JP2010256452A - Method of manufacturing micro mechanical structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To more easily form a metallic film having a desired shape on both faces of a mirror structure manufactured by using an SOI ( silicon-on-insulator) substrate. <P>SOLUTION: An electrodeposition resist layer 107 is formed by electro-depositing an electrodeposition resist on the surface of the metallic film 106, the electrodeposition resist layer 107 is patterned by a photolithography, thus an electrodeposition resist pattern 171 is formed in the region facing the metallic pattern 141 of a mirror part 131. The electrodeposition resist pattern 171 is so formed to cover a metallic pattern region formed while facing the metallic pattern 141 on the back face side of the mirror part 131. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a method for manufacturing a micromechanical structure formed using an SOI substrate.

  Development of MEMS mirrors by micromachining using silicon as an optical device such as a communication device or a scanner is progressing. These optical devices are often intended for infrared. On the other hand, silicon used as a material has a very high transparency to infrared rays, and cannot be used as a mirror as it is. For this reason, a metal film having high reflectivity, such as aluminum or gold, is formed on the surface of silicon so as to function as a mirror for infrared rays. When thin silicon is used as the mirror structure, it is ideal to form a metal film on both surfaces of the mirror structure to maintain a stress balance so that the mirror surface is flat.

JP 2003-057574 A US Pat. No. 6,369,931

  However, at present, there is a problem that it is not easy to form metal films on both surfaces of the mirror structure.

  For example, there is a technique for manufacturing a MEMS (Micro Electro Mechanical Systems) mirror using an SOI (Silicon On Insulator) substrate (see Patent Document 1). In this technique, a mirror structure is formed by patterning an SOI layer disposed via a buried insulating layer on a base portion, an opening is formed in the base portion in a region corresponding to the formed mirror structure, The mirror structure can perform operations such as rotation.

  Here, on the surface side of the SOI layer in a flat state, a metal film is formed, and the formed metal film is patterned by a known lithography technique and an etching technique, so that a region that becomes a mirror structure is selectively used. It is easy to leave a metal film on the surface.

  On the other hand, on the back side of the mirror structure exposed in the opening on the base portion side, the region of the mirror structure of the base portion having a thickness of several hundreds of μm and the buried insulating layer is removed. Is forming. For this reason, when viewed from the base portion side (the back surface of the SOI substrate), the back surface side of the above-described mirror structure exists substantially in the depth of the base portion. In other words, there is almost a step in the thickness of the base portion on the back side of the mirror structure.

  When a metal film is selectively formed on the back surface side of the mirror structure in the same manner as described above, a resist film for forming an etching mask is formed where a large step exists. In general, a resist film is formed by applying a resist by spin coating. However, when a resist film is formed by spin coating, the resist is likely to remain in a recess having a large step, resulting in a non-uniform film thickness.

  For example, as shown in the cross-sectional view of FIG. 2, the recess 201 a is formed from the base portion 201 side of the SOI substrate including the base portion 201, the buried insulating layer 202, and the SOI layer 203. In this state, the metal film 204 is formed on the surface of the base body 201 (the back surface of the SOI substrate) including the inside of the recess 201a. Thereafter, when a photoresist is applied to the surface of the base portion 201 by spin coating, a non-uniform photoresist film 205 having a thicker film thickness is formed at the peripheral edge of the recess 201a.

  Thereafter, exposure by photolithography is performed. In this exposure, in general, the amount of light is substantially constant in the entire region of the recess 201a irradiated with light transmitted through the photomask. However, since the film thickness of the photoresist film 205 is not uniform as described above, the exposure conditions differ greatly between the terminal portion and the central portion of the recess 201a, and accurate patterning is easy. is not. If accurate patterning cannot be performed, a pattern having a desired shape and size cannot be formed with high accuracy, and a metal film cannot be formed in a desired shape.

  In addition to the formation of a mask pattern by spin coating and lithography, formation of a mask pattern by a screen printing method can be considered. In this method, as shown in FIG. 3, a recess 301a is formed from the base portion 301 side of an SOI substrate including a base portion 301, a buried insulating layer 302, and an SOI layer 303. In this state, a metal film 304 is formed on the surface of the base body 301 (the back surface of the SOI substrate) including the inside of the recess 301a. Thereafter, the resist material 351 is disposed on the screen 306 and the squeegee 307 is slid to selectively supply the resist material 351 from the opening 306 a of the screen 306. As a result, a resist pattern 305 is formed in the recess 301a. However, even in this method, as shown in FIG. 3, for example, the resist pattern 305 to be formed cannot obtain a uniform film thickness in the recess 301a, and it is not easy to form an accurate pattern.

