Patent Publication Number: US-2007109714-A1

Title: Embossing chuck enabling wafer to be easily detached therefrom

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      This application claims all benefits of Korean Patent Application No. 10-2005-108585 filed on Nov. 14, 2005 in the Korean Intellectual Property Office, the disclosures of which are incorporated herein by reference.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to an embossing chuck, and more specifically, to an embossing chuck enabling a wafer to be easily detached from the chuck after putting off the plasma.  
      2. Description of the prior art  
      Even after putting off the plasma, there exists an electrostatic force between a wafer and a chuck. Accordingly, it is difficult to easily detach the wafer from the chuck.  FIGS. 1A and 1B  illustrate a conventional wafer chuck  20 , wherein  FIG. 1A  shows a detailed shape of the wafer chuck  20  and  FIG. 1B  shows an equivalent circuit of a case where a wafer  10  is put on the wafer chuck  20 .  
      As shown in  FIG. 1A , a body of the wafer chuck  20  on which the wafer  10  is put on consists of aluminum and a periphery of the body is anodized and is surrounded by a dielectric layer  22  made of alumina (Al 2 O 3 ). Therefore, the wafer  10  is put on the dielectric layer  22 .  
      Referring to  FIG. 1B , when the plasma  40  is put off, the charges discharged to the wafer  10  through the plasma  40  escape from the wafer  10  to the chuck  20  along an arrow route (A). When the plasma  40  is completely put off, a resistance of the plasma  40  becomes infinite, so that the charges cannot flow. Accordingly, the flow of the charges as described above occurs for a short time until the plasma  40  is completely vanished. At this time, if the charges do not completely escape and remain at the wafer  10  due to surface resistances (R 11 , R 12 , R 13  . . . ) of the wafer  10 , the wafer  10  is not detached well from the chuck  20  due to the residual charge. The reference numerals C 11 , C 12 , C 13  and C 14  indicate capacitances between the chuck  20  and the wafer  10 , and a reference numeral C 21  indicates a capacitance between the chuck  20  and an external applying power  30 .  
      As described above, when the conventional wafer chuck  20  is used, the charges accumulated on the wafer  10  cannot properly escape to the exterior due to a resistance (R 41 ) of the plasma and the resistances (R 11 , R 12 , . . . ) of the wafer after the plasma  40  is put off, so that the wafer  10  is not detached well from the chuck  20 . As a result, it is difficult to take out the wafer  10  having completed the process from a chamber.  
     SUMMARY OF THE INVENTION  
      Accordingly, the present invention has been made to solve the above problems. An object of the invention is to provide an embossing chuck having an embossing part protruding from an upper surface of a body of the chuck so as to enable charges accumulated at a wafer to easily escape to an exterior after putting off the plasma.  
      In order to achieve the above object, there is provided an embossing chuck having an embossing part protruding, in a uniform height, from an upper surface of a body on which a wafer is put on, wherein an area of the embossing part is 5˜30% for a total area of the body, viewed from the above.  
      The embossing part is preferably formed along an edge of the body. At this time, the embossing part may be discrete and thus consist of plural segments each of which having a predetermined length. For example, when the body is circular viewed from the above, the embossing part consists of plural segments having an arc shape along an edge of the body.  
      The embossing part preferably has a height of 0.05˜0.5 mm. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The above and other objects, features and advantages of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:  
       FIGS. 1A and 1B  illustrate a conventional wafer chuck  20 , wherein  FIG. 1   a  shows a detailed shape of the wafer chuck  20  and  FIG. 1   b  shows an equivalent circuit of a case where a wafer  10  is put on the wafer chuck  20 ;  
       FIGS. 2A and 2B  illustrate an embossing chuck  20  according to an embodiment of the invention, wherein  FIG. 2A  is a plan view of an embossing chuck  120  and  FIG. 2B  is a sectional view of a case where a wafer  100  is put on the embossing chuck  120 ;  
       FIG. 3  is a circuit diagram for illustrating distribution of charges at an embossing chuck according to an embodiment of the invention; and  
       FIG. 4  is a view for illustrating another example of an embossing chuck  120  according to an embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      Hereinafter, a preferred embodiment of the present invention will be described with reference to the accompanying drawings. In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear.  
       FIGS. 2A and 2B  illustrate an embossing chuck  20  according to an embodiment of the invention, wherein  FIG. 2A  is a plan view of an embossing chuck  120  and  FIG. 2B  is a sectional view of a case where a wafer  110  is put on the embossing chuck  120 .  
      As shown in  FIG. 2A , an embossing part  124  protruding, in a uniform height, from an upper surface of a body of an embossing chuck  120  is formed along an edge of the body. When viewed from the above, an area of the embossing part  124  is preferably 5˜30% for a total area of the body. When the area of the embossing part  124  is excessively large, a contact area of a wafer to the chuck is substantially large, so that it is restored to the prior art. When the body of the chuck  120  is circular viewed from the above, the embossing part  124  may consist of plural segments  124   a ,  124   b , . . . each of which having an arc shape along the edge of the body of the chuck  120 . However, the invention is not limited thereto. For example, the segments  124   a ,  124   b , . . . may be continuously connected to each other, thereby forming a single circle shape.  
      Referring to  FIG. 2B , when the height of the embossing part  124  is too high, the plasma may be formed at a back surface of the wafer  100 . Accordingly, it is preferable to make the height of the embossing part  124  0.05˜0.5 mm so that it is not too high. The body of the embossing chuck  120  consists of a metal material such as aluminum and a dielectric layer  122  such as alumina is formed at a periphery thereof.  
      [Distribution of Charges] 
       FIG. 3  is a circuit diagram for illustrating distribution of charges at an embossing chuck according to an embodiment of the invention.  
      Referring to  FIG. 3 , Q 1 , C 1  and A 1  are charge, capacitance and area of the embossing part  124  and Q 2 , C 2  and A 2  are charge, capacitance and area of a part in which the embossing part  124  is not provided. d 1  is a vacuum thickness and d 2  is a thickness of the dielectric layer  122 . ε 0  is a vacuum permittivity and ε 1  is a permittivity of the dielectric layer  122 .  
      Since the voltages applied to the embossing part  124  and the part in which the embossing part is not provided are same,  
             V   =       Q   C     =         Q   ⁢           ⁢   1       C   ⁢           ⁢   1       =       Q   ⁢           ⁢   2       C   ⁢           ⁢   2                   (   1   )                 C   ⁢           ⁢   1     =       ɛ   ⁢           ⁢     1   ·   A     ⁢           ⁢   1       d   ⁢           ⁢   1               (   2   )             
 
