JP2010198035A - Micro mirror element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a micro mirror element, in which improper operation of a mirror forming part such as rotation of a mirror surface around normal is controlled while setting torsion resistance of a torsion connecting part low. <P>SOLUTION: The micro mirror element 100 includes: a frame 113; a mirror forming part 111 having a mirror plane 114; and a torsion connecting part 112 parallel to the mirror plane 114, which extends to connect the frame 113 to the mirror forming part, and regulates a rotational axis X1 for rotating the mirror forming part 111 relative to the frame 113. The torsion connecting part 112 is composed of two torsion bars 112a, and the two torsion bars 112a regulate the width of torsion connecting part 112. This width is regulated to be relatively large in the part connected to the mirror forming part 111, and to be gradually reduced toward the frame 113 with distance from the mirror forming part 111. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention is an element incorporated in an optical device such as an optical disc device that performs data recording / reproduction processing on an optical disc or an optical switching device that switches an optical path between a plurality of optical fibers. The present invention relates to a micromirror element used for changing.

  The micromirror element includes a mirror surface for reflecting light, and the light reflection direction can be changed by swinging the mirror surface. Many optical devices employ electrostatically driven micromirror elements that use electrostatic force to swing the mirror surface. Various structures are known as electrostatically driven micromirror elements, and these can be roughly classified into two types based on the manufacturing method. A micromirror element manufactured by a so-called surface micromachining technique and a micromirror element manufactured by a so-called bulk micromachining technique.

  In surface micromachining technology, a material thin film corresponding to each component part is processed into a desired pattern on a substrate, and such a pattern is sequentially laminated to configure elements such as a support, a mirror surface, and an electrode part. Each part to be formed and a sacrificial layer to be removed later are formed. An electrostatically driven micromirror element manufactured by such surface micromachining technology is disclosed in, for example, Japanese Patent Application Laid-Open No. 7-287177.

  On the other hand, in the bulk micromachining technique, the support substrate, the mirror forming portion, and the like are formed into a desired shape by etching the material substrate itself, and a mirror surface and electrodes are formed as a thin film as necessary. Examples of the electrostatic drive type micromirror element manufactured by such a bulk micromachining technique include Japanese Patent Laid-Open Nos. 9-146032, JP-A-9-146034, JP-A-10-62709, and Japanese Patent Laid-Open No. 2001-2001. This is disclosed in Japanese Patent No. 13443.

  One of the technical matters required for the micromirror element is that the flatness of the mirror surface responsible for light reflection is high. According to the surface micromachining technology, since the mirror surface finally formed is thin, the mirror surface is easy to bend and high flatness is guaranteed when the length of one side is several tens of μm in the size of the mirror surface. Limited to. On the other hand, according to the bulk micromachining technology, a relatively thick material substrate itself is shaved to form a mirror forming portion, and a mirror surface is provided on the mirror forming portion. However, the rigidity can be ensured, and as a result, a mirror surface having sufficiently high optical flatness can be formed. Therefore, bulk micromachining technology is widely employed in the manufacture of micromirror devices that require a mirror surface with a length of several hundreds of μm or more.

  FIG. 10 shows a conventional electrostatically driven micromirror device 400 manufactured by bulk micromachining technology. The micromirror element 400 has a structure in which a mirror substrate 410 and a base substrate 420 are laminated. As shown in FIG. 11, the mirror substrate 410 includes a mirror forming portion 411, a frame 414, and a pair of torsion bars 412 that connect them. On the surface of the mirror forming portion 411, a mirror surface 411a is provided. A pair of electrodes 414 a and 414 b are provided on the back surface of the mirror forming portion 411. As shown in FIG. 10, the base substrate 420 is provided with an electrode 421a facing the electrode 414a of the mirror forming portion 411 and an electrode 421b facing the electrode 414b.

  According to such a configuration, for example, when the electrode 421a of the base substrate 420 is set to the negative electrode in a state where the electrodes 414a and 414b of the mirror forming portion 411 are positively charged, an electrostatic attractive force is generated between the electrode 414a and the electrode 421a. The mirror forming portion 411 swings or rotates in the arrow M3 direction while twisting the pair of torsion bars 412. The mirror forming portion 411 swings to an angle at which the electrostatic attractive force between the electrodes and the total of the torsional resistance force of each torsion bar 412 are balanced, and stops. Instead, when the electrode 421b is made negative while the electrodes 414a and 414b of the mirror forming portion 411 are positively charged, an electrostatic attractive force is generated between the electrode 414b and the electrode 421b, and the mirror forming portion 411 It swings in the direction opposite to the arrow M3 and stops. By such a swing driving of the mirror forming portion 411, the reflection direction of the light reflected by the mirror surface 411a is switched.

JP 7-287177 A Japanese Patent Laid-Open No. 9-146032 Japanese Patent Laid-Open No. 9-146034 JP-A-10-62709 JP 2001-13443 A

  In the electrostatically driven micromirror element, as described above, the mirror forming portion swings to an angle at which the electrostatic force between the electrodes and the total of the torsional resistance force of each torsion bar balance, and stops. Therefore, the swing angle of the mirror forming portion is adjusted by the torsional resistance of each torsion bar and the magnitude of the generated electrostatic force. On the other hand, since the micromirror element is a structure having dimensions of several hundreds of micrometers, the total torsional resistance of the torsion bar tends to increase with respect to the electrostatic force. Therefore, conventionally, in order to balance the electrostatic force and the total torsional resistance force at an appropriate swing angle, the torsion resistance of the torsion bar is set as low as possible while generating sufficient electrostatic force. Until now, measures have been taken to ensure a large area of the electrode. Specifically, in order to set a low torsional resistance with respect to the torsion bar included in the conventional micromirror element, the torsion bar is usually thinned uniformly in the width direction. For example, in the conventional torsion bar 412 shown in FIG. 11, the width L is set to be uniformly narrow.

