Abstract:
A semiconductor manufacturing apparatus includes a supporting unit for supporting a semiconductor wafer received from a CMP apparatus and a vacuuming system for holding the wafer on the supporting unit. The vacuuming is applied only in a peripheral area of the wafer. In the peripheral area of the wafer, any circuit such as interconnections and devices are not manufactured. When the wafer is released by supplying gas to the vacuumed space, even if static electricity occurs, the electronic circuit to be manufactured on the wafer does not harmed, because the static electricity occurs only in the peripheral area where any circuit does not exist.

Description:
This application is related to Japanese Patent Application No. 2006-336172. The disclosure of that application is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a technique for holding a semiconductor wafer by a vacuum chuck. 
     2. Description of Related Art 
     In a manufacturing process of a semiconductor device, a vacuum chuck is used for holding a semiconductor wafer. 
       FIG. 1  shows a part of a semiconductor manufacturing process using a vacuum chuck. A semiconductor wafer is mounted on a wafer cassette (step S 1 ). A transit mechanism takes out the semiconductor wafer from the wafer cassette, and passes it to a CMP (Chemical Mechanical Polishing) apparatus (step S 2 ). The semiconductor wafer is attached to a polishing head of the CMP apparatus. The semiconductor wafer is polished with a CMP process (step S 3 ). The transit mechanism receives the semiconductor wafer treated with the CMP process, and conveys it to a washing apparatus (step S 4 ). The washing apparatus washes the semiconductor wafer (step S 5 ). The washed and dried semiconductor wafer is returned to the wafer cassette (step S 6 ). 
       FIG. 2  is an example of the side view of the transit mechanism for conveying the semiconductor wafer in steps S 2  and S 4 . A transit mechanism  107  includes a supporting unit  108 , a vacuum system  114 , an air supply system  116 , and a switching valve  118 . An upper surface of the supporting unit  108  is a flat sucking surface  110  for supporting the semiconductor wafer  2  horizontally. Wafer sucking openings  112  are formed on the sucking surface  110 . The wafer sucking openings  112  connect to the vacuum system  114  and the air supply system  116  via the switching valve  118 . 
       FIG. 3  shows an example of the arrangement of the wafer sucking openings  112  as the sucking surface is seen from above. The wafer sucking openings  112  are formed in appropriate positions suitable for sucking the semiconductor wafer  2 . 
     At step S 2 , the semiconductor wafer  2  is taken out from the wafer cassette, and is placed on the sucking surface  110 . The vacuum system  114  implements vacuuming for the wafer sucking openings. The semiconductor wafer  2  is held by the vacuum chuck. 
     The transit mechanism  107  moves the semiconductor wafer  2  held on the sucking surface  110  to the CMP apparatus. The polishing head of the CMP apparatus is lowered or the transit mechanism is lifted and a wafer underside surface  6  contacts to a polishing head. The polishing head sucks the semiconductor wafer  2  in vacuum, and conveys the semiconductor wafer  2  onto the polishing table. 
     Slurry is supplied and flowed on a rotating polishing pad and the polishing head pushes the surface for manufacturing devices (wafer front surface  4 ) of the semiconductor wafer  2  to the polishing pad with rotating. After the polishing process of a predetermined amount is completed, the semiconductor wafer  2  is sucked in vacuum and fixed to the polishing head, and released from the polishing pad. The polishing head holding the semiconductor wafer  2  moves to a place over the transit mechanism  107 . The polishing head is lowered or the transit mechanism is lifted and the wafer surface  4  of the semiconductor wafer  2  contacts to the sucking surface  110  of the transit mechanism  107 . The polishing head releases the semiconductor wafer  2 . Similar to step S 2 , the transit mechanism  107  holds the semiconductor wafer  2  by the vacuum chuck. 
     When a conveying robot holds the semiconductor wafer  2  and the transit mechanism  107  releases it from the vacuum suction, the semiconductor wafer  2  is passed to the conveying robot. The conveying robot returns the semiconductor wafer  2  to the wafer cassette. When the washing apparatus is installed in the system, the semiconductor wafer  2  is returned to the wafer cassette after conveyed to the washing apparatus to be washed. 
     Depending on the manufacturing system, the polishing process may be implemented on a plurality of the polishing tables in order to improve process performance of the apparatus. When the polishing is implemented on the plurality of the polishing tables, the semiconductor wafer  2  is returned to the transit mechanism from the polishing head, and is treated by another polishing head via another transit mechanism. 
     In Japanese Laid-Open Patent Application JP-A-Heisei 07-302832, an example of a vacuum suction apparatus is described. In this Patent Application, a vacuum suction apparatus for preventing working fluid to flow between the vacuum sucking surface and the underside surface of a specimen is disclosed. 
     SUMMARY 
     The present inventor has recognized that the transit mechanism as described above may have following problems. 
