Method for producing semiconductor chips

According to a method for producing semiconductor chips, first grooves are formed in a semiconductor wafer at a front surface, dividing the semiconductor water into a plurality of regions, each region including a single device or an integrated circuit; a first metallization layer is formed in the first grooves; the semiconductor wafer is thinned to a desired thickness from the rear surface of the wafer; second grooves are formed in the semiconductor wafer at the rear surface at positions opposite the first grooves, exposing the first metallization layer; a second metallization layer is formed in the second grooves; a metal layer for heat radiation is formed on the rear surface of the wafer but not on the second metallization layer; and the first and second metallization layers in the first grooves are cut with a dicing blade to produce a plurality of semiconductor chips. Burrs of the metallization layers caused by the dicing are small and never protrude beyond the rear surface of the chip, resulting in a reliable junction between the chip and a mounting substrate in a subsequent die-bonding process.

FIELD OF THE INVENTION 
The present invention relates to a method for producing high power 
semiconductor devices and, more particularly, to a method for dividing a 
semiconductor wafer into chips. 
BACKGROUND OF THE INVENTION 
FIG. 3(a) is a plan view illustrating a semiconductor wafer in which a 
plurality of ICs are formed in chequerboard pattern, and FIG. 3(b) is a 
cross section of a portion of FIG. 3(a). A surface protection film 11 is 
disposed on each chip region 10 containing an IC. Regions 12 where the 
surface protection films 11 are absent are dicing lines. 
FIG. 4 illustrates a semiconductor wafer used in production of high output 
semiconductor devices. In FIG. 4, the wafer 1 is as thin as 20.about.30 
microns and a plated heat sink (hereinafter referred to as PHS) 20 
comprising Au or the like and having a thickness of 40.about.60 microns is 
disposed on the rear surface of the wafer 1 to improve heat radiation of 
the device. In production of usual devices, the PHS 20 is present except 
for regions opposite to the dicing lines 12. In case of high powered 
output devices, however, since the wafer is thin for the reason described 
above, the PHS 20 covers all the rear surface of the wafer 1 to prevent 
ICs contained in the wafer from being damaged by warping of the wafer 
which is caused by a difference in expansion coefficients between the 
wafer and the PHS. 
A method for dividing the semiconductor wafer of FIG. 4 into chips by 
dicing is illustrated in FIGS. 5(a)-5(c). 
Initially, as illustrated in FIG. 5(a), a dicing tape 40 is attached to the 
rear surface of the PHS 20. Then, as illustrated in FIG. 5(b), a dicing 
saw 30 cuts the wafer 1 along the dicing line 12. The dicing is carried 
out along all dicing lines 12 until the tip of the dicing saw 30 reaches 
into the dicing tape 40, whereby the wafer 1 is divided into chips as 
shown in FIG. 5(c). At this time, a burr 21 20.about.30 microns long is 
produced on the rear surface of the chip due to the ductility of the PHS 
20. 
After removing the dicing tape 40, each chip is bonded to a mount substrate 
50 with solder 60 as shown in FIG. 6. Since the burr 21 protrudes from the 
rear surface of the chip, the solder 60 is not favorably adhered to the 
entire surface of the PHS 20, resulting in a faulty assembly. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a method for producing 
semiconductor chips in which burrs caused by dicing do not adversely 
affect the subsequent diebonding process. 
Other objects and advantages of the present invention will become apparent 
from the detailed description given hereinafter; it should be understood, 
however, that the detailed description and specific embodiment are given 
by way of illustration only, since various changes and modifications 
within the spirit and the scope of the invention will become apparent to 
those skilled in the art from this detailed description. 
According to a first aspect of the present invention, in a method for 
producing semiconductor chips, first grooves are formed in a semiconductor 
wafer at a front surface of the semiconductor wafer, dividing the 
semiconductor wafer into a plurality of regions each region including a 
single device or an integrated circuit, first metallization layers are 
formed in the first grooves, the semiconductor wafer is thinned to a 
desired thickness from the rear surface of the wafer, second grooves are 
formed in the semiconductor wafer at the rear surface of the semiconductor 
wafer at positions opposite the first grooves so that the bottom surfaces 
of the first metallization layers are exposed, second metallization layers 
are formed in the second grooves, metal layers for heat radiation are 
formed on the rear surface of the wafer but not on the second 
metallization layers, and the first and second metallization layers in the 
first grooves are cut with a dicing blade to produce a plurality of 
semiconductor chips. 