      Since C 2  can be assumed as a series connection of the dielectric layer  122  and a vacuum layer,  
                 1     C   ⁢           ⁢   2       =       1     C   ⁡     (     dielectric   ⁢           ⁢   layer     )         +     1     C   ⁡     (     vacuum   ⁢           ⁢   layer     )             ⁢     
     ⁢     therefore   ,     
     ⁢             C   ⁢           ⁢   2     ⁢           =       ⁢     1       1     C   ⁡     (     dielectric   ⁢           ⁢   layer     )         +     1     C   ⁡     (     vacuum   ⁢           ⁢   layer     )                         =       ⁢     1         d   ⁢           ⁢   1       ɛ   ⁢           ⁢     1   ·   A     ⁢           ⁢   2       +       d   ⁢           ⁢   2       ɛ   ⁢           ⁢     0   ·   A     ⁢           ⁢   2                             (   3   )             
 
      When substituting the equations (2) and (3) for the equation (1),  
       V   =           Q   ⁢           ⁢   1       ɛ   ⁢           ⁢     1   ·   A     ⁢           ⁢   1       ⁢   d   ⁢           ⁢   1     =           Q   ⁢           ⁢   2       ɛ   ⁢           ⁢     1   ·   A     ⁢           ⁢   2       ⁢   d   ⁢           ⁢   2     +         Q   ⁢           ⁢   2       ɛ   ⁢           ⁢     0   ·   A     ⁢           ⁢   2       ⁢   d   ⁢           ⁢   2             
 
