Abstract:
The present invention relates to a method for exposing twice by two masks in a semiconductor process, which includes: (a) providing a substrate having a surface; (b) forming a negative-type photosensitive material on the surface of the substrate; (c) providing a first mask having a first pattern; (d) performing a first exposure procedure on the negative-type photosensitive material by utilizing a first light beam through the first mask; (e) providing a second mask having a second pattern, wherein the entire texture of the second pattern is substantially identical to that of the first pattern; and (f) performing a second exposure procedure on the negative-type photosensitive material by utilizing a second light beam through the second mask. Thus, the negative-type photosensitive material will not be damaged and will not cause yield loss.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a method for exposing twice. More particularly, the present invention relates to a method for exposing twice by two masks in a semiconductor process. 
         [0003]    2. Description of the Related Art 
         [0004]      FIGS. 1 to 4  show schematic views of exposing and developing processes of a wafer in a conventional semiconductor process. Firstly, referring to  FIG. 1 , a wafer  10  is provided. The wafer  10  has a surface  101  and a plurality of bonding pads  11  disposed on the surface  101 . Next, referring to  FIG. 2 , a polyimide (PI) passivation layer  12  is formed on the surface  101  of the wafer  10 . The PI passivation layer  12  is of a negative-type photosensitive material. 
         [0005]    Then, referring to  FIG. 3 , a mask  14  is provided. The mask  14  has a pattern  141  and a non-exposed pattern  142 . The non-exposed pattern  142  corresponds to the bonding pads  11  in order to expose the bonding pads  11  in subsequent processes. Normally, the mask  14  may have extra impurities or an extra particle  143  located in the pattern  141 . After that, a light beam  16  is utilized to pass through the mask  14 , so as to perform an exposure procedure on the PI passivation layer  12 . The light beam  16  passes through the pattern  141 , so that the corresponding PI passivation layer  12  has chemical reactions, and is not removed during development. However, as the particle  143  blocks the light beam  16 , a part of the area that should be irradiated by the light beam  16  originally is not irradiated by the light beam  16 , and does not have chemical reactions. 
         [0006]    Then, referring to  FIG. 4 , after the mask  14  is removed, a developer is used to proceed with a developing procedure on the PI passivation layer  12 . The area not irradiated by the light beam  16  will be washed out by the developer, but the area irradiated by the light beam  16  will remain because of the chemical reactions thereon. Thus, only the bonding pads  11  are exposed for the subsequent processes. However, it is known from  FIG. 4  that a part of the PI passivation layer  12  does not have chemical reactions as it is blocked by the particle  143 , so this part will also be washed out by the developer, causing damage of the PI passivation layer  12  and unexpectedly exposing part of the surface  101  of the wafer  10 , which will result in yield loss. 
         [0007]    Therefore, it is necessary to provide a method for exposing twice in a semiconductor process to solve the above problems. 
       SUMMARY OF THE INVENTION 
       [0008]    The object of the present invention is to provide a method for exposing twice in a semiconductor process, which includes: 
         [0009]    (a) providing a substrate having a surface; 
         [0010]    (b) forming a negative-type photosensitive material on the surface of the substrate; 
         [0011]    (c) providing a first mask having a first pattern; 
         [0012]    (d) performing a first exposure procedure on the negative-type photosensitive material by utilizing a first light beam through the first mask; 
         [0013]    (e) providing a second mask having a second pattern, in which the entire texture of the second pattern is identical to that of the first pattern; and 
         [0014]    (f) performing a second exposure procedure on the negative-type photosensitive material by utilizing a second light beam through the second mask. 