According to the second aspect of the present invention, in a method for 
producing semiconductor chips, first grooves are formed in a semiconductor 
wafer at a front surface of a semiconductor wafer, diving the 
semiconductor wafer into a plurality of regions each region including a 
single device or an integrated circuit, first metallization layers are 
formed in the first grooves, the semiconductor wafer is thinned to a 
thickness thicker than a desired thickness from the rear surface of the 
wafer, second grooves are formed in the semiconductor wafer at the rear 
surface of the semiconductor wafer at positions opposite the first grooves 
so that the bottom surfaces of the first metallization layers are exposed, 
second metallization layers are formed in the second grooves, portions of 
the second metallization layers on the rear surface of the wafer are 
removed and the wafer is thinned to the desired thickness, metal layers 
for heat radiation are formed on the rear surface of the wafer but not on 
the second metallization layers, and the first and second metallization 
layers in the first grooves are cut with a dicing blade to produce a 
plurality of semiconductor chips. 
In these methods, the first and second metallization layers are much 
thinner than the semiconductor chip, burrs of the metallization layers 
caused by the dicing never protrude over the rear surface of the chip and 
never adversely affect the subsequent die-bonding process.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIGS. 1(a)-1(h) are cross-sectional views illustrating a method for 
producing semiconductor chips in accordance with a first embodiment of the 
present invention. In the figures, the same reference numerals as in FIGS. 
5(a)-5(c) designate the same or corresponding parts. Reference numerals 2 
and 4 designate chip separating grooves covered with metallization layers 
3 and 5, respectively. Reference numeral 6 designates a PHS disposed on 
the rear surface of the substrate 1. Reference numeral 7 designates burrs 
of the metallization layers 3 and 5. Reference numeral 8 designates a 
glass plate and numeral 9 designates wax. In addition; the size of the 
groove 2 and its vicinity is made larger in the drawing than actual size 
for easy understanding. 
A description is given of the production method. 
First of all, a GaAs substrate 1 about 600 microns thick, in which desired 
components or circuits have been produced, is prepared. Then, as 
illustrated in FIG. 1(a), portions of the GaAs substrate 1 are selectively 
removed by wet or dry etching to form first chip separating grooves 2 
5.about.15 microns deep. 
As illustrated in FIG. 1(b), the inside of the first grooves 2 are 
metallized using conventional Au plating method, forming first 
metallization layers 3 about 10 microns thick. 
As illustrated in FIG. 1(c), a glass plate 8 is adhered to the upper 
surface of the substrate 1 using wax 9, and the substrate 1 is thinned 
from the rear surface by polishing or the like to a thickness a little 
thicker than a desired thickness. Then, as illustrated in FIG. 1(d), 
portions of the substrate 1 opposite to the first grooves 2 are 
selectively etched by wet or dry etching until the metallization layers 3 
are exposed, forming second chip separating grooves 4. 
Thereafter, as illustrated in FIG. 1(e), photoresist films 10 are 
selectively formed on the rear surface of the substrate 1 except for the 
second grooves 4, and the inside of the second grooves 4 are metallized 
using a conventional Au plating method using the photoresist films 10 as a 
mask, forming second metallization layers 5 about 10 microns thick which 
increase the strength of the wafer. At this time, the metallization layers 
5 extend onto the rear surface of the substrate 1 because of the limit of 
precision in the formation of the photoresist films 10. 
After removing the photoresist films 10, as illustrated in FIG. 1(f), 
portions of the metallization layers 5 extending on the rear surface of 
the substrate 1 are removed by polishing while reducing the thickness of 
the substrate 1 to the desired thickness, i.e., 20.about.30 microns. 
Thereafter, as illustrated in FIG. 1(g), PHS layers 6 40.about.60 microns 
thick are selectively formed on the rear surface of the GaAs substrate 1 
except for the second metallization layers 5. Even if the PHS 6 is formed 
in contact with the metallization layer 5, since the element production 
region of the substrate 1 is covered with the surface protection film 11 
and is not in contact with the metallization layer 3, no leakage occurs. 
Then, as illustrated in FIG. 1(h), the glass plate 8 is removed from the 
wafer by melting the wax 9, and dicing is carried out with a dicing tape 
40 attached to the rear surface of the wafer, to separate the chips from 
each other. Since the metallization layers 3 and 5 connecting the 
respective chips to each other are about 20 microns thick in total, a burr 
7 caused by the dicing is only 10 microns in size, which is significantly 
smaller than the thickness of the chip with the PHS 6. Therefore, the burr 
7 never protrudes over the rear surface of the chip, with a result that a 
reliable junction is achieved between the chip and a mounting substrate in 
the subsequent die-bonding process. 
