U.S. patent application number 09/931771 was filed with the patent office on 2002-01-31 for wafer processing apparatus and method, wafer convey robot, semiconductor substrate fabrication method, and semiconductor fabrication apparatus.
Invention is credited to Sakaguchi, Kiyofumi, Yanagita, Kazutaka.
Application Number | 20020013065 09/931771 |
Document ID | / |
Family ID | 26358901 |
Filed Date | 2002-01-31 |
United States Patent
Application |
20020013065 |
Kind Code |
A1 |
Yanagita, Kazutaka ; et
al. |
January 31, 2002 |
Wafer processing apparatus and method, wafer convey robot,
semiconductor substrate fabrication method, and semiconductor
fabrication apparatus
Abstract
A holder driving mechanism holds a wafer holder with gripping
portions, and swings it within a wafer processing bath. When the
peripheral portion of a wafer comes into contact with the distal
end portion of a swing support member, the wafer rotates and
vertically moves in the wafer holder. The wafer can be efficiently
swung, and processing can be made uniform. By supplying ultrasonic
waves from an ultrasonic bath, the processing rate can be
increased.
Inventors: |
Yanagita, Kazutaka;
(Yokohama-shi, JP) ; Sakaguchi, Kiyofumi;
(Yokohama-shi, JP) |
Correspondence
Address: |
MORGAN & FINNEGAN, L.L.P.
345 Park Avenue
New York
NY
10154
US
|
Family ID: |
26358901 |
Appl. No.: |
09/931771 |
Filed: |
August 20, 2001 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
09931771 |
Aug 20, 2001 |
|
|
|
09015582 |
Jan 29, 1998 |
|
|
|
Current U.S.
Class: |
438/747 ;
257/E21.122; 257/E21.219; 257/E21.228; 257/E21.251; 438/745 |
Current CPC
Class: |
H01L 21/31111 20130101;
H01L 21/2007 20130101; H01L 21/67057 20130101; H01L 21/30604
20130101; H01L 21/02052 20130101 |
Class at
Publication: |
438/747 ;
438/745; 156/345 |
International
Class: |
C23F 001/02; H01L
021/302; H01L 021/461 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 4, 1997 |
JP |
9-021796 |
Feb 14, 1997 |
JP |
9-030887 |
Claims
What is claimed is:
1. A wafer processing apparatus for processing a wafer by dipping
the wafer into a processing solution, comprising: a wafer
processing bath; a holding portion for directly or indirectly
holding the wafer; and a driving portion for supporting said
holding portion from above said processing bath to swing said
holding portion within said processing bath.
2. The apparatus according to claim 1, wherein said driving portion
also serves as a convey mechanism for conveying the wafer between
the apparatus and another apparatus.
3. The apparatus according to claim 1, further comprising
ultrasonic generating means for generating ultrasonic waves in said
processing bath.
4. The apparatus according to claim 1, further comprising a swing
support member that comes into contact with a peripheral portion of
the wafer in swinging the wafer by said driving portion, thereby
supporting swinging by said driving portion.
5. The apparatus according to claim 4, wherein a portion of said
swing support member which may come into contact with the
peripheral portion of the wafer is rounded.
6. The apparatus according to claim 4, wherein a portion of said
swing support member which may come into contact with the
peripheral portion of the wafer has a groove in a direction
substantially parallel to a wafer surface.
7. The apparatus according to claim 6, wherein the groove has a V
shape.
8. The apparatus according to claim 6, wherein the groove has a
rectified full-wave shape.
9. The apparatus according to claim 1, wherein said processing bath
comprises a circulating mechanism including an overflow bath.
10. The apparatus according to claim 4, wherein said driving
portion swings said holding portion to rotate the wafer when the
peripheral portion of the wafer comes into contact with said swing
support member.
11. The apparatus according to claim 3, wherein said ultrasonic
generating means comprises an ultrasonic bath, an ultrasonic
source, and an adjusting mechanism for adjusting a position of said
ultrasonic source in said ultrasonic bath, and ultrasonic waves are
transmitted to said processing bath via an ultrasonic transmitting
medium placed in said ultrasonic bath.
12. The apparatus according to claim 1, wherein said driving
portion comprises a first driving portion for horizontally driving
said holding portion, and a second driving portion for vertically
driving said holding portion.
13. The apparatus according to claim 1, wherein said holding
portion holds the wafer substantially perpendicular to a bottom
surface of said processing bath, and said driving portion swings
the wafer within a plane substantially perpendicular to the bottom
surface of said processing bath.
14. The apparatus according to claim 1, wherein said driving
portion swings said holding portion within said processing bath to
substantially uniformly process the wafer with a processing
solution.
15. The apparatus according to claim 1, wherein said holding
portion can hold a wafer holder capable of storing a plurality of
wafers.
16. The apparatus according to claim 1, wherein at least portions
of said processing bath, said holding portion, and said driving
portion, which may come into contact with a processing solution,
are made of a material selected from the group consisting of quartz
and plastic.
17. The apparatus according to claim 1, characterized in that at
least portions of said processing bath, said holding portion, and
said driving portion, which may come into contact with a processing
solution, are made of a material selected from the group consisting
of a fluorine resin, vinyl chloride, polyethylene, polypropylene,
polybutyleneterephthalate (PBT), and polyetheretherketone
(PEEK).
18. A wafer convey apparatus for conveying a wafer, comprising: a
holding portion for directly or indirectly holding the wafer; and a
driving portion for driving said holding portion along a convey
path, said driving portion dipping the wafer into a wafer
processing bath and swinging the wafer midway along the convey
path.
19. The apparatus according to claim 18, wherein said driving
portion comprises a first driving portion for horizontally driving
said holding portion, and a second driving portion for vertically
driving said holding portion.
20. The apparatus according to claim 18, wherein said holding
portion holds the wafer substantially perpendicular to a bottom
surface of said processing bath, and said driving portion swings
the wafer within a plane substantially perpendicular to the bottom
surface of said processing bath.
21. The apparatus according to claim 18, wherein said driving
portion swings said holding portion within said processing bath to
substantially uniformly process the wafer with a processing
solution in said processing bath.
22. The apparatus according to claim 18, wherein said driving
portion swings said holding portion within said processing bath to
enhance swinging of the wafer when a peripheral portion of the
wafer comes into contact with a projection formed in said
processing bath.
23. The apparatus according to claim 18, wherein said driving
portion swings said holding portion within said processing bath to
rotate the wafer when a peripheral portion of the wafer comes into
contact with a projection formed in said processing bath.
24. The apparatus according to claim 18, wherein said holding
portion can hold a wafer holder capable of storing a plurality of
wafers.
25. A semiconductor fabrication apparatus comprising the apparatus
according to claim 18, and one or a plurality of wafer processing
apparatuses.
