JP2004157527A - Variable shape reflecting mirror and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a variable shape reflecting mirror, which is formed with a deformable film having uniform stiffness configurable with a method of high productivity, operable even at a comparatively low drive voltage, and provides a high imaging performance, without increasing the number of fixed side electrodes. <P>SOLUTION: The mirror is provided with a flexible thin film whose periphery is supported by a frame member, a reflective surface arranged on the film and a plurality of conductive electrodes arranged in the film, and electrostatic force is made to act on the reflective surface to vary the shape through the conductive electrode. The conductive electrode is divided circumferentially around the central part of the film, and also divided in a radial direction. The number of in the circumferential divisions in an external periphery is increased than that of the circumferential ones in the central part. <P>COPYRIGHT: (C)2004,JPO

Description

  The present invention relates to a deformable reflecting mirror, and more particularly to a small deformable reflecting mirror capable of controlling a shape with high precision, and a manufacturing method for manufacturing such a deformable reflecting mirror using semiconductor manufacturing technology.

  In micro optical systems applied to micro optics such as optical pickups, ultra-small optical systems that can change the curvature of the reflecting surface for the purpose of simplifying mechanisms related to focusing etc., which used to use electromagnetic actuators Has been proposed. Further, the application of the variable focus mirror can greatly contribute to further miniaturization of a small-sized imaging optical system.

  In such a variable focus mirror, by applying a so-called MEMS (Micro Electro-Mechanical System) technology based on a semiconductor manufacturing technology, it is expected to manufacture a low-cost and highly accurate product. As an example of this type of technology, for example, a technology proposed in Patent Literature 1 is cited. This technique will be described with reference to FIGS.

  In FIG. 17, a fixed-side electrode layer 12 made of a conductive thin film is adhered to an upper surface of an insulating substrate 11 made of glass or the like. On one main surface of the silicon substrate 13, a silicon dioxide thin film 14 is formed as an insulating thin film. A void 15 is formed in the other main surface of the central portion of the silicon substrate 13, and the central portion of the silicon dioxide thin film 14 can be displaced in the thickness direction by the void 15. Further, a movable electrode layer 16 is laminated on the silicon dioxide thin film 14. The central portion of the silicon dioxide thin film 14 and the electrode layer 16 constitutes a reflector 17. The reflecting mirror portion 17 is deformed in a convex shape toward the fixed electrode layer 12 by a voltage applied between the electrode layers 12 and 16.

  Further, the silicon substrate 13 is joined to the insulating substrate 11 via the spacer member 18 with the silicon dioxide thin film 14 side facing downward in the drawing. A silicon dioxide thin film 19 is also formed on the other main surface of the silicon substrate 13.

  The manufacture of such a reflecting mirror device is performed as shown in FIGS. 18 (A) to 18 (E). First, as shown in FIG. 18 (A), silicon dioxide thin films 14, 19 having a thickness of 400 to 500 nm are formed on both surfaces of a silicon substrate 13 having a plane orientation of <100>, both surfaces of which are mirror-polished. A metal film having a thickness of about 100 nm is deposited as an electrode layer 16 on.

  Next, as shown in FIG. 18B, a photoresist 20 having a predetermined pattern is applied, and a circular window hole 21 is formed by photolithography. After that, while the lower surface of the substrate is protected, a window is formed in the silicon dioxide thin film 14 with a hydrofluoric acid-based solution using the photoresist 20 as a mask.

Next, as shown in FIG. 18C, the silicon substrate 13 is immersed in an aqueous solution of ethylene, diamine and pyrocatechol, and the silicon substrate is etched from the window hole 21 in FIG. 18B. At this time, as shown, the etching stops when the silicon dioxide thin film 14 on the lower surface side is exposed. In this manner, the reflecting mirror portion 17 on the thin film composed of the silicon dioxide thin film 14 and the electrode layer 16 remains.
On the other hand, as shown in FIG. 18D, a metal film having a thickness of 100 nm is formed as a fixed electrode on the upper surface of the insulating substrate 11 having a thickness of 300 μm as the electrode layer 12.

  Next, as shown in FIG. 18 (E), by bonding to the insulating substrate 11 via a polyethylene spacer member 18 having a thickness of about 100 μm, the reflector device shown in FIG. 17 is manufactured.

  In such a deformable mirror, a uniform potential difference occurs between the silicon dioxide thin film 14 and the fixed-side electrode layer 12, but the deformed shape in this case is different from the spherical surface when the maximum displacement is equal. FIG. 19 schematically shows a comparison, in particular, since the amount of deformation in the peripheral portion is insufficient and large spherical aberration occurs, so that high imaging performance cannot be expected. Further, when a small reflecting mirror is applied to an imaging optical system, it is general that light is obliquely incident. In this case, a rotationally asymmetric aspherical surface is required to obtain good imaging performance. .

