Abstract:
A micro movable device is made by processing a material substrate of a multilayer structure including a first layer, a second layer having a finely rough region on its surface on the side of the first layer, and an intermediate layer provided between the first and the second layer. The micro movable device includes a first structure formed in the first layer and a second structure formed in the second layer. The second structure includes a portion opposing the first structure via a gap and having a finely rough region on the side of the first structure, and being relatively displaceable with respect to the first structure.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a micro movable device produced by micromachining techniques. It also relates to a wafer used for manufacturing the micro movable device, and to a method of manufacturing the wafer. 
         [0003]    2. Description of the Related Art 
         [0004]    Recently, micromachined devices have been used for a wide variety of applications. Such devices include a micro-oscillation element that has a minute movable portion or oscillating portion, such as an angular speed sensor, an acceleration sensor, or a micromirror device. The angular speed sensor and the acceleration sensor are employed, for example, in a video camera or a mobile phone with camera for stabilizing an image against the user&#39;s hand motion, a car navigation system, an airbag release timing system, or a robot for controlling the posture thereof. The micromirror device serves to reflect light, for example in the field of optical disk technique or optical communication technique. Such micro movable device generally includes a stationary portion, a movable structure that can be displaced, and a link portion that connects the stationary portion and the movable structure. The micro movable device thus configured can be found, for example, in patent documents 1 to 3 listed below.
       Patent document 1: JP-A-2003-19700   Patent document 2: JP-A-2004-341364   Patent document 3: JP-A-2006-72252       
 
         [0008]      FIG. 13  depicts a micro movable device X 2  which is an example of a conventional micro movable device. The micro movable device X 2  includes a stationary portion  81  and a movable structure  82 , and is designed to perform a predetermined function. The stationary portion  81  and the movable structure  82  are connected via a link portion not shown in  FIG. 13 . The movable structure  82  is provided so as to be displaced, for example, as indicated by an arrow D in  FIG. 13 . 
         [0009]      FIG. 14  shows some of the manufacturing process of the micro movable device X 2 . To manufacture the micro movable device X 2 , first a material substrate  90  as shown in  FIG. 14(   a ) is prepared. The material substrate  90  is what is known as a silicon-on-insulator (hereinafter, SOI) wafer, and has a multilayer structure including a silicon layer  91 , a silicon layer  92 , and an intermediate layer  93  provided therebetween. The thickness of the intermediate layer  93  is approximately 1 μm. 
         [0010]    Then as shown in  FIG. 14(   b ), an anisotropic dry etching process is performed over the silicon layer  91  via a predetermined mask, so as to form the portions to be provided on the silicon layer  91  (for example, a part of the stationary portion  81 , the movable structure  82 , and the link portion). 
         [0011]    Another anisotropic dry etching process is performed over the silicon layer  92  via a predetermined mask, so as to form the portions to be provided on the silicon layer  92  (for example, a part of the stationary portion  81 ), as shown in  FIG. 14(   c ). 
         [0012]    Proceeding to  FIG. 14(   d ), an isotropic etching process is performed over the intermediate layer  93 , so as to remove the exposed portion thereof and the portion thereof located between the stationary portion  81  and the movable structure  82 . Through a method including such process, the micro movable device X 2  can be obtained. 
         [0013]    In the micro movable device X 2 , the movable structure  82  can accidentally stick to the stationary portion  81  as shown in  FIG. 15 , after the etching process described above referring to  FIG. 14(   d ), or during the operation of the device. Such sticking inhibits the movable structure  82  from being displaced, thereby causing the micro movable device X 2  to fail to work normally. 
         [0014]    To avoid such sticking, mainly a predetermined isotropic dry etching or isotropic wet etching process may be performed over the surface  81   a  of the stationary portion  81  opposing the movable structure  82 , and the surface  82   a  of the movable structure  82  opposing the stationary portion  81 , after the etching process described referring to  FIG. 14(   d ), to roughen the surfaces  81   a ,  82   a . Giving certain roughness to the surfaces  81   a ,  82   a  allows preventing the sticking. Otherwise, primarily the surfaces  81   a ,  82   a  may be subjected to water-repellent silylation coating after the etching process described referring to  FIG. 14(   d ), to avoid the sticking. 
