Abstract:
A wafer transfer method using a robot arm for sucking the front-side of the uppermost one of a plurality of wafers stored in a cassette, and for transferring the wafer having a tape adhered to the front-side thereof to a semiconductor tape-peeling device for tape-peeling. Although the wafer warps, the undesired effect that the robot arm crashes any of the wafers can be avoided by using this method.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to a method for transferring wafers in a semiconductor tape-peeling apparatus, and more particularly, to a wafer transfer method which prevents a wafer from being broken during a wafer transfer process. 
     BACKGROUND OF THE INVENTION 
     In a semiconductor manufacturing process, a tape is generally adhered to the front-side (the surface where a wiring pattern is formed) of a wafer before carrying out back-side lapping in order to protect the wiring pattern of the wafer. Usually, the wafer is lapped to the thickness of, for example, 200 μm by back-side lapping. 
     Referring to FIGS. 1 and 2, a conventional semiconductor tape-peeling apparatus includes a first cassette  1 , a second cassette  2 , a robot arm  3 , a flat positioner  6 , and a tape-peeling device  5 . A suction means  7  is provided on the robot arm  3  to clamp and transfer a wafer  4  to be processed in the tape-peeling step. 
     Referring to FIGS. 2 and 3, the first cassette  1  includes twenty five wafer storage slots S 01  to S 25  (slots S 06  to S 25  are not shown). The wafers W 01  to W 25  (wafers W 06  to W 25  are not shown) are stored in the wafer storage slots S 01  to S 25  respectively of the first cassette  1 . A tape (not shown) is adhered to the front-side of each of the wafers W 01  to W 25  that have been processed by back-side lapping. The thickness of each of the wafers W 01  to W 25  is about 200 μm. It should be noted that the dimensions of these parts are not on the same scale, and the relationship among these parts is only shown schematically. 
     The operation method of the semiconductor tape-peeling apparatus are described hereinbelow. It should be noted that 25 wafers W 01  to W 25  are stored in the first cassette  1 , but no wafer is stored in the second cassette  2  having the same construction as the first cassette  1 . The second cassette  2  also includes  25  wafer storage slots S 01  to S 25  (not shown). Referring to FIGS. 2 and 3, the operation method includes the steps of: 
     (1) moving the robot arm  3  to the first cassette  1  so that the suction means  7  enters the first cassette  1 ; 
     (2) sucking the back-side of the wafer Wi(i=01 to 25) by the suction means  7  (it should be noted that the wafer Wi corresponds to the wafer  4  in FIG. 2 at this moment); 
     (3) activating the robot arm  3  to unload the wafer Wi from the first cassette  1 ; 
     (4) transferring the wafer Wi to the flat positioner  6 ; 
     (5) positioning the wafer Wi by the flat positioner  6  so that the flat side or notch of the wafer Wi directs to a predetermined direction; 
     (6) activating the robot arm  3  to suck the back-side of the wafer Wi by the suction means  7 ; 
     (7) transferring the wafer Wi to the tape-peeling device  5 ; 
     (8) peeling the tape on the wafer Wi by the tape-peeling device  5 ; 
     (9) activating the robot arm  3  to suck the back-side of the wafer Wi by the suction means  7 ; 
     (10) transferring the wafer Wi to the second cassette  2 ; 
     (11) storing the wafer Wi to the wafer storage slot Si(i=01 to 25) of the second cassette  2 ; and 
     (12) repeating steps (1) to (11) until the tapes on the wafers W 01  to W 25  are peeled and the wafers W 01  to W 25  are stored in the wafer storage slots S 01  to S 25  respectively. 
     Under the idealized condition, i.e., the condition in which the wafer  4  does not warp, each of the wafers W 01  to W 25  are stored in each of the wafer storage slots S 01  to S 25  as shown in FIG.  3 . The positions of the suction means  7  where the suction means  7  sucks the wafers W 01  to W 25  are illustrated in FIG.  3 . 