  In response to such demands, in order to deform the deformable mirror arbitrarily or to a specific ideal shape, the fixed-side electrode layer is divided into a plurality of regions, each of which has a different shape from the electrode on the deformed surface. A method of giving a potential difference is considered. Such electrode division forms include concentric circles, grids, and honeycombs. For example, Non-Patent Document 1 proposes a method of dividing the fixed-side electrodes into honeycombs.

In addition, as a method for adjusting a deformed shape to a specific shape such as a spherical surface or a paraboloid, Non-Patent Document 2 proposes a method of forming a deformed surface having a different thickness depending on a portion.
JP-A-2-101402 JP-A-8-334708 J. Opt. Soc. Am., Vol. 67, No. 3, March 1977, `` The membrane mirror as an adaptive optical element '' Journal of the Japan Society of Precision Engineering, Vol.61, No5, 1995, "Aberration Reduction of Si Diaphragm Variable Focus Mirror"

  However, in order to obtain high shape accuracy by a method of dividing the fixed electrode into a plurality of regions, it is necessary to increase the number of divided electrodes. That is, many lead wires for applying different voltages are required to be connected, which hinders miniaturization of the device. In addition, an increase in the number of electrodes leads to a complicated control circuit. Further, as shown in FIG. 19, with a uniform potential difference, the amount of deformation of the outer peripheral portion is generally insufficient in the case of a spherical surface or a paraboloid, and a large potential difference is necessarily applied to the outer peripheral portion. However, this leads to a substantial increase in drive voltage.

  On the other hand, although the above-mentioned problem does not occur in the method of giving a distribution to the rigidity of the deformed surface, it is difficult to locally control the thickness or the elastic modulus, and a high productivity method is required. It is very difficult to obtain an accurate deformed shape. In addition, for example, in the area where the thickness is distributed, the minimum rigidity is required (in the case of deformation into a spherical surface or parabolic surface, it is generally near the outer periphery). It will be thinnest at a certain level, and inevitably thicker in other areas. Therefore, since the average thickness of the deformed film becomes large, a large driving voltage is required as compared with the case where a uniform thickness is used.

  The present invention has been made in view of the above circumstances, and is formed of a deformable film having uniform rigidity that can be configured in a highly productive manner without increasing the number of fixed electrodes, and has a relatively low driving voltage. It is an object of the present invention to provide a deformable reflecting mirror which is operable even with the above and can obtain high imaging performance, and a method of manufacturing such a deformable reflecting mirror.

  In order to achieve the above object, a deformable reflecting mirror according to the first aspect of the present invention includes a reflecting surface and a plurality of conductive electrodes, and the plurality of conductive thin films of a flexible thin film supported around a frame member. In the deformable reflecting mirror that changes the shape of the reflecting surface by applying an electrostatic force to a flexible electrode, the plurality of conductive electrodes are divided in a circumferential direction around a central portion of the flexible thin film. In addition, the flexible thin film is divided in the radial direction, and the number of divisions in the circumferential direction at the outer peripheral portion of the flexible thin film is larger than the number of divisions in the circumferential direction at the central portion.

  In other words, the divided conductive electrode provided on the flexible thin film has a larger number of divisions in the circumferential direction in the outer peripheral portion than in the central portion. Is finely controlled.

  In order to achieve the above object, a deformable reflecting mirror according to the second invention of the present application includes a reflecting surface and a plurality of conductive electrodes, and the plurality of flexible thin films supported around by a frame member. A deformable mirror that changes the shape of the reflective surface by applying electrostatic force to the conductive electrode of the flexible thin film, in the vicinity of the outer periphery of the flexible thin film, a portion having lower rigidity than other regions of the flexible thin film. Is provided.

  That is, by providing a portion having low rigidity on the outer peripheral portion of the deformable reflecting mirror, the bending rigidity in this region is reduced, and the shape of the reflecting surface is greatly deformed even with a small force.

  In order to achieve the above object, in the deformable reflecting mirror according to the third aspect of the present invention, in the second aspect of the present invention, the low rigidity portion may be the flexible thin film, the reflecting surface, or the conductive film. The opening is provided discretely in at least one of the conductive electrodes.

  That is, by providing discrete openings in the deformable reflecting mirror, the bending rigidity in this region is reduced, and the shape of the reflecting surface is greatly deformed even with a small force.

  In order to achieve the above object, a deformable reflecting mirror according to a fourth aspect of the present invention is the deformable mirror according to the second aspect of the present invention, wherein the flexible thin film is provided near the outer peripheral portion at the time of deformation, and at the time of flattening. The displacement gradient in the vertical direction with respect to the reflecting surface is different depending on the region, and the proportion of the low rigidity portion in the portion where the displacement gradient is large is larger than the proportion of the low rigidity portion in the portion where the displacement gradient is small. Features.

  In other words, even when the same electrostatic force is applied to the reflection surface, the displacement gradient becomes large in a portion having low rigidity, and the displacement gradient becomes small in a portion having high rigidity.

