Abstract:
A membrane for vacuum suction of a silicon water typically used inside a polishing head. The membrane has a flat main body and a plurality of protrusions each having a particle-like profile over the surface of the flat main body. The protrusions are formed in positions that correspond to the holes of a supporting multiple-hole panel. The protrusions on the flat main body lower the suction pressure between the wafer and the membrane somewhat so that wafer unloading failure is minimized.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
         [0001]    This application claims the priority benefit of Taiwan application serial no. 91102579, filed Feb. 15, 2002.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of Invention  
           [0003]    The present invention relates to a semiconductor transport device. More particularly, the present invention relates to a vacuum suction memory for holding a silicon wafer.  
           [0004]    2. Description of Related Art  
           [0005]    Wafer transport systems use a variety of mechanisms for transport, the most common and widely used method of which is creating a vacuum to suck up a silicon wafer. The vacuum suction method is used, for example, in a chemical-mechanical polishing device to hold a silicon wafer.  
           [0006]    [0006]FIG. 1 is simplified and localized cross-sectional view of a conventional chemical-mechanical polishing device. As shown in FIG. 1, the chemical-mechanical polishing device includes a polishing head  100  and a polishing table  110 . A polishing pad  120  covers the polishing table  110 . The polishing head  100  further includes a gripping pan  102  having an elastic membrane  106  therein. When the polishing head  100  presses upon a silicon wafer  108 , the downward pressure produced by the polishing head  100  on the wafer  108  is evenly spread out so that the wafer  108  can be polished smoothly.  
           [0007]    However, at the end of a chemical-mechanical polishing operation, an external robotic arm is often used to unload the wafer  108  from the polishing table  110  and then transfer the wafer  108  elsewhere. To smooth the process and reduce operating cost, the polishing head  100  often incorporates a vacuum system. In other words, the gripping pan  102  structure is frequently modified to include a set of internal gaseous pipelines. In addition, a multiple-hole panel is inserted between the gripping pan  102  and the membrane  106  such that the membrane  106  also encloses the bottom section of the multiple-hole panel. After a chemical-mechanical polishing operation, a vacuum system may be triggered to create a vacuum state inside the polishing head  100  through the set of internal gaseous pipelines. Hence, the membrane  106  originally pressed against the wafer  108  now attaches to the wafer  108  through suction. Thereafter, the polishing head  100  may move to carry the wafer  108  away. On releasing the vacuum inside the polishing head  100 , suction between the membrane  106  and the wafer  108  disappears and the wafer  108  drops off from the polishing head  100 .  
           [0008]    [0008]FIG. 2 is a schematic top view of a conventional multiple-hole panel inside a vacuum-suction polishing head. As shown in FIG. 2, the multiple-hole panel  200  has a shape that corresponds to a silicon wafer. Hence, the multiple-hole panel  200  is circular and contains a number of holes  202 . At the end of a polishing operation, the polishing head is turned into a vacuum state. Through differential pressure acting via the holes  202 , the elastic membrane  106  contracts into the hole  202  resulting in a suction pressure on the wafer.  
           [0009]    However, the conventional technique has some drawbacks in real applications. The polishing head must return to normal pressure after a polishing operation so that the wafer attached to the membrane can drop off. Due to considerable suction between the membrane and the wafer, the wafer may not unload normally. In other words, the wafer is still attached to the membrane after the polishing head has returned to a normal pressure. Eventually, the wafer may be damaged due to subsequent mishandling.  
           [0010]    In addition, because there is no membrane between the multiple-hole panel for sucking up the wafer and the wafer, the process of creating a suction vacuum also carries some micro-particles from the surrounding atmosphere towards the wafer leading to wafer contamination.  
         SUMMARY OF THE INVENTION  
         [0011]    Accordingly, one object of the present invention is to provide a membrane for vacuum suction of a silicon wafer such that excessive suction pressure between the membrane and the wafer that may lead to unloading failure is prevented.  
           [0012]    A second object of this invention is to provide a membrane for vacuum suction of a silicon wafer such that time and labor for processing unloading failure is reduced.  
           [0013]    A third object of this invention is to provide a membrane for vacuum suction of a silicon wafer such that contamination of the wafer is prevented.  
           [0014]    To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a device having a membrane therein typically incorporated into a polishing head for sucking up a silicon wafer. The device includes a flat main body and a plurality of minute protrusions such as micro-particles on the surface of the flat main body. The minute protrusions are positioned over corresponding holes of a polishing head suction panel.  
           [0015]    The minute protrusions on the vacuum suction membrane according to this invention are able to reduce suction pressure between the wafer and the membrane after the removal of suction. Hence, the design is able to minimize wafer damage due to unloading failure.  
           [0016]    The membrane for vacuum suction of a silicon wafer according to this invention is quite effective in unloading a wafer. Thus, time and labor required to process failure in wafer unloading is minimized and yield of the wafer is increased.  
           [0017]    Furthermore, the provision of a membrane between the wafer suction panel and the wafer cuts off all deposition of contaminant particles from surrounding air in the process of creating a vacuum.  
