JP5098059B2 - Mirror device and method of manufacturing mirror device - Google Patents

Description

  The present invention relates to a mirror device having a variable focal point and an approximate paraboloidal mirror, and a manufacturing method thereof.

  In recent years, optical MEMS (Micro Electro Mechanical System) and optical microsystems have been actively studied and continue to grow greatly. In particular, there are significant developments in various applications such as data communications and high resolution image displays. This is because attention has been paid to improvement in function and miniaturization of optical devices such as cameras.

  For example, in a camera, a problem of chromatic aberration occurs in an optical system using refracted light from a lens, but no chromatic aberration occurs in an optical system using reflected light from a mirror. However, in either of the optical systems described above, it is necessary to move the lens or mirror in order to adjust the focal length, and the size is reduced while maintaining the optical performance due to the movement of the optical system. It is difficult.

  Furthermore, in an optical system using light reflected by a mirror, chromatic aberration does not occur, but if the mirror shape is a non-uniform spherical surface or a non-uniform paraboloid, aberration occurs and the light condensing property is reduced. Is known to decrease. Further, when the mirror has a uniform paraboloid, incident parallel light can be collected at one point without aberration, and light emitted from a point light source can be converted into parallel light. it can.

On the other hand, if a micro mirror having a uniform approximate paraboloid shape and a variable focus is used, it is possible to configure a small optical system having excellent light collecting properties. For example, Non-Patent Documents 1 and 2 report variable focus micromirror devices.
FIG. 15A is a schematic cross-sectional view during non-operation in the configuration example of the conventional micromirror device 70, and FIG.
15A, the micromirror device 70 includes a micromirror 71, a fixed portion 72 that supports the periphery of the micromirror 71, and a fixed electrode 73 disposed below the micromirror 71. Yes. The peripheral edge of the micromirror 71 is supported with respect to the fixed portion 72, and a fixed electrode 73 is disposed below the micromirror 71 with a gap therebetween. The micromirror 71 can be formed using a silicon nitride film (Si ₃ N ₄ ) or the like made of a thin disk. Support of the periphery of the micromirror 71 with respect to the fixing portion 72 is performed by partially supporting the suspension by a suspension or the like and fixing and holding the periphery in a stationary manner (see Non-Patent Documents 3 and 4).
In the micromirror device 70 configured as described above, when a voltage is applied between the micromirror 71 and the fixed electrode 73, the micromirror 71 is deformed by electrostatic attraction. Specifically, as shown in FIG. 15B, the micromirror 71 is deformed downward in a parabolic shape by electrostatic attraction to form a reflective surface having a variable parabolic shape with a variable focus. be able to.

FIG. 16 shows an example of a paraboloidal surface shape when the periphery of the micromirror 71 is partially supported by the suspension 72 or the like with respect to the fixed portion 72.
FIG. 16 is a graph showing a deformation state of the micromirror 71 of FIG. As is apparent from FIG. 16, in the micromirror 71, the actual deformed shape is shifted from 5% to 100% or more in each place with respect to the uniform approximate paraboloid shape B, as indicated by reference numeral A. It will occur.

Non-Patent Documents 3 and 4 report a variable focus micromirror device similar to the micromirror device 70 of FIG. 15 except that the periphery of the micromirror 71 is fixedly held with respect to the fixed portion 72. . The operation of this micromirror device is substantially the same as that of the micromirror device 70 shown in FIG.
FIG. 17 is a graph showing a deformed state when the peripheral edge of the conventional micromirror 71 is fixedly held with respect to the fixing portion 72. The actual deformed shape A of the micromirror 71 is greatly deviated from the uniform approximate paraboloid shape B.

Y. Shao, DL Dickensheets and P. Himmer, "3-D MOEMS m-irror for laser beam pointing and focus control", IEEE J. Sel. Topi. Qua-ntum Electron., Vol.10, No.3, pp 528-534, 16 August 2004 Y. Shao, "MEMS 3D-scan mirror for an endoscopic confocal microscope", Ph.D. Thesis, p.82, Montana State University, November 14, 2005 U. M. Mescheder, C. Estan, G. Somogyi and M. Freudenre-ich, "Distortion optimized focusing mirror device with large aperture", Sensor Actuators, Vol.A130-131, pp.20-27, November 14, 2005 Greger W, Arnold D, Juurischka R, Schoth A, Muller C, Wilde J and Reinecke H, "A new approach for focusing deformable mirror f-abricated in polymer technology", IEEE / LEOS Int. Conf. Optical MEMS, pp. 45 -46, August 1, 2005

In the micromirror device 70 of Non-Patent Documents 1 and 2, a double electrode is provided inside the fixed portion 72 of the micromirror 71 made of a silicon nitride film to which tension is applied, and a shape close to a paraboloid is generated. Yes. Further, the periphery of the fixing portion 72 of the micromirror 71 is drilled to improve deformation around the fixing portion 72.
However, in the conventional micromirror device 70, there is a problem that a uniform paraboloidal mirror with high accuracy cannot be obtained in any case.

  In view of the above problems, the present invention has an object to provide a mirror device capable of obtaining a shape such as a uniform approximate paraboloid with variable focus and high accuracy with a simple configuration, and a method for manufacturing the same. Yes.