  In order to achieve the above object, a deformable reflecting mirror according to a fifth aspect of the present invention is the deformable reflecting mirror according to the third aspect of the present invention, wherein the flexible thin film is provided near the outer peripheral portion at the time of deformation and at the time of flattening. The displacement gradient in the vertical direction with respect to the reflecting surface differs depending on the region, and the ratio of the opening in a region with a large displacement gradient is larger than the ratio of the opening in a region with a small displacement gradient.

  In order to achieve the above object, a deformable reflecting mirror according to a sixth aspect of the present invention includes a reflecting surface and a plurality of conductive electrodes, and the plurality of flexible thin films supported around by a frame member. In the deformable reflecting mirror that changes the shape of the reflecting surface by applying an electrostatic force to the conductive electrode, a portion having low rigidity is provided along the circumferential direction of the flexible thin film, It is characterized in that the distribution of the stiffness of the low part is different in the circumferential direction.

  That is, since portions having different rigidity distributions are provided in the circumferential direction of the flexible thin film, the amount of deformation of the reflecting surface is different due to the difference in rigidity even when the same electrostatic force is applied.

  In order to achieve the above object, a deformable reflecting mirror according to a seventh aspect of the present invention includes a reflecting surface and a plurality of conductive electrodes, and the plurality of flexible thin films supported around by a frame member. In the deformable reflecting mirror that changes the shape of the reflecting surface by applying an electrostatic force or an electromagnetic force to the conductive electrode, an opening is provided along a circumferential direction of the flexible thin film. It is characterized in that the occupying ratio differs in the circumferential direction.

  That is, since the opening is provided in the circumferential direction of the flexible thin film, the amount of deformation of the reflection surface is different even when the same electrostatic force is applied.

  In order to achieve the above object, a deformable reflecting mirror according to an eighth aspect of the present invention includes a fixed lower electrode, a periphery supported by a frame member, and a reflection surface and a plurality of conductive electrodes. And a flexible thin film having a flexible thin film, wherein the lower electrode is provided with openings which are discretely arranged at different intervals depending on the portion, and an outer periphery of the flexible thin film is provided. The portion is provided with a portion having lower rigidity than other regions.

  That is, by providing a portion having lower rigidity than the other region on the outer peripheral portion of the flexible thin film, and further providing an opening in the lower electrode, the deformation of the flexible thin film is more finely controlled.

  In order to achieve the above object, a ninth aspect of the present invention provides the deformable reflecting mirror according to the eighth aspect of the present invention, wherein the low rigidity portion is formed of the flexible thin film, the reflecting surface, or the conductive film. The opening is provided discretely in at least one of the conductive electrodes.

  That is, by providing a portion having lower rigidity than the other region on the outer peripheral portion of the flexible thin film, and further providing an opening in the lower electrode, the deformation of the flexible thin film is more finely controlled.

  In order to achieve the above object, a method of manufacturing a deformable reflector according to a tenth aspect of the present invention includes a step of forming a protective film on first and second main surfaces of a semiconductor substrate; A step of forming a flexible thin film on the main surface, a step of discretely forming openings in the flexible thin film by photolithography, a step of forming an electrode on the flexible thin film, Forming an opening by photolithography from the second main surface, and forming an outer frame with the remaining semiconductor substrate.

  That is, since an opening is formed in the flexible thin film by photolithography, and the electrode is formed after the opening is formed, a fine and high-precision through hole is easily formed.

  According to the present invention, without increasing the number of fixed-side electrodes, it is formed of a deformable film having uniform rigidity that can be configured in a highly productive manner, and can operate even at a relatively low drive voltage. Thus, it is possible to provide a deformable reflecting mirror capable of obtaining high imaging performance and a method for manufacturing such a deformable reflecting mirror.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[First Embodiment]
A first embodiment of the present invention will be described with reference to FIGS. FIG. 1 schematically shows a configuration of an optical system to which the deformable reflecting mirror according to the present embodiment is applied.

  The front-group lens 101 on the incident side and the rear-group lens 103 on the solid-state imaging device 102 are arranged so that their optical axes are orthogonal to each other, and a variable-shape reflecting mirror 104 is arranged at the intersection. The deformable film 105 having the reflecting surface of the deformable reflecting mirror 104 is continuously deformed from a flat surface (shown by a broken line in the drawing) to a concave surface (shown by a solid line in the drawing) by an electrostatic force, thereby forming an optical system. Change the focus position. That is, the focus can be adjusted without extending the lens group by deforming the deformable reflecting mirror 104.

  In this case, when the reflecting surface is flat, the focus is at infinity, and when the reflecting surface is concave, the focus is on the near point. However, since the light flux enters the concave mirror obliquely, the deformed surface In the case where is a simple spherical surface or parabolic surface, large spherical aberration occurs. At this time, since high-resolution imaging cannot be performed, it is necessary to transform the reflecting surface into a rotationally asymmetric free-form surface.

