Abstract:
There are provided a wafer processing method comprising the steps of grinding an underside ( 21 ) of a wafer which is provided, on its front surface ( 29 ), with a plurality of semiconductor devices ( 10 ); polishing a ground surface ( 22 ) formed by the grinding operation; and carrying out a plasma-processing for a polished surface ( 23 ) formed by the polishing operation under a predetermined gaseous atmosphere in a plasma chamber, to form an oxide layer on the polished surface, and a wafer processing method comprising the steps of carrying out a first plasma-processing for a polished surface formed by the polishing operation under a first gaseous atmosphere (CF 4  or SF 6 ) in a plasma chamber, to clean the polished surface; and carrying out a second plasma-processing for the polished surface after the cleaning operation under a second gaseous atmosphere (O 2 ) in the plasma chamber, to form an oxide layer on the polished surface, and a wafer processing apparatus for carrying out these methods. Thus, the wafer can be processed while the occurrence of an electrical failure in a thin wafer is restricted.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to method and apparatus for processing a wafer when a semiconductor is manufactured.  
         [0003]     2. Description of the Related Art  
         [0004]     In the semiconductor manufacturing field, the size of a wafer tends to increase year after year. In order to improve a packing density, the thickness of a wafer tends to be reduced. In order to reduce the thickness of a wafer, an underside grinding operation is carried out, i.e., a surface protection tape is adhered to a front surface of a wafer, on which semiconductor devices are formed, to draw and hold the wafer and, then, the underside of the wafer is ground. However, as the thickness of a wafer is reduced, it is more difficult to handle the wafer, and the reliability of a chip mounting operation, after the wafer is cut into chips, is reduced. Accordingly, the ground surface (underside) obtained after the underside grounding operation is carried out, is polished, so that a fracture layer occurring on the ground surface, in the underside grounding operation, is removed.  
         [0005]     In some cases, a plasma-processing operation is carried out on a wafer when a semiconductor is manufactured. In Japanese Unexamined Patent Publication (Kokai) No. 5-182935, Kokai No. 5-299385, Kokai No. 8-167595, Kokai No. 9-293876, Kokai No. 11-260793, WO98/33362, Kokai No. 2000-216140, Kokai No. 2001-127016, Kokai No. 2001-160551, Japanese Examined Patent Publication (Kokoku) No. 7-111965, Japanese Patent No. 2534098, Japanese Patent No. 2594448, Japanese Patent No. 2673526, Japanese Patent No. 3093445 and Japanese Patent No. 3231202, various plasma devices used when a semiconductor is manufactured or various processing methods of a wafer to be plasma-processed are disclosed.  
         [0006]     Usually, in order to improve the level of cleanliness of a wafer, for example, a gettering method, in which the level of cleanliness of a device active region on the front surface of a wafer is maintained by forming a site to collect heavy metal pollutants on the underside of the wafer, is adopted. However, as described above, if the thickness of a wafer is reduced, it is necessary to provide a process, subsequent to the grinding process, in which a layer damaged by grinding is removed. Accordingly, the effect of the gettering cannot be expected, and ion contamination sometimes occurs. Especially, in recent years, a further reduction in the thickness of a wafer is required. Thus, it is difficult to obtain the effect of gettering, and there is a high possibility that an electrical failure may occur due to ion contamination of a manufactured semiconductor.  
         [0007]     When dicing a wafer, a dicing tape is applied to the underside of the wafer, and a dicing saw cuts halfway through the dicing tape, from the front surface of the wafer, so that a part of the dicing tape remains and, thus, the separated dies can be prevented from scattering. However, when the dicing tape is directly applied to a polished surface of the wafer immediately after polishing, an adhesion force between the dicing tape and the polished surface is increased because the polished surface is activated. Therefore, it is difficult to pick up the dies from the dicing tape in a die bonding operation.  
         [0008]     Further, when a wafer is not sufficiently cleaned, a natural oxide layer having a nonuniform thickness is partly formed on the underside of the wafer. Accordingly, there is a possibility that the underside of the wafer may be mottled in a later thin film forming process due to the above natural oxide layer. In this case, not only a problem of appearance but also a variation in electrical properties of the semiconductor may occur.  