  In order to achieve the above object, a mirror device of the present invention has a thin mirror portion and a suspension that suspends the mirror portion, surrounds at least a part of the periphery of the mirror portion, and the mirror portion is surrounded by the suspension. A mirror substrate that is movably supported in a direction perpendicular to the surface; and a support substrate disposed on the surface of the base portion of the mirror substrate. And a fixed electrode portion formed on the outer side of the support portion and facing the mirror portion, and between the fixed electrode portion and the mirror portion. By applying a voltage, the area outside the support part of the mirror part is displaced toward the corresponding fixed electrode side by electrostatic attraction, and the area inside the support part of the mirror part is deformed into a parabolic cross section. That And butterflies.

In the above configuration, preferably, the mirror part is formed in a circular shape, the suspensions are arranged at equiangular intervals with respect to the center of the mirror part, and the support part is formed in an annular shape concentric with the mirror part. The mirror part may be formed in a rectangular shape. In this case, the suspension is arranged with respect to the mutually opposing edges of the mirror part, and the support part is arranged along the inside of the mutually opposing edges of the mirror part.
Preferably, the mirror substrate is composed of a semiconductor layer, and the base portion of the mirror substrate is formed on the semiconductor substrate via an insulating layer. Preferably, the support substrate is made of a glass substrate or a semiconductor substrate.
The fixed electrode portion may be disposed in a recessed portion formed on the surface of the support substrate.
The amount of deformation due to electrostatic attraction in the region inside the support portion of the mirror portion preferably changes corresponding to the voltage, and the focal length of the mirror portion deformed into a uniform approximate paraboloid can be changed. .

  According to the mirror device of the present invention, by applying a voltage between the fixed electrode portion of the support substrate and the mirror portion, the region outside the support portion of the mirror portion is displaced toward the fixed electrode portion by electrostatic attraction. To do. Therefore, a certain upward bending moment about the support portion acts on the region inside the support portion of the mirror portion. Accordingly, the region inside the support portion of the mirror portion is deformed into a uniform approximate paraboloid shape having a concave shape with high accuracy toward the top with the center as the apex. At that time, the magnitude of the electrostatic attractive force is adjusted by appropriately adjusting the applied voltage. Thereby, the magnitude | size of the bending moment mentioned above is adjusted, and the focal distance by the uniform approximate paraboloid shape of the area | region inside the support part of a mirror part is adjusted.

  In order to achieve the above object, the mirror device manufacturing method of the present invention defines the mirror part and the suspension by etching reaching the sacrificial layer from the upper layer side with respect to the first substrate having the upper layer via the sacrificial layer. A first step of forming a groove portion and removing a region corresponding to the mirror portion of the first substrate by etching reaching the sacrificial layer from the first substrate side to produce a mirror substrate; and a surface of the second substrate The second step of forming the support portion with respect to the substrate, the third step of forming the support substrate by forming the fixed electrode portion outside the support portion on the surface of the second substrate, and the third step A fourth step of inverting the mirror substrate fabricated in the first step on the formed support substrate and anodically bonding the base portion of the upper layer of the mirror substrate to the surface of the support substrate. Features.

In the above configuration, preferably, in the second stage, each support portion is defined by forming a recessed portion around the surface region to be the support portion of the support substrate.
In the third step, a metal layer that prevents bonding to the surface of the mirror portion may be formed on the upper surface of each support portion. The metal layer may be formed simultaneously with the fixed electrode portion using the same material as the fixed electrode portion. The mirror substrate may be configured using a semiconductor substrate, and the support substrate may be configured using a glass substrate or a semiconductor substrate.

  According to the method for manufacturing a mirror device of the present invention, a mirror substrate and a support substrate are produced, and the substrate has an accurate uniform parabolic shape with a simple process of anodic bonding of these substrates. A mirror device can be manufactured.

  According to the mirror device of the present invention, a uniform approximate paraboloid shape with variable focus and high accuracy can be obtained with a simple configuration.

  According to the method for manufacturing a mirror device of the present invention, a mirror substrate and a support substrate are produced, and the substrate has an accurate uniform parabolic shape with a simple process of anodic bonding of these substrates. A mirror device can be manufactured.

Hereinafter, the present invention will be described in detail based on the embodiments shown in the drawings.
(Mirror device)
1A and 1B are diagrams schematically showing a configuration of a mirror device according to a first embodiment of the present invention. FIG. 1A is a perspective perspective view, FIG. 1B is a plan view, and FIG. (B) is a schematic sectional drawing at the time of operation | movement at the time of non-operation of the mirror apparatus 10 of FIG.
As shown in FIG. 1, the mirror device 10 includes a mirror substrate 11, and a support substrate 12 including a support portion 12a that supports the mirror substrate 11 and a fixed electrode portion 12b.

  The mirror substrate 11 is made of a Si substrate or the like, and includes a thin mirror portion 11a and a base portion 11c that surrounds the periphery of the mirror portion 11a and supports the mirror portion 11a by a plurality of suspensions 11b. Yes.

In the case of illustration, the mirror part 11a is formed in a circular shape. The peripheral part of the mirror part 11a and the base part 11c are separated from each other by the gap part 11g, and the part not separated by the gap part 11g at the peripheral part of the mirror part 11a is the base part by the suspension 11b which is a plurality of springs. 11c. That is, the mirror part 11a is suspended from the base part 11c via the suspension 11b and supported so as to be movable in the vertical direction.
Here, the suspension 11b has a spring shape such as a linear shape or a zigzag linear shape. The suspensions 11b are arranged at equal angular intervals with respect to the center of the mirror part 11a, so that uniform deformation is not prevented in each radial direction of the mirror part 11a.