  2 and 3 show examples of the shape of the reflecting surface designed to suppress the spherical aberration at the near point with respect to the actual lens configuration. FIG. 2 is a diagram three-dimensionally showing the shape of the reflection surface. Here, the size of the region where the reflection surface is deformed is a shape in which a pair of semicircles having a radius of 3 mm sandwich a rectangle of 6 mm × 2 mm. FIG. 3 is a contour diagram showing the displacement of the reflection surface. Note that FIG. 3 also shows an image area for an effective pixel of the solid-state imaging device 102 when the deformable reflecting mirror having the reflecting surface shown in FIGS. 2 and 3 is applied to the optical system of FIG. .

  Here, the distribution of the error between the deformed shape when uniform electrostatic force is applied to the deformed surface of the deformable reflecting mirror and the ideal shape based on the optical design shown in FIG. 2 or FIG. 3 is shown in FIG. Shown in Actually, only the error in the illustrated image area becomes a problem, but the error is particularly large near the outer periphery of the deformed surface. In addition, it can be seen that the error is not uniform in the outer circumferential portion of the deformed surface in the circumferential direction, and there is a large difference in the degree of the error. As a matter of course, such an error distribution differs depending on the design of the optical system. However, when combined with a normal rotationally symmetric lens, the same tendency is generally exhibited.

  In addition, in order to perform high-definition imaging, it is indispensable to bring the deformed shape of the reflecting surface closer to the ideal shape. For that purpose, as proposed in the above-described conventional technology, one of the opposing electrodes is divided. Therefore, it is necessary to provide a distribution to the electrostatic force acting on the deformable surface of the deformable reflecting mirror.

  Here, the configuration of the deformable reflecting mirror 104 in the present embodiment will be described with reference to FIG. The deformable reflecting mirror 104 has a configuration in which an upper substrate 106 and a lower substrate 107 are bonded together with a spacer 108 formed on the lower substrate 107 therebetween. Note that FIG. 5 shows a state in which the upper substrate 106 and the lower substrate 107 are separated for explanation. The upper substrate 106 has a deformation film 105 supported by a frame member 109. Further, a fixed electrode 110 divided into a plurality of regions is formed in a region on the lower substrate 107 facing the deformation film 105. The deformable film 105 corresponds to a “flexible thin film” described in the claims.

  Although not shown here, a “reflective surface” is formed on the deformable film 105. Further, the deformable film 105 has conductivity, and the respective regions of the deformable film 105 and the fixed electrode 110 are electrically connected to an external controller to be given independent potentials.

  It is desirable to paint the light incident side of the frame member 109 black or to attach a black plate having an opening in the image area of the deformable film 105 in order to prevent flare.

  FIG. 6 shows the shape of the fixed electrode 110 divided so as to conform to the shape shown in FIG. 2 or FIG. 3, and the electrostatic force acting on other areas when the electrostatic force acting on the vicinity of the center is set to 1. Is shown. By applying the electrostatic force in this manner, the shape error can be reduced to 100 nm or less over almost the entire image area.

  Here, as can be seen from FIG. 6, the dividing line in the circumferential direction of the fixed electrode 110 is finely divided at the outer peripheral portion of the deformation region as compared with the central portion. This indicates that, as described above, the difference in the error in the circumferential direction is larger in the outer peripheral portion of the deformation region than in the vicinity of the center, so that it is necessary to apply electrostatic force finely. Note that the dividing line in the radial direction has a shape substantially along the contour line shown in FIG.

  In addition, as can be seen from FIG. 3, a plurality of contour lines cross the outer circumference of the image area or the outer circumference of the deformation area, the height of the outer circumference of the deformation area in the optical design is not uniform. However, in the case of a deformable reflecting mirror, it is necessary to make the height of the outer periphery of the deformation area equal due to its structure, and in the area from the outer circumference of the deformation area to the outer circumference of the image area, the radial gradient is large in the circumferential direction. It is generally different.

  Therefore, the electrode at the outer peripheral portion of the deformation region where the difference in the amount of error in the circumferential direction is relatively large is divided more finely than the electrode near the center, thereby simply dividing the electrode into a rectangular shape or a honeycomb shape. The error from the ideal shape can be reduced with a smaller number of divisions as compared with.

[Second embodiment]
A second embodiment of the present invention will be described with reference to FIGS. In the first embodiment, as shown in FIG. 5, it is necessary to apply an extremely large electrostatic force to the outer peripheral portion as compared to the central portion. Therefore, it is necessary to apply a particularly high voltage to the outer peripheral portion, which leads to an increase in the driving voltage. One of the causes is that the deformed film is completely fixed in the outer peripheral portion of the deformed region, and a large force is required to sharply bend the deformed film in this region.

  This problem can be avoided by increasing the distance from the image area to the outer periphery of the deformation area, but this is not desirable because it leads to an increase in the size of the deformable reflecting mirror itself. Therefore, an object of the second embodiment is to obtain a small-sized variable-shape reflecting mirror with high shape accuracy without increasing the driving voltage.

  FIG. 7 shows the shape of the upper substrate of the deformable reflecting mirror according to the present embodiment. The circular deformable film 202 having a diameter of 7.5 mm supported by the frame member 201 has a two-layer structure of an aluminum thin film 203 having a thickness of 50 nm serving as a reflective film and an electrode film and a polyimide thin film 204 having a thickness of 1 μm. In the vicinity of the outer peripheral portion, circular openings 205 are formed at equal intervals.