         [0009]     Further, when discrete devices are formed from a wafer, it is preferable that a polishing process is adopted to obtain an excellent uniform thickness of the wafer. However, the underside of the wafer is flattened more than necessary after the polishing process. Accordingly, when the polished surface of the wafer is coated with a metal coating in a later metalizing process, an adhesion force between the metal coating and the polished surface of the wafer is reduced, and the metal coating may be stripped.  
         [0010]     In view of the above problems, the object of the present invention is to provide a wafer processing method in which a wafer can be processed while the occurrence of an electrical failure is restricted even if the thickness of the wafer is reduced and to provide a wafer processing apparatus in which the wafer processing method is carried out.  
       SUMMARY OF THE INVENTION  
       [0011]     In order to achieve the above object, according to a first aspect of the present invention, there is provided a wafer processing method comprising the steps of grinding an underside of a wafer which is provided, on its front surface, with a plurality of semiconductor devices; polishing a ground surface formed by the grinding operation; and carrying out a plasma-processing for a polished surface formed by the polishing operation under a predetermined gaseous atmosphere in a plasma chamber, to form an oxide layer on the polished surface.  
         [0012]     Namely, in the first aspect of the present invention, the oxide layer is formed on the polished surface on the underside of the wafer and, accordingly, the occurrence of ion contamination can be prevented. Therefore, the wafer can be processed while the occurrence of an electrical failure is restricted even if the thickness of the wafer is reduced. The plasma-processing operation can be carried out immediately after the polishing process. Accordingly, the first aspect is different from a situation when it is necessary to transfer the wafer from a polishing machine to a plasma-processing machine, the mixing of contamination from a polluted atmosphere to the wafer can be prevented and, thus, the occurrence of an electrical failure can be further restricted. Further, in the first aspect, even if the dicing tape is applied, an adhesion force between the dicing tape and the wafer is not extremely large because the oxide layer is formed. Therefore, the difficulty of picking up of dies can be prevented. Also, in the first aspect, the wafer can be prevented from being mottled in a later thin film forming process because the oxide layer can be formed on the entire surface of the wafer. Oxygen is supplied to the plasma chamber to provide an oxygen atmosphere in the plasma-processing operation to form the oxide layer.  
         [0013]     According to a second aspect of the present invention, there is provided a wafer processing method comprising the steps of grinding an underside of a wafer which is provided, on its front surface, with a plurality of semiconductor devices; polishing a ground surface formed by the grinding operation; carrying out a first plasma-processing for a polished surface formed by the polishing operation under a first gaseous atmosphere in a plasma chamber, to clean the polished surface; and carrying out a second plasma-processing for the polished surface after the washing operation under a second gaseous atmosphere in the plasma chamber, to form an oxide layer on the polished surface.  
         [0014]     Namely, in the second aspect of the present invention, the oxide layer is formed on the polished surface on the underside of the wafer and, accordingly, the occurrence of ion contamination can be prevented. Also, in this case, the oxide layer is more uniform and excellent because the oxide layer is formed after a cleaning operation and, thus, the wafer can be processed while the occurrence of an electrical failure is further restricted even if the thickness of the wafer is reduced. The first and second plasma-processing operations can be carried out immediately after the polishing process, and can be carried out in the same plasma chamber. Accordingly, the second aspect is different from the situation, when it is necessary to transfer the wafer from a polishing machine to a first plasma-processing machine, and from the first plasma-processing machine to a second plasma-processing machine, the mixing of contamination from a polluted atmosphere to the wafer can be prevented and, thus, the occurrence of an electrical failure can be further restricted. Further, in the second aspect, even if the dicing tape is applied, an adhesion force between the dicing tape and the wafer is not extremely large because the oxide layer is formed. Therefore, the difficulty of picking up of dies can be prevented. Also, in the second aspect, the wafer can be prevented from being mottled in a later thin film forming process because the oxide layer can be formed on the entire surface of the wafer. Carbon tetrafluoride (CF 4 ) or sulfur hexafluoride (SF 6 ) is supplied to the plasma chamber to provide an atmosphere of CF 4  or SF 6  in the first plasma-processing operation to clean the wafer, and oxygen is supplied to the same plasma chamber to provide an atmosphere of oxygen in the second plasma-processing operation to form the oxide layer.  
