Abstract:
An adhesive sheet for affixation of a wafer includes a first substrate, first adhesive layer arranged on the first substrate, second substrate arranged on the first adhesive layer, and second adhesive layer arranged on the second substrate. A chemical reaction which causes reduction in the adhesion of the first adhesive layer and a chemical reaction which causes reduction in the adhesion of the second adhesive layer are different. A method for processing using this sheet includes the steps of affixing the sheet to a wafer, dicing the wafer with the sheet affixed thereto, peeling the first substrate and first adhesive layer away from the diced wafer by reducing the adhesion of the first adhesive layer and, thereby, dividing the wafer into a plurality of chips, and peeling the second substrate and second adhesive layer away from each of the chips by reducing the adhesion of the second adhesive layer.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Fiend of the Invention  
         [0002]     The present invention relates to an adhesive sheet for affixation of a wafer and a method for processing using the same. More particularly, the present invention relates to an adhesive sheet for affixation of a wafer used in dicing of a semiconductor wafer into chips and to a method for dicing a semiconductor wafer by using the same.  
         [0003]     2. Description of the Related Art  
         [0004]     In general, semiconductor wafers made of silicon, gallium arsenide, etc., are manufactured in the condition of having a large diameter. This wafer is cut and separated (diced) into element chips and, thereafter, the resulting chips are subjected to a mounting step. Conventionally, the semiconductor wafer is subjected to each step of dicing, cleaning, drying, expanding, picking up and mounting in the condition of being affixed to an adhesive sheet in advance. As the adhesive sheet for affixation of a wafer used in dicing, sheets described in, for example, Japanese Patent Laid-Open No. 7-86212, are known. The adhesive sheet for affixation of a wafer described in Japanese Patent Laid-Open No. 7-86212 is composed of a radiation-setting adhesive layer arranged on a substrate. This sheet can be peeled away from a semiconductor wafer with ease by being irradiated with radioactive rays after dicing.  
         [0005]     However, there is the following problem in the method for processing using the aforementioned conventional adhesive sheet for affixation of a wafer. That is, when there is another step between the steps of picking up and mounting, foreign matter, etc., may adhere to even a chip having been already cleaned and dried. In particular, since the back of the chip becomes a mounting surface, when adhesion of foreign matter, etc., occurs, problems of reduction in mounting precision, etc., are brought about.  
       SUMMARY OF THE INVENTION  
       [0006]     It is an object of the present invention to provide a reliable adhesive sheet for affixation of a wafer capable of overcoming the aforementioned problems in the conventional technology and reducing adhesion of foreign matter, etc., before mounting of the chip.  
         [0007]     The aforementioned object of the present invention can be achieved by an adhesive sheet for affixation of a wafer, the adhesive sheet including a first substrate, a first adhesive layer arranged on the first substrate, a second substrate arranged on the first adhesive layer, and a second adhesive layer arranged on the second substrate, wherein a chemical reaction which causes reduction in the adhesion of the first adhesive layer and a chemical reaction which causes reduction in the adhesion of the second adhesive layer are different.  
         [0008]     Regarding the aforementioned adhesive sheet for affixation of a wafer, for example, the first adhesive layer can be formed from a radiation-setting adhesive, and the second substrate can be formed from a heat-shrinkable plastic film. Furthermore, the first substrate may be formed from a heat-shrinkable plastic film and the second adhesive layer may be formed from a radiation-setting adhesive.  
         [0009]     A method for processing using the aforementioned adhesive sheet for affixation of a wafer includes the step of affixing the sheet to a wafer, the step of dicing the wafer with the sheet affixed thereto, the step of peeling the first substrate and the first adhesive layer away from the diced wafer by reducing the adhesion of the first adhesive layer of the sheet and, thereby, dividing the wafer into a plurality of chips, and the step of peeling the second substrate and the second adhesive layer away from each of the chips by reducing the adhesion of the second adhesive layer of the sheet.  