  The support substrate 12 is composed of a glass substrate or the like, and as shown in FIG. 2A, is disposed below the above-described mirror substrate 11 in parallel with a predetermined gap g. When the mirror portion 11a is circular, the support substrate 12 includes an annular support portion 12a that protrudes upward from the upper surface thereof, and a fixed electrode portion 12b that is annularly disposed outside the support portion 12a.

  The support part 12a is formed in an annular shape concentric with the center of the mirror part 11a of the mirror substrate 11, and supports the mirror part 11a from below inside the periphery of the mirror part 11a.

The fixed electrode portion 12b is formed on the surface of the support substrate 12 outside the support portion 12a, and is disposed so as to face the outer region 11d outside the support portion 12a at the periphery of the mirror portion 11a. A mirror driving power source 18 for applying a voltage is connected between the mirror substrate 11 and the fixed electrode portion 12b.
Thereby, when a voltage is applied between the mirror unit 11a and the fixed electrode unit 12b from the mirror driving power source 18, an electrostatic attractive force P acts between the fixed electrode unit 12b and the outer region 11d of the mirror unit 11a. . At this time, the electrostatic attractive force P acts on the outer region 11d of the mirror portion 11a at a position outside the support point by the support portion 12a by a distance L and is moved downward. Thus, the mirror portion 11a, inside the inner region 11e from the support point by the support portion 12a, receives a constant bending moment M ₀ around the supporting point, as shown in FIG. 2 (B), centered above Deforms to move toward.

(Deformation of circular mirror)
Here, the deformation | transformation of the mirror part 11a is considered.
FIG. 3 is a schematic diagram for calculating a displacement amount when a load is applied to a beam having both ends fixed.
As shown in FIG. 3, first, when a bending moment M acts on both ends of the beam 20 fixed at both ends, the longitudinal position of the beam 20 is x, the height is y, the Young's modulus is E, and the secondary cross section. When the moment is I, the differential equation of the deflection curve expressed by the following equation (1) is established.
Therefore, when the bending moment M is a function of x, the deflection curve becomes a curve of the cubic or higher of x.
On the other hand, if the bending moment M is constant (M ₀ ), when the above equation (1) is solved for y, y is expressed by the following equation (2), and the deflection of the beam 20 becomes an approximate parabola. I understand that.
That is, when a constant load is applied to the outside of both ends of the beam 20, a constant bending moment M ₀ acts on both ends of the beam 20 and deforms into a uniform approximate parabolic shape.

Next, a method for calculating the displacement amount of the mirror unit 11a of the mirror device 10 shown in FIG. 1 will be described.
4A and 4B are model diagrams used for calculating deformation of the disk 21 supported by the annular support portion when a load is applied, in which FIG. 4A is a perspective view of a mirror device model, and FIG. FIG. 4C is a cross-sectional view.
As shown in FIG. 4A, instead of the beam 20, the disk 21 is supported by the annular support portion 22 inside the peripheral edge 21a, and when a downward load P is applied to the peripheral edge 21a, In an arbitrary cross section passing through the central axis of the disk 21, a bending moment M similar to that in the case of the beam 20 described above is generated, so that the region inside the support portion 22 of the disk 21 is similarly uniform in an approximate paraboloid. It will be transformed into a surface shape. That is, in the disk 21, the center of the disk is the origin, the optical axis is z (positive downward), the length from the fulcrum to the action point is L, and the displacement of the action point is r (r ² = x ² + y ² ). Assuming that the load distribution is P (r) and the bending stiffness is D, this bending stiffness D is given by the following equation (3) when the plate thickness is h and the Poisson's ratio ν.

The differential equation of the deflection curve of the disk 21 is given by the following equation (4).
The general solution of this equation is given by the following equation (5) where Zs is a special solution and C ₁ , C ₂ , C ₃ , and C ₄ are arbitrary constants.
Incidentally, particular solutions Zs, when the P (r) = Cr ^n, given by the following equation (6).
Then, when the bending moment in the circumferential direction, the bending moment in the radial direction, the deflection angle and the shearing force are calculated and the initial conditions and boundary conditions are taken into consideration, the deflection curve of the disk is expressed by the following equation (7).

The deflection curve of the disk corresponds to the deflection of the inner region 11e of the mirror portion 11a shown in FIG. Therefore, from the above equation (7), as shown in FIG. 2B, the center of the inner region 11e of the mirror portion 11a moves upward to be deformed into a uniform approximate paraboloid with high accuracy. Led. In other words, the inner region 11e of the mirror portion 11a is deformed in an approximate paraboloid shape receives a constant bending moment M ₀ around the support point by the support portion 12a by electrostatic attraction P

Here, the electrostatic attractive force P is expressed by the following equation (8), where V is the applied voltage, ε _{0 is} the dielectric constant of vacuum, S is the area of the mirror portion 11a, and u (r) is the amount of movement of the mirror portion 11a. Represented.
The bending moment M ₀ is expressed by M ₀ = P × L 1 where L 1 is the distance from the point of action of the electrostatic attractive force P to the support point by the support portion 12 a.