         [0015]    Thus, the negative-type photosensitive material will not be damaged and will not cause yield loss. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIGS. 1 to 4  are schematic views of exposing and developing processes of a wafer in a conventional semiconductor process; 
           [0017]      FIGS. 5 to 9  are schematic views of exposing and developing processes of a wafer in a semiconductor process according to the present invention; 
           [0018]      FIGS. 10 to 12  are schematic views showing errors when exposing twice by two masks having identical patterns according to the present invention, in which the width of the first non-exposed pattern is identical to that of the second non-exposed pattern; 
           [0019]      FIGS. 13 to 15  are schematic views showing errors when exposing twice by two masks having identical patterns according to the present invention, in which the width of the first non-exposed pattern is larger than that of the second non-exposed pattern; and 
           [0020]      FIGS. 16 to 18  are schematic views showing errors when exposing twice by two masks having identical patterns according to the present invention, in which the width of the first non-exposed pattern is smaller than that of the second non-exposed pattern. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0021]      FIGS. 5 to 9  show schematic views of exposing and developing processes of a wafer in a semiconductor process according to the present invention. Firstly, referring to  FIG. 5 , a substrate (e.g., a wafer  20 ) is provided. The wafer  20  has a surface  201  and a plurality of bonding pads  21  on the surface  201 . Referring to  FIG. 6 , a negative-type photosensitive material (e.g., polyimide, PI) passivation layer  22  is formed on the surface  201  of the wafer  20 . 
         [0022]    Referring to  FIG. 7 , a first mask  24  is provided. The first mask  24  has a first pattern  241  and a first non-exposed pattern  242 . The first non-exposed pattern  242  corresponds to the area to be exposed (e.g., the bonding pads  21 ), so as to expose the area in the subsequent processes. Normally, the first mask  24  may have extra impurities or particles (e.g., a first particle  243 ), and the first particle  243  is located in the first pattern  241 . After that, a first light beam  26  is utilized to pass through the first mask  24 , so as to perform a first exposure procedure on the PI passivation layer  22 . The first light beam  26  passes through the first pattern  241 , so that the corresponding PI passivation layer  22  has chemical reactions, and is not removed during development. However, as the first particle  243  blocks the first light beam  26 , a part of the area that should be irradiated by the first light beam  26  originally is not irradiated by the first light beam  26 , and does not have chemical reactions. 
         [0023]    Referring to  FIG. 8 , a second mask  28  is provided. The second mask  28  has a second pattern  281  and a second non-exposed pattern  282 . The entire texture of the second pattern  281  is identical to that of the first pattern  241 . Normally, the second mask  28  may also have extra impurities or particles (e.g., a second particle  283 ), and the second particle  283  is located in the second pattern  281 . It can be understood that it is almost impossible for the second particle  283  to be located at the same position as the first particle  243 . 
         [0024]    A second light beam  30  is utilized to pass through the second mask  24 , so as to perform a second exposure procedure on the PI passivation layer  22 . The second light beam  30  passes through the second pattern  281 , SO that the corresponding PI passivation layer  22  has chemical reactions, and is not removed during development. During this exposure procedure, as no particle exists at the position corresponding to the first particle  243 , the area of the PI passivation layer  22  blocked by the first particle  243  and not having chemical reactions on the first exposure procedure will have chemical reactions as it is irradiated by the second light beam  30  in this second exposure procedure. In addition, the area blocked by the second particle  283  has already had chemical reactions in the first exposure procedure. 
         [0025]    Referring to  FIG. 9 , after the second mask  28  is removed, a developer is used to perform a developing procedure on the PI passivation layer  22 . After the above two exposure procedures, the area irradiated by the first light beam  26  or the second light beam  30  remains because of the chemical reactions thereon, so as to form a plurality of openings  221  to expose the bonding pads  21  for the subsequent processes. Thus, the damage to the PI passivation layer  12  (as shown in  FIG. 4 ) and the yield loss in the conventional art will not occur. 
         [0026]    It should be noted that the present invention uses two masks having identical patterns for exposing twice, and thus when aligning them, it is possible that the openings  221  in the PI passivation layer  22  are not aligned with or have positional differences compared to the bonding pads  21  because of mechanical errors or human errors.  FIGS. 10 to 12  are schematic views showing errors when exposing twice by two masks having identical patterns according to the present invention, in which the width of the first non-exposed pattern is identical to that of the second non-exposed pattern. Referring to  FIG. 10 , the width W 1  of the first non-exposed pattern  242  of the first mask  24  is 60 μm (identical to the horizontal width of the bonding pads  21 ). Then, the first light beam  26  is utilized to pass through the first mask  24  to perform the first exposure procedure on the PI passivation layer  22 . After that, the first mask  24  is removed, and the second mask  28  is provided. 