     Under the actual condition, when the tapes are adhered to the front-side of the wafers W 01  to W 25 , the tapes are in a tensile mode. Therefore, the tapes adhered to the front-sides of the wafers W 01  to W 25  are capable of warping the center portions of the wafers W 01  to W 25  downwardly. 
     Furthermore, because each of the lapped wafers W 01  to W 25  is so thin that the strength thereof is not enough to resist the tensile force of the tape, and owing to the effect of the high temperature in the manufacturing process, each of the wafers W 01  to W 25  tends to warp easily, as shown in FIG.  4 . As a result, when entering the first cassette  1 , the wafers W 01  to W 25  can be crashed by the suction means  7 . 
     In order to prevent the suction means  7  from crashing any of the wafers W 01  to W 25 , a method for repositioning the suction means  7  is adopted, as shown in FIG.  5 . According to this method, the position of the suction means  7  is adjusted to avoid crashing the wafers W 01  to W 25 . However, because the warpage degrees of the wafers W 01  to W 25  are not uniform, the wafers W 01  to W 25  can still be crashed by the suction means  7 , as shown in FIG.  6 . 
     Referring to FIG. 7, vacuuming conduits  71  are formed on two sides of the suction means  7 . The wafer W 01  is sucked downwardly by the vacuuming conduits  71 . The deformation of the wafer W 01  becomes large, and the wafer W 01  can be damaged. 
     Thus, the above problem cannot be completely solved using the method for repositioning the suction means  7 . Furthermore, an unexpected damage can be caused when using the method for sucking the back-side of the wafer. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a wafer transfer method for use with a semiconductor tape-peeling apparatus so as to prevent the robot arm from crashing the wafer. 
     In accordance with the first aspect of the invention, a method for transferring wafers in a semiconductor tape-peeling apparatus is provided. The semiconductor tape-peeling apparatus comprises: a first cassette for storing a plurality of wafers, each of the wafers having a front-side to which a tape is adhered and a back-side; and a robot arm including a suction means for sucking and transferring the wafers, the wafer transfer method comprises the step of: 
     sucking the front side of the uppermost one of the wafers stored in the first cassette and unloading the wafer. 
     According to the above wafer transfer method, the undesired result that the warped wafers stored in the cassette are crashed by the robot arm can be avoided. 
     The semiconductor tape-peeling apparatus further comprises a flat positioner, a tape-peeling device, and a second cassette, the wafer transfer method further comprises the steps of: transferring the wafer to the flat positioner; positioning the wafer by the flat positioner; sucking the back-side of the wafer by the robot arm; transferring the wafer to the tape-peeling device; peeling the tape on the wafer by the tape-peeling device; sucking the back-side of the wafer; and transferring the wafer to the second cassette. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects and the features of the present invention can be best understood by referring to the following detailed description of a preferred embodiment and the accompanying drawings, wherein: 
     FIG. 1 is a pictorial view showing a semiconductor tape-peeling apparatus; 
     FIG. 2 is a schematic view of the semiconductor tape-peeling apparatus; 
     FIG. 3 is an ideally partial sectional illustration showing the first cassette for storing 25 wafers in the semiconductor tape-peeling apparatus as shown in FIG. 2; 
     FIG. 4 is a practically partial sectional illustration showing the first cassette for storing 25 wafers in FIG. 2; 
     FIG. 5 shows another situation of the first cassette as shown in FIG. 4; 
     FIG. 6 shows yet another situation of the first cassette as shown in FIG. 4; 
     FIG. 7 is an illustration showing the wafer sucked by the suction means in the conventional semiconductor tape-peeling apparatus; 
     FIG. 8 is a schematic illustration showing a semiconductor tape-peeling apparatus in accordance with a preferred embodiment of the invention; 
     FIG. 9 is a practically partial sectional illustration showing the positions of the first cassette, the suction means, and the wafers in the semiconductor tape-peeling apparatus in accordance with the preferred embodiment of the invention; and 
     FIG. 10 is an illustration showing the wafer sucked by the suction means in the semiconductor tape-peeling apparatus in accordance with the preferred embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to FIG. 8, a semiconductor tape-peeling apparatus in accordance with a preferred embodiment of the invention includes a first cassette  1 , a second cassette  2 , a robot arm  3 , a flat positioner  6 , and a tape-peeling device  5 . The robot arm  3  includes a suction means  7  for sucking a wafer  4  and transfers the wafer  4  to a predetermined position for peeling. Referring to FIG. 9, both of the first cassette  1  and the second cassette  2  include 25 wafer storage slots S 25  to S 01  (slots S 20  to S 01  are not shown) for storing the wafers W 25  to W 01  (wafers W 21  to W 01  are not shown). 
