U.S. patent application number 09/047327 was filed with the patent office on 2002-03-14 for method and apparatus for separating composite member using fluid.
Invention is credited to OHMI, KAZUAKI, SAKAGUCHI, KIYOFUMI, YANAGITA, KAZUTAKA, YONEHARA, TAKAO.
Application Number | 20020029849 09/047327 |
Document ID | / |
Family ID | 26416627 |
Filed Date | 2002-03-14 |
United States Patent
Application |
20020029849 |
Kind Code |
A1 |
OHMI, KAZUAKI ; et
al. |
March 14, 2002 |
METHOD AND APPARATUS FOR SEPARATING COMPOSITE MEMBER USING
FLUID
Abstract
To separate a composite member consisting of a plurality of
bonded members without destructing or damaging it, a fluid is
jetted against the composite member from a nozzle to separate it
into a plurality of members at a position different from a bonding
position.
Inventors: |
OHMI, KAZUAKI;
(KANAGAWA-KEN, JP) ; YONEHARA, TAKAO;
(KANAGAWA-KEN, JP) ; SAKAGUCHI, KIYOFUMI;
(KANAGAWA-KEN, JP) ; YANAGITA, KAZUTAKA;
(KANAGAWA-KEN, JP) |
Correspondence
Address: |
FITZPATRICK CELLA HARPER & SCINTO
30 ROCKEFELLER PLAZA
NEW YORK
NY
10112
US
|
Family ID: |
26416627 |
Appl. No.: |
09/047327 |
Filed: |
March 25, 1998 |
Current U.S.
Class: |
156/708 ;
156/757 |
Current CPC
Class: |
H01L 21/67092 20130101;
Y10T 156/1933 20150115; Y10T 156/1939 20150115; Y10T 29/49821
20150115; H01L 21/6838 20130101; Y10T 156/1137 20150115; Y10T
156/1922 20150115; Y10T 83/364 20150401; Y10T 156/1374
20150115 |
Class at
Publication: |
156/344 ;
156/584 |
International
Class: |
H01L 021/44 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 27, 1997 |
JP |
9-075498 |
May 28, 1997 |
JP |
9-138477 |
Claims
What is claimed is:
1. A method of separating a composite member having a plurality of
members as mutually bonded, at a position different from the
bonding position of the plurality of members, comprising jetting a
fluid against a side surface of the composite member to separate
the composite member.
2. The method according to claim 1 wherein the composite member has
inside one of the members a separation region containing
microcavities and the fluid is jetted against the neighborhood of
the separation region to separate it into the plurality of members
around the separation region.
3. The method according to claim 2 wherein a recessed portion is
formed near the separation region, the recessed portion receiving
the fluid to extend the separation region.
4. The method according to claim 2 wherein the separation region
has a lower mechanical strength than the bonding position.
5. The method according to claim 2 wherein the separation region
comprises a porous layer formed by anodization.
6. The method according to claim 2 wherein the separation region
can provide microcavities formed by ion implantation.
7. The method according to claim 1 wherein as the method of jetting
the fluid a water jet method that jets a flow of high-pressure
water from a nozzle is used.
8. Members obtained by the separation method according to claim
1.
9. A method of producing a semiconductor substrate comprising the
steps of: preparing on a substrate a first substrate having a
porous single crystal semiconductor layer and a nonporous single
crystal semiconductor layer provided on the porous single crystal
semiconductor layer; bonding the first substrate to a second
substrate to form a composite member; and jetting a fluid to the
vicinity of the porous single crystal semiconductor layer of the
composite member to separate the composite member at the porous
single crystal semiconductor layer.
10. The method according to claim 9 wherein a recessed portion is
formed near the porous single crystal semiconductor layer of the
composite member, the recessed portion receiving the fluid to
extend the porous single crystal semiconductor layer.
11. The method according to claim 9 wherein the porous single
crystal semiconductor layer has a lower mechanical strength than
the bonding surface between the first and second substrates.
12. The method according to claim 9 wherein the porous single
crystal semiconductor layer is formed by anodization.
13. The method according to claim 9 wherein as the method of
jetting the fluid a water jet method that jets a flow of
high-pressure water from a nozzle is used.
14. The method according to claim 9 wherein the first substrate is
formed by partly making a single crystal silicon substrate porous
to form a porous single crystal silicon layer and allowing a
nonporous single crystal silicon layer to grow epitaxially on the
porous single crystal silicon layer.
15. The method according to claim 14 wherein the first and second
substrates are bonded mutually via at least one insulating layer
and the insulating layer is formed by oxidizing the surface of the
nonporous single crystal silicon layer.
16. The method according to claim 9 wherein the second substrate
comprises a light-transmissive substrate.
17. The method according to claim 9 wherein the second substrate
comprises a silicon substrate.
18. A method of producing a semiconductor substrate comprising the
steps of: implanting ions into a first substrate comprising a
single crystal semiconductor at a predetermined depth to form an
ion-implanted layer such that a microcavity layer can be obtained;
bonding the first substrate and a second substrate to each other
via an insulating layer therebetween to form a composite member;
and jetting a fluid against the vicinity of the ion-implanted layer
of the composite member to separate the composite member at the
ion-implanted layer.
19. The method according to claim 18 wherein a recessed portion is
formed near the ion-implanted layer in the composite member, the
recessed portion receiving the fluid to extend the ion-implanted
layer.
20. The method according to claim 18 wherein the ion-implanted
layer has a lower mechanical strength than the bonding surface
between the first and second substrates.
21. The method according to claim 18 wherein as the method of
jetting the fluid a water jet method that jets a flow of
high-pressure water from a nozzle is used.
22. A semiconductor substrate produced by using the method
according to claim 9.
23. A separation apparatus executing the separation method
according to claim 1.
24. The separation apparatus according to claim 23 wherein a flow
of the fluid is jetted by using the water jet method for jetting a
flow of high-pressure water from a nozzle.
25. The separation apparatus according to claim 24 wherein the
composite member and the nozzle are moved relatively to scan the
flow of water.
26. The separation apparatus according to claim 25 wherein the
composite member is fixed while the nozzle is scanned in order to
scan the flow of water.
27. The separation apparatus according to claim 26 having a holder
for holding the composite member; a nozzle horizontal movement
mechanism for moving the nozzle in the horizontal direction along
the bonding position of the composite material; and a nozzle
vertical movement mechanism for adjusting the vertical distance
between the composite member and the nozzle.
28. The separation apparatus according to claim 26 having a
mechanism for scanning the nozzle in such a way as to draw a fan
around a supporting point.
29. The separation apparatus according to claim 26 wherein the
nozzle rotates around the composite member.
30. The separation apparatus according to claim 26 including a
plurality of the nozzles.
31. The separation apparatus according to claim 25 wherein the
composite member is scanned while the nozzle is fixed in order to
scan the flow of water.
32. The separation apparatus according to claim 31 having a
rotation mechanism for rotating the composite member.
33. The separation apparatus according to claim 32 wherein the
nozzle is located so as to be directed toward the rotational center
of the composite member.
34. The separation apparatus according to claim 32 having a
rotation holding member for holding the rotational center of the
composite member.
35. A separation method comprising the steps of: rotatably holding
a first surface of a composite member having a plurality of members
as mutually bonded by using a first holder; rotatably holding a
second surface of the disc-like composite member by using a second
holder; rotating the first and second holders in synchronism;
jetting a fluid against the end surface of the composite member,
which is rotating; and separating the composite member into a
plurality of members using as a starting point the portion on which
the fluid has been jetted.
36. The separation method according to claim 35 wherein the fluid
is jetted against a separation position different from the bonding
position of the composite member.
37. The separation method according to claim 35 wherein a recessed
portion is provided in the end surface of the composite member and
the fluid is jetted against the bottom of the recessed portion.
38. A separation apparatus comprising a first holder for rotatably
holding a first surface of a disc-like composite member having a
plurality of members as bonded mutually; a second holder for
rotatably holding a second surface of the disc-like composite
member; synchronizing means for allowing the first and second
holders during rotation to synchronize mutually; and a nozzle that
jets a fluid against the end surface of the composite member, which
is rotating, in order to separate the composite member into a
plurality of members using as a starting point the position on
which the fluid has been jetted.
39. The separation apparatus according to claim 38 having means for
setting the position of the nozzle so that the fluid is jetted
against a separation position different from the bonding position
of the composite member.
40. The separation apparatus according to claim 38 wherein a
recessed portion is provided in the end surface of the composite
member and the apparatus has means for setting the position of said
nozzle so that the fluid is jetted against the bottom of the
recessed portion.
41. A method of separating a composite member having a plurality of
members, at a region including cavities or pores, comprising
jetting a fluid consisting essentially of an abrasive particle-free
liquid against a side surface of the composite member to separate
the composite member.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a method and apparatus for
separating a composite member, separated members, and a
semiconductor substrate and its production method.
[0003] 2. Related Background Art
[0004] The formation of a single crystal Si semiconductor layer on
an insulating surface of a substrate is widely known as a
semiconductor on insulator (SOI) technique, and many efforts have
been made to research this technique because devices produced using
the SOI technique have many advantages that cannot be achieved by
bulk Si substrates used to fabricate normal Si integrated
circuits.
[0005] The use of the SOI technique provides the following
advantages:
[0006] (1) The dielectric separation can be easily made to attain
high integration.
[0007] (2) Radiation resistance is excellent.
[0008] (3) The stray capacity is reduced to attain high speed.
[0009] (4) The well formation process can be omitted.
[0010] (5) Latch-up can be prevented.
[0011] (6) The thickness can be reduced to provide a fully depleted
field effect transistor.
[0012] To achieve the many advantages of the device, methods for
forming SOI structures have been researched for decades. One of
such known methods is SOS (silicon on sapphire) in which Si is
heteroepitaxially formed by CVD (chemical vapor deposition) on a
single crystal sapphire substrate. This technique has been
successful as the maturest SOI technique, but its applications are
limited by a large amount of crystal defects due to the
misalignment of lattices in the interface between an Si layer and a
sapphire substrate, by the mixture of aluminum from the sapphire
substrate into the Si layer, and in particular, by the high costs
of the substrate and the still insufficient the enlargement of area
of the device. More recently, an attempt has been made to implement
an SOI structure without the sapphire substrate. This attempt can
be roughly classified into the following two methods.
[0013] 1. After the surface of an Si single crystal substrate is
oxidized, a window is made in the oxidized film to expose a part of
the surface of the Si substrate, and this part is used as a seed to
allow a horizontal epitaxial growth to form an Si single crystal
layer on the SiO.sub.2 (in this case, an Si layer is deposited on
SiO.sub.2).
[0014] 2. The Si single crystal substrate is used as an active
layer and SiO.sub.2 is formed under this layer (this method does
not require an Si layer to be deposited).
