Abstract:
A three-dimensional structure element having a plurality of three-dimensional structural bodies and capable of being uniformly formed without producing a dispersion in shape of the three-dimensional structural bodies, comprising a substrate ( 11 ) and the three-dimensional structural bodies ( 1 ) disposed in a predetermined effective area ( 20 ) on the substrate ( 11 ), the three-dimensional structural bodies ( 1 ) further comprising space parts formed in the clearances thereof from the substrate ( 11 ) by removing sacrificing layers, the substrate ( 11 ) further comprising a dummy area ( 21 ) having dummy structural bodies ( 33 ) so as to surround the effective area ( 20 ), the dummy structural body ( 33 ) further comprising space parts formed in the clearances thereof from the substrate ( 11 ) by removing the sacrificing layers, whereby since the dummy area ( 21 ) is heated merely to approx. the same temperature as the effective area ( 20 ) in an ashing process for removing the sacrificing layers to prevent a temperature distribution from occurring in the effective area ( 20 ).

Description:
PRIORITY STATEMENT 
   This application claims the benefit of PCT Application No. PCT/JP03/09734 filed on Jul. 31, 2003, which is incorporated herein by reference in its entirety. 
   BACKGROUND OF THE INVENTION 
   The present invention relates to an element having a three-dimensional structure that is formed accurately on a substrate such as a silicon wafer using a sacrificial layer and a method of manufacturing the element. In particular, the invention relates to an optical switch that is formed using a sacrificial layer and a method of manufacturing the optical switch. 
   In recent years, a method of forming a sacrificial layer on a substrate such as a silicon wafer, forming a thin film structure patterned in a desired shaped on the sacrificial layer, and thereafter forming a desired three-dimensional structure by removing the sacrificial layer has been attracting attention. Since it is possible to form a large number of fine three-dimensional structures accurately and at a high density with this method, the method is suitable for manufacturing a spatial light modulation element and the like. 
   As a method of removing the sacrificial layer present between the substrate and the thin film structure in such a method of manufacturing a three-dimensional structure using a sacrificial layer, Japanese Patent Laid-open Publication No. 2001-13426 and Japanese Patent Laid-open Publication No. 2001-129798 disclose use of a solution for wet etching such as a hydrofluoric acid water solution. However, in the solution for etching like the hydrofluoric acid water solution that uses water as a solvent, a phenomenon in which water molecules adhere to the thin film structure at the time of etching and the thin film structure adheres to the substrate due to a surface tension of the water molecules tends to occur. When the fine thin film structure adheres to the substrate once, it is not easy to peel off the thin film structure. Thus, the thin film structure may keep adhering to the substrate after drying, making it impossible to obtain a desired three-dimensional shape. In particular, when a thin film structure of a three-dimensional shape including a movable portion is formed, if the thin film structure adheres to a substrate, a function of the movable portion cannot be performed. 
   On the other hand, as another method of removing a sacrificial layer, a method of removing a sacrificial layer with a dry process such as ashing has been proposed. For example, when the ashing is used, it is known that an organic resist film is used as the sacrificial layer. 
   SUMMARY OF THE INVENTION 
   According to the method of removing a sacrificial layer using the dry process such as the ashing, since water molecules do not adhere to the thin film structure and the substrate, it is possible to prevent the thin film structure from sticking to the substrate. However, according to experiments performed by the inventors, it has been found that, in the removal method using the ashing, a large temperature difference occurs in an area where the sacrificial layer is sandwiched between the thin film structure and the substrate and an area where only the sacrificial layer is exposed on the substrate even if the areas are on the same substrate. More specifically, whereas temperature reaches as high as several hundred degrees at the time of the ashing in the area where only the sacrificial layer is exposed on the substrate, temperature does not rise to such high temperature in the area where the sacrificial layer is sandwiched between the thin film structure and the substrate. 