     In the transit mechanism, static electricity is generated on the sucking surface  110  depending on a condition. The wafer front surface  4  is damaged due to the static electricity, as a result, a circuit thereof may be a defect. It is required to take some measures for this problem. 
     In more detail, under a status described below, there is a possibility of causing a problem. When the semiconductor wafer  2  is moved to the polishing head or the conveying robot from the status where the semiconductor wafer  2  is sucked by the transit mechanism  107  in vacuum, the air supply system  116  supplies air for releasing the semiconductor wafer  2  and the air flows from the wafer sucking openings  112 . Water being sucked when the polished semiconductor wafer  2  retains on the sucking surface  10  and mixes with the flowing air, and the air-in-water is sprayed onto a wafer surface on which devices are formed. 
     The air and the water sprayed onto the wafer surface are charged by the static electricity when passing in pipes connecting to the wafer sucking openings  112  with high speed. For that reason, the static electricity is accumulated in an area on the wafer surface  4  to which the air mixing with the water is sprayed. In a planarization process for an oxidized film on interconnections, this static electricity may destroy an insulation layer on the interconnections. Furthermore, in a process for polishing a surplus of a metal layer embedded in grooves and holes, a metal existing in a dimple may melt because of the electric charge. Since destruction of a gate oxidization film in the semiconductor wafer  2 , destruction of an intermediate film in an interconnection layer, and destruction of embedded metal may be caused due to such phenomenon, and the yield ratio of the product may be fallen. 
     According to an aspect of the present invention, a semiconductor manufacturing apparatus includes: a supporting unit configured to support a semiconductor wafer received from a chemical mechanical polishing apparatus; and a vacuuming system vacuuming to hold the semiconductor wafer on the supporting unit, wherein the vacuuming is applied only in a peripheral area outer than a predetermined radius from a center of the semiconductor wafer. 
     According to another aspect of the present invention, a semiconductor manufacturing method includes: supporting a semiconductor wafer received from a chemical mechanical polishing apparatus by putting on a supporting member; and holding the semiconductor wafer on the supporting member, wherein the vacuuming is applied only in a peripheral area outer than a predetermined radius from a center of the semiconductor wafer. 
     By the apparatus or method having such characteristics, when the wafer is released by supplying gas to the vacuumed space, even if static electricity occurs, the electronic circuit to be manufactured on the wafer is not harmed, because the static electricity occurs only in the peripheral area where any circuit does not exist. 
     According to the present invention, in supporting of a semiconductor by a vacuum chuck, a product can be prevented from being influenced by static electricity. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, advantages and features of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a flowchart showing a semiconductor manufacturing process; 
         FIG. 2  is a side view of a transit mechanism for conveying a semiconductor wafer; 
         FIG. 3  is a view showing an arrangement of wafer sucking openings of the transit mechanism; 
         FIG. 4  is a side view of a transit mechanism in a first embodiment; 
         FIG. 5  is a view showing an arrangement of wafer sucking openings of the transit mechanism in the first embodiment; 
         FIG. 6  is a side view of a transit mechanism in a second embodiment; and 
         FIG. 7  is a view showing an arrangement of wafer sucking openings of the transit mechanism in the second embodiment. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The invention will be now described herein with reference to illustrative embodiments. Those skilled in the art will recognize that many alternative embodiments can be accomplished using the teachings of the present invention and that the invention is not limited to the embodiments illustrated for explanatory purposes. 
     Referring now to  FIG. 4 , a side view of a transit mechanism  7  in a first embodiment of the present invention is shown. The transit mechanism  7  includes a supporting unit (which is also called as a supporting member)  8 , a vacuuming system  14 , a gas supply system  16 , and a switching valve  18 . The shape of the supporting unit  8  is symmetry of rotation against a central axis parallel with a vertical direction. An upper surface of the supporting unit  8  is a flat sucking surface  10  for supporting the semiconductor wafer  2  horizontally. 
     Wafer sucking openings  12  are formed in the supporting unit  8  and open on the sucking surface  10 . The wafer sucking openings  12  selectively connect to the vacuuming system  14  and the gas supply system  16  via the switching valve  18 . When the semiconductor wafer  2  is pressed to the sucking surface  10 , the wafer sucking openings  12  is sealed with the wafer  2  and do not connect to the ambient air of the supporting unit  8 . 
     Referring to  FIGS. 4 and 5 , the semiconductor wafer  2  includes a non-mounting area  20  and a mounting area  21  other than the non-mounting area  20 . An area inside a circle with predetermined radius from a rotation center of the semiconductor wafer  2  is the mounting area  21 . A peripheral area of the semiconductor wafer  2  outside the mounting area  21 , that is, an area of annulus shape with predetermined width from the outer contour of the wafer  2  is the non-mounting area  20 . Electronic circuits such as transistors and interconnections are formed only inside the mounting area  21 . No circuit is formed in the non-mounting area  20 . 