  The upper substrate is manufactured based on a semiconductor manufacturing technique, and the formation of the opening 205 can be easily performed by applying a normal photolithography technique. By providing discrete openings in the outer peripheral portion in this way, the bending rigidity of the deformable film at the outer peripheral portion is significantly reduced, and as a result, the deformable film is deformed into a predetermined shape without applying a strong electrostatic force to the outer peripheral portion. It becomes possible.

  Although a relatively large opening is described in FIG. 7 for easy understanding, if the size of the opening is too large, swelling due to uneven rigidity may occur on the reflecting surface. It is desirable to arrange small openings at fine intervals.

  Further, in the present embodiment, the opening 205 is a complete through-hole. However, since it is important to discretely form a region having low bending rigidity, the aluminum thin film 203 or the polyimide thin film 204 is required. The opening may be formed only in any one of them.

  Further, in this embodiment, one row of openings is formed in the circumferential direction, but it is also possible to form two rows as shown in FIG. By arranging a plurality of rows in this manner, the bending rigidity in this area can be significantly reduced.

[Third Embodiment]
Next, a third embodiment of the present invention will be described with reference to FIGS.
FIG. 9 shows the shape of the upper substrate of the deformable reflecting mirror according to the third embodiment. The deformation film 302 supported by the frame member 301 has a two-layer structure of an aluminum thin film 303 having a thickness of 50 nm serving as a reflection film and an electrode film and a polyimide thin film 304 having a thickness of 1 μm. Circular openings 305 are formed at uniform intervals. In general, a deformable reflecting mirror applied in the configuration as shown in FIG. 1 is required to have a rotationally asymmetric deformed shape. Therefore, the displacement gradient toward the center in the vicinity of the outer peripheral portion differs depending on the portion.

  FIG. 10 three-dimensionally shows a deformed shape based on the optical design in the present embodiment. Here, the deformation area of the deformable reflecting mirror is a circle having a diameter of 7.5 mm as shown in FIG. At this time, FIG. 11 shows the average displacement gradient toward the center in the counterclockwise direction in the circumferential direction of the outer circumference with the portion indicated by C in the figure as a base point. As can be seen from this figure, the displacement gradient is small at the portions C and E in FIG. 9 and large at the portions D and F in FIG. For this reason, when applying an electrostatic force to the deformable film 302, it is desirable that the bending stiffness be increased in the portions C and E and be reduced in the regions D and F. At this time, since the bending rigidity of the outer peripheral portion depends on the interval between the openings 305, the bending rigidity can be reduced by reducing the interval. On the other hand, by increasing the interval or not forming the opening 305, the bending rigidity can be increased.

  Therefore, by adjusting the interval between the openings 305 in accordance with the displacement gradient of each portion of the outer peripheral portion, the electrostatic force acting on the deformable film 302 does not largely change depending on the portions of the deformable film, and the deformed shape shown in FIG. Can be approached.

  In the present embodiment, the size and shape of all the openings 305 are equalized so that the intervals are different depending on the portions. However, the same effect can be obtained by changing the size or shape of the openings at the same interval. Needless to say, it can be obtained. Also, as shown in FIG. 8 described above, by disposing the openings 305 in two rows, it is possible to increase the difference in bending stiffness between the parts.

[Fourth Embodiment]
Next, a fourth embodiment of the present invention will be described with reference to FIG.
FIG. 12 shows a form of the upper substrate of the deformable reflecting mirror in the present embodiment. The deformation film 402 supported by the frame member 401 has a two-layer structure of an aluminum thin film 403 having a thickness of 50 nm serving as a reflection film and an electrode film and a polyimide thin film 404 having a thickness of 1 μm. Circular openings 405 are formed at uniform intervals, and circular openings 406 are formed at irregular intervals on a circumference having a radius of 2 mm from the center of the deformation film 402. The shape of the deformation film 402 to be deformed is the same as that of the third embodiment shown in FIG. 10, and the deformation region is also the shape shown in FIG. The openings 405 are arranged at the same shape and at the same interval as the openings 305 in FIG.

  Here, on the circumference having a radius of 2 mm centered on the center of the deformable film 402 shown in FIG. 12, the average going toward the center in the counterclockwise direction in the circumferential direction with the portion shown in FIG. FIG. 13 shows the displacement gradient. As can be seen from this figure, the displacement gradient is large at the portions G and I in FIG. 12, and small at the portions H and J in FIG. For this reason, when applying an electrostatic force to the deformable film 402, it is desirable that the rigidity be reduced in the G and I regions and the rigidity be increased in the H and J regions. At this time, the rigidity in the vicinity of the circumference GHIJ in FIG. 12 depends on the interval between the openings 406. Therefore, the rigidity can be reduced by reducing the interval. On the other hand, by increasing the interval or not forming the opening 406, the rigidity can be relatively increased.

