness, area, and formation method of the mirror layer 7, etc. In this embodiment, the mirror layer 7 is curved convexly before heating, and the warpage amount of the mirror layer 7 decreases due to the heating process. However, the mirror layer 7 is curved convexly before heating, and the warpage amount of the mirror layer 7 may increase due to the heating process. Also, as in the modification example described later, the mirror layer 7 may be curved concavely before heating, and the warpage amount of the mirror layer 7 may increase due to the heating process. Or, the mirror layer 7 may be curved concavely before heating, and the warpage amount of the mirror layer 7 may decrease due to the heating process. Further, the mirror layer 7 that was curved convexly before heating may be curved concavely due to the heating process, or the mirror layer 7 that was curved concavely before heating may be curved convexly due to the heating process. Note that an increase in the warpage amount means an increase in the absolute value of the warpage amount. For example, when the warpage amount changes from 200 nm to 300 nm or from -200 nm to -300 nm. A decrease in the warpage amount means a decrease in the absolute value of the warpage amount. For example, when the warpage amount changes from 200 nm to 100 nm or from -200 nm to -100 nm. Also, a positive warpage amount means that the height of the central portion of the mirror layer 7 is higher than the peripheral portion (convex shape), and a negative warpage amount means that the height of the central portion of the mirror layer 7 is lower than the peripheral portion (concave shape).

[0062] Subsequently, for each of the plurality of portions S, the warpage amount of the mirror layer 7 is measured (measurement step). For example, the PV value and the shape data (3D data) of the mirror layer 7 are measured using a laser interferometer. As described above, the diameter of the mirror layer 7 in the present embodiment is 2 mm. In the present embodiment, the PV value and the shape data of the region having a diameter of 1.9 mm concentric with the mirror layer 7 are measured. The PV value represents the height difference between the highest point and the lowest point of the mirror layer 7 (mirror surface 73a) in the measurement range. Since the PV value is represented by an absolute value, the shape data is also measured in order to determine whether the mirror layer 7 is convex or concave (whether the warpage amount is a positive value or a negative value). A predetermined mark is attached to the structure 50 in which the warpage amount of the mirror layer 7 is larger than a predetermined value (marking). The marked structure 50 (mirror device 1) is removed, for example, after the cutting step. Note that the warpage amount of the mirror layer 7 may be measured by measuring the curvature of the mirror layer 7.

[0063] Subsequently, the SOI wafer 80 is cut at the dicing line L so that the plurality of portions S are separated from each other (cutting step, FIG. 7). For example, by irradiating a laser beam, a modified region is formed inside the SOI wafer 80 along the dicing line L, and the SOI wafer 80 is cut by expanding a crack in the thickness direction of the SOI wafer 80 from the modified region by means of tape expansion or the like. In the cutting step, the SOI wafer 80 may be cut by another cutting method such as blade dicing. Through the above steps, a plurality of mirror devices 1 are obtained.

[0064] Thereafter, as shown in FIG. 8, each mirror device 1 is housed in a package 60. The package 60 includes a main body portion 61 that houses the mirror device 1, and a transparent window member 62 that is disposed so as to close the opening 61a of the main body portion 61. The light reflected by the mirror device 1 passes through the window member 62 and enters the mirror layer 7. [Operations and Effects]