      As a result, it is obtained a following result  
               Q   ⁢           ⁢   1   ⁢     (       d   ⁢           ⁢   1       ɛ   ⁢           ⁢     1   ·   A     ⁢           ⁢   1       )       =     Q   ⁢           ⁢   2   ⁢     (         d   ⁢           ⁢   1       ɛ   ⁢           ⁢     1   ·   A     ⁢           ⁢   2       +       d   ⁢           ⁢   2       ɛ   ⁢           ⁢     0   ·   A     ⁢           ⁢   2         )               (   4   )             
 
      In the mean time,
 
 Q=Q 1 +Q 2  (5)
 
      Accordingly, when substituting the equation (4) for the equation (5), it is obtained a following equation.  
                 Q   ⁢           ⁢   1     =           (       d   ⁢           ⁢   1       ɛ   ⁢           ⁢     1   ·   A     ⁢           ⁢   2       )     +     (       d   ⁢           ⁢   2       ɛ   ⁢           ⁢     0   ·   A     ⁢           ⁢   2       )             d   ⁢           ⁢   1       ɛ   ⁢           ⁢     1   ·   A     ⁢           ⁢   1       +     (         d   ⁢           ⁢   1       ɛ   ⁢           ⁢     1   ·   A     ⁢           ⁢   2       +       d   ⁢           ⁢   2         ɛ   ·   A     ⁢           ⁢   2         )         ·   Q       ⁢     
     ⁢     Therefore   ,     
     ⁢   when     ⁢     
     ⁢         A   ⁢           ⁢   1     =       6.8   100     ·   A       ,     
     ⁢       A   ⁢           ⁢   2     =       93.2   100     ·   A       ,     
     ⁢       ɛ   ⁢           ⁢   1     =       9   ·   ɛ     ⁢           ⁢   0         ⁢     
     ⁢       d   ⁢           ⁢   1     =     0.05   ⁢           ⁢   mm       ⁢     
     ⁢   and   ⁢     
     ⁢         d   ⁢           ⁢   2     =     1   ⁢           ⁢   mm       ,     
     ⁢       Q   ⁢           ⁢   1     =     0.9296   ⁢     Q   .                   (   6   )             
 
      In other words, Q 1  is 93% of the overall Q and Q 2  is 7% of the overall Q.  
      This means that about 93% of the overall charge exists at the embossing part  124  and 7% of the charge exits at the part in which the embossing part is not provided.  
      [Charge Per Unit Area] 
      The charge per unit area in the embossing part  124  is as follows:  
                 C   ⁢           ⁢   1       A   ⁢           ⁢   2       =         ɛ   ⁢           ⁢   1       d   ⁢           ⁢   1       =         9   ·   ɛ     ⁢           ⁢   0       0.05   ⁢           ⁢   mm                 (   7   )             
 
      and the charge per unit area in which the embossing part  124  is not provided as follows:  
                 C   ⁢           ⁢   2       A   ⁢           ⁢   2       =       1         d   ⁢           ⁢   1       ɛ   ⁢           ⁢   1       +       d   ⁢           ⁢   2       ɛ   ⁢           ⁢   0           =     1         0.05   ⁢           ⁢   mm         9   ·   ɛ     ⁢           ⁢   0       +       1   ⁢           ⁢   mm       ɛ   ⁢           ⁢   0                     (   8   )               Accordingly   ,                               (       C   ⁢           ⁢   1       A   ⁢           ⁢   1       )       (       C   ⁢           ⁢   2       A   ⁢           ⁢   2       )       =   181           (   9   )             
 
      When 93% of the overall charge is collected in the embossing part  124 , the area of the embossing part  124  is only 6.8% of the overall area, but the capacitance (C 1 /A 1 ) per unit area of the embossing part  124  is 181 times as large as the capacitance (C 2 /A 2 ) per unit area of the part in which the embossing part is not provided.  
      [Electrostatic Force] 
      In case that the embossing part  124  is provided, it is assumed as follows: 93% of the overall charge first escapes through the embossing part  124  and the residual charge of 7% is redistributed to the embossing part  124 , so that the charge of 6.5% (=7%×93/100) is accumulated at the embossing part  124  and the charge of 0.5% (=7%×7/100) is accumulated at the part in which the embossing part  124  is not provided. In this assumption, the force (F 1 ) acting between the wafer  120  and the chuck  110  is as follows:  
               F   ⁢           ⁢   1     =             (     0.065   ⁢   Q     )     2         2   ·   ɛ     ⁢           ⁢     0   ·   A     ⁢           ⁢   1       +         (     0.005   ⁢   Q     )     2         2   ·   ɛ     ⁢           ⁢     0   ·   A     ⁢           ⁢   2         =     0.062   ⁢       Q   2         2   ·   ɛ     ⁢           ⁢     0   ·   A                     (   10   )             
 
