U.S. patent application number 10/081068 was filed with the patent office on 2002-06-27 for composite member and separating method therefor, bonded substrate stack and separating method therefor, transfer method for transfer layer, and soi substrate manufacturing method.
Invention is credited to Kurisu, Hirokazu, Ohmi, Kazuaki, Sakaguchi, Kiyofumi, Yanagita, Kazutaka.
Application Number | 20020081822 10/081068 |
Document ID | / |
Family ID | 12167341 |
Filed Date | 2002-06-27 |
United States Patent
Application |
20020081822 |
Kind Code |
A1 |
Yanagita, Kazutaka ; et
al. |
June 27, 2002 |
Composite member and separating method therefor, bonded substrate
stack and separating method therefor, transfer method for transfer
layer, and SOI substrate manufacturing method
Abstract
A bonded substrate stack formed by bonding first and second
substrates is appropriately separated. A first substrate having a
porous layer inside and a single-crystal Si layer and insulating
layer on the porous layer is brought into tight contact with a
second substrate while shifting their central positions to prepare
a bonded substrate stack having a projecting portion at which the
outer peripheral edge of the first substrate projects outside that
of the second substrate. First, a fluid is ejected to the
projecting portion to form a separation start portion, and then,
separation is started from the separation start portion while
rotating the bonded substrate stack.
Inventors: |
Yanagita, Kazutaka;
(Yokohama-shi, JP) ; Ohmi, Kazuaki; (Yokohama-shi,
JP) ; Sakaguchi, Kiyofumi; (Yokohama-shi, JP)
; Kurisu, Hirokazu; (Nagoya-shi, JP) |
Correspondence
Address: |
MORGAN & FINNEGAN, L.L.P.
345 Park Avenue
New York
NY
10154-0053
US
|
Family ID: |
12167341 |
Appl. No.: |
10/081068 |
Filed: |
February 21, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10081068 |
Feb 21, 2002 |
|
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09494851 |
Feb 1, 2000 |
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6376332 |
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Current U.S.
Class: |
438/455 ;
257/E21.567; 257/E21.57 |
Current CPC
Class: |
H01L 21/76251 20130101;
H01L 21/76259 20130101; H01L 2223/54493 20130101 |
Class at
Publication: |
438/455 |
International
Class: |
H01L 021/30; H01L
021/46 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 2, 1999 |
JP |
11-025484 |
Claims
What is claimed is:
1. A method of separating a composite member having a structure in
which a first member having a separation layer inside is brought
into tight contact with a second member, wherein said composite
member has a projecting portion at which an outer peripheral edge
of said first member projects outside that of said second member,
and said method comprises the separation step of starting
separating said composite member from said projecting portion and
then separating said composite member into two members at said
separation layer.
2. The method according to claim 1, wherein a major surface of said
first member has the same shape as that of said second member, and
said composite member has a structure in which the major surface of
said first member is brought into tight contact with the major
surface of said second member while shifting central positions from
each other.
3. The method according to claim 1, wherein a major surface of said
second member is smaller than that of said first member, and said
composite member has a structure in which the major surface of said
first member is brought into tight contact with the major surface
of said second member.
4. The method according to claim 1, wherein the separation step
comprises: the pre-separation step of processing said projecting
portion to form a separation start portion; and the main separation
step of starting separating said composite member from said
separation start portion and then breaking substantially only said
separation layer to separate said composite member into two members
at said separation layer.
5. A method of bringing a first member having a separation layer
inside into tight contact with a second member to manufacture a
composite member having a projecting portion at which an outer
peripheral edge of said first member projects outside that of said
second member.
6. A method of transferring a transfer layer on a surface of a
first member to a second member, comprising: the preparation step
of bringing a first member having a separation layer inside and
said transfer layer on said separation layer into tight contact
with a second member to prepare a composite member in which an
outer peripheral edge of said first member projects outside that of
said second member; and the separation step for starting separating
said composite member from said projecting portion and separating
said composite member into two members at said separation layer,
thereby transferring said transfer layer of said first member to
said second member.
7. A separating method of separating into two substrates a bonded
substrate stack having a structure formed by bringing a transfer
layer of a first substrate having a separation layer inside and
said transfer layer on said separation layer into tight contact
with a second substrate, wherein said bonded substrate stack has a
projecting portion at which an outer peripheral edge of said first
substrate projects outside that of said second substrate, and said
separation method comprises the separation step of starting
separating said bonded substrate stack from said projecting portion
and then separating said bonded substrate stack into two substrates
at said separation layer.
8. The method according to claim 7, wherein said first substrate
has the same size as that of said second substrate, and said bonded
substrate stack has a structure in which said first substrate and
said second substrate are brought into tight contact while shifting
central positions from each other.
9. The method according to claim 7, wherein said bonded substrate
stack has a structure in which said first substrate is brought into
tight contact with said second substrate smaller than said first
substrate.
10. The method according to claim 7, wherein said second substrate
has one of an orientation flat and a notch, and said bonded
substrate stack has, as said projecting portion, a portion where
said first substrate is exposed in the presence of the orientation
flat or notch of said second substrate.
11. The method according to claim 7, wherein each of said first
substrate and said second substrate has one of an orientation flat
and a notch, and said bonded substrate stack is formed by bringing
said first substrate and said second substrate into tight contact
with each other without matching the orientation flat or notch of
said first substrate with the orientation flat or notch of said
second substrate, and has, as said projecting portion, a portion
where said first substrate is exposed in the presence of the
orientation flat or notch of said second substrate.
12. A method of bonding a transfer layer of a first substrate
having a separation layer inside and said transfer layer on said
separation layer to a second substrate to manufacture a bonded
substrate stack having a projecting portion at which an outer
peripheral edge of said first substrate projects outside that of
said second substrate.
13. A transfer method of transferring a transfer layer on a surface
of a first substrate to a second substrate, comprising: the
preparation step of bonding said transfer layer of said first
substrate having a separation layer inside and said transfer layer
on said separation layer to said second substrate to prepare a
bonded substrate stack having a projecting portion at which an
outer peripheral edge of said first substrate projects outside that
of said second substrate; and the separation step of starting
separating said bonded substrate stack from said projecting portion
and then separating said bonded substrate stack at said separation
layer, thereby transferring said transfer layer of said first
substrate to said second substrate.
14. The method according to claim 13, wherein the preparation step
comprises bringing said first substrate and said second substrate,
which have the same size, into tight contact with each other while
shifting central positions to prepare said bonded substrate
stack.
15. The method according to claim 13, wherein the preparation step
comprises bringing said first substrate into tight contact with
said second substrate smaller than said first substrate to prepare
said bonded substrate stack.
16. The method according to claim 13, wherein the preparation step
comprises bringing said first substrate into tight contact with
said second substrate having one of an orientation flat and a notch
to prepare said bonded substrate stack having, as said projecting
portion, a portion where said first substrate is exposed in the
presence of the orientation flat or notch of said second
substrate.
17. The method according to claim 13, wherein the preparation step
comprises preparing said first substrate and said second substrate
each having one of an orientation flat and a notch, and bringing
said first substrate and said second substrate into tight contact
with each other without matching the orientation flat or notch of
said first substrate with the orientation flat or notch of said
second substrate to prepare said bonded substrate stack.
18. The method according to claim 13, wherein the separation step
comprises: the pre-separation step of processing said projecting
portion to form a separation start portion; and starting separating
said bonded substrate stack from said separation start portion and
then breaking substantially only said separation layer to separate
said bonded substrate stack into two substrates at said separation
layer.
19. The method according to claim 18, wherein the pre-separation
step comprises ejecting a fluid to said projecting portion to form
said separation start portion by the fluid.
20. The method according to claim 18, wherein the pre-separation
step comprises inserting a wedge-shaped member into a gap between
said first substrate and said second substrate at said projecting
portion to form said separation start portion.
21. The method according to claim 18, wherein the pre-separation
step comprises supplying a vibration energy to said projecting
portion to form said separation start portion.
22. The method according to claim 18, wherein the pre-separation
step comprises dipping said projecting portion in a liquid and
supplying a vibration energy to said projecting portion through the
liquid to form said separation start portion.
23. The method according to claim 22, wherein water is used as the
liquid.
24. The method according to claim 22, wherein an etchant is used as
the liquid.
25. The method according to claim 18, wherein the pre-separation
step comprises etching said transfer layer and said separation
layer at said projecting portion to form said separation start
portion.
26. The method according to claim 13, wherein the separation step
comprises ejecting a fluid to said projecting portion to form said
separation start portion on said bonded substrate stack and
continuing separating said bonded substrate stack while changing a
position where the fluid is injected.
27. The method according to claim 13, wherein the separation step
comprises inserting a wedge-shaped member into a gap between said
first substrate and said second substrate at said projecting
portion to separate said bonded substrate stack.
28. The method according to claim 18, wherein said separation start
portion is a portion where said separation layer at said portion
has the most fragile structure.
29. The method according to claim 18, wherein said separation start
portion is a portion where said transfer layer at said portion is
removed, and said separation layer under said transfer layer is
exposed.
30. The method according to claim 18, wherein said separation start
portion is a portion where said separation layer at said portion is
exposed, and an outer peripheral edge of said separation layer is
located inside said bonded substrate stack.
31. The method according to claim 13, wherein said separation layer
is a porous layer.
32. The method according to claim 13, wherein said first substrate
is a substrate formed by anodizing a substrate to form a porous
layer as the separation layer and forming said transfer layer on
said separation layer.
33. The method according to claim 13, wherein said first substrate
has, as said separation layer, a porous layer formed by ion
implantation.
34. The method according to claim 13, wherein said transfer layer
includes a single-crystal Si layer.
35. The method according to claim 13, wherein said transfer layer
sequentially has a single-crystal Si layer and an insulating layer
as said transfer layer.
36. A method of manufacturing an SOI substrate, comprising: the
preparation step of bringing a surface of a first substrate having
a porous layer inside and a transfer layer including a
single-crystal Si layer on said porous layer into tight contact
with a second substrate to prepare a bonded substrate stack having
a projecting portion at which an outer peripheral edge of said
first substrate projects outside that of said second substrate; the
separation step for starting separating said bonded substrate stack
from said projecting portion and separating said bonded substrate
stack at said porous layer, thereby transferring said transfer
layer of said first substrate to said second substrate; and the
removal step of removing said porous layer remaining on a surface
of said second substrate after separation.
37. The method according to claim 36, wherein said first substrate
has, as said transfer layer, not only said single-crystal Si layer
but also an insulating layer on said single-crystal Si layer.
38. The method according to claim 36, wherein said second substrate
has an insulating layer on a surface.
39. The method according to claim 36, wherein the preparation step
comprises bringing said first substrate and said second substrate,
which have the same size, into tight contact with each other while
shifting central positions to prepare said bonded substrate
stack.
40. The method according to claim 36, wherein the preparation step
comprises bringing said first substrate into tight contact with
said second substrate smaller than said first substrate to prepare
said bonded substrate stack.
41. The method according to claim 40, wherein the preparation step
comprises bringing said first substrate into tight contact with
said second substrate while making the central positions match with
each other.
