Patent Publication Number: US-11031276-B2

Title: Wafer expanding method and wafer expanding apparatus

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a wafer expanding method and apparatus for expanding a wafer having a plurality of rectangular devices respectively formed in a plurality of separate regions defined by a plurality of division lines, thereby increasing the spacing between any adjacent ones of the devices. 
     Description of the Related Art 
     A plurality of devices such as integrated circuits (ICs) and large-scale integrated circuits (LSIs) are formed on the front side of a wafer so as to be separated from each other by a plurality of division lines. The wafer thus having the plural devices on the front side is divided along the division lines by using a dicing apparatus or a laser processing apparatus to obtain a plurality of individual device chips. The device chips thus obtained from the wafer are used in various electrical equipment such as mobile phones and personal computers. 
     In dividing the wafer, the wafer is supported through an adhesive tape to a ring frame. The wafer attached to the adhesive tape is divided into the individual device chips, and the adhesive tape is expanded by an expanding apparatus to increase the spacing between any adjacent ones of the individual device chips attached to the adhesive tape, thereby facilitating a pickup operation for picking up each device chip from the adhesive tape (see Japanese Patent Laid-open No. 2002-334852, for example). 
     SUMMARY OF THE INVENTION 
     In the case that a plurality of rectangular devices are formed on the wafer so as to be separated by a plurality of division lines, the number of exposed portions of the adhesive tape between the rectangular devices in the direction where the shorter sides of the rectangular devices extend is larger than that in the direction where the longer sides of the rectangular devices extend. Accordingly, when the wafer is expanded uniformly both in the direction along the shorter sides and in the direction along the longer sides, the spacing between the adjacent devices in the direction along the shorter sides becomes smaller than the spacing between the adjacent devices in the direction along the longer sides, so that the spacing between the devices is not uniform. 
     This problem may also occur in the case of forming a modified layer inside the wafer along each division line and next applying an external force to the adhesive tape attached to the wafer, thereby dividing the wafer along each division line to obtain the individual device chips (see Japanese Patent Laid-open No. 2005-129607, for example). 
     It is therefore an object of the present invention to provide a wafer expanding method which can equalize the spacing between the adjacent devices in the direction along the shorter sides and the spacing between the adjacent devices in the direction along the longer sides in expanding the adhesive tape attached to the wafer having the plural rectangular devices. 
     It is another object of the present invention to provide a wafer expanding apparatus for performing the wafer expanding method described above. 
     In accordance with an aspect of the present invention, there is provided a wafer expanding method for expanding a wafer having a plurality of rectangular devices respectively formed in a plurality of separate regions defined by a plurality of division lines, thereby increasing spacing between any adjacent ones of the devices, each rectangular device having a pair of shorter sides and a pair of longer sides, the wafer expanding method including a wafer preparing step of supporting the wafer through an adhesive tape to a ring frame having an inside opening for accommodating the wafer in a condition where an annular exposed portion of the adhesive tape is defined between an outer circumference of the wafer and an inner circumference of the ring frame, the wafer being divided along each division line or having division start points inside the wafer along each division line; a jig preparing step of preparing an annular jig having an elliptical opening, the elliptical opening having a shorter portion for restricting a width of the annular exposed portion in a first direction where the shorter sides of the devices extend to a first width and a longer portion for restricting the width of the annular exposed portion in a second direction where the longer sides of the devices extend to a second width larger than the first width; a fixing step of mounting the ring frame on a cylindrical frame fixing member, next mounting the annular jig on the ring frame, and next fixing the ring frame and the annular jig to the cylindrical frame fixing member; and an expanding step of operating a cylindrical pushing member having an outer circumference corresponding to the outer circumference of the wafer to push up the annular exposed portion of the adhesive tape and thereby lift the wafer away from the ring frame after performing the fixing step, thereby expanding the annular exposed portion and increasing the spacing between the adjacent devices, by which when the wafer is lifted away from the ring frame by operating the cylindrical pushing member in the expanding step, the annular exposed portion in the first direction is attached to the shorter portion of the annular jig to thereby restrict the width of the annular exposed portion to the first width, and at the same time the annular exposed portion in the second direction is attached to the longer portion of the annular jig to thereby restrict the width of the annular exposed portion to the second width. 