  However, if the torsion bar is uniformly thinned in the width direction, the width of the end portion of the torsion bar that is directly joined to the mirror forming portion becomes narrow, and the mirror forming portion is easily rotated around the normal line of the mirror surface. For example, the mirror forming portion 411 shown in FIG. 11 is easily rotated around the normal line N3. Then, in the mirror forming part at the time of driving, along with the appropriate rotation around the rotation axis defined by the torsion bar, the rotation around the normal of the mirror surface tends to occur at the same time, and high-precision control of the micromirror element is possible. May be hindered.

  The present invention has been conceived under such circumstances, and it is an object of the present invention to solve or alleviate the above-mentioned conventional problems, and the torsion resistance of the torsion bar is set to be low while the mirror surface. An object of the present invention is to provide a micromirror element in which inappropriate operation of the mirror forming portion such as rotation around the normal line is suppressed.

  The micromirror element provided by the first aspect of the present invention extends to connect a frame, a mirror forming portion having a mirror plane, the frame and the mirror forming portion, and rotates the mirror forming portion with respect to the frame. And a torsional connection part that is parallel to the mirror plane and has a width in a direction transverse to the rotation axis, the width of the torsional connection part being in the mirror forming part It is characterized by being relatively wide at the connected part and gradually becoming narrower as it moves away from the mirror forming part until at least halfway to reach the frame.

  According to such a configuration, it is possible to suppress an inappropriate operation of the mirror forming portion while setting the torsional resistance of the torsion coupling portion or torsion bar of the micromirror element low. Specifically, the torsional coupling part has a relatively narrow part away from the mirror forming part, and the presence of the narrow part or, if formed, a narrower part. Thus, a desired low torsional resistance is achieved at the torsional connection. At the same time, the torsional coupling part gradually increases in width from the narrow part to the mirror forming part and has a relatively wide part connected to the mirror forming part. Provides a function to suppress rotation around the normal of the mirror surface.

  Preferably, further comprising an additional frame and an additional torsional connection, the additional torsional connection extending to connect the additional frame and the frame, and for rotating the frame and the mirror forming part relative to the additional frame Define additional rotational axes. With such a configuration, a biaxial micromirror element in which inappropriate operation of the mirror forming portion is suppressed can be obtained.

  Preferably, the additional torsion coupling portion has a width parallel to the mirror plane and transverse to the additional rotation axis, and the additional torsion coupling portion has a relative width at a portion connected to the frame. Widely, at least part way up to the additional frame, gradually becomes narrower as the distance from the frame increases. According to such a configuration, in the biaxial micromirror element, the torsional resistance of the additional torsion coupling part or the torsion bar for coupling the frame and the additional frame is set low by the same structural action as described above. In addition, an inappropriate operation of the frame can be suppressed, and an inappropriate operation of the mirror forming unit can be further suppressed.

  The micromirror element provided by the second aspect of the present invention includes an inner frame and an outer frame, a mirror forming part having a mirror plane, an inner twist connecting part extending so as to connect the inner frame and the mirror forming part, It extends to connect the inner frame and the outer frame, defines a rotation axis for rotating the inner frame and the mirror forming portion with respect to the outer frame, and is parallel to the mirror plane and with respect to the rotation axis An outer torsion coupling portion having a width in a transverse direction, and the width of the outer torsion coupling portion is relatively wide at a portion connected to the inner frame, and at least halfway to reach the outer frame It is characterized by being gradually narrowed away from the distance.

  According to such a configuration, in the biaxial micromirror element, the torsion of the outer torsion connecting portion or the torsion bar for connecting the inner frame and the outer frame by the same structural action as described above with respect to the first side surface. It is possible to suppress inappropriate operation of the inner frame and the mirror forming portion while setting the resistance low.

  In the first aspect and the second aspect of the present invention, the torsion coupling part, the additional torsion coupling part, the inner torsion coupling part, and the outer torsion coupling part can be constituted by a single torsion bar, or a plurality of torsion bars. The torsion bar can also be configured.

  Even when the torsional connection part, the additional torsional connection part, the inner torsional connection part, or the outer torsional connection part is composed of a plurality of torsion bars, by the same action as described above, while setting these torsional resistances low, Inappropriate operation of the mirror forming surface can be suppressed. However, in this case, the width of each torsional coupling portion is defined by the two torsion bars existing at the extreme ends in the transverse direction of the rotation axis defined by each torsional coupling portion and parallel to the mirror plane. In this case, each torsional coupling portion also includes a gap portion interposed between the two torsion bars existing at the extreme ends and, if present, a further torsion bar.

  When each torsional connection part includes a plurality of torsion bars, these torsion bars are preferably separated into two or more different potential transmission paths. With such a configuration, the degree of freedom of wiring of the mirror forming unit driving circuit can be increased.

  In the present invention, preferably, the width of the torsion coupling part, the additional torsion coupling part, the inner torsion coupling part, or the outer torsion coupling part reaches each corresponding frame, that is, the frame, the additional frame, the inner frame, or the outer frame. Continue to decrease gradually. In such a configuration, in each torsion coupling portion, that is, in a region occupied by one torsion bar or a plurality of torsion bars, the portion farthest from the mirror forming portion is the narrowest, and the mirror forming portion The closest part is the widest. Accordingly, it is possible to satisfactorily suppress an inappropriate operation of the mirror forming surface while achieving a low torsional resistance in each torsional coupling portion. In the present invention, instead of this, the width of each torsional connecting portion may be gradually increased to the corresponding frame after being gradually reduced to the middle.

  In a preferred embodiment, the torsion coupling part, the additional torsion coupling part, the inner torsion coupling part, or the outer torsion coupling part, or each of the plurality of torsion bars included therein is formed of a group consisting of a rectangle, a circle, and an ellipse. It has a selected cross-sectional outline shape. Each torsional connection or torsion bar may have a hollow structure. Moreover, each torsional connection part or torsion bar may have a branched structure. By adopting these configurations, it is possible to adjust torsional rigidity, bending rigidity, and the like for each torsional coupling portion.