42. The method according to claim 36, wherein the preparation step
comprises bringing said first substrate into tight contact with
said second substrate having one of an orientation flat and a notch
to prepare said bonded substrate stack having, as said projecting
portion, a portion where said first substrate is exposed in the
presence of the orientation flat or notch of said second
substrate.
43. The method according to claim 36, wherein the preparation step
comprises preparing said first substrate and said second substrate
each having one of an orientation flat and a notch, and bringing
said first substrate and said second substrate into tight contact
with each other without matching the orientation flat or notch of
said first substrate with the orientation flat or notch of said
second substrate to prepare said bonded substrate stack.
44. The method according to claim 36, wherein the separation step
comprises: the pre-separation step of processing said projecting
portion to form a separation start portion; and starting separating
said bonded substrate stack from said separation start portion and
then breaking substantially only said porous layer to separate said
bonded substrate stack into two substrates at said porous
layer.
45. The method according to claim 44, wherein the pre-separation
step comprises ejecting a fluid to said projecting portion to form
said separation start portion by the fluid.
46. The method according to claim 44, wherein the pre-separation
step comprises inserting a wedge-shaped member into a gap between
said first substrate and said second substrate at said projecting
portion to form said separation start portion.
47. The method according to claim 44, wherein the pre-separation
step comprises supplying a vibration energy to said projecting
portion to form said separation start portion.
48. The method according to claim 44, wherein the pre-separation
step comprises dipping said projecting portion in a liquid and
supplying a vibration energy to said projecting portion through the
liquid to form said separation start portion.
49. The method according to claim 48, wherein water is used as the
liquid.
50. The method according to claim 48, wherein an etchant is used as
the liquid.
51. The method according to claim 44, wherein the pre-separation
step comprises etching said transfer layer and said porous layer at
said projecting portion to form said separation start portion.
52. The method according to claim 36, wherein the separation step
comprises ejecting a fluid to said projecting portion to form said
separation start portion on said bonded substrate stack and
continuing separating said bonded substrate stack while changing a
position where the fluid is injected.
53. The method according to claim 36, wherein the separation step
comprises inserting a wedge-shaped member into a gap between said
first substrate and said second substrate at said projecting
portion to separate said bonded substrate stack.
54. The method according to claim 36, wherein said separation start
portion is a portion where said porous layer at said portion has
the most fragile structure.
55. The method according to claim 36, wherein said separation start
portion is a portion where said transfer layer at said portion is
removed, and said porous layer under said transfer layer is
exposed.
56. The method according to claim 36, wherein said separation start
portion is a portion where said porous layer at said portion is
exposed, and an outer peripheral edge of said porous layer is
located inside said bonded substrate stack.
57. A composite member having a structure in which a first member
having a separation layer inside is brought into tight contact with
a second member, comprising: a projecting portion at which an outer
peripheral edge of said first member projects outside that of said
second member.
58. A bonded substrate stack having a structure in which a first
substrate having a separation layer inside and a transfer layer on
said separation layer is brought into tight contact with a second
substrate, comprising: a projecting portion at which an outer
peripheral edge of said first substrate projects outside that of
said second substrate.
59. A bonded substrate stack formed by bonding a surface of a first
substrate having a porous layer inside and a transfer layer
including a single-crystal Si layer on said porous layer to a
second substrate, comprising: a projecting portion at which an
outer peripheral edge of said first substrate projects outside that
of said second substrate.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a composite member and
separating method therefor, a bonded substrate stack and separating
method therefor, a transfer method for transfer layer, and an SOI
substrate manufacturing method.
[0003] 2. Description of the Related Art
[0004] A substrate (SOI substrate) having an SOI (Silicon On
Insulator) structure is known as a substrate having a
single-crystal Si layer on an insulating layer. A device using this
SOI substrate has many advantages that cannot be achieved by
ordinary Si substrates. Examples of the advantages are as
follows.
[0005] (1) The integration degree can be increased because
dielectric isolation is easy.
[0006] (2) The radiation resistance can be increased.
[0007] (3) The operating speed of the device can be increased
because the stray capacitance is small.
[0008] (4) No well step is necessary.
[0009] (5) Latch-up can be prevented.
[0010] (6) A complete depletion type field effect transistor can be
formed by thin film formation.
[0011] Since an SOI structure has the above various advantages,
researches-have been made on its formation method for several
decades.
[0012] As one SOI technology, the SOS (Silicon On Sapphire)
technology by which Si is heteroepitaxially grown on a
single-crystal sapphire substrate by CVD (Chemical Vapor
Deposition) has been known for a long time. This SOS technology
once earned a reputation as the most matured SOI technology.
However, the SOS technology has not been put into practical use to
date because, e.g., a large amount of crystal defects are produced
by lattice mismatch in the interface between the Si layer and the
underlying sapphire substrate, aluminum that forms the sapphire
substrate mixes in the Si layer, the substrate is expensive, and it
is difficult to obtain a large area.
[0013] Attempts have recently been made to realize the SOI
structure without using any sapphire substrate. The attempts are
roughly classified into two methods.
[0014] In the first method, the surface of a single-crystal Si
substrate is oxidized, and a window is formed in the oxide film
(SiO.sub.2 layer) to partially expose the Si substrate.
Single-crystal Si is epitaxially grown laterally using the exposed
portion as a seed, thereby forming a single-crystal Si layer on
SiO.sub.2 (in this method, an Si layer is deposited an SiO.sub.2
layer).
[0015] In the second method, a single-crystal Si substrate itself
is used as an active layer, and an SiO.sub.2 layer is formed on the
lower surface of the substrate (in this method, no Si layer is
deposited).
[0016] As a means for realizing the first method, a method of
directly epitaxially growing single-crystal Si in the horizontal
direction from the single-crystal Si layer by CVD (CVD), a method
of depositing amorphous Si and epitaxially growing single-crystal
Si laterally in the solid phase by annealing (solid phase epitaxial
growth), a method of irradiating an amorphous silicon layer or a
polysilicon layer with a focused energy beam such as an electron
beam or laser beam to grow a single-crystal Si layer on an
SiO.sub.2 layer by melting recrystallization (beam annealing), or a
method of scanning band-shaped melting regions by a rod-like heater
(zone melting recrystallization) is known.
[0017] All of these methods have both advantages and disadvantages
and many problems of controllability, productivity, uniformity, and
quality, and therefore have not been put into practical use in
terms of industrial applications. For example, CVD requires
sacrifice oxidation to form a flat thin film. Solid phase epitaxial
growth is poor in crystallinity. In beam annealing, the process
time required to scan the focused beam and controllability for beam
superposition or focal point adjustment pose problems. Zone melting
recrystallization is the most matured technique, and relatively
large-scaled integrated circuits have been fabricated on a trial
basis. However, since a number of crystal defects such as a
subboundary undesirably remain, minority carrier devices cannot be
created.
[0018] As the above second method, i.e., as the method without
using the Si substrate as a seed for epitaxial growth, the
following four techniques can be used.
[0019] As the first technique, an oxide film is formed on a
single-crystal Si substrate having a V-shaped groove formed in the
surface by anisotropic etching. A polysilicon layer having nearly
the same thickness as that of the single-crystal Si substrate is
deposited on the oxide film. After this, the single-crystal Si
substrate is polished from the lower surface, thereby forming, on
the thick polysilicon layer, a substrate having a single-crystal Si
region surrounded and dielectrically isolated by the V-shaped
groove. With this technique, a substrate having satisfactory
crystallinity can be formed. However, there are problems of
controllability and productivity in association with the process of
depositing polysilicon as thick as several hundred micron or the
process of polishing the single-crystal Si substrate from the lower
surface to leave the isolated Si active layer.
[0020] The second technique is SIMOX (Separation by Ion Implanted
Oxygen). In this technique, oxygen ions are implanted into a
single-crystal Si substrate to form an SiO.sub.2 layer. In this
technique, to form an SiO.sub.2 layer in a substrate, oxygen ions
must be implanted at a dose of 10.sup.18 (ions/cm.sup.2) or more.
This implantation takes a long time to result in low productivity
and high manufacturing cost. In addition, since a number of crystal
defects are generated, the quality is too low to manufacture
minority carrier devices.
[0021] As the third technique, an SOI structure is formed by
dielectric isolation by oxidizing a porous Si layer. In this
technique, an n-type Si island is formed on the surface of a p-type
single-crystal Si substrate by proton ion implantation (Imai et
al., J. Crystal Growth, vol. 63, 547 (1983)) or epitaxial growth
and patterning. This substrate is anodized in an HF solution to
convert only the p-type Si substrate around the n-type Si island
into a porous structure. After this, the n-type Si island is
dielectrically isolated by accelerated oxidation. In this
technique, since the Si region to be isolated must be determined
before the device process, the degree of freedom in device design
is limited.
[0022] As the fourth technique, an SOI structure is formed by
bonding a single-crystal Si substrate to another thermally oxidized
single-crystal Si substrate by annealing or an adhesive. In this
technique, an active layer for forming a device must be uniformly
thin. More specifically, a single-crystal Si substrate having a
thickness of several hundred micron must be thinned down to the
micron order or less.
[0023] To thin the substrate, polishing or selective etching can be
used.
[0024] A single-crystal Si substrate can hardly be uniformly
thinned by polishing. Especially, in thinning to the submicron
order, the variation range is several ten %. As the wafer size
becomes large, this difficulty becomes more pronounced.
[0025] Selective etching is effective to uniformly thin the
substrate. However, the selectivity ratio is as low as about
10.sup.2, the surface planarity after etching is poor, and the
crystallinity of the SOI layer is unsatisfactory.
[0026] A transparent substrate represented by a glass substrate is
important in forming a contact sensor as a light-receiving element
or a projection liquid crystal display device. To realize highly
precise pixels (picture elements) having higher density and
resolution for the sensor or display device, a high-performance
driving element is required. For this purpose, a demand has arisen
for a technique of forming a single-crystal Si layer having
excellent crystallinity on a transparent substrate.
[0027] However, when an Si layer is deposited on a transparent
substrate represented by a glass substrate, only an amorphous Si
layer or a polysilicon layer is obtained. This is because the
transparent substrate has an amorphous crystal structure, and the
Si layer formed on the substrate reflects the disorderliness of the
crystal structure of the transparent substrate.
[0028] The present applicant has disclosed a new SOI technology in
Japanese Patent Laid-Open No. 5-21338. In this technique, a first
substrate obtained by forming a porous layer on a single-crystal Si
substrate and a non-porous single-crystal layer on its surface is
bonded to a second substrate via an insulating layer. After this,
the bonded substrate stack is separated into two substrates at the
porous layer, thereby transferring the non-porous single-crystal
layer to the second substrate. This technique is advantageous
because the film thickness uniformity of the SOI layer is good, the
crystal defect density in the SOI layer can be decreased, the
surface planarity of the SOI layer is good, no expensive
manufacturing apparatus with special specifications is required,
and SOI substrates having about several hundred-.ANG. to 10-.mu.m
thick SOI films can be manufactured by a single manufacturing
apparatus.
[0029] The present applicant has also disclosed, in Japanese Patent
Laid-Open No. 7-302889, a technique of bonding first and second
substrates, separating the first substrate from the second
substrate without breaking the first substrate, smoothing the
surface of the separated first substrate, forming a porous layer
again on the first substrate, and reusing this substrate. Since the
first substrate is not wasted, this technique is advantageous in
largely reducing the manufacturing cost and simplifying the
manufacturing process.