         [0010]     Regarding the aforementioned method for processing, when the first adhesive layer is composed of a radiation-setting adhesive, and the second substrate is composed of a heat-shrinkable plastic film, the first substrate is peeled away from the wafer by irradiating the first adhesive layer with radioactive rays, and the second substrate is peeled away from each of the chips by being allowed to heat-shrink.  
         [0011]     On the other hand, regarding the aforementioned method for processing, when the first substrate is composed of a heat-shrinkable plastic film, and the second adhesive layer is composed of a radiation-setting adhesive, the first substrate is peeled away from the wafer by being allowed to heat-shrink, and the second substrate is peeled away from each of the chips by irradiating the second adhesive layer with radioactive rays so as to cure the second adhesive layer.  
         [0012]     Further objects, features and advantages of the present invention will become apparent from the following description of the preferred embodiments with reference to the attached drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]      FIG. 1  is a schematic sectional view showing an adhesive sheet for affixation of a wafer according to a first embodiment of the present invention.  
         [0014]      FIG. 2A  to  FIG. 2D  are schematic sectional views for illustrating a method for processing a wafer by using the adhesive sheet for affixation of a wafer according to the first embodiment.  
         [0015]      FIG. 3  is a schematic sectional view showing an adhesive sheet for affixation of a wafer according to a second embodiment of the present invention.  
         [0016]      FIG. 4A  to  FIG. 4D  are schematic sectional views for illustrating a method for processing a wafer by using the adhesive sheet for affixation of a wafer according to the second embodiment. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0017]     The embodiments of the present invention will be described below in detail with reference to the drawings.  
       First Embodiment  
       [0018]      FIG. 1  is a schematic sectional view showing an adhesive sheet for affixation of a wafer according to a first embodiment of the present invention. As shown in  FIG. 1 , an adhesive sheet  101  for affixation of a wafer is composed of a first substrate  102 , a first adhesive layer  103 , a second substrate  104 , and a second adhesive layer  105 . In order to protect the second adhesive layer  105  before being subjected to use, preferably, a strippable sheet  106  is temporarily adhered on the second adhesive layer  105 .  
         [0019]     As the first substrate  102 , preferably, a synthetic resin film having extensibility in the length direction and width direction is used. Specific examples of such films include polyethylene films, polypropylene films, polybutene films, poly(vinyl chloride) films, poly(ethylene terephthalate) films, poly(butylene terephthalate) films, polybutadiene films, polyurethane films, polymethylpentene films, ethylene-vinyl acetate films, ionomers, ethylene-methacrylic acid copolymer films, etc., and cross-linked films thereof. The first substrate  102  may be composed of a laminate of these films. In general, the film thickness of the first substrate  102  is 10 to 300 μm, and preferably, is 50 to 200 μm.  
         [0020]     The first adhesive layer  103  is composed of a radiation-setting adhesive, and a system primarily containing the adhesive and a system primarily containing a radiation-polymerized synthetic oligomer are uniformly dispersed. The adhesion of this radiation-setting adhesive is significantly reduced by irradiation of radioactive rays.  
         [0021]     The second substrate  104  is composed of a heat-shrinkable plastic film. Examples of such films suitably used include transparent films having been subjected to adequate extension processing and being made of, for example, polyolefins, e.g., polyethylene, polypropylene, and polymethylpentene, poly(vinyl chloride), polyester, and polystyrene. In particular, a film having a film thickness of 10 to 300 μm is preferable. The heat shrinkage factor (%) of this heat-shrinkable plastic film is preferably 5% or more in any one of the vertical direction and the horizontal direction of the film, more preferably, is 10% or more, and especially preferably, 20% or more.  
         [0022]     The second adhesive layer  105  is composed of a material containing at least a partially cross-linked material of a carboxyl group-containing hydrophilic polymer in which a part of the carboxyl groups are partially neutralized and a surfactant. This surfactant is composed of at least one surfactant selected from the group consisting of anionic surfactants and cationic surfactants, and is in a liquid state at room temperature.  
         [0023]     In order to peel the second substrate  104  and the second adhesive layer  105  away from the wafer affixed thereto, the second substrate  104  is heated so as to bring about heat-shrinkage. The heating is performed in a furnace or in a hot water bath. The heating temperature is determined depending on the material of the heat-shrinkable plastic film of the second substrate  104 , and it is essential that the heating temperature is equivalent to or more than the temperature at which this heat-shrinkable plastic film brings about heat-shrinkage. However, the heating must be performed within the range in which circuits arranged on the wafer surface are not adversely-affected. Specifically, regarding the furnace, the heating is desirably performed at 60° C. to 200° C., and preferably, at 80° C. to 100° C. Desirably, the heating time is 20 seconds to 5 minutes, and preferably, is 40 seconds to 2 minutes. Regarding the hot water bath, desirably, the heating temperature is 60° C. to 100° C., and preferably, at 76° C. to 100° C., while the heating time is 20 seconds to 5 minutes, and preferably, is 40 seconds to 2 minutes. According to such a heating, the heat-shrinkable plastic film as the second substrate  104  is allowed to heat-shrink into the shape of a roll or cluster, and accompanying this, the adhesion of the second adhesive layer  105  is reduced.  
         [0024]     Next, a method for processing a wafer by using the adhesive sheet for affixation of a wafer according to the first embodiment will be described with reference to schematic sectional views shown in  FIG. 2A  to  FIG. 2D . In  FIG. 2A  to  FIG. 2D , the same members are indicated by the same reference numerals.  
         [0025]      FIG. 2A  shows the condition that the adhesive sheet  101  for affixation of a wafer according to the first embodiment is affixed to a silicon wafer  110 . Reference numerals  102 ,  103 ,  104 , and  105  denote the first substrate, first adhesive layer, second substrate, and second adhesive layer, respectively, similarly to those in  FIG. 1 .  
         [0026]     The silicon wafer  110  provided with the adhesive sheet  101  for affixation of a wafer by affixation is diced into the condition shown in  FIG. 2B . Although the wafer  110  is cut into a plurality of silicon chips  10   a,  these are joined to each other by the sheet  101 . Subsequently, radioactive rays are applied from the first substrate  102  side and, therefore, the adhesive of the first adhesive layer  103  is cured. According to this, the adhesion of the first adhesive layer  103  is significantly reduced and, therefore, the first substrate  102  and the first adhesive layer  103  can be peeled away from the wafer  110 .  
         [0027]      FIG. 2C  shows the condition that the first substrate  102  and the first adhesive layer  103  have been peeled off. Individual silicon chips  110   a  are in the condition of being separated from each other, and under this condition, it is also possible to electrically connect by tape automated bonding (TAB) and inner lead bonding (ILB).  
         [0028]     The separated individual silicon chips  11   a  are heated from the second substrate  104  side and, therefore, the second substrate  104  is allowed to heat-shrink. Accompanying this, the adhesion of the second adhesive layer  105  is reduced. Consequently, the second substrate  104  and the second adhesive layer  105  can be peeled away from the silicon chip  110   a.  As shown in  FIG. 2D , the chip  110   a  after these are peeled away therefrom is mounted on a mount member  120  immediately after the peeling.  
         [0029]     As described above, according to the present embodiment, since the silicon chip  110   a  is covered with the second substrate  104  as the back between the instant when the silicon wafer  110  is cut and the instant when the silicon chip  110   a  is mounted, adhesion of foreign materials, etc., can be prevented. Consequently, reduction in mounting precision due to adhesion of foreign materials, etc., can be avoided during mounting and, therefore, a semiconductor chip having high reliability can be provided.  
       Second Embodiment  
       [0030]      FIG. 3  is a schematic sectional view showing an adhesive sheet for affixation of a wafer according to a second embodiment of the present invention. As shown in  FIG. 3 , an adhesive sheet  201  for affixation of a wafer is composed of a first substrate  202 , a first adhesive layer  203 , a second substrate  204 , and a second adhesive layer  205 . In order to protect the second adhesive layer  205  before being subjected to use, preferably, a strippable sheet  206  is temporarily adhered on the second adhesive layer  205 .  