         [0027]    Referring to  FIG. 11 , the width W 2  of the second non-exposed pattern  282  of the second mask  28  is 60 μm. Then, the second light beam  30  is used to pass through the second mask  28  to perform the second exposure procedure on the PI passivation layer  22 . The position of the s second mask  28  has a shift of 2 μm relative to the position of the first mask  24 . Referring to  FIG. 12 , a developer is used to perform a developing procedure on the PI passivation layer  22 . After the above two exposure procedures, the area irradiated by the first light beam  26  or the second light beam  30  remains, so as to form a plurality of openings  221 . The width W 3  of each of the openings  221  is 58 μm, which is smaller than the horizontal width of the bonding pads  21 , so the width of the openings  221  is smaller than the required width. 
         [0028]    In order to eliminate the above disadvantages, two methods can be adopted when designing the patterns of the masks. The first method is that the width of the second non-exposed pattern  282  of the second mask  28  is the actual required width, and the width of the first non-exposed pattern  242  of the first mask  24  is designed to be larger than the width of the second non-exposed pattern  282  by 2 μm to 4 μm. The second method is that the width of the first non-exposed pattern  242  of the first mask  24  is the actual required width, and the width of the second non-exposed pattern  282  of the second mask  28  is designed to be larger than the width of the first non-exposed pattern  242  by 2 μm to 4 μm. 
         [0029]      FIGS. 13 to 15  are schematic views showing errors when exposing twice by two masks having identical patterns according to the present invention, in which the width of the first non-exposed pattern is greater than that of the second non-exposed pattern, i.e., the aforementioned first method. Referring to  FIG. 13 , the width W 1  of the first non-exposed pattern  242  of the first mask  24  is 64 μm (larger than the horizontal width of the bonding pads  21 ). Then, the first light beam  26  is utilized to pass through the first mask  24  to perform the first exposure procedure on the PI passivation layer  22 . After that, the first mask  24  is removed, and the second mask  28  is provided. 
         [0030]    Referring to  FIG. 14 , the width W 2  of the second non-exposed pattern  282  of the second mask  28  is 60 μm. Then, the second light beam  30  is used to pass through the second mask  28  to perform the second exposure procedure on the PI passivation layer  22 . The position of the second mask  28  has a shift of 2 μm with respect to the position of the first mask  24 . Referring to  FIG. 15 , a developer is used to perform a developing procedure on the PI passivation layer  22 . After the above two exposure procedures, the area irradiated by the first light beam  26  or the second light beam  30  remains, so as to form a plurality of openings  221 . The width W 3  of each of the openings  221  is 60 μm, which is identical to the horizontal width of the bonding pads  21 . 
         [0031]      FIGS. 16 to 18  are schematic views showing errors when exposing twice by two masks having identical patterns according to the present invention, in which the width of the first non-exposed pattern is smaller than that of the second non-exposed pattern, i.e., the aforementioned second method. Referring to  FIG. 16 , the width W 1  of the first non-exposed pattern  242  of the first mask  24  is 60 μm (identical to the horizontal width of the bonding pads  21 ). Then, the first light beam  26  is utilized to pass through the first mask  24  to perform the first exposure procedure on the PI passivation layer  22 . After that, the first mask  24  is removed, and the second mask  28  is provided. 
         [0032]    Referring to  FIG. 17 , the width W 2  of the second non-exposed pattern  282  of the second mask  28  is 64 μm. Then, the second light beam  30  is used to pass through the second mask  28  to perform the second exposure procedure on the PI passivation layer  22 . The position of the second mask  28  has a shift of 2 μm with respect to the position of the first mask  24 . Referring to  FIG. 18 , a developer is used to perform a developing procedure on the PI passivation layer  22 . After the above two exposure procedures, the area irradiated by the first light beam  26  or the second light beam  30  remains, so as to form a plurality of openings  221 . The width W 3  of each of the openings  221  is 60 μm, which is identical to the horizontal width of the bonding pads  21 . 
         [0033]    While several embodiments of the present invention have been illustrated and described, various modifications and improvements can be made by those skilled in the art. The embodiments of the present invention are therefore described in an illustrative but not restrictive sense. It is intended that the present invention should not be limited to the particular forms as illustrated, and that all modifications which maintain the spirit and scope of the present invention are within the scope defined in the appended claims.