[0015] Known means for realizing the above method 1 include a
method for allowing the direct horizontal epitaxial growth of
single crystal layer Si using CVD, a method of depositing amorphous
Si and allowing its horizontal epitaxial growth in a solid phase by
thermal treatment, a method of irradiating an amorphous or
polycrystal Si layer with converging energy beams such as electron
or laser beams, and allowing a single crystal layer to grow on
SiO.sub.2 by means of melting recrystallization, and a method of
using a bar-like heater to scan a molten area in such a way that
the scanning trace appears like a band (zone melting
recrystallization). Although these methods have both advantages and
disadvantages, they still have many problems in terms of their
controllability, productivity, uniformity, and quality and none of
them have been put to industrially practical use. For example, the
CVD method requires sacrificial oxidization to provide flat films.
The solid phase growth method provides poor crystallinity. The beam
anneal method has problems in terms of the time required for
converging-beam scanning, and control of the superposition of
beams, and focusing. Among them, the zone melting recrystallization
method is maturest and has been used to produce
relatively-large-scale integrated circuits on an experimental
basis, but it still causes a large amount of crystal defects such
as sub-grains to remain in the device, thereby failing to fabricate
minor-carrier devices and to provide sufficiently excellent
crystals.
[0016] The above method 2 that does not use the Si substrate as a
seed for epitaxial growth includes the following four methods.
[0017] (1) An oxide film is formed on an Si single crystal
substrate with a V-shaped groove etched anisotropically in its
surface, a polycrystal Si layer is deposited on the oxide film so
as to be as thick as the Si substrate, and then an Si single
crystal region surrounded by the V-shaped groove so as to be
separated dielectricly is formed on the thick polycrystal Si layer
by polishing from the rear surface of the Si substrate. This method
provides excellent crystallinity but the steps for depositing
polycrystal Si by a thickness of several hundred microns and
polishing the single crystal Si substrate from its rear surface to
leave only the separated Si active layer have problems in terms of
controllability and productivity.
[0018] (2) SIMOX (Separation by Ion-Implemented Oxygen) that forms
an SiO.sub.2 layer in an Si single crystal substrate by means of
oxygen ion implantation and that is the presently maturest
technique due to its excellent compatibility with the Si process.
To form an SiO.sub.2 layer, however, 10.sup.18 ions/cm.sup.2 or
more of oxygen ions must be implanted, resulting in the need for a
large amount of time for the implantation, thereby leading to
reduced productivity. In addition, the costs of wafers are high.
Furthermore, this method cause a large amount of crystal defects to
remain in the device and does not industrially provide a sufficient
quality to fabricate minor-carrier devices.
[0019] (3) A method for forming an SOI structure by dielectric
separation through the oxidization of porous Si. In this method, an
N-type Si layer is formed like an island on a surface of a P-type
Si single crystal substrate by proton-ion implantation (Imai et
al., J. Crystal Growth, vol. 63, 547 (1983)) or by epitaxial growth
and patterning. Only the P-type Si substrate is made porous by an
anodization method using an HF solution in such a way that the
porous region surrounds the Si island from the surface, and the
N-type Si island is then oxidized at a high speed for dielectric
separation. In this method, the separating Si region is determined
prior to the device step, thereby limiting the degree of freedom of
device design.
[0020] (4) A method for forming an SOI structure using thermal
treatment or an adhesive to bond an Si monocrystal substrate on a
different Si single crystal substrate that is thermally oxidized is
attracting attention. This method requires an active layer for a
device to be formed as a uniformly thin film. That is, the
thickness of a several-hundred-micron-thick Si single crystal
substrate must be reduced to the order of micron or less.
[0021] The following two methods can be used to provide a thinner
film.
[0022] 1) Thickness reduction by polishing
[0023] 2) Thickness reduction by selective etching
[0024] The polishing in 1) cannot provide uniformly thin films
easily. In particular, if the thickness is reduced to the order of
submicron, the thickness variation will be several tens %,
resulting in a serious problem for providing uniformity. The
difficulty in achieving uniformity further increases with
increasing size of the substrate.
[0025] In addition, although the etching in 2) is supposed to be
effective in providing uniform thin films, it has the following
problems.
[0026] The selection ratio is at most 10.sup.2 and is
insufficient.
[0027] The surface obtained after etching is bad.
[0028] The crystallinity of the SOI layer is bad due to the use of
ion implantation or epitaxial or heteroepitaxial growth on a high
concentration B-doped Si layer.
[0029] A semiconductor substrate formed by bonding requires two
substrates, one of which is mostly uselessly removed and disposed
of through polishing and etching, thereby wasting limited global
resources. Thus, SOI with bonding presently has many problems in
terms of its controllability, uniformity, and costs.
[0030] In addition, generally due to the disorder of the crystal
structure of a light-transmissive substrate represented by glass, a
thin film Si layer deposited on the substrate can only form an
amorphous layer or a polycrystal layer based on the disorder of
substrates, and therefore high-performance devices cannot be
produced. This is because since amorphous structure of the
substrate is amorphous, an excellent single crystal layer cannot be
obtained by simply depositing an Si layer. The light-transmissive
substrate is important in producing a contact sensor or a
projection liquid-crystal image display device that is a
light-receiving element. Not only the improvement of pixels but
also a high-performance drive element are required to attain higher
density, higher resolution, and finer definition of the pixels in
the sensor or display device. Thus, to provide elements on the
light-transmissive substrate, a single crystal layer of an
excellent crystallinity is required.
[0031] Among such SOI substrate production methods, the method of
forming a non-single-crystal semiconductor layer on a porous layer
and transferring the layer onto a supporting substrate via an
insulating layer as disclosed in Japanese Patent Application
Laid-Open No. 5-21338 is very excellent due to the uniform
thickness of the SOI layer, its capability of maintaining the
crystal-defect density of the SOI layer at a low level easily, the
flatness of the surface of the SOI layer, no need for an expensive
apparatus of a special specification for fabrication, and the
capability of using the same apparatus for various SOI film
thicknesses ranging from about several 100 Angstrom to 10
micron.
[0032] Furthermore, by combining the above method with the method
disclosed in Japanese Patent Application Laid-Open No. 7-302889,
that is, by forming a nonporous single crystal semiconductor layer
on a porous layer formed on a first substrate, bonding the
nonporous single crystal layer onto a second substrate via an
insulating layer, separating the first substrate and the second
substrate by the porous layer without destruction, and smoothing
the surface of the first substrate and forming porous layer again
for reuse, the first substrate can be used many times. This method
can significantly reduce production costs and simplify the
production steps.
[0033] There are several methods for separating the bonded
substrates mutually to divide into the first substrate and the
second substrate without destruction. For example, one of them is
to pull the substrate in a direction vertical to the bonded
surface. Another method is to apply a shearing stress in parallel
with the bonded surface (for example, moving the substrates in the
opposite directions within planes in parallel with the bonded
surface or rotating the substrates in the circumferentially
opposite directions). A pressure can be applied to the bonded
surface in the vertical direction. Furthermore, a wave energy such
as ultrasonic waves can be applied to the separation region. A
peeling member (for example, a sharp blade such as a knife) can
also be inserted into the separation region in parallel with the
bonded surface from the side of the bonded substrates. Furthermore,
the expansion energy of a material infiltrated into the porous
layer that functions as the separation region may be used. The
porous layer functioning as the separation region may also be
thermally oxidized from the side of the bonded substrates to expand
the volume of this layer. The porous layer functioning as the
separation region may also be selectively etched from the side of
the bonded substrates to separate the substrates. Finally, a layer
formed by ion implantation to provide microcavities may be used as
the separation region and the substrates may then be irradiated
with laser beams from the normal direction of the bonded surface to
heat the separation region containing the microcavity for
separation.
[0034] However, these methods for separating the two bonded
substrates mutually are ideally excellent, but all of them are not
suitable for the production of semiconductor substrates. One of the
difficulties is that the bonded semiconductor substrates are
generally shaped like discs and have a small thickness, for
example, 0.5 to 1.0 mm and that the bonded portion has few
relatively large recesses on which a jig can be caught. Thus, a
method of catching on an orientation flat portion of each substrate
a jig having a recessed portion that fits the orientation flat
portion and rotating the substrates in parallel with the bonded
surface, or a method of catching the jig on a small recessed
portion made in the bonded portion in the side of the bonded
substrates to peel them are limited. The pressure-based separation
requires a very large pressure, thereby forcing the size of the
apparatus to be increased. In the wave energy method, the wave
irradiation method must be substantially improved to irradiate the
bonded substrates with wave energy efficiently, and immediately
after separation, the separated substrates may partly contact and
damage each other. In the separation from the side, the substrates
may be bent to allow only their sides to be peeled, with their
central portions remaining unseparated. In the method of inserting
the peeling member into the separation region from the side of the
bonded substrates, the insertion of the peeling member may damage
the bonded surface between the substrates due to the friction of
the peeling member and the substrates.
[0035] One solution for avoiding these problems is to reduce the
mechanical strength of the separation region appropriately. This
method, however, may increase the possibility that the separation
region is destroyed by an external impact prior to the bonding of
the substrates. In such a case, part of the destroyed separation
region may become particles and contaminate the inside of the
production apparatus. Although the conventional separation methods
have the major advantages, they still have the above problems.
SUMMARY OF THE INVENTION
[0036] It is an object of this invention to provide an improved
separation method and apparatus that can separate the bonded
substrates mutually without destruction to prevent the separated
substrates from being damaged and that is unlikely to destroy the
separation region prior to the step of separating bonded substrates
even when an external force is applied thereto, thereby preventing
the production apparatus from being contaminated with
particles.
[0037] The feature of this invention resides in that a composite
member having a plurality of members as mutually bonded is
separated into a plurality of members at positions different from
the bonded position (separation region) of the plurality of members
by jetting a fluid against the composite member.
[0038] With respect to the separation method, the composite member
may be any member having a separation region inside, whereas with
respect to the semiconductor substrate production method, it must
have the following structure. A major example of the composite
member is bonded substrates by bonding a first substrate and a
second substrate, the first substrate being a semiconductor
substrate in which a separation region is formed as a layer in a
portion located deeper than its surface and in parallel therewith
and in which the surface and the portion shallower than it has no
separation region. That is, when this invention is applied to the
semiconductor substrate production method, the members obtained
after separation are not the same as the first and second
substrates prior to bonding.
[0039] According to this invention, the separation region is
located at a position different from the bonding interface
(junction surface) between the first and second substrates. In the
separation step, the substrates must be separated by the separation
region located at the position different from the bonding
interface.
[0040] Thus, the separation region is adapted to be mechanically
weaker than the bonding interface so that the separation region is
destroyed before the bonding interface. Thus, when the separation
region is destroyed, a portion of the surface side of the first
substrate which has a predetermined thickness is separated from the
first substrate while remaining bonded on the second substrate,
thereby transferring the portion to the second substrate. The
separation region may be a porous layer formed by the anodization
method or a layer formed by ion implantation to provide
microcavities. These layers have a large amount of microcavities.
This region may also be a heteroepitaxial layer in which distortion
and defects are concentrated in crystal lattices.
[0041] The separation region may also be multiple layers of
different structures. For example, it may consist of multiple
porous layers having different porosities or a porous layer of a
porosity changing in the direction perpendicular to the layers, as
required.
