Abstract:
The present invention discloses an apparatus for transporting wafers. The apparatus includes a tray having a sloped portion on which a wafer having a sidewall can be mounted, a plurality of guides that disposed about the tray, and a plurality of sensors for detecting the position of the sidewall of the wafer with respect to the tray on which it is mounted by sensing the position of the sidewall. The present invention also discloses an apparatus for polishing wafers having the apparatus for transporting wafers comprising the circular tray and a plurality of guides and a plurality of sensors above-mentioned.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This U.S. non-provisional patent application claims priority under 35 U.S.C. § 119 of Korean Patent Application 2003-87141 filed on Dec. 3, 2003, the entire contents of which are hereby incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     The present invention relates to a wafer transfer and a wafer polishing apparatus, and more specially, to a wafer transfer and a polishing apparatus capable of sensing the existence of the wafer as well as the proper loading of the wafer.  
         [0003]     Recent rapid progress in semiconductor device integration demands smaller and smaller wiring patterns or interconnections and also narrower spaces between interconnections which connect active areas. One process available for forming such interconnections is photolithography. A photolithographic process requires that surfaces on which pattern images are to be focused by a stepper should be as flat as possible because depth of focus of an optical system is relatively small. It is therefore necessary to make surfaces of semiconductor wafers flat for photolithography.  
         [0004]     One customary way of planarizing the surface of the semiconductor wafer is to polish the semiconductor wafer by a CMP (Chemical Mechanical Polishing) process. The polishing apparatus to planarize the surfaces of the semiconductor wafers generally comprises a polishing table to which a polishing pad is attached, and top rings are employed to hold the semiconductor wafers onto the polishing table. In this polishing apparatus, semiconductor wafers are mounted on respective top rings, and then all the semiconductor wafers held by the top rings are simultaneously pressed down against the polishing pad on the polishing table, and then the wafers are polished.  
         [0005]     An exemplary of polishing apparatus is disclosed in the U.S. Pat. No. 6,629,883 “Polishing apparatus” by Katsuoka, et al. According to the patent above-mentioned, the polishing apparatus has a transfer for transporting the semiconductor wafers from the top rings or to the top rings.  
         [0006]     Referring to FIG. 10 in the U.S. Pat. No. 6,629,883 above-mentioned, wafer detecting sensors are provided at positioned spaced from the transfer. Each sensor is a photo-sensor comprising a light-emitting element and a light-receiving element. These sensors detect whether the semiconductor wafers are chucked on the transfer or not.  
         [0007]     However, because the light-emitting and light-receiving elements are installed at a tilted position with respect to the surface of the semiconductor wafer, these sensors have a difficulty for sensing proper positioning of the wafer. Improper wafer positioning may lead to wafer damage in the subsequent processing or even breakdown of the semiconductor manufacturing apparatus, e.g. polishing apparatus.  
       SUMMARY OF THE INVENTION  
       [0008]     In one embodiment, an apparatus includes a tray having a sloped portion on which a wafer having a sidewall can be mounted, a plurality of guides that disposed about the tray, and a plurality of sensors for detecting the position of the sidewall of the wafer with respect to the tray on which it is mounted by sensing the position of the sidewall.  
         [0009]     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 example embodiments of the present invention and, together with the description, serve to explain principles of the present invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  illustrates a cross-sectional view of a wafer transfer according to an exemplary embodiment of the present invention;  
         [0011]      FIG. 2  illustrates a front view of a wafer transfer according to an exemplary embodiment of the present invention;  
         [0012]      FIG. 3  illustrates a top view of the disposition of sensors in a wafer transfer of  FIG. 1  according to an exemplary embodiment of the present invention;  
         [0013]      FIG. 4  illustrates a top view of the disposition of sensors in a wafer transfer of  FIG. 1  according to an alternate exemplary embodiment of the present invention;  
         [0014]      FIG. 5  illustrates a top view of the disposition of sensors in a wafer transfer of  FIG. 1  according to another alternate exemplary embodiment of the present invention;  
         [0015]      FIG. 6  illustrates a cross-sectional view of sensing operation of sensors in a wafer transfer of  FIG. 1  according to an exemplary embodiment of the present invention; and  
         [0016]      FIG. 7  illustrates a top view of an apparatus for polishing a wafer comprising a wafer transfer of  FIG. 1  according to an exemplary embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0017]     Preferred embodiments of the present invention will be described below in more detail with reference to the accompanying drawings. The present invention may, however, be embodied in different forms and should not be constructed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numerals refer to like elements throughout the specification. Hereinafter, an exemplary embodiment of the present invention will be described in conjunction with the accompanying drawings.  