  In a preferred embodiment, each of the torsion coupling portion, the additional torsion coupling portion, the inner torsion coupling portion, or the outer torsion coupling portion, or the plurality of torsion bars included in the torsion coupling portion, the first torsion bar that expands with a first curvature. It has a proximal end and / or a second proximal end. According to such a configuration, it is possible to improve the support strength for the mirror forming portion or each frame in each torsion coupling portion or torsion bar.

  In the present invention, electrostatic force or electromagnetic force can be used to swing the mirror forming portion. In a preferred embodiment, the mirror forming portion has a first comb electrode portion, and the frame or the inner frame displaces the mirror forming portion by generating an electrostatic force with the first comb electrode portion. Having a second comb electrode portion. In the biaxial type, the frame or the inner frame has a third comb-tooth electrode portion, and the additional frame or the outer frame generates an electrostatic force between the third comb-tooth electrode portion and the frame or the inner frame. It is preferable to have a fourth comb electrode part for displacing the mirror forming part. Thus, the micromirror element according to the present invention can be configured in a comb electrode type.

  Instead, a base part facing the mirror forming part is further provided, and a first flat plate electrode facing the mirror forming part is provided on the base part, and the mirror forming part includes a first flat electrode facing the first flat plate electrode. By providing two plate electrodes, the micromirror element of the present invention may be configured as a plate electrode type. However, when at least a part of the mirror forming portion itself is made of a conductive material, the second flat plate electrode is not necessarily provided.

  Alternatively, the first electromagnetic coil is provided in the mirror forming portion and the second electromagnetic coil or permanent magnet is provided in the base portion, or the permanent magnet is provided in the mirror forming portion and the electromagnetic coil is provided in the base portion. The micromirror element of the present invention may be configured as an electromagnetic drive type.

  In a preferred embodiment, at least a part of the frame, the additional frame, the inner frame, or the outer frame has a multilayer structure including a plurality of conductor layers and an insulating layer between the conductor layers. With such a configuration, the degree of freedom of wiring by the conductor layer can be increased in the mirror forming portion driving circuit by the conductor layer. Preferably, each frame has a plurality of sections insulated from each other by an insulating film or a gap so that the frame is appropriately insulated in the structure of the micromirror element.

1 is an exploded perspective view of a micromirror element according to a first embodiment of the present invention. It is sectional drawing along line II-II in the assembly state of the micromirror element shown in FIG. It is the top view and bottom view of the micromirror element which concerns on the 2nd Embodiment of this invention. It is sectional drawing of the micromirror element shown in FIG. FIG. 4 is a cross-sectional view taken along line EE in FIG. 3, showing a part of the method for manufacturing the micromirror element shown in FIG. 3. FIG. 4 is a cross-sectional view taken along line EE in FIG. 3, showing a part of the method for manufacturing the micromirror element shown in FIG. 3. It is a top view of the mask for mask pattern formation used in the manufacturing process shown in FIG. FIG. 7 is a plan view of a mask for forming a mask pattern used in the manufacturing process shown in FIG. 6. It is the top view and sectional drawing of another torsion coupling part which concern on this invention. It is sectional drawing of the conventional micromirror element. It is a perspective view of the mirror board | substrate which the micromirror element shown in FIG. 10 has.

  Hereinafter, preferred embodiments of the present invention will be specifically described with reference to the drawings.

  FIG. 1 is an exploded perspective view of the micromirror element 100 according to the first embodiment of the present invention, and FIG. FIG. The micromirror element 100 of this embodiment has a structure in which a mirror substrate 110 and a base substrate 120 are stacked.

  As shown in FIG. 1, the mirror substrate 110 includes a mirror forming portion 111, a frame 113 surrounding the mirror forming portion 111, and a pair of twisted connecting portions 112 that connect the frame 113 and the mirror forming portion 111. The mirror substrate 110 is formed by a bulk machining technique from a silicon substrate provided with conductivity by doping an n-type impurity such as P or As or a p-type impurity such as B, for example. Specifically, Si etching by deep RIE method is performed on a plate-shaped conductive silicon substrate using an etching mask that covers portions corresponding to the mirror forming portion 111, the frame 113, and the pair of twisted connecting portions 112. The plurality of gaps 110a are provided by means such as wet Si etching such as KOH. As a result, the mirror forming portion 111, the frame 113, and the pair of torsional coupling portions 112 are formed by the plurality of gap portions 110a. In the present embodiment, the width of each gap 110a between the mirror forming part 111 and the frame 113 is, for example, 10 to 200 μm, and the thickness of the mirror forming part 111 and the frame 113 is, for example, 10 to 200 μm.

  As clearly shown in FIG. 2, a mirror surface 114 is provided on the surface of the mirror forming portion 111, and a pair of electrodes 115a and 115b are provided on the back surface thereof. The mirror surface 114 and the electrodes 115a and 115b are formed by evaporating a metal film. However, when the conductivity of the mirror substrate 110 is sufficiently high by doping impurities, the electrodes 115a and 115b are not necessarily provided.

  As clearly shown in FIG. 1, each torsional coupling portion 112 is integrally connected to the vicinity of the center of the side surface extending in the longitudinal direction of the mirror forming portion 111 and the vicinity of the center of the inner side surface extending in the longitudinal direction of the frame 113. is doing. Accordingly, the micromirror element 100 of the present embodiment is configured as a uniaxial type in which the rotation axis X1 is defined by the pair of torsional coupling portions 112. In the present embodiment, each torsional coupling portion 112 includes two torsion bars 112a, and the two torsion bars 112a define the width of the torsional coupling portion 112, that is, the length in the Y direction in the drawing. The width of the torsional coupling portion 112 is, for example, 30 to 300 μm at a portion connected to the mirror forming portion 111, and gradually decreases from the mirror forming portion 111 to the frame 113, and 1 to 30 μm at a portion connecting to the frame 113. It is.