(Example of circular mirror design)
Table 1 is a table summarizing the relationship between the parameters affecting the deflection amount of the circular mirror portion 11a and the spring constant. The design example of the diameter of the mirror part 11a in the mirror apparatus 10 provided with the circular mirror part 11a, the diameter of the circle of the support part 12a, the spring constant of the mirror part 11a, and the spring constant of the suspension 11b is shown. The number of suspensions 11b was four. The calculation was performed assuming that the Young's modulus of Si was 162 GPa, the Poisson's ratio was 0.22, the vacuum dielectric constant was 8.85 × 10 ⁻¹² F / m, and the mirror thickness was 10 μm. The spring constant of the suspension 11b is designed to be about one-hundred of the spring constant of the mirror part 11a.

(Modification of mirror device)
Next, a mirror device according to a second embodiment of the present invention will be described.
5A and 5B are diagrams schematically showing the configuration of the mirror device 15 according to the second embodiment of the present invention, in which FIG. 5A is a perspective perspective view, and FIG. 5B is a plan view.
As shown in FIG. 5A, the mirror device 15 is different from the mirror device 10 in that the mirror portion 11a of the mirror substrate 11 is rectangular.

  The support substrate 12 includes support portions 12c and 12d that support the mirror portion 11a. The two support parts 12c and 12d have a rectangular parallelepiped shape, and their longitudinal directions are arranged in parallel on both short sides of the mirror part 11a. The longitudinal dimension of the support parts 12c and 12d may be about the short side dimension (b) of the mirror part 11a. The length of the long side from the center of the mirror part 11a to the support parts 12c and 12d is a, and the length of the short side is b.

  The two fixed electrode portions 12e and 12f are rectangular electrodes, and their longitudinal directions are arranged outside the two support portions 12c and 12d, respectively. That is, the two fixed electrode portions 12e and 12f are disposed at the lower portion on the short side of the mirror portion 11a. The two fixed electrode portions 12e and 12f are connected to each other and connected to the mirror drive power source 18.

  As shown in FIG. 5B, the suspension 11b is disposed at each rectangular vertex of the mirror portion 11a, and the mirror portion 11a is suspended from the base portion 11c. Other configurations such as the mirror driving power source 18 are the same as those of the mirror device 10, and the description thereof is omitted.

(Deformation of rectangular mirror)
The operation of the mirror of the mirror portion 11a having a rectangular shape will be described.
The rectangular mirror portion 11a is regarded as a beam, and a deflection curve is calculated. The bending moment M _{0 in} the case of a beam is given by the following equation (9).
Here, P is electrostatic attraction, and L is the distance from the point of action of electrostatic attraction to the support point by the support portion 12d (see FIG. 2A).

From equation (1), when boundary condition x = a, y = 0, and from symmetry, x = 0 and dy / dx = 0, the following equation (10) is obtained.

Moment of inertia of area I, since it is given by I = ^bh 3/12, the equation (10) repositioning the down exactly, represented by the following (11).
Here, b is the length of the short side of the mirror part 11a, and h is the thickness of the mirror part 11a. Thus, by setting the variables P, L, a, b, and h in the equation (11), the deflection shape of the mirror portion 11a having a rectangular shape can be changed.

(Design example of rectangular mirror)
Table 2 is a table summarizing the relationship between the parameters affecting the deflection amount of the rectangular mirror portion 11a and the spring constant. The calculation example of the length of the mirror part 11a which influences the deflection amount of a rectangular mirror, the support space | interval by the support part 12a, the spring constant of the mirror part 11a, and the spring constant of the suspension 11b is shown. Since the width (short side b) of the rectangular mirror supporting the two sides is irrelevant to the deflection, the width is 500 μm, and the number of suspensions 11b is four. The Si Young's modulus, Poisson's ratio, vacuum dielectric constant, and thickness of the mirror portion 11a were the same as those of the circular mirror portion 11a. The spring constant of the suspension 11b was designed to be about 1/100 of the mirror spring constant.

  According to the mirror devices 10 and 15 of the present invention, the driving means of the mirror portion 11a, that is, the mirror portion 11a, the support portion 12a, and the fixed electrode portion 12b can be manufactured by so-called MEMS technology as will be described later. Thereby, the mirror devices 10 and 15 are configured in a small size, and the mirror portion 11a is formed in a uniform parabolic shape with high accuracy, and the focal length can be changed.

(Example of mirror device configuration)
Next, a specific configuration example of the mirror device will be described.
6 is a plan view showing the configuration of the mirror device 30, and FIG. 7 is a cross-sectional view in the XX direction of FIG.
As shown in FIGS. 6 and 7, the mirror device 30 includes a mirror substrate 31 and a support substrate 32 in the same manner as the mirror devices 10 and 15 shown in FIGS. 1 and 5. The mirror substrate 31 is composed of a Si substrate or the like, and includes a thin plate-like mirror portion 31a and a base portion 31c that surrounds the periphery of the mirror portion 31a and is supported by a suspension 31b. As the Si substrate used for the mirror substrate 31, a so-called SOI (Silicon On Insulator) wafer can be used. The mirror part 31a is formed in a circular shape as shown in FIG. 6, for example. Most of the periphery of the mirror part 31a and the base part 31c are separated by the gap part 31g, and the part that is not separated by the gap part 31g at the periphery of the mirror part 31a is the base part by the suspension 11b serving as a plurality of springs. 31c. In the case of illustration, it is suspended by the base part 31c by the four suspensions 31b, and is supported so that a movement to an up-down direction is possible. The suspension 31b has a spring shape such as a zigzag line or a line as illustrated.