   It is surmised that such a large temperature distribution occurs because of a distribution of reaction rates. In the portion where the sacrificial layer is sandwiched between the thin film structure and the substrate, since a gas supplied at the time of the ashing reacts with the sacrificial layer while invading between the substrate and the thin film structure, the reaction proceeds slowly. On the other hand, in the portion where only the sacrificial layer is placed on the substrate, a reaction rate is high because the gas reacts with the sacrificial layer while coming into contact with the sacrificial layer from an entire upper surface thereof without stopping, and heat of reaction is generated rapidly. In the portion where only the sacrificial layer is placed on the substrate, since temperature reaches several hundred degrees at the time of the ashing, the temperature may be higher than substrate temperature at the time of formation of the thin film structure and heat treatment temperature. On the other hand, in the portion where the sacrificial layer is sandwiched between the thin film structure and the substrate, temperature does not rise to such high temperature. 
   Consequently, for example, in the case of an element in which plural thin film structures are arranged precisely in a part of an effective area on the substrate and the substrate is exposed in a peripheral area of the part, high heat generated at the time of the ashing of the peripheral area is conducted to a peripheral portion of the effective area to bring the peripheral portion into a state of being subjected to high heat treatment. Consequently, in the effective area, there is a problem in that a difference occurs in a residual stress of the thin film between the thin film structure in the peripheral edge and the thin film structure in the center and fluctuation occurs in a shape of the thin film structure or fluctuation occurs in an amount of distortion of the thin film structure that utilizes distortion by the residual stress. When the fluctuation occurs in the amount of distortion, a drive unit for displacing the thin film structure is required to change a drive signal for each amount of distortion, which complicates a control system. 
   It is an object of the present invention to provide a three-dimensional structure element including plural three-dimensional structures, in a configuration that the three-dimensional structures can be formed uniformly without causing fluctuation in a shape of the three-dimensional structures. 
   In order to attain the object, according to the present invention, a three-dimensional structure element as described below is provided. 
   In short, the present invention provides a three-dimensional structure element including: a substrate; and three-dimensional structures arranged in a predetermined effective area on the substrate, wherein 
   the three-dimensional structures have space portions, which are formed by removing a sacrificial layer, between the three-dimensional structures and the substrate, and 
   on the substrate, a dummy area is arranged to surround the effective area, dummy structures are arranged in the dummy area, and the dummy structures have space portions, which are formed by removing a sacrificial layer, between the dummy structures and the substrate. 
   In the three-dimensional structure element, it is possible to form a portion of the dummy structures opposed to the substrate in the same shape as the three-dimensional structures. 
   In the three-dimensional structure element, it is possible to form the dummy structures in a configuration having columns for fixing at least one section thereof to the substrate. 
   In the three-dimensional structure element, it is possible to form the dummy structures in a configuration having a thin film covering the dummy area and plural columns arranged between the thin film and the substrate. 
   In addition, according to the present invention, an optical switch as described below is provided. 
   In short, the present invention provides an optical switch including: an optical waveguide substrate; and a three-dimensional element substrate including displaceable reflecting mirrors, wherein 
   the three-dimensional structure element substrate has a substrate and three-dimensional structures arranged in a predetermined effective area on the substrate, 
   the three-dimensional structures have the reflecting mirrors and displacement portions on which the reflecting mirrors are placed, and the displacement portions have space portions, which are formed by removing a sacrificial layer, between the displacement portions and the substrate, and 
   on the substrate, a dummy area is arranged to surround the effective area, dummy structures are arranged in the dummy area, and the dummy structures have space portions, which are formed by removing a sacrificial layer, between the dummy structures and the substrate. 
   Further, according to the present invention, a micro device as described below is provided. 
   In short, the present invention provides a micro device including displaceable thin film three-dimensional structures, characterized in that 
   the micro device has a substrate and the thin film three-dimensional structures arranged in a predetermined effective area on the substrate, 
   the thin film three-dimensional structures have space portions, which are formed by removing a sacrificial layer, between the thin film three-dimensional structures and the substrate, and 
   on the substrate, a dummy area is arranged to surround the effective area, dummy structures made of a thin film are arranged in the dummy area, and the dummy structures have space portions, which are formed by removing a sacrificial layer, between the dummy structures and the substrate. 
