Patent Publication Number: US-2007117247-A1

Title: Manufacturing method of microstructure

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
      This Non-provisional application claims priority under 35 U.S.C. §119(a) on Patent Application No(s). 094141108 filed in Taiwan, Republic of China on Nov. 23, 2005, the entire contents of which are hereby incorporated by reference.  
     BACKGROUND OF THE INVENTION  
      1. Field of Invention  
      The invention relates to a manufacturing method of a microstructure and, in particular, to a manufacturing method for a microstructure with a high aspect ratio.  
      2. Related Art  
      An inclined lateral wall structure is frequently seen in a micro electromechanical system (MEMS), and may serve as a contact plug or a via plug, or may be applied to form a precision mold. The conventional manufacturing method for the inclined lateral wall structure is usually performed by way of mechanical machine processing, such as planing, polishing, laser processing or electricity discharge processing.  
       FIGS. 1A  to  1 C are schematic illustrations showing a conventional manufacturing process for a conventional inclined lateral wall structure. As shown in  FIG. 1A , a workpiece  10  having a surface  101  is provided, and a tool  11  having an inclined surface  111  is selected. Next, as shown in  FIG. 1B , the tool  11  is used to processing the surface  101  of the workpiece  10  by way of, for example, cutting, polishing, or planing. Finally, after the processing procedures have been finished, a recess C 1  with an inclined lateral wall is formed on the workpiece  10 .  
      However, the above-mentioned processing method is restricted by the size and the precision of the tool itself, and cannot easily form an inclined lateral wall structure with high-precision, high-resolution and low surface roughness in the micro electromechanical system, so the technological threshold and cost are very high. Thus, it is an important subject to provide a method for manufacturing a microstructure with high-precision, high-resolution and low surface roughness in the micro electromechanical system. Also, it is an important subject to provide a method for manufacturing a microstructure to make the batch production possible and reduce production cost.  
     SUMMARY OF THE INVENTION  
      In view of the foregoing, the invention is to provide a manufacturing method of a microstructure with high-precision, high-resolution and low surface roughness, wherein the method makes the batch production possible, shortens the manufacturing time and reduces production cost.  
      To achieve the above, the invention discloses a manufacturing method of a microstructure. The method includes the steps of: providing a substrate, forming a photoresist layer on the substrate, providing a first mask, which includes at least one opaque area and at least one first lens, over the photoresist layer, providing a light source to illuminate the photoresist layer through the first mask, and removing a portion of the photoresist layer to form at least one recess in the photoresist layer. The recess has a lateral wall, a depth and a width. An inclined angle of the lateral wall is not less than 5 degrees, and a ratio of the depth to the width is not less than 2.  
      To achieve the above, the invention also discloses a manufacturing method of a microstructure. The method includes the steps of: providing a substrate, which has a surface including at least one opaque area and at least one first lens, forming a photoresist layer on the surface of the substrate, providing a light source to illuminate the photoresist layer through the substrate, and removing a portion of the photoresist layer to form at least one recess in the photoresist layer. The recess has a lateral wall, a depth and a width. An inclined angle of the lateral wall is not less than 5 degrees, and a ratio of the depth to the width is not less than 2.  
      As mentioned above, the manufacturing method of the microstructure according to the invention is to dispose the photoresist layer on the substrate and then to form the microstructure using a semiconductor process (e.g., a photo-lithographic process). Therefore, the resolution, precision and surface roughness of the microstructure are better than those of the conventional microstructures which are formed by using prior art processing methods. According to the advantage of the semiconductor process, the microstructure can be produced in batches, and the manufacturing time and cost may be reduced. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The invention will become more fully understood from the detailed description given herein below illustration only, and thus is not limitative of the present invention, and wherein:  
       FIGS. 1A  to  1 C are schematic illustrations showing a conventional manufacturing method for a conventional inclined lateral wall structure;  
       FIGS. 2A  to  2 E are schematic illustrations showing the procedures of a manufacturing method of a microstructure according to a first embodiment of the invention;  
       FIGS. 3A and 3B  are schematic illustrations showing the procedures of a manufacturing method of a microstructure according to another first embodiment of the invention;  
       FIGS. 4A  to  4 G are schematic illustrations showing the procedures of a manufacturing method of a microstructure according to a second embodiment of the invention;  
       FIGS. 5A  to  5 D are schematic illustrations showing the procedures of a manufacturing method of a microstructure according to a third embodiment of the invention; and  
       FIGS. 6A  to  6 F are schematic illustrations showing the procedures of a manufacturing method of a microstructure according to a fourth embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      The present invention will be apparent from the following detailed description, which proceeds with reference to the accompanying drawings, wherein the same references relate to the same elements.  
      Referring to  FIGS. 2A  to  2 E, a manufacturing method of a microstructure according to a first embodiment of the invention includes the following steps. As show in  FIG. 2A , a substrate  21  having a surface  211  is firstly provided. In this embodiment, the substrate  21  may be a light-permeable substrate, a translucent substrate or an opaque substrate.  
