Semiconductor device manufacturing: process – Bonding of plural semiconductor substrates – Subsequent separation into plural bodies
Reexamination Certificate
1998-12-18
2001-04-10
Bowers, Charles (Department: 2823)
Semiconductor device manufacturing: process
Bonding of plural semiconductor substrates
Subsequent separation into plural bodies
C438S405000, C438S409000, C438S455000, C438S960000, C438S977000
Reexamination Certificate
active
06214701
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor substrate having a semiconductor thin film formed at one surface side of a substrate body a separation layer, a thin film semiconductor device formed by using the semiconductor substrate, a manufacturing method of the semiconductor substrate and the thin film semiconductor device, and an anodizing apparatus.
In the technical field of thin film semiconductor devices such as solar batteries, for example, there has been promoted such a research that a semiconductor thin film of silicon is formed on the substrate body of a substrate of silicon (Si) through a porous separation layer, and then the semiconductor thin film is separated from the substrate body through the separation layer to reuse the semiconductor substrate (Japanese Unexamined Patent Publication No. Hei-8-213645). The method can contribute to resource-saving and cost-down. In order to reuse the substrate body as described above, it is required to easily separate the semiconductor thin film and the substrate body from each other, and it has been considered that the separation layer is formed of a porous layer whose porosity is varied.
For example, the thin film semiconductor device can be formed as illustrated in
FIGS. 1A
to
1
E. That is, a substrate body
11
made of p-type single crystal silicon having resistance of 0.01 to 0.02 &OHgr;cm is prepared (see FIG.
1
A); and a porous separation layer
12
is formed at one surface side of the substrate body by anodization (see FIG.
1
B). In the anodization process, current is supplied to the substrate body
11
serving as an anode with electrolyte. As shown in
FIG. 2
, for instance, the current is supplied while an electrolyte tank
41
is disposed at the one surface side of the substrate body
11
and an electrode
42
is disposed in the electrolyte tank
41
. Alternatively, as shown in
FIG. 3
, the current supply is performed while the substrate body
11
is disposed between two electrolyte tanks
43
and
44
and electrodes
45
and
46
are disposed in the electrolyte tanks
43
and
44
, respectively.
In the anodization process, a low-porous layer of low porosity is formed on the surface by supplying current at a low current density of 0.5 to 3 mA/cm
2
for 8 min. Thereafter, a middle-porous layer of intermediate-level porosity is formed inside by supplying current at a middle current density of 3 to 20 mA/cm
2
for 8 min., and then a high-porous layer of high porosity is formed inside the middle-porous layer by supplying current at a high current density of 40 to 300 mA/cm
2
for several seconds. After forming a separation layer
12
, a heat treatment is performed to form a semiconductor thin film
13
on the surface of the separation layer
12
(see FIG.
1
C). Next, an adhesive substrate
15
a
is adhesively attached to the surface of the semiconductor thin film
13
through an adhesive layer
14
a
, and then pulled to separate the semiconductor thin film
13
from the substrate body
11
and transfer it to the adhesive substrate
15
a
(see FIG.
1
D). The separation layer
12
adhering to the separated semiconductor thin film
13
is removed therefrom, and an adhesive substrate
15
b
is adhesively attached to the semiconductor thin film
13
through an adhesive layer
14
b
, thereby achieving a thin film semiconductor device such as a solar battery or the like (see FIG.
1
E). On the other hand, the substrate body
11
is used again to form a semiconductor thin film
13
after the separation layer
12
is removed therefrom.
However, since single crystal silicon constituting the substrate body
11
has a cleavage face, the mechanical strength of the substrate body
11
is low, and the substrate body
11
is easily broken at the cleavage face even by small external force. Upon repetitive use of the substrate body
11
, the mechanical strength of the substrate body
11
is further lowered due to increase of crystal defects through a heat treatment. Furthermore, if the substrate body
11
is handled with no stress in order to increase the recycle frequency or if a temperature increasing time and a temperature decreasing time are set to longer values so that no crystal defect occurs, a long time is needed for the manufacturing process. Accordingly, there has been such a problem that it is difficult to increase the recycle frequency of the substrate body
11
.
In order to reuse the substrate body
11
, the separation layer
12
remaining on the surface of the substrate body
11
must be removed after the semiconductor thin film
13
is separated, thereby keeping a good surface condition. Therefore, an etching treatment, and if occasion demands, a surface polishing or electrolytic polishing treatment are needed. Therefore, the repetitive recycle causes reduction of the thickness of the substrate body
11
, and thus the recycle frequency is limited. In addition, the number of steps such as the surface polishing step, etc. to promote the recycle is increased, so that the manufacturing cost is increased.
In addition, if an elongated substrate
11
is achieved to obtain a large area, a single crystal silicon ingot having a cylindrical shape must be cut out along its longitudinal direction, so that a larger unusable portion occupies in the ingot, that is, there occurs a problem that material is wasted.
As means of solving these problems, it may be considered that the substrate
11
is composed of sapphire. Sapphire has high strength, high rigidity, high wear resistance, high heat resistance, high abrasion resistance, and high chemicals resistance, and it is well known as a material constituting a reusable semiconductor monitor wafer. Also, it can provide large-aperture single crystal, and can provide a large-area thin film semiconductor device. Further, it was reported by Manasevit et al. in 1964 that a single crystal silicon layer can be formed on the surface of sapphire.
However, in order to separate the large-area semiconductor thin film
13
from the substrate body
11
, the separation layer
12
having uniform porosity over the large area must be formed on the surface of the substrate body
11
. The anodization process is suitably used as a method of forming such a separation layer
12
, and it is preferable that a silicon layer is formed on the surface of the substrate body
11
and made porous by the anodization process. However, sapphire is an insulator unlike p-type silicon which has been hitherto used as a constituent material of the substrate body
11
, so that no current can be passed therethrough by a conventional anodizing apparatus shown in
FIG. 2
or
3
and thus it cannot be made porous. That is, such a manufacturing problem occurs when the substrate body
11
of sapphire is used to solve the above problem.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above problem, and has an object to provide a semiconductor substrate and a thin film semiconductor device, a method of manufacturing the same and an anodizing apparatus which can reduce the manufacturing cost and save the resources.
The semiconductor substrate according to the present invention has a substrate body of sapphire and a semiconductor thin film which is formed through a separation layer at one surface side of the substrate body.
The thin film semiconductor device according to the present invention includes the semiconductor thin film which is formed through the separation layer at one surface side of the substrate body of sapphire, and is separated through the separation layer and transferred to an adhesive substrate.
A method of manufacturing a semiconductor substrate according to the present invention comprises a growth layer forming step of forming a porosity layer of semiconductor at one surface side of a substrate body of sapphire, a separation layer forming step of making the porosity layer porous to form a separation layer, and a semiconductor thin film forming step for forming a semiconductor thin film at the opposite side of the separation layer to the substrate body.
A met
Kusunoki Misao
Matsushita Takeshi
Tatsumi Takaaki
Bowers Charles
Brewster William M.
Sonnenschein Nath & Rosenthal
Sony Corporation
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