26. A wafer processing method of processing a wafer by dipping the
wafer into a processing solution, comprising dipping a wafer into
the processing solution while supporting the wafer from above a
wafer processing bath, and swinging the wafer within said
processing bath.
27. The method according to claim 26, wherein, while the wafer is
swung within said processing bath, ultrasonic waves are generated
in the processing solution.
28. The method according to claim 26, wherein, when the wafer is
swung within said processing bath, a peripheral portion of the
wafer is brought into contact with a projection formed in said
processing bath to enhance swinging of the wafer.
29. The method according to claim 26, wherein, when the wafer is
swung within said processing bath, a peripheral portion of the
wafer is brought into contact with a projection formed in said
processing bath to rotate the wafer.
30. The method according to claim 26, wherein the wafer is swung to
substantially uniformly process the wafer with the processing
solution.
31. The method according to claim 26, wherein the wafer is etched
by using an etching solution as the processing solution.
32. The method according to claim 26, wherein a wafer having a
porous silicon layer is etched by using an etching solution as the
processing solution.
33. A semiconductor substrate fabrication method comprising
fabricating a semiconductor substrate by using the method according
to claim 32 in a part of fabrication steps.
34. A wafer processing method comprising processing a wafer by
using the apparatus according to claim 1.
35. A wafer processing method comprising etching a specific layer
formed on a wafer by using the apparatus according to claim 1.
36. A semiconductor substrate fabrication method comprising
fabricating a semiconductor substrate by using the method according
to claim 35 in a part of fabrication steps.
37. A wafer processing method of processing a wafer while supplying
ultrasonic waves, comprising: completely dipping the wafer into a
processing solution, and processing the wafer while changing a
strength of ultrasonic waves which act on the wafer.
38. A wafer processing method of processing a wafer while supplying
ultrasonic waves, comprising: completely dipping the wafer into a
processing solution, and processing the wafer while moving the
wafer.
39. A wafer processing method of processing a wafer while supplying
ultrasonic waves, comprising: completely dipping the wafer in a
processing solution, and processing the wafer while swinging the
wafer.
40. A wafer processing method of processing a wafer while supplying
ultrasonic waves, comprising: completely dipping the wafer in a
processing solution, and processing the wafer while swinging the
wafer to cross a plane of vibration of ultrasonic waves.
41. A wafer processing method of processing a wafer while supplying
ultrasonic waves, comprising: completely dipping the wafer in a
processing solution, supporting the wafer substantially
perpendicular to a plane of vibration of ultrasonic waves, and
processing the wafer while swinging the wafer to cross the plane of
vibration of ultrasonic waves.
42. A wafer processing method of processing a wafer while supplying
ultrasonic waves, comprising: completely dipping the wafer in a
processing solution, supporting the wafer substantially parallel to
a plane of vibration of ultrasonic waves, and processing the wafer
while swinging the wafer to cross the plane of vibration of
ultrasonic waves.
43. A semiconductor substrate fabrication method comprising: the
step of forming an unporous layer on a porous layer formed on a
surface of a first substrate; the step of adhering a first
substrate side of a prospective structure and a second substrate
prepared separately to sandwich said unporous layer between the
first substrate side and said second substrate; the removal step of
removing said first substrate from the adhered structure to expose
said porous layer on a second substrate side thereof; and the
etching step of etching said porous layer while the second
substrate side on which said porous layer is exposed is completely
dipped into an etching solution, and ultrasonic waves are supplied,
thereby exposing a surface of the second substrate side, the
etching step changing a strength of ultrasonic waves which act on
the second substrate side.
44. A semiconductor substrate fabrication method comprising: the
step of forming an unporous layer on a porous layer formed on a
surface of a first substrate; the step of adhering a first
substrate side of a prospective structure and a second substrate
prepared separately to sandwich said unporous layer between the
first substrate side and said second substrate; the removal step of
removing said first substrate from the adhered structure to expose
said porous layer on a second substrate side thereof; and the
etching step of etching said porous layer while the second
substrate side on which said porous layer is exposed is completely
dipped into an etching solution, and ultrasonic waves are supplied,
thereby exposing a surface of the second substrate side, the
etching step moving the second substrate side.
45. A semiconductor substrate fabrication method comprising: the
step of forming an unporous layer on a porous layer formed on a
surface of a first substrate; the step of adhering a first
substrate side of a prospective structure and a second substrate
prepared separately to sandwich said unporous layer between the
first substrate side and said second substrate; the removal step of
removing said first substrate from the adhered structure to expose
said porous layer on a second substrate side thereof; and the
etching step of etching said porous layer while the second
substrate side on which said porous layer is exposed is completely
dipped into an etching solution, and ultrasonic waves are supplied,
thereby exposing a surface of the second substrate side, the
etching step swinging the second substrate side.
46. A semiconductor substrate fabrication method comprising: the
step of forming an unporous layer on a porous layer formed on a
surface of a first substrate; the step of adhering a first
substrate side of a prospective structure and a second substrate
prepared separately to sandwich said unporous layer between the
first substrate side and said second substrate; the removal step of
removing said first substrate from the adhered structure to expose
said porous layer on a second substrate side thereof; and the
etching step of etching said porous layer while the second
substrate side on which said porous layer is exposed is completely
dipped into an etching solution, and ultrasonic waves are supplied,
thereby exposing a surface of the second substrate side, the
etching step swinging the second substrate side to cross a plane of
vibration of ultrasonic waves.
47. A semiconductor substrate fabrication method comprising: the
step of forming an unporous layer on a porous layer formed on a
surface of a first substrate; the step of adhering a first
substrate side of a prospective structure and a second substrate
prepared separately to sandwich said unporous layer between the
first substrate side and said second substrate; the removal step of
removing said first substrate from the adhered structure to expose
said porous layer on a second substrate side thereof; and the
etching step of etching said porous layer while the second
substrate side on which said porous layer is exposed is completely
dipped into an etching solution and supported substantially
perpendicular to a plane of vibration of ultrasonic waves, and
ultrasonic waves are supplied, thereby exposing a surface of the
second substrate side, the etching step swinging the second
substrate side to cross the plane of vibration of ultrasonic
waves.
48. A semiconductor substrate fabrication method comprising: the
step of forming an unporous layer on a porous layer formed on a
surface of a first substrate; the step of adhering a first
substrate side of a prospective structure and a second substrate
prepared separately to sandwich said unporous layer between the
first substrate side and said second substrate; the removal step of
removing said first substrate from the adhered structure to expose
said porous layer on a second substrate side thereof; and the
etching step of etching said porous layer while the second
substrate side on which said porous layer is exposed is completely
dipped into an etching solution and supported substantially
parallel to a plane of vibration of ultrasonic waves, and
ultrasonic waves are supplied, thereby exposing a surface of the
second substrate side, the etching step swinging the second
substrate side to cross the plane of vibration of ultrasonic
waves.