     In accordance with another aspect of the present invention, there is provided a wafer expanding apparatus for expanding a wafer having a plurality of rectangular devices respectively formed in a plurality of separate regions defined by a plurality of division lines, thereby increasing spacing between any adjacent ones of the devices, each rectangular device having a pair of shorter sides and a pair of longer sides, the wafer expanding apparatus including a cylindrical frame fixing member; a cylindrical pushing member provided inside the cylindrical frame fixing member so as to be vertically movable relative to the cylindrical frame fixing member; a wafer unit including a ring frame supporting the wafer through an adhesive tape in a condition where an annular exposed portion of the adhesive tape is defined between an outer circumference of the wafer and an inner circumference of the ring frame, the ring frame having an inside opening for accommodating the wafer, the ring frame being adapted to be mounted on the cylindrical frame fixing member, the wafer being divided along each division line or having division start points inside the wafer along each division line; an annular jig adapted to be mounted on the ring frame, the annular jig having an elliptical opening, the elliptical opening having a shorter portion for restricting a width of the annular exposed portion in a first direction where the shorter sides of the devices extend to a first width and a longer portion for restricting the width of the annular exposed portion in a second direction where the longer sides of the devices extend to a second width larger than the first width, the annular exposed portion in the first direction being attached to the shorter portion by operating the cylindrical pushing member, the annular exposed portion in the second direction being attached to the longer portion by operating the cylindrical pushing member; and fixing means fixing the ring frame and the annular jig to the cylindrical frame fixing member. 
     According to the wafer expanding method of the present invention, the fixing step is performed to fix the annular jig to the upper surface of the ring frame fixed to the cylindrical frame fixing member, in which the annular jig has the shorter portion and the longer portion, so as to make the spacing between the rectangular devices uniform. Accordingly, the annular exposed portion of the adhesive tape in the first direction can be expanded more than the annular exposed portion in the second direction, in which a relatively large number of devices are arranged in the first direction and a relatively small number of devices are arranged in the second direction. Accordingly, the spacing between the adjacent devices in the first direction and the spacing between the adjacent devices in the second direction can be made equal to each other in expanding the wafer. 
     According to the wafer expanding apparatus of the present invention, the annular jig is fixed to the upper surface of the ring frame fixed to the cylindrical frame fixing member, in which the annular jig has the shorter portion and the longer portion, so as to make the spacing between the rectangular devices uniform. Accordingly, the annular exposed portion of the adhesive tape in the first direction can be expanded more than the annular exposed portion in the second direction, in which a relatively large number of devices are arranged in the first direction and a relatively small number of devices are arranged in the second direction. Accordingly, the spacing between the adjacent devices in the first direction and the spacing between the adjacent devices in the second direction can be made equal to each other in expanding the wafer. 
     The above and other objects, features, and advantages of the present invention and the manner of realizing them will become more apparent, and the invention itself will best be understood from a study of the following description and appended claims with reference to the attached drawings showing a preferred embodiment of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a perspective view illustrating two kinds of wafers and a ring frame with an adhesive tape attached thereto; 
         FIG. 1B  is a perspective view illustrating a wafer unit formed by supporting one of the wafers illustrated in  FIG. 1  through the adhesive tape to the ring frame; 
         FIG. 2  is a perspective view of a wafer expanding apparatus according to a preferred embodiment of the present invention; 
         FIG. 3A  is a plan view of an annular jig included in the wafer expanding apparatus illustrated in  FIG. 2 ; 
         FIG. 3B  is a cross section taken along the line A-A in  FIG. 3A  (sectional view of a shorter portion); 
         FIG. 3C  is a cross section taken along the line B-B in  FIG. 3A  (sectional view of a longer portion); 
         FIG. 4  is a perspective view illustrating a frame fixing step using the wafer expanding apparatus illustrated in  FIG. 2 ; 
         FIG. 5A  is a cross section taken along the line C-C in  FIG. 4 ; 
         FIG. 5B  is a cross section taken along the line D-D in  FIG. 4 ; 
         FIG. 6A  is a cross section corresponding to  FIG. 5A , illustrating an expanding step; 
         FIG. 6B  is a cross section corresponding to  FIG. 5B , illustrating the expanding step; and 
         FIG. 7  is a plan view of an essential part of the wafer expanded in the expanding step, illustrating the condition where the spacing between the adjacent devices in the first direction and the spacing between the adjacent devices in the second direction are made equal to each other. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A preferred embodiment of the wafer expanding method and the wafer expanding apparatus according to the present invention will now be described with reference to the drawings. In the wafer expanding method according to the present invention, a wafer preparing step is first performed to prepare a wafer supported through an adhesive tape to a ring frame having an inside opening for accommodating the wafer, the wafer being divided along a plurality of division lines or being formed with a division start point inside the wafer along each division line. 