     In FIGS. 8 and 9, the first cassette  1 , the second cassette  2 , the robot arm  3 , the wafers W 25  to W 01 , the tape-peeling device  5 , the flat positioner  6 , the suction means  7 , and the wafer storage slots S 25  to S 01  are similar to those in FIGS. 2 and 3. Therefore, a detail description is omitted. 
     By comparing FIGS. 8 and 2, it can be known that the embodiment of the invention is characterized in that the front-sides of the wafers are sucked by the suction means  7 . This characteristic is described hereinbelow. 
     Referring to FIG. 9 again, in order to prevent the suction means  7  from crashing any of the wafers W 25  to W 01 , the method for transferring wafers W 25  to W 01  includes the steps of: 
     (1) activating the robot arm  3  to the first cassette  1  so that the suction means  7  enters the first cassette  1 ; 
     (2) sucking the front-side of the wafer Wi(i=25 to 01) by the suction means  7  (it should be noted that the wafer Wi corresponds to the wafer  4  in FIG. 8 at this moment); 
     (3) activating the robot arm  3  to unload the wafer Wi from the first cassette  1 ; 
     (4) transferring the wafer Wi to the flat positioner  6 ; 
     (5) positioning the wafer Wi by the flat positioner  6  so that the flat side or notch of the wafer Wi directs to a predetermined direction; 
     (6) activating the robot arm  3  to suck the back-side of the wafer Wi by the suction means  7 ; 
     (7) transferring the wafer Wi to the tape-peeling device  5 ; 
     (8) peeling the tape on the wafer Wi by the tape-peeling device  5 ; 
     (9) activating the robot arm  3  to suck the back-side of the wafer Wi by the suction means  7 ; 
     (10) transferring the wafer Wi to the second cassette  2 ; 
     (11) storing the wafer Wi to the wafer storage slot Si(i=25 to 01) of the second cassette  2 ; and 
     (12) repeating steps (1) to (11) for 24 iterations with i=i−1 until the tapes on all the wafers W 25  to W 01  are peeled and the wafers W 25  to W 01  are stored in the wafer storage slots S 25  to S 01 , respectively. 
     By comparing the wafer transfer methods of the invention and the prior art, it can be known that the difference between the methods lies in step (2). By making a start-up from the uppermost wafer to the lowermost wafer, and by sucking the front-side of the wafer and transferring the wafer to the flat positioner  6 , the undesired effect that the suction means  7  crashes the wafer can be entirely avoided. Furthermore, the positioning processes of the robot arm  3  only need to be done once so that the positioning points of the robot arm need not to be adjusted frequently. 
     Referring to FIG. 10, the suction means  7  also includes a plurality of vacuuming conduits  71 . By making use of the vacuuming conduits  71 , the wafer W 25  can be sucked and unloaded, and the deformation of the wafer W 25  can be reduced. Therefore, the excessive deformation and destruction can be avoided. 
     When sucking the wafer by the suction means  7  of the vacuum type, the suction means  7  must be reversible so as to selectively suck the front-side or the back-side of the wafer in the above steps (1) to (12). The reversibility is easily achieved in the conventional robot arm. Therefore, the present invention can be easily carried out. 
     While the invention has been described by way of example and in terms of a preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiment. To the contrary, it is intended to cover various modifications. Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications.