Abstract:
A release layer is formed on a substrate, and plural thin-film patterns are formed on the release layer. The release layer is etched back at a prescribed depth at least in regions close to the circumferences of the thin-film patterns. The thin-film patterns are transferred sequentially to a counter substrate to be laminated on the counter substrate and to thereby form a micro structure. This manufacturing method is employed in a case that the combination of thin-film patterns and are lease layer is such that when a prescribed pressure is applied to each of the thin-film patterns on the release layer in the transferring, the height of a raised portion of the release layer that would be appeared in a region close to the circumference of the thin-film pattern if the release layer were not be etched back is greater than or equal to the thickness of the thin-film pattern.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a manufacturing method of a micro structure such as a micro gear or a microscopic optical component manufactured by a laminated formation method or a die for molding of such a component. In particular, the invention relates to a manufacturing method of a micro structure capable of laminating very thin films at a high transfer rate. 
   2. Description of the Related Art 
   In recent years, the laminated formation method has spread rapidly as a method for forming a computer-designed three-dimensional object having complex shape in a short period (i.e., a period short enough to meet an early appointed date of delivery). Three-dimensional objects formed by the laminated formation method are used as models (prototypes) of components of various apparatus to check whether their operations and shapes are proper. In the past, in many cases, components to which this method were applied were of relatively large sizes, that is, on the order of centimeters or larger. However, in recent years, there has occurred demand for application of this method to micro parts produced by the precision machining such as micro gears and microscopic optical components. Prior art references relating to this technology are JP-A-2000-238000 (patent document-1) and JP-A-11-28768 (patent document-2). 
     FIGS. 7A-7C  to  FIGS. 9A and 9B  show a manufacturing method of a micro structure that is described in patent document-1. First, as shown in  FIG. 7A , a silicon wafer as a substrate  101  is prepared and a polyimide release layer  102  is formed on the surface of the substrate  101  at a thickness of 2 to 5 μm by spin coating. 
   Then, as shown in  FIG. 7B , an 8-μm-thick A 1  thin film  103  is deposited on the release layer  102  by sputtering and a resist  104  is formed thereon. After a photolithography step, as shown in  FIG. 7C  the A 1  thin film  103  is etched into plural thin-film patterns  105   a ,  105   b , and  105   c  having partial sectional shapes of a desired micro structure. A resulting substrate is called a donor substrate  106 . 
   Then, as shown in  FIG. 8 , the donor substrate  106  is fixed to an xyθ stage  107  that is provided in a vacuum chamber  110  and can be moved in the x-axis and y-axis directions and rotated about the z axis (i.e., in the θ direction). A target substrate  109  is fixed to a z stage  108  that can be moved in the z-axis direction. Then, FABs (fast atom beams) that are Ar neutral beams are emitted from particle beam emission ends  111  and  112  and applied to the surfaces of the donor substrate  106  on the xyθ stage  107  and the target substrate  109  on the z stage  108 , whereby oxide films, impurities, etc. on the surface of the donor substrate  106  and the target substrate  109  are removed to produce clean surfaces. 
   Subsequently, as shown in  FIG. 9A , the surface of the target substrate  109  is brought into contact with the surface of the first thin-film pattern  105   a  and pressed against it with a load of 50 kgf/cm 2  for 5 minutes, whereby the target substrate  109  and the first thin-film pattern  105   a  are joined to each other strongly. 
   Then, as shown in  FIG. 9B , the z stage  108  is elevated. Since the joining of the target substrate  109  and the first thin-film pattern  105   a  is stronger than the adhesion between the first thin-film pattern  105   a  and the release layer  102  on the donor substrate  106 , the first thin-film pattern  105   a  is transferred from the donor substrate  106  to the target substrate  109 . 
   Then, the xyθ stage  107  is moved by a prescribed pitch and positioning, FAB illumination, and transfer steps are repeatedly executed for the second thin-film pattern  105   b  and then for the third thin-film pattern  105   c  in the same manner as done for the first thin-film substrate  105   a  as shown in  FIGS. 8 ,  9 A and  9 B, whereby a micro structure is completed. Then, the target substrate  109  is removed from the z stage  108  and the necessary micro structure is separated from the target substrate  109 . 
   The conventional manufacturing method of a micro structure described in patent document-2 is as follows. A release layer is formed on a substrate and plural thin-film patterns having prescribed two-dimensional patterns are formed on the release layer. The release layer is etched back at a prescribed depth to form recesses. The thin-film patterns are peeled off the release layer and laminated (joined together) on a stage, whereby a micro structure is obtained. With this manufacturing method, even if particles such as fragments of glass or an Si wafer as a substrate, peeled pieces of metal, or a fine powder exist between the substrate and the stage, the surface contact between the state and the thin-film patterns is not obstructed. 