         [0015]    The foregoing measures, however, may be unsuitable for example if the surfaces  81   a ,  82   a  are excessively large, because in such case it is difficult to adequately roughen or coat the opposing surfaces  81   a ,  82   a . Besides, whereas the foregoing measures are additionally performed after completing the fabrication of the respective portions of the micro movable device X 2 , performing such additional process is undesirable from the viewpoint of the yield from the manufacturing of the micro movable device X 2 . 
       SUMMARY OF THE INVENTION 
       [0016]    The present invention has been proposed under the circumstances described above. It is therefore an object of the present invention to provide a micro movable device configured to prevent sticking and manufacturable with a high yield rate. Other objects of the present invention are to provide a wafer used for manufacturing such a micro movable device, and to provide a method of manufacturing such a wafer. 
         [0017]    A first aspect the present invention provides a micro movable device. The micro movable device is obtained by processing a material substrate of a multilayer structure including a first layer, a second layer having a finely rough region on its surface on the side of the first layer, and an intermediate layer provided between the first layer and the second layer. The micro movable device includes a first structure formed in the first layer, and a second structure formed in the second layer, where the second structure includes a portion opposing the first structure via a gap and having a finely rough region on the side of the first structure. The second structure is displaceable relative to the first structure (for example, moving toward and away from the first structure). The micro movable device may serve as part of an angular speed sensor or an acceleration sensor. 
         [0018]    The first structure of the micro movable device is formed in the first layer, for example by performing an anisotropic dry etching process over the first layer so as to partially expose the intermediate layer of the material substrate having the foregoing multilayer structure. The second structure is formed in the second layer, for example by performing an anisotropic dry etching process over the second layer. Then, performing for example an isotropic wet etching, so as to remove a portion of the intermediate layer located between the first and the second structure, can cause the first structure and the second structure to oppose each other via a gap. The surface of the second structure on the side of the first structure is a part of the finely rough region on the first layer side, of the second layer, formerly a part of the material substrate, and hence has a finely rough structure. Because of such finely rough region provided on the second structure, the first structure and the second structure are prevented from accidentally sticking to each other, in this micro movable device. 
         [0019]    Moreover, the finely rough structure which serves to prevent the sticking is already present prior to forming the first and the second structure in the manufacturing process of the micro movable device, which eliminates the need to perform an etching process or a coating process for inhibiting the sticking, after forming at least one of the first structure and the second structure. Such arrangement is advantageous for manufacturing the micro movable device with higher yield. 
         [0020]    Thus, the micro movable device according to the first aspect of the present invention is appropriate for preventing the sticking between the first and the second structure, as well as for manufacturing with higher yield. 
         [0021]    A second aspect of the present invention provides a wafer. The wafer has a multilayer structure including a first layer, a second layer having a finely rough region on the side of the first layer, and an intermediate layer provided between the first and the second layer. Such wafer may be employed as the material substrate for manufacturing the micro movable device according to the first aspect. 
         [0022]    In the first and the second aspect of the present invention, it is preferable that the finely rough region on the second layer is provided by depositing one of polysilicon and amorphous silicon on the second layer, or performing an etching process over the surface of the second layer. These methods allow forming an appropriate finely rough structure on the second layer for preventing the sticking. The surface roughness of the finely rough region of the second layer is, for example, not less than 10 nm, and not exceeding 20% of the thickness of the intermediate layer. 
         [0023]    A third aspect of the present invention provides a method of manufacturing a wafer having a multilayer structure including a first layer, a second layer having a finely rough region on the side of the first layer, and an intermediate layer provided between the first and the second layer. The method includes depositing polysilicon or amorphous silicon over a surface of a pre-second layer, or performing an etching process over the surface of the pre-second layer, thereby forming the finely rough region. Then, a pre-intermediate layer is formed over the finely rough region of the pre-second layer. The pre-second layer and the pre-first layer are joined to each other via the pre-intermediate layer formed over the finely rough region. 