      Next, as shown in  FIG. 2B , a photoresist layer  22  is formed on the surface  211  of the substrate  21 . In this embodiment, the photoresist layer  22  is made of a positive photosensitive material, and the thickness of the photoresist layer  22  is not less than 0.03 mm. It is noted that the material of the photoresist layer  22  is not limited to the positive photosensitive material. Instead, the photoresist layer  22  may be made of a negative photosensitive material, a single-layer photosensitive material or a multi-layer photosensitive material. The photosensitive material of the photoresist layer  22  and the number of the photoresist layer(s)  22  may be selected according to actual requirements.  
      Next, as shown in  FIG. 2C , a first mask  23  is provided over the photoresist layer  22 . The first mask  23  has an opaque area  231  and a first lens  232 , both of which are alternately arranged on a surface of the first mask  23 . In this embodiment, the first lens  232  is a focusing lens.  
      Then, as shown in  FIG. 2D , a light source  24  is provided to illuminate the photoresist layer  22  through the first mask  23 .  
      Finally, as shown in  FIG. 2E , a portion of the photoresist layer  22  is removed such that a recess  221  is formed in the photoresist layer  22 . The recess  221  has a lateral wall  222 , a depth D 1  and a width W 1 . An inclined angle θ 1  of the lateral wall  222  is not less than 5 degrees, and a ratio of the depth D 1  to the width W 1  is not less than 2.  
      The recess  221  is formed by a photo-lithographic process. Because the photoresist layer  22  is made of the positive photosensitive material, the portion illuminated by the light source  24  is formed into the recess  221  after the photo-lithographic process is performed. The photo-lithographic process pertains to the typical semiconductor process that is often used, and the removing of a portion of the photoresist layer  22  may be performed by way of development, which is the typical semiconductor process that is usually adopted, so detailed descriptions thereof will be omitted.  
      In this embodiment, the depth D 1  of the recess  221  is not less than 0.03 mm. The depth D 1  of the recess  221  substantially equals to the thickness (0.03 mm) of the photoresist layer  22 . Under the definition that the ratio of the depth D 1  to the width W 1  is not less than 2, the width W 1  of the recess  221  is not greater than 0.015 mm, the feature size of the recess  221  is not greater than 0.5 mm, and the processing precision is not greater than 0.01 mm.  
      The inclined angle θ 1  of the recess  221  is formed according to a focusing phenomenon obtained when the light source  24  illuminates the photoresist layer  22  through the first lens  232 . The first lens  232  of this embodiment is a focusing lens, so the light rays of the light source  24  pass through the first lens  232  and are then focused, as shown in  FIG. 2D . Thus, the inclined angle θ 1  of the lateral wall  222 , which is generated when a portion of the photoresist layer  22  is removed, may be controlled in order to form the recess  221 .  
      A microstructure  2 , as shown in  FIG. 2E , to be applied to a micro electromechanical system may be manufactured according to the above-mentioned manufacturing method. The microstructure  2  includes the substrate  21  and the photoresist layer  22 . The substrate  21  has the surface  211 . The photoresist layer  22  is disposed on the surface  211  of the substrate  21 . The photoresist layer  22  has at least one recess  221 , which has the lateral wall  222 , the depth D 1  and the width W 1 . In addition, the lateral wall  222  of the recess  221  with the inclined angle θ 1  may be symmetrically arranged or non-symmetrically arranged. That is, the inclined angle θ 1  of the lateral wall  222  of the recess  221  can be changed according to actual requirements.  
      In the above-mentioned embodiment, the first mask  23  has, without limitation to, one opaque area  231  and one first lens  232 . It is also possible to utilize a mask (not shown) used in the typical photo-lithographic process in conjunction with a light modulation device (not shown) to achieve the same effect and object as those of the first mask  23 . The light modulation device may be a lens or a liquid lens, and the lens may also be a focusing lens or a defocusing lens. Thus, the light rays passing through the mask can define the exposure positions. Meanwhile, by using the light modulation device can change the focusing or defocusing phenomenon of the light rays and thus achieve the same effect.  
       FIGS. 3A and 3B  are schematic illustrations showing the procedures of a manufacturing method of a microstructure according to another first embodiment of the invention. In  FIG. 3A , a first lens  332  of a first mask  33  is a defocusing lens, so the light rays of a light source  34  pass through the first lens  332  and are then defocused. Thus, it is possible to control the inclined angle θ 1  of a lateral wall  322 , when a portion of a photoresist layer  32  is removed, to form a recess  321  such that a microstructure  3  is formed, as shown in  FIG. 3B .  
       FIGS. 4A  to  4 G are schematic illustrations showing the procedures of a manufacturing method of a microstructure according to a second embodiment of the invention. Referring to  FIGS. 4A  to  4 G, the manufacturing method includes the following steps. In the second embodiment, the steps of  FIGS. 4A  to  4 D are the same as those of  FIGS. 2A  to  2 D, so detailed descriptions thereof will be omitted.  
      As shown in  FIG. 4E , the difference between this embodiment and the first embodiment is that a second mask  45  is provided over a photoresist layer  42  after the step described and shown in  FIG. 4D . The second mask  45  has an opaque area  451  and a second lens  452 , which are arranged on the surface of the second mask  45  alternately. In this embodiment, the second lens  452  is a defocusing lens.  