[0030] To separate the bonded substrate stack into two substrates
without breaking the first and second substrates, for example, the
two substrates are pulled in opposite directions while applying a
force in a direction perpendicular to the bonding interface, a
shearing force is applied parallel to the bonding interface (for
example, the two substrates are moved in opposite directions in a
plane parallel to the bonding interface, or the two substrates are
rotated in opposite directions while applying a force in the
circumferential direction), a pressure is applied in a direction
perpendicular to the bonding interface, a wave energy such as an
ultrasonic wave is applied to the separation region, a peeling
member (e.g., a sharp blade such as knife) is inserted into the
separation region parallel to the bonding interface from the side
surface of the bonded substrate stack, the expansion energy of a
substance filling the pores of the porous layer functioning as the
separation region is used, the porous layer functioning as the
separation region is thermally oxidized from the side surface of
the bonded substrate stack to expand the volume of the porous layer
and separate the substrates, or the porous layer functioning as the
separation region is selectively etched from the side surface of
the bonded substrate stack to separate the substrate.
[0031] Porous Si was found in 1956 by Uhlir et al. who were
studying electropolishing of semiconductors (A. Uhlir, Bell Syst.
Tech. J., vol. 35, 333 (1956)). Porous Si can be formed by
anodizing an Si substrate in an HF solution.
[0032] Unagami et al. studied the dissolution reaction of Si upon
anodizing and reported that holes were necessary for anodizing
reaction of Si in an HF solution, and the reaction was as follows
(T. Unagami, J. Electrochem. Soc., vol. 127, 476 (1980)).
Si+2HF+(2-n)e.sup.+.fwdarw.SiF.sub.2+2H.sup.+ne.sup.-
SiF.sub.2+2HF.fwdarw.SiF.sub.4+H.sub.2
SiF.sub.4+2HF.fwdarw.H.sub.2SiF.sub.6
[0033] or
Si+4HF+(4-.lambda.)e.sup.+.fwdarw.SiF.sub.4+4H.sup.++.lambda.e.sup.-
SiF.sub.4+2HF.fwdarw.H.sub.2SiF.sub.6
[0034] where e.sup.+ and e.sup.- represent a hole and an electron,
respectively, and n and .lambda. are the number of holes necessary
to dissolve one Si atom. According to them, when n>2 or
.lambda.>4, porous Si is formed.
[0035] The above fact suggests that p-type Si having holes is
converted into porous Si while n-type Si is not converted. The
selectivity in this conversion has been reported by Nagano et al.
and Imai (Nagano, Nakajima, Anno, Onaka, and Kajiwara, IEICE
Technical Report, vol. 79, SSD79-9549 (1979)), (K. Imai,
Solid-State Electronics, vol. 24, 159 (1981)).
[0036] However, it has also been reported that n-type at a high
concentration is converted into porous Si (R. P. Holmstrom and J.
Y. Chi, Appl. Phys. Lett., vol. 42, 386 (1983)). Hence, it is
important to select a substrate which can be converted into a
porous Si substrate independently of p- or n-type.
[0037] To form a porous layer, in addition to anodization, ions may
be implanted into a silicon substrate.
[0038] For example, in the method described in Japanese Patent
Laid-Open No. 5-213:38, i.e., the method in which a substrate (to
be referred to as a bonded substrate stack hereinafter) obtained by
bonding a first substrate having a non-porous layer such as a
single-crystal Si layer on a porous layer to a second substrate via
an insulating layer is separated at the porous layer, thereby
transferring the non-porous layer formed on the first substrate
side to the second substrate, the technique of separating the
bonded substrate stack is very important.
[0039] For example, in separating the bonded substrate stack, if it
is separated at a portion except the porous layer as the separation
layer, the non-porous layer (e.g., a single-crystal Si layer) to be
used as an active layer is broken, and no desired SOI substrate can
be obtained.
SUMMARY OF THE INVENTION
[0040] The present invention has been made in consideration of the
above situation, and has as its object to make it possible to
appropriately separate a composite member such as a bonded
substrate stack at a separation layer such as a porous layer.
[0041] According to the first aspect of the present invention,
there is provided a method of separating a composite member having
a structure in which a first member having a separation layer
inside is brought into tight contact with a second member,
characterized in that the composite member has a projecting portion
at which an outer peripheral edge of the first member projects
outside that of the second member, and the method comprises the
separation step of starting separating the composite member from
the projecting portion and then separating the composite member
into two members at the separation layer.
[0042] In the composite member separating method according to the
first aspect of the present invention, preferably, for example, a
major surface of the first member has the same shape as that of the
second member, and the composite member has a structure in which
the major surface of the first member is brought into tight contact
with the major surface of the second member while shifting central
positions from each other.
[0043] In the composite member separating method according to the
first aspect of the present invention, preferably, for example, a
major surface of the second member is smaller than that of the
first member, and the composite member has a structure in which the
major surface of the first member is brought into tight contact
with the major surface of the second member.
[0044] In the composite member separating method according to the
first aspect of the present, invention, for example, the separation
step preferably comprises the pre-separation step of processing the
projecting portion to form a separation start portion, and the main
separation step of starting separating the composite member from
the separation start portion and then breaking substantially only
the separation layer to separate the composite member into two
members at the separation layer.
[0045] According to the second aspect of the present invention,
there is provided a composite member manufacturing method
characterized by comprising bringing a first member having a
separation layer inside into tight contact with a second member to
manufacture a composite member having a projecting portion at which
an outer peripheral edge of the first member projects outside that
of the second member.
[0046] According to the third aspect of the present invention,
there is provided a method of transferring a transfer layer on a
surface of a first member to a second member, characterized by
comprising the preparation step of bringing a first member having a
separation layer inside and the transfer layer on the separation
layer into tight contact with a second member to prepare a
composite member in which an outer peripheral edge of the first
member projects outside that of the second member, and the
separation step for starting separating the composite member from
the projecting portion and separating the composite member into two
members at the separation layer, thereby transferring the transfer
layer of the first member to the second member.
[0047] According to the fourth aspect of the present invention,
there is provided a separating method of separating into two
substrates a bonded substrate stack having a structure formed by
bringing a transfer layer of a first substrate having a. separation
layer inside and the transfer layer on the separation layer into
tight contact with a second substrate, characterized in that the
bonded substrate stack has a projecting portion at which an outer
peripheral edge of the first substrate projects outside that of the
second substrate, and the separation method comprises the
separation step of starting separating the bonded substrate stack
from the projecting portion and then separating the bonded
substrate stack into two substrates at the separation layer.
[0048] In the bonded substrate stack separating method according to
the fourth aspect of the present invention, preferably, for
example, the first substrate has the same size as that of the
second substrate, and the bonded substrate stack has a structure in
which the first substrate and the second substrate are brought into
tight contact while shifting central positions from each other.
[0049] In the bonded substrate stack separating method according to
the fifth aspect of the present invention, for example, the bonded
substrate stack preferably has a structure in which the first
substrate is brought into tight contact with the second substrate
smaller than the first substrate.
[0050] In the bonded substrate stack separating method according to
the fifth aspect of the present invention, preferably, for example,
the second substrate has one of an orientation flat and a notch,
and the bonded substrate stack has, as the projecting portion, a
portion where the first substrate is exposed in the presence of the
orientation flat or notch of the second substrate.
[0051] In the bonded substrate stack separating method according to
the fifth aspect of the present invention, preferably, for example,
each of the first substrate and the second substrate has one of an
orientation flat and a notch, and the bonded substrate stack is
formed by bringing the first substrate and the second substrate
into tight contact with each other without matching the orientation
flat or notch of the first substrate with the orientation flat or
notch of the second substrate, and has, as the projecting portion,
a portion where the first substrate is exposed in the presence of
the orientation flat or notch of the second substrate.
[0052] According to the sixth aspect of the present invention,
there is provided a bonded substrate stack manufacturing method
characterized by comprising bonding a transfer layer of a first
substrate having a separation layer inside and the transfer layer
on the separation layer to a second substrate to manufacture a
bonded substrate stack having a projecting portion at which an
outer peripheral edge of the first substrate projects outside that
of the second substrate.
[0053] According to the seventh aspect of the present invention,
there is provided a transfer method of transferring a transfer
layer on a surface of a first substrate to a second substrate,
characterized by comprising the preparation step of bonding the
transfer layer of the first substrate having a separation layer
inside and the transfer layer on the separation layer to the second
substrate to prepare a bonded substrate stack having a projecting
portion at which an outer peripheral edge of the first substrate
projects outside that of the second substrate, and the separation
step of starting separating the bonded substrate stack from the
projecting portion and then separating the bonded substrate stack
at the separation layer, thereby transferring the transfer layer of
the first substrate to the second substrate.
[0054] In the transfer layer transfer method according to the
seventh aspect of the present invention, for example, the
preparation step preferably comprises bringing the first substrate
and the second substrate, which have the same size, into tight
contact with each other while shifting central positions to prepare
the bonded substrate stack.
[0055] In the transfer layer transfer method according to the
seventh aspect of the present invention, for example, the
preparation step preferably comprises bringing the first substrate
into tight contact with the second substrate smaller than the first
substrate to prepare the bonded substrate stack.
[0056] In the transfer layer transfer method according to the
seventh aspect of the present invention, for example, the
preparation step preferably comprises bringing the first substrate
into tight contact with the second substrate having one of an
orientation flat and a notch to prepare the bonded substrate stack
having, as the projecting portion, a portion where the first
substrate is exposed in the presence of the orientation flat or
notch of the second substrate.
[0057] In the transfer layer transfer method according to the
seventh aspect of the present invention, for example, the
preparation step preferably comprises preparing the first substrate
and the second substrate each having one of an orientation flat and
a notch, and bringing the first substrate and the second substrate
into tight contact with each other without matching the orientation
flat or notch of the first substrate with the orientation flat or
notch of the second substrate to prepare the bonded substrate
stack.
[0058] In the transfer layer transfer method according to the
seventh aspect of the present invention, for example, the
separation step preferably comprises the pre-separation step of
processing the projecting portion to form a separation start
portion and starting separating the bonded substrate stack from the
separation start portion and then breaking substantially only the
separation layer to separate the bonded substrate stack into two
substrates at the separation layer.
[0059] In the transfer layer transfer method according to the
seventh aspect of the present invention, for example, the
pre-separation step preferably comprises ejecting a fluid to the
projecting portion to form the separation start portion by the
fluid.
[0060] In the transfer layer transfer method according to the
seventh aspect of the present invention, for example, the
pre-separation step preferably comprises inserting a wedge-shaped
member into a gap between the first substrate and the second
substrate at the projecting portion to form the separation start
portion.
[0061] In the transfer layer transfer method according to the
seventh aspect of the present invention, for example, the
pre-separation step preferably comprises supplying a vibration
energy to the projecting portion to form the separation start
portion.
[0062] In the transfer layer transfer method according to the
seventh aspect of the present invention, for example, the
pre-separation step preferably comprises dipping the projecting
portion in a liquid and supplying a vibration energy to the
projecting portion through the liquid to form the separation start
portion.