49. The apparatus according to claim 4, wherein swing support
member are made of a material selected from the group consisting of
a fluorine resin, vinyl chloride, polyethylene, polypropylene,
polybutyleneterephthalate (PBT), and polyetheretherketone (PEEK).
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a wafer processing
apparatus and method, a wafer convey robot, a semiconductor
substrate fabrication method, and a semiconductor fabrication
apparatus and, more particularly, to a wafer processing apparatus
and method which process a wafer by dipping the wafer into a
processing solution, a wafer convey robot suitable for this
processing, and a semiconductor substrate fabrication method and
semiconductor fabrication apparatus to which the processing is
applied.
[0003] 2. Description of the Related Art
[0004] Wet etching is a typical example of processing performed by
dipping a wafer into a solution. One subject of wet etching is to
improve the in-plane uniformity. Conventionally, the in-plane
uniformity is ensured by supplying fresh etching solution to the
reaction surface by circulating the etching solution in a bath.
[0005] Another example of the processing performed by dipping a
wafer into a solution is wafer cleaning processing. Japanese Patent
Laid-Open No. 8-293478 has disclosed a wafer cleaning apparatus
which increases the wafer cleaning efficiency by applying
ultrasonic waves while dipping part of a wafer into a solution and
rotating the wafer.
[0006] The wafer cleaning apparatus disclosed in Japanese Patent
Laid-Open No. 8-293478 rotates a wafer upon bringing the wafer into
contact with a rotating cam, which makes the cam and its
accessories generate particles.
[0007] In this wafer cleaning apparatus, the strength of standing
waves of ultrasonic waves changes at the center and peripheral
portion of the wafer. Since the cam obstructs the transmission of
ultrasonic waves, the ultrasonic waves cannot be uniformly supplied
to the entire surface of the wafer. Accordingly, the wafer cannot
be uniformly processed.
[0008] In the wafer cleaning apparatus, ultrasonic waves vibrate
the cam and the solution in the bath, and as a result, the wafer
also vibrates. The wafer and the cam tend to slip with respect to
each other, and the wafer cannot rotate uniformly.
[0009] In the wafer cleaning apparatus, when a wafer having an
orientation flat is to be processed, the conditions for
transmitting the rotating force from the cam to the wafer change at
the orientation flat and the remaining portion. For this reason,
the wafer -cannot rotate uniformly.
SUMMARY OF THE INVENTION
[0010] The present invention has been made in consideration of the
above problems and has as its object to make wafer processing
uniform.
[0011] It is another object of the present invention to prevent
contamination of a wafer caused by particles.
[0012] A wafer processing apparatus according to the present
invention is a wafer processing apparatus for processing a wafer by
dipping the wafer into a processing solution, characterized by
comprising a wafer processing bath, a holding portion for directly
or indirectly holding the wafer, and a driving portion for
supporting the holding portion from above the processing bath to
swing the holding portion within the processing bath.
[0013] In the wafer processing apparatus, the driving portion
preferably also serves as a convey mechanism for conveying the
wafer between the apparatus and another apparatus.
[0014] The wafer processing apparatus preferably further comprises
ultrasonic generating means for generating ultrasonic waves in the
processing bath.
[0015] The wafer processing apparatus preferably further comprises
a swing support member that comes into contact with a peripheral
portion of the wafer in swinging the wafer by the driving portion,
thereby supporting swinging by the driving portion.
[0016] In the wafer processing apparatus, a portion of the swing
support member which may come into contact with the peripheral
portion of the wafer is preferably rounded.
[0017] In the wafer processing apparatus, a portion of the swing
support member which may come into contact with the peripheral
portion of the wafer preferably has a groove in a direction
substantially parallel to a wafer surface.
[0018] In the wafer processing apparatus, the groove preferably has
a V shape.
[0019] In the wafer processing apparatus, the groove preferably has
a full-wave rectifying shape.
[0020] In the wafer processing apparatus, the processing bath
preferably comprises a circulating mechanism including an overflow
bath.
[0021] In the wafer processing apparatus, the driving portion
preferably swings the holding portion to rotate the wafer when the
peripheral portion of the wafer comes into contact with the swing
support member.
[0022] In the wafer processing apparatus, the ultrasonic generating
means preferably comprises an ultrasonic bath, an ultrasonic
source, and an adjusting mechanism for adjusting a position of the
ultrasonic source in the ultrasonic bath, and ultrasonic waves are
preferably transmitted to the processing bath via an ultrasonic
transmitting medium placed in the ultrasonic bath.
[0023] In the wafer processing apparatus, the driving portion
preferably comprises a first driving portion for horizontally
driving the holding portion, and a second driving portion for
vertically driving the holding portion.
[0024] In the wafer processing apparatus, the holding portion
preferably holds the wafer substantially perpendicular to a bottom
surface of the processing bath, and the driving portion preferably
swings the wafer within a plane substantially perpendicular to the
bottom surface of the processing bath.
[0025] In the wafer processing apparatus, the driving portion
preferably swings the holding portion within the processing bath to
substantially uniformly process the wafer with a processing
solution.
[0026] In the wafer processing apparatus, the holding portion can
preferably hold a wafer holder capable of storing a plurality of
wafers.
[0027] In the wafer processing apparatus, at least portions of the
processing bath, the holding portion, and the driving portion,
which may come into contact with a processing solution, are
preferably made of a material selected from the group consisting of
quartz and plastic.
[0028] In the wafer processing apparatus, at least portions of the
processing bath, the holding portion, and the driving portion,
which may come into contact with a processing solution, are
preferably made of a material selected from the group consisting of
a fluorine resin, vinyl chloride, polyethylene, polypropylene,
polybutyleneterephthalate (PBT), and polyetheretherketone
(PEEK).
[0029] A wafer convey apparatus according to the present invention
is a wafer convey apparatus for conveying a wafer, characterized by
comprising a holding portion for directly or indirectly holding the
wafer, and a driving portion for driving the holding portion along
a convey path, the driving portion dipping the wafer into a wafer
processing bath and swinging the wafer midway along the convey
path.
[0030] In the wafer convey apparatus, the driving portion
preferably comprises a first driving portion for horizontally
driving the holding portion, and a second driving portion for
vertically driving the holding portion.
[0031] In the wafer convey apparatus, the holding portion
preferably holds the wafer substantially perpendicular to a bottom
surface of the processing bath, and the driving portion preferably
swings the wafer within a plane substantially perpendicular to the
bottom surface of the processing bath.
[0032] In the wafer convey apparatus, the driving portion
preferably swings the holding portion within the processing bath to
substantially uniformly process the wafer with a processing
solution in the processing bath.