[0065] As described above, residual stress may occur in the mirror layer 7 during the formation of the mirror layer 7, and warping may occur in the mirror layer 7 due to the residual stress. If the mirror device 1 is shipped in such a state, there is a concern that the amount of warping of the mirror layer 7 may change when the residual stress is relaxed by the environmental temperature or self-heating during use. On the other hand, in the manufacturing method of the mirror device 1 according to the embodiment, a plurality of portions S each corresponding to the structure 50 are formed on the SOI wafer 80, and after the mirror layer 7 is formed on the portion corresponding to the first movable portion 3 in each of the plurality of portions S, the SOI wafer 80 (the portion corresponding to the first movable portion 3 in each of the plurality of portions S) is heated. Thereby, the residual stress existing in the mirror layer 7 can be relaxed (released), and it is possible to suppress a change in the amount of warping of the mirror layer 7 during the use of the mirror device 1. As a result, it is possible to suppress a change in the size and focal position of the spot of the laser light reflected by the mirror layer 7 during the use of the mirror device 1. Further, in the manufacturing method of the mirror device 1 according to the embodiment, the SOI wafer 80 is cut after the heating step. Thereby, compared with the case where the heat treatment is performed after the wafer is cut, the temperature of the mirror layer 7 during heating can be made uniform among the plurality of portions S. That is, as described above, the heat treatment is performed, for example, in a constant temperature bath, but due to the influence of air convection, the position of the heat source and the heated object, etc., there may be a temperature variation depending on the position in the constant temperature bath. When the heat treatment is performed for each chip after the wafer is cut (after chip formation), there is a concern that the chip may be heated at a temperature different from the set temperature depending on the location where the chip is placed. On the other hand, in the manufacturing method of the mirror device 1 according to the embodiment, the heat treatment is performed in the state of the SOI wafer 80 having high thermal conductivity, and since heat easily conducts in the SOI wafer 80, the temperature of the mirror layer 7 can be made uniform among the plurality of portions S. As a result, it is possible to suppress variations in the quality of the mirror device 1. Further, by heating in the wafer state, a large number of mirror devices 1 can be arranged in the constant temperature bath. As a result, the manufacturing efficiency of the mirror device 1 can be improved. Furthermore, in the measurement step, the amount of warping of the mirror layer 7 can be measured in the wafer state.Accordingly, since the position of the mirror layer 7 can be easily grasped accurately, the measurement efficiency can be improved. Further, when a cleaning process of cleaning the mirror layer 7 after heating is carried out, it can be cleaned in the wafer state, and the workability of cleaning can be improved. Further, in the manufacturing method of the mirror device 1 according to the embodiment, since the SOI wafer 80 is cut after the heating process, the fragments of the SOI wafer 80 generated during cutting and attached to the mirror layer 7 are heated, so that the semiconductor material constituting the fragments diffuses into the mirror layer 7. This situation can be suppressed, and the quality of the mirror device 1 can be ensured. Also, it is not necessary to form a protective film on the mirror layer 7 to prevent the attachment of the fragments to the mirror layer 7. Further, when the heating process is carried out after the mirror device 1 is housed in the package 60, since the sealing resin or the like used for the package 60 may be deteriorated by heating, the upper limit of the heating temperature is restricted. In contrast, in the manufacturing method of the mirror device 1 according to the embodiment, since heating is performed in the wafer state, the heating temperature can be set regardless of the deterioration start temperature of the sealing resin, and the manufacturing efficiency can be improved. As described above, according to the manufacturing method of the mirror device 1 according to the embodiment, the mirror device 1 having a movable part can be manufactured favorably.

[0066] A measurement process for measuring the amount of warpage of the mirror layer 7 is carried out between the heating process and the cutting process. Accordingly, the amount of warpage of the mirror layer 7 can be measured in the wafer state, and the measurement efficiency can be improved.

[0067] In the cutting process, a modified region is formed inside the SOI wafer 80 by irradiating with a laser beam, and the SOI wafer 80 is cut by extending a crack in the thickness direction of the SOI wafer 80 from the modified region (stealth dicing). Thereby, the stress acting on the SOI wafer 80 during cutting can be reduced, and deformation of the mirror layer 7 and the first movable part 3 due to the stress can be suppressed. Also, it is possible to suppress a change in the warpage amount of the mirror layer 7 during cutting. Further, in the above-described embodiment, in addition to the first movable part 3 being swingable before the cutting process, since the mirror layer 7 is heated before the cutting process, it is particularly effective to use stealth dicing capable of suppressing breakage of the first movable part 3 and a change in the warpage amount.

[0068] The second forming step is performed after the first forming step. Thereby, it is possible to suppress a situation in which the quality of the mirror layer 7 deteriorates due to heat when forming the plurality of portions S. That is, contrary to the above-described embodiment, when the mirror layer 7 is formed on the portion corresponding to the first movable part 3 and then the plurality of portions S are formed in the SOI wafer 80, metal diffusion may occur between the adhesion layer 71 (titanium) and the reflective layer 73 (gold) constituting the mirror layer 7 due to heat when forming the plurality of portions S, and the reflectance of the mirror layer 7 may decrease. On the other hand, by forming the mirror layer 7 after forming the plurality of portions S as in the above-described embodiment, such a situation can be suppressed and the quality of the mirror layer 7 can be ensured. When the diffusion prevention layer 72 is formed of tungsten, metal diffusion between the adhesion layer 71 and the reflective layer 73 can be effectively suppressed as compared with the case where the diffusion prevention layer 72 is formed of platinum. On the other hand, when the diffusion prevention layer 72 is formed of platinum, the stress generated by the diffusion prevention layer 72 can be reduced and handling can be facilitated as compared with the case where the diffusion prevention layer 72 is formed of tungsten.