According to the first embodiment of the present invention, the strength of 
the wafer before dicing is maintained by the metallization layers 3 and 5. 
In addition, since the metallization layers 3 and 5, which connect the 
chips in the wafer to each other, are cut during dicing, the burr of the 
metallization layers caused by the dicing is small and does not protrude 
over the rear surface of the chip, resulting in a reliable junction in the 
subsequent die-bonding process. 
FIGS. 2(a)-2(g) are cross-sectional views illustrating a method for 
producing semiconductor chips in accordance with a second embodiment of 
the present invention. This method is different from the above-described 
method of the first embodiment only in that portions of the second 
metallization layers 5 extending on the rear surface of the substrate 1 
are not removed and the PHS 6 is formed thereon. 
A description is given of the production method. 
Steps illustrated in FIGS. 2(a) and 2(b) are identical to the steps already 
described with respect to FIGS. 1(a) and 1(b) and, therefore, repeated 
description is not necessary. 
Turning to FIG. 2(c), a glass plate 8 is adhered to the upper surface of 
the substrate 1 using wax 9, and the substrate 1 is thinned a desired 
thickness. Preferably, the thickness is 20.about.30 microns. 
As illustrated in FIG. 2(d), portions of the substrate 1 opposite to the 
first grooves 2 are removed by wet or dry etching to expose the 
metallization layers 3, forming second chip separating grooves 4. 
As illustrated in FIG. 2(e), photoresist films 10 are selectively formed on 
the rear surface of the substrate 1 except for the second grooves 4, and 
the insides of the second grooves 4 are metallized using a conventional Au 
plating method, forming second metallization layers 5 about 10 microns 
thick which increase the strength of the wafer. At this time, the 
metallization layers 5 extend onto the rear surface of the substrate 1 
because of the limit of precision in forming the photoresist films 10. 
As illustrated in FIG. 2(f), the photoresist films 10 are removed and PHS 
layers 6 40.about.60 microns thick are selectively formed on the rear 
surface of the GaAs substrate 1 except for the second metallization layers 
5. At this time, projections 61 are on the rear surface of the PHS 6 are 
as high as the portions of the metallization layers 5 remaining on the 
rear surface of the substrate 1. 
As illustrated in FIG. 1(g), the glass plate 8 is removed from the wafer by 
melting the wax 9, and dicing is carried out with a dicing tape 40 
attached to the rear surface of the wafer to separate the chips from each 
other. 
According to the second embodiment of the present invention, since the step 
of removing the portions of the second metallization layers 5 extending 
onto the rear surface of the substrate can be dispensed with, the 
production is simplified as compared with the first embodiment. Although a 
projection 61 of about 10 microns in size is formed on the rear surface of 
the chip, it does not become a large obstacle during die-bonding process 
when a very high precision in assembly is not required. 
While in the above-described first and second embodiments GaAs is employed 
as the material of the substrate 1, the present invention can also be 
applied to cases where other semiconductor materials, such as AlGaAs, InP, 
Si, and the like are employed with the same effects as described above. 
While in the above-described first and second embodiments gold is employed 
as the material of the metallization layers 3 and 5, a metal having a 
lower ductility than gold, for example, nickel, may be employed, further 
reducing the size of the burrs. 
As is evident from the foregoing description, in a method for producing 
semiconductor chips according to the present invention, first grooves are 
formed in a semiconductor wafer at a front surface of a semiconductor 
wafer, dividing the semiconductor wafer into a plurality of regions each 
region including a single device or an integrated circuit, and first 
metallization layers are formed in the first grooves. Second grooves are 
formed in the semiconductor wafer at the rear surface of the semiconductor 
wafer at positions opposite to the first grooves so that the bottom 
surfaces of the first metallization layers are exposed, and second 
metallization layers are formed in the second grooves. Thus, the wafer is 
divided into a plurality of chips connected to each other by the first and 
second metallization layers. Then, the metallization layers in the first 
grooves are cut with a dicing blade to separate the chips from each other. 
Burrs of the metallization layer caused by the dicing are small and never 
protrude over the rear surface of the chip, resulting in a reliable 
junction between the chip and a mounting substrate in a subsequent 
die-bonding process.