         [0024]    A fourth aspect of the present invention provides another method of manufacturing a wafer having a multilayer structure including a first layer, a second layer having a finely rough region on the side of the first layer, and an intermediate layer provided between the first and the second layer. The method includes depositing polysilicon or amorphous silicon over a surface of a pre-second layer, or performing an etching process over the surface of the pre-second layer, thereby forming the finely rough region. Then, a pre-intermediate layer is formed over the finely rough region of the pre-second layer. Then, the first layer is formed by depositing a material over the pre-intermediate layer 
         [0025]    In the third and the fourth aspect of the present invention, preferably the pre-intermediate layer may be an insulating layer such as a silicon oxide layer, a silicon nitride layer, or an alumina layer. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]      FIG. 1  is a fragmentary plan view showing a gyro sensor according to the present invention; 
           [0027]      FIG. 2  is another fragmentary plan view showing the gyro sensor according to the present invention; 
           [0028]      FIG. 3  is a cross-sectional view taken along a line III-III in  FIG. 1 ; 
           [0029]      FIG. 4  is a cross-sectional view taken along a line IV-IV in  FIG. 1 ; 
           [0030]      FIG. 5  is a cross-sectional view taken along a line V-V in  FIG. 1 ; 
           [0031]      FIG. 6  is a cross-sectional view taken along a line VI-VI in  FIG. 1 ; 
           [0032]      FIG. 7  is a cross-sectional view taken along a line VII-VII in  FIG. 1 ; 
           [0033]      FIG. 8  is a cross-sectional view taken along a line VIII-VIII in  FIG. 1 ; 
           [0034]      FIG. 9  shows in section some steps of a manufacturing process of the gyro sensor shown in  FIG. 1 ; 
           [0035]      FIG. 10  shows some steps of the manufacturing process which are subsequent to those shown in  FIG. 9 ; 
           [0036]      FIG. 11  shows some steps of the manufacturing process which are subsequent to those shown in  FIG. 10 ; 
           [0037]      FIG. 12  shows a manufacturing process of another wafer; 
           [0038]      FIG. 13  is a cross-sectional view illustrating a conventional micro movable device; 
           [0039]      FIG. 14  shows in section some steps of a manufacturing process of the micro movable device shown in  FIG. 13 ; and 
           [0040]      FIG. 15  is a sectional view illustrating the sticking of the micro movable device shown in  FIG. 13 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0041]      FIGS. 1 to 8  illustrate a gyro sensor X 1  according to the present invention.  FIG. 1  is a fragmentary plan view of the gyro sensor X 1 , and  FIG. 2  is another fragmentary plan view of the gyro sensor X 1 .  FIGS. 3 to 8  are cross-sectional views taken along lines III-III, IV-IV, V-V, VI-VI, VII-VII, and VIII-VIII in  FIG. 1 , respectively. 
         [0042]    The gyro sensor X 1  includes a land portion  10 , an inner frame  20 , an outer frame  30 , a pair of link portions  40 , a pair of link portions  50 , a detecting electrode  61  (not shown in  FIG. 1 ), detecting electrodes  62 A,  62 B (not shown in  FIG. 2 ), and driving electrodes  71 A,  71 B,  72 A,  72 B, and serves as an angular speed sensor. The gyro sensor X 1  is of a type to be manufactured by processing a wafer, which is so called a SOI substrate, with use of a bulk micromachining technique such as MEMS technique. The wafer has a multilayer structure including, for example, a first and a second silicon layers, and an insulating layer provided between the silicon layers, which are given a predetermined conductivity by doping impurity. Hatched sections in  FIG. 1  indicate portions derived from the first silicon layer and located closer to the viewer than the insulating layer, and hatched sections in  FIG. 2  indicate portions derived from the second silicon layer and located closer to the viewer than the insulating layer. 
         [0043]    The land portion  10  is a portion derived from the first silicon layer. As shown in  FIGS. 3 and 5 , the land portion  10  includes a conductive plug  11  buried therein. 
         [0044]    The inner frame  20  has, as shown in  FIG. 3  for example, a multilayer structure including a first layer portion  21  derived from the first silicon layer, a second layer portion  22  derived from the second silicon layer, and an insulating layer  23  provided therebetween. The first layer portion  21  includes segments  21   a ,  21   b ,  21   c ,  21   d ,  21   e ,  21   f , as shown in  FIG. 1 . The segments  21   a  to  21   f  are separated from each other by a gap. 
         [0045]    The outer frame  30  has, as shown in  FIGS. 3 and 4  for example, a multilayer structure including a first layer portion  31  derived from the first silicon layer, a second layer portion  32  derived from the second silicon layer, and an insulating layer  33  provided therebetween. The first layer portion  31  includes segments  31   a ,  31   b ,  31   c ,  31   d ,  31   e ,  31   f ,  31   g ,  31   h , as shown in  FIG. 1 . The segments  31   a  to  31   h  are separated from each other by a gap, and constitute a terminal portion in the gyro sensor X 1  for external connection. 