      Next, as shown in  FIG. 4F , a light source  44  is provided to illuminate the photoresist layer  42  through the second mask  45 .  
      Finally, as shown in  FIG. 4G , a portion of the photoresist layer  42  is removed to form a recess  421  in the photoresist layer  42  and thus to form a microstructure  4 . In this embodiment, the recess  421  is formed after two exposing procedures. Because the photoresist layer  42  is a positive photosensitive material, the portion illuminated by the light source  44  is formed into the recess  421  after the photo-lithographic process, and the microstructure  4  is thus formed.  
      A manufacturing method of a microstructure according to a third embodiment of the invention includes the following steps. As shown in FIG  5 A, a substrate  51  having a surface  511  is firstly provided. The surface  511  has an opaque area  512  and a first lens  513 . In this embodiment, the substrate  51  may be a light-permeable substrate or a translucent substrate, and the first lens  513  is a focusing lens.  
      As shown in FIG  5 B, a photoresist layer  52  is formed on the surface  511  of the substrate  51 . In this embodiment, the photoresist layer  52  is made of a positive photosensitive material, and the thickness of the photoresist layer  52  is not less than 0.03 mm.  
      Next, as shown in FIG  5 C, a light source  53  is provided to illuminate the photoresist layer  52  through the substrate  51 .  
      Finally, as shown in FIG  5 D, a portion of the photoresist layer  52  is removed to form at least one recess  521  in the photoresist layer  52 , and thus to form a microstructure  5 . In addition, the recess  521  has a lateral wall  522 , a depth D 1  and a width W 1 , an inclined angle θ 1  of the lateral wall  522  is not less than 5 degrees, and a ratio of the depth D 1  to the width W 1  is not less than 2. In this embodiment, the recess  521  is formed by a photo-lithographic process. Because the photoresist layer  52  is made of a positive photosensitive material, the portion illuminated by the light source  53  is formed into the recess  521  after the photo-lithographic process.  
      The depth D 1  of the recess  521  is not less than 0.03 mm. In this embodiment, the depth D 1  of the recess  521  and the thickness of the photoresist layer  52  are 0.03 mm. Under the definition that the ratio of the depth D 1  to the width W 1  is not less than 2, the width W 1  of the recess  521  is not greater than 0.015 mm. In this embodiment, the feature size of the recess  521  is not greater than 0.5 mm, and the processing precision is not greater than 0.01 mm.  
      The inclined angle θ 1  of the recess  521  is formed through a focusing phenomenon, which is generated after the light source  53  illuminates the photoresist layer  52  through the first lens  513 . The first lens  513  of this embodiment is a focusing lens. Thus, the focusing effect (FIG  5 C), which is generated after the light rays of the light source  53  pass through the first lens  513 , can control the inclined angle θ 1  of the lateral wall  522  when a portion of the photoresist layer  52  is removed. Then, the recess  521  is formed. Of course, the first lens  513  may also be a defocusing lens in this embodiment.  
       FIGS. 6A  to  6 F are schematic illustrations showing the procedures of a manufacturing method of a microstructure according to a fourth embodiment of the invention. The manufacturing method of the microstructure includes the following steps. In the fourth embodiment, the steps of  FIGS. 6A  to  6 C are the same as those of  FIGS. 5A  to  5 C, and detailed descriptions thereof will be omitted.  
      As shown in  FIG. 6D , the difference between this embodiment and the third embodiment is that a mask  64  is provided over a photoresist layer  62  after the step of  FIG. 6C  is performed. The mask  64  has an opaque area  641  and a second lens  642 , which are arranged on a surface of the mask  64  alternately. In this embodiment, the second lens  642  may be a focusing lens.  
      Next, as shown in  FIG. 6E , a light source  63  is provided to illuminate the photoresist layer  62  through the mask  64 .  
      Finally, as shown in  FIG. 6F , a portion of the photoresist layer  62  is removed to form a recess  621  in the photoresist layer  62  and thus to form a microstructure  6 . In this embodiment, the recess  621  is formed after two exposing procedures are performed. Because the photoresist layer  62  is made of a positive photosensitive material, the portion illuminated by the light source  63  is formed into the recess  621  after the photo-lithographic procedure. Thus, the microstructure  6  is formed.  
      In summary, the manufacturing method of the microstructure according to the invention is to dispose the photoresist layer on the substrate and then to form the microstructure by using a semiconductor process (e.g., a photo-lithographic process). Therefore, the resolution, precision and surface roughness of the microstructure are better than those of the conventional microstructures formed by using the prior art processing methods. According to the advantage of the semiconductor process, the microstructure can be produced in batches, and the manufacturing time and cost may be reduced.  
      Although the invention has been described with reference to specific embodiments, this description is not meant to be construed in a limiting sense. Various modifications of the disclosed embodiments, as well as alternative embodiments, will be apparent to persons skilled in the art. It is, therefore, contemplated that the appended claims will cover all modifications that fall within the true scope of the invention.