  The suspensions 31b are arranged at equiangular intervals with respect to the center of the mirror part 31a, so that uniform deformation in each radial direction of the mirror part 31a is not prevented.

  On the upper surface of the base portion 31c of the mirror substrate 31, a Si substrate 31e is formed via a sacrificial layer 31d. Thereby, the base part 31c is reinforced by the Si substrate 31e. Here, the mirror part 31a, the suspension 31b, and the base part 31c are selected to have a thickness of about 10 μm, for example.

  The support substrate 32 is composed of a glass substrate or the like, and as shown in FIG. 7, on the surface of the glass substrate, an annular support portion 32a protruding upward, and a fixed annularly arranged outside the support portion 32a. Electrode portion 32b. Here, the support portion 32a has an inner edge and an outer edge defined by recessed portions 32c and 32d formed on the surface of the glass substrate, and the upper surface thereof is the same height as the surface of the glass substrate.

  Thereby, the mirror part 31a of the mirror substrate 31 is supported by the upper end of the support part 32a, and the mirror part 31a of the mirror substrate 31 is placed on the bottom surfaces of the concave parts 32c and 32d of the glass substrate by the concave parts 32c and 32d. On the other hand, they are arranged in parallel at a predetermined interval g.

  Here, the gap g is selected to be, for example, about 2 to 15 μm, and the radius a of the support portion 32a is selected to be about 50 to 1000 μm.

  Simultaneously with the recessed portions 32c and 32d, another recessed portion 32e is also formed on the surface of the support substrate 32 outside the recessed portion 32d. The recess 32e is used as an electrode wiring groove.

The fixed electrode portion 32b of the support substrate 32 is annularly arranged on the bottom surface of the outer recessed portion 32d. Thereby, the fixed electrode part 32b is arrange | positioned so that it may oppose the area | region 31f outside the support part 32a of the periphery of the mirror part 31a on the outer side of the support part 32a.
In addition, the shape of the mirror part 31a of the mirror device 30 is not limited to a circle but may be a rectangle. When the mirror part 31a has a rectangular shape, the fixed electrode part 32b may have the same shape as the fixed electrode parts 12e and 12f shown in FIG.

  Therefore, the mirror devices 10, 15, and 30 according to the present invention can form a uniform parabolic shape with high accuracy and are small and light, compared with a mirror device that does not use the conventional MEMS technology. Configured. By integrating, for example, processing circuits on the mirror substrates 11 and 31 or the support substrates 12 and 32, high performance, high speed, low power consumption, and low cost can be realized.

(Manufacturing method of mirror device)
A method for manufacturing the mirror device 30 will be described. The mirror device 30 will be described as the configuration shown in FIGS.
First, manufacture of the mirror substrate 31 will be described.
FIG. 8 is a schematic cross-sectional view sequentially showing a manufacturing method of the mirror substrate 31 shown in FIG.
As the mirror substrate 31, a first substrate 40 having an SOI structure is used. In the first substrate 40, a sacrificial layer 42 made of SiO ₂ and an upper Si layer 43 are sequentially stacked on a silicon substrate 41. Specifically, for example, an upper Si layer 43 having a thickness of 10 μm is formed on the surface of a silicon substrate 41 having a thickness of 200 μm via a sacrificial layer 42 made of SiO ₂ having a thickness of 2 μm.
Then, as shown in FIG. 8A, for example, a positive resist mask pattern 44 is formed on the lower surface of the first substrate 40, and ion etching (referred to as ICP-RIE method) using inductively coupled plasma is performed. Then, etching 45 reaching the sacrificial layer 42 is performed.
Thereby, the region of the silicon substrate 41 corresponding to the mirror part 31a is removed leaving a part.

  Subsequently, as shown in FIG. 8B, a high-resolution positive resist mask pattern 46 is formed on the upper surface of the first substrate 40, that is, the surface of the upper Si layer 43, and the ICP-RIE method is similarly applied. Etching 47 reaching the sacrificial layer 42 is performed by, for example. By this etching 47, the mirror part 31a, the suspension 31b, and the base part 31c are formed in the upper Si layer 43.

Thereafter, as shown in FIG. 8C, the lower surface of the first substrate 40 is subjected to etching 45 of the silicon substrate 41, for example, by vapor-phase hydrofluoric acid, and the remaining region is removed and the mirror portion 31a is formed. The corresponding region of the sacrificial layer 42 is removed.
As a result, the mirror portion 31a is released from the silicon substrate 41 and is supported by the suspension 31b in a floating state.
Thus, the mirror substrate 31 is manufactured.

(Manufacturing method of support substrate)
Next, production of the support substrate 32 will be described.
FIG. 9 is a schematic cross-sectional view sequentially showing a method of manufacturing the support substrate 32 shown in FIG.
A second substrate, for example, a glass substrate 50 is prepared, and as shown in FIG. 9A, a Cr film 51 is formed on the surface of the glass substrate 50 by sputtering or the like. The Cr film 51 is selected to have a thickness of about 250 to 300 nm, for example.
Then, as shown in FIG. 9B, for example, a positive resist mask pattern 52 is formed on the surface of the Cr film 51 and Cr etching 53 is performed. In this case, as an etchant for etching the Cr film 51, for example, a mixed solution of 4.5 g of HCl0 ₄ (70%), H ₂ O 89 cm ^3, and 20 g of diammonium cerium (II) nitrate can be used.

