Patent Publication Number: US-6910956-B1

Title: Wafer grinding apparatus

Description:
BACKGROUND OF INVENTION 
     1. Field of the Invention 
     The present invention relates to a wafer grinding apparatus, and more specifically, to a wafer backside grinding apparatus capable of preventing cross-shaped flaws from forming in the wafer. 
     2. Description of the Prior Art 
     A wafer grinding apparatus is used for grinding a back-side of a semiconductor wafer, so that a thickness of the wafer can be well controlled for facilitating the following packaging processes. Generally, the wafer grinding apparatus includes a positioning table for adjusting an orientation of the wafer, grinding tables where a wafer grinding process is performed, and a spinner table where a cleaning process is performed. Additionally, the wafer grinding apparatus further includes a wafer-transporting device for transferring the wafer from one table to another table. Since the wafer-transporting device contacts the semiconductor wafer frequently, the wafer-transporting device should be well designed for preventing the semiconductor wafer from being damaged. 
     Please refer to  FIG. 1  and  FIG. 2 .  FIG. 1  is a schematic diagram of a wafer-transporting device of a wafer grinding apparatus according to the prior art.  FIG. 2  is a schematic diagram illustrating a wafer having a cross-shaped flaw thereon. As shown in  FIG. 1 , a prior art wafer-transporting device  10  includes a suction pad  12  for sucking a wafer  16  through vacuum suction, and a transporting arm  14  connected to the suction pad  12  for transferring the wafer  16  sucked by the suction pad  12 . Additionally, the suction pad  12  comprises a ceramic material so that an upper surface  12   a  and a lower surface  12   b  of the suction pad  12  are both quite hard. 
     Generally, a wafer backside grinding process is performed in the wafer grinding apparatus for grinding a backside of the wafer  16 . As a result of the wafer backside grinding process, a thickness of the wafer  16  can be reduced to 30 micrometers (μm) or less, thereby facilitating the following packaging processes. However, a lot of particles  18 , such as silicon powder, are generated while the wafer backside grinding process is performed. The particles  18  are always attached on the wafer  16 , and the upper surface  12   a  and the lower surface  12   b  of the suction pad  12 , as shown in  FIG. 1  and  FIG. 2 . Since the particles  18  are attached on the ground wafer  16  whose thickness is quite thin, and the suction pad  12  has a large and hard lower surface  12   b , a cross-shaped flaw  20  is therefore formed in the ground wafer  16  when the ground wafer  16  is sucked by the suction pad  12  through vacuum suction. Unfortunately, once the cross-shaped flaw is formed in the wafer  16 , the wafer  16  usually should be scrapped. Nevertheless, a lot of integrated circuits and metal interconnects have been manufactured in the wafer  16  before the wafer backside grinding process is performed, so that it not only reduces a production yield but also increases a production cost to scrap the wafer  16 . 
     SUMMARY OF INVENTION 
     It is therefore a primary objective of the claimed invention to provide a wafer grinding apparatus in order to solve the above-mentioned problem. 
     According to the claimed invention, a wafer grinding apparatus is provided. The wafer grinding apparatus includes a wafer-transporting device for transporting a wafer, a first nozzle, and a second nozzle. The wafer-transporting device includes at least a suction pad having a first surface and a second surface that is flexible for sucking the wafer, and a transporting mechanism connected to the first surface of the suction pad for transporting the wafer. The first nozzle is used for ejecting a first liquid to the first surface of the suction pad for cleaning the first surface, and the second nozzle is used for ejecting a second liquid to the second surface of the suction pad and the wafer for cleaning the second surface and the wafer. 
     It is an advantage over the prior art that the claimed invention provides the flexible second surface for sucking the wafer, thereby decreasing an impact force sustained by the wafer while the wafer is sucked by the suction pad. Additionally, the claimed invention further provides the first nozzle and the second nozzle to wash the contaminants from the suction pad, thus preventing cross-shaped flaws from forming in the wafer. 
     These and other objectives of the claimed invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment, which is illustrated in the multiple figures and drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic diagram of a wafer-transporting device of a wafer grinding apparatus according to the prior art. 
         FIG. 2  is a schematic diagram illustrating a wafer having a cross-shaped flaw thereon. 