[0042] The layer transferred from the first substrate to the second
substrate by, for example, separating the composite member
comprising the first and second substrates bonded together with
each other via the insulating layer is used as a semiconductor
layer (an SOI layer) on the insulating layer to fabricate a
semiconductor device.
[0043] Jet of a fluid that can be used for the separation can be
conducted by a so-called water jet method that injects a flow of
high-pressure water through a nozzle. Instead of water, this fluid
may be an organic solvent such as alcohol, an acid such as
hydrofluoric or nitric acid, an alkali such as potassium hydroxide,
or a liquid capable of selectively etching the separation region. A
fluid consisting essentially of an abrasive particle-free liquid is
preferable. Furthermore, a fluid consisting of a gas such as air, a
nitrogen gas, carbon dioxide, or a rare gas may be used. A fluid
consisting of a gas or plasma that can etch the separation region
may also be used.
[0044] The above separation method can be applied to the
semiconductor substrate production method to enable the following
methods:
[0045] 1) A semiconductor substrate production method comprising
the steps of preparing a first substrate comprising a porous single
crystal semiconductor layer and a nonporous single crystal
semiconductor layer sequentially stacked on a substrate; bonding
the first substrate and a second substrate so as to provide a
composite member having the nonporous single crystal semiconductor
layer located inside; and jetting a fluid to the vicinity of the
porous single crystal semiconductor layer in the composite member
to separate the composite member at the porous single crystal
semiconductor layer, or
[0046] 2) a semiconductor substrate production method comprising
the steps of implanting ions into a first substrate of a single
crystal semiconductor at a predetermined depth to form an
ion-implanted layer that can provide a microcavity layer; bonding
the first substrate and a second substrate via an insulating layer
so as to provide a composite member in which the ion-implanted
surface of the first substrate is located inside; and jetting a
fluid against the vicinity of the ion-implanted layer of the
composite member to separate the composite member at the
ion-implanted layer. This invention thus provides the semiconductor
substrate production method that can solve the conventional
problems.
BRIEF DESCRIPTION OF THE DRAWINGS
[0047] FIGS. 1A, 1B and 1C are schematic views illustrating a
method for separating a composite member according to this
invention;
[0048] FIGS. 2A and 2B are schematic views illustrating an example
of a method for separating the composite member using a fluid
according to this invention;
[0049] FIG. 3 is a perspective view showing an example of a
separation apparatus according to this invention;
[0050] FIG. 4 is a sectional view showing another example of a
separation apparatus according to this invention;
[0051] FIG. 5 is a perspective view showing yet another example of
a separation apparatus according to this invention;
[0052] FIG. 6 is a schematic view showing still another example of
a separation apparatus according to this invention;
[0053] FIG. 7 is a schematic view showing still another example of
a separation apparatus according to this invention;
[0054] FIG. 8 is a schematic view illustrating another example of a
method for separating a composite member using a fluid according to
this invention;
[0055] FIG. 9 is a schematic view showing another example of a
separation apparatus according to this invention;
[0056] FIGS. 10A and 10B are schematic views showing yet another
example of a separation apparatus according to this invention;
[0057] FIG. 11 is a schematic view showing still another example of
a separation apparatus according to this invention;
[0058] FIG. 12 is a schematic view showing still another example of
a separation apparatus according to this invention;
[0059] FIG. 13 is a schematic view showing still another example of
a separation apparatus according to this invention;
[0060] FIG. 14 is a top view of another separation apparatus
according to this invention;
[0061] FIG. 15 is a side view of the separation apparatus shown in
FIG. 14;
[0062] FIG. 16 is a schematic view showing a state of separating
the composite member;
[0063] FIG. 17 is a sectional view of the separation apparatus
shown in FIG. 15, in its standby state;
[0064] FIG. 18 is a sectional view of the separation apparatus
shown in FIG. 15, in its substrate-holding state;
[0065] FIG. 19 is a sectional view of the separation apparatus
shown in FIG. 15, in its separating-operation starting state;
and
[0066] FIG. 20 is a sectional view of the separation apparatus
shown in FIG. 15, in its separating-operation ending state.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0067] FIGS. 1A to 1C are schematic views illustrating a method of
separating a composite member according to this invention.
[0068] FIG. 1A shows a state prior to the bonding of a first member
1 and a second member 2. The first member 1 has inside a separation
region 3 which is a separation position of this member. The
separation region 3 shaped like a layer has a lower mechanical
strength than a layer region 5 located on the side of a bonding
surface 4a.
[0069] The two members 1 and 2 are bonded such that the bonding
surface 4a is faced to a bonding surface 4b in order to form a
disc-like composite member having a bonding interface 14, as shown
in FIG. 1B. A fluid 7 is jetted from a nozzle 8 toward the end of
the separation region 3 located on the side (end surface) 6 of the
composite member. The separation region 3 against which the fluid 7
is jetted is removed or collapsed. Thus, the composite member is
separated into two members 11 and 12 at the separation region 3, as
shown in FIG. 1C.
[0070] The layer region 5 is not present on a separation surface
13a of the separated member 11, and a layer region 5 has been
transferred onto a bonding surface 4b of the original second member
2 so as to expose a separated surface 13b.
[0071] Thus, a member having the thin layer region 5 on the second
member 2 is obtained.
[0072] By forming the second member 2 and layer region 5 by using
different materials, a member having a heterogeneous bonding can be
produced easily. Specific examples of such materials include
conductors, semiconductors, and insulators, and two of which are
selected to form the second member 2 and the layer region 5.
[0073] In particular, silicon, quartz, glass, or silicon having an
insulating film formed on its surface is preferably used as the
second member.
[0074] A semiconductor material such as silicon, silicon germanium,
silicon carbide, gallium arsenide, or indium phosphorus is
preferably used as the layer region. The layer region of such a
material may partially include an thin insulating layer.
[0075] The most preferred composite member that is separated into
at least two is obtained by bonding two semiconductor substrates,
or one semiconductor substrate and one insulating substrate and is
called bonded substrates or bonded wafers.
[0076] Separating such a composite member provides a semiconductor
substrate of an excellent SOI structure.
[0077] Prior to bonding, the separation region is desirably formed
inside a substrate along the bonding surface.
[0078] The separation region may be fragile enough to allow the
composite member to be separated into two at the separation region
by the jetted fluid and to prevent damage to other regions other
than the separation region.
[0079] Specifically, it can be made fragile by containing a
plurality of microcavities inside the separation region or
implanting heterogeneous ions to cause strain.
[0080] The microcavity is formed of pores of a porous body or
bubbles generated by ion implantation, as described below. The
separation region is preferably 0.1 to 900 .mu.m and more
preferably 0.1 to 10 .mu.m.
[0081] The flow of a fluid used to execute separation according to
this invention can be implemented by jetting the fluid through a
nozzle. A method for converting the injected flow into thin beams
at a high speed and a high pressure may be the water jet method
using water as the fluid such as that introduced in "Water Jet"
Vol. 1, No. 1, p. 4. In the water jet that can be used for this
invention, high-pressure water at several-thousand kgf/cm.sup.2
pressurized by a high-pressure pump is jetted through a thin nozzle
and can cut or process ceramics, metal, concrete, resin, rubber, or
wood (an abrasive material such as SiO.sub.2 grains is added to
water if the material is hard), remove a paint film from a surface
layer, or wash the surface of a member. The water jet has been
mainly used to remove a part of the material, as described above.
That is, water jet cutting has been carried out to remove a cut
edge from a main member, and the removal of the paint film and the
washing of the member surface has been executed to remove unwanted
portions. If the water jet is used to form the flow of a fluid
according to this invention, it can be jetted toward the bonding
interface on the side (end surface) of bonded substrates to remove
at least a part of the separation region from the side. In this
case, the water jet is jetted against the separation region exposed
on the side of the bonded substrates and against a part of the
first and second substrates in the vicinity of the separation
region. Then, the separation region of a low mechanical strength is
removed or destroyed by the water jet to separate the composite
member into two substrates without damage to each substrate. Even
if the separation region is not exposed on the side but is instead
covered with a certain thin layer for any reason, the water jet may
be used to remove the layer covering the separation region on the
side and then to remove the separation region exposed from the
side.
[0082] Although not often used in the prior art, the water jet may
be jetted against a small recessed portion on the side of two
bonded chamfered substrates, that is, on their circumference to
penetrate and extend microcavities or pores in the separation
region of a fragile structure to separate the bonded substrates.
This operation is not intended to perform for cutting or removal,
so little chips occur from the separation region and the composite
member can be separated without the need for abrasive particles or
damage to surfaces obtained by separation, even if the material of
the separation region cannot be removed by the water jet. This is
not a cutting or polishing effect but a kind of wedge effect
provided by the fluid. Thus, this is very effective if there is a
recessed or narrow gap on the side of the bonded substrates and the
jetting force of the water jet is applied in a direction in which
the substrates are peeled off at the separation region. To obtain a
sufficient effect, the side of the bonded substrates is preferably
recessed rather than protruding.
[0083] FIGS. 2A and 2B show this effect. In FIGS. 2A and 2B, 901
and 911 indicate first substrates, 902 and 912 second substrates,
903 and 913 separation regions, 904 and 914 semiconductor layers,
905 and 915 insulating layers, 906 and 916 bonding interfaces, 907
a jet of a fluid, and 908 and 918 the directions of forces applied
to the substrates by the fluid.
[0084] FIG. 2A conceptually shows the direction of a force applied
to the substrates by the water jet when the side of the end of the
bonded substrates is recessed. The force is applied in a direction
in which the recessed portion is extended, that is, in a direction
in which the bonded substrates are peeled off. On the contrary,
FIG. 2B conceptually shows the direction of a force applied to the
substrates by the water jet when the side of the end of the bonded
substrates is protruding. In this case, a force is not applied in
the direction in which the bonded substrates are peeled off, so the
substrates cannot be separated mutually unless a part of the
separation region can be initially removed.
[0085] Even if the separation region is not exposed on the side but
is instead covered with a certain thin layer for any reason, a
sufficient separation effect can be obtained when the side of the
bonded substrates is recessed as described above because a force is
applied in the direction in which the vicinity of the separation
region is extended to destroy the thin layer covering the
separation region on the side and then to extend and destroy the
separation region. To efficiently receive the flow of the water
jet, the aperture width of the recessed portion is desirably equal
to or larger than the diameter of the water jet. When this
invention is applied to manufacture a semiconductor substrate,
since the thickness of the first and second substrates is less than
1.0 mm, the thickness of the bonded substrates, that is, of the
composite member is less than 2.0 mm. Since the aperture width of
the recessed portion is normally about half this value, the
diameter of the water jet is preferably 1.0 mm or less. Actually, a
water jet of about 0.1 mm diameter can be put to practical use.
[0086] The nozzle jetting the fluid may have any shape including a
circle. A long slit-like nozzle can also be used. By jetting the
fluid through such a nozzle, thin band-like flows can be
formed.
[0087] Various jet conditions of the water jet can be selected
arbitrarily depending on the type of the separation region or the
shape of the side of the bonded substrates. For example, the
pressure of the jet and its scanning speed, the diameter of the
nozzle (=the diameter of the water jet) and its shape, the distance
between the nozzle and the separation region, and the flow rate of
the fluid are important parameters.