  As described above, it is not easy to form an accurate resist pattern at the bottom of the recess, and it is not easy to form metal films on both surfaces of the mirror structure. Therefore, at present, a metal film is formed on the back surface of the SOI substrate including the inside of the recess, and the metal film is used without patterning. However, when a metal film is formed over the entire area in this way, a metal film is also formed on a connecting part that connects and supports the mirror structure to the surrounding frame part, and the mirror part is rotated. This may interfere with the operation of the machine.

  For this reason, a metal film is formed only on the surface side of the portion that becomes the mirror structure of the SOI layer in a flat state to form a MEMS mirror (see Patent Document 2). In this MEMS mirror, as shown in FIG. 4, a base portion 401 having a recess 401a, a buried insulating layer 402, a mirror structure 431, and a frame portion 432 are formed on an electrode substrate 411 having drive electrodes 412 and 413. The formed SOI layer 403 is disposed. In addition, a metal film 441 is provided on the surface side of the mirror structure 431.

  In this MEMS mirror, the base body portion 401 is used as a support, and the mirror structure 431 is disposed on the drive electrodes 412 and 413 so as to be separated from each other. The reflective surface of the metal film 441 is displaced.

  In this structure, the distance between the drive electrodes 412 and 413 and the mirror structure 431 is substantially determined by the thickness of the base portion 401, which significantly impairs the design freedom and makes it difficult to obtain desired drive characteristics. Further, since the metal film 441 is formed only on one surface, there is a problem that it is not easy to maintain the flatness of the mirror surface by this stress.

  The present invention has been made to solve the above-described problems, and a metal film having a desired shape can be more easily formed on both surfaces of a mirror structure manufactured using an SOI substrate. The purpose is to.

  The method for manufacturing a micromechanical structure according to the present invention includes forming a first metal pattern in a region to be a mirror portion on a surface silicon layer made of silicon disposed on a base portion via a buried insulating layer. A second step of patterning the surface silicon layer to form a mirror part, a frame part arranged around the mirror part, and a connecting part for connecting the mirror part and the frame part; A third step of forming an opening in the base portion and the buried insulating layer corresponding to the region including the connecting portion and reaching the back surface of the front surface silicon layer, and an electrodeposition resist pattern formed by lithography using an electrodeposition resist are used. Thus, at least a fourth step of forming the second metal pattern in the region of the back surface of the mirror portion at the bottom of the opening facing the first metal pattern is provided.

  In the method for manufacturing the micromechanical structure, in the fourth step, a metal film is formed on the surface of the base portion including the inside of the opening, and the second metal is formed on the metal film on the region facing the first metal pattern. A second metal pattern may be formed by forming an electrodeposition resist pattern that covers a region where the metal pattern is to be formed, and selectively etching the metal film using the electrodeposition resist pattern as a mask.

  In the micromechanical structure manufacturing method, in the fourth step, an electrodeposition resist pattern is formed in which a region for forming the second metal pattern on the back surface of the mirror portion at the bottom of the opening is opened, facing the first metal pattern. Then, a second metal pattern may be formed by forming a metal film on the electrodeposition resist pattern, and then removing the electrodeposition resist pattern after forming the metal film. It is what.

  As described above, according to the present invention, by using the electrodeposition resist pattern, the second metal pattern is formed in the back surface region of the mirror portion at the bottom of the opening facing the first metal pattern. Therefore, an excellent effect is obtained that a metal film having a desired shape can be more easily formed on both surfaces of a mirror structure manufactured using an SOI substrate.