      In the mean time, in case that the embossing part  124  is not provided to the chuck, only the charge of 6.8% proportional to the area of the embossing part  124  first escapes, so that the charge of 93.2% remains. Accordingly, as shown in  FIG. 1A , in case that the embossing part  124  is not provided to the chuck, the force (F 2 ) acting between the wafer  20  and the chuck  10  is as follows:  
               F   ⁢           ⁢   2     =           (     0.932   ⁢   Q     )     2         2   ·   ɛ     ⁢           ⁢     0   ·   A         =     0.869   ⁢       Q   2         2   ·   ɛ     ⁢           ⁢     0   ·   A                     (   11   )               Therefore   ,                                 F   ⁢           ⁢   1       F   ⁢           ⁢   2       ×   100     =       7.16   ⁢   %     ≅     7.2   ⁢   %               (   12   )             
 
      In other words, as shown in  FIG. 2B , the electrostatic force of the case where the embossing part  124  is provided is only about 7.2%, as compared to the electrostatic force of the case where the embossing part  124  is not provided as shown in  FIG. 1A .  
      The result as described above is obtained on the assumption that the charge of 93% accumulated at the embossing part  124  first escapes completely. If all the charge accumulated at the embossing part  124  does not escape and only about 80% escapes and 20% remains, the overall charge remaining in the embossing chuck  120  is as follows:
 
0.93 Q ×0.2+0.07 Q =0.256 Q   (13)
 
      If such charge is redistributed, the following charge is accumulated at the embossing part  124 :  
         0.256   ⁢   Q   ×     93   100       =     0.238   ⁢   Q         
 
      and the following charge is accumulated at the part in which the embossing part  124  is not provided:  
         0.256   ⁢   Q   ×     7   100       =     0.0179   ⁢   Q         
 
      Accordingly, in this case, the electrostatic force (F 1 ′) is as follows:  
                     F   ⁢           ⁢     1   ′       =       ⁢           (     0.238   ⁢   Q     )     2         2   ·   ɛ     ⁢           ⁢     0   ·     (     0.068   ⁢   A     )           +         (     0.0179   ⁢   Q     )     2       2   ·   ɛ0   ·     (     0.932   ⁢   A     )                       =       ⁢     0.834   ⁢       Q   2       2   ·   ɛ0   ·   A                       (   14   )             
 
      This force corresponds to  
           0.834   0.869     ×   100     =     96   ⁢   %         
 
 with respect to the electrostatic force (F 2 ) (refer to the equation 11) of the case where the embossing part is not provided to the chuck. Accordingly, if the charge of 20% or more accumulated at the embossing part  124  cannot escape, it is difficult to expect that the wafer would be easily detached, which is the desired effect of the invention. Since the amount of the charge escaping from the embossing part  124  depends on various factors such as types of the plasma, pressure, materials of the electrostatic chuck, it is required to control the factors, too. 
 
       FIG. 4  is a view for illustrating another example of an embossing chuck  120  according to an embodiment of the invention. Since only the edge of the wafer  110  is supported by the embossing part  124 , a center part of the wafer  100  may be sagged down when the wafer  110  is large. Accordingly, it is preferable to additionally provide embossing parts  150  for supporting the wafer in a circle pattern.  
      As described above, according to the invention, since most of the charges existing in the chuck are concentrated at the embossing part  124  and escape through the embossing part, when the embossing part  124  is provided, the electrostatic force attracting the wafer  110  becomes weak, as compared to a case where the embossing part  124  is not provided to the chuck. Therefore, it is possible to easily detach the wafer  110  from the chuck  120 .  
      While the invention has been shown and described with reference to certain preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made thereto without departing from the spirit and scope of the invention as defined by the appended claims.