  When the micromirror element 100 is assembled, the lower surface of the frame 113 of the mirror forming portion 111 is bonded to the upper surface of the convex step portion 121 of the base substrate 120 as shown in FIG. The base substrate 120 includes a pair of electrodes 122a and 122b that are opposed to the pair of electrodes 115a and 115b of the mirror forming portion 111 with an appropriate interval. That is, the micromirror element 100 according to the present embodiment is configured as a so-called flat plate type.

  According to such a configuration, for example, when the electrodes 115a and 115b of the mirror forming portion 111 are charged to the positive electrode and the electrode 122a of the base substrate 120 is set to the negative electrode, an electrostatic force is generated between them, and the mirror The forming part 111 swings in the direction of the arrow M <b> 1 while twisting the pair of torsional coupling parts 112. Alternatively, if the electrode 122b is a negative electrode, the mirror forming portion 111 will swing in the opposite direction. Thus, by swinging the mirror forming portion 111, the reflection direction of the light traveling toward the mirror surface 114 and reflected by the mirror surface 114 can be switched to a predetermined direction. When the mirror forming portion 111 swings, the torsional coupling portion 112 has a relatively narrow portion, so that the torsional resistance of the torsional coupling portion 112 is reduced. At the same time, since the torsional coupling portion 112 is connected to the mirror forming portion 114 at a relatively wide portion, it is possible to satisfactorily suppress the mirror forming portion 111 from rotating around the normal line N1.

  The potential application to the electrodes 115a and 115b of the mirror forming portion 111 is performed through the frame 113 made of a conductive material, the torsion coupling portion 112, and the mirror forming portion 111. The potential application to the electrodes 122a and 122b of the base substrate 120 is performed through wiring (not shown) appropriately provided on the base substrate 120 made of an insulating material. In the mirror substrate 110 of the micromirror element 100 of the present embodiment, the mirror forming part 111, the twist coupling part 112, and the frame 113 are integrally formed of a conductive material, and the mirror forming part 111 is interposed via the twist coupling part 112. Since the potential can be appropriately applied to the electrodes 115a and 115b, the wiring for applying the potential to the electrodes 115a and 115b of the mirror substrate 110 is different from the conventional micromirror element by using the twist coupling portion 112. There is no need to form it separately.

  In order to drive the mirror forming portion 111 of the micromirror element 100, a comb electrode may be provided instead of the flat plate electrode. Moreover, it can replace with the electrostatic force by a flat electrode, a comb-tooth electrode, etc., and the electromagnetic force by an electromagnetic coil, a permanent magnet, etc. can also be utilized. Specifically, the electrodes 115a and 115b of the mirror forming portion 111 are replaced with electromagnetic coils, and the electrodes 122a and 122b of the base substrate are replaced with electromagnetic coils or permanent magnets. Alternatively, the electrodes 115a and 115b of the mirror forming portion 111 are replaced with permanent magnets, and the electrodes 122a and 122b of the base substrate are replaced with electromagnetic coils. In these configurations, the mirror forming unit 111 can be driven by adjusting the energization state of the electromagnetic coil.

  3 and 4 show a micromirror element 200 according to the second embodiment of the present invention. 3A is a top view of the micromirror element 200, and FIG. 3B is a bottom view. 4A to 4C are cross-sectional views taken along line AA, line BB, and line CC in FIG. 3, respectively.

  As shown in FIG. 3, the micromirror element 200 according to the present embodiment connects a mirror forming part 210, an inner frame 220 surrounding the mirror forming part 210, an outer frame 230 surrounding the inner frame 220, and the mirror forming part 210 and the inner frame 220. A pair of torsional connection parts 240 and a pair of torsional connection parts 250 that connect the inner frame 220 and the outer frame 230 are provided. The pair of torsional coupling portions 240 define a rotational axis X2 of the rotational movement of the mirror forming portion 210 relative to the inner frame 220. The pair of torsional coupling portions 250 defines a rotational axis X3 of the rotational motion of the inner frame 220 relative to the outer frame 230. In the present embodiment, the rotation axis X2 and the rotation axis X3 are orthogonal to each other. The micromirror element 200 is integrally formed of a conductive material except for a mirror surface 211 and an insulating layer 260 described later. As the conductive material, a semiconductor such as Si doped with an n-type impurity such as P or As or a p-type impurity such as B is used. However, instead of this, a metal such as W may be used.

  As shown in FIG. 3A, the mirror forming part 210 has a mirror surface 211 formed as a thin film on the upper surface thereof. In addition, first comb electrodes 210 a and 210 b are extended and formed on two opposite side surfaces of the mirror forming portion 210.

  As shown in FIGS. 3B and 4, the inner frame 220 has a laminated structure including an inner frame main part 221, a pair of electrode bases 222, and an insulating layer 260 therebetween. The inner frame main part 221 and the electrode base 222 are electrically separated. The pair of electrode bases 222 are integrally formed with second comb-teeth electrodes 222a and 222b extending inward, and the inner frame main portion 221 has third comb-teeth extending outward. Electrodes 221a and 221b are integrally formed. As shown in FIG. 4A, the second comb electrodes 222a and 222b are positioned below the first comb electrodes 210a and 210b of the mirror forming unit 210, but the mirror forming unit 210 swings. In order to prevent the teeth of the first comb electrodes 210a and 210b and the teeth of the second comb electrodes 222a and 222b from coming into contact with each other, the teeth of each other are misaligned as shown in FIG. 4C. It is arranged to do.

  As shown in FIG. 3, each of the pair of torsional connection parts 240 includes two torsion bars 241. The width of the torsional coupling part 240 defined by the two torsion bars 241 is 30 to 300 μm at the location where it is connected to the mirror forming part 210, and gradually decreases from the mirror forming part 210 to the inner frame 220. It is 1-30 micrometers in the location connected to. As shown in FIG. 4B, the torsion bar 241 is thinner than the mirror forming part 210 and the inner frame 220, and bridges the mirror forming part 210 and the inner frame main part 221 of the inner frame 220.