[0088] In an actual separation step, separation can be achieved by
scanning the nozzle along the bonded surface while jetting the
water jet from a direction in parallel with the bonding surface or
fixing the water jet while moving the bonded substrates in
parallel. In addition, the water jet may be scanned so as to draw a
fan around the nozzle, or the bonded substrates may be rotated
around the position of the fixed nozzle as a rotational center if,
as is often the case, the bonded substrates are shaped like discs
such as wafers with orientation flats or notches. Furthermore, the
water jet may be jetted against the separation region from an
angled direction as required instead of placing the nozzle in the
same plane as the bonded interface. The scanning of the water jet
is not limited to these methods but may be carried out by any other
method as required. Since the water jet has a very small diameter
and the injection direction is almost parallel with the surface of
the substrate, vector resolution shows that a high pressure of
several-thousand kgf/cm.sup.2 is rarely applied to the substrates.
Since the water jet applies a force of only several hundred grams
to the bonded substrates except for the separation region, the
substrates are prevented from being destroyed.
[0089] Instead of water, an organic solvent such as alcohol, acid
such as hydrofluoric or nitric acid, or alkali such as potassium
hydroxide, or a liquid that can selectively etch the separation
region may be used. Furthermore, a gas such as air, nitrogen gas,
carbon dioxide gas, or rare gas may be used as fluid. A gas or
plasma that can etch the separation region may also be used. As
water to be used for a composite member separation method
introduced into the process of producing a semiconductor substrate,
pure water with a minimized amount of an impurity metal and
particles, and ultrapure water are desirably used, but the
substrates may be washed and the impurity metal and particles are
removed after separation using the water jet, due to the perfect
low-temperature process. In particular, in this invention, the
fluid is preferably free of abrasive particles so as not to leave
unwanted scratches in the substrates.
[0090] A semiconductor substrate according to this invention can be
used to fabricate a semiconductor device and to form a single
crystal semiconductor layer on the insulating layer into a fine
structure instead of an electronic device.
[0091] FIG. 3 is a schematic view showing a separation apparatus
according to one embodiment of this invention.
[0092] Reference numeral 101 denotes bonded wafers as a composite
member; 102 a fluid jet nozzle; 103 a vertical movement mechanism
for adjusting the vertical position of the nozzle 102; 104 a
horizontal movement mechanism for adjusting the horizontal position
of the nozzle 102; 115 a horizontal movement mechanism for
adjusting the horizontal position of the wafer; and 105 a wafer
holder as a holder.
[0093] Reference numerals 113, 114, and 116 denote guides.
[0094] In the apparatus shown in FIG. 3, the wafer separation
operation is performed by using the movement mechanisms 103, 104,
and 115 to align the nozzle 102 with the end of the separation
region of the wafer 101 and jetting a highly pressurized fluid from
the nozzle 102 to the end of the separation region on the side of
the wafer 101 while moving the nozzle in the horizontal and
vertical directions with the wafer 101 remaining fixed.
[0095] Reference numeral 106 indicates a backing material used as
required and consisting of a porous or nonporous elastic body.
[0096] FIG. 4 is a schematic perspective view showing another
example of a separation apparatus used for this invention. In FIG.
4, 401 indicates two semiconductor wafers of Si integrally bonded
as a composite member having inside a porous layer that acts as a
separation region. Reference numerals 403 and 404 indicate holders
that suck and fix the semiconductor wafer 401 using a vacuum chuck
and that are rotatably mounted on the same rotating shaft. The
holder 404 is fitted in a bearing 408 and supported by a supporting
stand 409, and its rear end is directly coupled to a rotating shaft
of a speed control motor 410. Thus, controlling the motor 410
enables the holder 404 to be rotated at any speed. The other holder
403 is fitted in a bearing 411 and supported by the supporting
stand 409, and a compression spring 412 is provided between the
rear end of the holder 403 and the supporting stand 409 to apply a
force in a direction in which the holder 403 leaves the
semiconductor wafer 401.
[0097] The semiconductor wafer 401 is set so as to correspond to a
recessed portion of a positioning pin 413 and is sucked and held by
the holder 404. The holder 404 can hold the middle of the
semiconductor wafer 401 by using the pin 413 to adjust the vertical
position of the wafer 401. The holder 403 is moved leftward against
the spring 412 to a position at which it sucks and holds the
semiconductor wafer 401. In this case, a rightward force is applied
to the holder 403 by the compression spring 412. The returning
force applied by the compression spring 412 and the force of the
holder 403 for sucking the semiconductor wafer 401 are balanced so
that the force of the compression spring 412 will not cause the
holder 403 to leave the wafer 401.
[0098] A fluid is fed from a jet pump 414 to the jet nozzle 402 and
continues to be output until the jet fluid is stabilized. Once the
flow of the fluid has been stabilized, the nozzle is moved, a
shutter 406 is opened, and the fluid is jetted from the jet nozzle
402 to the side of the substrate 101 against the center of
thickness of the semiconductor wafer 401. At this point, the holder
404 is rotated by the motor 410 to rotate the semiconductor wafer
401 and holder 403. By jetting the fluid against the vicinity of
the thickness-wise center of the semiconductor wafer 401, the
semiconductor wafer 401 is extended to cause a porous layer in the
semiconductor wafer 401 that is relatively weak to be destroyed and
is finally separated into two.
[0099] As described above, the fluid is applied to the
semiconductor wafer 401 uniformly and a rightward force is applied
to the holder 403 holding the semiconductor wafer 401, so that
separated semiconductor wafers 401 are unlikely to slide after
separation.
[0100] The bonded wafer 401 can also be separated by scanning the
nozzle 402 in parallel with the bonding interface (surface) of the
bonded wafer 401 without rotating the wafer 401. When, however,
separation is executed by scanning the nozzle 402 without rotating
the bonded wafer 401, high-pressure water at 2000 kgf/cm.sup.2 is
required for a nozzle diameter of 0.15 mm, whereas only 200
kgf/cm.sup.2 of pressure is required when separation is carried out
by rotating the bonded wafer 401 with the nozzle 402 fixed.
[0101] This is because water is jetted to the center of the bonded
wafer 401 to enable the water pressure to act efficiently as an
extending force compared with the scanning of the nozzle.
[0102] The following effects can be obtained by reducing the water
pressure.
[0103] 1) The wafer can be separated without destruction.
[0104] 2) A large number of jets can be simultaneously used due to
the increased available capacity of the pump.
[0105] 3) The size and weight of the pump can be reduced.
[0106] 4) A wider range of materials are available for the pump and
piping to allow the apparatus to easily utilize pure water.
[0107] 5) The sound of the pump and, in particular, of the jet is
reduced to allow sound-proof measures to be taken easily.
[0108] The wafer holding means shown in FIG. 4 holds the wafer by
using the holders 403 and 404 to pull the wafer from both sides,
but the wafer may also be held by pressing it from both sides of
the holders 403 and 404. In this case, the high-pressure water also
advances while extending the bonded wafer 401 to form a small gap
in them, and finally separates them into two.
[0109] The smaller the contact portion between the holders 403 and
404 and the bonded wafer 401 is, the more flexibly the bonded wafer
401 can move when the high-pressure water extends the wafer 401.
Stress concentration caused by the excessively high pressure and
the presence of water in the separation interface of the bonded
wafer 401 serve to prevent cracks and to allow the wafer to be
extended easily. These points enable effective separation. For
example, when the contact portion between the holders 403 and 404
and the bonded wafer 401 has a diameter of 30 mm or less, the
bonded wafer 401 does not crack and can be separated into two
during a single rotation of the bonded wafer 401, under the
conditions of the nozzle having a diameter of 0.2 mm and the
pressure of 400 kgf/cm.sup.2.
[0110] In addition, the larger the contact portion between the
holders 403 and 404 and the bonded wafer 401 is, the more firmly
the rear surface of the bonded wafer 401 is supported when the
high-pressure water extends the wafer 401, thereby preventing
cracks during separation. When the contact portion between the
holders 403 and 404 and the bonded wafer 401 has a diameter of 100
mm or more, the bonded wafer 401 can be separated into two without
cracks under the conditions of the nozzle having a diameter of 0.2
mm and the pressure of 400 kgf/cm.sup.2.
[0111] If foreign matters such as particles are sandwiched between
the holder 403 or 404 and the bonded wafer 401, the bonded wafer
401 is no longer held in the vertical direction to cause the nozzle
402 to be offset from its perpendicular direction toward the top of
the bonded wafer 401 to the longitudinal or lateral direction,
thereby failing to effectively hit the high-pressure fluid against
the separation interface in the wafer 401. To prevent this, the
surfaces of the holders 403 and 404 that contact the bonded wafer
401 can be formed with a large number of fine protrusions to
minimize the contact area in order to reduce the effect of possible
sandwiched foreign matters.
[0112] In the supporting apparatus shown in FIG. 4, the holder 404
is rotated to rotate the holder 403 with it, so that a slight force
is effected in the direction in which the rotation is stopped and
torsion may occur in the separation surface until the bonded wafer
401 is entirely separated. In this case, the holders 403 and 404
can be rotated synchronously to prevent torsion in the separation
surface. This method is described below in detail.
[0113] FIG. 5 shows another separation apparatus according to this
invention. In this figure, numeral 204 indicates a wafer
horizontal-drive mechanism, 205 a wafer carrier, and 206 a wafer
transfer arm. As shown in this figure, the wafer cassette 205 is
placed on a cassette stand 207 such that a wafer 201 is arranged in
the horizontal direction. The wafer 201 is loaded on a wafer
supporting stand 204 using a wafer loading robot 206. The wafer
supporting stand 204 on which the wafer 201 is loaded is
transferred to the position of high-pressure jet nozzles 202 and
203 by a supporting stand movement mechanism such as a belt
conveyor. A high-pressure fluid is jetted against a separation
region in a recessed potion in the wafer formed by bevelling,
through the nozzles 202 and 203 of a fluid jet apparatus located on
the side of the wafer, from a direction parallel with the bonded
interface (surface) in the bonded wafer. In this case, the nozzles
are fixed and the bonded wafer is scanned in the horizontal
direction to receive the high-pressure fluid along the recessed
portion formed by bevelling. One or both of the nozzles 202 and 203
may be used as required.
[0114] This operation enables the wafer to be divided into two at a
porous Si layer. Although not shown in the drawing, another loading
robot stores the separated wafers as a first and a second
substrates.
[0115] In the horizontal jet method, the wafer need not be fixed
and, after separation, is unlikely to jump out from the wafer
supporting stand 204 due to its own weight. Alternatively, after
the wafer has been loaded on the wafer supporting stand, a jump
prevention pin may be installed on the top of the wafer so as to
protrude from the wafer supporting stand 204 to over the wafer or
the top of the wafer may be pressed softly.