         [0018]     According to  FIG. 1  and  FIG. 2 , a wafer transfer apparatus  100  of an exemplary embodiment of the present invention comprises a tray  110 , a plurality of guides  120 , a pusher  130 , and a plurality of sensors  140  and  150 .  
         [0019]     A wafer  300  is mounted on the tray  110 . There is a sloped portion  115  around the tray  110  on which the wafer  300  is mounted. The top surface of the sloped portion  115  is flat and inner side of the sloped portion  115  is tapered from the vertical to allow the wafer  300  to be centered when the wafer  300  is mounted.  
         [0020]     A plurality of guides  120 , for example four guides  120  depicted in  FIG. 2 , are disposed around the tray  110  at spaced intervals. The guides  120  direct the position and path of the wafer  300  when the wafer  300  is unloaded from the tray  110  and transferred to a holder such as a top ring, or when wafer  300  is loaded from a top ring to the tray  110 . It is preferably that sides of the guides  120  that face the center of the tray  110  are tapered to mount the wafer  300  on the tray  110  more easily.  
         [0021]     The pusher  130  moves the tray  110  up and down when the wafer  300  mounted on the tray  110  is transferred to another apparatus, or when a new wafer is transferred to the tray  110 .  
         [0022]     Assuming that a wafer is the object to be polished, it is unloaded by a robot from the carrier or FOUP, and is mounted on the tray  110 . To polish the wafer  300  mounted on the tray  110 , the wafer  300  should be transferred to the polishing part including a polishing table (not shown) to which a polishing pad is attached, and a wafer holding part  200  is employed to hold the wafer like a top ring. The wafer holding part  200  is positioned over the wafer transfer  100 , and the tray  110  is moved to the wafer holding part  200  by means of the pusher  130 . The wafer  300  is held by vacuum on the wafer holding part  200  from the tray  110 . The wafer holding part  200  transfers the wafer to a position over the polishing table. Then, the wafer holding part  200  presses and rotates the wafer against the moving polishing pad. In this way, the wafer is polished.  
         [0023]     The polished wafer is moved to the wafer transfer apparatus  100  by operation of the wafer holding part  200 . The tray  110  is moved to the wafer holding part  200  by the pusher  130 , and the wafer is mounted on the tray  110  from the wafer holding part  200 .  
         [0024]     A plurality of sensors, for example, sensors  140  and  150 , detect whether the wafer  300  is loaded exactly and properly on the tray  110 . Each of the sensors  140  and  150  detects the sidewall of the wafer  300  on the tray  110 . It may be desirable that more than sensors  140  and  150  are installed around the tray  110  for the purpose of more precisely sensing the position of the wafer  300 .  
         [0025]     It is preferable that the sensors  140  and  150  are located at the same level as the sidewall of the wafer  300  in order to effectively sense the sidewall of the wafer  300 . For purposes of convenience, in  FIG. 1 , the sensor  140  on the left is designated as first sensor  140 , and the sensor  150  on the right is designated as second sensor  150 .  
         [0026]     The first sensor  140  may comprise a light-emitting element  140   a  and a light-receiving element  140   b . The light-emitting element  140   a  may comprise a light emitting diode, and the light-receiving element  140   b  may comprise a photo diode. In addition, the light-emitting element  140   a  may use a laser. Light emitted from the light-emitting element  140   a  is indicated as a solid line arrow, and light passing into the light-receiving element  140   b  is indicated as a dotted line arrow.  
         [0027]     In the respective light-emitting and light-receiving elements  140   a  and  140   b , for example, the light-emitting element  140   a  may be disposed above the light-receiving element  140   b  in the direction of the thickness of the wafer  300 . As depicted in the following  FIG. 3 , the light-emitting element  140   a  may be located adjacent to light-emitting element  140   b  laterally in the direction of diameter of the wafer  300 .  
         [0028]     In another configuration, the light-emitting and light-receiving elements  140   a  and  140   b  of the first sensor  140  are formed in a unitary construction. Similarly to the first sensor  140 , a light-emitting element  150   a  and a light-receiving element  150   b  of the second sensor  150  are respectively stacked above and below with respect to each other, or are arranged in a lateral position with respect to each other.  
         [0029]     According to  FIG. 3 , the first sensor  140  and the second sensor  150  face each other across the body of wafer  300  as depicted in the  FIG. 1 . The light-emitting element  140   a  and the light-receiving element  140   b  of the first sensor  140  are disposed laterally. Similarly, the light-emitting element  150   a  and the light-receiving element  150   b  are disposed laterally. This lateral disposition of the sensors  140  and  150  has an advantage with respect to sensing the horizontality of the wafer  300 .  
         [0030]     This relative position of the sensors  140  and  150  can be employed to detect the horizontality of the wafer  300  this is the case even though the wafer  300  is tilted to one side on its axis which links sensors  140  and  150  via the center of the wafer  300 .  
         [0031]     As illustrated in  FIG. 4 , it is desirable that sensors  140  and  150  are positioned not to face each other across the body of the wafer  300 . Compared with the arrangement of sensors  140  and  150  in  FIG. 3 , the position of sensors  140  and  150  in  FIG. 4  can more accurately detect the horizontality of the wafer  300 .  
         [0032]     According to  FIG. 5 , three sensors  140  and  150  and  160 , respectively, may be arranged around the wafer  300 . It is preferable that these three sensors  140  and  150  and  160  be spaced around the wafer  300  at regular intervals in the circumferential direction to detect more accurately detect the horizontality of the wafer  300 .  
         [0033]     The operation of the wafer transfer apparatus  100  is as follows:  
         [0034]     Referring to  FIG. 6 , when the wafer that is polished in the polishing process is unloaded from the wafer holding part  200 , such like a top ring, the tray  110  is moved into the wafer holding part  200  by operation of the pusher  130 . The re-positioned tray  110  receives the wafer  300  from the wafer holding part  200 . The unloaded wafer  300  is then mounted on the inclined part  115  of the tray  110 . The wafer  300  may be unloaded from the wafer holding part  200  after predetermined time so that the wafer  300  is not properly mounted on the tray  110 . Especially, the wafer  300  is so tilted that one side of the wafer  300  is on the guide  120 .  
         [0035]     When the wafer  300  is unloaded from the wafer holding part  200 , and is mounted on the tray  110  of the wafer transfer  100 , the sensors  140  and  150  detect the sidewalls of the wafer  300 . The light-emitting element  140   a  of the first sensor  140  emits a specific wavelength of light into the sidewall of the wafer  300 , and the light-receiving element  140   b  of the first sensor  140  receives the light emitted from the light-emitting element  140   a . If the light-receiving element  140   b  accepts the light emitted from the light-emitting element  140   a , it indicates that the wafer  300  is mounted on the tray  110  in a proper position. If the light-receiving element  140   b  does not accept the light emitted from the light-emitting element  140   a , it indicates that the wafer  300  is not mounted on the tray  110  in a proper position. The function of the second sensor  150  is the same as that of the first sensor  140 . Any additional sensors, if any, function in the same manner.  
         [0036]     If the wafer  300  is not properly mounted on the guide  120 , the light-receiving element  140   a  of the first sensor  140  cannot accept the light emitted from the light-emitting element  150   b . Similarly, if the wafer  300  is not properly loaded on the guide  120 , the light-receiving element  140   a  of the first sensor  140  cannot accept the light emitted from the light-emitting element  150   b . Thus, in either case, the apparatus  100  has indicated that the wafer  300  has not been mounting on the guide  120 .  
         [0037]     If either of the sensors  140  and  150  does not detect proper positioning of wafer  300 , the process does not advance to the next step. Stated in any way, the wafer  300  will advance to the next process step if all sensors  140  and  150  detect that proper positioning of wafer  300 .  
         [0038]     It is preferable that an alarm means (not shown) for aurally or visually informing a user as to the state of the wafer  300 , which functions in conjunction with a signal from the sensors  140  and  150 , can be included in the wafer transfer apparatus  100 . Examples of the alarm means may include a bell for sounding an auditory signal or a lamp for illuminating a light to inform a user of the substandard condition of the wafer. This alarm means will enable workers to quickly stop the wafer transfer process, or allow the wafer transfer to be stopped automatically.  
         [0039]     Referring to  FIG. 7 , a polishing apparatus used in conjunction with the wafer transfer apparatus  100  according to an exemplary embodiment of the present invention comprises a power station  450  to provide the energy to operate the apparatus  100 , a wafer stocking assembly  350  for stocking a plurality of wafers, a polishing assembly  250  for performing the polishing process, a rinsing assembly  650  for rinsing the wafers polished, a drying assembly  750  for drying the wafers rinsed, robots  550  and  850  for transferring the wafers, and a space for providing the wafer transfer apparatus  100  with a moving road.  