[0033] In the wafer convey apparatus, the driving portion
preferably swings the holding portion within the processing bath to
enhance swinging of the wafer when a peripheral portion of the
wafer comes into contact with a projection formed in the processing
bath.
[0034] In the wafer convey apparatus, the driving portion
preferably swings the holding portion within the processing bath to
rotate the wafer when a peripheral portion of the wafer comes into
contact with a projection formed in the processing bath.
[0035] In the wafer convey apparatus, the holding portion can
preferably hold a wafer holder capable of storing a plurality of
wafers.
[0036] A semiconductor fabrication apparatus according to the
present invention is characterized by comprising the wafer convey
apparatus, and one or a plurality of wafer processing
apparatuses.
[0037] A wafer processing method according to the present invention
is a wafer processing method of processing a wafer by dipping the
wafer into a processing solution, characterized by comprising
dipping a wafer into the processing solution while supporting the
wafer from above a wafer processing bath, and swinging the wafer
within the processing bath. In the wafer processing method, while
the wafer is swung within the processing bath, ultrasonic waves are
preferably generated in the processing solution.
[0038] In the wafer processing method, when the wafer is swung
within the processing bath, a peripheral portion of the wafer is
preferably brought into contact with a projection formed in the
processing bath to enhance swinging of the wafer.
[0039] In the wafer processing method, when the wafer is swung
within the processing bath, a peripheral portion of the wafer is
preferably brought into contact with a projection formed in the
processing bath to rotate the wafer.
[0040] In the wafer processing method, the wafer is preferably
swung to substantially uniformly process the wafer with the
processing solution.
[0041] The wafer processing method is suitable for etching the
wafer by using an etching solution as the processing solution.
[0042] The wafer processing method is suitable for etching a wafer
having a porous silicon layer by using an etching solution as the
processing solution.
[0043] An SOI wafer fabrication method according to the present
invention is characterized by comprising fabricating an SOI wafer
by using the wafer processing method in a part of fabrication
steps.
[0044] A wafer processing method according to the present invention
is characterized by comprising processing a wafer by using the
wafer processing apparatus.
[0045] A wafer processing method according to the present invention
is characterized by comprising etching a specific layer formed on a
wafer by using the wafer processing apparatus.
[0046] An SOI wafer fabrication method according to the present
invention is characterized by comprising fabricating an SOI wafer
by using the wafer processing method in a part of fabrication
steps.
[0047] A wafer processing method according to the present invention
is a wafer processing method of processing a wafer while supplying
ultrasonic waves, characterized by comprising completely dipping
the wafer into a processing solution, and processing the wafer
while changing a strength of ultrasonic waves which act on the
wafer.
[0048] A wafer processing method according to the present invention
is a wafer processing method of processing a wafer while supplying
ultrasonic waves, characterized by comprising completely dipping
the wafer into a processing solution, and processing the wafer
while moving the wafer.
[0049] A wafer processing method according to the present invention
is a wafer processing method of processing a wafer while supplying
ultrasonic waves, characterized by comprising completely dipping
the wafer in a processing solution, and processing the wafer while
swinging the wafer.
[0050] A wafer processing method according to the present invention
is a wafer processing method of processing a wafer while supplying
ultrasonic waves, characterized by comprising completely dipping
the wafer in a processing solution, and processing the wafer while
swinging the wafer to cross a plane of vibration of ultrasonic
waves.
[0051] A wafer processing method according to the present invention
is a wafer processing method of processing a wafer while supplying
ultrasonic waves, characterized by comprising completely dipping
the wafer in a processing solution, supporting the wafer
substantially perpendicular to a plane of vibration of ultrasonic
waves, and processing the wafer while swinging the wafer to cross
the plane of vibration of ultrasonic waves.
[0052] A wafer processing method according to the present invention
is a wafer processing method of processing a wafer while supplying
ultrasonic waves, characterized by comprising completely dipping
the wafer in a processing solution, supporting the wafer
substantially parallel to a plane of vibration of ultrasonic waves,
and processing the wafer while swinging the wafer to cross the
plane of vibration of ultrasonic waves.
[0053] A semiconductor substrate fabrication method according to
the present invention is characterized by comprising the step of
forming an unporous layer on a porous layer formed on a surface of
a first substrate, the step of adhering a first substrate side of a
prospective structure and a second substrate prepared separately to
sandwich the unporous layer between the first substrate side and
the second substrate, the removal step of removing the first
substrate from the adhered structure to expose the porous layer on
a second substrate side thereof, and the etching step of etching
the porous layer while the second substrate side on which the
porous layer is exposed is completely dipped into an etching
solution, and ultrasonic waves are supplied, thereby exposing a
surface of the second substrate side, the etching step changing a
strength of ultrasonic waves which act on the second substrate
side.
[0054] A semiconductor substrate fabrication method according to
the present invention is characterized by comprising the step of
forming an unporous layer on a porous layer formed on a surface of
a first substrate, the step of adhering a first substrate side of a
prospective structure and a second substrate prepared separately to
sandwich the unporous layer between the first substrate side of a
prospective structure and the second substrate, the removal step of
removing the first substrate from the adhered structure to expose
the porous layer on a second substrate side thereof, and the
etching step of etching the porous layer while the second substrate
side on which the porous layer is exposed is completely dipped into
an etching solution, and ultrasonic waves are supplied, thereby
exposing a surface of the second substrate side, the etching step
moving the second substrate side.
[0055] A semiconductor substrate fabrication method according to
the present invention is characterized by comprising the step of
forming an unporous layer on a porous layer formed on a surface of
a first substrate, the step of adhering a first substrate side of a
prospective structure and a second substrate prepared separately to
sandwich the unporous layer between the first substrate side and
the second substrate, the removal step of removing the first
substrate from the adhered structure to expose the porous layer on
a second substrate side thereof, and the etching step of etching
the porous layer while the second substrate side on which the
porous layer is exposed is completely dipped into an etching
solution, and ultrasonic waves are supplied, thereby exposing a
surface of the second substrate side, the etching step swinging the
second substrate side.
[0056] A semiconductor substrate fabrication method according to
the present invention is characterized by comprising the step of
forming an unporous layer on a porous layer formed on a surface of
a first substrate, the step of adhering a first substrate side of a
prospective structure and a second substrate prepared separately to
sandwich the unporous layer between the first substrate side and
the second substrate, the removal step of removing the first
substrate from the adhered structure to expose the porous layer on
a second substrate side thereof, and the etching step of etching
the porous layer while the second substrate side on which the
porous layer is exposed is completely dipped into an etching
solution, and ultrasonic waves are supplied, thereby exposing a
surface of the second substrate side, the etching step swinging the
second substrate side to cross a plane of vibration of ultrasonic
waves.