  As shown in FIG. 4A, the outer frame 230 has a laminated structure including a first outer frame portion 231, a second outer frame portion 232, and an insulating layer 260 therebetween. The first outer frame portion 231 and the second outer frame portion 232 are electrically separated. As shown in FIG. 3B, the second outer frame portion 232 is provided with a first island 233, a second island 234, a third island 235, and a fourth island 236 through a gap. ing. As clearly shown in FIGS. 4B and 4C, the first island 233 and the third island 235 are integrally formed with fourth comb electrodes 232a and 232b extending inward, respectively. It is molded into. The fourth comb electrodes 232a and 232b are respectively positioned below the third comb electrodes 221a and 221b of the inner frame main portion 221, but when the inner frame 220 swings, the third comb electrodes The teeth of 221a and 221b and the teeth of the fourth comb-tooth electrodes 222a and 222b are arranged so that their teeth are displaced from each other so that they do not come into contact with each other.

  Each of the pair of torsional connection portions 250 includes one torsion bar 251 and two torsion bars 252 as shown in FIG. The width of the torsional coupling portion 250 defined by the two torsion bars 252 disposed at both ends is 30 to 300 μm at a position where it is connected to the inner frame 220 and gradually decreases from the inner frame 220 to the outer frame 230. In a portion connected to the outer frame 230, the thickness is 1 to 30 μm. The torsion bars 251 and 252 are thinner than the inner frame 220 and the outer frame 230 as shown in FIG. The torsion bar 251 bridges the inner frame main part 221 of the inner frame 220 and the first outer frame part 231 of the outer frame 230. The torsion bar 252 bridges the electrode base 222 of the inner frame 220 and the second outer frame portion 232 of the outer frame 230.

  In the present embodiment, when a potential is applied to the first outer frame portion 231, the first outer frame portion 231 is integrally formed of the same conductive material as can be understood with reference to FIG. Through the two torsion bars 251, the inner frame main part 221, a pair of torsional connection parts 240 or a total of four torsion bars 241, and the mirror forming part 210, the first comb-tooth electrodes 210 a and 210 b and the third comb The tooth electrodes 221a and 221b have the same potential. In this state, a desired potential is applied to the second comb-tooth electrode 222a or the second comb-tooth electrode 222b, and between the first comb-tooth electrode 210a and the second comb-tooth electrode 222a, or the first comb-tooth electrode 210b. By generating an electrostatic force between the second comb electrode 222b and the second comb electrode 222b, the mirror forming part 210 can be swung around the rotation axis X2. In addition, a desired potential is applied to the fourth comb electrode 232a or the fourth comb electrode 232b, and between the third comb electrode 221a and the fourth comb electrode 232a, or between the third comb electrode 221b and the second comb electrode 221b. By generating an electrostatic force between the four comb electrodes 232b, the inner frame 220 and the mirror forming part 210 can be swung around the rotation axis X3.

  As can be understood with reference to FIG. 4A, the potential application to the second comb-tooth electrode 222a is performed by the fourth island 236 of the second outer frame portion 232, which is integrally formed of the same conductive material. This is done through a torsion bar 252 connected to this and an electrode base 222 connected to this. Similarly, the potential application to the second comb electrode 222b is performed through the second island 234, the torsion bar 252 connected thereto, and the electrode base 222 connected thereto. On the other hand, the application of potential to the fourth comb electrode 232a is performed via the first island 233 of the second outer frame portion 232, as can be understood with reference to FIG. 4B, and the fourth comb electrode 232b. The potential is applied to the first island 235 through the third island 235. Since the four islands 233, 234, 235, and 236 in the second outer frame portion 232 are electrically independent, the potential application to the second comb electrodes 222a and 222b and the fourth comb electrodes is selectively performed. It can be carried out. As a result, the mirror forming part 210 can be inclined in a desired direction. When the mirror forming portion 210 swings, the torsional coupling portions 240 and 250 have relatively narrow portions, so that the torsional resistance of the torsional coupling portions 240 and 250 is reduced. At the same time, the torsional coupling part 240 is connected to the mirror forming part 210 at a relatively wide part, and the torsional coupling part 250 is connected to the inner frame 220 at a relatively wide part. Can be satisfactorily suppressed from rotating around the normal line (not shown).

  Next, with reference to FIG. 5 and FIG. 6, a manufacturing method of the micromirror element 200 having the above-described configuration will be described. FIG. 5 shows a part of the process of manufacturing the micromirror element 200 shown in FIG. 3 in a cross-sectional view taken along the solid line EE in FIG. FIG. 6 is a cross-sectional view of the process following FIG. 5 and taken along the line EE in FIG.

  As shown in FIG. 5A, in the manufacture of the micromirror element 200, first, two silicon wafers 200 ′ that are made conductive by doping an n-type impurity such as As are prepared. A 500 nm silicon dioxide film 260 is grown on the surface of the wafer 200 ′ by thermal oxidation. The resistivity of the wafer is desirably in the range of 0.01 to 0.1 Ω · cm. Further, when imparting conductivity to the wafer, p-type impurities such as B may be used.

Next, as shown in FIG. 5B, the two silicon wafers 200 ′ are stacked by combining the silicon dioxide films 260 and performing a nitrogen annealing process at about 1100 ° C. Thereafter, the wafer surface is polished to adjust the thickness of each wafer 200 ′ to 100 μm. As a result, an SOI (Silicon on Insulator) wafer 201 ′ having a thickness structure of 100 μm / 1 μm / 100 μm with the structure of Si / SiO ₂ / Si is obtained.

