Patent Publication Number: US-2013240131-A1

Title: Method of fabricating semiconductor device and semiconductor production apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2012-057280, filed on Mar. 14, 2012, the entire contents of which are incorporated herein by reference. 
     FIELD 
     Embodiments relate to a method of fabricating a semiconductor device and a semiconductor production apparatus. 
     BACKGROUND 
     In fabricating a semiconductor device, a semiconductor element is formed on a semiconductor substrate (wafer) and then a back surface of the wafer is subjected to grinding, polishing, and the like, thus reducing the thickness of the wafer. 
     In the process of reducing the thickness of the wafer, in order to protect the semiconductor device formed on a side of a main surface of the wafer, a surface protection tape (hereinafter, referred to as back side grinding (BSG) tape) is bonded to the main surface of the wafer and then the back surface of the wafer is subjected to grinding, polishing, and the like, thus reducing the thickness of the wafer. The BSG tape is removed after the thickness of the wafer is reduced. 
     When the BSG tape is removed, the wafer is placed on an adsorption stage with the back surface of the wafer facing down. Then, a removal tape is pressure-bonded to a main surface of the BSG tape. The BSG tape is integrally removed with the removal tape. Generally, the BSG tape is removed from the main surface of the wafer in such a manner. 
     However, after the thickness of the wafer is reduced, the mechanical strength (rigidity) of the wafer, particularly a wafer with the thickness smaller than 80 μm, is reduced. Therefore, when the protection tape is removed, the wafer floats on the adsorption stage and is deformed, with the result that problems such as cracks, fractures, and the like occur in the wafer. 
     In view of the problems, various methods have been conventionally proposed in order to prevent the wafer from being deformed and cracks, fractures, and the like from occurring when the protection tape is removed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view showing a configuration of a semiconductor production apparatus according to a first embodiment; 
         FIGS. 2A ,  2 B, and  2 C are a front view, a side view, and an overhead view, respectively, showing a configuration of an adsorption stage and a configuration of a press unit of the semiconductor production apparatus according to the first embodiment; 
         FIG. 3  is a front view showing a bonding roller of the semiconductor production apparatus according to the first embodiment; 
         FIGS. 4A and 4B  are cross-sectional views each showing an operation of the semiconductor production apparatus according to the first embodiment; 
         FIGS. 5A and 5B  are cross-sectional views each showing an operation of the semiconductor production apparatus according to the first embodiment; 
         FIGS. 6A and 6B  are cross-sectional views each showing an operation of the semiconductor production apparatus according to the first embodiment; and 
         FIGS. 7A and 7B  are overhead views each showing a configuration of an adsorption stage according to a second embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     An aspect of the present embodiment, there is provided a method of fabricating a semiconductor device, including curving a semiconductor substrate onto which a protection tape is bonded, and removing the protection tape in a state where the semiconductor substrate is curved. 
     Another aspect of the present embodiment, there is provided a semiconductor production apparatus including a stage having a mounting surface with a curved shape and maintaining a semiconductor substrate onto which a protection tape is bonded, on the mounting surface in a state that the curved shape is maintained, and a removing unit removing the protection tape bonded onto the semiconductor substrate maintained on the mounting surface. 
     First Embodiment 
       FIG. 1  is a cross-sectional view showing a configuration of a semiconductor production apparatus according to a first embodiment. A semiconductor production apparatus  1  is a removing apparatus to remove a surface protection tape B (hereinafter, referred to as back side grinding (BSG) tape B) bonded to a semiconductor substrate W (wafer W). The semiconductor production apparatus  1  includes an adsorption stage  10 , a press unit  20 , a removing unit  30 , and a vacuum unit  40 . 
       FIGS. 2A ,  2 B, and  2 C are a front view, a side view, and an overhead view, respectively, showing a configuration of the adsorption stage  10  and a configuration of the press unit  20 . 
     The adsorption stage  10  includes a porous adsorption portion  11  and a frame  12 . The porous adsorption portion  11  is formed by sintering and molding metal or ceramic particles. The frame  12  fixes the adsorption portion  11 . The top surface of the adsorption stage  10  serves as a mounting surface  10   a  on which the wafer W is placed. The adsorption portion  11  has a diameter substantially the same as that of the wafer W. The adsorption stage  10  is connected to the vacuum unit  40 . 
     As shown in  FIGS. 2A ,  2 B, and  2 C, the adsorption stage  10  has a semicylindrical shape in which a cross-sectional shape of the mounting surface  10   a  of the adsorption stage  10  viewed in a Z direction is gently curved to be convex. In the case where the thickness of the wafer W is smaller than 80 μm, problems that the wafer W is deformed and cracks, fractures, and the like occur in the wafer may be caused when the protection tape is removed. Therefore, the thickness of the wafer W, from which the BSG tape B is removed, is preferably smaller than 80 μm in the embodiment. 
     The press unit  20  includes a plurality of press pins  21   a ,  21   b ,  21   c , a supporting plate  22 , and a driving unit  23 . The supporting plate  22  supports the plurality of press pins  21   a ,  21   b ,  21   c . The driving unit  23  is coupled to the supporting plate  22 . The plurality of press pins  21   a ,  21   b ,  21   c  is a group of pins, with which the wafer W, to which the BSG tape B is bonded and whose thickness is reduced by grinding, is adsorbed along the shape of the mounting surface  10   a  of the adsorption stage  10 . 
     The pin  21   b  arranged in the middle of the plurality of press pins  21   a ,  21   b ,  21   c  is shortest, and the pins  21   a ,  21   c  arranged on both sides of the pin  21   b  are longer than the pin  21   b . The driving unit  23  is an air cylinder, for example. The driving unit  23  drives the supporting plate  22  in a substantially perpendicular direction to the adsorption stage  10 . 
     As shown in  FIG. 1 , the removing unit  30  includes a supply reel  31 , a rolling reel  32 , a bonding roller  33 , and a guide roller  34 . A removal tape S to remove the BSG tape B bonded to the wafer W is supplied from the supply reel  31  and rolled up together with the removed BSG tape B by the rolling reel  32 . The bonding roller  33  bonds the removal tape S to the BSG tape B. The guide roller  34  controls a supply position (height) of the removal tape S. 
       FIG. 3  is a front view showing the bonding roller  33 . As shown in  FIG. 3 , an outer peripheral surface  33   a  of the bonding roller  33  has a curved shape that fits the shape of the mounting surface  10   a  of the adsorption stage  10 . 
     As shown in  FIG. 1 , the vacuum unit  40  includes a vacuum pipe  41 , a valve  42 , and a vacuum pump  43 . The vacuum pipe  41  is connected to the adsorption stage  10  at one end of the vacuum pipe  41 . The valve  42  is provided in a path of the vacuum pipe  41 . The vacuum pump  43  is connected to the vacuum pipe  41  at the other end of the vacuum pipe  41 . The valve  42  is opened and closed by clean dry air (CDA) or N 2  gas supplied from an outside. The valve  42  used in the embodiment is a normal close (NC) valve. However, the valve  42  may be a normal open (NO) valve. 
     (Operation of Semiconductor Production Apparatus  1 ) 
       FIGS. 4A to 6B  are cross-sectional views each showing an operation of the semiconductor production apparatus  1 . Hereinafter, operations of the semiconductor production apparatus  1  to remove the BSG tape B will be described with reference to  FIGS. 4A to 6B . In the embodiment, the removal tape S is set in the supply reel  31  and the rolling reel  32  in advance. 
     As shown in  FIG. 4A , the wafer W, to which the BSG tape B is bonded and whose thickness is reduced by grinding, is placed on the mounting surface  10   a  of the adsorption stage  10 . 
     As shown in  FIG. 4B , the driving unit  23  lowers the supporting plate  22  with respect to the adsorption stage  10 . The wafer W, to which the BSG tape B is bonded, is aligned with the shape of the mounting surface  10   a  of the adsorption stage  10  by using the press pins  21   a ,  21   b ,  21   c.    
     The CDA or N 2  gas is supplied to the valve  42  of the vacuum unit  40  so that the valve  42  is opened. Then, the wafer W is adsorbed to the porous adsorption portion  11 . Note that the driving unit  23  may lower the supporting plate  22  with respect to the adsorption stage  10  after the CDA or N 2  gas is supplied to the valve  42 , to open the valve  42 . 