[0057] A semiconductor substrate fabrication method according to
the present invention is characterized by comprising the step of
forming an unporous layer on a porous layer formed on a surface of
a first substrate, the step of adhering a first substrate side of a
prospective structure and a second substrate prepared separately to
sandwich the unporous layer between the first substrate side and
the second substrate, the removal step of removing the first
substrate from the adhered structure to expose the porous layer on
a second substrate side thereof, and the etching step of etching
the porous layer while the second substrate side on which the
porous layer is exposed is completely dipped into an etching
solution and supported substantially perpendicular to a plane of
vibration of ultrasonic waves, and ultrasonic waves are supplied,
thereby exposing a surface of the second substrate side, the
etching step swinging the second substrate side to cross the plane
of vibration of ultrasonic waves.
[0058] A semiconductor substrate fabrication method according
to-the present invention is characterized by comprising the step of
forming an unporous layer on a porous layer formed on a surface of
a first substrate, the step of adhering a first substrate side of a
prospective structure and a second substrate prepared separately to
sandwich the unporous layer between the first substrate side and
the second substrate, the removal step of removing the first
substrate from the adhered structure to expose the porous layer on
a second substrate side thereof, and the etching step of etching
the porous layer while the second substrate side on which the
porous layer is exposed is completely dipped into an etching
solution and supported substantially parallel to a plane of
vibration of ultrasonic waves, and ultrasonic waves are supplied,
thereby exposing a surface of the second substrate side, the
etching step swinging the second substrate side to cross the plane
of vibration of ultrasonic waves.
[0059] Further objects, features and advantages of the present
invention will become apparent from the following detailed
description of embodiments of the present invention with reference
to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0060] FIG. 1A is a view showing an outline of the construction of
a wafer processing apparatus according to a preferred embodiment of
the present invention;
[0061] FIG. 1B is a view showing an outline of the construction of
a holder driving mechanism;
[0062] FIGS. 2A to 2E are views for explaining a wafer swinging
method;
[0063] FIG. 3 is a view showing an example of the construction of a
swing support member;
[0064] FIGS. 4A and 4B are views each showing another example of
the construction of the swing support member;
[0065] FIG. 5A is a perspective view showing an outline of the
construction of a wafer processing system incorporating the wafer
processing apparatus;
[0066] FIG. 5B is a front view showing an outline of the
construction of the wafer processing system incorporating the wafer
processing apparatus;
[0067] FIGS. 6A to 6D are views for explaining another example of
the wafer swinging method;
[0068] FIG. 7 is a view showing an outline of the construction of a
wafer processing apparatus according to another embodiment of the
present invention; and
[0069] FIGS. 8A to 8F are views, respectively, showing a method of
fabricating a semiconductor substrate.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0070] A preferred embodiment of the present invention will be
described below with reference to the accompanying drawings.
[0071] [First Embodiment]
[0072] FIG. 1A is a view showing an outline of the construction of
a wafer processing apparatus according to the preferred embodiment
of the present invention. The wafer processing apparatus according
to this embodiment can be widely applied to etching, cleaning, and
another processing which supplies a processing solution to a
wafer.
[0073] In a wafer processing apparatus 100 according to this
embodiment, portions which may come into contact with a processing
solution are preferably made from quartz or plastic in accordance
with the intended use. Preferable examples of the plastic are a
fluorine resin, vinyl chloride, polyethylene, polypropylene,
polybutyleneterephthalate (PBT), and polyetheretherketone (PEEK).
Preferable examples of the fluorine resin are PVDF, PFA, and
PTFE.
[0074] This wafer processing apparatus 100 has a wafer processing
bath 11, and a holder driving mechanism 31 for swinging a wafer
holder 21 in the wafer processing bath 11. The wafer processing
apparatus 100 preferably comprises an ultrasonic bath 61.
[0075] To process wafers, the wafer processing bath 11 is filled
with a processing solution. A 4-plane overflow bath 12 is mounted
on the wafer processing bath 11, and supplies a processing solution
from the bottom portion of the wafer processing bath 11 into the
wafer processing bath 11 by a circulator 71 incorporating a filter.
The processing solution overflowing from the wafer processing bath
11 is stored in the 4-plane overflow bath 12, and discharged from
the bottom portion of the 4-plane overflow bath 12 toward the
circulator 71. Since the wafer processing apparatus 100 agitates
the processing solution while swinging the wafer holder 21 by the
holder driving mechanism 31, the liquid level of the processing
solution can be kept constant. Therefore, the circulating system
including the 4-plane overflow bath 12 is very useful.
[0076] The wafer holder 21 may be a commercially available product,
and is preferably made from quartz or plastic. Preferable examples
of the plastic are a fluorine resin, vinyl chloride, polyethylene,
polypropylene, polybutyleneterephthalate (PBT), and
polyetheretherketone (PEEK). Preferable examples of the fluorine
resin are PVDF, PFA, and PTFE.
[0077] The holder driving mechanism 31 has a pair of gripping
portions 31a for gripping the wafer holder 21. The wafer holder 21
is gripped by the pair of gripping portions 31a and dipped in the
wafer processing bath 11. While the wafer holder 21 is swung within
the wafer processing bath 11, desired processing can be performed
for a wafer 41. The holder driving mechanism 31 functions to convey
the wafer holder 21 holding the wafer 41 having undergone previous
processing to the wafer processing bath 11 or the next processing,
whereas it functions as part of the wafer processing apparatus
100.
[0078] In this embodiment, the wafer 41 is indirectly held by
holding the wafer holder 21 with the gripping portions 31a.
Alternatively, the wafer 41 can be directly held by, e.g., a
chucking pad in place of the gripping portions 31a. The direction
to hold the wafer 41 is not limited to a direction perpendicular to
the bottom surface of the wafer processing bath 11, and may be a
direction parallel to the bottom surface.
[0079] A swing support member 13 for increasing the swing
efficiency of the wafer 41 in swinging the wafer 41 by the holder
driving mechanism 31 is preferably arranged at the bottom portion
of the wafer processing bath 11. When the wafer holder 21 moves,
the swing support member 13 contacts the peripheral portion of the
wafer 41 held by the wafer holder 21 to rotate the wafer 41 by the
frictional force and vertically move it within the wafer holder 21.
The swing support member 13 is useful for improving the in-plane
uniformity of the processed wafer.
[0080] It is also effective to arrange a driving mechanism for
moving the swing support member 13 vertically (y-axis direction)
and/or horizontally (x-axis direction). In this case, the swing
support member 13 itself can move to rotate the wafer 41 and
vertically move it within the wafer holder 21. Accordingly, the
moving range of the wafer holder 21 by the holder driving mechanism
31 can be reduced, and in other words, the wafer processing bath 11
can be downsized.
[0081] An ultrasonic source 51 is arranged in the ultrasonic bath
61, and filled with an ultrasonic transmitting medium (e.g.,
water). The ultrasonic source 51 is fixed to an adjusting mechanism
62 for vertically and/or horizontally adjusting the position of the
ultrasonic source 51. Ultrasonic waves to be supplied to the wafer
processing bath 11, more specifically, to the wafer 41 can be
optimized by adjusting the positional relationship between the
ultrasonic source 51 and the wafer processing bath 11 by the
adjusting mechanism 62. The ultrasonic source 51 preferably has a
function of adjusting the frequency or strength of ultrasonic waves
to be generated. This can further optimize the supply of ultrasonic
waves. Since the ultrasonic source 51 has the function for
optimizing the supply of ultrasonic waves to the wafer 41, various
types of wafers can be processed.
[0082] FIG. 1B is a view showing an outline of the construction of
the holder driving mechanism 31. The gripping portions 31a are
opened by extending opening/closing rods 31b, and closed by
contracting these rods 31b. The holder driving mechanism 31 moves
in the x-axis direction along a horizontal driving shaft 31c and in
the y-axis direction along a vertical driving shaft 31d.
[0083] FIGS. 2A to 2E are views for explaining a wafer swinging
method. In FIGS. 2A to 2E, the arrows indicate the moving direction
of the wafer holder 21. FIG. 2A shows a state immediately before
starting swinging a wafer. When the start of wafer swinging is
instructed, the holder driving mechanism 31 depresses the gripping
portions 31a downward under computer control, as shown in FIG. 2B.
During this depression, the peripheral portion of the wafer 41
comes into contact with the swing support member 13. As a result,
the lower portion of the wafer 41 is supported by the swing support
member 13.
[0084] The swing support member 13 may generate a few particles
upon contact with the wafer 41. The swing support member 13
preferably smoothly contacts the wafer 41 by rounding the distal
end portion of the swing support member 13, as shown in FIG. 3.
[0085] Since the swing support member 13 suffices to support the
swing of the wafer 41, it can be formed into a shape, e.g., a thin
plate not to obstruct the transmission of ultrasonic waves. With
this shape, the ultrasonic waves to be supplied to the wafer 41 can
be uniformed to uniformly process the wafer 41.
[0086] Slight ultrasonic nonuniformity caused by the swing support
member 13 does not pose any problem because the wafer processing
apparatus 100 processes the wafer 41 while changing the relative
positional relationship between the wafer 41 and the swing support
member 13, in other words, the relative positional relationship
between the wafer 41 and the wafer processing bath 11.
[0087] Since a slightly larger depression amount of the wafer
holder 21 can increase the contact pressure between the wafer 41
and the swing support member 13, a slip between the swing support
member 13 and the wafer 41 can be prevented to prevent operation
failure. This is because, if the depression amount is too small,
the gravity for the wafer 41 acts on the wafer holder 21 more
greatly than on the distal end portion of the swing support member
13. When the swing support member 13 having the shape according to
this embodiment is used, the depression amount is preferably about
30 mm after the wafer 41 comes into contact with the swing support
member 13.
[0088] Upon depressing the wafer holder 21, the holder driving
mechanism 31 moves the gripping portions 31a rightward (positive
direction of the X axis) under computer control, as shown in FIG.
2C. As a result, the wafer 41 substantially horizontally moves
rightward (positive direction of the X axis) in the wafer
processing bath 11 while rotating clockwise. The moving amount of
the gripping portions 31a must be set to fall within the range in
which these gripping portions 31a do not collide against an opening
portion at the lower portion of the wafer holder 21.
[0089] After the wafer holder 21 has moved rightward (positive
direction of the X axis), the holder driving mechanism 31
vertically moves the gripping portions 31a under computer control,
as shown in FIG. 2D. The moving amount of the gripping portions 31a
preferably falls within the range in which the wafer 41 does not
come close to a liquid surface 14 of the processing solution. This
is because particles may attach to the surface of the wafer 41 if
the wafer 41 comes close to the liquid surface 14.
[0090] Upon completion of the upward movement of the wafer holder
21, the holder driving mechanism 31 moves the gripping portions 31a
leftward (negative direction of the X axis) under computer control
to return them in the initial state (FIG. 2A), as shown in FIG.
2E.
[0091] By repeatedly performing the above operation (FIG.
2A.fwdarw.FIG. 2B.fwdarw.FIG. 2C.fwdarw.FIG. 2D.fwdarw.FIG. 2E),
the wafer 41 can be properly swung and uniformly processed.
[0092] According to the wafer processing apparatus 100, since the
wafer 41 is swung in the region where the supply of ultrasonic
waves is optimized by adjusting the ultrasonic bath 61, ultrasonic
waves which act on the wafer 41 can be optimized.
[0093] The standing waves of ultrasonic waves have loops
(high-strength portions) and nodes (low-strength portions) at
constant separation. Therefore, ultrasonic waves are difficult to
uniform in the wafer processing bath 11.
[0094] However, since the wafer processing apparatus 100 swings the
wafer 41 with the holder driving mechanism 31, it can uniformly
process the wafer 41 regardless of a somewhat nonuniform
distribution of the ultrasonic wave strength. Even if the direction
to move the wafer 41 is a simple direction such as only the
horizontal, vertical, or oblique direction, it can contribute to
the processing uniformity of the wafer 41. By swinging the wafer 41
in its axial direction (z-axis direction), the processing
nonuniformity between wafers attributed to high-strength portions
of ultrasonic waves in the horizontal plane can be corrected.
[0095] Since the wafer processing apparatus 100 further comprises
the swing support member 13, the swinging amount of the wafer 41
can be efficiently increased. The fixed position of the swing
support member 13 is not limited to the bottom portion of the wafer
processing bath 11. As far as the swing support member 13 can
contact with all wafers 41 of the wafer holder 21, it can be fixed
to, e.g., the side wall of the wafer processing bath 11 or the
holder driving mechanism 31 (in this case, a mechanism of changing
the relative positional relationship between the swing support
member 13 and the gripping portions 31a is arranged).
[0096] According to the wafer processing apparatus 100, since no
driving mechanism exists in the wafer processing bath 11, no
particle is produced by the driving mechanism.
[0097] Even if the wafer processing apparatus 100 does not comprise
any ultrasonic bath 61, it can function as an apparatus suitable
for wafer processing. More specifically, if the wafer processing
apparatus 100 has a function of swinging the wafer holder 21 within
the wafer processing bath 11 by the holder driving mechanism 31, it
can uniformly process the wafer 41 with only this function, and
effectively agitate the processing solution. A gas or the like
produced upon processing the wafer 41 can be efficiently removed
from the surface of the wafer 41. Since the holder driving
mechanism 31 can serve as both convey and swinging mechanisms for
the wafer 41, wafers can be efficiently processed.