         [0015]     According to a third aspect of the present invention, there is provided a wafer processing method comprising the steps of grinding an underside of a wafer which is provided, on its front surface, with a plurality of semiconductor devices; polishing a ground surface formed by the grinding operation; and carrying out a plasma-processing for a polished surface formed by the polishing operation under a predetermined gaseous atmosphere in a plasma chamber, to roughen the polished surface.  
         [0016]     Namely, in the third aspect of the present invention, the underside of the wafer is appropriately roughened by plasma-processing and, accordingly, a metal coating coated in a later metalizing process bites into the roughed portion. Thus, even on a thin wafer the metal coating can be prevented from being stripped. Carbon tetrafluoride (CF 4 ) or sulfur hexafluoride (SF 6 ) is supplied to the plasma chamber to provide an atmosphere of CF 4  or SF 6  in the plasma-processing operation to roughen the surface.  
         [0017]     According to a fourth aspect of the present invention, there is provided a wafer processing apparatus comprising grinding means for grinding an underside of a wafer whose front surface has a plurality of semiconductor devices formed thereon; polishing means for polishing a ground surface formed by the grinding means; and plasma-processing means for carrying out a plasma-processing for a polished surface formed by the polishing operation under a predetermined gaseous atmosphere in a plasma chamber, to form an oxide layer on the polished surface.  
         [0018]     Namely, in the fourth aspect of the present invention, the oxide layer is formed on the polished surface on the underside of the wafer and, accordingly, the occurrence of ion contamination can be prevented. Therefore, the wafer can be processed while the occurrence of an electrical failure is restricted even if the thickness of the wafer is reduced. The plasma-processing operation can be carried out immediately after the polishing process. Accordingly, the fourth aspect is different from a situation when it is necessary to transfer the wafer from a polishing machine to a plasma-processing machine, the mixing of contamination from a polluted atmosphere to the wafer can be prevented and, thus, the occurrence of an electrical failure can be further restricted. Further, in the fourth aspect, even if the dicing tape is applied, an adhesion force between the dicing tape and the wafer is not extremely large because the oxide layer is formed. Therefore, a difficulty in picking up of dies can be prevented. Also, in the fourth aspect, the wafer can be prevented from being mottled in a later thin film forming process because the oxide layer can be formed on the entire surface of the wafer. Oxygen is supplied to the plasma chamber to provide an atmosphere of oxygen in the plasma-processing operation to form the oxide layer.  
         [0019]     According to a fifth aspect of the present invention, there is provided a wafer processing apparatus comprising grinding means for grinding an underside of a wafer whose front surface has a plurality of semiconductor devices formed thereon; polishing means for polishing a ground surface formed by the grinding means; and plasma-processing means in which, after a first plasma-processing is carried out on a polished surface formed by the polishing operation under a first gaseous atmosphere in a plasma chamber, to clean the polished surface, a second plasma-processing is carried out on the polished surface under a second gaseous atmosphere in the plasma chamber, to form an oxide layer on the polished surface.  
         [0020]     Namely, in the fifth aspect of the present invention, the oxide layer is formed on the polished surface on the underside of the wafer and, accordingly, the occurrence of ion contamination can be prevented. Also, in this case, the oxide layer is more uniform and excellent because the oxide layer is formed after the cleaning operation and, thus, the wafer can be processed while the occurrence of an electrical failure is further restricted even if the thickness of the wafer is reduced. The first and second plasma-processing operations can be carried out immediately after the polishing process, and can be carried out in the same plasma chamber. Accordingly, the fifth aspect is different from the situation when it is necessary to transfer the wafer from a polishing machine to a first plasma-processing machine, and from the first plasma-processing machine to a second plasma-processing machine, the mixing of contamination from a polluted atmosphere to the wafer can be prevented and, thus, the occurrence of an electric failure can be further restricted. Further, in the fifth aspect, even if the dicing tape is applied, an adhesion force between the dicing tape and the wafer is not extremely large because the oxide layer is formed. Therefore, a difficulty of picking up the dies can be prevented. Also, in the fifth aspect, the wafer can be prevented from being mottled in a later thin film forming process because the oxide layer can be formed on the entire surface of the wafer. Carbon tetrafluoride (CF 4 ) or sulfur hexafluoride (SF 6 ) is supplied to the plasma chamber to provide an atmosphere of CF 4  or SF 6  in the first plasma-processing operation to clean the wafer, and oxygen is supplied to the same plasma chamber to provide an atmosphere of oxygen in the second plasma-processing operation to form the oxide layer.  