         [0046]    The pair of link portions  40  serves to connect the land portion  10  and the inner frame  20 , and is derived from the first silicon layer. Each link portion  40  includes two torsion bars  41 . As shown in  FIG. 1 , the respective torsion bars  41  of one of the link portions  40  are connected to the land portion  10  and to the segment  21   a  of the first layer portion  21  of the inner frame  20 , so as to electrically connect the land portion  10  and the segment  21   a . The respective torsion bars  41  of the other link portion  40  are connected to the land portion  10  and to the segment  21   d  of the first layer portion  21  of the inner frame  20 , so as to electrically connect the land portion  10  and the segment  21   d . The pair of link portions  40  thus configured defines an axial center A 1  of the oscillating motion of the land portion  10 . Each link portion  40 , which includes the two torsion bars  41  defining therebetween a space gradually increasing from the inner frame  20  toward the land portion  10  is advantageous for suppressing an unnecessary displacement component in the oscillating motion of the land portion  10 . 
         [0047]    The pair of link portions  50  serves to connect the inner frame  20  and the outer frame  30 , and is derived from the first silicon layer. Each link portion  50  includes three torsion bars  51 ,  52 ,  53 . As shown in  FIG. 1 , the torsion bar  51  of one of the link portions  50  is connected to the segment  21   a  of the first layer portion  21  of the inner frame  20  and to the segment  31   a  of the first layer portion  31  of the outer frame  30 , so as to electrically connect the segment  21   a  and the segment  31   a . The torsion bar  52  is connected to the segment  21   b  of the first layer portion  21  of the inner frame  20  and to the segment  31   b  of the first layer portion  31  of the outer frame  30 , so as to electrically connect the segment  21   b  and the segment  31   b . The torsion bar  53  is connected to the segment  21   c  of the first layer portion  21  of the inner frame  20  and to the segment  31   c  of the first layer portion  31  of the outer frame  30 , so as to electrically connect the segment  21   c  and the segment  31   c . The torsion bar  51  of the other link portions  50  is connected to the segment  21   d  of the first layer portion  21  of the inner frame  20  and to the segment  31   d  of the first layer portion  31  of the outer frame  30 , so as to electrically connect the segment  21   d  and the segment  31   d . The torsion bar  52  is connected to the segment  21   e  of the first layer portion  21  of the inner frame  20  and to the segment  31   e  of the first layer portion  31  of the outer frame  30 , so as to electrically connect the segment  21   e  and the segment  31   e . The torsion bar  53  is connected to the segment  21   f  of the first layer portion  21  of the inner frame  20  and to the segment  31   f  of the first layer portion  31  of the outer frame  30 , so as to electrically connect the segment  21   f  and the segment  31   f . The pair of link portions  50  thus configured defines an axial center A 2  of the oscillating motion of the inner frame  20 . Each link portion  50 , which includes the two torsion bars  51 ,  53  defining therebetween a space gradually increasing from the outer frame  30  toward the inner frame  20  is advantageous for suppressing emergence of an unnecessary displacement component in the oscillating motion of the inner frame  20 . 
         [0048]    The detecting electrode  61  is a portion derived from the second silicon layer, and corresponds to the second structure according to the present invention. The detecting electrode  61  includes a finely rough region  61   a , for example as shown in  FIGS. 4 and 5  in an enlarged scale. The surface roughness (Rz) of the finely rough region  61   a  is, for example, 10 to 200 nm. Referring also to  FIGS. 3 and 5 , the detecting electrode  61  is joined to the land portion  10  via the insulating layer portion  12  derived from the insulating layer, and is electrically connected to the land portion  10  via the conductive plug  11  provided so as to penetrate through the land portion  10  and the insulating layer portion  12 . 
         [0049]    The detecting electrode  62 A is a portion derived from the first silicon layer, and corresponds to the first structure according to the present invention. As shown in  FIG. 5 , the detecting electrode  62 A includes a portion extending from the segment  21   b  of the first layer portion  21  of the inner frame  20  toward the land portion  10 , so as to oppose the detecting electrode  61 . The detecting electrode  62 A includes a plurality of openings. 