FIG. 1A is a process diagram illustrating a method for manufacturing a micromechanical structure according to an embodiment of the present invention. FIG. 1B is a process diagram illustrating a method for manufacturing a micromechanical structure according to an embodiment of the present invention. FIG. 1C is a process diagram illustrating a method for manufacturing a micromechanical structure according to an embodiment of the present invention. FIG. 1D is a process diagram illustrating a method for manufacturing a micromechanical structure according to an embodiment of the present invention. FIG. 1E is a process diagram illustrating a method for manufacturing a micromechanical structure according to an embodiment of the present invention. FIG. 1F is a process diagram illustrating a method for manufacturing a micromechanical structure according to an embodiment of the present invention. FIG. 1G is a process diagram illustrating a method for manufacturing a micromechanical structure according to an embodiment of the present invention. FIG. 1H is a process diagram illustrating a method for manufacturing a micromechanical structure according to an embodiment of the present invention. FIG. 1I is a process diagram illustrating a method for manufacturing a micromechanical structure according to an embodiment of the present invention. FIG. 1J is a process diagram illustrating a method for manufacturing a micromechanical structure according to an embodiment of the present invention. FIG. 1K is a process diagram illustrating a method for manufacturing a micromechanical structure according to an embodiment of the present invention. FIG. 1L is a process diagram illustrating a method for manufacturing a micromechanical structure according to an embodiment of the present invention. FIG. 2 is a cross-sectional view illustrating a method for manufacturing a micromechanical structure. FIG. 3 is a cross-sectional view illustrating a method for manufacturing a micromechanical structure. FIG. 4 is a cross-sectional view showing the configuration of the micromechanical structure.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. 1A to 1L are process diagrams illustrating a method for manufacturing a micromechanical structure according to an embodiment of the present invention.

  First, as shown in FIG. 1A, an SOI substrate including a base portion 101 made of, for example, single crystal silicon, a buried insulating layer 102, and a surface silicon layer (SOI layer) 103 made of single crystal silicon is prepared. For example, the base portion 101 has a thickness of 625 μm, the buried insulating layer 102 has a thickness of 1 μm, and the SOI layer 103 has a thickness of 10 μm.

  Next, a metal film 104 is formed over the SOI layer 103. The metal film 104 includes, for example, a titanium layer having a thickness of 10 nm formed on the SOI layer 103 side and a gold layer having a thickness of 70 nm formed on the titanium layer. The titanium layer functions as an adhesion layer that adheres the gold layer and silicon. These can be formed by, for example, an electron beam evaporation method. Moreover, these metal layers can also be formed by sputtering or plating. In addition, the thickness of each metal layer may be arbitrarily selected within a range in which a necessary reflectance can be secured according to the wavelength range of the target light.

  Next, the metal film 104 is patterned by a known lithography technique and etching technique, and as shown in FIG. 1B, a metal pattern (first metal pattern) 141 that becomes a reflection surface of a mirror structure to be described later, and not shown. A metal wiring terminal portion is formed. In the etching in this patterning, first, the gold layer may be etched using aqua regia diluted as an etchant. In addition, the etching of the gold layer may be wet etching using an iodine-potassium iodide solution or dry etching. On the other hand, the titanium layer may be etched with dilute hydrofluoric acid.

  Next, the SOI layer 103 is patterned by a known lithography technique and etching technique to form a mirror part 131, a frame part 132, and the like as shown in FIG. 1C. By this patterning, as illustrated in the plan view of FIG. 1D, a mirror part 131 is formed by opening a gap 133 in the frame part 132, and the mirror part 131 is connected to the frame part 132 by a pair of connecting parts 134. The state is supported. In patterning these structures, etching may be performed using RIE (Reactive Ion Etching) using a resist pattern formed by lithography as a mask. In this etching process, the buried insulating layer 102 can be used as an etching stopper layer.

  Next, as shown in FIG. 1E, a protective layer 105 made of an organic resin is formed on the surface of the SOI layer 103 on which the metal pattern 141 is formed. The protective layer 105 can be formed by applying an organic resin made of, for example, polybenzoxazole as a material and heat-treating it. The heat treatment may be performed under a nitrogen atmosphere / temperature of 300 ° C./30 minutes. As a material for the protective layer 105, it has been confirmed that polyimide or resist may be used.

  Next, as shown in FIG. 1F, an opening 101a through which the buried insulating layer 102 is exposed is formed in the base 101. The opening 101a is formed so as to correspond to the regions such as the mirror 131 and the connecting portion 134 described above. The opening 101a can also be formed by a known photolithography technique and etching technique. This etching is performed by dry etching, and the buried insulating layer 102 may be used as an etching stop layer. As is well known, the single crystal silicon constituting the base portion 101 can be etched using an alkaline solution such as a KOH aqueous solution or a tetramethylammonium hydroxide aqueous solution. Also in this wet etching, the buried insulating layer 102 becomes an etching stop layer.