[0116] Furthermore, a plurality of bonded wafers may be placed and
set in the vertical direction relative to their surfaces, and one
separation region of the bonded wafers may then be separated
through horizontal scanning. A wafer set jig may subsequently be
moved in the vertical direction over a distance equal to the wafer
interval to allow the second separation region of the bonded wafer
to be separated sequentially through horizontal scanning similarly
to the first separation of the bonded wafers.
[0117] FIG. 6 schematically shows another separation apparatus
according to this invention. This figure conceptually shows a
nozzle of a water jet apparatus used in this embodiment and its
movement. As shown in FIG. 6, a bonded wafer 301 is held by a
holder 310 so as to stand in the vertical direction. A
high-pressure fluid is jetted against a recessed potion of the
wafer formed by bevelling, through the nozzle 302 of the jet
apparatus located above the wafer, from a direction parallel with
the bonding interface (surface) of the bonded wafer. In this case,
the nozzle 302 and a supporting point 303 that allows the nozzle to
oscillate within a plane so as to draw a fan are placed in the same
plane as the bonded surface in the wafer. The nozzle is oscillated
within the bonded surface in the wafer to oscillate the flow of the
jet within this surface. This operation enables the high-pressure
jet to be moved and jetted along the recessed portion or gap in the
bonding portion in the edge of the bonded wafer. This in turn
enables the fluid to be jetted against a wide separation region
without the need for a robot that moves the nozzle within the
bonding surface accurately or a more mechanically complicated
mechanism for moving or rotating the bonded wafer.
[0118] FIG. 7 conceptually shows another separation apparatus
according to this invention, that is, another method for jetting a
jet 503 against the periphery of a bonded wafer 501. The bonded
wafer 501 is fixed by a holder 510 and a nozzle 502 can be rotated
around the wafer to allow the jet 503 to be jetted against the
bonding portion all over the edge of the wafer. The center of the
wafer is held and a rail (not shown in the drawing) concentric with
the wafer is installed around the wafer 501, and a jig 512 with the
nozzle 502 fixed thereto can be slid on the rail to allow the jet
503 to be jetted against the bonding portion from around the wafer
501.
[0119] FIG. 8 shows another example of a separation apparatus
according to this invention. In this figure, 601 is a first wafer,
602 is a second wafer, 603 is a bonding surface, 604 is a fluid
jet, 605 is a direction of a force applied to the wafer by the
fluid jet, and reference numeral 606 indicates an angle between the
fluid jet and the bonding surface. According to this embodiment,
the positions of the nozzle 611 and holder 610 are set so that the
direction of the jet jetted from the nozzle 611 is inclined at an
angle .alpha. from a direction parallel with the separation surface
in the wafer.
[0120] The wafer can be held by the apparatus shown in FIG. 4 and
the nozzle can be disposed as shown in FIG. 8 to jet the fluid
against the side of the wafer. Since the jet 604 is inclined at an
angle .alpha. (606) from the bonding surface 603, different
pressures are applied to the two wafers 601 and 602. In the example
shown in FIG. 8, a relatively small force is applied to the wafer
602 toward which the jet is inclined, whereas a larger force is
applied to the opposite wafer 601. When the jet is inclined at a
side opposite to the wafer in which porous Si is formed, porous Si
or a microcavity layer can be destroyed easily. Thus, the bonded
wafers are desirably installed such that the wafer 601 contains
porous Si.
[0121] FIG. 9 shows another separation apparatus according to this
invention. In this figure, 705 and 706 are vertical drive
mechanisms for fluid jet apparatus nozzles 702 and 703, 707 is a
horizontal drive mechanism for a water jet apparatus nozzle 704,
and 708 is a wafer holder.
[0122] A shown in FIG. 9, the wafer holder 708 is used to hold both
sides of the bonded wafer 701 so as to stand in the vertical
direction. In this case, a side of the wafer having an orientation
flat portion is directed upward. A high-pressure fluid is jetted
against a recessed potion or gap in the wafer 701 formed by
bevelling, through the nozzles 702, 703, and 704 of the plurality
of (in this example, three) jet apparatuses located above or on the
side of the wafer, from a direction parallel with the bonding
interface (surface) in the bonded wafer. The configuration of each
nozzle is the same as in FIG. 3. In this case, the plurality of
nozzles 702, 703, and 704 are scanned along guides 711, 712, and
713 in a direction in which the high-pressure fluid moves along the
gap formed by bevelling.
[0123] In this way, the bonded wafers are divided into two.
[0124] When only one nozzle is used, a high pressure is required
that is sufficient to separate the wafer over a distance
corresponding to its diameter. When the pressure is only sufficient
to separate the wafer over a distance corresponding to its radius,
the wafer must be turned upside down and separated again over a
distance corresponding to its radius. The plurality of nozzles can
be used to allow each nozzle to separate the wafer only over a
distance corresponding to its radius, and the need to jet the
high-pressure fluid against the wafer again after turning it upside
down is omitted, and the overall surface of the wafer can be
separated during a single step.
[0125] FIGS. 10A and 10B show another separation apparatus
according to this invention. In this figure, 801 is bonded wafers
as a composite member, 802 is a nozzle for a fluid jet, and 803 is
a fluid. A high-pressure pure water is jetted against a gap in the
wafer formed by bevelling, through the nozzle with slit-like
openings of the jet apparatus located above or on the side of the
wafer, from a direction parallel with the bonding interface
(surface) in the bonded wafer while allowing the bonded wafer to
stand perpendicularly to the holder 811, as shown in FIGS. 10A and
10B. The slit is located parallel with the bonding interface
(surface) in the bonded wafer and positioned so that a linear flow
of water is jetted accurately against the gap in the wafer formed
by bevelling. A plurality of nozzles are scanned in a direction in
which the high-pressure fluid moves along the gap formed by
bevelling.
[0126] The need to scan the nozzle is omitted by increasing the
length of the slit above the diameter of the wafer.
[0127] The effect of this slit-like nozzle is that the wafer can be
divided under a lower pressure than with a single nozzle of a very
small diameter. Despite the low pressure, by increasing the area
from which the high-pressure fluid is jetted, the energy used to
separate the wafer can be increased to enable it to be divided
easily.
[0128] Not only a nozzle having a slit-like opening but also a
plurality of nozzles 1202 placed closely in a line to jet a fluid
against a bonded wafer 1201 as shown in FIG. 11 can be used for
this invention to obtain similar results. Reference numeral 1211
indicates a wafer holder.
[0129] FIG. 12 shows another separation apparatus according to this
invention which can use a plurality of jets to separate a plurality
of wafers at the same time. In a basic configuration of the
apparatus in FIG. 12, components similar to those in FIG. 3 are
installed independently. A wafer 1001a is set on a holder 1005a. A
high-pressure fluid jetted from a nozzle 1002a hits against a
bevelled portion of the wafer 1001a. The nozzle 1002a can be moved
in a direction perpendicular to the sheet of the drawing by a
horizontal-movement mechanism 1004a while jetting the high-pressure
fluid against the bevelled portion. A similar operation can be
performed by the apparatus in the right of the figure having a
nozzle 1002b, a horizontal-movement mechanism 1004b, and a holder
1005b. This configuration doubles the throughput. Although this
figure shows two sets of the jet apparatus, three or more of such
apparatuses may be installed.
[0130] In addition, when the high-pressure pump does not have a
large capacity, the right wafer can be changed while the left
high-pressure fluid is being jetted, and vice versa. This requires
only one set of a loader and an unloader robots.
[0131] FIG. 13 shows another separation apparatus according to this
invention in which wafers 1001a, 1001b, 1001c, 1001d, and 1001e are
set on a wafer holding means 1105. A plurality of nozzles 1102a to
1102e are installed in a set of nozzle movement mechanisms 1103 and
1104. The nozzle interval is the same as the wafer fixation
interval. The holding mechanism and nozzle movement method are
similar to those in FIG. 3.
[0132] By using the central axis of each wafer for alignment, the
five wafers are each fixed between the holders 1115a and 1115b,
between the holders 1115b and 1115c, between the holders 1115c and
1115d, between the holders 1115d and 1115e, or between the holders
1115e and 1115f, all of which can move on a guide 1114 in the
horizontal direction.
[0133] A movable supply pipe 1112 acting as both a common fluid
supply pipe and a nozzle vertical-movement mechanism is connected
to the five nozzles 1102a to 1102e via a distributor 1113.
[0134] After the amount and pressure of fluid jetted from each
nozzle have been stabilized at a nozzle standby position, all
nozzles 1102a to 1102e are moved along the guide 1111 to a wafer
separation position and then further advance along the guide 1111
to separate the wafers.
[0135] Once the separation has been finished, the amount of jetted
fluid is reduced or the jetting is stopped to return the nozzles to
their standby positions.
[0136] In the apparatuses shown in FIGS. 10A to 13, separation can
be carried out by jetting the fluid while rotating the holders for
the wafers to rotate the wafers.
[0137] FIGS. 14 and 15 are a top and a side views showing a
separation apparatus for a composite member used for this
invention.
[0138] This separation apparatus has a rotation synchronization
mechanism and can rotate a first holder for holding a first surface
of the composite member and a second holder for holding a second
surface of the composite member, at the same angular speed in the
same direction.
[0139] When a rotational drive force is applied to only one surface
of the composite member or synchronization such as that described
above is not provided, the following phenomenon is likely to
occur.
[0140] Immediately before a wafer that is a composite member is
completely separated over the entire wafer, there is a moment at
which a very small region, which is finally separated, remains
unseparated somewhere on the separation surface. The following two
separation modes can be assumed depending on a position of this
very small unseparated region.
[0141] A first mode is a case in which the unseparated region
remains almost at the center of the separation surface and a second
mode is a case in which it remains in an area other than the
center. FIG. 16 conceptually shows these modes.
[0142] The first mode occurs if separation progresses uniformly
from the circumference of the wafer toward its center or if the
strength of the vicinity of the center of the separation surface is
high. In this case, if a rotational drive force is applied to only
one of the holders 21 of one side of the wafer, this rotation
causes the very small unseparated region to be twisted off and
separated.
[0143] The second separation mode occurs if during the initial step
of fluid jetting, a crack extends over the radius of the wafer or
longer from a certain circumferential portion resulting in quick
separation or if the strength of areas other than the vicinity of
the center of the separation surface is high. In this case, if a
rotational drive force is applied to only one of the holders 21 of
one side of the wafer, this rotation causes sharing stress, thereby
causing the very small unseparated region to be separated.
[0144] This is because the opposite holder 22 is subjected to no
independent drive force and is only rotated through the wafer,
causing a slight force to be effected in a direction in which the
rotation of the holder 22 is stopped even if softly the holder 22
is held by a bearing.
[0145] Such torsion or shear causes complicated forces in
directions other than the vertical one to be applied to the
separation surface, resulting in the unwanted separation of an area
other than the separation surface.
[0146] Thus, when the wafer is separated while being rotated and if
the wafer is rotationally driven without allowing both sides of it
to synchronize mutually, separation may occur from a surface other
than a desired separation surface or the wafer or an active layer
may be damaged. These phenomena may significantly reduce the
yield.
