Semiconductor device manufacturing: process – Formation of semiconductive active region on any substrate – On insulating substrate or layer
Reexamination Certificate
2001-01-19
2002-10-22
Elms, Richard (Department: 2824)
Semiconductor device manufacturing: process
Formation of semiconductive active region on any substrate
On insulating substrate or layer
C438S478000, C438S400000, C136S255000, C252S501100, C252S510000
Reexamination Certificate
active
06468884
ABSTRACT:
This invention is based on patent application No. 20005-12618 Pat. filed in Japan, the contents of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method of forming a silicon-contained crystal thin film which can be used, e.g., in substrates for a solar battery, a liquid crystal display and a semiconductor device.
2. Description of the Background Art
In recent years, attention has been focused on a hydrogen ion injection peeling method as a method for forming a silicon-contained crystal thin film on a support substrate. The hydrogen ion injection peeling method is utilized for producing an SOI (Silicon On Insulator) substrate, a solar battery substrate and others.
An example of a method of forming an SOI substrate by the hydrogen ion injection peeling method will now be described with reference to FIG.
9
.
First, a thermal oxide film (SiO
2
film)
911
is formed on an Si crystal substrate (see a step (B) in FIG.
9
).
Then, hydrogen ions are injected into the Si crystal substrate
91
from the side of the thermal oxide film (see a step (C) in FIG.
9
). By an ion acceleration voltage, an injection depth of hydrogen ions is controlled. In a later step, the crystal substrate
91
is separated (divided) in a position
913
where hydrogen ions are injected as described above. For this purpose, the hydrogen ions are injected at an injection density of about 5×10
16
ions/cm
2
or more.
Then, a support substrate
92
is laid on the ion-injected surface (thermal oxide film) of Si crystal substrate
91
, and they are heated so that many voids or fine holes
914
are formed in the ion-implanted position
913
of the Si crystal substrate
91
(see a step (D) in FIG.
9
). The hydrogen injected into the Si crystal substrate
91
is gasified by the heat so that the voids
914
are formed. The heating for forming the voids
914
is performed for several minutes at a temperature of about 350° C.-600° C. The neighboring voids are connected together. As a result of this connection and others, a weak or fragile portion having a layer-like form is formed in the void-formed portion of the Si crystal substrate
91
. Since the ion-injected surface (thermal oxide film) of the Si crystal substrate
91
is subjected to a pressure applied by support substrate
92
, this suppresses such a situation that the surface portion of the substrate
91
is partially peeled off due to the pressure by the hydrogen gas. Peeling which produces crater-like portions of several micrometers or less in diameter would occur in the surface portion of the crystal substrate
91
unless a pressure is applied to the ion-injected surface of the Si crystal substrate
91
by the foregoing manner or another appropriate manner.
Then, the Si crystal substrate
91
and the support substrate
92
are heated and adhered together at a high temperature of about 1000° C. or more.
Thereafter, the Si crystal substrate
91
is divided along the voids
914
(see a step (E) in FIG.
9
). Thereby, an Si crystal thin film
9121
, which was a portion of the crystal substrate
91
, is left on the SiO
2
film
911
. In this manner, the SOI substrate, i.e., the support substrate
92
, on which the Si crystal thin film
9121
and the SiO
2
film (insulating film)
911
are layered, is formed. An Si crystal substrate portion
9122
other than the above can be used again in the next process of forming the SOI substrate.
However, the following problems arise in the above method of forming the silicon-contained crystal thin film on the support substrate, e.g., by implanting ions into the silicon-contained crystal substrate to form the voids.
One of the problems is that the foregoing method cannot efficiently form a relatively thick silicon-contained crystal thin film of tens of micrometers in thickness on the support substrate without difficulty. This will be described below in greater detail.
In the case where the substrate provided with the Si crystal thin film is to be utilized for manufacturing a solar battery, the Si crystal thin film must have a thickness of 7 pm or more, and more preferably, about 10 &mgr;m for achieving a high photoelectric conversion.
The thickness of the Si crystal thin film formed on the support substrate corresponds to the ion implantation depth in the hydrogen ion implanting processing, and can be increased by increasing the ion implantation depth. By increasing the ion acceleration voltage in the ion implantation process, the ion implantation depth can be increased within a limited extent. For implanting hydrogen ions to a position at a depth of, e.g., 10 &mgr;m from the surface (ion-injected surface) of the crystal substrate, the ion implantation is performed with an acceleration voltage of about 700 keV. However, for achieving the implantation depth of about 10 &mgr;m or more, a large-scale ion implanting device is required so that the ion implanting process requires a high cost. For suppressing excessive increase in temperature of the crystal substrate subjected to the ion implantation, it is necessary to suppress an ion beam current, and therefore it is impossible to perform efficiently the ion implantation achieving a required density.
According to the above manner, it is difficult to produce a relatively thick silicon-contained crystal thin film with high efficiency and low cost.
Another problem also arises. If particles are present on the ion-injected surface of the Si-contained crystal substrate, peeling of minute portions and/or cracks occur in the surface layer of the crystal substrate when heating the substrate for forming the voids. This will be further described below with reference to FIG.
10
.
As can be seen in a step (A) shown in
FIG. 10
, a particle
93
is present on an ion-injected surface
915
of crystal substrate
91
, and is interposed between the support substrate
92
and the crystal substrate
91
. In this case, the ion-injected surface
915
has a portion, which is not pressed by the support substrate
92
. When the heating for forming the voids is performed in the above state, peeling of minute portions and/or cracks may occur in and around the portion, which is not pressed by the support substrate
92
, of the surface layer of crystal substrate
91
, as can be seen in a step (B) shown in FIG.
10
. Such minute peeled portions and cracks, which are present during the formation of voids, will cause a defect in the final product, i.e., the substrate provided with the crystal thin film. This lowers the productivity of the silicon-contained crystal thin films, and increases the manufacturing cost and selling price of the silicon-contained crystal thin film.
For example, it can be envisaged that the foregoing problem due to particles can be suppressed by executing the respective steps in a clean room of a high cleanliness. However, the clean room of a high cleanliness, which is required for overcoming the above problem due to particles, requires high construction, maintenance and operation costs, and thus increases the manufacturing cost of the substrate with the silicon-contained crystal thin film.
SUMMARY OF THE INVENTION
Accordingly, an object of the invention is to provide a method of forming a silicon-contained crystal thin film, which allows formation of the silicon-contained crystal thin film with high productivity and low cost.
More specifically, an object of the invention is to provide a method of forming a crystal thin film containing silicon, and particularly a method of forming a silicon-contained crystal thin film, which allows formation of the silicon-contained crystal thin film of a relatively large thickness with high efficiency.
Another object of the invention is to provide a method of forming a crystal thin film containing silicon on a support substrate, and particularly a method of forming the silicon-contained crystal thin film on the support substrate, which allows formation of the silicon-contained crystal thin film of a relatively large thickness with high efficiency.
Still another object of
Miyake Koji
Ogata Kiyoshi
Arent Fox Kintner Plotkin & Kahn
Elms Richard
Luu Pho M.
Nissin Electric Co. Ltd.
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