[0063] In the transfer layer transfer method according to the
seventh aspect of the present invention, for example, water is
preferably used as the liquid.
[0064] In the transfer layer transfer method according to the
seventh aspect of the present invention, for example, an etchant is
preferably used as the liquid.
[0065] In the transfer layer transfer method according to the
seventh aspect of the present invention, for example, the
pre-separation step preferably comprises etching the transfer layer
and the separation layer at the projecting portion to form the
separation start portion.
[0066] In the transfer layer transfer method according to the
seventh aspect of the present invention, for example, the
separation step preferably comprises ejecting a fluid to the
projecting portion to form the separation start portion on the
bonded substrate stack and continuing separating the bonded
substrate stack while changing a position where the fluid is
injected.
[0067] In the transfer layer transfer method according to the
seventh aspect of the present invention, for example, the
separation step preferably comprises inserting a wedge-shaped
member into a gap between the first substrate and the second
substrate at the projecting portion to separate the bonded
substrate stack.
[0068] In the transfer layer transfer method according to the
seventh aspect of the present invention, for example, the
separation start portion is preferably a portion where the
separation layer at the portion has the most fragile structure.
[0069] In the transfer layer transfer method according to the
seventh aspect of the present invention, for example, the
separation start portion is preferably a portion where the transfer
layer at the portion is removed, and the separation layer under the
transfer layer is exposed.
[0070] In the transfer layer transfer method according to the
seventh aspect of the present invention, for example, the
separation start portion is preferably a portion where the
separation layer at the portion is exposed, and an outer peripheral
edge of the separation layer is located inside the bonded substrate
stack.
[0071] In the transfer layer transfer method according to the
seventh aspect of the present invention, for example, the
separation layer is preferably a porous layer.
[0072] In the transfer layer transfer method according to the
seventh aspect of the present invention, for example, the first
substrate is preferably a substrate formed by anodizing a substrate
to form a porous layer as the separation layer and forming the
transfer layer on the separation layer.
[0073] In the transfer layer transfer method according to the
seventh aspect of the present invention, for example, the first
substrate preferably has, as the separation layer, a porous layer
formed by ion implantation.
[0074] In the transfer layer transfer method according to the
seventh aspect of the present invention, for example, the transfer
layer preferably includes a single-crystal Si layer.
[0075] In the transfer layer transfer method according to the
seventh aspect of the present invention, for example, the transfer
layer preferably sequentially has a single-crystal Si layer and an
insulating layer as the transfer layer.
[0076] According to the eighth aspect of the present invention,
there is provided a method of manufacturing an SOI substrate,
characterized by comprising the preparation step of bringing a
surface of a first substrate having a porous layer inside and a
transfer layer including a single-crystal Si layer on the porous
layer into tight contact with a second substrate to prepare a
bonded substrate stack having a projecting portion at which an
outer peripheral edge of the first substrate projects outside that
of the second substrate, the separation step for starting
separating the bonded substrate stack from the projecting portion
and separating the bonded substrate stack at the porous layer,
thereby transferring the transfer layer of the first substrate to
the second substrate, and the removal step of removing the porous
layer remaining on a surface of the second substrate after
separation.
[0077] In the SOI substrate manufacturing method according to the
eighth aspect of the present invention, for example, the first
substrate preferably has, as the transfer layer, not only the
single-crystal Si layer but also an insulating layer on the
single-crystal Si layer.
[0078] In the SOI substrate manufacturing method according to the
eighth aspect of the present invention, for example, the second
substrate preferably has an insulating layer on a surface.
[0079] In the SOI substrate manufacturing method according to the
eighth aspect of the present invention, for example, the
preparation step preferably comprises bringing the first substrate
and the second substrate, which have the same size, into tight
contact with each other while shifting central positions to prepare
the bonded substrate stack.
[0080] In the SOI substrate manufacturing method according to the
eighth aspect of the present invention, for example, the
preparation step preferably comprises bringing the first substrate
into tight contact with the second substrate smaller than the first
substrate to prepare the bonded substrate stack.
[0081] In the SOI substrate manufacturing method according to the
eighth aspect of the present invention, for example, the
preparation step preferably comprises bringing the first substrate
into tight contact with the second substrate while making the
central positions match with each other.
[0082] In the SOI substrate manufacturing method according to the
eighth aspect of the present invention, for example, the
preparation step preferably comprises bringing the first substrate
into tight contact with the second substrate having one of an
orientation flat and a notch to prepare the bonded substrate stack
having, as the projecting portion, a portion where the first
substrate is exposed in the presence of the orientation flat or
notch of the second substrate.
[0083] In the SOI substrate manufacturing method according to the
eighth aspect of the present invention, for example, the
preparation step preferably comprises preparing the first substrate
and the second substrate each having one of an orientation flat and
a notch, and bringing the first substrate and the second substrate
into tight contact with each other without matching the orientation
flat or notch of the first substrate with the orientation flat or
notch of the second substrate to prepare the bonded substrate
stack.
[0084] In the SOI substrate manufacturing method according to the
eighth aspect of the present invention, for example, the separation
step preferably comprises the pre-separation step of processing the
projecting portion to form a separation start portion, and starting
separating the bonded substrate stack from the separation start
portion and then breaking substantially only the porous layer to
separate the bonded substrate stack into two substrates at the
porous layer.
[0085] In the SOI substrate manufacturing method according to the
eighth aspect of the present invention, for example, the
pre-separation step preferably comprises ejecting a fluid to the
projecting portion to form the separation start portion by the
fluid.
[0086] In the SOI substrate manufacturing method according to the
eighth aspect of the present invention, for example, the
pre-separation step preferably comprises inserting a wedge-shaped
member into a gap between the first substrate and the second
substrate at the projecting portion to form the separation start
portion.
[0087] In the SOI substrate manufacturing method according to the
eighth aspect of the present invention, for example, the
pre-separation step preferably comprises supplying a vibration
energy to the projecting portion to form the separation start
portion.
[0088] In the SOI substrate manufacturing method according to the
eighth aspect of the present invention, for example, the
pre-separation step preferably comprises dipping the projecting
portion in a liquid and supplying a vibration energy to the
projecting portion through the liquid to form the separation start
portion.
[0089] In the SOI substrate manufacturing method according to the
eighth aspect of the present invention, for example, water is
preferably used as the liquid.
[0090] In the SOI substrate manufacturing method according to the
eighth aspect of the present invention, for example, an etchant is
preferably used as the liquid.
[0091] In the SOI substrate manufacturing method according to the
eighth aspect of the present invention, for example, the
pre-separation step preferably comprises etching the transfer layer
and the porous layer at the projecting portion to form the
separation start portion.
[0092] In the SOI substrate manufacturing method according to the
eighth aspect of the present invention, for example, the separation
step preferably comprises ejecting a fluid to the projecting
portion to form the separation start portion on the bonded
substrate stack and continuing separating the bonded substrate
stack while changing a position where the fluid is injected.
[0093] In the SOI substrate manufacturing method according to the
eighth aspect of the present invention, for example, the separation
step preferably comprises inserting a wedge-shaped member into a
gap between the first substrate and the second substrate at the
projecting portion to separate the bonded substrate stack.
[0094] In the SOI substrate manufacturing method according to the
eighth aspect of the present invention, for example, the separation
start portion is preferably a portion where the porous layer at the
portion has the most fragile structure.
[0095] In the SOI substrate manufacturing method according to the
eighth aspect of the present invention, for example, the separation
start portion is preferably a portion where the transfer layer at
the portion is removed, and the porous layer under the transfer
layer is exposed.
[0096] In the SOI substrate manufacturing method according to the
eighth aspect of the present invention, for example, the separation
start portion is preferably a portion where the porous layer at the
portion is exposed, and an outer peripheral edge of the porous
layer is located inside the bonded substrate stack.
[0097] According to the ninth aspect of the present invention,
there is provided a composite member having a structure in which a
first member having a separation layer inside is brought into tight
contact with a second member, characterized by comprising a
projecting portion at which an outer peripheral edge of the first
member projects outside that of the second member.
[0098] According to the 10th aspect of the present invention, there
is provided a bonded substrate stack having a structure in which a
first substrate having a separation layer inside and a transfer
layer on the separation layer is brought into tight contact with a
second substrate, characterized by comprising a projecting portion
at which an outer peripheral edge of the first substrate projects
outside that of the second substrate.
[0099] According to the 11th aspect of the present invention, there
is provided a bonded substrate stack formed by bonding a surface of
a first substrate having a porous layer inside and a transfer layer
including a single-crystal Si layer on the porous layer to a second
substrate, characterized by comprising a projecting portion at
which an outer peripheral edge of the first substrate projects
outside that of the second substrate.
[0100] Further objects, features and advantages of the present
invention will become apparent from the following detailed
description of the embodiments of the present invention with
reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0101] FIG. 1A is a schematic view for explaining the step of
forming a porous layer in a method of manufacturing an SOI
substrate according to a preferred embodiment of the present
invention;
[0102] FIG. 1B is a schematic view for explaining the step of
forming a single-crystal Si layer and insulating layer in the
method of manufacturing the SOI substrate according to the
preferred embodiment of the present invention;
[0103] FIG. 1C is a schematic view for explaining the bonding step
in the method of manufacturing the SOI substrate according to the
preferred embodiment of the present invention;
[0104] FIG. 1D is a schematic view for explaining the step of
forming a separation start region (pre-separation step) in the
method of manufacturing the SOI substrate according to the
preferred embodiment of the present invention;
[0105] Fig. 1E is a schematic view for explaining the separation
step (main separation step) in the method of manufacturing the SOI
substrate according to the preferred embodiment of the present
invention;
[0106] FIG. 1F is a schematic view for explaining the step of
removing the porous layer on the second substrate side and the SOI
substrate in the method of manufacturing the SOI substrate
according to the preferred embodiment of the present invention;
[0107] FIG. 1G is a schematic view for explaining the step of
removing the porous layer on the first substrate side in the method
of manufacturing the SOI substrate according to the preferred
embodiment of the present invention;
[0108] FIG. 2 is a perspective view showing an example of a bonded
substrate stack having a projecting portion formed by bonding first
and second substrates whose central positions are shifted;
[0109] FIG. 3 is a view schematically showing formation of a
separation start portion on the bonded substrate stack shown in
FIG. 2;
[0110] FIG. 4 is a view schematically showing separation of the
bonded substrate stack shown in FIG. 3;
[0111] FIG. 5 is a view showing an example of a bonded substrate
stack having a projecting portion formed by bringing a first
substrate and a second substrate smaller than the first substrate
into tight contact with each other;
[0112] FIG. 6 is a view schematically showing formation of a
separation start portion on the bonded substrate stack shown in
FIG. 5;
[0113] FIG. 7 is a view schematically showing separation of the
bonded substrate stack shown in FIG. 6;
[0114] FIG. 8 is a view showing the schematic arrangement of a
processing apparatus according to another preferred embodiment of
the present invention; and
[0115] FIG. 9 is a view showing the schematic arrangement of a
processing apparatus according to still another preferred
embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0116] Preferred embodiments of the present invention will be
described below with reference to the accompanying drawings.
[0117] FIGS. 1A to 1E are schematic views for explaining a method
of manufacturing an SOI substrate according to a preferred
embodiment of the present invention.