  Therefore, by adjusting the interval between the openings 406 in accordance with the displacement gradient of each portion of the outer peripheral portion, the electrostatic force acting on the deformable film 402 can be brought close to the deformed shape shown in FIG. Can be.

  In the present embodiment, the size and shape of all the openings 406 are equalized so that the interval differs depending on the region. However, the same effect can be obtained by changing the size or shape of the openings at the same interval. Needless to say, it can be obtained.

  Also, as shown in FIG. 8, by disposing the openings 406 in two rows, it is possible to increase the difference in bending stiffness depending on the location. Further, in the present embodiment, for the sake of simplicity, the opening 406 formed in the deformable film 402 is arranged only on the circumference GHIJ, but the opening 406 has a density corresponding to the displacement gradient. Needless to say, it may be arranged on the entire surface 402.

  Furthermore, even if the openings 406 are formed on the circumference GHIJ or on the entire surface of the deformed film 402 at a uniform density, the rigidity of the deformed film 402 is reduced, and the driving voltage can be reduced. Also, unlike the second and third embodiments, in the method of the present embodiment in which the opening 406 is formed in the image area, the imaging performance of the optical system is not reduced to some extent. However, the number of apertures 406 is determined according to the permissible degradation of the imaging performance. The size of the aperture 406 is desirably as small as possible in terms of both diffraction at the end and light loss, and is particularly desirably a diameter equal to or smaller than the wavelength of light.

  In the present embodiment, the openings 405 or 406 are provided on two circumferences near the outer circumference and on a circumference with a radius of 2 mm. An opening having a density may be provided, or an opening having a density corresponding to a displacement gradient of a shape to be deformed over the entire surface of the deformable film. Furthermore, in the present embodiment, the deformable film 402 has a circular shape, but it goes without saying that other shapes such as an elliptical shape can be similarly applied.

  Further, in the second to fourth embodiments, the description has been made on the premise of the configuration of the electrostatically driven variable shape reflecting mirror shown in the first embodiment. It is also possible to apply the present invention to an electromagnetic deformable reflecting mirror in which a coil is formed on a film and a magnet for generating a magnetic field orthogonal to the coil is arranged. In the case of an electromagnetic variable shape reflecting mirror, particularly a small electromagnetic type, it is difficult to apply different forces to each part of the deformable film due to its structure, as described in Patent Document 2, for example. For this reason, as shown in the second embodiment to the fourth embodiment, the method of giving the rigidity distribution to the deformable film is particularly effective considering the controllability of the shape.

  Next, a method of manufacturing the upper substrate of the deformable reflecting mirror according to the present embodiment will be described with reference to FIGS. First, as shown in FIG. 14A, a silicon nitride film 452 is formed on both surfaces of a silicon substrate 451, and an opening 453 is formed in the silicon nitride film on the back surface by ordinary photolithography.

  Next, as shown in FIG. 14B, a polyimide thin film 404 having a thickness of 1 μm is formed on the surface side by spin coating, and openings 405 and 406 are formed at predetermined portions of the polyimide thin film 404 by photolithography.

  Next, as shown in FIG. 14 (C), the silicon substrate is etched from the back surface side with the alkaline solution until the silicon nitride film 452 on the front surface is exposed from the back surface while protecting the front surface side. . At this time, the remaining portion of the silicon substrate 451 becomes the frame member 401 of the upper substrate.

  Next, as shown in FIG. 14D, the silicon nitride film 452 on the front side exposed from the back side is etched by reactive ion etching. Next, an aluminum thin film 403 having a thickness of 50 nm is formed on the surface side by sputtering or vapor deposition. At this time, by making the size of the openings 405 and 406 sufficiently larger than the thickness of the aluminum thin film 403, the openings 405 and 406 become through holes. Here, the aluminum thin film 403 functions as a reflection surface and an electrode for applying an electrostatic force.

  By forming the through holes by photolithography in this way, it is possible to easily form a large number of fine through holes with high precision.

  Next, another method of manufacturing the upper substrate of the deformable reflecting mirror according to the present embodiment will be described with reference to FIGS. First, as shown in FIG. 14A, a silicon nitride film 452 is formed on both surfaces of a silicon substrate 451, and an opening 453 is formed in the silicon nitride film on the back surface by ordinary photolithography. 1A, a polyimide thin film 404 having a thickness of 1 μm and an aluminum thin film 403 having a thickness of 50 nm are sequentially formed on the surface side by spin coating.

Next, as shown in FIG. 15B, an opening 454 and an opening 455 are formed in the aluminum thin film 403 by a normal photolithography technique. These correspond to the opening 405 and the opening 406 in FIG.
Next, as shown in FIG. 15C, the silicon substrate is etched from the back surface side with an alkaline aqueous solution until the silicon nitride film 452 on the front surface is exposed from the back surface while protecting the front surface. I do.
Next, as shown in FIG. 15D, the silicon nitride film 452 on the front side exposed from the back side is etched by reactive ion etching.

  In the upper substrate based on such a manufacturing method, the openings 454 and 455 are not through-holes, but the rigidity of the deformable film is reduced in the corresponding region. A similar effect can be expected, though varying in degree.