         [0050]    The detecting electrode  62 B is a portion derived from the first silicon layer, and corresponds to the first structure according to the present invention. As shown in  FIG. 5 , the detecting electrode  62 B includes a portion extending from the segment  21   e  of the first layer portion  21  of the inner frame  20  toward the land portion  10 , so as to oppose the detecting electrode  61 . The detecting electrode  62 B includes a plurality of openings. 
         [0051]    The driving electrode  71 A is a combtooth-like electrode derived from the first silicon layer, and includes a plurality of electrode teeth  71   a  extending from the segment  21   c  of the inner frame  20 , as shown in  FIG. 1 . The electrode teeth  71   a  are parallel to each other, for example as shown in  FIGS. 1 and 6 . 
         [0052]    The driving electrode  71 B is a combtooth-like electrode derived from the first silicon layer, and includes a plurality of electrode teeth  71   b  extending from the segment  21   f  of the inner frame  20 . The electrode teeth  71   b  are parallel to each other. 
         [0053]    The driving electrode  72 A is a combtooth-like electrode derived from the first silicon layer, and located so as to oppose the driving electrode  71 A. The driving electrode  72 A includes a plurality of electrode teeth  72   a  extending from the segment  31   g  of the outer frame  30 . The electrode teeth  72   a  are parallel to each other, for example as shown in  FIGS. 1 and 6 , and also parallel to the electrode teeth  71   a  of the driving electrode  71 A. 
         [0054]    The driving electrode  72 B is a combtooth-like electrode derived from the first silicon layer, and located so as to oppose the driving electrode  71 B. The driving electrode  72 B includes a plurality of electrode teeth  72   b  extending from the segment  31   h  of the outer frame  30 . The electrode teeth  72   b  are parallel to each other, and also parallel to the electrode teeth  71   b  of the driving electrode  71 B. 
         [0055]    When the gyro sensor X 1  is driven, the movable portion (land portion  10 , inner frame  20 , driving electrodes  61 ,  62 A,  62 B) is caused to oscillate about the axial center A 2  at a predetermined frequency or cycle. Such oscillating motion is achieved by alternately and repeatedly applying a voltage between the driving electrodes  71 A,  72 A and between the driving electrodes  71 B,  72 B. For this operation, the potential can be given to the driving electrode  71 A through the segment  31   c  of the outer frame  30 , the torsion bar  53  of one of the link portions  50 , and the segment  21   c  of the inner frame  20 . The potential can be given to the driving electrode  71 B through the segment  31   f  of the outer frame  30 , the torsion bar  53  of the other link portion  50 , and the segment  21   f  of the inner frame  20 . The potential can be given to the driving electrode  72 A through the segment  31   g  of the outer frame  30 . The potential can be given to the driving electrode  72 B through the segment  31 h of the outer frame  30 . In this embodiment, for example alternately and repeatedly giving the potential to the driving electrode  72 A and to the driving electrode  72 B, with the driving electrodes  71 A,  71 B being grounded, can cause the movable portion to oscillate. 
         [0056]    When a predetermined angular speed or acceleration acts on the gyro sensor X 1 , hence on the movable portion while the movable portion is being caused to oscillate or vibrate as described above for example, the land portion  10  is rotationally displaced about the axial center A 1  together with the driving electrode  61 , to a predetermined extent, so as to change the gap volume between a portion of the detecting electrode  61  opposing the detecting electrode  62 A and the detecting electrode  62 A, as well as the gap volume between a portion of the detecting electrode  61  opposing the detecting electrode  62 B and the detecting electrode  62 B (the detecting electrode  61  and the detecting electrodes  62 A,  62 B can relatively move toward or away from each other). The change in volume of those gaps incurs a change in static capacitance between the detecting electrodes  61 ,  62 A, as well as between the detecting electrodes  61 ,  62 B. The amount of the rotational displacement of the land portion  10  and the driving electrode  61  can be detected based on the change in static capacitance between the detecting electrodes  61 ,  62 A, and between the detecting electrodes  61 ,  62 B. Then the detection result thus obtained serves for calculation of the angular speed or acceleration acting on the movable portion, or on the gyro sensor X 1 . 