[0147] A motor support 36 for supporting a motor 32 that can
control the speed and a pair of shaft supports 37 and 38 for
rotatably supporting a motor shaft 31 are fixed on a supporting
stand 40.
[0148] Furthermore, a first holder support 33 for rotatably
supporting the holder 21 and a second holder support 34 for
rotatably supporting the holder 22 are fixed on the supporting
stand 40.
[0149] A timing pulley 29 mounted on the motor shaft 31 and a
timing pulley 25 mounted at the rear end of a rotating shaft 23 of
the holder 21 are connected together in such a way as to rotate in
the same direction by means of a timing belt 27.
[0150] Likewise, a timing pulley 30 mounted on the motor shaft 31
and a timing pulley 26 mounted at the rear end of a rotating shaft
24 of the holder 22 are connected together in such a way as to
rotate in the same direction by means of a timing belt 28.
[0151] The pulleys 25 and 26 have the same driving radius, and the
pulleys 29 and 30 have the same driving radius.
[0152] The timing belts 27 and 28 are the same.
[0153] A drive force from the motor 32 is transmitted from the
shaft 31 to the holders 21 and 22 via the pulleys and belts in
order to rotate the holders 21 and 22 at the same angular speed in
the same direction with the same timing.
[0154] In FIG. 15, 60 is a jet nozzle that jets a fluid and 61 is a
shutter. For clarity, the illustration of the nozzle and shutter
are simplified.
[0155] The nozzle 60 is fixed on the supporting stand 40 using a
fixation jig (not shown), and a wafer positioning member 35 is
provided on the supporting stand 40 so as to be aligned with the
nozzle 60.
[0156] FIG. 17 is a partially sectional view of the holder of the
separation apparatus before it holds the wafer 20.
[0157] The holder 21 or 22 is an assembly of a holding section 45a
or 46a that actually sucks and holds a wafer; a fixation section
45b or 46b that rotates the holding section 45a or 46a together
with the rotating shaft 23 or 24; and detents 41 and 42 or 43 and
44.
[0158] Using a tube 52 and a pressurized gas passed through a
pressurizing passage 56, the holding section 45a can move against a
compression spring (a coil spring 47) in a direction in which it
leaves the rotating shaft 23 (rightward in the figure).
[0159] An opening op is provided near the center of the holding
section 45a and is in communication with a pressure reducing
passage 55 in the rotating shaft. Using a vacuum pump (not shown)
connected to the opening op via a pressure reducing tube 51, vacuum
is drawn into the opening op to reduce the atmospheric
pressure.
[0160] The holder 21 or 22 is moved forward (rightward in the
figure) by having its holder section 45a that directly sucks the
wafer, guided by the rotating shaft 23, as shown in FIG. 17, and
using the pressure of air introduced from the pressurizing tube 52.
The holder 21 or 22 is moved backward (leftward in the figure) by
the compression spring 47. The holding section 45a rotates with the
rotating shaft 23 using the detents 41 and 42. Basically, the
holder 22 is specularly symmetrical with the holder 21 and has the
same mechanism as it. To allow the bonded wafer 20 and nozzle 60 to
be always set at specified positions when the bonded wafer 20 is
positioned and held on the holder 22, pressure is controlled and
adjusted so that a stronger force is applied to the holder 21 than
to the holder 22 during a forward operation, while a stronger force
is applied to the holder 22 than to the holder 21 during a backward
operation.
[0161] The usage of this apparatus, that is, the method for
separating a composite member according to this invention is
described below. The bonded wafer 20 is set so as to fit on a notch
in a positioning stand 35, as shown in FIG. 17. Pressurized air is
then introduced to cause the holding section 45a to advance,
thereby allowing the holder 21 to suck and hold the wafer, as shown
in FIG. 18. The holder 21 can fit the bonded wafer 20 on the notch
in the positioning stand 35 to hold the center of the bonded wafer
20. When the bonded wafer 20 is held in an accurate position, the
nozzle 60 is located perpendicularly to the top of the bonded wafer
20 and the distance between the bonded wafer 20 and the nozzle 60
is 10 to 30 mm. The holding section 46a of the holder 22 is moved
forward (leftward in the figure) to suck and hold the bonded wafer
20, and the feeding of pressurized air of the holding section 46a
is stopped. The bonded wafer 20 is stopped due to a force acting
rightward in the figure which is an combination of a force effected
by the compression spring and a vacuum suction force. The force
effected by the compression spring does not exceed the force
required by the holding section 46a to suck the bonded wafer 20, so
the vacuum destruction of the inside of the pressure reducing
passage 55 or 57 does not occur, which may in turn eliminate the
suction force to cause the wafer 20 to fall.
[0162] A fluid is then fed from a pump 62 to the nozzle 60 for a
specified period of time until the jetted fluid is stabilized. Once
the fluid has been stabilized, the shutter 61 is opened to jet the
high-pressure fluid from the nozzle 60 against the thickness-wise
center of the bonded wafer 20. At this point, the speed controller
motor 32 is rotated to rotate the holders 21 and 22 in synchronism
in order to rotate the wafer 20. By jetting the high-pressure fluid
against the thickness-wise center of the wafer 20, the
high-pressure fluid also enters the separation region to extend the
bonded wafer 20, thereby finally separating it into two.
[0163] Since the high-pressure fluid is applied uniformly against
the bonded wafer 20 and the holders 21 and 22 each apply a force in
a direction in which the bonded wafer 20 is drawn, as described
above, separated pieces further leave each other and are prevented
from sliding.
[0164] In addition, in the wafer supporting means shown in FIGS. 17
to 20, the wafer is supported while being subjected to a force by
the holders 21 and 22 in a direction in which the holders move
backward from the wafer, but the holders 21 and 22 may effect a
force in a forward direction and this pressure may be used to hold
the wafer. In this case, the high-pressure fluid also advances
while extending the bonded wafer 20 to create a small gap, thereby
finally causing the wafer to be separated into two. In this method,
if the holders 21 and 22 do not synchronize mutually, the bonding
surfaces of the separated pieces damage each other due to sliding,
whereas if the holders rotate in synchronism, no damage occurs.
Furthermore, when a force is applied in a direction in which the
holders 21 and 22 move backward, the wafer 20 is pulled to move
backward during separation by the holders 21 and 22 and there may
occur a difference in the amount of displacement between a
separated portion and an unseparated portion to unbalance the
bonded wafer 20, thereby causing a crack when the high-pressure
fluid is jetted. If, however, a force is applied to the holders 21
and 22 in a direction in which they move forward, the bonded wafer
20 will maintain balance to enable the wafer to be separated
stably.
[0165] A high- or atmospheric-pressure fluid can be injected
against the entirely separated wafer to effect a force in a
direction in which it moves backward in order to break the surface
tension of intervening water, thereby separating it into two
completely.
[0166] As described above, the separation apparatus according to
this invention sequentially or simultaneously separates one or more
composite members using a fluid. The composite members may be
juxtaposed in the normal direction of the surface or in parallel
with the surface.
[0167] Alternatively, the composite members may be rotated or moved
parallel with the surface to receive the fluid, or the flow of the
fluid may be moved parallel with the surface so as to hit against
the sides of the composite members, or the composite members and
fluid may be moved together.
EXAMPLE 1
One Porous Layer and Nozzle Scanning
[0168] A first P-type (or N-type) single crystal Si substrate
having a resistivity of 0.01 .OMEGA..multidot.cm was placed in an
HF solution for anodization. The anodization conditions are listed
below.
[0169] Current density: 7 (mA.multidot.cm.sup.-2)
[0170] Anodization solution: HF: H.sub.2O:
C.sub.2H.sub.5OH=1:1:1
[0171] Time: 11 (minute)
[0172] Thickness of the porous Si layer: 12 (.mu.m)
[0173] The porous Si layer is also used as a separation layer to
form a high-quality epitaxial Si layer, that is, a single porous Si
layer provides multiple functions.
[0174] The thickness of the porous Si layer is not limited to the
above value but may be between 0.1 and several hundred .mu.m.
[0175] This substrate was oxidized in an oxygen atmosphere at
400.degree. C. for one hour. The oxidization caused the inner wall
of the pores in the porous Si layer to be covered with a thermally
oxidized film. The surface of the porous Si layer was treated with
hydrofluoric acid to remove only the oxidized film on the surface
of the porous Si layer while leaving the oxidized film on the inner
wall of the pores, and the CVD was then used to allow single
crystal Si to epitaxially grow by 0.3 .mu.m on the porous Si layer.
The growth conditions are listed below.
[0176] Source gas: SiH.sub.2Cl.sub.2/H.sub.2
[0177] Gas flow rate: 0.5/180 1/min.
[0178] Gas pressure: 80 Torr
[0179] Temperature: 950.degree. C.
[0180] Growth speed: 0.3 .mu.m/min.
[0181] Furthermore, a 200 nm thick oxide film (an SiO.sub.2 layer)
was formed on the epitaxial Si layer as an insulating layer, using
thermal oxidation.
[0182] The surface of a separately prepared second Si substrate was
placed on the surface of the SiO.sub.2 layer to contact them
mutually. These substrates were then subjected to thermal treatment
at 1180.degree. C. for five minutes for bonding.
[0183] To separate the bonded substrate formed in this manner using
the apparatus shown in FIG. 3, this bonded wafer was supported from
both sides by the wafer holders so as to stand perpendicularly. An
abrasive-material-free and high-pressure pure water was jetted at
2,000 kgf/cm.sup.2 from a 0.15-mm nozzle of a water jet apparatus
located above the wafer against a gap in the wafer formed by
bevelling, from a direction parallel with a bonding interface
(surface) in the bonded wafer. A nozzle horizontal drive mechanism
was used to scan the nozzle in a direction in which the
high-pressure pure water moved along the gap formed by bevelling.
In this case, when an elastomer 106 (e.g., Viton, fluoro rubber, or
silicone rubber) was used in the portion in which the wafer and
holder contact each other, the wafer could be opened in the
vertical direction relative to its surface to allow the
high-pressure water to enter that part of the porous Si layer which
was sandwiched by the wafer holders, thereby enabling the wafer to
be separated.
[0184] As a result, the SiO.sub.2 layer, the epitaxial Si layer,
and part of the porous Si layer which were originally formed on the
surface of the first substrate were transferred to the second
substrate. Only the remaining part of the porous Si layer remained
on the surface of the first substrate.
[0185] Subsequently, the porous Si layer transferred to the second
substrate was selectively etched by being stirred using a mixture
of 49% hydrofluoric acid and 30% hydrogen peroxide solution. The
single crystal Si layer remained without being etched, whereas the
porous Si layer was entirely removed by selective etching using the
single crystal Si layer as an etch stop material.
[0186] The speed at which a nonporous Si single crystal is etched
by the etching solution is very low, and the selective ratio of
this etching speed and the etching speed of the porous layer is
1:10.sup.5 or more. Thus, the amount of the etched portion of the
nonporous layer (about several tens of Angstrom) corresponds to the
practically negligible reduction of the thickness.