         [0021]     According to a sixth aspect of the present invention, there is provided a wafer processing apparatus comprising grinding means for grinding an underside of a wafer whose front surface has a plurality of semiconductor devices formed thereon; polishing means for polishing a ground surface formed by the grinding means; and plasma-processing means for carrying out a plasma-processing for a polished surface formed by the polishing operation under a predetermined gaseous atmosphere in a plasma chamber, to roughen the polished surface.  
         [0022]     Namely, in the sixth aspect of the present invention, the underside of the wafer is appropriately roughened by plasma-processing and, accordingly, a metal coating coated in a later metalizing process bites into the roughened portion. Thus, the metal coating can be prevented from being stripped even from a thin wafer. Carbon tetrafluoride (CF 4 ) or sulfur hexafluoride (SF 6 ) is supplied to the plasma chamber to provide an atmosphere of CF 4  or SF 6  in the plasma-processing operation to roughen the surface.  
         [0023]     According to a seventh aspect of the present invention, there is provided a wafer processing apparatus comprising grinding and polishing means for grinding an underside of a wafer which is provided, on its front surface, with a plurality of semiconductor devices and polishing a ground surface formed by the grinding operation; plasma-processing means for carrying out a plasma-processing for a polished surface formed by the polishing operation under a predetermined gaseous atmosphere in a plasma chamber, to form an oxide layer on the polished surface; applying means for applying a DAF tape and/or a dicing tape to the underside of the wafer; and stripping means for stripping the DAF tape and/or the dicing tape or releases thereof from the underside of the wafer, wherein the grinding and polishing means, the plasma-processing means, the applying means and the removing means are integral with one another; and the wafer can be transferred between the grinding and polishing means, the plasma-processing means, the applying means and the stripping means.  
         [0024]     Namely, in the seventh aspect of the present invention, time management for grinding and polishing operations in the grinding and polishing means, a plasma-processing operation in the plasma-processing means, an applying operation in the applying means, and a stripping operation in the stripping means, can be controlled together. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]      FIG. 1  is a schematic view of a wafer processing apparatus according to the present invention;  
         [0026]      FIGS. 2   a  to  2   e  are views of processes showing a wafer processing method according to the present invention; and  
         [0027]      FIG. 3  is a schematic sectional view of a plasma-processing machine in a wafer processing apparatus according to the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0028]     Embodiments of the present invention will be described below with reference to the accompanying drawings. In the following drawings, the same members are designated by the same reference numerals. For ease of understanding, the scale is changed as necessary in the drawings.  
         [0029]      FIG. 1  is a schematic view of a wafer processing apparatus according to the present invention. As shown in  FIG. 1 , the wafer processing apparatus comprises a grinding and polishing machine  100  capable of grinding and polishing a surface of a wafer and, particularly, an underside of the wafer. Further, as illustrated, a plasma-processing machine  200  is disposed adjacent to the grinding and polishing machine  100 . In the plasma-processing machine  200 , a desired plasma-processing operation can be carried out for a wafer which has been ground and polished in the grinding and polishing machine  100 . The plasma-processing machine  200 , which will be described in detail, may be integrally formed with the grinding and polishing machine  100 . Even in ether case, a grinding and polishing operation in the grinding and polishing machine  100  and a plasma-processing operation in the plasma-processing machine  200  can be continuously carried out in a line.  