         [0057]      FIGS. 9 to 11  illustrate a method of manufacturing the gyro sensor X 1 . The method represents an example of application of a micromachining technique to the manufacturing of the gyro sensor X 1 .  FIGS. 9(   a ) to  11 ( d ) sequentially illustrate the forming process of a land portion L, frames F 1 , F 2 , link portions C 1 , C 2 , and electrodes E 1 , E 2 , E 3 , E 4  shown in  FIG. 11(   d ), in a form of changes in profile of a certain cross-section. Such certain cross-section is a schematically expressed model of a cross-section of one of a plurality of predetermined portions included in a single fabrication section of the gyro sensor, in a wafer being subjected to processing. The land portion L corresponds to a portion of the land portion  10 . The frame F 1  corresponds to the inner frame  20 , and represents a transverse cross-section of a predetermined position of the inner frame  20 . The frame F 2  respectively corresponds to the outer frame  30 , and represents a transverse cross-section of a predetermined position of the outer frame  30 . The link portion C 1  corresponds to the link portion  40 , and represents a transverse cross-section of the torsion bar  41 . The link portion C 2  corresponds to the link portion  50 , and represents a vertical cross-section of one of the torsion bars  51 ,  52 ,  53 . The electrode E 1  corresponds to a portion of the driving electrode  61 . The electrode E 2  corresponds to the driving electrodes  62 A,  62 B. The electrode E 3  corresponds to the detecting electrodes  71 A,  71 B. The electrode E 4  corresponds to the detecting electrode  72 A,  72 B. 
         [0058]    To manufacture the gyro sensor X 1 , first, an insulating layer  102  is formed on a wafer  101  on one hand, and on the other hand a surface-roughened layer  103 A and an insulating layer  104  are sequentially formed on a wafer  103 , as shown in  FIG. 9(   a ). 
         [0059]    The wafer  101  corresponds to the pre-first layer according to the present invention, and is constituted of, for example, a silicon material doped with impurity for giving conductivity. Suitable examples of the impurity include a p-type impurity such as B, and an n-type impurity such as P and Sb. The insulating layer  102  may be constituted of a silicon oxide layer, a silicon nitride layer, or an alumina layer. The insulating layer  102  can be formed through depositing a predetermined material on the wafer  101 , for example by a CVD or sputtering process. 
         [0060]    The wafer  103  corresponds to the pre-second layer according to the present invention, and is constituted of, for example, a silicon material doped with impurity for giving conductivity. Suitable examples of the impurity include a p-type impurity such as B, and an n-type impurity such as P and Sb. The surface-roughened layer  103 A is constituted of polysilicon or amorphous silicon for example, and includes a finely rough region  103 a. The wafer  103  has a thickness of, for example, 100 to 525 μm. The surface-roughened layer  103 A has a thickness of 1 to 2 μm for example, and the surface roughness (Rz) of the finely rough region  103   a  is preferably 10 nm or more, for example 10 to 200 nm. The surface-roughened layer  103 A can be formed through depositing polysilicon or amorphous silicon on the wafer  103 , for example by a CVD process. The insulating layer  104  may be formed from the same material and through the same process, as those for the insulating layer  102 . 
         [0061]    Referring then to  FIG. 9(   b ), the wafers  101 ,  103  subjected to the foregoing process are joined. Examples of the joining method include so-called direct bonding and room-temperature bonding. This process provides a multilayer structure including a silicon layer  201  derived from the wafer  101 , a silicon layer  202  derived from the wafer  103  and the surface-roughened layer  103 A, and including the finely rough region  103   a , and an insulating layer  203  formed upon bonding the insulating layers  102 ,  104 . The insulating layer  203  has a thickness of 1 to 2 μm, for example. It is preferable that the surface roughness Rz of the finely rough region  103   a  is 20% or less of the thickness of the insulating layer  203 . 
         [0062]    Then as shown in  FIG. 9(   c ), a polishing process is performed so as to reduce the thickness of the silicon layer  201 . In this case, for example a CMP process may be adopted. After this process, the thickness of the silicon layer  201  becomes 10 to 100 μm, for example. Through the series of steps shown in  FIGS. 9(   a ) to  9 ( c ), a SOI wafer  200  can be obtained. 