[0118] In the step shown in FIG. 1A, a single-crystal Si substrate
11 is prepared, and a porous Si layer 12 is formed on the surface
of the single-crystal Si substrate 11 by, e.g., anodizing.
[0119] In the step shown in FIG. 1B, a non-porous single-crystal Si
layer 13 is formed on the porous Si layer 12 by epitaxial growth.
The surface of the non-porous single-crystal Si layer 13 is
oxidized to form an insulating layer (SiO.sub.2) layer14. With this
process, a first substrate 10 is formed.
[0120] The porous Si layer 12 may be formed by, e.g., a method of
implanting ions of hydrogen, helium, or an inert gas into the
single-crystal Si substrate 11 (ion implantation). The porous Si
layer formed by this method has a number of microcavities and is
therefore called a microcavity layer.
[0121] In the step shown in FIG. 1C, a second substrate 20 of
single-crystal Si is prepared and brought into tight contact with
the first substrate 10 at room temperature while making the
insulating layer 14 oppose the second substrate 20, thereby forming
a bonded substrate stack.
[0122] In the preferred embodiment of the present invention, a
bonded substrate stack 30 is formed. The bonded substrate stack 30
has a portion (to be referred to as a projecting portion
hereinafter) where the outer peripheral edge of the first substrate
which has the porous layer 12 as a layer for separation (separation
layer) is partially located outside that of the second substrate
20. To form this bonded substrate stack 30, for example, the
following methods are preferably used.
[0123] (1) The first substrate 10 is brought into tight contact
with the second substrate 20 which has the same size as that of the
first substrate while shifting the central positions of the
substrates.
[0124] (2) The first substrate 10 is brought into tight contact
with the second substrate 20 smaller than the first substrate
10.
[0125] (3) A substrate having a notch or an orientation flat is
employed as the second substrate 20. The surface of the first
substrate 10 is exposed at the notch or orientation flat portion of
the second substrate. In this case, at the notch or orientation
flat portion of the second substrate 20, the outer peripheral edge
of the first substrate 10 projects outward from the outer
peripheral edge of the second substrate 20.
[0126] (4) After the first substrate 10 and second substrate 20 are
bonded, the outer peripheral portion of the second substrate is
partially or entirely ground.
[0127] In the method (3), when a substrate having a notch or an
orientation flat is employed as the first substrate 10, too, the
substrates are stacked such that the notch or orientation flat of
the first substrate 10 does not correspond with the notch or
orientation flat of the second substrate 20.
[0128] FIG. 1C schematically shows an example in which the method
of bringing the first substrate 10 and second substrate 20, which
have the same size, into tight contact with each other while
shifting their central positions. A projection amount D of the part
of the first substrate 10 need be, e.g., only about 0.1 to 0.5 mm,
and may be larger.
[0129] FIG. 2 is a perspective view schematically showing an
example of the bonded substrate stack 30 shown in FIG. 1C. FIG. 5
is a perspective view showing an example of the bonded substrate
stack 30 formed by bringing the first substrate 10 and the second
substrate 20 smaller than the first substrate 10 into tight contact
with each other while making their central positions match.
[0130] The insulating layer 14 may be formed on the single-crystal
Si layer 13 side, on the second substrate 20, or on both
single-crystal Si layer 13 and second substrate20 as far as the
state shown in FIG. lC is obtained upon bringing the first and
second substrates into tight contact with each other. However, when
the insulating layer 14 is formed on the side of the single-crystal
Si layer 13 serving as an active layer, an SOI substrate having a
higher quality can be obtained. This is because the bonding
interface between the first substrate 10 and the second substrate
20 can be apart: from the active layer.
[0131] In the step shown in FIG. 1D, a separation start portion 40
as a portion where separation starts is formed at the projecting
portion. More specifically, at least a part of the transfer layer
(single-crystal Si layer 13 and insulating layer 14) in a region of
the projecting portion of the first substrate 10 is removed, and
the porous layer under the transfer layer can be optionally
removed, to form the separation start portion 40. To form the
separation start portion 40, for example, the following methods are
preferably used.
[0132] (1) A fluid is ejected to the projecting portion to break
and remove the transfer layer and underlying porous layer 12 at
that portion.
[0133] (2) A wedge is inserted near the bonding interface (bonding
interface between the first substrate 10 and the second substrate
20) at the projecting portion, thereby breaking and removing the
transfer layer and underlying porous layer 12.
[0134] (3) A vibration energy such as an ultrasonic wave is applied
to the projecting portion to break the porous layer 12 at that
portion and peel the transfer layer on the porous layer 12.
[0135] (4) The projecting portion is dipped in an etchant, and the
transfer layer and underlying porous layer 12 are moved by
etching.
[0136] Referring to FIG. 1D, reference numeral 12a denotes a porous
layer after formation of the separation start portion 40; 13a, a
single-crystal Si layer after formation of the separation start
portion 40; and 14a, an insulating layer after formation of the
separation start portion 40.
[0137] The separation start portion 40 preferably has a structure
that allows only the porous layer 12 to break to separate the
bonded substrate stack into two substrates in the subsequent
separation step. Alternatively, the separation start portion 40 is
preferably a portion where the porous layer 12 is mechanically more
fragile than the single-crystal layer 13a, insulating layer 14a,
second substrate 20, single-crystal Si substrate, and the
interfaces between the layers or substrates.
[0138] More specifically, the separation start portion 40
preferably has a structure in which the porous layer 12 is exposed
to the side surface of the bonded substrate stack. More preferably,
the outer peripheral edge of the porous layer 12 is located inside
that of the transfer layer, as shown in FIG. 1D.
[0139] When the bonded substrate stack 30 having a projecting
portion is formed, the transfer layer and underlying porous layer
at that portion can be easily removed. This is because the transfer
layer at the projecting portion is exposed to a larger degree than
the transfer layer at the remaining portions. Hence, when a bonded
substrate stack having a projecting portion is formed, the
separation start portion can be easily formed.
[0140] When the separation start portion 40 is formed, the porous
layer 12 can be selectively broken to separate the bonded substrate
stack in the subsequent separating step. This effectively prevents
defects in the separation step.
[0141] In the step shown in FIG. 1E, for the bonded substrate stack
having the separation start portion 40, separation at the porous
layer 12 of the separation start portion 40 is started. Finally,
the bonded substrate stack is completely separated into two
substrates at the porous layer 12. To separate the bonded substrate
stack, for example, the following methods are preferably used.
[0142] (1) Separation Using Fluid
[0143] A stream of fluid (e.g., a liquid such as water or a gas
such as air or nitrogen) is ejected to the gap at the outer
peripheral portion of a bonded substrate stack. The bonded
substrate stack is separated into two substrates at the porous
layer 12 by the fluid.
[0144] (2) Separation Using Wedge
[0145] When a thin wedge of, e.g., a resin is gradually inserted
into the gap at the outer peripheral portion of a bonded substrate
stack, the bonded substrate stack is separated into two substrates
at the porous layer 12.
[0146] (3) Separation by Peeling
[0147] One surface of a bonded substrate stack is fixed, and the
other surface is pulled in the axial direction of the bonded
substrate stack using a flexible tape or the like, thereby
separating the bonded substrate stack at the porous layer.
[0148] (4) Separation Using Shearing Stress
[0149] One surface of a bonded substrate stack is fixed, and a
force is applied to the other surface so as to move the other
surface in the planar direction of the bonded substrate stack,
thereby separating the bonded substrate stack at the porous layer
by shearing stress.
[0150] The separation start portion formation step (pre-separation
step) shown in FIG. 1D and the separation step (main separation
step) shown in FIG. 1E may be continuously executed by one
processing apparatus. For example, preferably, a water jet
apparatus (separating apparatus using a fluid) is used, and the
separation start portion formation step (pre-separation step) and
the separation step (main separation step) are continuously
executed using a fluid such as water. In this case, separation
processing is started at the projecting portion and continued until
the bonded substrate stack is completely separated.
[0151] As described above, when the separation start portion is
formed, and then, separation processing is started from the
separation start portion, the bonded substrate stack can
substantially be separated only at the porous layer. Hence, break
(generation of defects) of the single-crystal layer 13a, insulating
layer 14a, second substrate 20, and single-crystal Si substrate 11,
and the interfaces between the layers or substrates can be
prevented.
[0152] In use of a bonded substrate stack having a projecting
portion, when a separation start portion is formed at the
projecting portion first, and overall separation is started from
the separation start portion, the bonded substrate stack can
substantially be separated only at the porous layer. Hence, the
single-crystal layer 13, insulating layer 14, second substrate 20,
and single-crystal Si substrate 11, and the interfaces between the
layers or substrates can be prevented from breaking.
[0153] When a bonded substrate stack (normal bonded substrate
stack) formed by bringing the first substrate 10 and second
substrate 20 which have the same size into tight contact with each
other while making their notches or orientation flats match is to
be directly separated, the single-crystal Si layer 13, insulating
layer 14, second substrate 20, and single-crystal Si substrate 11,
and the interfaces between the layers or substrates may break to
generate defects. This probably occurs due to the following
mechanism.
[0154] In a bonded substrate stack, it is ideal that the porous
layer 12 is most fragile. In fact, due to, e.g., stress acting
between the porous layer 12, single-crystal Si layer 13, insulating
layer 14, and second substrate 20 or bonding failure, a local
portion as fragile as the porbus layer 12 or a portion more fragile
than the porous layer 12 (these portions will be referred to as
defect inducing portions hereinafter) may be generated.
[0155] Such a defect inducing portion is preferentially broken in
separation processing to result in defects. Defects are readily
generated at a portion where separation processing starts, i.e., a
portion to which the force for separation (separation force) is
applied first. At the portion where separation processing starts,
i.e., the outer peripheral portion of the bonded substrate stack,
the same force acts on the porous layer 12, single-crystal Si layer
13, insulating layer 14, and second substrate 20. For this reason,
if a defect inducing portion is present, it may be broken prior to
the porous layer 12 at a high probability. As separation processing
progresses, the force for separation (separation force)
concentrically acts on the porous layer 12 as a layer whose average
strength is most fragile, and the separation force hardly acts on
the remaining portions. Hence, the porous layer 12 is selectively
separated independently of the presence/absence of the defect
inducing portion.
[0156] As in this embodiment, it is preferable to form the bonded
substrate stack 30 having a projecting portion, form the separation
start portion at the projecting portion, and start the subsequent
separation processing from the separation start portion 40.
[0157] With the separation step shown in FIG. 1E, a first substrate
10' after separation has a structure wherein a porous Si layer 12b
is formed on the single-crystal Si substrate 11. On the other hand,
a second substrate 20' after separation has a multilayered
structure of a porous layer 12c/single-crystal Si layer
13b/insulating layer 14b/single-crystal Si substrate 20.
[0158] That is, with the above process, the single-crystal Si layer
13 and insulating layer 14 on the porous layer 12 of the first
substrate can be transferred to the second substrate. The porous
layer 12 is an example of the separation layer, and the
single-crystal Si layer 13 and insulating layer 14 are examples of
the transfer layer to be transferred from the first substrate to
the second substrate.