[0069] In the heating process, by heating the SOI wafer 80, the warpage amount of the mirror layer 7 can be reduced. Thereby, the residual stress existing in the mirror layer 7 can be relaxed, and it is possible to suppress a change in the warpage amount of the mirror layer 7 during the use of the mirror device 1. Also, as described above, in the heating process, the warpage amount of the mirror layer 7 may be increased by heating the SOI wafer 80. Also in this case, the residual stress existing in the mirror layer 7 can be relaxed, and it is possible to suppress a change in the warpage amount of the mirror layer 7 during the use of the mirror device 1.

[0070] In the second formation process, the mirror layer 7 is formed by sputtering. Thereby, the mirror layer 7 can be formed favorably. That is, when forming the mirror layer 7 by sputtering, since it is not necessary to rotate the wafer as in the case of vapor deposition, damage or the like is less likely to occur in the structure 50 including the hollow structure. Also, in sputtering, the directivity is high, and it is difficult for the metal to adhere to locations other than the mirror layer 7. In vapor deposition with low directivity, there is a risk that the metal passes through the slit (gap) between the support portion 2 and the movable mirror portion 10 and wraps around to the back side of the movable mirror portion 10 or adheres to the support portion 2. On the other hand, by using sputtering with high directivity, such a situation can be suppressed. Also, in sputtering, a high melting point material that is difficult to use in vapor deposition can be used. Also, the thickness of the mirror layer 7 can be easily controlled. On the other hand, when forming the mirror layer 7 by vapor deposition, since about 20 wafers can be processed at a time, the manufacturing efficiency can be improved. As described above, when using sputtering, the warpage amount of the mirror layer 7 is likely to increase due to argon atom trapping during film formation, and since the trapped argon is released into the atmosphere in the heating process, the warpage amount changes greatly. According to the manufacturing method of the mirror device 1 according to the embodiment, even in such a case, it is possible to effectively suppress a change in the warpage amount of the mirror layer 7 during the use of the mirror device 1.

[0071] The mirror device 1 includes a first driving coil 11 and a second driving coil 12 for applying a driving force to the movable mirror section 10. In this case, heat is likely to be generated when the mirror device 1 is in use. However, according to the manufacturing method of the mirror device 1 according to the embodiment, even in such a case, it is possible to suppress a change in the amount of warping of the mirror layer 7 when the mirror device 1 is in use.

[0072] In the heating step, the SOI wafer 80 is heated to 60°C or higher and 300°C or lower. Thereby, the residual stress existing in the mirror layer 7 can be effectively relaxed.

[0073] The maximum width of the mirror layer 7 is 0.5 mm or more and 30 mm or less. In this case, the amount of warping of the mirror layer 7 is likely to change when the mirror device 1 is in use. However, according to the manufacturing method of the mirror device 1 according to the embodiment, even in such a case, it is possible to suppress a change in the amount of warping of the mirror layer 7 when the mirror device 1 is in use.

[0074] The mirror layer 7 includes an adhesion layer 71, a diffusion prevention layer 72, and a reflection layer 73 formed in this order on the first movable section 3. Thereby, by including the adhesion layer 71, the mirror layer 7 can be stably formed on the first movable section 3. Also, by including the diffusion prevention layer 72, it is possible to suppress the occurrence of metal diffusion between the reflection layer 73 and the adhesion layer 71 during heating.

[0075] The mirror layer 7 includes an adhesion layer 71 and a diffusion prevention layer 72 in which compressive stress remains at the completion of the second formation step, and a reflection layer 73 in which tensile stress remains at the completion of the second formation step. Thereby, the amount of warping of the mirror layer 7 before the heating step can be reduced. Also, the change in the amount of warping of the mirror layer 7 in the heating step can be reduced. As a result, the heating time can be shortened and the amount of warping of the mirror layer 7 can be easily controlled.

[0076] In the heating process, the entire SOI wafer 80 is heated. As a result, the temperature of the mirror layer 7 during heating can be made uniform among a plurality of portions S. [Modification Example]

[0077] FIGS. 9(a) and 9(b) are diagrams for explaining a method of manufacturing the mirror device 1 according to the modification example. In this modification example, as shown in FIG. 9(a), the mirror layer 7 is curved in a concave shape before the heating process. Then, as shown in FIG. 9(b), by heating the SOI wafer 80 in the heating process, the amount of warpage of the mirror layer 7 increases.