Thereafter, as shown in FIG. 9C, isotropic etching 54 having a depth of, for example, about 3 μm is performed on the surface of the glass substrate 50 using a 50% HF solution.
Thereby, the recessed portions 32c, 32d, and 32e are formed on the surface of the glass substrate 50, and the support portion 32a is defined between the recessed portions 32c and 32d.

Subsequently, after removing the Cr film 51 and the mask pattern 52, as shown in FIG. 9D, for example, a Cr film 55 having a thickness of about 40 μm and a thickness of about 60 μm are formed over the entire surface of the glass substrate 50. An Au film 56 is formed.
Here, since the adhesion of the Au film 56 to the glass substrate 50 is not good, the Cr film 55 having good adhesion to both the Au film 56 and the glass substrate 50 is interposed, so that the Au film 56 indirectly. The adhesion to the glass substrate 50 is enhanced.

Finally, as shown in FIG. 9E, the Cr film 55 and the Au film 56 are pattern-etched to form the fixed electrode portion 32b in the recessed portion 32d and the electrode wiring 32f in the recessed portion 32e.
Note that the Cr film 55 and the Au film 56 on the support portion 32a are also left without being etched. In this case, Au film 56 as an etchant for etching, it can be used a mixed solution consisting of _{I 2} from 1.2g and NH ₄ I to 8g and _{H 2} O to 40 cm ³ and _CH 3 OH to 60cm ³ Prefecture. In order to form the fixed electrode portion 32b, a so-called lift-off process method or the like may be used.
Thus, the support substrate 32 is manufactured.

(Joint method of mirror substrate and support substrate)
FIG. 10 is a schematic cross-sectional view showing anodic bonding of the mirror substrate 31 and the support substrate 32.
As shown in FIG. 10, the mirror substrate 31 manufactured by the method shown in FIG. 8 is inverted and placed on the support substrate 32 manufactured by the method shown in FIG. 9 and heated by the heater 57. At the same time, a voltage is applied by the power source 58 to perform anodic bonding. The conditions for anodic bonding are, for example, 400 ° C. and 100V. This is because, when the voltage is increased to, for example, about 200 to 300 V, the mirror portion 31a is drawn into and joined to the glass substrate 50, so that such joining is excluded. In the mirror device 30, it is not necessary to adhere the entire joint surface with good airtightness, so that the joining can be performed even with low-voltage anodic joining.

  At this time, since the Cr film 55 and the Au film 56 are present on the upper surface of the support portion 32a, the upper surface of the support portion 32a is not bonded to the surface of the mirror portion 31a. Thereby, when the mirror part 31a deform | transforms into a paraboloid shape by a bending moment, it can deform | transform smoothly, without receiving the influence of the support part 32a.

  For example, in the embodiment described above, the mirror substrate 31 is configured by the Si substrate 41, the sacrificial layer 42, and the upper Si layer 43, but is not limited thereto, and is configured by another semiconductor substrate and an upper semiconductor layer. It may be. Although the support substrate 32 is composed of a glass substrate, it is obvious that the support substrate 32 may be composed of other substrates.

  As described above, according to the present invention, extremely excellent mirror devices 10, 15 and 10 that can obtain a uniform approximate paraboloid shape with variable focus and high accuracy can be obtained with a simple configuration. 30 and its manufacturing method are provided.

As Example 1, a mirror device 30 provided with a circular mirror portion 31a having a thickness of 10 μm was manufactured in various dimensions by the manufacturing method described with reference to FIGS. The mirror substrate 31 was made of an SOI substrate, and the support substrate 32 was made of Pyrex (registered trademark) glass.
Here, the diameter of the mirror part 31a was 500 μm, and the diameter of the corresponding support part 32b was 100 μm and 200 μm. When the diameter of the mirror part 31a was 1000 μm, the corresponding support part had a circular diameter of 300 μm and 400 μm. When the diameter of the mirror part 31a was 1500 μm, the diameter of the circle of the corresponding support part 32b was 600 μm. The support interval g was 10 μm in all cases.

  11A and 11B are diagrams showing scanning electron microscope images of the mirror device 30 according to the first embodiment, in which FIG. 11A shows the main part of the surface of the mirror substrate 31 and FIG. 11B shows the main part of the surface of the support substrate 32. Yes. As is clear from FIG. 11, it can be seen that the mirror substrate 31 and the support substrate 32 are manufactured with high precision by fine processing.

The operation characteristics of the mirror device 30 manufactured in the first embodiment will be described.
Shape measurement was performed by applying various voltages of a sine wave (1 Hz) between the mirror portion 31a and the fixed electrode portion 32b of the mirror device 30. A white light interferometer (Zygo) was used for shape measurement.
FIG. 12 is a diagram illustrating the applied voltage dependency in the cross-sectional shape of the mirror portion 31a according to the first embodiment. The diameter of the measured circular mirror part 31a is 1000 μm, and the diameter of the circle of the support part 32b is 400 μm. The horizontal axis in the figure is the dimension (mm) in the diameter direction of the mirror part 31a, and the vertical axis in the figure is the deformation amount (μm) of the mirror part 31a.
As is clear from FIG. 12, at an applied voltage of 100 V or less, the contact of the mirror portion 31a with the support was weak and the shape was inclined. It can be seen that when the applied voltage is 100 V or higher, the contact with the support of the mirror part 31a is strong and the shape is stable, and the central part of the mirror part 31a swells upward as the applied voltage increases.