         [0063]    Proceeding to  FIG. 10(   a ), a through-hole  201   a  is formed so as to penetrate through the silicon layer  201  and the insulating layer  203 . More specifically, after forming a resist pattern (not shown) with a predetermined opening on the silicon layer  201 , a deep reactive ion etching (hereinafter, DRIE) process is performed utilizing the resist pattern as the mask, thereby performing an anisotropic dry etching process over the silicon layer  201  until the insulating layer  203  is partially exposed. The DRIE process facilitates properly performing the anisotropic dry etching, in a Bosch process of alternately executing the etching and protection of the sidewall. For this and subsequent DRIE process, the Bosch process may be adopted. Then the exposed portion of the insulating layer  203  is removed by a different etching process (for example, wet etching utilizing buffered hydrofluoric acid (hereinafter, BHF) composed of fluoric acid and ammonium fluoride). Thus, the through-hole  201   a  can be obtained. 
         [0064]    Referring to  FIG. 10(   b ), the conductive plug  11  is formed. In this case, filling the through-hole  201   a  with a conductive material provides the conductive plug  11 . 
         [0065]    Referring then to  FIG. 10(   c ), an oxide layer pattern  204  and a resist pattern  205  are formed on the silicon layer  201 , and an oxide layer pattern  206  is formed on the silicon layer  202 . The oxide layer pattern  204  has a pattern shape corresponding to the land portion L, the frames F 1 , F 2 , the link portions C 1 , C 2 , and the electrodes E 2 , E 4 . The resist pattern  205  has a pattern shape corresponding to the electrode E 3 . The oxide layer pattern  206  has a pattern shape corresponding to the frames F 1 , F 2  and the electrode E 1 . 
         [0066]    To form the oxide layer pattern  204 , first a CVD process is performed so as to deposit silicon oxide on the surface of the silicon layer  201 , until the thickness reaches, for example, 1 μm. Then an etching process is performed with a predetermined resist pattern serving as the mask, so as to shape the oxide layer on the silicon layer  201  into the predetermined pattern. The oxide layer pattern  206  may also be formed on the silicon layer  202  through depositing an oxide material and forming a resist pattern on the oxide layer, followed by the etching process. On the other hand, to form the resist pattern  205 , a predetermined liquid photoresist is first deposited on the silicon layer  201  by spin-coating. Then after the exposure and development process, the photoresist is patterned. 
         [0067]    Proceeding to  FIG. 10(   d ), the DRIE process is performed utilizing the oxide layer patterns  204 ,  205  as the mask, thereby performing the etching over the silicon layer  201  to a predetermined depth, thicknesswise of the silicon layer  201 . Such depth corresponds to the height of the electrode E 3  (driving electrodes  71 A,  71 B). 
         [0068]    After removing the resist pattern  205  as shown in  FIG. 11(   a ), the DRIE process is performed utilizing the oxide layer pattern  204  as the mask, thereby performing the etching over the silicon layer  201  as shown in  FIG. 11(   b ). At this stage, the land portion L, a part of the frame F 1 , a part of the frame F 2 , the link portions C 1 , C 2 , and the electrodes E 2 , E 3 , E 4  are obtained. 
         [0069]    Then referring to  FIG. 11(   c ), the DRIE process is performed utilizing the oxide layer pattern  206  as the mask, thereby performing the etching over the silicon layer  202 . At this stage, the remaining part of the frames F 1 , F 2  and the electrode E 1  are obtained. 
         [0070]    Referring finally to  FIG. 11(   d ), exposed portions of the insulating layer  203 , and the oxide layer patterns  204 ,  206  are removed by etching. Here, either a dry etching or wet etching may be performed. In the case of dry etching, for example CHF 3  may be employed as the etching gas. For wet etching, for example BHF may be employed as the etching solution. 
         [0071]    Throughout the foregoing steps, the land portion L, the frames F 1 , F 2 , the link portions C 1 , C 2 , and the electrodes E 1  to E 4  are formed, and the gyro sensor X 1  can be obtained. 
         [0072]    The surface of the detecting electrode  61  (finely rough region  61   a ) in the gyro sensor X 1 , on the side of the detecting electrode  62 A,  62 B, for example shown in  FIG. 5 , is a part of the finely rough region  103   a  of the silicon layer  202 , formerly a part of the SOI wafer  200 , and has the finely rough structure. Because of the finely rough region  61   a  provided on the detecting electrode  61 , the detecting electrode  61  and the detecting electrodes  62 A,  62 B are prevented from accidentally sticking to each other, in the gyro sensor X 1 . 