Next, as shown in FIG. 5C, a silicon dioxide film 30 ′ as an etching mask is formed on the upper surface of the SOI wafer 201 ′. The film thickness is in the range of 100 to 1000 nm. At this time, a silicon dioxide film may be formed on the lower surface. However, in the formation of an etching mask, if a film forming material that can function as a mask material in the subsequent Si etching by the Deep RIE method, that is, a film forming material having an etching rate slower than Si, SiO ₂ is used. Without limitation, other materials may be used. As the film forming means, a thermal oxidation method or a CVD method may be employed.

Next, as shown in FIG. 5D, the silicon dioxide film 30 ′ is etched to form a first mask pattern 30. For this etching, the first mask 40 having the configuration shown in FIG. The first mask 40 includes a mirror forming portion 210, a pair of first comb electrodes 210a and 210b, an inner frame main portion 221, a pair of third comb electrodes 221a and 221b, and a first outer frame in the micromirror element 200. This corresponds to the planar view shape of the portion 231. Therefore, the first mask pattern 30 is formed in the same shape as the first mask 40 on the SOI wafer 201 ′. This etching may be performed by a wet etching method using a solution containing HF, or by a dry etching method using a gas such as CHF ₃ or C ₄ F ₈ .

Next, a photoresist film as a second etching mask is formed on the SOI wafer 201 ′ in the thickness range of 0.5 to 50 μm. However, as the second etching mask, a Si ₃ N ₄ film may be formed instead of the photoresist film. As the film forming means, a thermal oxidation method or a CVD method may be employed. Then, this is etched to form a second mask pattern 50 as shown in FIG. For this etching, the second mask 60 having the configuration shown in FIG. 7B is used. The second mask 60 corresponds to the shape of the pair of torsional connecting portions 240 in the micromirror element 200 or a total of four torsion bars 241, the pair of torsion bars 251, and the support beam 270 in plan view. Therefore, the second mask pattern 50 also has the same shape as the second mask 60. Here, the support beam is a temporary connecting portion that is provided to prevent mechanical stress during the manufacturing process of the micromirror element from being concentrated on the twisting connecting portion and is cut and removed in a later step. In the present embodiment, four support beams 270 that connect the inner frame 220 and the mirror forming portion 210 and four support beams 270 that connect the outer frame 230 and the inner frame 220 are provided. Further, this etching may be performed by a wet etching method using a solution containing HF, if possible, or by a dry etching method using a gas such as CHF ₃ or C ₄ F ₈ instead of the photo etching. Although it is good, it is performed under the condition that the first mask pattern 30 is not etched.

Next, as shown in FIG. 5F, a first etching process is performed on the wafer 201 ′ using the first mask pattern 30 and the second mask pattern 50 as a mask. This etching is performed to a desired depth of 5 μm by deep RIE using SF ₆ gas and C ₄ F ₈ gas. However, a wet etching method using a KOH solution or the like may be employed instead of the Deep RIE method.

Next, as shown in FIG. 5G, only the second mask pattern 50 is removed by exposure to an organic solvent or oxygen plasma. As the organic solvent at this time, according to the constituent material of the second mask pattern 50, for example, tripropylene glycol methyl ether, aminoethylethanolamine, phosphoric acid aqueous solution, mixed solution of monoethanolamine and dimethylsulfoxide, and the like Can be used. However, it is necessary to select a solvent that does not significantly remove the first mask pattern 30. For example, when the first mask pattern 30 is made of SiO _{2 and} the second mask pattern 50 is made of Si ₃ N ₄ , the second mask pattern 30 is left with the phosphoric acid aqueous solution while leaving the first mask pattern 30. Only the mask pattern 50 can be selectively removed.

Next, as shown in FIG. 5H, a second etching process is performed using only the first mask pattern 30 as a mask. The second etching process is performed to a depth of 95 μm from the surface of the material constituting the wafer by deep RIE using SF ₆ gas and C ₄ F ₈ gas. If necessary, overetching is further performed to a depth of 1 μm to absorb manufacturing process errors.

  Through the above steps, the mirror forming part 210 in the micromirror element 200, the pair of first comb electrodes 210a and 210b, the inner frame main part 221, the pair of third comb electrodes 221a and 221b, A first outer frame portion 231, a pair of torsion coupling portions 240 to a total of four torsion bars 241, a pair of torsion bars 251, and a total of eight support beams 270 are formed. Further, when the second etching process is performed by the Deep RIE method as in the present embodiment, as shown in FIG. 5 (h), the roots or base end portions of the torsion bar 241 and the torsion bar 251 have a uniform thickness. Instead, the shape has a curvature.

  Next, in order to prevent the upper structure of the insulating layer 260 from being damaged in the subsequent steps, liquid glass is applied and annealed to form a sacrificial film 70 as shown in FIG. . However, instead of such protection means, a resist material such as AZ or TSCR may be applied and formed, or the film may be protected by attaching a film capable of controlling the adhesive force such as an ultraviolet curable adhesive film sheet. Also good.

  After the sacrificial film 70 is formed, the lower layer of the insulating layer 260 is processed by a method substantially similar to that described with reference to FIG. First, a silicon dioxide film as a third etching mask is formed on the lower surface of the wafer 201 ′ with a film thickness in the range of 100 to 1000 nm, and this is etched, as shown in FIG. Then, a third mask pattern 31 is formed. For this etching, a third mask 41 having the configuration shown in FIG. The third mask 41 includes a pair of electrode bases 222 in the micromirror element 200, second comb electrodes 222a and 222b, a second outer frame portion 232 including first to fourth islands 233, 234, 235, and 236, and This corresponds to a plan view form of the fourth comb electrodes 232a and 232b. Therefore, the third mask pattern 31 also has the same shape as the third mask 41.

  Next, a photoresist film as a fourth etching mask is formed on the wafer 201 ′ in a thickness range of 0.5 to 50 μm, and this is etched under the condition that the third mask pattern 31 is not removed. Similarly, as shown in FIG. 6B, a fourth mask pattern 51 is formed. For this etching, a fourth mask 61 having the configuration shown in FIG. 8B is used. The fourth mask 61 corresponds to the planar shape of the four torsion bars 252 in total. Therefore, the fourth mask pattern 51 also has the same shape as the fourth mask 61.