Table 3 is a table showing the height difference in the applied voltages 0V, 100V, 150V, 200V, and 215V of the actual mirror part 31a. As is apparent from Table 3, the height differences at the applied voltages of 0 V, 100 V, 150 V, 200 V, and 215 V were 150 nm, 840 nm, 1700 nm, and 2600 nm (2.6 μm), respectively. These height differences were found to be in good agreement with the design values.

Table 4 is a table showing the applied voltage, the average double deviation of the deformation amount with respect to the paraboloid at each part of the mirror portion 31a, and the focal length. As shown in Table 4, in the support inner region of the mirror portion 31a, which becomes a uniform approximate paraboloid in principle, the mean square deviation is stable and an error of about several nanometers. Furthermore, it can be seen that when the applied voltage is 100 V, 150 V, 200 V, and 215 V, the focal length varies as 140 mm, 77 mm, 36 mm, and 24 mm. In the external support region, the error from the paraboloid is increasing due to an increase in the amount of change caused by increasing the applied voltage. From this, the focal length could be varied from 24 mm to infinity (∞).

  A mirror device 30 of Example 2 was manufactured in the same manner as Example 1 except that the mirror part 31a was rectangular. The long sides of the rectangle in the mirror part 31a were 1000 μm and 1500 μm, and the short sides were 400 μm.

13A and 13B are diagrams showing a scanning electron microscope image of the mirror device 30 according to the second embodiment, in which FIG. 13A shows the main part of the surface of the mirror substrate 31 and FIG. 13B shows the main part of the surface of the support substrate 32. Yes.
As is apparent from FIG. 13, it can be seen that the mirror substrate 31 and the support substrate 31 having the linear support portions 32a parallel to each other are manufactured with high precision by fine processing.

The operation characteristics of the mirror device 30 manufactured in the second embodiment will be described.
FIG. 14 is a diagram illustrating the applied voltage dependency in the cross-sectional shape of the mirror portion 31a of the second embodiment. The length of the long side of the measured rectangular mirror part is 1000 μm. The horizontal axis in the figure is the dimension (mm) in the long side direction of the mirror part 31a, and the vertical axis in the figure is the deformation amount (μm) of the mirror part 31a.
As apparent from FIG. 14, the contact of the support portion 32a to the mirror portion 31a is strong due to the applied voltage, the shape is stable, and when the applied voltage is increased from 50V to 200V every 50V, as the applied voltage increases, It can be seen that the central part of the mirror part 31a swells upward.

Table 5 is a table showing the height difference of the mirror portion 31a when the applied voltage is 0V, 100V, and 200V. As shown in Table 5, the height differences at the applied voltages of 0 V, 100 V, and 200 V were found to be 75 nm, 400 nm, and 1900 nm (1.9 μm), respectively. These height differences were found to be in good agreement with the design values.

Table 6 is a table showing the average double deviation and the focal length of the applied voltage and the deformation amount with respect to the paraboloid at each part of the mirror portion 31a in Example 2.
As is apparent from Table 6, when the applied voltage is 0 V to 200 V, the mean square deviation is stably about 1.1 nm or less in the support inner region of the mirror portion 31 a that becomes a uniform approximate paraboloid in principle. It was a very small error. In the entire region of the mirror part, when the applied voltage is 0V, 50V, 100V, 150V, and 200V, the mean square deviations are as small as 2.58 nm, 4.53 nm, 10.7 nm, 23.3 nm, and 51.1 nm, respectively. It was.
Further, in the mirror device 30 according to the second embodiment, the focal lengths obtained when the applied voltage is changed to 0V, 50V, 100V, 150V, and 200V are changed to 710 mm, 370 mm, 150 mm, 70 mm, and 32 mm, respectively. I found out.

  The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the invention described in the claims, and it goes without saying that these are also included in the scope of the present invention. Absent. The shape and dimensions of the mirror part 31a and the support part 32a in the above-described embodiment can be appropriately designed according to desired parabolic characteristics.

