Semiconductor device manufacturing: process – Packaging or treatment of packaged semiconductor – Making plural separate devices
Reexamination Certificate
1999-10-27
2001-06-12
Lee, Eddie C. (Department: 2815)
Semiconductor device manufacturing: process
Packaging or treatment of packaged semiconductor
Making plural separate devices
C438S114000, C438S113000, C438S122000, C438S462000, C438S464000, C438S465000
Reexamination Certificate
active
06245596
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor device having a heat dissipation metal layer (PHS: Plated Heat Sink) provided on the back side thereof, and a method of producing the semiconductor device wherein devices are separated by laser cutting.
2. Description of the Related Art
FIG.
3
A through
FIG. 3k
show a method of producing a semiconductor device having a heat dissipation metal layer of the prior art disclosed in PCT application No. JP/96/02758.
According to such a method, a first separation groove
3
is formed by etching the surface of a GaAs substrate
1
, on which semiconductor elements have been formed in advance, by using a photoresist layer
2
as a mask (FIG.
3
A), then a first metal layer is formed in the first separation groove
3
by plating or another process (FIG.
3
B).
Then the GaAs substrate
1
is coated with a wax
5
and is bonded onto a carrier substrate
6
such as glass plate or sapphire plate, with the GaAs substrate
1
being polished on the back side to reduce the thickness thereof to about 20 to 30 &mgr;m (FIG.
3
C).
Next, a photoresist layer
14
is formed on the back side of the GaAs substrate
1
in a first patterning step so that an opening is provided on the back of the first separation groove
3
(FIG.
3
D). The back side of the GaAs substrate
1
is etched by using the photoresist layer
14
as a mask until the bottom of a metal layer
4
in the first separation groove is exposed, thereby forming a second separation groove
33
(FIG.
3
E).
Then, after removing the photoresist layer
14
, a plated feeder layer
7
is formed over the entire back surface of the GaAs substrate
1
(FIG.
3
F). A second metal layer
16
made of the same metal as the first metal layer is formed in the second separation groove
33
by plating, using a photoresist layer
15
formed in a second patterning step as a mask (FIG.
3
G).
Then, a photoresist layer
17
having a width smaller than that of the second separation groove
33
is formed in the second separation groove
33
, using a third patterning step, and a gold PHS layer
8
is formed on the back side by an electrolytic plating method, using the photoresist layer
17
as a mask (FIG.
3
H). The GaAs substrate
1
is then separated from the carrier substrate
6
(
FIG. 2I
) and an expand film
10
is attached to the PHS layer
8
(FIG.
3
J).
Finally, the first and the second metal layers in the first separation groove are severed in the first separation groove
3
side by laser cutting operation using YAG laser or the like, thereby separating the elements to obtain a semiconductor device forming the fused metal mass
12
at the periphery of the semiconductor device (FIG.
3
K).
According to the method of producing the semiconductor device as described above where the semiconductor devices connected with each other by means of the first and the second metal layers are separated by laser cutting of the metal layers, since the semiconductor elements are connected with each other by the two metal layers, the connection are resistant to bending and cracking during the producing process, while deposition of foreign matters on the element surface and defective appearance of the elements can be reduced thereby improving the production yield of the semiconductor devices, compared to a method of separating devices by dicing.
In the conventional method, three patterning steps are required from the first through the third patterning steps after the polishing step in which the GaAs substrate
1
is turned into a thin film of about 20 to 30 &mgr;m in thickness. In case the patterning steps are carried out a plurality of times, the wax
5
softens due to the heat generated during baking in the patterning processes and removal of photoresist, thus causing thermal stresses in the GaAs substrate
1
and mechanical stresses in the GaAs substrate
1
during contact exposure, thereby making cracks or other defects likely to occur in the GaAs substrate
1
. Thus there has been a limitation to the improvement in the production yield and it has been difficult to reduce the production costs due to the complicated producing process.
While the use of the two metal layers has an advantage that bending and cracking of the metal layer can be reduced during the production steps, the thick film may cause poor appearance of the cut portion and the generation of devices having poor appearance has been impeding the improvement in the production yield.
There has also been such a problem that the first metal layer and the second metal layer peel off each other when the second metal layer is formed in an electrolytic plating process.
SUMMARY OF THE INVENTION
Hence, an object of the present invention is to provide a method of producing a semiconductor device wherein number of patterning processes is reduced, laser cutting produces a better profile, while the first and the second metal layers are prevented from separating from each other, and a semiconductor device produced by the method.
Hence, the present inventors have found the followings thereby accomplishing the present invention. First, the number of patterning steps can be reduced by employing flat exposure step for photoresist without carrying out mask alignment. Second, better profile can be obtained by forming the metal layer which connects semiconductor devices with each other from the first layer of metal having a low melting point and the second layer of metal having a high melting point, and cutting off the first metal layer and the second metal layer successively from the first metal layer side. Third, the second metal layer can be prevented from peeling off by preventing the oxidation of a plated feeder layer in the step of plating the second metal layer.
The present invention provides a method of producing a semiconductor device, which comprises forming a first separation groove and a first metal layer covering the surface of the first separation groove on the surface of a semiconductor substrate; thinning the semiconductor substrate from the back surface thereof; forming a second separation groove wherein the first metal layer is exposed and a second metal layer covering the surface of the second separation groove on the back side of the first separation groove; and cutting off the first metal layer and the second metal layer from the first metal layer side by means of laser; wherein the second separation groove is formed by etching the semiconductor substrate until the first metal layer is exposed by using the heat dissipating metal layer formed in a region of the back surface of the semiconductor substrate except for the back surface of the first separation groove as a mask, and that the first metal layer and the second metal layer have a reflectivity of 80% or lower for the laser light.
Having the reflectivity of 80% or lower for the laser light makes it possible to keep the decrease in the efficiency of laser cutting due to the reflection of laser light to such an extent that is acceptable in practice.
The melting point of the second metal layer is preferably higher than that of the first metal layer.
This is because it is made possible that the two metal layers connecting the semiconductor devices with each other are cut off one by one by means of laser beam and, even when the total thickness of the two metal layers is large, cut face of the metal layer which has been cut off by the laser beam can be made in a favorable linear profile thereby preventing the decrease of production yield due to defective appearance.
The second metal layer is preferably formed in such a process as: after the second metal layer is formed to cover the second separation groove surface and the heat dissipating metal layer surface, a photoresist, applied over the entire surface of the second metal layer in such a way that the second separation groove is embedded, is removed by exposing the entire surface so that the portion of photoresist filling the second separation groove remains, and the second metal layer located on the hea
Kosaki Katsuya
Matsuoka Hiroshi
Tamaki Masahiro
Diaz José R.
Lee Eddie C.
Leydig , Voit & Mayer, Ltd.
Mitsubishi Denki & Kabushiki Kaisha
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