[0078] FIG. 10 is a graph showing an example of the change in the amount of warpage of the mirror layer 7 in the heating process of the modification example. In this example, the SOI wafer 80 was heated at 150° C. for 30 hours. In FIG. 10, the changes in the amount of warpage for five samples are shown by different line types. As shown in FIG. 10, for any of the samples, the amount of warpage at the start of heating was about 100 nm, but the amount of warpage increased to about 250 - 350 nm due to the heating process, and it can be seen that the change in the amount of warpage became smaller with the passage of time. In the case of FIG. 10, since the change in the amount of warpage reached saturation in about 2 hours, the heating time may be 2 hours or more. By setting the heating time to about the time until the change in the amount of warpage reaches saturation, the energy for heating can be reduced.

[0079] FIG. 11 is a graph showing an example of the change in the amount of warpage of the mirror layer 7 in the reliability test. In this reliability test, the mirror device 1 obtained by the method of manufacturing the mirror device 1 according to the modification example was operated, and the amount of warpage of the mirror layer 7 during operation was measured. Specifically, the amount of warpage of the mirror layer 7 in the initial state (0 hours) was set to 0 nm, and the change in the amount of warpage of the mirror layer 7 was measured every 250 hours up to 1000 hours. The first movable part 3 was continuously operated with an optical swing angle of 10° around the first axis X1 and an optical swing angle of 10° around the second axis X2. As shown in FIG. 11, it can be seen that the change in the amount of warpage of the mirror layer 7 during operation was suppressed to ±50 nm or less.

[0080] The present invention is not limited to the above-described embodiments. For example, the materials and shapes of the respective components are not limited to the materials and shapes described above, and various materials and shapes can be adopted. In the above embodiment, the mirror device 1 was configured to be electromagnetic drive type, but the mirror device 1 may be configured to be piezoelectric drive type or electrostatic drive type. In the case of piezoelectric drive type, for example, a piezoelectric film (piezoelectric element) may be provided instead of the first drive coil 11 and the second drive coil 12.

[0081] The first drive coil 11 may be provided on the second movable part 4. Even in this case, the first movable part 3 can be swung around the first axis X1 at the resonance frequency. Specifically, when a drive current having a frequency equal to the resonance frequency of the first movable part 3 around the first axis X1 is input to the first drive coil 11, the second movable part 4 vibrates slightly around the first axis X1 at that frequency. When this vibration is transmitted to the first movable part 3 via the first connecting part 5, the first movable part 3 can be swung around the first axis X1 at that frequency. When the first drive coil 11 or the piezoelectric element is provided on the first movable part 3, heat is likely to be transmitted to the mirror layer 7 because the heat source is close to the mirror layer 7. However, according to the manufacturing method of the mirror device 1 described above, even in such a case, it is possible to suppress a change in the amount of warpage of the mirror layer 7 during use of the mirror device 1.

[0082] The second forming step may be performed before the first forming step. For example, after the wiring forming step described above is performed, the mirror layer 7 may be formed on the portion of the SOI wafer 80 corresponding to the first movable part 3, and then the structure forming step may be performed. The measurement step may be omitted. The first connecting part 5 may connect the first movable part 3 to the support part 2 so that the first movable part 3 can move along a predetermined direction. For example, the first movable part 3 may be movable along the optical axis direction A (direction perpendicular to the mirror layer 7).

[0083] The mirror layer 7 may not include the adhesion layer 71. For example, if the mirror device 1 does not become hot during operation, the adhesion layer 71 may be omitted. The mirror layer 7 may not include the anti-reflection layer 72. For example, when a high reflectance is not required for the mirror layer 7, or when the appearance quality of the mirror layer 7 is not a concern, etc., the anti-reflection layer 72 may be omitted. By omitting at least one of the adhesion layer 71 and the anti-reflection layer 72, the thickness of the mirror layer 7 can be reduced. As a result, the warpage amount of the mirror layer 7 before the heating process can be decreased, and the change in the warpage amount of the mirror layer 7 during the heating process can be reduced.

