Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Coating selected area
Reexamination Certificate
1998-12-15
2001-07-10
Valentine, Donald R. (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Coating selected area
C205S147000, C205S157000, C205S210000, C205S316000, C205S665000, C204S22400M, C204S225000, C204S297140, C156S150000
Reexamination Certificate
active
06258240
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an anodizing apparatus and method of anodizing a substrate to be processed in an electrolytic solution, and a porous substrate manufactured by the apparatus and method.
Porous silicon was found by A. Uhlir and D. R. Turner who were studying electropolishing of single-crystal silicon biased to a positive potential in an aqueous solution of hydrofluoric acid (to be abbreviated as HF hereinafter).
Later, to exploit the excellent reactivity of porous silicon, application to element isolation in which a thick insulating structure need be formed in manufacturing a silicon integrated circuit was examined, and a full isolation technology using a porous silicon oxide film (FIPOS: Full Isolation by Porous Oxidized Silicon) was developed (K. Imai, Solid State Electron 24, 159, 1981).
Recently, an applied technology to direct bonding in which a silicon epitaxial layer grown on a porous silicon substrate is bonded to an amorphous substrate or single-crystal silicon substrate via an oxide film has been developed (Japanese Patent Laid-Open No. 5-21338).
As another application example, porous silicon which emits light by itself has received a great deal of attention as a so-called photoluminescence or electroluminescence material (Japanese Patent Laid-Open No. 6-338631).
FIG. 5
is a view showing the arrangement of an anodizing apparatus for manufacturing porous silicon by anodizing a silicon substrate, disclosed in Japanese Patent Laid-Open No. 60-94737.
This anodizing apparatus is constituted by arranging anodizing tanks
1802
a
and
1802
b
consisting of Teflon (trade mark of du Pont in U.S.A) having an HF resistance to sandwich a silicon substrate
1801
. The anodizing tanks
1802
a
and
1802
b
have platinum electrodes
1803
a
and
1803
b
, respectively.
The anodizing tanks
1802
a
and
1802
b
have grooves in side walls contacting the silicon substrate
1801
, and
0
-rings
1804
a
and
1804
b
of fluororubber are fitted in these grooves, respectively. The anodizing tanks
1802
a
and
1802
b
and the silicon substrate
1801
are sealed by the
0
-rings
1804
a
and
1804
b
, respectively. The sealed anodizing tanks
1802
a
and
1802
b
are filled with HF solutions
1805
a
and
1805
b
, respectively.
In these anodizing tanks, the silicon substrate does not come into direct contact with the metal electrodes and is hardly contaminated by the metal electrodes. However, since the silicon substrate to be anodized is sealed by the
0
-rings on its upper and lower surfaces, unanodized portions remain in the peripheral regions on the surfaces of the silicon substrate. In addition, since the silicon substrate to be processed itself is directly set and integrated with the anodizing tanks, the silicon substrate cannot be quickly exchanged.
To solve these problems, an anodizing apparatus which supports a silicon substrate at its side surface (beveling) regions has been developed (Japanese Patent Laid-Open No. 5-198556). This anodizing apparatus can anodize all surface regions of the substrate while preventing contamination from the metal electrode. Additionally, in this anodizing apparatus, since a wafer to be processed is fixed in a holder, and the holder is fixed in the anodizing tanks, i.e., the wafer is fixed in the anodizing tank in two steps, operability is largely improved as compared to the conventional apparatus which directly fixes a wafer in the anodizing tank to integrate the wafer with the anodizing tank.
Another anodizing apparatus has been developed, in which a silicon substrate is arranged between a silicon substrate to be processed and a metal electrode, and the electrode component from the metal electrode is shielded by the silicon substrate to prevent contamination due to the electrode component dissolved in the electrolytic solution (Japanese Patent Laid-Open No. 6-275598).
As still another method of preventing contamination from the electrode, a method of directly fixing the electrode to a silicon substrate to be processed via another silicon substrate has been developed (Japanese Patent Laid-Open No. 8-037173).
The anodizing apparatuses disclosed in Japanese Patent Laid-Open Nos. 5-198556, 6-275598, and 8-037173 are very practical because metal contamination rarely occurs, and all surface regions of a substrate can be anodized.
However, an anodizing apparatus having higher productivity is desired. For example, the silicon substrate arranged between the silicon substrate to be processed and the metal electrode is anodized. The silicon substrate must be discarded because it is in direct contact with the metal electrode or is contaminated by the metal component dissolved in the electrolytic solution, so the silicon material is wasted.
In the method of inserting the silicon substrate as an intermediate substrate between the electrode and the silicon substrate to be processed, the intermediate substrate is also dipped in the electrolytic solution and anodized. Hence, the intermediate substrate must be frequently exchanged, and the silicon material is wasted.
SUMMARY OF THE INVENTION
The present invention has been made to solve the above problems, and has as its object to provide an anodizing apparatus and method capable of efficiently performing anodizing while preventing wafer contamination.
It is another object of the present invention to provide a porous substrate manufactured by the apparatus and method.
In order to solve the above problems and achieve the above object, an anodizing apparatus according to the present invention has the following arrangement.
There is provided an anodizing apparatus for anodizing a substrate to be processed in an electrolytic solution, comprising a process tank for storing the electrolytic solution, the process tank having an opening in a wall, a negative electrode arranged in the process tank to oppose the opening, and a positive electrode contacting a surface of the substrate to be processed which is arranged to close the opening from an inside of the process tank, the surface being open outside the process tank through the opening.
A porous substrate according to the first aspect of the present invention has the following arrangement.
There is provided a porous substrate manufactured by the anodizing apparatus of any one of claims
1
to
14
.
An anodizing method according to the present invention has the following steps.
There is provided an anodizing method of anodizing a substrate to be processed in an electrolytic solution, comprising the setting step of setting the substrate to be processed inside a process tank having an opening on a wall to close the opening, the supply step of supplying the electrolytic solution into the process tank, the contacting step of bringing a positive electrode into contact with a portion of the substrate to be processed, which is open outside the process tank through the opening, and the process step of flowing a current between the positive electrode and a negative electrode arranged to oppose the substrate to be processed in the process tank to anodize the substrate to be processed.
A porous substrate according to the second aspect of the present invention has the following structure.
There is provided a porous substrate manufactured by the anodizing method of any one of claims
16
to
17
.
Other objects and advantages besides those discussed above shall be apparent to those skilled in the art from the description of a preferred embodiment of the invention which follows. In the description, reference is made to accompanying drawings, which form a part hereof, and which illustrate an example of the invention. Such example, however, is not exhaustive of the various embodiments of the invention, and therefore reference is made to the claims which follow the description for determining the scope of the invention.
REFERENCES:
patent: 3345274 (1967-10-01), Schmidt
patent: 4069121 (1978-01-01), Baud et al.
patent: 4447306 (1984-05-01), Ushio et al.
patent: 5437777 (1995-08-01), Kishi
patent: 563625 A2 (1993-10-01), None
patent: 0 597 428 A1 (1
Matsumura Satoshi
Yamagata Kenji
Canon Kabushiki Kaisha
Morgan & Finnegan , LLP
Valentine Donald R.
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