         [0031]     The first substrate  202  is composed of a heat-shrinkable plastic film. The material, thickness, and heat shrinkage factor suitably adopted for this film are similar to those for the second substrate  104  in the first embodiment. As the first adhesive layer  203 , one similar to the second adhesive layer  105  in the first embodiment is used suitably.  
         [0032]     The peeling of the first substrate  202  and the first adhesive layer  203  is performed by heating the second substrate  104  so as to bring about heat-shrinkage. The heating is performed in a furnace or in a hot water bath. Regarding the heating temperature and the heating time, suitable conditions are similar to those in the peeling of the second substrate  104  and the second adhesive layer  105  in the first embodiment.  
         [0033]     As the second substrate  204 , preferably, a synthetic resin film having extensibility in the length direction and width direction is used. The specific material and suitable thickness of such a film can be similar to those of the first substrate  102  in the first embodiment. As the second adhesive layer  205 , a radiation-setting adhesive similar to the first adhesive layer  103  in the first embodiment can be used suitably.  
         [0034]     Next, a method for processing a wafer by using the adhesive sheet for affixation of a wafer according to the second embodiment will be described with reference to schematic sectional views shown in  FIG. 4A  to  FIG. 4D . In  FIG. 4A  to  FIG. 4D , the same members are indicated by the same reference numerals.  
         [0035]      FIG. 4A  shows the condition that the adhesive sheet  201  for affixation of a wafer according to the second embodiment is affixed to a silicon wafer  210 . Reference numerals  202 ,  203 ,  204 , and  205  denote the first substrate, first adhesive layer, second substrate, and second adhesive layer, respectively, similarly to those in  FIG. 3 . The silicon wafer  210  in the present embodiment has openings arranged by anisotropic etching from the back of the silicon wafer. Since openings are arranged, it is possible to use the chips for an ink feed path in an ink-jet head.  
         [0036]     The silicon wafer  210  provided with the adhesive sheet  201  for affixation of a wafer by affixation is diced into the condition shown in  FIG. 4B . Although the wafer  210  is cut into a plurality of silicon chips  210   a,  these are joined to each other by the sheet  201 . Subsequently, heating is performed from the first substrate  202  side and, therefore, the first substrate  202  is allowed to shrink. As a result, the adhesion of the first adhesive layer  203  is significantly reduced and, therefore, the first substrate  202  and the first adhesive layer  203  can be peeled away from the wafer  210 .  
         [0037]      FIG. 4C  shows the condition that the first substrate  202  and the first adhesive layer  203  have been peeled off. Individual silicon chips  210   a  are in the condition of being separated from each other, and under this condition, it is also possible to electrically connect by TAB and ILB.  
         [0038]     The separated individual silicon chips  210   a  are irradiated with radioactive rays from the second substrate  204  side and, therefore, the second adhesive layer  205  is cured so that the adhesive thereof is significantly reduced. Consequently, the second substrate  204  and the second adhesive layer  205  can be peeled away from the silicon chip  210   a.  As shown in  FIG. 4D , the chip  210   a,  after these are peeled away therefrom, is mounted on a mount member  220  immediately after the peeling. As described above, according to the present embodiment, since the silicon chip  210   a  is covered with the second substrate  204  as the back between the instant when the silicon wafer  210  is cut and the instant when the silicon chip  210   a  is mounted, adhesion of foreign materials, etc., can be prevented. Consequently, reduction in mounting precision due to adhesion of foreign materials, etc., can be avoided during mounting and, therefore, a semiconductor chip having high reliability can be provided. When the silicon chip having an opening for an ink feed path in an ink-jet head is used, intrusion of foreign materials into the opening causes non-ejection during ejection of ink. However, when the adhesive sheet for affixation of a wafer according to the present embodiment is used, intrusion of foreign materials into the opening can be reduced and, therefore, significant improvement of the reliability in manufacture of the ink-jet head is achieved.  
         [0039]     While the present invention has been described with reference to what are presently considered to be the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. On the contrary, the invention is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.