[0187] The single crystal Si layer of 0.2 .mu.m thickness was
formed on the Si oxide film. The single crystal Si layer was not
affected by the selective etching of the porous Si layer. When 100
points of the overall surface of the single crystal Si layer formed
were measured for thickness, the value obtained was 201 nm.+-.4
nm.
[0188] An observation of the cross section by a transmission
electron microscope indicated that new crystal defects did not
occur in the Si layer and that excellent crystallinity was
maintained.
[0189] Thermal treatment was further carried out in hydrogen at
1100.degree. C. for one hour and the surface roughness was
evaluated using an interatomic force microscope. The mean square
roughness of a 50-.mu.m square region was about 0.2 nm and was
similar to that of commercially available Si wafers.
[0190] Similar effects can be obtained by forming the oxide film on
the surface of the second substrate instead of the surface of the
epitaxial layer or forming it on both surfaces.
[0191] In addition, the porous Si layer remaining on the first
substrate was selectively etched by being stirred using a mixture
of 40% hydrofluoric acid and 30% hydrogen peroxide solution.
Subsequently, using hydrogen annealing or surface treatment such as
surface polishing, the first or second substrate could be reused
for the above process.
EXAMPLE 2
Two Porous Layers and Nozzle Scanning
[0192] A first P-type single crystal Si substrate having a
resistivity of 0.01 .OMEGA..multidot.cm was subjected to two-step
anodization in an HF solution to form two porous layers. The
anodization conditions are listed below.
First Step
[0193] Current density: 7 (mA.multidot.cm .sup.-2)
[0194] Anodization solution: HF: H.sub.2O:
C.sub.2H.sub.5OH=1:1:1
[0195] Time: 5 (minute)
[0196] Thickness of the first porous Si layer: 4.5 (.mu.m)
Second Step
[0197] Current density:30 (mA.multidot.cm.sup.-2)
[0198] Anodization solution: HF: H.sub.2O:
C.sub.2H.sub.5OH=1:1:1
[0199] Time: 10 (second)
[0200] Thickness of the second porous Si layer: 0.2 (.mu.m)
[0201] The two porous Si layers were formed, and the surface
porous-Si layer anodized by a low current was used to form a
high-quality epitaxial Si layer while the lower porous Si layer
anodized by a high current was used as a separation layer. That is,
the functions were assigned to the different layers. Thus, the
thickness of the low-current porous Si layer is not limited to the
above value but may be between 0.1 to several hundred .mu.m.
[0202] In addition, a third and subsequent layers may be formed on
the second porous Si layer.
[0203] This substrate was oxidized in an oxygen atmosphere at
400.degree. C. for one hour. The oxidization caused the inner wall
of the pores in the porous Si layer to be covered with a thermally
oxidized film. The surface of the porous Si layer was treated with
hydrofluoric acid to remove only the oxidized film on the surface
of the porous Si layer while leaving the oxidized film on the inner
wall of the pores, and the CVD was then used to allow single
crystal Si to epitaxially grow by 0.3 .mu.m on the porous Si layer.
The growth conditions are listed below.
[0204] Source gas: SiH.sub.2Cl.sub.2/H.sub.2
[0205] Gas flow rate: 0.5/180 1/min.
[0206] Gas pressure: 80 Torr
[0207] Temperature: 950.degree. C.
[0208] Growth speed: 0.3 .mu.m/min.
[0209] Furthermore, a 200 nm thick oxide film (an SiO.sub.2 layer)
was formed on the epitaxial Si layer as an insulating layer, using
thermal oxidation.
[0210] The surface of a separately prepared second Si substrate was
placed on the surface of the SiO.sub.2 layer to contact them
mutually. These substrates were then subjected to thermal treatment
at 1180.degree. C. for five minutes for bonding.
[0211] The bonded substrate formed in this manner was separated
using the apparatus shown in FIG. 3. A separation process similar
to that in Embodiment 1 was used. As a result, the SiO.sub.2 layer,
the epitaxial Si layer, and part of the porous Si layer which were
originally formed on the surface of the first substrate were
transferred to the second substrate. Only the remaining part of the
porous Si layer remained on the surface of the first substrate.
[0212] Subsequently, the porous Si layer transferred to the second
substrate was selectively etched by being stirred using a mixture
of 49% hydrofluoric acid and 30% hydrogen peroxide solution. The
single crystal Si layer remained without being etched, whereas the
porous Si layer was entirely removed by selective etching using the
single crystal Si layer as an etch stop material.
[0213] The single crystal Si layer of 0.2 .mu.m thickness was
formed on the Si oxide film. The single crystal Si layer was not
affected by the selective etching of the porous Si layer. When 100
points of the overall surface of the single crystal Si layer formed
were measured for thickness, the value obtained was 200 nm.+-.4
nm.
[0214] An observation of the cross section by the transmission
electron microscope indicated that new crystal defects did not
occur in the Si layer and that excellent crystallinity was
maintained.
[0215] Thermal treatment was further carried out in hydrogen at
1100.degree. C. for one hour and the surface roughness was
evaluated using the interatomic force microscope. The mean square
roughness of a 50-.mu.m square region was about 0.2 nm and was
similar to that of commercially available Si wafers.
[0216] Similar effects can be obtained by forming the oxide film on
the surface of the second substrate instead of the surface of the
epitaxial layer or forming it on both surfaces.
[0217] In addition, the porous Si layer remaining on the first
substrate was selectively etched by being stirred using a mixture
of 49% hydrofluoric acid and 30% hydrogen peroxide solution.
Subsequently, using hydrogen annealing or surface treatment such as
surface polishing, the first or second substrate could be reused to
repeat the above process.
EXAMPLE 3
Porous Si Layer+Separation Layer Formed by Ion Implantation and
Nozzle Scanning
[0218] A first P-type single crystal Si substrate having a
resistivity of 0.01 .OMEGA..multidot.cm was subjected to
anodization in an HF solution.
[0219] The anodization conditions are listed below.
[0220] Current density: 7 (mA.multidot.cm.sup.-2)
[0221] Anodization solution: HF: H.sub.2O:
C.sub.2H.sub.5OH=1:1:1
[0222] Time: 11 (minute)
[0223] Thickness of the porous Si layer: 12 (.mu.m)
[0224] This substrate was oxidized in an oxygen atmosphere at
400.degree. C. for one hour. The oxidization caused the inner wall
of the pores in the porous Si layer to be covered with a thermally
oxidized film. The surface of the porous Si layer was treated with
hydrofluoric acid to remove only the oxidized film on the surface
of the porous Si layer while leaving the oxidized film on the inner
wall of the pores, and the CVD was then used to allow single
crystal Si to epitaxially grow by 0.3 .mu.m on the porous Si layer.
The growth conditions are listed below.
[0225] Source gas: SiH.sub.2Cl.sub.2/H.sub.2
[0226] Gas flow rate: 0.5/180 1/min.
[0227] Gas pressure: 80 Torr
[0228] Temperature: 950.degree. C.
[0229] Growth speed: 0.3 .mu.m/min.
[0230] Furthermore, a 200-nm oxide film (an SiO.sub.2 layer) was
formed on the epitaxial Si layer as an insulating layer, using
thermal oxidation.
[0231] Ions were implanted from the surface of the first substrate
in such a way that their projected flights exists within the
epitaxial layer/porous Si interface, the porous Si/substrate
interface, or the porous Si layer. This allowed a layer acting as a
separation layer to be formed at a depth corresponding to the
projected flight as a strain layer formed by microcavities or
concentrated implanted ions.
[0232] After pre-treatment such as N.sub.2 plasma processing, the
surface of a separately prepared second Si substrate was placed on
the surface of the SiO.sub.2 layer to contact them mutually. These
substrates were then subjected to thermal treatment at 600.degree.
C. for 10 hours for bonding.
[0233] The bonded substrate formed in this manner was separated
using the apparatus shown in FIG. 3. A separation process similar
to that in Example 1 was used. As a result, the SiO.sub.2 layer,
the epitaxial Si layer, and part of the porous Si layer which were
originally formed on the surface of the first substrate were
transferred to the second substrate. Only the remaining part of the
porous Si layer remained on the surface of the first substrate.
[0234] Subsequently, the porous Si layer transferred to the second
substrate was selectively etched by being stirred using a mixture
of 49% hydrofluoric acid and 30% hydrogen peroxide solution. The
single crystal Si layer remained without being etched, whereas the
porous Si layer was entirely removed by selective etching using the
single crystal Si layer as an etch stop material.
[0235] The single crystal Si layer of 0.2 .mu.m thickness was
formed on the Si oxide film. The single crystal Si layer was not
affected by the selective etching of the porous Si layer. When 100
points of the overall surface of the single crystal Si layer formed
were measured for thickness, the value obtained was 201 nm.+-.4
nm.
[0236] An observation of the cross section by the transmission
electron microscope indicated that new crystal defects did not
occur in the Si layer and that excellent crystallinity was
maintained.
[0237] Thermal treatment was further carried out in hydrogen at
1100.degree. C. for one hour and the surface roughness was
evaluated using the interatomic force microscope. The mean square
roughness of a 50-.mu.m square region was about 0.2 nm and was
similar to that of commercially available Si wafers.
[0238] Similar effects can be obtained by forming the oxide film on
the surface of the second substrate instead of the surface of the
epitaxial layer or forming it on both surfaces.
[0239] In addition, the porous Si layer remaining on the first
substrate was selectively etched by being stirred using a mixture
of 49% hydrofluoric acid and 30% hydrogen peroxide solution.
Subsequently, using hydrogen annealing or surface treatment such as
surface polishing, the first or second substrate could be reused to
repeat the above process.
[0240] According to this example, the ion implantation was carried
out after the formation of the epitaxial Si layer, but ions may be
implanted into the porous Si layer or the porous Si/Si substrate
interface prior to the epitaxial growth.
EXAMPLE 4
Bubble Layer Formed by Ion Implantation and Nozzle Scanning
[0241] A 200 nm thick oxide film (an SiO.sub.2 layer) was formed on
the first single crystal Si layer as an insulating layer, using
thermal oxidation.
[0242] Ions were implanted from the surface of the first substrate
in such a way that their projected flight exists within the Si
substrate. This allowed a layer acting as a separation layer to be
formed at a depth corresponding to the projected flight as a strain
layer formed by microcavities or concentrated implanted ions.
[0243] After pre-treatment such as N.sub.2 plasma processing, the
surface of a separately prepared second Si substrate was placed on
the surface of the SiO.sub.2 layer to contact them mutually. These
substrates were then subjected to thermal treatment at 600.degree.
C. for 10 hours for bonding.
[0244] The bonded substrate formed in this manner was separated
using the apparatus shown in FIG. 3. A separation process similar
to that in Example 1 was used.
[0245] As a result, the SiO.sub.2 layer, the surface single crystal
layer, and part of the separation layer which were originally
formed on the surface of the first substrate were transferred to
the second substrate. Only the remaining part of the separation
layer remained on the surface of the first substrate.
[0246] Subsequently, the separation layer transferred to the second
substrate was selectively etched by being stirred using a mixture
of 49% hydrofluoric acid and 30% hydrogen peroxide solution. The
single crystal Si layer remained without being etched, whereas the
separation layer was entirely removed by selective etching using
the single crystal Si layer as an etch stop material.