   However, in the conventional manufacturing method of patent document-1, if a thin-film pattern  105  is too thin, the thin film pattern  105  is buried in the release layer  102  and the top surfaces of the thin-film pattern  105  and the release layer  102  are made flush with the bottom surface of the target substrate  109 . A load from the target substrate  109  is imposed uniformly on the thin-film pattern  105  and the release layer  102 . Contrary to the intention of applying a load to the thin-film pattern  105  to join and transfer the thin-film pattern  105  to the target substrate  109 , as shown in  FIG. 10  a portion of the release layer  102  is raised in a region close to the circumference of the thin-film pattern  105  and the top surface of the raised portion  102   a  becomes flush with that of the thin-film pattern  105 . The load imposed on the thin-film pattern  105  becomes insufficient, resulting in insufficient joining and transfer. 
   On the other hand, in the conventional manufacturing method of patent document-2, although the release layer is etched back, the etch-back is performed to decrease the transfer yield reduction due to particles. Therefore, the conditions relating to the thicknesses of the thin-film patterns and the release layer are different from the conditions of the problem to be solved by the invention. Therefore, this manufacturing method cannot solve the problem that arises when the height of a raised portion of the release layer in a region close to the circumference of a thin-film pattern is greater than or equal to the thickness of the thin-film pattern in the transfer step. 
   SUMMARY OF THE INVENTION 
   The present invention has been made in view of the above circumstances, and provides a manufacturing method of a micro structure capable of laminating very thin films at a high transfer rate. 
   The invention provides a manufacturing method of a micro structure including the steps of forming a release layer on a substrate; forming the plural thin-film patterns having prescribed two-dimensional patterns on the release layer; etching back the release layer at a prescribed depth at least in regions close to circumferences of the thin-film patterns; and transferring the thin-film patterns sequentially to a counter substrate so that they are laminated on the counter substrate and a micro structure is thereby formed, wherein a combination of the thin-film patterns and the release layer is such that when a prescribed pressure is applied to each of the thin-film patterns on the release layer in the transferring step, a height of a raised portion of the release layer that would be appeared in a region close to a circumference of the thin-film pattern if the release layer were not be etched back is greater than or equal to a thickness of the thin-film pattern. 
   With the above method, since the release layer is etched back at least in the regions close to the circumferences of the thin-film patterns, even if a portion of the release layer is raised in the transfer step the raised portion can be prevented from contacting the counter substrate or a thin-film pattern that has been transferred to the counter substrate. A prescribed pressure can be exerted on the entire surface of the thin-film pattern. 
   That is, according to the manufacturing method of a micro structure according to the invention, even if a portion of the release layer is raised in the transfer step, the raised portion is prevented from contacting the counter substrate or a thin-film pattern that has been transferred to the counter substrate. Therefore, the thin-film patterns can be transferred in such a manner that a sufficient load is imposed thereon reliably. This makes it possible to laminate thin films at a high transfer rate. Further, since a very thin film can be used, the resolution in the lamination direction can be increased. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Preferred embodiments of the present invention will be described in detail based on the following figures, wherein: 
       FIGS. 1A-1E  are sectional views showing a manufacturing method of a micro structure according to a first embodiment of the invention; 
       FIG. 2  shows the manufacturing method of a micro structure according to the first embodiment of the invention; 
       FIG. 3A  shows the manufacturing method of a micro structure according to the first embodiment of the invention; 
       FIG. 3B  is an enlarged view of part of  FIG. 3A ; 
       FIG. 4  shows the manufacturing method of a micro structure according to the first embodiment of the invention; 
       FIGS. 5A-5D  are sectional views showing a manufacturing method of a micro structure according to a second embodiment of the invention; 
       FIGS. 6A-6D  are sectional views showing a manufacturing method of a micro structure according to a third embodiment of the invention; 
       FIGS. 7A-7C ,  FIG. 8 , and  FIGS. 9A and 9B  show conventional manufacturing methods of a micro structure; and 
       FIG. 10  is a sectional view illustrating a problem of the conventional manufacturing method. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 1A-1E  to  4  show a manufacturing method of a micro structure according to a first embodiment of the present invention. First, as shown in  FIG. 1A , an Si wafer as a substrate  101  is prepared and a release layer  102  made of polyimide (polyimide PIX3400 of Hitachi Chemical Co., Ltd.) is formed on the substrate  101  by spin coating at a thickness (e.g., 2 μm) that is thicker than an A 1  thin film that will be formed in a later step. 