         [0030]      FIGS. 2   a  to  2   e  show processes of a wafer processing method according to the present invention. A wafer processing method according to the present invention will be described with reference to  FIGS. 1 and 2 . In  FIG. 2   a , a plurality of semiconductor devices  10  are formed on a front surface (pattern-formed surface)  29  of a wafer  20 , for example, a silicon wafer, having a thickness of L 0 . The semiconductor devices  10  are spaced at equal distances on the pattern-formed surface  29 .  
         [0031]     As shown in  FIG. 2   b , a retaining layer  40  suitable for retaining the plural semiconductor devices  10  is formed on the pattern-formed surface  29  (front surface) of the wafer  20  by a retaining layer forming device (not shown). The retaining layer  40  is formed by applying an adhesive resin film to the pattern-formed surface by, for example, a laminating device, or by applying a liquid resin to the pattern-formed surface. As will be described later, the retaining layer  40  protects the semiconductor devices  10  on the pattern-formed surface  29  when grinding and polishing the wafer.  
         [0032]     The wafer  20  in the above state is introduced to the grinding and polishing machine  100  of the wafer processing apparatus shown in  FIG. 1 . The wafer  20  is held by a drawing and holding table (not shown) while the underside  21 , on which no semiconductor devices  10  is formed, faces upward. As can be seen from  FIG. 2   c , the underside  21  of the wafer  20 , on which no semiconductor devices  10  is formed, is ground by a grinding machine (not shown) of the grinding and polishing machine  100 . To grind the underside of a wafer as described above is called “back grinding”. In the grinding operation of the present invention, the infeed grinding, in which the wafer  20  is drawn and held by a rotatable drawing and holding chuck (not shown) while the pattern-formed surface thereof faces downward and, then, a grinding device is downwardly moved to the underside  21  of the wafer  20 , to grind the same, is adopted. As a matter of course, another grinding method, for example, creepfeed grinding, in which a grinding device is rotated while a plurality of substrates are rotated on a table, may be adopted. The retaining layer  40  is provided between the semiconductor devices  10  and a drawing and holding surface of the drawing and holding chuck and, accordingly, the semiconductor devices  10  on the pattern-formed surface  29  of the wafer  20  are not in direct contact with the drawing and holding chuck. Thus, the semiconductor devices  10  can be protected. As shown in  FIG. 2   c , the underside  21  of the wafer  20  is ground, by a thickness L 1 , toward the pattern-formed surface  29 , by the grinding device and, thus, the thickness of the wafer  20  is reduced. In a ground surface  22  (underside) formed by grinding the underside  21  of the wafer  20 , an affected layer, i.e., a brittle fracture layer occurs.  
         [0033]     As can be seen from  FIGS. 2   c  and  2   d , after washing the wafer  20 , the wafer  20  is further reduced, by a thickness L 2 , by polishing the ground surface  22  of the wafer  20 . In the present invention, a polishing method, in which a polishing device using a polishing liquid containing a chemical abrasive compound, is adopted. As shown in the drawing, the substrate is polished to only a thickness L 2  smaller than the thickness L 1 , so that the brittle fracture layer in the ground surface  22  is removed. Therefore, the adhesiveness of a semiconductor  11  when the semiconductor is mounted, and the strength of the semiconductor, can be improved. For ease of understanding, the thickness L 1  and the thickness L 2  are indicated as relatively small dimensions with respect to the thickness L 0  in  FIG. 2 . However, in practice, a polished surface  23  of the wafer  20  obtained after the grinding and polishing operations, is located so close to the pattern-formed surface  29  that ion contamination can occur in normal use.  
         [0034]     With reference to  FIG. 1 , the wafer  20  ground and polished in the grinding and polishing machine  100  is transferred to the plasma-processing machine  200  by a loader etc. (not shown). As illustrated, in the present invention, the plasma-processing machine  200  is disposed adjacent to the grinding and polishing machine  100 , or is integrally formed with the grinding and polishing machine  100 . Accordingly, the wafer  20  is not exposed to a polluted environment when transferred from the grinding and polishing machine  100  to the plasma-processing machine  200 . Therefore, electrical failures in the final semiconductor products, due to the mixing of contamination from a polluted environment, can be reduced.  