   Moreover, according to the present invention, a method of manufacturing a three-dimensional structure element as described below is provided. 
   In short, the present invention provides a method of manufacturing a three-dimensional structure element including: 
   a step of forming a sacrificial layer and predetermined thin film three-dimensional structures in a predetermined effective area on a substrate and forming a sacrificial layer and predetermined thin film dummy structures in a dummy area surrounding the effective area; and 
   a step of removing the sacrificial layers in the effective area and the dummy area with a dry process. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an explanatory diagram showing a shape of an upper surface of a three-dimensional structure element including an effective area  20 , a dummy area  21 , an ineffective area  22  according to an embodiment of the invention; 
       FIG. 2(   a ) is a plan view showing a shape of an upper surface of a three-dimensional structure  1  arranged in the effective area  20  of the three-dimensional structure element in  FIG. 1 ; 
       FIG. 2(   b ) is a plan view showing a shape of an upper surface of a dummy structure  33  arranged in the dummy area  21  of the three-dimensional structure element in  FIG. 1 ; 
       FIG. 3  is a sectional view along line A-A of the three-dimensional structure element in  FIG. 2(   a ); 
       FIG. 4(   a ) is a sectional view showing a shape of an optical switch that is constituted by superimposing the three-dimensional structure element in  FIG. 1  and an optical waveguide substrate  190 ; 
       FIG. 4(   b ) is a sectional view showing a shape of an optical switch in a state in which a reflecting mirror  2  of the three-dimensional structure  1  is lowered by a Lorentz force in the optical switch constituted by superimposing the three-dimensional structure in  FIG. 1  and the optical waveguide substrate  190 ; 
       FIG. 5  is a perspective view showing a shape of a part of the optical waveguide substrate  190  of the optical switch in  FIG. 4 ; 
       FIGS. 6(   a ) to  6 ( g ) are sectional views explaining a process of manufacturing the three-dimensional structure element in  FIG. 1 ; 
       FIG. 7(   a ) is an explanatory diagram showing a shape of an upper surface in a state in which two three-dimensional structure elements in  FIG. 1  are continuously formed; 
       FIG. 7(   b ) is an explanatory diagram showing a sectional shape and a temperature distribution of respective portions in an ashing process in the state in which two three-dimensional structure elements in  FIG. 1  are continuously formed; 
       FIG. 8(   a ) is an explanatory diagram showing a structure of an upper surface of the effective area  20  and the dummy area  21  in a case in which dummy structures  34  of a different shape are used as the dummy structures in a three-dimensional structure element according to the embodiment of the invention; 
       FIG. 8(   b ) is an explanatory diagram showing a structure of an upper surface of the dummy structure  34 ; 
       FIG. 9  is an explanatory diagram showing a structure of an upper surface of the effective area  20  and the dummy area  21  in a case in which dummy structures  35  of a different shape are used as the dummy structure in a three-dimensional structure element according to the embodiment of the invention; 
       FIG. 10(   a ) is an explanatory diagram showing a shape of an upper surface in a state in which two three-dimensional structure elements not including dummy areas are continuously formed as a comparative example; and 
       FIG. 10(   b ) is an explanatory diagram showing a sectional shape in a state in which two three-dimensional structure elements of the comparative example are continuously formed and a temperature distribution of respective portions in an ashing process. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   An embodiment of the present invention will be explained with reference to the accompanying drawings. 
   A three-dimensional structure element according to this embodiment includes a substrate  11 , an effective area  20  provided in the center of the substrate  11 , a dummy area  21  surrounding the effective area  20 , and an ineffective area  22  around the dummy area  21 . 