   Then, as shown in  FIG. 1B , a very thin A 1  thin film  103  is deposited on the release layer  102  by sputtering at a thickness (e.g., 0.17 μm) that is smaller than 1 μm and a resist  104  is formed thereon. After a photolithography step, as shown in  FIG. 1C  the A 1  thin film  103  is etched into plural thin-film patterns  105   a ,  105   b , and  105   c  having partial sectional shapes of a desired micro structure. 
   Then, as shown in  FIG. 1D , etching is performed in, for example, regions where the release layer  102  is exposed, whereby recesses  102   b  having a prescribed depth are formed. The etching may be wet etching in which the substrate is immersed in a liquid for a prescribed time and dry etching that is performed in a vacuum apparatus.  FIG. 1D  shows a case of dry etching. With the dry etching, etching surfaces are formed almost perpendicularly to the substrate. On the other hand, in the case of wet etching, the side etching proceeds to under the bottom surfaces of the thin-film patterns  105   a ,  105   b , and  105   c  and a sufficient load may not be imposed on the thin-film patterns  105   a ,  105   b , and  105   c  in a transfer step. However, the wet etching can well be used depending on the shape accuracy that is required for the thin-film patterns  105   a ,  105   b , and  105   c.    
   A mixed gas of CF 4  and O 2  is typically used as a gas for etching back the release layer  102 . Since the gas etches such a metal as A 1  of which the thin-film patterns  105   a ,  105   b , and  105   c  are made at a sufficiently low etching rate, it can be said that there is no influence on the surfaces of thin-film patterns  105   a ,  105   b , and  105   c . If this etch-back step is executed by dry etching in a state that the resist patterns  201  exist, not only is the polyimide release layer  102  etched back but also the thickness of the resist patterns  201  are decreased. However, there is no influence on the surfaces of thin-film patterns  105   a ,  105   b , and  105   c  because they are not etched. The etch-back may be performed by using the thin-film patterns  105   a ,  105   b , and  105   c  as a mask after removing the resist patterns  201 . 
   In the above-described manner, a donor substrate  106  shown in  FIG. 1E  is formed. In the next, transfer step, as shown in  FIG. 2 , the donor substrate  106  is fixed to an xyθ stage  107  that is provided in a vacuum chamber  110  and can be moved in the x-axis and y-axis directions and rotated about the z axis (i.e., in the θ direction). A target substrate  109  is fixed to a z stage  108  that can be moved in the z-axis direction. Then, FABs (fast atom beams) that are Ar neutral beams are emitted from particle beam emission ends  111  and  112  and applied to the surfaces of the donor substrate  106  on the xyθ stage  107  and the target substrate  109  on the z stage  108 , whereby oxide films, impurities, etc. on the surfaces of the donor substrate  106  and the target substrate  109  are removed to produce clean surfaces. 
   Subsequently, as shown in  FIG. 3A , the surface of the target substrate  109  is brought into contact with the surface of the first thin-film pattern  105   a  and pressed against it with a load of 50 kgf/cm 2  for 5 minutes, whereby the target substrate  109  and the first thin-film pattern  105   a  are joined to each other strongly. Measured joining strength of 50 to 100 MPa is obtained in a tension test.  FIG. 3B  shows this state in detail. The recesses  102   b  are formed in the regions where the release layer  102  is exposed. Therefore, although a portion of the release layer  102  is raised in a region close to the circumference of the first thin-film pattern  105   a  in the transfer step, the raised portion  102   a  does not contact the target substrate  109 . 
   Then, as shown in  FIG. 4 , the z stage  108  is elevated. Since the joining of the target substrate  109  and the first thin-film pattern  105   a  is stronger than the adhesion between the first thin-film pattern  105   a  and the release layer  102  on the donor substrate  106 , the first thin-film pattern  105   a  is transferred from the donor substrate  106  to the target substrate  109 . 
   Then, the xyθ stage  107  is moved by a prescribed pitch and positioning, FAB illumination, and transfer steps are repeatedly executed for the second thin-film pattern  105   b  and then for the third thin-film pattern  105   c  in the same manner as done for the first thin-film substrate  105   a  as shown in  FIGS. 2 ,  3 A and  4 , whereby a micro structure is completed. FABs are applied to the surface of the thin-film pattern  105   a  or  105   b  that has been transferred to the target substrate  109  and the surface of the thin-film pattern  105   b  or  105   c  on the donor substrate  106  that will be transferred next. Then, the target substrate  109  is removed from the z stage  108  and the necessary micro structure is separated from the target substrate  109 . 