[0084] In the heating process of the above-described embodiment, the entire SOI wafer 80 was heated using a thermostatic bath. However, it is sufficient that the portions corresponding to the first movable portions 3 in each of the plurality of portions S are heated, and the heating means is not limited. For example, without heating the entire SOI wafer 80, spot light such as laser light may be irradiated so that only the portions corresponding to the first movable portions 3 in each of the plurality of portions S are simultaneously heated. Even in this case, heat conduction within the SOI wafer 80 enables uniform heating of the portions corresponding to the first movable portions 3 in each of the plurality of portions S. Also, even if there are variations in the output of the irradiated laser light, uniform heating can be achieved. In the heating process, heating is performed using a heat source located outside the mirror device 1, rather than self-heating generated by driving the mirror device 1.

Explanation of Reference Numerals

[0085] 1... mirror device, 2... support portion, 3... first movable portion, 4... second movable portion, 5... first connecting portion, 6... second connecting portion, 7... mirror layer, 11... first driving coil, 12... second driving coil, 50... structure, 80... SOI wafer, S... portion.

Claims

1. A method for manufacturing a mirror device, comprising a structure having a support portion, a movable portion, and a connecting portion that connects the movable portion to the support portion so that the movable portion can swing or move, and a mirror layer provided on the movable portion, a first forming step of forming a plurality of portions each corresponding to the structure on a wafer such that a portion corresponding to the movable portion in each of the plurality of portions can swing or move with respect to a portion corresponding to the support portion in each of the plurality of portions; a second forming step of forming the mirror layer on a portion corresponding to the movable portion in each of the plurality of portions; a heating step of heating a portion corresponding to the movable portion in each of the plurality of portions in a state where the portion corresponding to the movable portion in each of the plurality of portions can swing or move with respect to a portion corresponding to the support portion in each of the plurality of portions after the first forming step and the second forming step; a cutting step of cutting the wafer so that the plurality of portions are separated from each other in a state where a portion corresponding to the movable portion in each of the plurality of portions can swing or move with respect to a portion corresponding to the support portion in each of the plurality of portions after the heating step. The method for manufacturing a mirror device includes the above steps.

2. The method for manufacturing a mirror device according to claim 1, wherein in the heating step, the portions corresponding to the movable portion in each of the plurality of portions are heated simultaneously.

3. The movable portion has a first portion provided with the mirror layer, and a second portion that surrounds the first portion when viewed from a direction perpendicular to the plane in which the support portion, the movable portion, and the connecting portion are arranged, and is connected to the support portion by the connecting portion. The method for manufacturing a mirror device according to claim 1 or 2.

4. The structure is formed of a semiconductor substrate including a support layer, a device layer, and an intermediate layer disposed between the support layer and the device layer. The support portion and the movable portion are constituted by the support layer, the device layer, and the intermediate layer. The method for manufacturing a mirror device according to any one of claims 1 to 3, wherein the thickness of the support layer constituting the movable portion is thinner than the thickness of the support layer constituting the support portion.

5. The method for manufacturing a mirror device according to any one of claims 1 to 4, wherein the thickness of the central portion of the mirror layer is thicker than the thickness of the edge portion of the mirror layer.

6. The method for manufacturing a mirror device according to any one of claims 1 to 5, wherein the lattice constant of the mirror layer is different from the lattice constant of the wafer.

7. The method for manufacturing a mirror device according to any one of claims 1 to 6, wherein at the end of the heating step, the mirror layer is curved convexly.

8. The method for manufacturing a mirror device according to any one of claims 1 to 6, wherein at the end of the heating step, the mirror layer is curved concavely.

9. In the second forming step, the mirror layer is formed by sputtering, and argon atoms penetrate into the mirror layer. The method for manufacturing a mirror device according to any one of claims 1 to 8, wherein in the heating step, the argon atoms trapped in the mirror layer are released into the atmosphere.

10. The method further includes a measuring step of measuring the amount of warpage of the mirror layer between the heating step and the cutting step. After the cutting step, the structure in which the amount of warpage of the mirror layer is determined to be greater than a predetermined value in the measuring step is removed. The method for manufacturing a mirror device according to any one of claims 1 to 9.

11. The method for manufacturing a mirror device according to any one of claims 1 to 10, wherein the wafer has a plurality of regions each corresponding to the structure and arranged in a lattice pattern.

12. The wafer has a plurality of regions each corresponding to the structure. A dicing line extending from one end to the other end of the wafer is set at the boundary between adjacent regions. The method for manufacturing a mirror device according to any one of claims 1 to 11.

13. In the heating step, the portion corresponding to the movable portion in each of the plurality of portions is heated in a state where no protective film is formed on the mirror layer. The method for manufacturing a mirror device according to any one of claims 1 to 12.

Images