[0159] In the step shown in FIG. iF, the porous layer 12c on the
surface of the second substrate 20' after separation is selectively
removed. With this process, an SOI substrate 50 having a
multilayered structure of a single-crystal Si layer 13b/insulating
layer 14b/single-crystal Si substrate 20, i.e., an SOI structure
can be obtained.
[0160] In the step shown in FIG. 1G, the porous layer 12b on the
single-crystal Si substrate 11 of the first substrate 10' after
separation is selectively removed by, e.g., etching. A
single-crystal Si substrate 11 obtained by this way can be reused
as a substrate used to form a first substrate 10, or a second
substrate 20 again.
[0161] As described above, according to this embodiment, a bonded
substrate stack having a projecting portion is formed, and a
separation start portion is formed at the projecting portion at the
start of separation processing. In the subsequent separation
processing, since the separation start portion is preferentially
broken, defects can be prevented.
[0162] A processing apparatus suitable for execution of the
separation start portion formation step (pre-separation step) and
separation step (main separation step) shown in FIGS. 1D and 1E
will be described next.
[0163] [First Processing Apparatus]
[0164] FIGS. 3, 4, 6, and 7 are views schematically showing the
arrangement of a bonded substrate stack processing apparatus
according to a preferred embodiment of the present invention. FIGS.
3 and 4 show an example of processing of a bonded substrate stack
30 shown in FIG. 2. FIGS. 6 and 7 show an example of processing of
a bonded substrate stack 30 shown in FIG. 5.
[0165] A processing apparatus 100 shown in FIGS. 3, 4, 6, and 7 has
a pair of substrate holding portions 103 and 104. The bonded
substrate stack 30 is pressed and held from both sides by the
substrate holding portions 103 and 104. The substrate holding
portions 103 and 104 are coupled to rotating shafts 101 and 102
rotatably axially supported, respectively.
[0166] At least one of the rotating shafts 101 and 102 is coupled
to an actuator (e.g., an air cylinder) for applying a press force
to the bonded substrate stack 30 and increasing/decreasing the
interval between the substrate holding portion 103 and the
substrate holding portion 104. At least one of the rotating shafts
101 and 102 is coupled to the rotating shaft of a rotation source
(e.g., a motor). The bonded substrate stack 30 can be rotated by a
driving force generated by the rotation source.
[0167] This processing apparatus 100 has an ejection nozzle 105 for
ejecting a liquid such as water or a gas such as air or nitrogen,
i.e., a fluid. The ejection nozzle 105 preferably has a diameter
of, e.g., about 0.1 mm. An apparatus using water as the fluid is
especially called a water jet apparatus.
[0168] When this processing apparatus 100 is to be used in the
separation start portion formation step (pre-separation step) shown
in FIG. 1D, the bonded substrate stack 30 is fixed while keeping
the projecting portion of the bonded substrate stack 30 opposing
the ejection nozzle 105, as shown in FIG. 3 or 6. In this state, a
fluid is ejected from the ejection nozzle 105 to the projecting
portion of the bonded substrate stack 30.
[0169] When this processing apparatus 100 is to be used in the
separation step (main separation step) shown in FIG. 1E, the bonded
substrate stack 30 having the separation start portion 40 is set
such that the separation start portion 40 opposes the ejection
nozzle 105, as shown in FIG. 4 or 7. In this state, a fluid is
ejected from the ejection nozzle 105 to the separation start
portion 40. After that, separation is continued while rotating the
bonded substrate stack 30.
[0170] When the processing apparatus 100 is to be continuously used
in the separation start portion formation step (pre-separation
step) and the separation step (main separation step), first, the
bonded substrate stack is fixed, and in this state, a fluid is
ejected from the ejection nozzle 105 to the projecting portion of
the bonded substrate stack 30, as shown in FIG. 3 or 6. When the
separation start portion 40 is formed, the bonded substrate stack
30 is rotated as shown in FIG. 4 or 7 to shift the process to the
separation step (main separation step). After that, the bonded
substrate stack 30 is completely separated at the porous layer
while rotating the bonded substrate stack 30.
[0171] [Second Processing Apparatus]
[0172] FIG. 8 is a view schematically showing the arrangement of a
bonded substrate stack processing apparatus according to another
preferred embodiment of the present invention. A processing
apparatus 200 shown in FIG. 8 has a support table 201 having a
support portion 203 for supporting a bonded substrate stack 30, an
elastic body 202 for pressing the bonded substrate stack 30 against
the support portion 203, and a wedge 210.
[0173] When the processing apparatus 200 is to be used in the
separation start portion formation step (pre-separation step) shown
in FIG. 1D, the opposite side of the projecting portion of the
bonded substrate stack 30 is supported by the support portion 203.
In this state, the wedge 210 is moderately inserted in a
predetermined amount near the bonding interface of the bonded
substrate stack at the projecting portion. The porous layer and
transfer layer on the porous layer at the projecting portion are
broken, and the separation start portion is formed on the bonded
substrate stack 30.
[0174] When the processing apparatus 200 is to be used in the
separation step (main separation step) shown in FIG. 1E, the bonded
substrate stack 30 having the separation start portion is supported
by the support portion 203 at a portion on the opposite side of the
separation start portion. In this state, the wedge 210 is
moderately inserted into the separation start portion. After that,
the wedge 210 is pushed into to continue separation.
[0175] FIG. 8 shows formation of the separation start portion on
the bonded substrate stack 30 shown in FIG. 2. However, for the
bonded substrate stack 30 shown in FIG. 5 or another bonded
substrate stack having a projecting portion as well, a separation
start portion can be formed by this processing apparatus 200.
[0176] When this processing apparatus 200 is to be continuously
used in the separation start portion formation step (pre-separation
step) and the separation step (main separation step), after
formation of the separation start portion, the wedge 210 is further
pressed into the bonded substrate stack 30.
[0177] [Third Processing Apparatus]
[0178] FIG. 9 is a view schematically showing the arrangement of a
processing apparatus according to still another preferred
embodiment of the present invention. A processing apparatus 300
shown in FIG. 9 has a process tank 301, and a vibration source 302
for supplying a vibration energy such as an ultrasonic wave to the
process tank 301.
[0179] In this processing apparatus 300, the process tank 301 is
filled with a vibration energy transmission medium (e.g., water or
an etchant) 303. One or a plurality of bonded substrate stacks 30
stored in a carrier 310 are placed in the process tank 301, and in
this state, the bonded substrate stacks 30 are processed.
[0180] When this processing apparatus 300 is to be used in the
separation start portion formation step (pre-separation step) shown
in FIG. 1D, one or a plurality of bonded substrate stacks are
stored in the carrier 310 with their projecting portions facing
down, as shown in FIG. 9. After that, the carrier 310 is placed in
the process tank 301. The process tank 301 is filled with a
vibration transmission medium (e.g., water or an etchant) such that
the projecting portion of each bonded substrate stack 30 is dipped
in the transmission medium, and the vibration source 302 is
actuated. The vibration energy effectively acts on the porous layer
under the transfer layer at the projecting portion to break the
porous layer. Accordingly, the transfer layer on the porous layer
is peeled, and a separation start portion is formed on each bonded
substrate stack.
[0181] An SOI substrate manufacturing method has been described
above. As the semiconductor layer 13 to be transferred from the
first substrate to the second substrate, not the single-crystal Si
layer but another Si layer such as a polysilicon layer or an
amorphous Si layer may be formed. Alternatively, a Ge layer, SiGe
layer, SiC layer, C layer, or a compound semiconductor (e.g., GaAs,
InP, or GaN) layer may be formed. That is, the above SOI substrate
manufacturing method and first substrate recycling method can also
be applied to a method of manufacturing a semiconductor substrate
other than an SOI substrate and the first substrate recycling
method.
[0182] As the second substrate, in addition to the single-crystal
Si substrate, an Si substrate having an oxide film formed on the
surface, an insulating substrate (e.g., a quartz substrate), or a
transparent substrate (e.g., a quartz substrate) is preferably
used.
[0183] The first substrate 10 and second substrate 20 may be bonded
by an adhesive.
[0184] The above method can be applied to the manufacture of a
composite member formed by bringing a first member having a
separation layer inside into tight contact with a second member or
to separation of the composite member. In this case, the first
member corresponds to the first substrate 10, the second member
corresponds to the second substrate 20, the separation layer
corresponds to the porous layer, and the composite member
corresponds to the bonded substrate stack 30.
EXAMPLES
[0185] Specific examples of the above embodiments will be described
below.
Example 1
[0186] First, to form a first substrate 10, a p- or n-type
single-crystal Si substrate 11 having a resistivity of, e.g., 0.01
.OMEGA..multidot.cm was prepared. The single-crystal Si substrate
11 was anodized in an HF solution in two steps to form a porous Si
layer 12 having two porous layers with different porosities on the
surface of the single-crystal Si substrate (FIG. 1A). The anodizing
conditions were as follows.
[0187] <First Anodizing Conditions>
[0188] Current density: 7 (mA/cm.sup.2)
[0189] Anodizing solution: HF:H.sub.2O:C.sub.2H.sub.5OH=1:1:1
[0190] Process time: 5 (min)
[0191] Porous Si thickness: 4.5 (.mu.m)
[0192] <Second Anodizing Conditions>
[0193] Current density: 30 (mA/cm.sup.2)
[0194] Anodizing solution: HF:H.sub.2O:C.sub.2H.sub.5OH=1:1:1
[0195] Process time: 10 (min)
[0196] Porous Si thickness: 0.2 (.mu.m)
[0197] In Example 1, the porous layer 12 had a two-layered
structure. The surface-side porous layer formed in the first step
using a low current was used to form a high-quality epitaxial Si
Layer 13. The lower porous layer formed in the second step using a
high current was used as a separation layer. The thickness of the
porous layer formed in the first anodizing step is not limited to
the above example and preferably, e.g., several hundred to 0.1
.mu.m. The thickness of the porous layer formed in the second
anodizing step is not limited to the above example, either, and can
be appropriately changed in accordance with conditions of the
subsequent separation processing.
[0198] The porous layer 12 may have one layer or three or more
layers.
[0199] Next, this substrate was oxidized in an oxygen atmosphere at
400.degree. C. for 1 hr. With this oxidation, the inner walls of
pores in the porous layer 12 were covered with thermal oxide
films.
[0200] A 0.3-.mu.m thick single-crystal Si layer 13 was epitaxially
grown on the porous Si layer 12 by CVD (Chemical Vapor Deposition)
(FIG. 1B). The growth conditions were as follows. At the early
stage of epitaxial growth, the surface of the porous Si layer 12
was exposed to H.sub.2. Hence, holes on the surface were filled to
form a flat surface.
[0201] <Epitaxial Growth Conditions>
[0202] Source gas: SiH.sub.2Cl.sub.2/H.sub.2
[0203] Gas flow rate: 0.5/180 (1/min)
[0204] Gas pressure: 80 (Torr)
[0205] Temperature: 950 (.degree.C.)
[0206] Growth rate: 0.30 (.mu.m/min)
[0207] A 200-nm thick SiO.sub.2 layer 14 was formed on the surface
of the epitaxially grown single-crystal Si layer 13 by thermal
oxidation (FIG. 1B). With this process, the first substrate 10 was
obtained.