   According to the first embodiment, since etch-back is performed in the regions where the release layer  102  is exposed, even if a portion of the release layer  102  is raised in the transfer step the raised portion  102   a  is prevented from contacting the target substrate  109  or the thin-film pattern  105   a  or  105   b  that has been transferred to the target substrate  109 . Therefore, the thin-film patterns  105   a ,  105   b , and  105   c  can be transferred in such a manner that a sufficient load is imposed there on reliably. This makes it possible to laminate thin films at a high transfer rate. Further, since a very thin film can be used, the resolution in the lamination direction can be increased. It is noted that etch-back may be performed only in regions close to the circumferences of the thin-film patterns  105   a ,  105   b , and  105   c  instead of all the regions where the release layer  102  is exposed. 
     FIGS. 5A-5D  show a manufacturing method of a micro structure according to a second embodiment of the invention. The second embodiment is such that after the release layer  102  is etched back to such an extent that its thickness becomes zero in the etching step of the first embodiment the substrate  101  is etched back to form recesses  101   a  therein. Where the substrate  101  is made of Si or SiO 2 , CF 4  or the like suitable etching gas. The second embodiment is effective in a case that the height of the raised portions  102   a  of the release layer  102  is greater than the thickness of the thin-film patterns  105   a ,  105   b , or  105   c  in the transfer step even if the release layer  102  is made thin. In such a case, by etching back the substrate  101 , even if portions of the release layer  102  are projected laterally in the transfer step, the projected portions can be prevented from contacting the target substrate  109  or the thin-film pattern  105   a  or  105   b  that has been transferred to the target substrate  109 . Therefore, a sufficient load can reliably be imposed on the thin-film patterns  105   a ,  105   b , and  105   c.    
     FIGS. 6A-6D  show a manufacturing method of a micro structure according to a third embodiment of the invention. The third embodiment is different from the first embodiment in that an intermediate layer  301  is formed between the substrate  101  and the release layer  102  and that after the etch-back of the release layer  102  the intermediate layer  301  is etched back to form recesses  301   a  in the intermediate layer  301 . Where the intermediate layer  301  is made of SiO 2 , the etch-back can be performed by using such a gas as CF 4 . According to the third embodiment, the use of the intermediate layer  301  that can be etched back more easily than the substrate  101  provides the same advantage as the second embodiment does. That is, even if portions of the release layer  102  are projected laterally in the transfer step, the projected portions can be prevented from contacting the target substrate  109  or the thin-film pattern  105   a  or  105   b  that has been transferred to the target substrate  109 . Therefore, a sufficient load can reliably be imposed on the thin-film patterns  105   a ,  105   b , and  105   c.    
   The invention is not limited to the above embodiments and various modifications are possible. For example, the thin-film patterns may be made of a material other than Al, such as Cu, Ta, Ni, or Cr or an alloy thereof. The release layer may be made of a material other than polyimide, such as SiO 2 , SiOF, or polyimide fluoride. 
   The depth of recesses that are formed by etch-back may be determined in accordance with parameters relating to the thin-film patterns such as their area, pitch, and circumferential length and parameters relating to the release layer such as its material and thickness. In this case, the following measure may be taken. The heights of raised portions are measured for various combinations of thin-film patterns and a release layer and measured values are stored in a judging device as statistical data. Whether etch-back is necessary is judged by inputting values of the above parameters to the judging device. If it is judged that etch-back is necessary, the judging device is caused to output an etch-back depth. 
   The thin-film patterns may be transferred directly to the stage or the like without using the counter substrate. 
   As described above, the invention may be implemented in the following specific manners:
         (1) In the manufacturing method of a micro structure according to the invention, the etching-back step is executed on not only the release layer but also the substrate.   (2) The manufacturing method of a micro structure according to the invention further includes the step of forming an intermediate layer on the substrate before forming the release layer, wherein the etching-back step is executed on not only the release layer but also the intermediate layer.   (3) In the manufacturing method of a micro structure according to the invention, the etching-back step is executed by dry etching.   (4) In the manufacturing method of a micro structure according to the invention, in the etching-back step resist patterns on the thin-film patterns that are used in forming the thin-film patterns are etched together with the release layer.   (5) In the manufacturing method of a micro structure according to the invention, the etching-back step is executed by using the thin-film patterns as a mask.   (6) In the manufacturing method of a micro structure according to the invention, the prescribed depth is determined in accordance with parameters relating to the thin-film patterns including their area, pitch, and circumferential length and parameters relating to the release layer including its material and thickness.       

   The entire disclosure of Japanese Patent Application No. 2003-277815 filed on Jul. 22, 2003 including specification, claims, drawings and abstract is incorporated herein by reference in its entirety.