         [0040]     The wafer stocking assembly  350  has a plurality of tools to load the wafers, e.g. FOUP, so that the robot  850  (referred to as a robot dry or a first robot) takes out the wafers loaded on some FOUP in the wafer stocking part  350 .  
         [0041]     The wafer that is removed from the wafer stocking assembly  350  is loaded on the wafer transfer apparatus  100 . The wafer loaded on the wafer transfer apparatus  100  is then transferred to the polishing assembly  250 .  
         [0042]     The polishing assembly  250  may comprise a plurality of chambers, for example, a first chamber  250   a , a second chamber  250   b , a third chamber  250   c , and a fourth chamber  250   d . Each of the chambers  250   a - 250   d  comprises at least a wafer holding assembly like a top ring, and a polishing table to which a polishing pad is attached. The wafer is attached to a bottom surface of the wafer holding assembly. The wafer that attached to the bottom surface of the wafer holding assembly is pressed down against the polishing table and then the wafer is polished.  
         [0043]     The wafer  300  is transferred to the first chamber  250   a  via the wafer transfer apparatus  100  and then the wafer  300  is polished in the first chamber  250   a.    
         [0044]     The wafer loading from the wafer transfer apparatus  100  to the first chamber  250   a  has been previously described. The wafer that is polished in the first chamber  250   a  is transported from the first chamber  250   a  to the wafer transfer apparatus  100 . As previously mentioned above, a plurality of sensors  140  and  150  detect the sidewalls of the wafer  300  mounted on the tray  110  and then confirm the horizontality of the wafer  300 . When the result of the sensing the wafer  300  are deemed acceptable, the wafer  300  is advanced to the next processing step. When the result of the sensing the wafer  300  are not deemed acceptable, correction of any problems in the process sequence will typically need to be implemented prior to proceeding with the process.  
         [0045]     The wafer transfer apparatus  100  mounting the wafer  300  unloaded from the first chamber  250   a  moves to the second chamber  250   b  along the moving space  800 . The wafer transfer apparatus  100  positioned near the second chamber  250   b  transfers the wafer  300  to the second chamber  250   b . The wafer  300  transferred to the second chamber  250   b  is polished again and then returns to the wafer transfer  100 . If the wafer  300  is returned to the wafer transfer  100 , the wafer  300  is repeatedly sensed by the sensors  140  and  150 . Similarly, the wafer transfer apparatus  100  mounting the wafer  300  unloaded from the second chamber  250   b  moves to the third chamber  250   c  along the moving space  800 . The wafer transfer apparatus  100  positioned near the third chamber  250   c  transfers the wafer  300  to the third chamber  250   c . The wafer  300  transferred to the third chamber  250   c  is polished again and then is returned to the wafer transfer  100 . When the wafer  300  is returned to the wafer transfer  100 , the wafer  300  is repeatedly sensed by the sensors  140  and  150 . Likewise, the wafer transfer apparatus  100  mounting the wafer  300  unloaded from the third chamber  250   c  moves to the fourth chamber  250   d  along the moving space  800 . The wafer transfer apparatus  100  positioned by the fourth chamber  250   d  transfers the wafer  300  to the fourth chamber  250   d . The wafer  300  transferred to the fourth chamber  250   d  is polished again and then is returned to the wafer transfer  100 . In returning the wafer  300  to the wafer transfer  100 , the wafer  300  is repeatedly sensed by the sensors  140  and  150 .  
         [0046]     The wafer  300  which is polished and loaded on the wafer transfer apparatus  100  and then into the rinsing apparatus  650  by means of the robot  550  (referred to as a robot wet or a second robot). The rinsing apparatus  650  may comprise a first chamber  650   a , a second chamber  650   b , and a third chamber  650   c . The wafer  300  loaded in the rinsing apparatus  650  via the second robot  550  is cleaned using washing solutions while the wafer  300  is traveling through the chambers  650   a - 650   d . The wafer  300  cleaned in the rinsing apparatus  650  is then moved to the drying apparatus  750  so that washing solution remaining on the surface of the wafer  300  is dried.  
         [0047]     As described above, sensors detect the location of the sidewalls of the wafer  300  mounted on the tray  110  so that the presence of a normal wafer mounting position can be determined. Therefore, many problems relating to wafer mis-positioning can be avoided, thereby improving the throughput and/or yield associated with wafer production.  
         [0048]     Although the present invention has been described in connection with the embodiment of the present invention illustrated in the accompanying drawings, it is not limited thereto. It will be apparent to those skilled in the art that various substitution, modifications and changes may be thereto without departing from the scope and spirit of the invention.