[0098] FIG. 4A is an overall view of another example of the
construction of the swing support member 13. FIG. 4B is an enlarged
view of part of the swing support member 13. If the strength of
ultrasonic waves is high, the distal end portion of the swing
support member 13 and the wafer 41 may slip and fail to efficiently
swing the wafer 41.
[0099] A swing support member 13' shown in FIGS. 4A and 4B has
V-shaped grooves 13a at constant intervals. By forming these
V-shaped grooves 13a, the contact area with the wafers 41 can be
increased. Since the swing support member 13' engages with the
wafer 41 so as to pinch it, the swing efficiency of the wafer 41
increases. Even if the wafer 41 vibrates to be temporarily spaced
apart from the swing support member 13', the frictional force with
the wafer 41 does not decrease unless the wafer 41 accurately
vertically moves.
[0100] The groove at the distal end portion of the swing support
member 13' may have a shape 13b, i.e., a full-wave rectifying
shape. In this case, since the groove does not have any top, unlike
the V-shaped groove 13a, generation of particles upon contact with
the wafer 41 can be suppressed.
[0101] [Second Embodiment]
[0102] FIG. 5A is a perspective view showing an outline of the
construction of a wafer processing system incorporating a wafer
processing apparatus 100. FIG. 5B is a front view showing part of
the wafer processing system shown in FIG. 5A.
[0103] This wafer processing system is preferably a combination of
a loader, a wafer processing apparatus (e.g., an etching or
cleaning apparatus), a spin dryer, an unloader, and the like.
[0104] Reference numeral 31' denotes a holder driving mechanism
having substantially the same function as that of the holder
driving mechanism 31, which has gripping portions 31a" for gripping
a wafer holder 21, a means for driving the wafer holder 21
horizontally (alignment direction of the respective apparatuses),
and a means for vertically driving the wafer holder 21.
[0105] This wafer processing system can automatically process a
wafer under computer control. Particles produced by the
intervention of the operator can be prevented from attaching to
wafers, and the processing efficiency can be increased.
[0106] [Third Embodiment]
[0107] The third embodiment will exemplify another wafer swinging
method. FIGS. 6A to 6D are views for explaining a wafer swinging
method in this embodiment. In FIGS. 6A to 6D, the arrows indicate
the moving direction of a wafer holder 21. FIG. 6A shows a state
immediately before starting swinging a wafer. When the start of
wafer swinging is instructed, a holder driving mechanism 31 moves
gripping portions 31a downwardly to the right under computer
control, as shown in FIG. 6B. The moving direction is suitably at
an angle of about 45.degree. with respect to the horizontal plane.
When the wafer holder 21 has moved downwardly to the right, a wafer
41 rotates clockwise about the distal end portion of a swing
support member 13 while its peripheral portion is pressed by the
left side wall of the wafer holder 21.
[0108] After the wafer holder 21 has moved downwardly to the right,
the center of gravity of the wafer 41 moves to the right with
respect to the distal end portion of the swing support member 13,
and the wafer 41 rotates toward the right side wall of the wafer
holder 21 to settle to a state shown in FIG. 6C.
[0109] Upon moving the wafer holder 21 downwardly to the right, the
holder driving mechanism 31 moves the gripping portions 31a
upwardly to the left, as shown in FIG. 6D. The moving direction is
preferably opposite to the moving direction shown in FIG. 6B.
[0110] When the wafer holder 21 has moved upwardly to the left, the
wafer 41 rotates counterclockwise about the swing support member 13
while its peripheral portion is pressed by the right side wall of
the wafer holder 21. By moving the wafer holder 21 to a state shown
in FIG. 6A, one operation is completed.
[0111] By repeatedly performing the above operation (FIG.
6A.fwdarw.FIG. 6B.fwdarw.FIG. 6C.fwdarw.FIG. 6D), the wafer 41 can
be properly swung and uniformly processed.
[0112] [Fourth Embodiment]
[0113] The fourth embodiment is directed to a wafer processing
apparatus having another construction. FIG. 7 is a view showing an
outline of the construction of the wafer processing apparatus
according to this embodiment. The same reference numerals as in the
construction of the wafer processing apparatus 100 according to the
first embodiment denote substantially the same constituent
elements, and a description thereof will be omitted.
[0114] A wafer processing apparatus 101 according to the fourth
embodiment holds a wafer 41 with a wafer moving mechanism 80 almost
parallel to the bottom surface of a wafer processing bath 11 (i.e.,
almost parallel to the plane of vibration of ultrasonic waves), and
swings the wafer 41 while completely dipping it into a processing
solution (e.g., cleaning or etching solution) within the wafer
processing bath 11. In this manner, the wafer 41 is uniformly
processed, and contamination of the wafer 41 by particles is
prevented.
[0115] The wafer moving mechanism 80 grips the wafer 41 with arms
81, and swings the wafer 41 in the wafer processing bath 11. The
wafer 41 is preferably swung in a direction perpendicular to the
plane of vibration of ultrasonic waves (i.e., vertical direction),
or in a direction parallel to the plane of vibration (i.e.,
horizontal direction).
[0116] Also in the wafer processing apparatus 101, the wafer 41 is
preferably processed while being completely dipped into the
processing solution. In this case, particles can be prevented from
attaching to the wafer 41 near the interface between the processing
solution and ambient atmosphere.
[0117] According to the wafer processing apparatus 101, the wafer
41 can be uniformly processed by swinging it in the wafer
processing bath 11.
[0118] [Application of Wafer Processing Apparatus]
[0119] The wafer processing apparatus 100 according to the above
embodiments is suitable as, e.g., an etching apparatus. According
to this etching apparatus, 1) a wafer can be uniformly etched, 2)
contamination by particles can be reduced, and 3) the etching rate
can be increased.
[0120] The wafer processing apparatus 100 is suited as an etching
apparatus for etching a wafer having a porous silicon layer. The
mechanism of etching of porous silicon is disclosed in K. Sakaguchi
et al., Jpn. Appl. Phys. Vol. 34, part 1, No. 2B, 842-847 (1995).
Porous silicon is etched when an etching solution penetrates into
the pores of porous silicon by a capillary action and etches the
walls of the pores. As the walls of the pores become thinner, these
walls cannot support themselves beyond some point. Finally, the
porous layer entirely collapses to complete the etching. When the
pore walls are left to collapse by the action of only the etching
solution without any etching assistance, the etching rate of the
hole wall is low, and the etching time is long. In a region where
the porous layer collapses, the underlayer is etched. For this
reason, variations in in-plane etching rate of a porous silicon
wafer and etching rate between wafers are preferably suppressed as
much as possible.