         FIG. 3  to  FIG. 6  are schematic diagrams of a wafer grinding apparatus according to the first embodiment of the present invention. 
         FIG. 7  is a schematic diagram of a suction pad according to the second embodiment of the present invention. 
         FIG. 8  is a schematic diagram of a suction pad according to the third embodiment of the present invention. 
         FIG. 9  is a schematic diagram of a suction pad according to the fourth embodiment of the present invention. 
         FIG. 10  is a schematic diagram of a suction pad according to the fifth embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Please refer to  FIG. 3  to  FIG. 6 .  FIG. 3  to  FIG. 6  are schematic diagrams of a wafer grinding apparatus according to the first embodiment of the present invention. As shown in  FIG. 3 , a wafer grinding apparatus  30  includes a housing  32 , two cassette supporting tables  34   a  and  34   b  for situating a plurality of wafers  36 , a positioning table  40  for adjusting an orientation of each wafer  36 , a spinner table  42  for washing each ground wafer  36 , and a robot  38  for transferring each wafer  36  from the cassette supporting table  34   a  to the positioning table  40  or from the spinner table  42  to the cassette supporting table  34   b . Additionally, the wafer grinding apparatus  30  further includes two thickness-measuring units  46   a  and  46   b  for measuring a thickness of each wafer  36 , and two grinding devices  48  and  58  for grinding a backside of each wafer  36  to reduce the thickness of each wafer  36 . The wafer grinding apparatus  30  is a wafer backside grinding apparatus, the grinding device  48  is a coarse-grinding device, and the grinding device  58  is a fine-grinding device. 
     As shown in  FIG. 3  and  FIG. 4 , the coarse-grinding apparatus  48  includes a grinding table  50 , a grinding wheel  56  (only shown in  FIG. 4 ), a rotary driving unit  52  connected to the grinding wheel  56 , and a sliding driving unit  54  connected to the rotary driving unit  52 . The grinding table  50  is used to situate and fix the wafer  36  whose front side faces the grinding table  50 , and a protection tape  50   a  is positioned on the grinding table  50  for protecting integrated circuits located on the front surface of the wafer  36 . Additionally, the rotary driving unit  52  is used to drive the grinding wheel  56  to rotate along a direction shown by double arrow AA of  FIG. 3 , while the sliding driving unit  54  functions to drive the rotary driving unit  52  and the grinding wheel  56  to move along a direction shown by double arrow BB of  FIG. 4 . Furthermore, the grinding wheel  56  has a plurality of wheel teeth (not shown) located thereon, and each wheel tooth is made of diamond particles and a binding agent for binding the diamond particles. As the rotary driving unit  52  drives the grinding wheel  56  to rotate, the backside of the wafer  36  is ground by the wheel teeth on the grinding wheel  56 . In addition, the fine-grinding device  58  includes a grinding table  60 , a grinding wheel (not shown), a rotary driving unit  62 , and a sliding driving unit  64 , as shown in  FIG. 3 . The detailed structure of the fine-grinding device  58  is similar to that of the coarse-grinding device  48 , and its description is therefore omitted. 
     As shown in  FIG. 3 , the wafer grinding apparatus  30  further includes a wafer-transporting device  44  utilized for transferring each wafer  36 . Due to the wafer-transporting device  44 , each wafer  36  can be moved between two neighboring tables among the positioning table  40 , the grinding tables  50  and  60 , and the spinner table  42 . Additionally, the wafer-transporting device  44  includes a transporting mechanism  72 , a suction pad  74 , a suction pad  76 , and a suction pad  78 . The transporting mechanism  72  is a T-shaped arm, which can be rotated along a direction shown by double arrow CC and has a transporting arm  66  connected to the suction pad  74 , a transporting arm  68  connected to the suction pad  76 , and a transporting arm  70  connected to the suction pad  78 . Generally, the transporting arm  66  and the suction pad  74  are used to transfer the wafer  36  from the positioning table  40  to the grinding table  50 , the transporting arm  68  and the suction pad  76  are used to move the wafer  36  from the grinding table  50  to the grinding table  60 , and the transporting arm  70  and the suction pad  78  are used to transfer the wafer  36  from the grinding table  60  to the spinner table  42 . When the wafer-transporting device  44  is idle, the suction pad  74 , the suction pad  76 , and the suction pad  78  are respectively parked in a parking region  80   a , a parking region  80   b , and a parking region  80   c . Furthermore, the wafer-transporting device  44  includes a plurality of air intake lines (not shown), and an air suction device (not shown) connected to the air intake lines for pumping air. The air intake lines are connected to the suction pad  74 , the suction pad  76 , and the suction pad  78 , and while the air suction device pumps air, the wafer  36  can be sucked by the suction pad  74 , the suction pad  76 , or the suction pad  78  through vacuum suction. 