It is a schematic perspective view which shows the structure of the mirror apparatus which concerns on embodiment of this invention. In the mirror device of FIG. 1, (A) is a schematic sectional view during non-operation, and (B) is a schematic sectional view during operation. It is a mimetic diagram for calculating the amount of displacement at the time of load application of a beam with both ends fixed. The deformation | transformation at the time of the load application of the disc supported by the cyclic | annular support part is demonstrated, (A) is a schematic perspective view, (B) is a top view, (C) is sectional drawing. It is a figure which shows typically the structure of the mirror apparatus which concerns on 2nd Embodiment, (A) is a perspective view, (B) is a top view. It is a top view which shows the structure of a mirror apparatus. It is sectional drawing of the XX direction of FIG. FIG. 8 is a schematic cross-sectional view sequentially showing a manufacturing method of the mirror substrate shown in FIG. 7. It is typical sectional drawing which shows the manufacturing method of the support substrate shown in FIG. 7 in order. It is typical sectional drawing which shows the anodic bonding of a mirror substrate and a support substrate. It is a scanning electron microscope image of the mirror apparatus of Example 1, (A) has shown the surface principal part of the mirror board | substrate, (B) has shown the surface principal part of the support substrate, respectively. It is a figure which shows the applied voltage dependence in the cross-sectional shape of the mirror part of Example 1. FIG. It is a scanning electron microscope image of the mirror apparatus of Example 1, (A) has shown the surface principal part of the mirror board | substrate, (B) has shown the surface principal part of the support substrate, respectively. It is a figure which shows the applied voltage dependence in the cross-sectional shape of the mirror part of Example 2. FIG. In a configuration example of a conventional micromirror, (A) is a schematic sectional view during non-operation, and (B) is a schematic sectional view during operation. In the conventional micromirror device, it is a graph which shows a deformation | transformation state in case the periphery of a mirror is supported by the suspension. It is a graph which shows the deformation | transformation state when the periphery of a mirror is fixedly held in the conventional micromirror device.

Explanation of symbols

10, 15, 30: Mirror device 11, 31: Mirror substrate 11a, 31a: Mirror portion 11b of mirror substrate, 31b: Mirror substrate suspension 11c, 31c: Base portion 11d of mirror substrate, 31f: Outside region 11e of mirror substrate : Inner regions 11g and 31g of the mirror substrate: gap portions 12 and 32 of the mirror substrate: support substrates 12a, 12c, 12d and 32a: support portions 12b, 12e, 12f and 32b of the support substrate: fixed electrode portion 18 of the support substrate: Mirror drive power supply 20: beam 21: disk 21a: peripheral edge 22: support portion 31d: sacrificial layer 31e: Si substrate 32c, 32d, 32e: recessed portion 40 of mirror substrate: first substrate 41: silicon substrate 42: sacrificial layer 43: Upper Si layers 44, 46, 52: Mask patterns 45, 47, 53, 54: Etching 50: Second substrate (glass Board)
51, 55: Cr film 56: Au film 57: Heater 58: Power supply

Claims (12)

A base having a thin plate-like mirror part and a suspension for suspending the mirror part, surrounding at least a part of the periphery of the mirror part and supporting the mirror part movably in a direction perpendicular to the surface by the suspension A mirror substrate comprising:
A support substrate disposed on the surface of the base portion of the mirror substrate;
With
The support substrate includes a support portion that faces the inner periphery of the mirror substrate and contacts the surface of the mirror portion, and a fixed electrode portion that is formed outside the support portion and faces the mirror portion. And
By applying a voltage between the fixed electrode portion and the mirror portion, the region outside the support portion of the mirror portion is displaced toward the corresponding fixed electrode side by electrostatic attraction, and the mirror portion A mirror device characterized in that a region inside the support portion is deformed into a parabolic cross section. The mirror part is formed in a circular shape, and the suspension is arranged at equiangular intervals with respect to the center of the mirror part;
The mirror device according to claim 1, wherein the support portion is formed in an annular shape concentric with the mirror portion. The mirror part is formed in a rectangular shape, and the suspension is disposed with respect to mutually facing edges of the mirror part;
The mirror device according to claim 1, wherein the support portion is disposed along the inner side of the opposite edge of the mirror portion. The mirror substrate is composed of a semiconductor layer;
The mirror device according to claim 1, wherein a base portion of the mirror substrate is formed on the semiconductor substrate via an insulating layer.   The mirror device according to claim 1, wherein the support substrate is made of a glass substrate or a semiconductor substrate.   The mirror device according to claim 1, wherein the fixed electrode portion is disposed in a recessed portion formed on a surface of the support substrate.   The amount of deformation due to electrostatic attraction in the region inside the support portion of the mirror portion changes corresponding to the voltage, and the focal length of the mirror portion deformed into a uniform approximate paraboloid can be changed. The mirror device according to claim 6, wherein: A groove portion that defines a mirror portion and a suspension is formed by etching reaching the sacrificial layer from the upper layer side with respect to the first substrate having the upper layer via the sacrificial layer, and the sacrificial layer from the first substrate side. A first step of removing the region corresponding to the mirror portion of the first substrate by etching reaching the layer to produce a mirror substrate;
A second step of forming a support for the surface of the second substrate;
A third stage in which a fixed electrode portion is formed outside the support portion on the surface of the second substrate to produce a support substrate;
A mirror substrate fabricated in the first stage is inverted on the support substrate fabricated in the third stage, and the base portion of the upper layer of the mirror substrate is anodically bonded to the surface of the support substrate. And the stage
A method for manufacturing a mirror device, comprising:   9. The mirror according to claim 8, wherein in the second stage, each support portion is defined by forming a recessed portion around a surface region to be the support portion of the support substrate. Device manufacturing method.   10. The method of manufacturing a mirror device according to claim 8, wherein, in the third stage, a metal layer that prevents bonding to the surface of the mirror portion is formed on the upper surface of each support portion.   The method for manufacturing a mirror device according to claim 10, wherein the metal layer is formed simultaneously with the fixed electrode portion using the same material as the fixed electrode portion.   The mirror device according to any one of claims 8 to 11, wherein the mirror substrate is configured using a semiconductor substrate, and the support substrate is configured using a glass substrate or a semiconductor substrate. Production method.