     Namely, the mounting area  21  of the semiconductor area  2  indicates an area of the wafer front surface  4  (on which elemental devices such as the transistor, capacitor, etc. are formed) which is made to form product, or an area including a part which is made to form product. The non-mounting area  20  indicates a peripheral area of the wafer front surface  4  which is not made to form product. On the other hand, on the sucking surface  10  of the transit mechanism  7 , an area corresponds to the mounting area  21  of the wafer front surface  4  of the semiconductor wafer  2  is called as the mounting area  21 , and an area corresponds to the non-mounting area  20  of the wafer front surface  4  is called as the non-mounting area  20 . Meanwhile, in  FIG. 4 , as a matter of convenience for drawing a cross-sectional view, the non-mounting area  20  and the mounting area  21  are indicated at the respective positions on the wafer underside surface  6  corresponding to those in the wafer front surface  4 . 
     The width of the non-mounting area  20  in the direction of the radius of the semiconductor wafer  2  is approximately 2 mm to 3 mm generally. Thus, the peripheral area where the vacuum chuck is applied has a radius 3 mm smaller than that of the semiconductor wafer  2 . 
     All the wafer sucking openings  12  are formed in the non-mounting area  20 . That is to say, the wafer sucking openings  12  are formed in line in the area of annulus shape having a width within 3 mm or 2 mm inside from the outer contour of the semiconductor wafer  2 . When the wafer surface  4  of the semiconductor wafer  2  and the sucking surface  10  contact with each other on their surfaces, the wafer sucking openings  12  are sealed by the annulus shape area of the wafer  2  and do not connect to the ambient air and the mounting area  21 . 
     As described above, by using the transit mechanism  7  instead of the transit mechanism  107  of  FIG. 1 , the process shown in  FIG. 1  described in the background art is implemented. In the step S 4 , the polishing head moves on the semiconductor wafer  2  toward the transit mechanism  7 . The semiconductor wafer  2  is released from the transit mechanism to be placed on the sucking surface  10 . The supporting unit supports the semiconductor wafer  2  from vertically below. 
     The switching valve  18  is set so that the wafer sucking openings  12  and the vacuuming system  14  are connected with each other. The vacuuming system  14  implements vacuuming for the wafer sucking openings  12 . The semiconductor wafer  2  is held by the vacuum chuck and fixed to the supporting unit  8  with vacuum contact. That is to say, the semiconductor wafer  2  is stably held by being attached firmly to the sucking surface  10  based on a difference in atmospheric pressure between the ambient air and the wafer sucking openings  12 . 
     The transit mechanism  7  moves the semiconductor wafer  2  to a washing apparatus and stops at a predetermined position. The switching valve  18  is set so that the wafer sucking openings  12  and the gas supply system  16  are connected with each other. The gas supply system  16  supplies gas (in general, air) for the wafer sucking openings  12  and the vacuum chuck is released. The semiconductor wafer  2  is detached from the sucking surface  10  and conveyed to the washing apparatus or a wafer cassette. If carbon dioxide is actively added to the air supplied from the gas supply system  16  at this stage, an effect for suppressing static electricity can be achieved. 
     Even if discharging is caused by static electricity in the vicinity of the wafer sucking openings  12  at this stage, a possibility of causing influence to a product (electronic circuit) function is reduced because the discharging area is the non-mounting area  20 . 
       FIG. 6  is a side view of a transit mechanism in a second embodiment of the present invention.  FIG. 7  is a top view of the transit mechanism. A transit mechanism  7   a  includes a supporting unit  8   a , a vacuuming system  14   a , a gas supply system  16   a , and a switching valve  18   a . Compared to the first embodiment, a shape of the sucking surface  10   a  which is an upper surface of the supporting unit  8   a  is different. The sucking surface  10   a  has an annulus shape approximately corresponding to the non-mounting area  20  of the semiconductor wafer  2  placed thereon. Thus, the supporting unit  8   a  contacts the semiconductor wafer  2  only in the peripheral non-mounting area  20 . That is to say, the supporting unit  8   a  includes a recess hole opening toward a direction of a place of the semiconductor wafer  2  in an area within a predetermined radius from a symmetry axis of rotation of the supporting unit  8   a . The wafer sucking openings  12  open on the annulus sucking surface  10   a . A relative position of the wafer sucking openings  12  for the semiconductor wafer  2  is the same as that of the first embodiment. 
     The transit mechanism having such construction operates as similar to the first embodiment. When the semiconductor wafer  2  in wet status after the CMP process is released from the vacuum chuck and detached from the sucking surface  10 , the semiconductor wafer  2  can be detached with small force due to small surface tension because the contacting area between the semiconductor wafer  2  and the sucking surface  10  is small in the second embodiment. 
     It is apparent that the present invention is not limited to the above embodiments, but may be modified and changed without departing from the scope and spirit of the invention.