   In the effective area  20 , plural three-dimensional structures  1  are arranged, that is, sixteen three-dimensional structures  1  are arranged vertically and horizontally, respectively (16×16 three-dimensional structures  1 ) (in  FIG. 1 , for convenience of illustration, eight three-dimensional structures  1  are arranged vertically and horizontally, respectively). As shown in  FIG. 2(   a ) in a plan view and as shown in  FIG. 3  in a sectional view, the three-dimensional structure  1  has a displacement portion  13  of a cantilever shape and a reflecting mirror  2  placed at one end of the displacement portion  13 . The displacement portion  13  has a configuration in which two thin films of different materials are stacked and has two legs  52  at ends on the opposite side of an end where the reflecting mirror  2  is placed. The two legs  52  are fixed to the substrate  11 . In a state in which no force is applied from the outside, the displacement portion  13  is bent as shown in  FIG. 3  by an internal stress of the thin films forming the displacement portion  13  to come into a state in which the displacement portion  13  lifts the reflecting mirror  2  to a position apart from the substrate  11 . In addition, a not-shown wiring pattern layer is formed in the displacement portion  13 . On the substrate  11 , a wiring pattern layer  58  is arranged in a position, where the legs  52  of the displacement portion  13  are in contact with the substrate  11 , and electrically connected to the wiring pattern layer of the displacement portion  13  to feed an electric current to the wiring pattern layer of the displacement portion  13 . On the other hand, in a portion on the substrate  11  and below the reflecting mirror  2 , a wiring pattern layer  16  for generating a magnetic field is arranged. With such a configuration, an electric current is fed to the wiring pattern layer of the displacement portion  13  and an electric current is fed to the wiring pattern layer  16  to generate a magnetic field, whereby it is possible to draw the displacement portion  13  toward the substrate  11  with the Lorentz force and lower the reflecting mirror  2  to the position of the substrate  11 . 
   As shown in  FIG. 1 , plural dummy structures  33  are arranged in the dummy area  21  on the substrate  11 . These dummy structures  33  are arranged to prevent the dummy area  21  from being heated to high temperature in a process of removing a sacrificial layer in a manufacturing method to be described later. The dummy structures  33  are formed in the same shape as the displacement portions  13  of the three-dimensional structures  1  and have legs  352  that are the same as the legs  52  of the displacement portions  13 . In addition, the dummy structures  33  are arranged vertically and horizontally at the same pitch as the three-dimensional structures  1  in the effective area  20 . However, the reflecting mirrors  2  and the wiring pattern layers are not formed in the dummy structures  33  in order to simplify a configuration thereof. Note that, in  FIG. 1 , in order to make it easy to distinguish the three-dimensional structures  1  from the dummy structures  33 , dot patterns and hatchings are added, respectively, in the figure for convenience.  FIG. 1  shows shapes of upper surfaces of the three-dimensional structures  1  and the dummy structures  33 . 
   On the other hand, the three-dimensional structures  1  and the dummy structures  33  are not arranged in the ineffective area  22  on the substrate  11 . Although not shown in the figure, wiring pattern layers  58  and  16  are arranged for drawing around wiring. 
   Next, a method of manufacturing a three-dimensional structure element according to this embodiment will be explained with reference to  FIGS. 6A to 6G . 
   In this embodiment, a wafer-like silicon substrate is used as the substrate  11 , a large number of the three-dimensional structure elements in  FIG. 1  are arranged two-dimensionally, and finally cut out to complete the three-dimensional structure elements. In  FIGS. 6A to 6G  to be referred to in the following explanation, only a sectional part of one three-dimensional structure  1  of one three-dimensional structure element is shown. However, treatments such as the film formation, the photolithography, and the etching are applied to the entire wafer-like substrate  11 . 
   First, a silicon oxide film  57  is formed over an entire upper surface of the wafer-like substrate  11  by a thermal oxidation method, an Al film to be the wiring pattern layer  58  and the wiring pattern layer  16  is formed on the silicon oxide film  57 , and by the photolithography and etching, the Al film is patterned into respective shapes of the wiring pattern layer  58  and the wiring pattern layer  16  ( FIG. 6A ). A resist layer to be a sacrificial layer  80  is formed over the entire upper surface of the wafer-like substrate  11  in this state by application and baking, and an opening  80   a  is formed in a position to be the legs  52  by the photolithography and the etching ( FIG. 6(   b )). 