         [0035]      FIG. 3  is a schematic sectional view of a plasma-processing machine in a wafer processing apparatus according to the present invention. As shown in  FIG. 3 , the plasma-processing machine  200  comprises a plasma chamber  31  in which plasma-processing is actually carried out. An upper planar electrode  34  made of a porous material is provided on the upper portion of an inner space  32  of the plasma chamber  31 . A lower planar electrode  33  opposite to the upper planar electrode  34  is provided on the bottom of the inner space  32  of the plasma chamber  31 . As shown in the drawing, the upper planar electrode  34  is connected to a power source  35 , and the lower planar electrode  33  is grounded. Accordingly, a desired voltage from the power source  35  can be applied between these planar electrodes  34 ,  33 . A source  41  containing one of carbon tetrafluoride (CF 4 ) and sulfur hexafluoride (SF 6 ) is connected to the planar electrode  34  via a pipe  47 . Likewise, a source  42  containing an inert gas, for example, helium (He) is connected to the planar electrode  34  via a pipe  48 , and a source  43  containing oxygen (O 2 ) is connected to the planar electrode  34  via a pipe  49 . As illustrated, these pipes  47 ,  48  and  49  are provided with open/close valves  44 ,  45  and  46 , respectively. Accordingly, a gas in respective sources  41 ,  42  and  43  can be supplied to the inner space  32  of the plasma chamber  31 , and through the planar electrode  34 , as necessary. The open/close valves  44 ,  45  and  46  are usually closed. In the source  41 , fluorinated gas other than CF 4  and SF 6 , Br 2  or HBr can be stored. An exhaust pipe  37  extending from the vicinity of the bottom of the plasma chamber  31 , is connected to a pump  38 , and is provided with a open/close valve  36 .  
         [0036]     The wafer  20 , ground and polished in the grinding and polishing machine  100 , is transferred to the plasma chamber  31  though an inlet (not shown) thereof, and is placed on the lower planar electrode  33 , with the ground surface  23  being upwardly oriented. Then, the inlet is closed and sealed. The open/close valve  36  is opened, and the pump  38  is activated, to decompress the inner space  32  of the plasma chamber  31  by discharging gas through the pipe  37 . Then, the open/close valve  44  is opened to supply CF 4  or SF 6  to the inner space  32  of the plasma chamber  31 , and through the planar electrode  34 , via the pipe  47 . A voltage is applied, by the power source  35 , between the lower planar electrode  33  and the upper planar electrode  34 , in the plasma chamber  31  which is slightly decompressed. The CF 4  or SF 6  supplied to the plasma chamber  31  functions as a reactive gas and, accordingly, plasma is formed in the inner space  32  of the plasma chamber  31 . The plasma is a low temperature plasma having a temperature of about 60 to 90° C. and, accordingly, the retaining layer  40  of the wafer  20  is not damaged. The plasma impinges on the polished surface  23  of the wafer  20  by a flow of CF 4  gas or SF 6  gas through the upper planar electrode  34  and, thus, the polished surface  23  is plasma-processed. If, for example, CF 4  is adopted as a reactive gas, the CF 4  is decomposed into carbon trifluoride (CF 3 ) and fluorine (F), and the F is applied to the polished surface  23  of the wafer  20  made of silicon. On the surface of the wafer  20 , silicon (Si) of the wafer  20  reacts with F to form silicon tetrafluoride (SiF 4 ) and, then, is removed from the polished surface  23  of the wafer  20 . Therefore, the underside of the wafer  20  is removed by, for example, about 20 Å to 40 Å, to produce a new surface of the wafer  20 . The same is almost true in other cases in which SF 6 , etc. is adopted as a reactive gas. Therefore, an effect similar to that of cleaning of the polished surface can be obtained by such plasma processing. Nitrogen dioxide NO 2  together with CF 4  and SF 6  may be supplied to the plasma chamber  31 , as necessary. Thus, a cleaning operation using plasma processing can be efficiently carried out.  