  Next, the embedded insulating layer 102 exposed in the opening 101a is removed by etching to form an opening 102a following the opening 101a as shown in FIG. 1G. By forming the opening 102a, an opening reaching the back surface of the surface silicon layer (SOI layer) 103 from the back surface side of the SOI substrate is formed. The buried insulating layer 102 may be etched by, for example, exposure to hydrogen fluoride gas in the atmosphere. As is well known, this hydrogen fluoride exposure may be carried out at a saturated vapor pressure of hydrogen fluoride at 1 atm from room temperature to about 50 ° C. In addition, nitrogen or an inert gas may be used as a carrier gas and the temperature and hydrogen fluoride partial pressure may be controlled within a range that does not affect silicon or the organic resin constituting the protective layer 105.

  Note that drying after such wet etching may be performed by, for example, supercritical drying. When supercritical drying is used, it is important that the organic resin or the like constituting the protective layer 105 is not dissolved by the supercritical fluid to be used.

  Next, as shown in FIG. 1H, a metal film 106 is formed on the surface of the base 101 (including the back surface of the SOI substrate) including the inside of the opening 101a. The metal film 106 is the same as the metal film 104 described above, and includes, for example, a titanium layer having a thickness of 10 nm formed on the SOI layer 103 side and a gold layer having a thickness of 70 nm formed on the titanium layer. Has been.

  Next, as shown in FIG. 1I, an electrodeposition resist layer 107 is formed by electrodepositing an electrodeposition resist on the surface of the metal film 106. For example, in the electrodeposition solution, if a predetermined voltage is applied to the metal film 106 as one electrode, the electrodeposition resist can be electrodeposited on the surface of the metal film 106. By electrodepositing the electrodeposition resist, the electrodeposition resist layer 107 can be formed with a uniform layer thickness on the surface of the metal film 106 formed with a large step in the opening 101a.

  Here, as the electrodeposition resist, either a positive type or a negative type can be used. However, a negative electrodeposition resist may be used in consideration of the case where the side wall of the opening 101a has an inversely tapered shape when viewed from the back side of the SOI substrate. In the case of an inversely tapered shape, the side wall of the opening 101a is a region that is not irradiated with light by photolithography exposure of the electrodeposition resist layer 107 described later. Even in such a case, if it is a negative type rest, the electrodeposition resist layer 107 adhering to the side wall can be removed by development. As the negative electrodeposition resist, for example, a cation electrodeposition negative type Elecoat EU-XC process (manufactured by Shimizu Corporation) may be used.

  In the electrodeposition resist, an uneven surface can be grown evenly on the surface where an electric field is applied and the electrodeposition resist solution is touched. Further, it is characteristic that a uniform coating can be formed. In addition, although it does not reach the uniformity using an electrodeposition resist, the resist can be uniformly applied at least to the bottom of the pixel even by using a spray coating method. If the spray coating film thus formed is patterned in the same manner as the electrodeposition resist pattern described later, this pattern can be used in the same manner as the electrodeposition resist pattern.

  Next, the electrodeposition resist layer 107 is patterned by photolithography to form an electrodeposition resist pattern 171 in a region facing the metal pattern 141 of the mirror part 131 as shown in FIG. 1J. The electrodeposition resist pattern 171 is formed so as to cover a region of the metal pattern formed facing the metal pattern 141 on the back surface side of the mirror part 131. In this patterning, for example, a mirror projection type exposure apparatus may be used. Further, laser exposure, electron beam exposure, or the like may be used.

  Next, using the electrodeposition resist pattern 171 as a mask, the metal film 106 is patterned by a known lithography technique and etching technique, and as shown in FIG. 1K, a metal pattern (second metal) that becomes the other reflecting surface of the mirror portion 131 is obtained. Pattern) 161 is formed. The metal pattern 161 is disposed to face the metal pattern 141 with the mirror part 131 interposed therebetween. Etching in the patterning of the metal pattern 161 is the same as in the case of the metal pattern 141 described above. First, the gold layer may be etched using diluted aqua regia as an etchant. In addition, the etching of the gold layer may be wet etching using an iodine-potassium iodide solution or dry etching. On the other hand, the titanium layer is etched with dilute hydrofluoric acid.

  Thereafter, the electrodeposition resist pattern 171 is peeled off by a known remover. Further, the protective layer 105 used for protection is removed by ashing by using active oxygen such as oxygen plasma or ozone (FIG. 1L). If the gold surfaces of the metal pattern 141 and the metal pattern 161 are oxidized by this treatment, electrical continuity cannot be obtained. In order to recover this, reduction is performed by heating at 80 ° C. in a hydrogen atmosphere. At this time, it has been confirmed that the temperature condition may be 60 ° C. or higher. Moreover, you may heat in a vacuum or inert gas atmosphere, and 200 degreeC or more is required in this case.

  Thereafter, dicing is performed to form a chip, and a series of steps is completed. For the dicing, known stealth dicing using a laser may be used. Further, without removing the protective layer 105, dicing with a normal dicing saw may be performed to form a chip, and thereafter, the protective layer 105 may be removed as described above.

  In the above description, metal is deposited on the SOI layer exposed on the SOI side of the SOI substrate and on the opening formed in the base portion, but the gist of the present invention is that a uniform resist is applied to the bottom region of the opening. In order to facilitate the manufacturing process, lithography may be performed simply to further process the silicon structure in the opening from the opening side without any metal deposition step. Those skilled in the art can easily guess that this process can be taken.

  For example, after forming the opening 101a and the opening 102a, before forming the metal film 106, an electrodeposition resist is electrodeposited on the surface of the base 101 (including the back surface of the SOI substrate) including the inside of the opening 101a. When using an electrodeposition resist having a weak adhesion to the silicon surface, the silicon surface may be treated with a silane coupling agent or the like before electrodeposition. The electrodeposition resist layer thus formed is patterned by a known photolithography technique to form an electrodeposition resist pattern in which a region to be the metal pattern 161 is opened. Thereafter, if a metal film is formed and the electrodeposition resist pattern is removed by a well-known lift-off method, the metal pattern can be formed on one surface of the mirror portion 131 so as to face the metal pattern 141.

  In a MEMS mirror using an SOI substrate, a metal film is formed on both surfaces of the surface of the mirror portion formed in the SOI layer and the back surface on the opening side formed in the base portion, and the metal becomes a reflective film on both surfaces. A mirror part (mirror structure) provided with a pattern can be formed.

  DESCRIPTION OF SYMBOLS 101 ... Base | substrate part, 101a ... Opening part, 102 ... Embedded insulating layer, 102a ... Opening part, 103 ... Surface silicon layer (SOI layer), 104 ... Metal film, 105 ... Protective layer, 106 ... Metal film, 107 ... Electrodeposition Resist layer 131... Mirror portion 132 132 frame portion 133 gap 134 connecting portion 141 metal pattern (first metal pattern) 161 metal pattern (second metal pattern) 171 electrodeposition resist pattern .

Claims (3)

A first step of forming a first metal pattern in a region to be a mirror portion on a surface silicon layer made of silicon disposed on a base portion via a buried insulating layer;
Patterning the surface silicon layer to form the mirror part, a frame part arranged around the mirror part, and a connecting part for connecting the mirror part and the frame part;
A third step of forming an opening in the base portion and the buried insulating layer corresponding to a region including the mirror portion and the connecting portion and reaching the back surface of the surface silicon layer;
By using an electrodeposition resist pattern formed by lithography using an electrodeposition resist, a second metal pattern is formed in a region on the back surface of the mirror portion at the bottom of the opening facing the first metal pattern. A process for producing a micromechanical structure comprising at least a process. In the manufacturing method of the micro mechanical structure of Claim 1,
In the fourth step,
A metal film is formed on the surface of the base portion including the inside of the opening, and a region on the metal film facing the first metal pattern is covered with a region where the second metal pattern is formed. A method for producing a micromechanical structure, wherein an electrodeposition resist pattern is formed, and the metal film is selectively etched using the electrodeposition resist pattern as a mask to form the second metal pattern. In the manufacturing method of the micro mechanical structure of Claim 1,
In the fourth step,
The electrodeposition resist pattern is formed in which the region for forming the second metal pattern on the back surface of the mirror portion at the bottom of the opening facing the first metal pattern is opened, and the electrodeposition resist pattern is formed on the electrodeposition resist pattern. After forming a metal film and forming this metal film, the said 2nd metal pattern is formed by removing the said electrodeposition resist pattern. The manufacturing method of the micro mechanical structure characterized by the above-mentioned.

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