   Next, a resist layer  81  to be a sacrificial layer is formed over the entire surface of the wafer-like substrate  11  in the state shown in  FIG. 6(   b ) by application and baking, and the resist layer  81  is left in a predetermined shape, for example, an island shape around the positions of the legs  52  and in a position where the reflecting mirror  2  is placed, by the photolithography and the etching ( FIG. 6(   c )). This left sacrificial layer  81  is arranged in order to form steps  59  and  158  in the displacement portion  13  as shown in  FIG. 3 . It is possible to increase strength of the displacement portion  13  by forming the steps  59  and  158 . 
   Next, according to steps of  FIGS. 6D to 6F , the displacement portions  13  and the legs  52  are formed in the effective area  20  using an Al film  73 , an SiN film  71 , and an Al film  72  and the dummy structures  33  having the same structure as the displacement portion  13  are formed in the dummy area  21 . In this embodiment, as shown in  FIG. 3 , the displacement portion  13  is formed to be made up of three portions, namely, a base  61  warped upward, a tip portion  62  warped downward, and a connecting portion  63  connecting the base  61  and the tip portion  62 . The directions of the warps of the base  61  and the tip portion  62  are set to be opposite in this way, whereby, even if a distance from the leg  52  to the tip of the displacement portion  13  is long, it is possible to reduce a space between the tip and the substrate  11 . Consequently, it is possible to switch a position where the reflecting mirror  2  is lifted to a position where the reflecting mirror  2  is drawn toward the substrate  11 , by a small Lorentz force. In order to realize the upward warp with internal stresses of the films, the base  61  has a configuration in which the SiN film  71  and the Al film  72  are stacked from the base  11  side. Conversely, in order to realize the downward warp, the tip portion  62  has a configuration in which the Al film  73  and the SiN film  71  are stacked from the base  11  side. The connecting portion  63  is constituted such that these films overlap partially. The legs  52  are formed integrally with the base  61 . Note that, when the Al films  73  and  72  and the SiN film  71  are formed, the substrate  11  is heated to a predetermined temperature in order to control internal stresses of the respective films. 
   A specific procedure will be explained. First, after an Al film to be the Al film  73  of the tip portion  62  is formed over the entire wafer-like substrate  11  with vapor deposition, sputtering, or the like, the Al film is patterned by the photolithography and the etching to have respective shapes of the tip portion  62  and the connecting portion  63  of the displacement portion  13  in the effective area  13  and the dummy structure  33  in the dummy area  21  ( FIG. 6(   d )). Next, after an SiN film to be the SiN film  71  of the base  61  and the tip portion  62  is formed over the entire wafer-like substrate  11  with the plasma CVD or the like, the SiN film is patterned by the photolithography and the etching to have shapes of the base  61 , the legs  52 , and the tip portion  62  of the displacement portion  13  and the dummy structure  33  ( FIG. 6(   e )). At this point, an opening is provided in the SiN film  71  in a position of a bottom of the opening  80   a  to be the legs  52 . Consequently, the Al film  72  and the wiring pattern layer  58  to be formed next are connected. Further, after an Al film to be the Al film  72  of the base  61  is formed over the entire wafer-like substrate  11 , the Al film is patterned to have shapes of the base  61 , the legs  52 , and the connecting portion  63  of the displacement portion  13  and the dummy structure  33  ( FIG. 6(   f )). With the procedure described above, the displacement portion  13  and the legs  52  having a shape, in which the Al film  72  of the base  61  and the Al film  73  of the tip portion  62  overlap in the connecting portion  63 , are formed. 
   Next, after a resist layer to be the sacrificial layer  82  is applied thick over the entire wafer-like substrate  11  and baked, an opening of a shape of the reflecting mirror  2  is formed by exposure and development in a position where the reflecting mirror  2  should be formed. Thereafter, Au, Ni, or another metal is grown by electrolytic plating to fill the opening. Consequently, the reflecting mirror  2  is formed. 
