Patent Publication Number: US-8110481-B2

Title: Method of segmenting semiconductor wafer

Description:
TECHNICAL FIELD 
     The present invention relates to a method of segmenting a semiconductor wafer into a plurality of chips by means of plasma etching. 
     BACKGROUND ART 
     As a semiconductor wafer has been thinner and thinner, instead of a method of segmenting a semiconductor wafer into a plurality of chips using a cutting tool such as a blade or the like, where there may occur defects or cracks in the semiconductor wafer, which may lead to low yield, a plasma etching method has recently attracted a great attention. In this plasma etching method, a semiconductor wafer whose circuit forming side is attached with a protective sheet is hermetically sealed in a plasma treating chamber and is segmented into a plurality of chips by subjecting the semiconductor wafer to plasma etching from other side of the semiconductor wafer, the protective sheet serving to prevent the chips from being dispersed and protect circuits (see Patent Document 1).
     [Patent Document 1] Japanese Unexamined Patent Application Publication No. 2005-191039   

     DISCLOSURE OF THE INVENTION 
     Technical Problem 
     After the semiconductor wafer is subjected to the plasma etching to be segmented into the plurality of chips, the semiconductor wafer can not keep a flat state, and there occur chippings (defects or cracks) due to contact between adjacent chips by bend or deflection of the protective sheet, which may result in low yield. It is expected that this problem becomes more serious as a gap between adjacent chips becomes smaller and smaller due to narrower etching width. 
     It is therefore an object of the invention to provide a method of segmenting a semiconductor wafer into a plurality of chips, which is capable of preventing chippings of the chips. 
     Technical Solution 
     According to an aspect of the invention, there is provided a method of segmenting a semiconductor wafer into a plurality of chips by means of plasma etching, a protective sheet being provided on a circuit forming surface of the semiconductor wafer, including the steps of segmenting a segmentation region, which is partitioned in an inner side of a ring-shaped region partitioned in the circumference of the semiconductor wafer, into the plurality of chips by cutting the segmentation region along a plurality of perpendicular cutting lines; and partitioning the ring-shaped region into four independent regions by cutting the ring-shaped region along two partition lines extending in parallel to the perpendicular cutting lines from the center of the semiconductor wafer. 
     Preferably, the method further includes the step of masking a region which is in a rear side of the semiconductor wafer and lies in the outside of the regions corresponding to the cutting lines and the partition line. The masked semiconductor wafer is subjected to plasma etching treatment to segment the segmentation region into the plurality of chips and partition the ring-shaped region into the four independent regions. 
     Preferably, the method further includes the steps of: attaching a continuous extensible maintenance sheet to the rear side of the semiconductor wafer in which the segmentation region is segmented into the plurality of chips and the ring-shaped region is partitioned into the four independent regions; peeling the protective sheet; and expanding a gap between adjacent chips and a gap between the chips and the ring-shaped region by extending the maintenance sheet from an inner side to an outer side of the semiconductor wafer. 
     According to another aspect of the invention, there is provided a method of segmenting a semiconductor wafer into a plurality of chips by means of plasma etching, a protective sheet being provided in a circuit forming surface of the semiconductor wafer, including the steps of: segmenting a segmentation region, which is partitioned in an inner side of a ring-shaped region partitioned in the circumference of the semiconductor wafer, into the plurality of chips by cutting the segmentation region along a plurality of perpendicular cutting lines; and partitioning the ring-shaped region into more than five independent regions by cutting the ring-shaped region along partition lines. The partition lines include at least two partition lines extending in parallel to the perpendicular cutting lines from the center of the semiconductor wafer, and a region whose circumferential length is more than ⅛ of the entire circumferential length of the semiconductor wafer is necessarily included in each of the regions partitioned along the two partition lines. 
