Semiconductor device manufacturing: process – Semiconductor substrate dicing – Having specified scribe region structure
Reexamination Certificate
2002-02-20
2004-08-03
Fourson, George (Department: 2823)
Semiconductor device manufacturing: process
Semiconductor substrate dicing
Having specified scribe region structure
C438S463000
Reexamination Certificate
active
06770544
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a substrate cutting method and particularly it relates to a substrate cutting method suitable for cutting a semiconductor wafer having a number of elements formed therein to produce semiconductor pellets.
2. Brief Description of the Prior Art
Semiconductor devices are produced, generally, by forming a number of elements (including integrated circuits; hereinafter the same) in a semiconductor wafer sliced from an ingot and polished, cutting said semiconductor wafer along scribed lines between said elements to provide pellets, die-bonding said pellets to a lead frame or the like, making wire-bonding between the elements and the leads, molding them in resin or the like, and dividing said lead frame or the like.
The cutting of said semiconductor wafer is effected, as shown in
FIGS. 10 and 11
, by sticking a wafer W formed with a number of elements P to an adhesive sheet S, holding the adhesive sheet S by suction through suction holes H in an x-y table ST, dicing the wafer along scribed lines between the elements P by a dicer D having a diamond blade B, thereby dividing the individual elements P to provide pellets P.
However, the method of cutting the wafer W using the dicer D by sticking it to the adhesive sheet S has the following problems.
First, cutting by mechanically forming and proliferating material defects by a dicer D results in cracks or chippings produced in the wafer W or elements P during cutting, thus decreasing the yield of the pellets P. Although apparent cracks or chippings can be detected and removed by imaging as by a camera, microcracks or the like produced in the interior are difficult to detect by external imaging, leading to defectives found as by characteristic examination after assembly, thus resulting in wasting not only adhesive agents, heat dissipation plates, etc., during die-bonding, and wires and other materials during wire-bonding but also time, electricity, gas, etc., which result from applying unnecessary process treatments.
Second, cutting by the dicer D inevitably involves cooling since heat of friction is produced. Further, cuttings are produced by dicing and to wash away the cuttings, a large amount of cooling water is required during dicing. Further, because of the cooling water, the device has to be made water-tight and hence the device becomes complicated and expensive.
Third, recently, there has been a growing demand for thin type semiconductor devices, such as solar cells, IC cards, and stack type semiconductor devices. However, thinning the wafer W to cope with such demand for thinning lowers the mechanical strength, so that the wafer W tends to be damaged by the pressing force with which the wafer W is stuck to the adhesive sheet S and moreover the pellets P tend to be damaged when peeled from the adhesive sheet S after cutting.
Therefore, for thinning the pellets P, a production method, referred to as foredicing, as shown in FIGS.
12
(A)-(D) has been developed. This method comprises the steps of (A) forming a number of elements P on the front side a of a relatively thick wafer W having a thickness t
1
(for example, 500 &mgr;m), and sticking the back b to a first adhesive sheet S
1
, (B) dicing the wafer W from the front side a along scribed lines between elements P to form a grove G of predetermined depth, (C) peeling the adhesive sheet S on the back side, and sticking a second adhesive sheet S
2
this time to the front a side, and (D) grinding the back b side to remove the material by an amount corresponding to a thickness t
3
which exceeds the groove G formed by said dicing, thereby forming a thinned back c and at the same time dividing into individual pellets P, thus providing pellets P of desired thickness t
2
(for example, 30-50 &mgr;m)
However, this production method referred to as foredicing is troublesome and greatly increases production costs. Further, when the pellets P are peeled from the adhesive sheet S
2
, the fact remains that the pellets P tend to be damaged.
Fourth, as shown in FIGS.
13
(A)-(D), there has been developed another production method based on a batch adhesive agent layer, comprising the steps of (A) forming an adhesive agent layer AD of solder, resin or the like on the back of the wafer W in advance by batch-processing and sticking the adhesive agent layer AD side to the adhesive sheet S, (B) cutting it into pellets P by dicing, (C) peeling the pellets P from the adhesive sheet S to provide pellets P having the adhesive agent layer AD on the back, and (D) die-bonding the pellets P to a heat dissipation plate R, such as a lead frame, by utilizing the adhesive agent layer AD on the back.
Since this method is not required to feed an adhesive agent to the heat dissipation plate R meticulously during die-bonding, the die-bonding process becomes easier and can be reduced in time. Moreover, the adhesive agent layers of the pellets P bonded to the heat dissipation plate R become uniform in thickness, the height of the bonding position becomes constant in the subsequent wire bonding process. Therefore, the troublesome height adjustment of the bonding tool for each bonding place becomes unnecessary; thus, the production method allows quick, easy and reliable wire bonding. With the production method for thinning the pellets P, referred to as foredicing, described above, however, pellets P having the adhesive agent layer AD on the back cannot be obtained by forming the adhesive agent layer AD of solder, resin or the like on the back of the wafer W in advance. Further, in the case where the adhesive agent layer AD is formed of soft material, such as solder, the adhesive agent clogs the blade B, making the satisfactory dicing impossible.
Fifth, the method using a dicer D comprises the steps of setting the height of the blade B at a position deviated from the wafer W position, horizontally moving an x-y table with the wafer W held thereon by drawing while maintaining the blade height, thereby reciprocating the blade from a position outwardly of one end of the wafer W to a position outwardly of the other end and vice versa to dice the wafer W; therefore, non-square pellets are produced in large numbers around the periphery of the wafer W, making it necessary to sort out square pellets from non-square pellets, which is a troublesome process.
Thus, a method may be contemplated which, rather than mechanically cutting the wafer W by the dicer D having a diamond blade B, comprises the steps, as shown in FIGS.
14
(A)-(C), of (A) irradiating CO
2
laser, YAG laser or other continuous wave laser, or long pulse laser L along scribed lines between the pellets P of a wafer W, (B) melting and scattering a laser-irradiated portion to form a groove G, and (C) repeatedly irradiating laser L to grow the groove G through the back so as to cut the wafer W.
However, since such laser L a continuous wave or has a large pulse width, laser irradiation results in a temperature rise in the vicinity of the laser-irradiated portion by heat conduction, producing a heat strain in the wafer W, which not only forms a cause of cracks or microcracks but also heats and melts up to the vicinity of the portion irradiated with the laser L. And since the melted portion is scattered together by the drastic scattering force of the melt of the portion irradiated with laser L, the width w of the groove G being formed becomes large and nonuniform. Further, since the angle of inclination of the groove G is small, it is necessary to set the scribed line width between the elements P at a large value, resulting in a decrease in the pellet yield. Moreover, the melted wafer material deposits on the edge of the groove G or scatters in the vicinity of the laser-irradiated portion to stick to the electrodes or the like of the elements (pellets) P. Further, since the angle of inclination of the lateral end surface Pa of the pellet P obtained is small, there has been a problem that it sometimes constitutes obstacle depending on the use of the pellets P.
SUMMARY OF THE INVENTION
Acco
Estrada Michelle
Fourson George
J. C. Patents
NEC Machinery Corporation
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