Next, as shown in FIG. 6C, a first etching process is performed on the wafer 201 ′ using the third mask pattern 31 and the fourth mask pattern 51 as a mask. This etching is performed to a desired depth of 5 μm by deep RIE using SF ₆ gas and C ₄ F ₈ gas. However, a wet etching method using a KOH solution or the like may be employed instead of the Deep RIE method.

Next, after removing only the fourth mask pattern 51 by exposure to an organic solvent or oxygen plasma, as shown in FIG. 6D, a second etching process is performed using only the third mask pattern 31 as a mask. . The second etching process is performed to a depth of 95 μm from the surface of the material constituting the wafer by deep RIE using SF ₆ gas and C ₄ F ₈ gas. If necessary, overetching is further performed to a depth of 1 μm to absorb manufacturing process errors.

  Through the above process, a pair of electrode bases 222, second comb electrodes 222a, 222b, second outer frame portion 232, fourth comb electrodes 232a, 232b, and Four torsion bars 252 are formed. In addition, when the second etching process is performed by the Deep RIE method as in the present embodiment, the base end portion of the torsion bar 252 is not uniform in thickness but has a curved shape.

  Next, as shown in FIG. 6E, the first mask pattern 30 and the third mask pattern 31 on the surface of the wafer 201 ′, and the insulating layer 260 at predetermined positions are removed by a wet etching method or the like, and then removed from the wafer. The micromirror element 200 with the support beam 270 is completed by cutting into chips. Support beam 270 is removed at an appropriate later stage. Upon removal, the support beam 270 may be blown and blown by a laser, or may be blown by Joule heat by passing an electric current.

  The mirror surface 211 of the mirror forming part 210 is formed in a predetermined shape at a place where the mirror forming part 210 is formed before the above series of steps. However, regarding the present embodiment, the process of forming the mirror surface 211 is not shown. In forming the mirror surface 210, for example, a titanium film having a thickness of 50 nm is formed on the mirror forming portion 210 or a place where the mirror surface 210 is to be formed, and then a gold film having a thickness of 500 nm is formed thereon and etched. According to such a configuration, the mirror surface 211 not only functions as an optical reflection film, but also can be electrically connected to the wafer material, and can be connected to a bonding wire if necessary.

  In the above embodiment, as a means for forming a void while leaving a cross-linked portion with respect to the substrate material, the cross-link finally formed by the first etching process using the first and second mask patterns as a mask. Substrate configuration so that the two members are connected only by the bridging portion by the second etching process using only the first mask pattern as a mask after removing the substrate constituent material to a depth substantially corresponding to the thickness of the portion. By removing the material, a method of simultaneously completing the bridge portion and the void portion is adopted. However, in the present invention, instead of this, the first etching process removes all of the substrate constituent material in the portion where the first and second mask patterns are not masked in the substrate, thereby forming the voids first. Then, a method of completing the cross-linked portion by removing the substrate constituent material until the cross-linked portion is formed by the second etching process may be adopted.

  FIGS. 9A to 9I are a plan view (left) and a cross-sectional view (right) of another torsion coupling portion according to the present invention. When each torsion coupling portion is provided in place of the torsion coupling portion 112 in the first embodiment, in the plan view thereof, the left end is connected to the mirror forming portion 111, and the right end is connected to the frame 113. . On the other hand, when the second embodiment is provided instead of the torsional coupling portion 240, the left end thereof is connected to the mirror forming portion 210 and the right end thereof is connected to the inner frame 220. In the second embodiment, when provided instead of the torsional coupling portion 250, the left end is connected to the inner frame 220, and the right end is connected to the outer frame 230.

  The torsional coupling portion 310 shown in FIG. 9A is composed of one torsion bar, and its width is gradually narrowed from the left end to the right end. The width of the widest portion at the left end is 30 to 300 μm, and the width of the narrowest portion at the right end is 1 to 30 μm.

  The torsional coupling portion 320 shown in FIG. 9B is made up of a single torsion bar, and has a portion that gradually narrows away from the left end and a portion that gradually widens away from the left end. The width of the widest part at the left end and the right end is 30 to 300 μm, and the width of the narrowest part at the center is 1 to 30 μm.

  The torsional coupling portion 330 shown in FIG. 9C includes two torsion bars 331 and 332. The width of the torsional coupling portion 330 defined by the two torsion bars 331 and 332 is gradually narrowed from the left end to the right end. The width of the widest portion at the left end is 30 to 300 μm, and the width of the narrowest portion at the right end is 1 to 30 μm. The torsion bars 331 and 332 are displaced in the thickness direction of the micromirror element. For example, in the micromirror element 200 of the above-described second embodiment, when the torsional connection part 330 is provided instead of the torsional connection part 250, the torsion bar 331 includes the inner frame main part 221 and the first outer frame part 231. The torsion bar 332 connects the electrode base 222 and the second outer frame portion 232.

  The torsional coupling portion 340 shown in FIG. 9 (d) is made up of one torsion bar having an X-shaped branch structure, and gradually becomes wider as it goes away from the left end, and gradually becomes wider as it goes away from the left end. It has a part which becomes. The width of the widest part at the left end and the right end is 30 to 300 μm, and the width of the narrowest part at the center is 1 to 30 μm.

  The torsional coupling portion 350 shown in FIG. 9 (e) includes three torsion bars 351, 352, and 353. The width of the torsional coupling portion 350 defined by the torsion bars 351 and 353 located at both ends is gradually narrowed from the left end to the right end. The width of the widest portion at the left end is 30 to 300 μm, and the width of the narrowest portion at the right end is 1 to 30 μm.

  The torsional coupling portion 360 shown in FIG. 9 (f) is composed of two torsion bars 361 and 362. The width of the torsional coupling portion 360 defined by the two torsion bars 361 and 362 is gradually narrowed from the left end to the right end. Both base ends of the torsion bars 361 and 362 have a curvature and spread in the width direction.

  The torsional coupling portion 370 shown in FIG. 9 (g) includes two torsion bars 371 and 372. The width of the torsional coupling portion 370 defined by the two torsion bars 371 and 372 gradually decreases from the left end to the right end. The width of the widest portion at the left end is 30 to 300 μm, and the width of the narrowest portion at the right end is 1 to 30 μm. The torsion bars 371 and 372 have a hollow structure.

  The torsional coupling portion 380 shown in FIG. 9 (h) includes two torsion bars 381 and 382. The width of the torsional coupling portion 380 defined by the two torsion bars 381 and 382 is gradually narrowed from the left end to the right end. The width of the widest portion at the left end is 30 to 300 μm, and the width of the narrowest portion at the right end is 1 to 30 μm. The torsion bars 381, 382 have a uniform elliptical cross section.

  The torsional coupling portion 390 shown in FIG. 9 (i) is composed of a single torsion bar having a Y-shaped branch structure, and a portion that gradually narrows away from the left end and a portion that has a uniform width. And have. The width of the widest portion at the left end is 30 to 300 μm, and the width of the portion having a uniform width is 1 to 30 μm.

  According to the present invention, the torsional coupling part has a relatively wide part connected to the mirror forming part or the inner frame and a part gradually narrowing from the wide part, so that a desired low torsional resistance is provided in the torsional coupling part. And the rotation of the mirror forming portion around the normal of the mirror surface can be suppressed. As a result, it is possible to control the micromirror element satisfactorily.

100, 200, 400 Micro mirror element 110, 410 Mirror substrate 111, 411 Mirror formation part 112 Twist connection part 112a Torsion bar 412 Torsion bar 113, 413 Frame 120, 420 Base substrate 210 Mirror formation part 210a, 210b First comb-teeth electrode 220 Inner frame 221 Inner frame main part 221a, 221b Third comb electrode 222 Electrode base 222a, 222b Second comb electrode 230 Outer frame 231 First outer frame part 232 Second outer frame part 232a, 232b Fourth comb tooth Electrode 240, 250 Twist connection part 241, 251, 252 Torsion bar 260 Insulating layer 270 Support beam

Claims (12)

Frame,
A mirror forming portion having a mirror plane;
Extending to connect the frame and the mirror forming part, defining a rotation axis for rotating the mirror forming part with respect to the frame, and a twist connecting part parallel to the mirror plane; With
The torsion coupling part is composed of two torsion bars, and the two torsion bars define a width of the torsion coupling part, and the width is relatively wide at a portion connected to the mirror forming part. The micromirror element is characterized by gradually becoming narrower as the distance from the mirror forming portion increases until the frame is reached. In addition, an additional frame,
And an additional torsional connection portion extending to connect the additional frame and the frame and defining an additional rotational axis for rotating the frame and the mirror forming portion relative to the additional frame. 2. The micromirror element according to 1.     The additional torsion coupling portion is parallel to the mirror plane and includes two torsion bars, and the two torsion bars define a second width of the additional torsion coupling portion, and 3. The micromirror element according to claim 2, wherein the width of 2 is relatively wide at a portion connected to the frame, and gradually decreases as the distance from the frame increases until the additional frame is reached. An inner frame and an outer frame;
A mirror forming portion having a mirror plane;
An inner torsion coupling portion that extends to connect the inner frame and the mirror forming portion and that defines a first rotational axis for rotating the mirror forming portion relative to the inner frame;
An outer torsion coupling portion that extends to connect the inner frame and the outer frame and that defines a second rotation axis for rotating the inner frame and the mirror forming portion with respect to the outer frame. ,
The outer torsion coupling part is parallel to the mirror plane and includes two torsion bars, and the two torsion bars define a width of the outer torsion coupling part, and the width is A micromirror element characterized by being relatively wide at a portion connected to an inner frame and gradually becoming narrower as it gets farther from the inner frame until it reaches the outer frame. Each torsional connection further includes a third torsion bar;
The two torsion bars bridge the inner frame main part of the inner frame and the first outer frame part of the outer frame, and the third torsion bar includes an electrode base of the inner frame and the outer frame. The microphone mirror element according to claim 4, wherein the second outer frame portion is bridged.     6. The micromirror element according to claim 5, wherein the two torsion bars and the third torsion bar are electrically separated into two or more different potential transmission paths. The mirror forming portion has a first comb electrode portion,
The said frame or the said inner frame has a 2nd comb-tooth electrode part for displacing the said mirror formation part by producing an electrostatic force between the said 1st comb-tooth electrode part. The micromirror element according to any one of the above. Furthermore, a base portion facing the mirror forming portion is provided,
The base portion is provided with a first flat electrode facing the mirror forming portion,
The micromirror element according to any one of claims 1 to 6, wherein the mirror forming portion is provided with a second flat plate electrode facing the first flat plate electrode. Furthermore, a base portion facing the mirror forming portion is provided,
The mirror forming part is provided with a first electromagnetic coil, and the base part is provided with a second electromagnetic coil or a permanent magnet facing the first electromagnetic coil. The micromirror element described in one. Furthermore, a base portion facing the mirror forming portion is provided,
The micromirror element according to any one of claims 1 to 6, wherein a permanent magnet is provided in the mirror forming part, and an electromagnetic coil facing the permanent magnet is provided in the base part.     The frame or the inner frame has a third comb electrode part, and the additional frame or the outer frame generates an electrostatic force between the frame or the inner frame and the frame or the inner frame. The micromirror element according to claim 2, further comprising a fourth comb electrode part for displacing the mirror forming part.     The micromirror element according to any one of claims 1 to 11, wherein at least a part of each frame has a multilayer structure including a plurality of conductor layers and an insulating layer between the conductor layers.

Images