     Preferably, the method further includes the step of masking a region which is in a rear side of the semiconductor wafer and lies in the outside of the regions corresponding to the cutting lines and the partition line. The masked semiconductor wafer is subjected to plasma etching treatment to segment the segmentation region into the plurality of chips and partition the ring-shaped region into more than five independent regions. 
     Preferably, the method further includes the steps of: attaching a continuous extensible maintenance sheet to the rear side of the semiconductor wafer in which the segmentation region is segmented into the plurality of chips and the ring-shaped region is partitioned into more than five independent regions; peeling the protective sheet; and expanding a gap between adjacent chips and a gap between the chips and the ring-shaped region by extending the maintenance sheet from an inner side to an outer side of the semiconductor wafer. 
     Advantageous Effects 
     According to the present invention, since bend of the maintenance sheet is suppressed as at least an edge of the semiconductor wafer is not segmented, generation of chippings due to contact between segmented chips is reduced, which results in increase of a yield. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a plan view of a segmented semiconductor wafer according to an embodiment of the present invention. 
         FIG. 2  is a sectional view taken along line A-A in  FIG. 1 . 
         FIG. 3  shows side sectional views for illustrating steps of a method of segmenting a semiconductor wafer by means of plasma etching according to an embodiment of the present invention. 
         FIG. 4  is a side sectional view showing a state where a semiconductor wafer is carried in a plasma treating chamber, according to an embodiment of the present invention. 
         FIG. 5  is a side sectional view showing a state where a semiconductor wafer is carried out of a plasma treating chamber, according to an embodiment of the present invention. 
         FIG. 6  is a side sectional view showing a state where a semiconductor wafer is absorbed to a robot hand, according to an embodiment of the present invention. 
         FIG. 7  shows side sectional views showing a state where a semiconductor wafer is mounted on a pickup stage, according to an embodiment of the present invention. 
         FIG. 8  is a plan view showing a state where a semiconductor wafer is mounted on a pickup stage, according to an embodiment of the present invention. 
         FIG. 9  is a plan view of a segmented semiconductor wafer according to another embodiment of the present invention. 
         FIG. 10  is a plan view of a segmented semiconductor wafer according to still another embodiment of the present invention. 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Embodiments of the present invention will be hereinafter described with reference to the drawings.  FIG. 1  is a plan view of a segmented semiconductor wafer according to an embodiment of the present invention and  FIG. 2  is a sectional view taken along line A-A in  FIG. 1 . A semiconductor wafer  1  is a disk-like plate formed by slicing an ingot, which is made by crystal-growing silicon, germanium, gallium-arsenic or the like into a cylindrical shape, at thickness of 0.5 mm to 1.5 mm. A diameter of the semiconductor wafer  1  is generally 5 inches (125 mm), 8 inches (200 mm) or 12 inches (300 mm). A circuit pattern (integrated circuit) is formed on one surface (circuit forming surface) of the semiconductor wafer  1  and is segmented into a plurality of parts, i.e., chips (IC chips)  2  by means of plasma etching. A protective sheet  3  is attached to the circuit forming surface and serves to prevent the chips  2  from being dispersed and prevent the circuit forming surface from being damaged when the circuit pattern is segmented. 
     The semiconductor wafer  1  is partitioned into a circumferential ring-shaped region  1   a  and a segmentation region  1   b  placed in the inner side of the ring-shaped region  1   a . The semiconductor wafer  1  included in the segmentation region  1   b  is cut into the form of a lattice along a plurality of perpendicular cutting lines  4  and is segmented into a plurality of chips  2 . On the other hand, the semiconductor wafer  1  included in the ring-shaped region  1   a  is cut along two partition lines  5  extending in parallel to the cutting lines  4  from the center O of the semiconductor wafer  1  and is partitioned into four independent regions. 