   With the process described above, in the respective three-dimensional structure elements of the wafer-like substrate  11 , as shown in  FIG. 6(   g ), the portions of the effective areas  20  and the dummy area  21  have a structure in which the displacement portion  13  and the dummy structure  33  are sandwiched between the sacrifice layer  80  and the sacrifice layer  82 . On the other hand, the portion of the ineffective area  22  has a structure in which the sacrificial layer  80  and the sacrificial layer  82  are stacked directly. 
   In this state, groove-like slits are formed in boundaries of the respective three-dimensional structure elements of the wafer-like substrate  11  by dicing or the like. The slits do not completely cut the substrate  11  but is formed in a shape of a groove. Thus, the substrate  11  maintains the wafer shape. 
   Next, the sacrificial layer  80 , the sacrificial layer  82 , and the sacrificial layer  81  are removed by plasma ashing. Consequently, the displacement portion  13  in the effective area  20  and the dummy structure  33  in the dummy area  21  stand from the substrate  11  to form a three-dimensional structure as shown in  FIG. 3 . 
   In a plasma ashing process, heat of reaction is generated by a reaction of the sacrificial layers  80  and  82  and the sacrificial layer  81  and the plasma. In particular, in the ineffective area  22 , since the sacrificial layer  80  and the sacrificial layer  82  overlap directly, the reaction with the plasma quickly develops from the entire upper surface to the substrate  11 . Thus, an ashing rate is high. Consequently, heat of reaction is generated suddenly in the ineffective area  22 , and temperature of the ineffective area  22  rises. On the other hand, in the effective area  20  and the dummy area  21 , since the displacement portion  13  and the dummy structure  33  are sandwiched between the sacrificial layer  80  and the sacrificial layer  82 , after the sacrificial layer  82  on the upper side is removed by the reaction with the plasma, the plasma reacts with the sacrificial layers  80  and  81  while gradually invading from gaps of the displacement portion  13  and the dummy structure  33 . Thus, a reaction rate of the effective area  20  and the dummy area  21  is low compared with that of the ineffective area  22 , and temperature of the effective area  20  and the dummy area  21  does not rise to high temperature like that of the ineffective area  22 . When the inventors performed an experiment to check a temperature distribution of a substrate, as shown in  FIG. 7(   b ), temperature of the ineffective area  22  rose to high temperature of several hundred degrees, which was higher than a substrate temperature at the time of formation of the Al films  73  and  72  and the SiN film  71  constituting the displacement portion  13 . On the other hand, temperature of the effective area  20  and the dummy area  21  was lower than the substrate temperature at the time of formation of the films. 
   Since heat of the high-temperature ineffective area  22  was conducted to a portion where the dummy area  21  was in contact with the ineffective area  22 , a temperature distribution in the dummy area  21  occurred. However, since the heat of the ineffective area  22  was not conducted to the effective area  20 , the temperature distribution was uniform. In this way, by providing the dummy area  21  and preventing temperature rise in the dummy area  21 , it is possible to prevent high heat generated in the ineffective area  22  from being conducted to the effective area  20 . Consequently, in the ashing process, since temperature of the Al films  73  and  72  and the SiN film  71  constituting the displacement portion  13  in the effective area  20  does not rise to temperature higher than that at the time of formation of the films uniformly, an internal stress of the 16×16 displacement portions  13  in the effective area  20  is kept in a state to be controlled by the substrate temperature at the time of formation of the films. Thus, shapes of warp of the 16×16 displacement portions  13  do not fluctuate, and it is possible to form all the displacement portions  13  in a predetermined three-dimensional structure. Note that, in this embodiment, a width of the dummy area  21  is kept at a width of about 500 μm. By giving a width of this level to the dummy area  21 , heat generated in the ineffective area  22  is prevented from being conducted to the effective area  20  significantly. 