         [0073]    Moreover, the finely rough structure which serves to prevent the sticking is already present prior to forming the detecting electrodes  61  and the detecting electrodes  62 A,  62 B in the manufacturing process of the gyro sensor X 1 , which eliminates the need to perform an etching process or a coating process for inhibiting the sticking, after forming at least one of the detecting electrode  61  and the detecting electrodes  62 A,  62 B. The gyro sensor X 1  thus configured is appropriate for manufacturing with higher yield. 
         [0074]    Thus, the gyro sensor X 1  according to the present invention is appropriate for preventing the sticking between the detecting electrode  61  and the detecting electrodes  62 A,  62 B, as well as for manufacturing with higher yield. 
         [0075]      FIG. 12  illustrates a method of manufacturing a SOI wafer that can be substituted with the foregoing SOI wafer  200 , in the manufacturing process of the gyro sensor X 1 . 
         [0076]    Referring first to  12 ( a ), an insulating layer  302  is formed on a wafer  301  on one hand, and on the other hand a finely rough region  303   a  is formed on a wafer  303 , after which an insulating layer  304  is formed on the finely rough region  303   a.    
         [0077]    The wafer  301  corresponds to the pre-first layer according to the present invention, and is constituted of, for example, a silicon material doped with an impurity for giving conductivity. Suitable examples of the impurity include a p-type impurity such as B, and an n-type impurity such as P and Sb. The insulating layer  102  may be constituted of a silicon oxide layer, a silicon nitride layer, or an alumina layer. The insulating layer  302  may be formed from the same material and through the same process, as those for the foregoing insulating layer  102 . 
         [0078]    The wafer  303  corresponds to the pre-second layer according to the present invention, and is constituted of, for example, a silicon material doped with an impurity for giving conductivity. The finely rough region  303   a  may be formed through performing an etching process over the surface of the wafer  303 . In this case, an isotropic dry etching process that employs SF 6  as the etching gas, or a wet etching process that employs a mixture of fluoronitric acid and acetic acid as the etching solution may be performed. The surface roughness (Rz) of the finely rough region  303   a  is preferably 10 nm or more, for example 10 to 200 nm. The insulating layer  304  may be formed from the same material and through the same process, as those for the insulating layer  102 . 
         [0079]    Then referring to  FIG. 12(   b ), the wafers  301 ,  303  subjected to the foregoing process are joined. Examples of the joining method include so-called direct bonding and room-temperature bonding. This process provides a multilayer structure including a silicon layer  401  derived from the wafer  301 , a silicon layer  402  derived from the wafer  303  and having the finely rough region  303   a , and an insulating layer  403  formed upon bonding the insulating layers  302 ,  304 . The insulating layer  403  has a thickness of 1 to 2 μm, for example. It is preferable that the surface roughness Rz of the finely rough region  303   a  is 20% or less of the thickness of the insulating layer  403 . 
         [0080]    Proceeding to  FIG. 12(   c ), a polishing process is performed so as to reduce the thickness of the silicon layer  401 . In this case, for example a CMP process may be adopted. After this process, the thickness of the silicon layer  401  becomes 10 to 100 μm, for example. Throughout the series of steps shown in  FIGS. 12(   a ) to  12 ( c ), a SOI wafer  400  can be obtained. Substituting the SOI wafer  200  with the SOI wafer  400  in the manufacturing process described referring to  FIGS. 10(   a ) to  11 ( d ) can equally provide the gyro sensor X 1 . 
         [0081]    The wafer employed for manufacturing the gyro sensor X 1  can also be obtained through depositing a predetermined material on the wafer  103  provided with the surface-roughened layer  103 A and the insulating layer  104  as shown in  FIG. 9(   a ). In this case, for example, the insulating layer  104  may be formed with a sufficient thickness on the surface-roughened layer  103 A, and then polished for planarization by CMP or the like, after which a polysilicon material such as Poly-Si or Poly-SiGe may be deposited on the insulating layer  104  so as to reach a predetermined thickness. 
         [0082]    The wafer employed for manufacturing the gyro sensor X 1  can also be obtained through depositing a predetermined material on the wafer  303  including the finely rough region  303   a  and provided with the insulating layer  304  as shown in  FIG. 12(   a ). In this case, for example, the insulating layer  304  may be formed with a sufficient thickness on the finely rough region  303   a , and then polished for planarization by CMP or the like, after which a polysilicon material such as Poly-Si or Poly-SiGe may be deposited on the insulating layer  304  so as to reach a predetermined thickness.