       FIG. 3  shows side sectional views for illustrating steps of a method of segmenting the semiconductor wafer. First, (a) the protective sheet  3  is attached to the circuit forming surface of the semiconductor wafer  1 , and (b) the semiconductor wafer  1  is polished until it has a predetermined thickness. Next, (c) regions, which are in a rear side of the circuit forming surface of the semiconductor wafer  1  and lie in the outside of the cutting lines  4  and the partition lines  5 , are masked with an etching-resistant resist  6 . The resist  6  is for masking a portion that will not be etched in a later plasma treating process. The resist  6  masks the entire rear surface of the semiconductor wafer  1  and then portions of the resist  6 , which correspond to the cutting lines  4  and the partition lines  5 , are removed. Next, (d) the semiconductor wafer  1  is subjected to plasma treatment, the semiconductor wafer  1  is cut along the cutting lines  4  and the partition lines  5 , the segmentation region  1   b  is segmented into the plurality of chips  2 , and the ring-shaped region  1   a  is partitioned into the four independent regions, and (e) the remaining resist  6  is ashed by ozone or plasma in vapor to be completely removed from the semiconductor wafer  1 . 
       FIG. 4  is a side sectional view showing a state where a semiconductor wafer is carried in a chamber for plasma treatment. A chamber  7  forms a sealed space therein, an electrode  9  connected to a high frequency power supply  8  is arranged in a lower side of the chamber  7 , and a grounded electrode  10  opposing the electrode  9 . The lower electrode  9  also serves as a support of the semiconductor wafer  1 . The semiconductor wafer  1  is supported on the electrode  9  with the protective sheet  3  directing downward. When a high frequency voltage is applied to the electrode  9  in a state where the chamber  7  is decompressed below a predetermined pressure and is filled with gas for plasma generation, the semiconductor wafer  1  is cut by plasma etching along the cutting lines  4  and the partitions  5 , both of which are not masked with the resist  6 . 
       FIG. 5  is a side sectional view showing a state where the semiconductor wafer is carried out of the chamber for plasma treatment. After the chamber  7  is opened to the air, a door  7   a  of a side wall of the chamber  7  is opened to form an opening  7   b  and a robot hand  11  is advanced into the chamber  7  through the opening  7   b  to vacuum-hold the semiconductor wafer  1  from its upper side and carry it out of the chamber  7  with it held to the robot hand  11 . 
       FIG. 6  is a side sectional view showing a state where the semiconductor wafer is vacuum-held to the robot hand. Although the circumferential ring-shaped region  1   a  of the plasma-etched semiconductor wafer is partitioned into the four independent regions, since each independent region has an area sufficiently larger than the individual chips  2 , it has a function of preventing the protective sheet  3  located in an inner side from being bent by its rigidity. On this account, even if there occurs an unbalance of a suction force due to shock, vibration or change of a negative pressure when the robot hand  11  vacuum-holds and carries the semiconductor wafer  1 , the bend of the protective sheet  3  is minimized, thereby preventing adjacent chips  2  from contacting with each other, which results in reduction of a risk to generate chippings (defects and cracks). 
     In the semiconductor wafer  1  carried out of the chamber  7  by the robot hand  11 , an extensible maintenance sheet  12  is attached to a rear side of the circuit forming surface and then the protective sheet  3  is peeled out to expose the circuit forming surface, as shown in a part (f) in  FIG. 3 . A shape maintenance ring  13  having high rigidity is provided in a portion surrounding the plurality of chips  2  of the maintenance sheet  12  in order to maintain flatness and tension of the maintenance sheet  12 . 