     As shown in  FIG. 5A , after the wafer W is adsorbed onto the adsorption portion  11  of the adsorption stage  10 , the driving unit  23  lifts the supporting plate  22  with respect to the adsorption stage  10  to retract the plurality of press pins  21   a ,  21   b ,  21   c . Note that the valve  42  remains open, that is, the wafer W is kept to be adsorbed. 
     As shown in  FIG. 5B , the removal tape S is drawn from the supply reel  31  of the removing unit  30  along with a horizontal movement of the bonding roller  33 . The bonding roller  33  is lowered in front of the wafer W and moves forward in a horizontal direction while pressing a main surface of the BSG tape B. Thus, the removal tape S is bonded to the BSG tape B. 
     As shown in  FIG. 6A , the rolling reel  32  is rotated to roll up the BSG tape B bonded to the wafer W while removing the BSG tape B from the wafer W. As shown in  FIG. 6B , after the BSG tape B is completely removed from the wafer W, the supply of the CDA or N 2  gas to the valve  42  is stopped so that the valve  42  is closed. The wafer W, from which the BSG tape is removed, is taken out from the adsorption stage  10 . Thus, the operations are terminated. 
     As described above, in the semiconductor production apparatus  1  according to the first embodiment, the wafer W, to which the BSG tape B is bonded, is aligned with the shape of the mounting surface  10   a  of the adsorption stage  10  and adsorbed onto the adsorption stage  10 . The adsorption stage  10  has a semicylindrical shape when viewed in the Z direction of the mounting surface  10   a  of the adsorption stage  10 . After that, the semiconductor production apparatus  1  keeps the curved state of the wafer W and removes the BSG tape B from the wafer W along the Z direction in which the wafer W has a curved cross section. 
     In other words, in the semiconductor production apparatus  1 , the mechanical strength (rigidity) of the wafer W is increased because the BSG tape B is removed in a state where the wafer W is curved. Therefore, when the BSG tape B is removed, the semiconductor production apparatus  1  can effectively prevent the wafer W from floating on the adsorption stage  10  to be deformed and cracks, fractures, and the like from occurring in the wafer W. 
     Further, it is unnecessary to use a self-removal tape, for example, as a special BSG tape. In the self-removal tape, a pressure-sensitive adhesive foams due to the application of heat or ultraviolet rays and thus an adhesive force is reduced. Therefore, the production cost of the semiconductor device can be reduced. 
     In addition, the press pins  21   a ,  21   b ,  21   c  are caused to abut against the BSG tape B so that the wafer W is pressed against the mounting surface  10   a  of the adsorption stage  10 . Therefore, the press pins  21   a ,  21   b ,  21   c  and the wafer W do not come into contact with each other. As a result, fractures or chipping of the wafer W due to the load of the press pins  21   a ,  21   b ,  21   c  are effectively prevented. 
     Second Embodiment 
       FIGS. 7A and 7B  are overhead views showing an adsorption stage  10 A and an adsorption stage  10 B according to the second embodiment, respectively. The adsorption stage  10  of the semiconductor production apparatus  1  according to the first embodiment has a shape in which a cross-sectional shape of the mounting surface  10   a  viewed in the Z direction is gently curved to be convex. On the other hand, the adsorption stage  10 A shown in  FIG. 7A  has a shape in which a cross-sectional shape of the mounting surface  10   a  viewed in the Z direction is gently curved to be concave. Further, the adsorption stage  10 B shown in  FIG. 7B  has a shape in which a cross-sectional shape of the mounting surface  10   a  viewed in the Z direction is wavy. 
     Also in the cases of  FIGS. 7A and 7B  showing the cross-sectional shapes of the mounting surface  10   a  viewed in the Z direction, the mechanical strength of the wafer W is increased. As a result, when the BSG tape B is removed, it is effectively prevented that the wafer W floats on the adsorption stage  10  to be deformed and cracks, fractures, and the like occur in the wafer W. Other effects are the same as those produced by the semiconductor production apparatus  1  according to the first embodiment. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.