[Fifth Embodiment]
A fifth embodiment of the present invention will be described with reference to FIG. FIG. 16 shows the electrode structure of the lower substrate in the present embodiment. A lower electrode 503 is formed on a silicon substrate 501 with an insulating film 502 interposed therebetween, and a number of openings 504 are formed near the center. A spacer 505 is formed outside the lower electrode 503. The spacer 505 corresponds to the spacer 108 in FIG. 5, and the upper substrate bonded thereto is the one shown in FIG. It is assumed that openings are provided at uneven intervals. In the operation of the deformable reflecting mirror of the present embodiment, the deformed film and the silicon substrate 501 are grounded, and a voltage is applied to the lower electrode 503. Note that a glass substrate may be used instead of the silicon substrate 501. In this case, the insulating film 502 is unnecessary.

  In the upper substrate described in the third embodiment, the bending rigidity is changed according to the circumferential displacement gradient at the outer peripheral portion to approximate the optical design shape. When an electrostatic force is applied by giving a uniform potential difference to the deformed film, an error from the ideal shape occurs. Therefore, the number of the lower portion may be smaller than that in the case where the opening is not provided in the deformed film, but as shown in the first embodiment, It is necessary to divide the electrode into several regions.

  However, in the present embodiment, by providing an opening in a part of the lower electrode, the deformation shape is controlled by giving a distribution to the electrostatic force acting on the deformation film. Compared with the method of the fourth embodiment, there is no effect of reducing the rigidity of the deformed film itself except for the outer peripheral portion, so that the driving voltage is increased, but the imaging performance is deteriorated due to diffraction at the opening of the deformed film. However, it can be deformed into a predetermined shape with a single or a very small number of drive voltages, and the control circuit can be simplified to contribute to cost reduction and miniaturization.

  In this embodiment, a relatively large opening having a uniform density is shown near the center for simplicity of description, but a large electrostatic force is applied so that the deformed film is deformed into a predetermined shape. It is desirable to reduce the density of the opening in the area where it is necessary to operate, and to increase the density of the opening and reduce the size of the opening itself as much as possible in the area where the arrangement of the small opening needs to apply the electrostatic force. .

  Further, in the present embodiment, as a method of giving a predetermined distribution to the electrostatic force acting on the deformed film, openings having different densities are arranged in the lower electrode depending on the region. It suffices if the ratio of the region where the lower electrode to which a different potential is applied is present is different depending on the region.

  Although the present invention has been described based on the embodiments, the present invention is not limited to the above-described embodiments, and various modifications and applications are possible within the scope of the present invention. is there.

  Furthermore, the embodiments described above include inventions at various stages, and various inventions can be extracted by appropriately combining a plurality of disclosed constituent features. For example, even if some components are deleted from all the components shown in the embodiment, the problem described in the column of the problem to be solved by the invention can be solved, and the effects described in the column of the effect of the invention can be solved. Is obtained, a configuration from which this configuration requirement is deleted can be extracted as an invention.

  Here, in the effect of the first invention of the present application, an error in the shape is likely to be large in the outer peripheral portion, but an ideal deformed shape is achieved with a smaller number of divisions than simply dividing the electrode into a rectangular or honeycomb shape. be able to.

  Further, according to the second and third aspects of the present invention, the outer peripheral portion can be deformed into a predetermined shape without applying a large electrostatic force to the outer peripheral portion.

  Further, in the fourth to seventh inventions of the present application, it is possible to deform the electrode into an ideal shape without largely changing the magnitude of the electrostatic force acting on the electrode depending on the part.

  In the eighth and ninth aspects of the present invention, the amount of deformation of the deformable reflecting mirror can be finely controlled to obtain a more ideal optical design shape.

  In the effect of the tenth aspect of the present invention, since an opening is formed in a flexible thin film by photolithography, and an electrode is formed after the opening is formed, a fine and high-precision through hole can be easily formed. .

FIG. 1 is a diagram schematically illustrating a configuration of an optical system to which a deformable reflecting mirror according to a first embodiment of the present invention is applied. It is a three-dimensional figure of the deformation | transformation shape of the reflection surface in 1st Embodiment. FIG. 3 is a contour diagram showing displacement of a reflection surface. FIG. 9 is a distribution diagram of an error between a deformed shape and an ideal shape when a uniform electrostatic force is applied to a deformed surface of the deformable reflecting mirror. FIG. 1 is a configuration diagram of a deformable reflecting mirror according to a first embodiment of the present invention. It is a figure which shows the shape of a fixed electrode, and the electrostatic force which acts on another area | region when the electrostatic force acting near this center is set to 1. FIG. It is a figure showing the shape of the upper substrate of the deformable reflector according to the second embodiment of the present invention. FIG. 14 is an explanatory diagram for a modification of the second embodiment. It is a figure showing the shape of the upper substrate of the deformable reflector according to the third embodiment of the present invention. It is a three-dimensional figure of the deformation | transformation shape of the reflective surface in 3rd Embodiment. It is a distribution figure showing the average displacement gradient which goes to the center in a 3rd embodiment. It is a figure showing the shape of the upper substrate of the variable shape reflector according to the fourth embodiment of the present invention. It is a distribution figure showing the average displacement gradient which goes to the center in a 4th embodiment. It is explanatory drawing of the manufacturing method of a variable shape reflection mirror. It is explanatory drawing of another manufacturing method of a variable shape reflection mirror. It is an electrode structure figure of a lower electrode of a variable shape reflector according to a fifth embodiment of the present invention. It is a structural diagram of the conventional deformable mirror. It is explanatory drawing of the manufacturing method of the conventional deformable mirror. It is explanatory drawing regarding the difference of the deformation amount of a deformable mirror when a uniform electric potential difference is given.