[0121] For example, a first substrate is prepared by forming a
porous silicon layer on a single-crystal silicon substrate, growing
an epitaxial layer on the porous silicon layer, and forming an
insulating film on the epitaxial layer. The first substrate and a
second substrate are so adhered as to sandwich the insulating film
between them. Then, the single-crystal silicon substrate is removed
from the lower surface of the first substrate, and the porous
silicon layer is etched to fabricate an SOI wafer. This method
requires an etching selectivity (porous silicon/epitaxial layer) of
only about 10.sup.5.
[0122] Even if an etching method having high selectivity is
employed, however, the surface of the SOI layer exposed upon
removing the porous silicon layer by etching is slightly etched.
Such slight unwanted etching does not seriously degrade the
thickness uniformity of the SOI layer, but higher selectivity and
higher thickness uniformity are demanded. In the future, as the
wafer size increases, higher thickness uniformity of the SOI layer
will be demanded.
[0123] When the wafer processing apparatus 100 is applied to a
porous silicon etching apparatus, in-plane variations of the SOI
layer and variations between wafers can be suppressed by swinging
wafers within the wafer processing bath, and higher-quality SOI
substrates can be fabricated.
[0124] By swinging wafers, and in addition, performing etching
while supplying ultrasonic waves, the collapse of the porous
silicon layer can be promoted, the etching time can be shortened,
and the etching selectivity can be increased.
[0125] An example of a method of fabricating a semiconductor
substrate using the wafer processing apparatus according to the
above embodiments will be described below.
[0126] FIGS. 8A to 8F are views, respectively, showing the method
of fabricating a semiconductor substrate. Roughly speaking, in this
fabrication method, the first substrate is prepared by forming a
porous silicon layer on a single-crystal silicon substrate, forming
an unporous layer on the porous silicon layer, and preferably
forming an insulating film on the unporous layer. The first
structure and a second substrate prepared separately are so adhered
as to sandwich the insulating film between them. After that, the
single-crystal silicon substrate is removed from the lower surface
of the first substrate, and the porous silicon layer is etched to
fabricate a semiconductor substrate.
[0127] The method of fabricating a semiconductor substrate will be
described in detail below with reference to FIGS. 8A to 8F.
[0128] A single-crystal Si substrate 501 for forming the first
substrate is prepared, and a porous Si layer 502 is formed on the
major surface of the single-crystal Si substrate 501 (see FIG. 8A).
At least one unporous layer 503 is formed on the porous Si layer
502 (see FIG. 8B). Preferable examples of the unporous layer 503
are a single-crystal Si layer, a poly-Si layer, an amorphous Si
layer, a metal film layer, a compound semiconductor layer, and a
superconductor layer. An element such as MOSFET may be formed on
the unporous layer 503.
[0129] An SiO.sub.2 layer 504 is preferably formed as another
unporous layer on the unporous layer 503, and used as the first
substrate (see FIG. 8C). The SiO.sub.2 layer 504 is useful because,
when the first substrate and a second substrate 505 are adhered in
the subsequent step, the interface energy at the adhered interface
can be removed from an active layer.
[0130] The first substrate and the second substrate 505 are tightly
adhered at room temperature so as to sandwich the SiO.sub.2 layer
504 between them (see FIG. 8D). This adhesion may be strengthened
by performing anode coupling, pressurization, or heat treatment, as
needed, or a combination of them.
[0131] When a single-crystal Si layer is formed as the unporous
layer 503, the first substrate is preferably adhered to the second
substrate 505 after the SiO.sub.2 layer 504 is formed on the
surface of the single-crystal Si layer by thermal oxidization or
the like.
[0132] Preferable examples of the second substrate 505 are an Si
substrate, a substrate having an SiO.sub.2 layer formed on an Si
substrate, a light-transmitting substrate such as a quartz
substrate or the like, and a sapphire substrate. The second
substrate 505 suffices to have a flat surface to be adhered, and
may be another type of substrate.
[0133] FIG. 8D shows the adhered state of the first and second
substrates via the SiO.sub.2 layer 504. The SiO.sub.2 layer 504
need not be formed when the unporous layer 503 or the second
substrate is not Si.
[0134] In adhesion, a thin insulating plate may be inserted between
the first and second substrates.
[0135] The first substrate is removed from the second substrate at
the boundary of the porous Si layer 502 (see FIG. 8E). The removal
method includes the first method (of discarding the first
substrate) using grinding, polishing, etching, or the like, and the
second method of separating the first and second substrates at the
boundary of the porous layer 502. In the second method, the first
substrate can be recycled by removing porous Si left on the
separated first substrate, and planarizing the surface of the first
substrate, as needed.
[0136] The porous Si layer 502 is selectively etched and removed
(see FIG. 8F). The wafer processing apparatus 100 or 101 is
suitable for this etching. Since this wafer processing apparatus
supplies ultrasonic waves while completely dipping a wafer (in this
case, the wafer shown in FIG. 8E) into an etching solution and
swinging it, the wafer is hardly contaminated by particles, and the
etching is made uniform. According to this wafer processing
apparatus, the etching time is shortened, and the etching
selectivity between the unporous layer 503 and the porous layer 504
increases. The etching time is shortened because etching is
promoted by ultrasonic waves, and the etching selectivity increases
because the promotion of etching by ultrasonic waves is more
remarkable on the porous layer 504 than on the unporous layer
503.
[0137] When the unporous layer 503 is single-crystal Si, the
following etching solutions are suited in addition to a general
etching solution for Si.
[0138] (a) hydrofluoric acid
[0139] (b) solution mixture prepared by adding at least one of
alcohol and hydrogen peroxide to hydrofluoric acid
[0140] (c) buffered hydrofluoric acid
[0141] (d) solution mixture prepared by adding at least one of
alcohol and hydrogen peroxide to buffered hydrofluoric acid
[0142] (e) solution mixture of hydrofluoric acid, nitric acid, and
acetic acid
[0143] Using these etching solutions, the porous layer 502 can be
selectively etched to leave the underlying unporous layer 503
(single-crystal Si). The porous layer 502 is readily selectively
etched by these etching solutions because porous Si has an enormous
surface area and hence etching progresses at a very high speed for
the unporous Si layer.
[0144] FIG. 8E schematically shows a semiconductor substrate
obtained by the above fabrication method. According to this
fabrication method, the flat unporous layer 503 (e.g.,
single-crystal Si layer) is uniformly formed on the entire surface
of the second substrate 505.
[0145] For example, if an insulating substrate is employed as the
second substrate 505, the semiconductor substrate obtained by the
above fabrication method is effectively used to form insulated
electronic elements.
[0146] The present invention can make wafer processing uniform, and
can prevent contamination of a wafer caused by particles.
[0147] The present invention is not limited to the above
embodiments and various changes and modifications can be made
within the spirit and scope of the present invention. Therefore, to
apprise the public of the scope of the present invention the
following claims are made.
* * * * *