     As shown in  FIG. 5 , the suction pad  78  has an upper surface  78   a  connected to the transporting arm  70 , and a lower surface  78   b  that is flexible. Additionally, as the suction pad  78  sucks the wafer  36 , the lower surface  78   b  is in contact with the wafer  36  and the transporting arm  70  moves the wafer  36  to one of the above-mentioned tables. Furthermore, the suction pad  78  includes a pedestal  82 , and six flexible suction trays  84  that are equally spaced and located on a peripheral region of the pedestal  82 , as shown in  FIG. 6 . Each of the flexible suction trays  84  has at least an opening  84   a  communicating with the corresponding air intake line, so that the wafer  36  can be sucked by the suction pad  78  through vacuum suction when the air suction device pumps air. In addition, as shown in  FIG. 5 , the wafer grinding apparatus  30  further includes a nozzle  86  positioned in the parking region  80   a  and under the suction pad  78 , and a spray nozzle  88  located in the parking region  80   a  and above the suction pad  78 . The nozzle  86  and the spray nozzle  88  are used to eject water to the suction pad  78  for cleaning the suction pad  78 . It should be noted that an area of the suction pad  78  is about one third of that of the suction pad  12  of  FIG. 1 . Moreover, the amounts, sizes, and shapes of the flexible suction trays  84  are not limited to those shown in  FIG. 6 . That is to say, the amounts, sizes, and shapes of the flexible suction trays  84  can be changed according to the requirements of processes. 
     The transporting arm  66  and the transporting arm  68  are both similar to the transporting arm  70 , and the suction pad  74  and the suction pad  76  are the same as the suction pad  78 . The detailed descriptions of the transporting arms  66 ,  68  and the suction pads  74 ,  76  are thereby omitted. Additionally, since the wafer  36  that has not been ground has a larger strength and the suction pad  74  is usually used to suck the wafer  36  that has not been ground, the suction pad  74  also can be designed as the suction pad  12  shown in  FIG. 1 . Furthermore, each of the parking region  80   b  and the parking region  80   c  includes a nozzle (not shown) and a spray nozzle (not shown) for washing the suction pad  76  and suction pad  74 . Because the nozzles and the spray nozzles located in the parking regions  80   b  and  80   c  are the same as those in the parking region  80   a , their detailed descriptions are omitted. 
     Please refer to  FIG. 3 . The operation of the wafer grinding apparatus  30  is explained as follows. First, the robot  38  takes out a wafer  36  from the cassette supporting table  34   a  or the cassette supporting table  34   b , and transfers the wafer  36  to the positioning table  40  to adjust an orientation of the wafer  36 . Then, the wafer-transporting device  44  drives the suction pad  74  to suck the wafer  36  on the positioning table  40 , and the transporting arm  66  transfers the wafer  36  to the grinding table  50  where a coarse-grinding process is performed on the wafer  36 . After the coarse-grinding process is completed, the transporting arm  68  rotates towards the grinding table  50  to make the suction pad  76  suck the wafer  36 , and then, the transporting arm  68  moves the wafer  36  to the grinding table  60  where a fine-grinding process is performed on the wafer  36 . After the fine-grinding process is completed, the wafer-transporting device  44  drives the suction pad  78  to suck the wafer  36  on the grinding table  60 , and the transporting arm  70  transfers the wafer  36  to the spinner table  42  where a cleaning process is performed on the wafer  36 . Thereafter, the robot  38  transfers the wafer  36  from the spinner table  42  to the cassette supporting table  34   a  or the cassette supporting table  34   b . Finally, the transporting arm  66 , the transporting arm  68 , and the transporting arm  70  respectively parks in the parking region  80   a , the parking region  80   b , and the parking region  80   c.    