         [0037]     After carrying out plasma processing for a predetermined time, the open/close valve  44  is closed, and the pump  38  is activated while the open/close valve  36  is opened, to discharge a gas in the inner space  32 , i.e., CF 4 , SF 6  or the like. Then, the open/close valve  45  is opened while the open/close valve  36  is closed, to supply an inert gas in the source  42 , for example, helium to the inner space  32  of the plasma chamber  31 , through the upper planar electrode  34 , via the pipe  48 . Once the inner space  32  of the plasma chamber  31  is charged with helium, the open/close valve  36  is opened while the open/close valve  45  is closed, to discharge the helium. Thus, the remaining gas such as CF 4  or SF 6  in the inner space  32  of the plasma chamber  31  is almost completely discharged, and the inner space  32  of the plasma chamber  31  can be cleaned.  
         [0038]     After closing the open/close valve  36 , the open/close valve  46  is opened to supply oxygen in the source  43  to the inner space  32  of the plasma chamber  31 , and through the upper planar electrode  34 , via the pipe  49 . A voltage is applied, by the power source  35 , between the lower planar electrode  33  and the upper planar electrode  34 , in the plasma chamber  31  which is slightly decompressed. In this case, oxygen functions as a reactive gas and, accordingly, plasma is formed in the inner space  32  of the plasma chamber  31 . The plasma is a low temperature plasma having a temperature of about 60 to 90° C. and, accordingly, the retaining layer  40  of the wafer  20  is not damaged. The plasma impinges on the polished surface  23  of the wafer  20  by a flow of oxygen gas through the upper planar electrode  34  and, thus, the polished surface  23  is plasma-processed and, thus, an oxide layer is formed on the polished surface  23  of the wafer  20 . In  FIG. 2   e , an oxide layer  25  is formed by plasma processing under an oxygen atmosphere. The oxide layer  25 , formed in such a manner, has a thickness L 3  of, for example, about 20 Å. As described above, in the present invention, the oxide layer  25  can be formed on the underside of the wafer and, accordingly, ion contamination can be prevented from occurring. Also, a wafer can be processed while the occurrence of an electrical failure is reduced, even if the thickness of the wafer is reduced. In contrast to a case in which a natural oxide layer is partially formed on the wafer  20 , the oxide layer is positively formed on the entire surface of the wafer  20  in the present invention. Thus, the surface of the wafer can be prevented from being mottled in a later thin film deposition process. Further, in the present invention, both the plasma processing operation under an atmosphere of CF 4  or SF 6  and the plasma processing operation under an atmosphere of O 2  are carried out in the single plasma chamber  31 . Accordingly, it is possible to prevent the moving of contamination from a polluted atmosphere to a wafer. Namely, the present invention is different from situations when it is necessary to transfer the wafer from a polishing machine to a plasma processing machine under an atmosphere of CF 4  or SF 6 , and when it is necessary to transfer the wafer from a plasma processing machine under an atmosphere of CF 4  or SF 6  to a plasma processing machine under an atmosphere of O 2 .  
         [0039]     With reference to  FIG. 1 , the wafer  20  discharged through an outlet (not shown) provided in the plasma chamber  31  of the plasma-processing machine  200  is transferred to a dicing tape applying machine  400  by a transferring machine  500 . A dicing tape is applied to the oxide layer  25  on the underside of the wafer  20 . The wafer  20  is cut into cubic dies, from the pattern-formed surface  29  of the wafer  20 , by a dicing saw and in a dicing apparatus (not shown). In this cutting, the dicing saw cuts halfway through the dicing tape. Thus, the dies are prevented from separating and scattering. After the dicing tape is expanded, each die is picked up from the dicing tape and, then, a die bonding operation is carried out. If the wafer  20  is polished, an adhesion force between the dicing tape and the polished surface  23  is extremely large because the polished surface  23  of the wafer  20  is activated after being polished. Accordingly, it is sometimes difficult to pick up the dies from the dicing tape in the die bonding operation. However, as described above, in the present invention, the oxide layer  25  is formed on the polished surface  23  of the wafer  20  and, accordingly, the adhesion force between the dicing tape and the oxide layer  25  on the underside of the wafer is not so large. Therefore, in the present invention, the dies can be easily picked up from the dicing tape in the die bonding operation.  
