Semiconductor device manufacturing: process – Chemical etching
Reexamination Certificate
2000-03-16
2002-06-25
Smith, Matthew (Department: 2825)
Semiconductor device manufacturing: process
Chemical etching
C438S455000, C438S459000, C438S691000, C438S745000, C438S753000
Reexamination Certificate
active
06410436
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method of cleaning a porous body, and a process for producing a porous body, a non-porous film or a bonded substrate. More particularly, this invention belongs to a technical field of a production process in which a method of cleaning a porous body after anodization can be improved to form a non-porous film having a uniform thickness.
2. Related Background Art
In the following description, porous silicon is used as an example of the porous body.
Porous silicon was discovered by A. Uhlir and D. R. Turner in the course of their research related to the electrolytic polishing of single-crystal silicon biased to positive potential, in an aqueous hydrogen fluoride (hereinafter often simply “HF”) solution (i.e., hydrofluoric acid).
Since then, utilizing porous silicon's high reactivity, studies were conducted related to its application to the step of interelement isolation that requires formation of a thick insulating material in a silicon integrated-circuit fabrication process, and a technique of FIPOS (full isolation by porous oxidized silicon) has been developed in which device elements are full isolated by a porous silicon oxide film (K. Imai, Solid-state Electron 24, 159, 1981).
Recently, in, e.g., Japanese Patent No. 2608351 and U.S. Pat. No. 5,371,037, there was proposed a technique in which a silicon epitaxial layer grown on a porous silicon substrate is bonded to the surface of an amorphous substrate or single-crystal silicon substrate, optionally via an oxide film, to obtain an SOI (silicon on insulator) substrate.
Besides, Japanese Patent Application Laid-Open No. 6-338631 discloses a technique that uses porous silicon as a light-emitting material such as what is called a photoluminescent material or an electroluminescent material.
Anodization is commonly used to form porous bodies.
As an example of the formation of porous bodies, an apparatus for producing porous silicon by subjecting a silicon substrate to anodization is shown in FIG.
18
.
The apparatus or unit shown in
FIG. 18
is the one disclosed in Japanese Patent Application Laid-Open No. 60-94737. This anodization apparatus comprises anodization baths
61
and
62
made of an HF-resistant material TEFLON (a trademark of Du Pont, U.S.A.) which are so provided as to hold between them a silicon substrate W as a treatment target. The baths
61
and
62
are provided with a negative electrode
63
and a positive electrode
64
, respectively. The baths
61
and
62
have grooves in the sidewalls coming into contact with the silicon substrate W. In these grooves, sealing members such as O-rings
65
and
66
made of fluorine rubber are respectively fitted. Thus, the baths
61
and
62
holding the silicon substrate W are sealed with the O-rings
65
and
66
. The baths
61
and
62
sealed in this way are filled with aqueous HF solutions
67
and
68
, respectively.
Other anodization apparatuses have also been proposed.
Meanwhile, with regard to methods of cleaning porous semiconductor substrates after the anodization has been effected, an example is reported in Japanese Patent Application Laid-Open No. 10-64870, but it appears that very few other examples have been reported.
For the cleaning of porous bodies structurally having a high surface activity, liquid chemicals that are commonly used to remove organic matter, particularly metal deposits, such as an aqueous solution of sulfuric acid and hydrogen peroxide (hereinafter “SPM”), an aqueous solution of ammonia and hydrogen peroxide (hereinafter “SC-
1
”) and an aqueous solution of hydrochloric acid and hydrogen peroxide (hereinafter “SC-
2
”), cannot be used. Accordingly, a cleaning method has been proposed in which pure water is used with ultrasonic energy instead of the liquid chemicals to remove foreign matter adhering to porous layer surfaces, as disclosed in Japanese Patent Application Laid-Open No. 10-64870.
FIG. 19
is a flow chart of the steps of such a cleaning method. A porous body, after it has been anodized in step STP
1
, is cleaned in step STP
2
with pure water and ultrasonic energy, followed by drying in step STP
3
.
The above publication also discloses a method in which the porous layer surface is hydrophilicly treated with ozone water or hydrogen peroxide water and thereafter cleaned with pure water and ultrasonic energy.
However, while in cleaning porous semiconductors cleaning the surfaces is crucial, it is also important to remove the anodizing electrolytic solution that entered the fine the pores. This is because, even though the surface has been cleaned, the electrolytic solution (usually an aqueous HF solution with a concentration of 10% by weight to 50% by weight) remaining in the pores causes a change in structure of the porous body.
In addition, the HF that vaporizes gradually as HF gas from the interior of the pores may corrode the surrounding devices. Moreover, particles generated as a result of corrosion may contaminate the substrate.
Furthermore, since it takes time to replace the HF in the pores with pure water, cleaning with pure water must be carried out for a long time. In such a case, the porous body maybe crushed in pure water to generate a large quantity particles.
Such porous bodies are also preferably used in the production of bonded substrates utilized in SOI techniques.
FIG. 20
is a diagrammatic view to illustrate a process of producing a bonded substrate.
First, in step S
1
, a non-porous substrate
1
such as a single-crystal silicon wafer is prepared and its surface is made porous by anodization to form a porous layer
2
formed of single-crystal silicon.
Next, in step S
2
, the porous layer
2
is cleaned with pure water to wash away the foreign matter adhering to the porous layer or the electrolytic solution for anodization.
Subsequently, in step S
3
, a non-porous layer
3
formed of single-crystal silicon is epitaxially grown on the porous layer
2
by, e.g., CVD (chemical vapor deposition).
Then, in step S
4
, the surface of the non-porous layer is thermally oxidized to form an insulating layer
4
.
In a subsequent step S
5
, the surface of the insulating layer
4
is bonded to a supporting base
5
prepared separately, to from a multi-layered structure in which the non-porous layer
4
is positioned inside.
In step S
6
, the non-porous portion of the substrate
1
is removed by grinding and by ion etching subsequent thereto.
Then, in step S
7
, the porous layer
2
thus uncovered is removed by etching with an aqueous solution containing HF and H
2
O
2
.
The surface of the non-porous semiconductor layer may optionally be smoothed by heat treatment in a reducing atmosphere containing hydrogen. Thus, a bonded substrate is obtained that has a thin semiconductor layer on an insulating layer formed on a supporting base.
FIG. 21
illustrates the top surface of a bonded substrate obtained in this fashion. Reference numeral
12
denotes a notch.
However, upon observing the surface of the non-porous semiconductor layer thus formed, few circular spots
11
(hazes) that look optically different from their surrounding area are often seen. As a result of a careful observation of the circular spots
11
, it has been found that these spots are due to the fact that the non-porous layer present on the insulating layer formed on the supporting base is locally thin. Namely, the non-porous layer proved to have locally caused microscopically uneven film thickness.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a porous-body cleaning method by which the anodizing solution can be removed from the porous body without causing any change in porous structure of the porous body, even when cleaned for a short time, and to provide a process for producing a porous body.
Another object of the present invention is to provide a porous-body cleaning method that may hardly cause any corrosion of the surrounding devices, and a process for producing a porous body.
The cleaning method of the present invention is directed to cleaning a porou
Matsumura Satoshi
Yamagata Kenji
Anya Igwe U.
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Smith Matthew
LandOfFree
Method of cleaning porous body, and process for producing... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of cleaning porous body, and process for producing..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of cleaning porous body, and process for producing... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2982377