     Noticeably, a size of the suction pad  78  is about one third of that of the prior art suction pad  12 , so that a contacting area between the suction pad  78  and the wafer  36  is so small that cross-shaped flaws can be prevented from forming in the wafer  36 . Additionally, since the suction pad  78  has six flexible suction trays  84 , the wafer  36  is in contact with six flexible surfaces as the suction pad  78  sucks the wafer  36 . Because of the flexible suction trays  84 , an impact force sustained by the wafer  36  when the suction pad  78  sucks the wafer  36  can be reduced, thus effectively preventing cross-shaped flaws from forming in the wafer  36 . Furthermore, since the lower surface  78   b  is flexible, the lower surface  78   b  can vary its shape to fit the surface of the wafer  36 . Accordingly, even though the wafer  36  contains particles thereon, cross-shaped flaws can be prevented from forming in the wafer  36 . Moreover, when the suction pad  78  parks in the parking region  80   a  of  FIG. 3 , the nozzle  86  of  FIG. 5  ejects water  87  to the upper surface  78   a  to wash the contaminants away from the upper surface  78   a , and simultaneously, the spray nozzle  88  of  FIG. 5  ejects water  89  to the lower surface  78   b  to wash the contaminants away from the lower surface  78   b . Noticeably, because the spray nozzle  88  can eject water  89  to the entire lower surface  78   b , the contaminants can be completely removed from the lower surface  78   b , thus preventing cross-shaped flaws from forming in the wafer  36 . In addition, when the suction pad  78  sucks the wafer  36  and passes through the parking region  80   a  of  FIG. 3 , the spray nozzle  88  of  FIG. 5  ejects water to wash the surface of the wafer  36 . 
     In addition, the structure of the suction pad  78  is not limited to that shown in  FIG. 6 , and the following description will introduce other embodiments of the present invention. For convenience of explanation, the same elements of  FIG. 6  to  FIG. 10  are indicated by the same symbols. Please refer to  FIG. 7 .  FIG. 7  is a schematic diagram of a suction pad according to the second embodiment of the present invention. As shown in  FIG. 7 , the suction pad  78  includes a pedestal  82 , an elastic pad  90 , and a plurality of openings  90   a . Each of the openings  90   a  is located in the pedestal  82  and the elastic pad  90 , and communicates with the corresponding air intake line. 
     Please refer to  FIG. 8 .  FIG. 8  is a schematic diagram of a suction pad according to the third embodiment of the present invention. As shown in  FIG. 8 , the suction pad  78  includes a pedestal  82 , a plurality of elastic rings  92 , and a plurality of openings  82   a . The elastic rings  92  are concentric circles, and each of the openings  82   a  is located in the pedestal  82  and communicates with the corresponding air intake line. 
     Please refer to  FIG. 9 .  FIG. 9  is a schematic diagram of a suction pad according to the fourth embodiment of the present invention. As shown in  FIG. 9 , the suction pad  78  includes a pedestal  82 , a plurality of elastic pads  94  located on the pedestal  82 , elastic rings  92  located on the pedestal  82  and surrounding the elastic pads  94 , and a plurality of openings  82   a  located in the pedestal  82  and communicating with the corresponding air intake line. 
     Please refer to  FIG. 10 .  FIG. 10  is a schematic diagram of a suction pad according to the fifth embodiment of the present invention. As shown in  FIG. 10 , the suction pad  78  includes a pedestal  82 , a radial elastic pad  96  located on the pedestal  82 , elastic rings  92  located on the pedestal  82  and surrounding the radial elastic pad  96 , and a plurality of openings  82   a  located in the pedestal  82  and communicating with the corresponding air intake line. Additionally, all of the flexible suction pads, the elastic pads, the elastic rings, and the radial elastic pad comprise flexible materials, such as rubber. 
     In comparison with the prior art, the suction pad  78  of the present invention includes a flexible and small-sized surface for sucking the wafer  36 . Additionally, the present invention further provides the nozzle  86  and the spray nozzle  88  to wash the contaminants from the upper surface and the lower surface of the suction pad  78 . As a result, the present invention can prevent cross-shaped flaws from forming in the wafer  36 . 
     Those skilled in the art will readily observe that numerous modifications and alterations of the device may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bound of the appended claims.