[0208] An Si substrate (second substrate) 20 having the same size
as that of the first substrate 10 was prepared. The surface of the
SiO.sub.2 layer 14 of the first substrate 10 was brought into tight
contact with the second substrate 20 while shifting their central
positions. The resultant structure was annealed at 1,180.degree. C.
for 5 min to form a bonded substrate stack 30 as shown in FIG. 2,
which had a projecting portion (FIG. 1C). In Example 1, the two
substrates were bonded while shifting the center of the first
substrate 10 from that of the second substrate 20 by 0.1 mm.
[0209] As shown in FIG. 3, the bonded substrate stack 30 was set in
a processing apparatus 100 while making the projecting portion of
the bonded substrate stack 30 oppose an ejection nozzle 105. A
fluid (in this case, water) at a pressure of 500 kgf/cm.sup.2 was
ejected from the ejection nozzle 105 having a diameter of 0.1 mm to
the projecting portion for several sec to form a separation start
portion 40 on the bonded substrate stack 30 (FIG. 1D).
[0210] As shown in FIG. 4, while the fluid was being injected into
the separation start portion 40, the pressure of the fluid ejected
from the ejection nozzle 105 was reduced to 400 kgf/cm.sup.2. As
shown in FIG. 4, while rotating the bonded substrate stack 30, the
bonded substrate stack 30 was completely separated at the porous
layer 12 (FIG. 1E).
[0211] A porous layer 12b remaining on the surface of a second
substrate 20' after separation was selectively etched using, as an
etchant, a solution mixture of 49% hydrofluoric acid, 30% hydrogen
peroxide, and water (FIG. 1F). With this process, an SOI substrate
as shown in FIG. 1F was obtained.
[0212] The porous layer 12b remaining on the surface of the
single-crystal Si substrate 11 was selectively etched using, as an
etchant, a solution mixture of 49% hydrofluoric acid, 30% hydrogen
peroxide, and water (FIG. 1G).
[0213] Instead of the single-crystal Si layer 13, for example,
another Si layer such as a polysilicon layer or an amorphous Si
layer may be formed, or a Ge layer, SiGe layer, SiC layer, C layer,
or a compound semiconductor (e.g., GaAs, InP, or GaN) layer may be
formed.
[0214] As the second substrate 20, instead of the single-crystal Si
substrate, an Si substrate having an oxide film formed on the
surface, an insulating substrate (e.g., a quartz substrate), or a
transparent substrate (e.g., a quartz substrate) may be used.
Example 2
[0215] First, to form a first substrate 10, a p- or n-type
single-crystal Si substrate 11 having a resistivity of, e.g., 0.01
.OMEGA..multidot.cm was prepared. The single-crystal Si substrate
11 was anodized in an HF solution in two steps to form a porous Si
layer 12 having two porous layers with different porosities on the
surface of the single-crystal Si substrate (FIG. 1A). The anodizing
conditions were as follows.
[0216] <First Anodizing Conditions>
[0217] Current density: 7 (mA/cm.sup.2),
[0218] Anodizing solution: HF:H.sub.2O:C.sub.2H.sub.5OH=1:1:1
[0219] Process time: 5 (min)
[0220] Porous Si thickness: 4.5 (.mu.m)
[0221] <Second Anodizing Conditions>
[0222] Current density: 30 (mA/cm.sup.2)
[0223] Anodizing solution., HF:H.sub.2O:C.sub.2H.sub.5OH=1:1:1
[0224] Process time: 10 (min)
[0225] Porous Si thickness: 0.2 (.mu.m)
[0226] In Example 2, the porous layer 12 had a two-layered
structure. The surface-side porous layer formed in the first step
using a low current was used to form a high-quality epitaxial Si
layer 13. The lower porous layer formed in the second step using a
high current was used as a separation layer. The thickness of the
porous layer formed in the first anodizing step is not limited to
the above example and preferably, e.g., several hundred to 0.1
.mu.m. The thickness of the porous layer formed in the second
anodizing step is not limited to the above example, either, and can
be appropriately changed in accordance with conditions of the
subsequent separation processing.
[0227] The porous layer 12 may have one layer or three or more
layers.
[0228] Next, this substrate was oxidized in an oxygen atmosphere at
400.degree. C. for 1 hr With this oxidation, the inner walls of
pores in the porous layer 12 were covered with thermal oxide
films.
[0229] A 0.3-.mu.m thick single-crystal Si layer 13 was epitaxially
grown on the porous Si layer 12 by CVD (Chemical Vapor Deposition)
(FIG. 1B). The growth conditions were as follows. At the early
stage of epitaxial growth, the surface of the porous Si layer 12
was exposed to H.sub.2. Hence, holes on the surface were filled to
form a flat surface.
[0230] <Epitaxial Growth Conditions>
[0231] Source gas:SiH.sub.2C1.sub.2/H.sub.2
[0232] Gas flow rate: 0.5/180 (1/min)
[0233] Gas pressure: 80 (Torr)
[0234] Temperature: 950 (.degree.C.)
[0235] Growth rate: 0.30 (.mu.m/min)
[0236] A 200-nm thick SiO.sub.2 layer 14 was formed on the surface
of the epitaxially grown single-crystal Si layer 13 by thermal
oxidation (FIG. 1B). With this process, the first substrate 10 was
obtained.
[0237] An Si substrate (second substrate) 20 having the same size
as that of the first substrate 10 was prepared. The surface of the
SiO.sub.2 layer 14 of the first substrate 10 was brought into tight
contact with the second substrate 20 while shifting their central
positions. The resultant structure was annealed at 1,180.degree. C.
for 5 min to form a bonded substrate stack 30 as shown in FIG. 2,
which had a projecting portion (FIG. 1C). In Example 2, the two
substrates were bonded while shifting the center of the first
substrate 10 from that of the second substrate 20 by 0.1 mm.
[0238] As shown in FIG. 8, a portion on the opposite side of the
projecting portion of the bonded substrate stack 30 was supported
by a support portion 203 of a processing apparatus 200. In this
state, a wedge 210 was inserted by 1.5 mm into the gap at the
projecting portion of the bonded substrate stack 30 in parallel to
the bonding interface of the bonded substrate stack 30 (FIG. 1D).
As the wedge 210, a PTFE wedge having a tip angle of 20.degree. was
used. With this process, the bonded substrate stack 30 having a
separation start portion was obtained.
[0239] As shown in FIG. 4, the bonded substrate stack 30 was set in
a processing apparatus 100 while making a separation start portion
40 of the bonded substrate stack 30 oppose an ejection nozzle 105.
A fluid at a pressure of 400 kgf/cm.sup.2 was ejected from the
ejection nozzle 105 having a diameter of 0.1 mm to the separation
start portion 40 to start separation. After that, separation was
continued while rotating the bonded substrate stack 30, and the
bonded substrate stack 30 was separated into two substrates at a
porous layer 12a (FIG. 1E).
[0240] A porous layer 12b remaining on the surface of a second
substrate 20' after separation was selectively etched using, as an
etchant, a solution mixture of 49% hydrofluoric acid, 30% hydrogen
peroxide, and water (FIG. 1F). With this process, an SOI substrate
as shown in FIG. 1F was obtained.
[0241] The porous layer 12b remaining on the surface of the
single-crystal Si substrate 11 was selectively etched using, as an
etchant, a solution mixture of 49% hydrofluoric acid, 30% hydrogen
peroxide, and water (FIG. 1G).
[0242] Instead of the single-crystal Si layer 13, for example,
another Si layer such as a polysilicon layer or an amorphous Si
layer may be formed, or a Ge layer, SiGe layer, SiC layer, C layer,
or a compound semiconductor (e.g., GaAs, InP, or GaN) layer may be
formed.
[0243] As the second substrate 20, instead of the single-crystal Si
substrate, an Si substrate having an oxide film formed on the
surface, an insulating substrate (e.g., a quartz substrate), or a
transparent substrate (e.g., a quartz substrate) may be used.
Example 3
[0244] First, to form a first substrate 10, a p- or n-type
single-crystal Si substrate 11 having a resistivity of, e.g., 0.01
.OMEGA..multidot.cm was prepared. The single-crystal Si substrate
11 was anodized in an HF solution in two steps to form a porous Si
layer 12 having two porous layers with different porosities on the
surface of the single-crystal Si substrate (FIG. 1A). The anodizing
conditions were as follows.
[0245] <First Anodizing Conditions>
[0246] Current density: 7 (mA/cm.sup.2)
[0247] Anodizing solution: HF:H.sub.2O: C.sub.2H.sub.5OH=1:1:1
[0248] Process time: 5 (min)
[0249] Porous Si thickness: 4.5 (.mu.m)
[0250] <Second Anodizing Conditions>
[0251] Current density: 30 (mA/cm.sup.2)
[0252] Anodizing solution: HF:H.sub.2O:C.sub.2H.sub.5OH=1:1:1
[0253] Process time: 10 (min)
[0254] Porous Si thickness: 0.2 (.mu.m)
[0255] In Example 3, the porous layer 12-had a two-layered
structure. The surface-side porous layer formed in the first step
using a low current was used to form a high-quality epitaxial Si
layer 13. The lower porous layer formed in the second step using a
high current was used as a separation layer. The thickness of the
porous layer formed in the first anodizing step is not limited to
the above example and preferably, e.g., several hundred to 0.1
.mu.m. The thickness of the porous layer formed in the second
anodizing step is not limited to the above example, either, and can
be appropriately changed in accordance with conditions of the
subsequent separation processing.
[0256] The porous layer 12 may have one layer or three or more
layers.
[0257] Next, this substrate was oxidized in an oxygen atmosphere at
400.degree. C. for 1 hr. With this oxidation, the inner walls of
pores in the porous layer 12 were covered with thermal oxide
films.
[0258] A 0.3-.mu.m thick single-crystal Si layer 13 was epitaxially
grown on the porous Si layer 12 by CVD (Chemical Vapor Deposition)
(FIG. 1B). The growth conditions were as follows. At the early
stage of epitaxial growth, the surface of the porous Si layer 12
was exposed to H.sub.2. Hence, holes on the surface were filled to
form a flat surface.
[0259] <Epitaxial Growth Conditions>
[0260] Source gas: SiH.sub.2Cl.sub.2/H.sub.2
[0261] Gas flow rate: 0.5/180 (1/min)
[0262] Gas pressure: 80 (Torr)
[0263] Temperature: 950 (.degree.C.)
[0264] Growth rate: 0.30 (.mu.m/min)
[0265] A 200-nm thick SiO.sub.2 -layer 14 was formed on the surface
of the epitaxially grown single-crystal Si layer 13 by thermal
oxidation (FIG. 1B). With this process, the first substrate 10 was
obtained.
[0266] An Si substrate (second substrate) 20 having the same size
as that of the first substrate 10 was prepared. The surface of the
SiO.sub.2 layer 14 of the first substrate 10 was brought into tight
contact with the second substrate 20 while shifting their central
positions. The resultant structure was annealed at 1,180.degree. C.
for 5 min to form a bonded substrate stack 30 as shown in FIG. 2,
which had a projecting portion (FIG. 1C). In Example 3, the two
substrates were bonded while shifting the center of the first
substrate 10 from that of the second substrate 20 by 0.1 mm.