   Finally, by dividing the wafer-like substrate  11  in positions of the grooves in the boundaries of the three-dimensional structure elements, individual three-dimensional structure elements can be completed. Note that it is also possible to adopt a procedure for cutting off the substrate  11  for each of the three-dimensional structure elements with the dicing before the ashing process and apply the ashing process to the individual three-dimensional structure elements. 
   Note that, in the case of the configuration in  FIG. 1  of this embodiment, since a part of the ineffective area  22  is allocated to the dummy area  21 , it is possible to reduce an area in which heat generation is large at the time of the ashing. Compared with the case in which dummy area  21  is not provided, a difference in temperature between a portion of high temperature and a portion of low temperature on a wafer is reduced. Thus, heat generated in the ineffective area  22  become less likely to be conducted to the effective area  20 , which makes it easy to manufacture the three-dimensional structures  1  with a uniform shape on the entire surface of the effective area. 
   As a comparative example, when a three-dimensional structure element of a structure not including the dummy area  21  was created as shown in  FIG. 10(   a ) to check a temperature distribution at the time of the ashing, the result was as shown in  FIG. 10(   b ). In the case of the configuration of the comparative example shown in  FIG. 10(   a ), since an area of the ineffective area  22  is large, temperature of the ineffective area  22  is higher than the temperature of the ineffective area  22  in this embodiment as shown in  FIGS. 7B and 10B . In addition, in the case of the comparative example, since the ineffective area  22  and the effective area  20  are in direct contact with each other, heat of the ineffective area  22  is conducted to an outer peripheral portion (an area A in  FIG. 10(   b )) of the effective area  20  to cause a temperature distribution in the effective area  20 . Consequently, the area A of the effective area  20  is heated to temperature higher than the substrate temperature at the time of formation of the films, and internal stresses of the films constituting the displacement portion  13  change. Thus, fluctuation occurs in three-dimensional shapes of the 16×16 displacement portions  13  of the effective area  20 . Therefore, even in the effective area  20 , shapes of the displacement portions  13  become different depending on a place, and it is impossible to form the three-dimensional structures  1  having the same shape over the entire surface in the effective area  20 . 
   Note that the method of removing a sacrificial layer is not limited to the plasma ashing, and it is also possible to use ion ashing, dry etching, and the like. In this case, it is also possible to prevent heat of reaction of an ineffective area from being conducted to an effective area by providing a dummy area in a boundary of the effective area and the ineffective area. 
   It is possible to form an optical switch by superimposing the three-dimensional structure element of this embodiment on an optical waveguide substrate  190  in which plural optical waveguides such as optical waveguides  193  and  194  are formed as shown in  FIG. 5 . Although only a part of the optical waveguide substrate  190  is shown in  FIG. 5 , a large number of optical waveguides such as the optical waveguides  193  and  194  are arranged in the optical waveguide substrate  190  to cross in a diamond lattice shape at fixed intervals, and a groove  196  is formed to traverse a point where the optical waveguides intersect. A pitch of the 16×16 three-dimensional structures  1  arranged on the substrate is defined to coincide with the intervals of the points where the optical waveguides of the optical waveguide substrate  190  intersect. Thus, by arranging and superimposing the three-dimensional structure element and the optical waveguide substrate  190 , it is possible to insert each of the reflecting mirrors  2  of the three-dimensional structures  1  in the groove  196  in the position where the optical waveguides of the optical waveguide substrate  190  intersect as shown in  FIG. 4(   a ). Consequently, for example, in the case of the configuration in  FIG. 5 , light propagated through the optical waveguide  193  can be emitted from a facet  193   b , reflected on the reflecting mirror  2 , and made incident on a facet  194   b  of the optical waveguide  194 . On the other hand, by lowering the displacement portion  13  of the three-dimensional structure  1  with the Lorentz force as shown in  FIG. 4(   b ), it is possible to remove the reflecting mirror  2  from the groove  196  and, for example, advance straight the light propagated through the optical waveguide  193  directly. In this way, by controlling an electric current fed to the wiring pattern layers  58  and  16 , it is possible to realize an optical switch that switches a traveling direction of light with the reflecting mirror  2 . 