Explanation of reference numerals

  Reference numeral 101: front group lens, 102: solid-state image sensor, 103: rear group lens, 104: variable shape reflecting mirror, 105, 202, 302, 402 ... deformable film, 106: upper substrate, 107: lower substrate, 108, 505 ... Spacer, 109, 201, 301, 401 frame member, 110 fixed electrode, 203, 303, 403 aluminum thin film, 204, 304, 404 polyimide thin film, 205, 305, 405, 406, 454, 455, 504 ... Opening, 451, 501: silicon substrate, 452: silicon nitride film, 453: opening, 502: insulating film, 503: lower electrode

Claims (10)

A deformable reflecting mirror comprising a reflecting surface and a plurality of conductive electrodes, wherein the shape of the reflecting surface is changed by applying an electrostatic force to the plurality of conductive electrodes of a flexible thin film supported around a frame member. At
The plurality of conductive electrodes are divided in the circumferential direction around the center of the flexible thin film, and are also divided in the radial direction,
The flexible thin film is characterized in that the number of divisions in the circumferential direction at the outer peripheral portion of the flexible thin film is larger than the number of divisions in the circumferential direction at the central portion. A deformable reflecting mirror comprising a reflecting surface and a plurality of conductive electrodes, wherein the shape of the reflecting surface is changed by applying an electrostatic force to the plurality of conductive electrodes of a flexible thin film supported around a frame member. At
A deformable reflecting mirror, wherein a portion having lower rigidity than other regions of the flexible thin film is provided near an outer peripheral portion of the flexible thin film.   The variable shape reflection according to claim 2, wherein the low rigidity portion is an opening discretely provided in at least one of the flexible thin film, the reflection surface, or the conductive electrode. mirror. The flexible thin film, in the vicinity of the outer peripheral portion at the time of deformation, the displacement gradient in the vertical direction with respect to the reflective surface at the time of flat is different depending on the portion,
3. The deformable mirror according to claim 2, wherein a ratio of the low rigidity portion in a portion having a large displacement gradient is larger than a ratio of the low rigidity portion in a portion having a small displacement gradient. The flexible thin film, in the vicinity of the outer peripheral portion at the time of deformation, the displacement gradient in the vertical direction with respect to the reflective surface at the time of flat is different depending on the portion,
4. The deformable mirror according to claim 3, wherein a ratio of the opening in a portion having a large displacement gradient is larger than a ratio of the opening in a portion having a small displacement gradient. 5. A deformable reflecting mirror comprising a reflecting surface and a plurality of conductive electrodes, wherein the shape of the reflecting surface is changed by applying an electrostatic force to the plurality of conductive electrodes of a flexible thin film supported around a frame member. At
A deformable reflecting mirror, wherein a portion having low rigidity is provided along a circumferential direction of the flexible thin film, and a distribution of rigidity of the low rigidity portion differs in a circumferential direction. A variable, which includes a reflecting surface and a plurality of conductive electrodes, and changes the shape of the reflecting surface by applying an electrostatic force or an electromagnetic force to the plurality of conductive electrodes of a flexible thin film supported around a frame member. In the shape reflector,
An opening is provided along the circumferential direction of the flexible thin film, and the ratio of the opening is different in the circumferential direction. A fixed lower electrode, the periphery of which is supported by the frame member, a flexible thin film having a reflective surface and a plurality of conductive electrodes, a deformable reflecting mirror having:
A part of the lower electrode is provided with openings that are discretely arranged at different intervals depending on the site,
A deformable reflecting mirror, wherein a portion having lower rigidity than other regions is provided on an outer peripheral portion of the flexible thin film.   The variable shape reflection according to claim 8, wherein the low rigidity portion is an opening discretely provided in at least one of the flexible thin film, the reflection surface, or the conductive electrode. mirror. Forming a protective film on the first and second main surfaces of the semiconductor substrate;
Forming a flexible thin film on the first main surface;
Forming discrete openings in the flexible thin film by photolithography;
Forming an electrode on the flexible thin film,
Forming an opening by photolithography from the second main surface of the semiconductor substrate, and forming an outer frame with the remaining semiconductor substrate;
A method for manufacturing a deformable reflecting mirror, comprising:

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