           [0018]    It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]    The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. In the drawings,  
         [0020]    [0020]FIG. 1 is simplified and localized cross-sectional view of a conventional chemical-mechanical polishing device;  
         [0021]    [0021]FIG. 2 is a schematic top view of a conventional multiple-hole panel inside a vacuum suction polishing head;  
         [0022]    [0022]FIG. 3A is a schematic cross-sectional view of a multiple-hole panel and a membrane that encloses the bottom section of the multiple-hole panel according to one preferred embodiment of this invention;  
         [0023]    [0023]FIG. 3B is a schematic cross-sectional view showing the configuration of the system in FIG. 3A after creating a suction pressure; and  
         [0024]    [0024]FIG. 4 is a local magnification of a portion IV shown in FIG. 3B. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0025]    Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts.  
         [0026]    This invention provides a membrane for vacuum suction of silicon wafers that can be incorporated with a chemical-mechanical polishing device. The membrane serves as a film for enclosing a multiple-hole panel inside a polishing head. However, the membrane can also be applied to various other vacuum suction devices for transferring or holding wafers.  
         [0027]    The chemical-mechanical polishing device used as an example in the description includes a polishing head and a polishing table. The polishing head is connected to a vacuum system. The polishing head further includes a gripping pan for stationing a wafer. Details inside the gripping panel are shown in FIGS. 3A, 3B and  4 .  
         [0028]    [0028]FIG. 3A is a schematic cross-sectional view of a multiple-hole panel and a membrane that encloses the bottom section of the multiple-hole panel according to one preferred embodiment of this invention. As shown in FIG. 3A, inside the gripping panel (not shown in the figure) of the polishing head is a multiple-hole panel  300  having a plurality of holes  302  therein. A membrane  304  fabricated according to this invention wraps around the bottom section of the multiple-hole panel  300 . The membrane  304  includes a flat main body  305  and a plurality of minute spiny protrusions  306  on the surface of the flat main body  305 . Both the flat main body  305  and the spiny protrusions  306  are made from an identical material. The spiny protrusions  306  may have a particle shape, for example. The protrusions  306  are positioned on the membrane  304  over corresponding holes  302  of the multiple-hole panel  300 , for example. For a membrane having a diameter of about 300 mm, each protrusion  306  has a diameter of about 2 mm and a height of about 2 mm. However, the protrusions  306  may have other shapes, dimensions or density on the membrane in order to produce a device having an optimal wafer suction/unloading capability. For example, the quantity of protrusions  306  on the membrane  304  may vary according to the size of holes  302  in the multiple-hole panel  300 . In other words, total quantity of protrusions in an area over a larger hole may be greater than total quantity of protrusions in an area over a smaller hole.  
         [0029]    When the polishing head is conducting a polishing operation, the multiple-hole panel  300  presses downward against the wafer. At the end of the polishing operation, the vacuum system is triggered to turn the interior of the polishing head into a vacuum state so that the polishing head can be used as a tool for moving the wafer elsewhere. How the vacuum system of this invention is able to suck up a wafer is explained in greater detail with reference to FIG. 3B.  
         [0030]    [0030]FIG. 3B is a schematic cross-sectional view showing the configuration of the system in FIG. 3A after creating a suction pressure. As shown in FIG. 3B, air within the polishing head is evacuated in step  308  to create a partial vacuum so that the multiple-hole panel  300  has a pressure differential between the interior and the exterior. Consequently, the portion of membrane  304  positioned directly over the holes  302  cave upward towards the upper section of the multiple-hole panel  300 . Originally, the membrane  304  is pressed tightly against the wafer, but now the membrane  304  attaches to the wafer through suction. Because the membrane  304  has a plurality of minute protrusions  306  on the surface, suction pressure between the membrane  304  and the wafer is slightly lowered when the wafer is attached. Details of how the membrane  304  functions over the hole  302  are further explained using FIG. 4.  
         [0031]    [0031]FIG. 4 is a local magnification of a portion IV shown in FIG. 3B. When a vacuum state is created inside the polishing head, the membrane region over the holes  304  caves upward towards the upper section of the multiple-hole panel  300 . Thus, the membrane  304  around the holes produces an upward suction.  
         [0032]    A comparison between the membrane of this invention and a conventional design can be made here. In a conventional design, a suction-like counteraction is often created trying to remove the downward pressure on the wafer during the polishing operation. Thus, the counteraction provides a suction force between the membrane and the wafer even before a vacuum suction is created. Hence, when the wafer is carried under vacuum suction, the suction between the wafer and the membrane at the bottom section of the multiple-hole panel exceeds the desired suction considerably. Such an excessive suction often results in a failure to unload the wafer from the polishing head even when the vacuum state is canceled. The failure of disengagement between the polishing head and the wafer may lead to defective polishing when the wafer undergoes a float polishing operation inside a float polisher, for example.  
         [0033]    On the contrary, the membrane fabricated according to this invention has protrusions around the holes of the multiple-hole panel. Since the protrusions cancel most of the suction due to counteraction after removing the pressure on the wafer, there is no excess counteraction before the creation of a vacuum suction between the wafer and the membrane. Once the vacuum state in the polishing head is relieved, suction between the wafer and the membrane immediately disappears and the wafer unloads from the membrane smoothly. Consequently, the probability of wafer unloading failure is greatly reduced.  
         [0034]    In addition, if this invention is applied to other vacuum suction transport or wafer holding systems, the presence of a membrane between the multiple-hold panel and the wafer prevents any deposition of contaminants on the wafer when the vacuum is created.  
         [0035]    It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.