[0267] As shown in FIG. 9, a plurality of bonded substrate stacks
30 were stored in a carrier 310 while making their projecting
portions face down. After that, the carrier 310 was placed in a
process tank 301. The carrier 310 was filled with pure water
(vibration transmission medium) such that the projecting portions
of the bonded substrate stacks 30 were dipped. A vibration source
302 was operated for about 1 hr to form a separation start portion
on each bonded substrate stack 30 (FIG. 1E).
[0268] Instead of pure water, an etchant can also be preferably
used. In this case, the vibration source 302 is still preferably
actuated to supply the vibration energy to the projecting portions.
Even when no vibration energy is supplied to the projecting
portions, separation start portions can be formed by the etching
function of the etchant. An example of use of an etchant will be
described. Preferably, the projecting portion of a bonded substrate
stack is dipped in hydrofluoric acid to remove the insulating layer
(SiO.sub.2 layer) 14 at the projecting portion, then, the
projecting portion is dipped in fluoronitric acid to remove the
single-crystal Si layer 13 at the projecting portion, and finally,
the porous layer 12 at the projecting portion is removed.
[0269] As shown in FIG. 4, the bonded substrate stack 30 was set in
a processing apparatus 100 while making a separation start portion
40 of the bonded substrate stack 30 oppose an ejection nozzle 105.
A fluid at a pressure of 400 kgf/cm.sup.2 was ejected from the
ejection nozzle 105 having a diameter of 0.1 mm to the separation
start portion 40 to start separation. After that, separation was
continued while rotating the bonded substrate stack 30, and the
bonded substrate stack 30 was separated into two substrates at a
porous layer 12a (FIG. 1E).
[0270] A porous layer 12b remaining on the surface of a second
substrate 20' after separation was selectively etched using, as an
etchant, a solution mixture of 49% hydrofluoric acid, 30% hydrogen
peroxide, and water (FIG. 1F). With this process, an SOI substrate
as shown in FIG. 1F was obtained.
[0271] The porous layer 12b remaining on the surface of the
single-crystal Si substrate 11 was selectively etched using, as an
etchant, a solution mixture of 49% hydrofluoric acid, 30% hydrogen
peroxide, and water (FIG. 1G).
[0272] Instead of the single-crystal Si layer 13, for example,
another Si layer such as a polysilicon layer or an amorphous Si
layer may be formed, or a Ge layer, SiGe layer, SiC layer, C layer,
or a compound semiconductor (e.g., GaAs, InP, or GaN) layer may be
formed.
[0273] As the second substrate 20, instead of the single-crystal Si
substrate, an Si substrate having an oxide film formed on the
surface, an insulating substrate (e.g., a quartz substrate), or a
transparent substrate (e.g., a quartz substrate) may be used.
[0274] Example 4
[0275] First, to form a first substrate 10, a p- or n-type
single-crystal Si substrate 11 having a resistivity of, e.g., 0.01
.OMEGA..multidot.cm was prepared. The single-crystal Si substrate
11 was anodized in an HF solution in two steps to form a porous Si
layer 12 having two porous layers with different porosities on the
surface of the single-crystal Si substrate (FIG. 1A). The anodizing
conditions were as follows.
[0276] <First Anodizing Conditions>
[0277] Current density: 7 (mA/cm.sup.2)
[0278] Anodizing solution: HF:H.sub.2O:C.sub.2H.sub.5OH=1:1:1
[0279] Process time: 5 (mim)
[0280] Porous Si thickness: 4.5 (.mu.m)
[0281] <Second Anodizing Conditions>
[0282] Current density: 30 (mA/cm.sup.2)
[0283] Anodizing solution: HF:H.sub.2O:C.sub.2H.sub.5OH=1:1:1
[0284] Process time: 10 (min)
[0285] Porous Si thickness: 0.2 (.mu.m)
[0286] In Example 4, the porous layer 12 had a two-layered
structure. The surface-side porous layer formed in the first step
using a low current was used to form a high-quality epitaxial Si
layer 13. The lower porous layer formed in the second step using a
high current was used as a separation layer. The thickness of the
porous layer formed in the first anodizing step is not limited to
the above example and preferably, e.g., several hundred to 0.1
.mu.m. The thickness of the porous layer formed in the second
anodizing step is not limited to the above example, either, and can
be appropriately changed in accordance with conditions of the
subsequent separation processing.
[0287] The porous layer 12 may have one layer or three or more
layers.
[0288] Next, this substrate was oxidized in an oxygen atmosphere at
400.degree. C. for 1 hr. With this oxidation, the inner walls of
pores in the porous layer 12 were covered with thermal oxide
films.
[0289] A 0.3-.mu.m thick single-crystal Si layer 13 was epitaxially
grown on the porous Si layer 12 by CVD (Chemical Vapor Deposition)
(FIG. 1B). The growth conditions were as follows. At the early
stage of epitaxial growth, the surface of the porous Si layer 12
was exposed to H.sub.2. Hence, holes on the surface were filled to
form a flat surface.
[0290] <Epitaxial Growth Conditions>
[0291] Source gas: SiH.sub.2Cl.sub.2/H.sub.2
[0292] Gas flow rate: 0.5/180 (1/min)
[0293] Gas pressure: 80 (Torr)
[0294] Temperature: 950 (.degree.C.)
[0295] Growth rate: 0.30 (.mu.m/min)
[0296] A 200-nm thick SiO.sub.2 layer 14 was formed on the surface
of the epitaxially grown single-crystal Si layer 13 by thermal
oxidation (FIG. 1B). With this process, the first substrate 10 was
obtained.
[0297] An Si substrate (second substrate) 20 having a diameter
smaller than that of the first substrate 10 by 0.5 mm was prepared.
The surface of the SiO.sub.2 layer 14 of the first substrate 10 was
brought into tight contact with the second substrate 20 while
making the center of the first substrate 10 match that of the
second substrate. The resultant structure was annealed at
1,180.degree. C. for 5 min to form a bonded substrate stack 30 as
shown in FIG. 2, which had a projecting portion (FIG. 1C). The
projecting portion may be formed by bringing the first substrate 10
and second substrate 20, which have the same size, into tight
contact with each other, annealing them to form a bonded substrate
stack, and then grinding the outer peripheral portion of the second
substrate 20 of the bonded substrate stack using an edge grinder or
the like.
[0298] As shown in FIG. 6, the bonded substrate stack 30 was set in
a processing apparatus 100 while making the projecting portion of
the bonded substrate stack 30 oppose an ejection nozzle 105. A
fluid (in this case, water) at a pressure of 400 kgf/cm.sup.2 was
ejected from the ejection nozzle 105 having a diameter of 0.1 mm to
the projecting portion to form a separation start portion 40 on the
bonded substrate stack 30 (FIG. 1D).
[0299] As shown in FIG. 7, while keeping the fluid ejected from the
ejection nozzle 105, rotation of the bonded substrate stack 30 was
started. Subsequently, while rotating the bonded substrate stack
30, it was completely separated at the porous layer 12 (FIG.
1E).
[0300] A porous layer 12b remaining on the surface of a second
substrate 20' after separation was selectively etched using, as an
etchant, a solution mixture of 49% hydrofluoric acid, 30% hydrogen
peroxide, and water (FIG. 1F). With this process, an SOI substrate
as shown in FIG. 1F was obtained.
[0301] The porous layer 12b remaining on the surface of the
single-crystal Si substrate 11 was selectively etched using, as an
etchant, a solution mixture of 49% hydrofluoric acid, 30% hydrogen
peroxide, and water (FIG. 1G).
[0302] Instead of the single-crystal Si layer 13, for example,
another Si layer such as a polysilicon layer or an amorphous Si
layer may be formed, or a Ge layer, SiGe layer, SiC layer, C layer,
or a compound semiconductor (e.g., GaAs, InP, or GaN) layer may be
formed.
[0303] As the second substrate 20, instead of the single-crystal Si
substrate, an Si substrate having an oxide film formed on the
surface, an insulating substrate (e.g., a quartz substrate), or a
transparent substrate (e.g., a quartz substrate) may be used.
[0304] Example 5
[0305] In Example 5, a porous layer (microcavity layer) was formed
by ion implantation.
[0306] First, a 200-.mu.m thick SiO.sub.2 layer was formed on the
surface of a single-crystal Si substrate by thermal oxidation. Ions
were implanted through the SiO.sub.2 layer in the single-crystal Si
substrate such that the projection range corresponds to a
predetermined depth in the single-crystal Si substrate. With this
ion implantation, a substrate substantially same to a first
substrate 10 shown in FIG. 1B, i.e., a substrate sequentially
having, on a single-crystal Si substrate 11, a porous layer (ion
implantation layer or microcavity layer) 12, single-crystal Si
layer 13, and insulating layer was formed.
[0307] The surface of an SiO.sub.2 layer of the first substrate 10
was brought into tight contact with the surface of an independently
prepared 8-inch Si substrate (second substrate) 20. Annealing was
performed at 600.degree. C. for 10 hrs to increase the bonding
strength. A bonded substrate stack as shown in FIG. 1C was
obtained. In Example 5, the two substrates were bonded while
shifting the center of the first substrate 10 from that of the
second substrate 20 by 0.1 mm.
[0308] As shown in FIG. 3, the bonded substrate stack 30 was set in
a processing apparatus 100 while making the projecting portion of
the bonded substrate stack 30 oppose an ejection nozzle 105. A
fluid (in this case, water) at a pressure of 500 kgf/cm.sup.2 was
ejected from the ejection nozzle 105 having a diameter of 0.1 mm to
the projecting portion for several sec to form a separation start
portion 40 on the bonded substrate stack 30 (FIG. 1D).
[0309] As shown in FIG. 4, while the fluid was being injected into
the separation start portion 40, the pressure of the fluid ejected
from the ejection nozzle 105 was reduced to 400 kgf/cm.sup.2. As
shown in FIG. 4, while rotating the bonded substrate stack 30, the
bonded substrate stack 30 was completely separated at the porous
layer 12 (FIG. 1E).
[0310] A porous layer 12b remaining on the surface of a second
substrate 20' after separation was selectively etched using, as an
etchant, a solution mixture of 49% hydrofluoric acid, 30% hydrogen
peroxide, and water (FIG. 1F). With this process, an SOI substrate
as shown in FIG. 1F was obtained.
[0311] The porous layer 12b remaining on the surface of the
single-crystal Si substrate 11 was selectively etched using, as an
etchant, a solution mixture of 49% hydrofluoric acid, 30% hydrogen
peroxide, and water (FIG. 1G).
[0312] Instead of the single-crystal Si layer 13, for example,
another Si layer such as a polysilicon layer or an amorphous Si
layer may be formed, or a Ge layer, SiGe layer, SiC layer, C layer,
or a compound semiconductor (e.g., GaAs, InP, or GaN) layer may be
formed.
[0313] As the second substrate 20, instead of the single-crystal Si
substrate, an Si substrate having an oxide film formed on the
surface, an insulating substrate (e.g., a quartz substrate), or a
transparent substrate (e.g., a quartz substrate) may be used.
[0314] According to the present invention, a composite member such
as a bonded substrate stack can be appropriately separated at a
separation layer such as a porous layer.
[0315] 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.
* * * * *