     As the wafer to be prepared in the wafer preparing step, a wafer  2  or  2 ′ illustrated in  FIG. 1  may be used. Both the wafer  2  and the wafer  2 ′ are formed of a suitable semiconductor material such as silicon (Si), and have a circular disk shape. The wafer  2  has a front side  2   a  and a back side  2   b . A plurality of crossing division lines  4  are formed on the front side  2   a  of the wafer  2  to thereby define a plurality of rectangular separate regions where a plurality of rectangular devices  6  such as ICs and LSIs are respectively formed. That is, the plural devices  6  are previously formed on the front side  2   a  of the wafer  2  so as to be separated by the division lines  4 . On the other hand, the wafer  2 ′ has a front side  2   a ′ and a back side  2   b ′. A plurality of division lines  4 ′ are formed on the front side  2   a ′ of the wafer  2 ′ to thereby define a plurality of rectangular separate regions where a plurality of rectangular devices  6 ′ such as ICs and LSIs are respectively formed. That is, the plural devices  6 ′ are previously formed on the front side  2   a ′ of the wafer  2 ′ so as to be separated by the division lines  4 ′. The division lines  4 ′ are composed of a plurality of crossing division lines in one part and a plurality of zigzag division lines in the other part. 
     The wafer preparing step will now be described in more detail with reference to  FIG. 1B . As illustrated in  FIG. 1B , a ring frame  8  having a circular inside opening  8   a  for accommodating the wafer  2  is used. A circular adhesive tape  10  is previously attached at its peripheral portion to the ring frame  8 . That is, the circular inside opening  8   a  of the ring frame  8  is closed by the central portion of the adhesive tape  10 . The back side  2   b  of the wafer  2  is attached to the adhesive tape  10  supported to the ring frame  8  in such a manner that the wafer  2  is located in the inside opening  8   a  of the ring frame  8 . Thus, the wafer  2  is supported through the adhesive tape  10  to the ring frame  8 , thereby forming a wafer unit  11 . As a modification, the front side  2   a  of the wafer  2  may be attached to the adhesive tape  10 . Thereafter, a dicing apparatus (not illustrated) having a rotatable cutting blade is used to cut the wafer  2  along each division line  4 , thereby dividing the wafer  2  along each division line  4 . As another method, a laser processing apparatus (not illustrated) for applying a laser beam may be used to perform ablation to the wafer  2  along each division line  4 , thereby dividing the wafer  2  along each division line  4 . In another case, a division start point such as a modified layer may be formed inside the wafer  2  along each division line  4  by using a laser processing apparatus to apply a laser beam to the wafer  2  along each division line  4 , in which the strength of the wafer  2  can be reduced at this division start point and the wafer  2  can therefore be broken along each division line  4 . As illustrated in  FIG. 1B , an annular exposed portion  10   a  of the adhesive tape  10  is defined between the outer circumference of the wafer  2  and the inner circumference of the ring frame  8 . In  FIG. 1B , a cut groove for dividing the wafer  2  along each division line  4  or the division start point formed inside the wafer  2  along each division line  4  is not illustrated for convenience of illustration. 
     In the case of using the wafer  2 ′ having the devices  6 ′ illustrated in  FIG. 1A , the wafer  2 ′ is first attached to the adhesive tape  10  supported to the ring frame  8  in a similar manner. Thereafter, a laser processing apparatus is used to apply a laser beam along each division line  4 ′, thereby dividing the wafer  2 ′ along each division line  4 ′ or forming a division start point inside the wafer  2 ′ along each division line  4 ′. 
     In the following description, the wafer  2  supported through the adhesive tape  10  to the ring frame  8  is used to perform the wafer expanding method according to this preferred embodiment. After performing the wafer preparing step, a frame fixing step is performed to fix the ring frame  8  to a cylindrical frame fixing member having an upper end for mounting the ring frame  8 . The frame fixing step may be performed by using a wafer expanding apparatus  12  (see  FIG. 2 ) according to this preferred embodiment. 
     As illustrated in  FIG. 2 , the wafer expanding apparatus  12  essentially includes a cylindrical frame fixing member  14  and a cylindrical pushing member  16 . The cylindrical frame fixing member  14  functions to fix the ring frame  8  supporting the wafer  2  through the adhesive tape  10 , the ring frame  8  having the inside opening  8   a  for accommodating the wafer  2 , the wafer  2  having been already divided along each division line  4  or having been already formed with the division start point inside the wafer  2  along each division line  4 . The cylindrical pushing member  16  has an outer circumference corresponding to the outer circumference of the wafer  2  and functions to push up the adhesive tape  10  to thereby lift the wafer  2  away from the ring frame  8  and expand the annular exposed portion  10   a  defined between the outer circumference of the wafer  2  and the inner circumference of the ring frame  8 . 
     The outer diameter and the inner diameter of the cylindrical frame fixing member  14  correspond to the outer diameter and the inner diameter of the ring frame  8 , respectively, so that the ring frame  8  can be mounted on the upper end of the cylindrical frame fixing member  14 . More specifically, the outer diameter of the cylindrical frame fixing member  14  is equal to the outer diameter of the ring frame  8 , and the inner diameter of the cylindrical frame fixing member  14  is equal to the inner diameter of the ring frame  8 . A plurality of clamps  18  for fixing the ring frame  8  to the upper end of the cylindrical frame fixing member  14  are provided on the outer circumference of the cylindrical frame fixing member  14  so as to be arranged at given intervals in the circumferential direction of the cylindrical frame fixing member  14 . 
     The cylindrical pushing member  16  is provided inside the cylindrical frame fixing member  14 . The outer circumference of the cylindrical pushing member  16  corresponds to the outer circumference of the wafer  2 . More specifically, the inner diameter of the cylindrical pushing member  16  is slightly larger than the diameter of the wafer  2 . The cylindrical pushing member  16  is vertically movable relative to the cylindrical frame fixing member  14  by any suitable driving means such as an air cylinder and a motor-driven cylinder. When the driving means is operated to raise the cylindrical pushing member  16  relative to the cylindrical frame fixing member  14 , the cylindrical pushing member  16  pushes up the adhesive tape  10  supporting the wafer  2  to thereby lift the wafer  2  away from the ring frame  8  fixed to the cylindrical frame fixing member  14 , so that the annular exposed portion  19   a  of the adhesive tape  10  defined between the outer circumference of the wafer  2  and the inner circumference of the ring frame  8  is expanded by the upper end of the cylindrical pushing member  16 . Although not illustrated, a plurality of rollers are preferably provided on the upper end of the cylindrical pushing member  16  so as to be arranged annularly, thereby reducing a frictional resistance between the pushing member  16  and the adhesive tape  10 , so that the expansion of the adhesive tape  10  attached to the wafer  2  can be promoted. 
     Referring to  FIG. 2  and  FIGS. 3A to 3C , the wafer expanding apparatus  12  further includes an annular jig  20  adapted to be provided on the upper surface of the ring frame  8  mounted on the upper end of the cylindrical frame fixing member  14 . The annular jig  20  functions to make the spacing between the rectangular devices  6  uniform. The annular jig  20  has an elliptical opening  20   c . The elliptical opening  20   c  has a shorter portion  20   a  extending along the minor axis and a longer portion  20   b  extending along the major axis. The shorter portion  20   a  functions to restrict the width of the annular exposed portion  10   a  of the adhesive tape  10  in such a manner that when the cylindrical pushing member  16  is raised to push up the adhesive tape  10  and lift the wafer  2  away from the ring frame  8 , the annular exposed portion  10   a  in the direction where the shorter sides of the rectangular devices  6  extend is attached to the shorter portion  20   a . The longer portion  20   b  functions to restrict the width of the annular exposed portion  10   a  of the adhesive tape  10  in such a manner that when the wafer  2  is lifted away from the ring frame  8  as mentioned above, the annular exposed portion  10   a  in the direction where the longer sides of the rectangular devices  6  extend is attached to the longer portion  20   b , in which the width of the annular exposed portion  10   a  is restricted to a width larger than that by the shorter portion  20   a . The length of the shorter portion  20   a  along the minor axis is smaller than the length of the longer portion  20   b  along the major axis ( 20   a &lt; 20   b ). 
     The frame fixing step will now be described in more detail with reference to  FIG. 4 . In the frame fixing step, the ring frame  8  supporting the wafer  2  through the adhesive tape  10  is first mounted on the upper end of the cylindrical frame fixing member  14 . Thereafter, the annular jig  20  is mounted on the upper surface of the ring frame  8 . At this time, as illustrated in  FIG. 4 , the positional relation between the wafer  2  and the jig  20  is adjusted so that the shorter portion  20   a  of the jig  20  (i.e., the minor axis of the elliptical opening  20   c ) becomes parallel to the direction where the shorter sides of the rectangular devices  6  extend (this direction will be hereinafter referred to as a first direction) and that the longer portion  20   b  of the jig  20  (i.e., the major axis of the elliptical opening  20   c ) becomes parallel to the direction where the longer sides of the rectangular devices  6  extend (this direction will be hereinafter referred to as a second direction). Thereafter, the plural clamps  18  of the cylindrical frame fixing member  14  are operated to press the upper end of the jig  20 , thereby fixing the jig  20  and the ring frame  8  to the upper end of the cylindrical frame fixing member  14  as illustrated in  FIG. 4 . 