       FIG. 7  shows side sectional views showing a state where the semiconductor wafer  1  is mounted on a pickup stage. (a) The maintenance sheet  12  is placed on a cylindrical expand member  14  provided in the pickup stage with the semiconductor wafer  1  directing upward, (b) the shape maintenance ring  13  is pressed down at an outer side of the expand member  14  and the maintenance sheet  12  is extended in a direction (arrow a) from the inner side to the outer side of the semiconductor wafer  1 . As shown in  FIG. 8 , since the ring-shaped region  1   a  surrounding the plurality of chips  2  is partitioned into the four independent regions along the perpendicular partition lines, when the maintenance sheet  12  is extended from the inner side to the outer side of the semiconductor wafer  1 , the four independent regions of the ring-shaped region  1   a  are moved (arrow b) in such a manner that they are alienated from each other, the maintenance sheet  12  located at the inner side of the ring-shaped region  1   a  is extended from the inner side to the outer side of the semiconductor wafer  1 , and a gap between adjacent chips  2  and a gap between the chips  2  and the ring-shaped region  1   a  are widened. (c) With the gap between adjacent chips  2  widened for pickup of the chips, the chips  2  are absorbed by a nozzle  15  from the circuit forming surface, and at the same time, the chips  2  are pushed up by an ejector  16  from a rear side of the maintenance sheet  12  to pick up the chips  2  from the maintenance sheet  12 . 
     In the above-described semiconductor wafer  1 , although the circumferential ring-shaped region  1   a  is partitioned into the four uniform independent regions along the two partition lines  5  extending in the direction in parallel to the cutting lines  4  from the center O of the semiconductor wafer  1 , the ring-shaped region  1   a  may be partitioned into more than five independent regions. In this case, it is a required condition that a region whose circumferential length is more than ⅛ of the entire circumferential length of the semiconductor wafer  1  is necessarily included in each of the four independent regions. Since the region having such a circumferential length has an area sufficiently larger than the individual chips  2 , bend of the protective sheet  3  can be effectively suppressed when such a region is arranged in balance in the circumference of the semiconductor wafer  1 . 
       FIGS. 9 and 10  are plan views of a segmented semiconductor wafer according to another embodiment of the present invention. In a semiconductor wafer  17  shown in  FIG. 9 , a circumferential ring-shaped region  17   a  is partitioned into eight independent regions by cutting the ring-shaped region  17   a  along two partition lines  18  extending in parallel to cutting lines  4  from the center O of the semiconductor wafer  17  and two partition lines  19  extending in a direction making an angle of 45 degrees with the two partition lines  18 . The eight independent regions are equally divided such that their circumferential length corresponds to ⅛ of the entire circumferential length of the semiconductor wafer. Although the eight independent regions each have an area corresponding to ½ of an area of each of the four independent regions, since the eight independent regions have the area sufficiently larger than the individual chips  2  and are arranged in balance every center angle of 45 degrees of the semiconductor wafer  17 , they can sufficiently exhibit a function of preventing the protective sheet located at the inner side from being bent. In addition, by partitioning the ring-shaped region  17   a  into the eight independent regions, since a degree of freedom of an extension direction of the maintenance sheet located in the inner side of the ring-shaped region  17   a  is increased, it is possible to expand the chips  2  with more suitable intervals. 
     In a semiconductor wafer  20  shown in  FIG. 10 , a circumferential ring-shaped region is partitioned into 12 independent regions by cutting the ring-shaped region along two partition lines  21  extending in parallel to cutting lines  4  from the center O of the semiconductor wafer  20  and four partition lines  22  similarly extending from the center O. While regions  20   a  of the 12 independent regions, which are partitioned along the partition lines  21  and the partition lines  22 , have a small area, regions  20   b  partitioned along the partition lines  22  and the partition lines  22  have a circumferential length which is more than ⅛ of the entire circumferential length of the semiconductor wafer and have an area sufficiently larger than the individual chips  2 . In addition, since the regions  20   b  are arranged in balance every center angle of 90 degrees of the semiconductor wafer  20 , they can sufficiently exhibit a function of preventing the protective sheet located at the inner side from being bent. 
     INDUSTRIAL APPLICABILITY 
     According to the present invention, since the bend of the maintenance sheet is suppressed as at least an edge of the semiconductor wafer is not segmented, generation of chippings due to contact between segmented chips is reduced, which results in increase of a yield, and thus the present invention is useful in a field of semiconductor chip mounting.