   Incidentally, in the embodiment described above, the dummy structure  33  is formed in the stacked structure of the Al films  73  and  72  and the SiN film  71  in the same manner as the displacement portion  13 . However, since the dummy structure  33  only has to set a reaction rate of the dummy area  21  at the time of the ashing to the same level as a reaction rate of the effective area  20 , it is possible to constitute the dummy structure  33  with any one of the layers. 
   A pattern shape of the dummy structure does not have to be the same as that of the displacement portion  13 . It is possible to form the dummy structure in a shape in which several displacement portions  13  of the three-dimensional structure  1  are continuously formed as in the dummy structure  34  shown in  FIGS. 8A and 8B  and form the dummy structure in a size larger than the displacement portion  13 . In the example of  FIG. 8 , in order to prevent the dummy structure  34  from sticking to the substrate  11  at the time of the ashing or curling up to make the sacrificial layer  80  on the substrate  11  side easily subjected to the ashing, columns  35  for fixing the substrate  11  are formed in plural places in the peripheral portion of the dummy structure  34 . The columns  35  have the same configuration as the legs  52  of the displacement portion  13  and can be formed integrally with thin films constituting the dummy structure  34 . By arranging the dummy structure  34  in this way, as in the dummy structure  33  described above, the dummy structure  34  has an action of substantially equalizing an ashing rate of the dummy area  21  with the ashing rate in the effective area  20 . Thus, it is possible to make a temperature distribution in the effective area  20  substantially constant. Note that, in this example, a width of the dummy area is also set to 500 μm. 
   An example of still another configuration of a dummy structure will be explained with reference to  FIG. 9 . In a dummy structure  36  in  FIG. 9 , the entire dummy area  21  in the peripheral portion of the effective area  20  is covered by one continuous thin film. Consequently, an ashing rate of the dummy area  21  is set smaller than that of the ineffective area  22 . In the dummy structure  36  in  FIG. 9 , the plural columns  35  are also arranged at fixed intervals to prevent the dummy structure  36  from sticking to the substrate  11  at the time of the ashing or curling up to make the sacrificial layer  80  on the substrate  11  side easily subjected to the ashing. Note that, in the example of  FIG. 9 , a width of the dummy area  22  is set to about 1 mm. 
   Therefore, in this embodiment, a shape of a dummy structure formed in the dummy area  21  is not limited, and any shape may be adopted as long as the dummy structure can cover the sacrificial layer  80  to thereby set an ashing rate of the dummy area  21  smaller than that of the ineffective area  22 . Thus, it is possible to select a shape and a dimension of the dummy area  21  freely. 
   As described above, according to the present invention, since the dummy area  21  including dummy structures is arranged to be in contact with the outer side of the effective area  20 , temperature of the dummy area  21  does nor rise to high temperature compared with the ineffective area  22  even during the ashing process and is not largely different from temperature in the effective area. Thus, in the three-dimensional structure elements  1  in the effective area  20  after completion, there is no distribution in a residual stress, and amounts of distortion of the three-dimensional structure elements  1  after removing a sacrificial layer are uniform. In addition, by constituting an optical switch using such a three-dimensional structure element, it is possible to control plural switching mechanisms with substantially the same control signal. 
   Note that, in this embodiment, the three-dimensional structure element, in which the 16×16 three-dimensional structures  1  are arranged two-dimensionally in the effective area  20 , is described as a three-dimensional structure element. However, in the present invention, the number of three-dimensional structures and an arrangement thereof are not limited to this configuration. For example, the present invention is also effective for a shape in which one three-dimensional structure is arranged for the entire effective area  20 . 
   In addition, as in this embodiment, it is possible to constitute a micro device other than the optical switch, such as an infrared ray sensor or a digital mirror device, using a three-dimensional structure element including a three-dimensional structure of a desired shape. 
   According to the present invention, it is possible to provide a three-dimensional structure element including plural three-dimensional structures, in a configuration that the three-dimensional structures can be formed uniformly without causing fluctuation in a shape of the three-dimensional structures.