     After performing the frame fixing step, an expanding step is performed to push up the adhesive tape  10  attached to the wafer  2  by raising the cylindrical pushing member  16  having an outer circumference slightly larger in size than the outer circumference of the wafer  2 , thereby lifting the wafer  2  away from the ring frame  8  and expanding the annular exposed portion  10   a  of the adhesive tape  10  defined between the outer circumference of the wafer  2  and the inner circumference of the ring frame  8 , so that the spacing between any adjacent ones of the devices  6  is increased. 
     The expanding step will now be described in more detail with reference to  FIGS. 5A to 6B .  FIGS. 5A and 5B  illustrate an initial position of the cylindrical pushing member  16  before starting the expanding step. In this initial position, the upper end of the cylindrical pushing member  16  is at substantially the same level as that of the upper end of the cylindrical frame fixing member  14 . In the expanding step, the cylindrical pushing member  16  is raised from this initial position relative to the cylindrical frame fixing member  14  by operating the driving means. Accordingly, the annular exposed portion  10   a  of the adhesive tape  10  is pushed up by the upper end of the cylindrical pushing member  16 , and the wafer  2  supported through the adhesive tape  10  to the ring frame  8  is accordingly lifted away from the ring frame  8  fixed to the cylindrical frame fixing member  14 . As a result, the annular exposed portion  10   a  defined between the outer circumference of the wafer  2  and the inner circumference of the ring frame  8  is expanded. As illustrated in  FIGS. 5A and 5B , the inner diameter of the cylindrical pushing member  16  is slightly larger than the diameter of the wafer  2  before performing the expanding step. 
     When the wafer  2  is lifted away from the ring frame  8  by operating the cylindrical pushing member  16  as described above, the annular exposed portion  10   a  in the first direction of the devices  6  is attached to the shorter portion  20   a  of the jig  20 , so that the width of the annular exposed portion  10   a  in the first direction of the devices  6  is restricted to a relatively small width as a first width by the shorter portion  20   a . At the same time, the annular exposed portion  10   a  in the second direction of the devices  6  is attached to the longer portion  20   b  of the jig  20 , so that the width of the annular exposed portion  10   a  in the second direction of the devices  6  is restricted to a second width larger than the first width by the longer portion  20   b.    
     In this manner, the width of the annular exposed portion  10   a  in the first direction of the rectangular devices  6  is restricted to the first width that is a relatively small width, and at the same time the width of the annular exposed portion  10   a  in the second direction of the rectangular devices  6  is restricted to the second width larger than the first width, in which a relatively large number of devices  6  are arranged in the first direction and a relatively small number of devices  6  are arranged in the second direction. Accordingly, the annular exposed portion  10   a  in the first direction of the devices  6  as restricted by the shorter portion  20   a  of the jig  20  can be expanded more than the annular exposed portion  10   a  in the second direction of the devices  6  as restricted by the longer portion  20   b  of the jig  20 . As a result, the amount of expansion of the wafer  2  in the first direction of the devices  6  becomes larger than the amount of expansion of the wafer  2  in the second direction of the devices  6  as illustrated in  FIGS. 6A and 6B . That is, after expansion of the wafer  2 , the length L 1  of the wafer  2  in the first direction of the devices  6  becomes larger than the length L 2  of the wafer  2  in the second direction of the devices  6 . In other words, the shape of the wafer  2  after expansion becomes elliptical in such a manner that the major axis is parallel to the first direction and the minor axis is parallel to the second direction. Further, the expansion of the adhesive tape  10  attached to each device  6  is suppressed as compared with the expansion of the adhesive tape  10  exposed between the devices  6 . Accordingly, as illustrated in  FIG. 7 , the spacing S 1  between the devices  6  in the first direction and the spacing S 2  between the devices  6  in the second direction can be made equal to each other after expansion of the wafer  2 . 
     The present invention is not limited to the details of the above described preferred embodiment. The scope of the invention is defined by the appended claims and all changes and modifications as fall within the equivalence of the scope of the claims are therefore to be embraced by the invention.