         [0040]     As illustrated, a die attach film tape (DAF tape) attaching machine  300  may be provided between the plasma-processing machine  200  and the dicing tape applying machine  400 . Thus, the DAF tape may be applied to the plasma-processed underside of the wafer  20  and, then, the dicing tape may be applied to the DAF tape in the dicing tape applying machine  400 . The DAF tape provided between the dicing tape and the underside of the wafer  20 , functions as an adhesive provided on the bottom surface of the die in the die bonding operation.  
         [0041]     As described above, in the present invention, the DAF tape applying machine  300  for applying the DAF tape and the dicing tape applying machine  400  for applying the dicing tape are provided adjacent to or integral with the grinding and polishing machine  100  and the plasma-processing machine  200 . Thus, the mixing of contamination can be prevented when the wafer is transferred. Further, with the above structure, time management of the grinding and polishing machine  100 , of the plasma-processing machine  200 , of the DAF tape applying machine  300  and of the dicing tape applying machine  400  can be controlled together. Thus, throughput in all processes can be improved, and a defective fraction can be reduced to a minimum. Further, a tape detaching machine (not shown) for detaching the DAF tape and/or the dicing tape or releases of these tapes, may be provided. Namely, the grinding and polishing machine  100 , the plasma-processing machine  200 , the DAF tape applying machine  300 , the dicing tape applying machine  400  and the tape stripping machine (not shown) may be integral with one another, and the wafer may be freely transferred among the grinding and polishing machine  100 , the plasma-processing machine  200 , the DAF tape applying machine  300 , the dicing tape applying machine  400  and the tape stripping machine, by transferring means (not shown). In such a case, time management of the grinding and polishing machine  100 , of the plasma-processing machine  200 , of the DAF tape applying machine  300 , of the dicing tape applying machine  400  and of the tape stripping machine can be controlled together. Thus, throughput in all processes can be improved, and a defective fraction can be further reduced.  
         [0042]     In the above-described embodiments, a cleaning operation for the polished surface  23  of the wafer  20  and a forming operation of an oxide layer have been described. However, the wafer processing apparatus according to the present invention can be used for another application that will be described later. The underside of the wafer, which is ground and polished in the grinding and polishing machine  100  is flattened more than usual. However, if, for example, the underside of the wafer is metalized in a later process, an adhesion force between the polished surface and a metal coating formed by metalizing is reduced and, accordingly, the metal coating may be stripped. However, in the present invention, the wafer  20  discharged from the grinding and polishing machine  100  is transferred to the plasma-processing machine  200  and, then, is placed in the manner described above. The above-described plasma-processing operation (under an atmosphere of CF 4  or SF 6 ) functioning as a cleaning operation, is carried out for a longer time than the above-described plasma-processing operation. Accordingly, the polished surface  23  of the wafer  20  can be removed so that the wafer has a thickness of, for example, about 2 to 3 micrometer. In this case, the roughness of a new surface precipitated after the plasma-processing operation is larger than that before the plasma-processing operation. Accordingly, the metal coating formed by metalizing, bites into the rough underside of the wafer  20  and, thus, the adhesion force between the metal coating and the polished surface is increased. Therefore, in the present invention, even if the metalizing operation is carried out in a later process, the metal coating of a thin wafer can be prevented from being stripped.  
         [0043]     In the embodiment which has been described with reference to  FIG. 2 , after the polished surface  23  of the wafer  20  is cleaned by plasma-processing under an atmosphere of CF 4  or SF 6 , an oxide layer is formed by plasma-processing under an atmosphere of O 2 . However, the plasma-processing under an atmosphere of CF 4  or SF 6  is not necessarily needed. It is apparent that the occurrence of ion contamination can be prevented even if only the plasma-processing under an atmosphere of O 2  is carried out to form an oxide layer. Further, the plasma-processing carried out after only one of the grinding operation and the polishing operation, and a combination of the above embodiments are included in the scope of the present invention.