[0247] This etching step may be omitted if the remaining separation
layer is sufficiently thin.
[0248] The single crystal Si layer of 0.2 .mu.m thickness was
formed on the Si oxide film. The single crystal Si layer was not
affected by the selective etching of the separation layer. When 100
points of the overall surface of the single crystal Si layer formed
were measured for thickness, the value obtained was 201 nm.+-.4
nm.
[0249] An observation of the cross section by the transmission
electron microscope indicated that new crystal defects did not
occur in the Si layer and that excellent crystallinity was
maintained.
[0250] Thermal treatment was further carried out in hydrogen at
1100.degree. C. for one hour and the surface roughness was
evaluated using the interatomic force microscope. The mean square
roughness of a 50-.mu.m square region was about 0.2 nm and was
similar to that of commercially available Si wafers.
[0251] Similar effects can be obtained by forming the oxide film on
the surface of the second substrate instead of the surface of the
epitaxial layer or forming it on both surfaces.
[0252] In addition, the separation layer remaining on the first
substrate was selectively etched by being stirred using a mixture
of 49% hydrofluoric acid and 30% hydrogen peroxide solution.
Subsequently, using hydrogen annealing or surface treatment such as
surface polishing, the first or second substrate could be reused to
repeat the above process.
[0253] According to this example, the surface area of the Si wafer
is transferred to the second substrate via the separation layer
formed by ion implantation, but an epi-wafer may be used to
transfer the epitaxial layer to the second substrate via the
separation layer formed by ion implantation. The following process
is also possible. After the ion implantation according to this
example, the surface SiO.sub.2 is removed and the epitaxial layer
and then the SiO.sub.2 layer are formed, followed by the bonding
step. The epitaxial layer is then transferred to the second
substrate via the separation layer formed by ion implantation. In
the latter case, the surface area of the Si wafer is also
transferred.
EXAMPLE 5
Horizontal Placement and Movement of the Wafer
[0254] A first P-type single crystal Si substrate having a
resistivity of 0.01 .OMEGA..multidot.cm was subjected to
anodization in an HF solution.
[0255] The anodization conditions are listed below.
[0256] Current density: 7 (MA.multidot.cm.sup.-2)
[0257] Anodization solution: HF: H.sub.2O:
C.sub.2H.sub.5OH=1:1:1
[0258] Time: 11 (minute)
[0259] Thickness of the porous Si layer: 12 (.mu.m)
[0260] Porous Si was used to form a high-quality epitaxial Si layer
and as a separation layer.
[0261] The thickness of the porous Si layer is not limited to the
above value but may be between 0.1 to several hundred .mu.m.
[0262] This substrate was oxidized in an oxygen atmosphere at
400.degree. C. for one hour. The oxidization caused the inner wall
of the pores in the porous Si layer to be covered with a thermally
oxidized film. The surface of the porous Si layer was treated with
hydrofluoric acid to remove only the oxidized film on the surface
of the porous Si layer while leaving the oxidized film on the inner
wall of the pores, and the CVD was then used to allow single
crystal Si to epitaxially grow by 0.3 .mu.m on the porous Si layer.
The growth conditions are listed below.
[0263] Source gas: SiH.sub.2Cl.sub.2/H.sub.2
[0264] Gas flow rate: 0.5/180 1/min.
[0265] Gas pressure: 80 Torr
[0266] Temperature: 950.degree. C.
[0267] Growth speed: 0.3 .mu.m/min.
[0268] Furthermore, a 200 nm thick oxide film (an SiO.sub.2 layer)
was formed on the epitaxial Si layer as an insulating layer, using
thermal oxidation.
[0269] The surface of a separately prepared second Si substrate was
placed on the surface of the SiO.sub.2 layer to contact them
mutually. These substrates were then subjected to thermal treatment
at 1180.degree. C. for 5 minutes for bonding.
[0270] The bonded substrate formed in this manner was separated
using the apparatus shown in FIG. 5. The wafer cassette 205 was
placed on the cassette base 207 in such a way that the wafer 201
extended in the horizontal direction, as shown in FIG. 5.
High-pressure pure water at 2,000 kgf/cm.sup.2 was jetted from the
0.15-mm nozzles 202 and 203 of the water jet apparatus located on
the side of the wafer against the bonding region in the bonded
wafer through the gap therein formed by bevelling, from a direction
parallel with the bonding interface (surface) in the bonded wafer.
The nozzles were fixed and the bonded wafer was scanned in the
horizontal direction to receive the high-pressure pure water along
the gap formed by bevelling.
[0271] This operation allowed the wafer to be divided into two via
the porous Si layer. Then, another loading robot was used to store
and collect the separated wafer as a first and a second
substrates.
[0272] The SiO.sub.2 layer, the epitaxial Si layer, and part of the
porous Si layer which were originally formed on the surface of the
first substrate were transferred to the second substrate. Only the
remaining part of the porous Si layer remained on the surface of
the first substrate.
[0273] Subsequently, the porous Si layer transferred to the second
substrate was selectively etched by being stirred using a mixture
of 49% hydrofluoric acid and 30% hydrogen peroxide solution. The
single crystal Si layer remained without being etched, whereas the
porous Si layer was entirely removed by selective etching using the
single crystal Si layer as an etch stop material.
[0274] The single crystal Si layer of 0.2 .mu.m thickness was
formed on the Si oxide film. The single crystal Si layer was not
affected by the selective etching of the porous Si layer. When 100
points of the overall surface of the single crystal Si layer formed
were measured for thickness, the value obtained was 200 nm.+-.5
nm.
[0275] An observation of the cross section by the transmission
electron microscope indicated that new crystal defects did not
occur in the Si layer and that excellent crystallinity was
maintained.
[0276] Thermal treatment was further carried out in hydrogen at
1100.degree. C. for one hour and the surface roughness was
evaluated using the interatomic force microscope. The mean square
roughness of a50-.mu.m square region was about 0.2 nm and was
similar to that of commercially available Si wafers.
[0277] Similar effects can be obtained by forming the oxide film on
the surface of the second substrate instead of the surface of the
epitaxial layer or forming it on both surfaces.
[0278] In addition, the porous Si layer remaining on the first
substrate was selectively etched by being stirred using a mixture
of 49% hydrofluoric acid and 30% hydrogen peroxide solution.
Subsequently, using hydrogen annealing or surface treatment such as
surface polishing, the first or second substrate could be reused to
repeat the above process.
EXAMPLE 6
Oscillation of the Nozzle
[0279] A first P-type single crystal Si substrate having a
resistivity of 0.01 .OMEGA..multidot.cm was subjected to
anodization in an HF solution.
[0280] The anodization conditions are listed below.
[0281] Current density: 7 (mA.multidot.cm.sup.-2)
[0282] Anodization solution: HF: H.sub.2O:
C.sub.2H.sub.5OH=1:1:1
[0283] Time: 11 (minute)
[0284] Thickness of the porous Si layer: 12 (.mu.m)
[0285] Porous Si was used to form a high-quality epitaxial Si layer
and as a separation layer.
[0286] This substrate was oxidized in an oxygen atmosphere at
400.degree. C. for one hour. The oxidization caused the inner wall
of the pores in the porous Si layer to be covered with a thermally
oxidized film. The surface of the porous Si layer was treated with
hydrofluoric acid to remove only the oxidized film on the surface
of the porous Si layer while leaving the oxidized film on the inner
wall of the pores, and the CVD was then used to allow single
crystal Si to epitaxially grow by 0.3 .mu.m on the porous Si layer.
The growth conditions are listed below.
[0287] Source gas: SiH.sub.2Cl.sub.2/H.sub.2
[0288] Gas flow rate: 0.5/180 1/min.
[0289] Gas pressure: 80 Torr Temperature: 950 .degree.C.
[0290] Growth speed: 0.3 .mu.m/min.
[0291] Furthermore, a 200 nm thick oxide film (an SiO.sub.2 layer)
was formed on the epitaxial Si layer as an insulating layer, using
thermal oxidation.
[0292] The surface of a separately prepared Si substrate was placed
on the surface of the SiO.sub.2 layer to contact them mutually.
These substrates were then subjected to thermal treatment at
1180.degree. C. for 5 minutes for bonding.
[0293] The bonded substrate formed in this manner was separated
using the apparatus shown in FIG. 6. As shown in this figure, the
bonded wafer 301 was allowed to stand in the vertical direction,
and high-pressure pure water at 2,000 kgf/cm.sup.2 was jetted from
the 0.15-mm nozzle 302 of the water jet apparatus located above the
wafer against the bonding region in the bonded wafer through the
gap therein formed by bevelling, from a direction parallel with the
bonding interface (surface) in the bonded wafer. Then, the nozzle
302 was oscillated within the same plane as the bonding surface in
the wafer so as to draw a fan, in order to oscillate the flow of
the jet within this plane.
[0294] This operation allowed the wafer to be divided into two via
the porous Si layer. As a result, the SiO.sub.2 layer, the
epitaxial Si layer, and part of the porous Si layer which were
originally formed on the surface of the first substrate were
transferred to the second substrate. Only the remaining part of the
porous Si layer remained on the surface of the first substrate.
[0295] Subsequently, the porous Si layer transferred to the second
substrate was selectively etched by being stirred using a mixture
of 49% hydrofluoric acid and 30% hydrogen peroxide solution. The
single crystal Si layer remained without being etched, whereas the
porous Si layer was entirely removed by selective etching using the
single crystal Si layer as an etch stop material.
[0296] The single crystal Si layer of 0.2 .mu.m thickness was
formed on the Si oxide film. The single crystal Si layer was not
affected by the selective etching of the porous Si layer. When 100
points of the overall surface of the single crystal Si layer formed
were measured for thickness, the value obtained was 201 nm.+-.4
nm.
[0297] An observation of the cross section by the transmission
electron microscope indicated that new crystal defects did not
occur in the Si layer and that excellent crystallinity was
maintained.
[0298] Thermal treatment was further carried out in hydrogen at
1100.degree. C. for one hour and the surface roughness was
evaluated using the interatomic force microscope. The mean square
roughness of a 50-.mu.m square region was about 0.2 nm and was
similar to that of commercially available Si wafers.
[0299] Similar effects can be obtained by forming the oxide film on
the surface of the second substrate instead of the surface of the
epitaxial layer or forming it on both surfaces.
[0300] In addition, the porous Si layer remaining on the first
substrate was selectively etched by being stirred using a mixture
of 49% hydrofluoric acid and 30% hydrogen peroxide solution.
Subsequently, using hydrogen annealing or surface treatment such as
surface polishing, the first or second substrate could be reused to
repeat the above process.
[0301] Similar results were obtained by separating wafers in which
a separation layer was formed according to Examples 2 to 4.
EXAMPLE 7
Rotation of the Wafer
[0302] A first P-type single crystal Si substrate having a
resistivity of 0.01 .omega..multidot.cm was subjected to
anodization in an HF solution.
[0303] The anodization conditions are listed below.
[0304] Current density: 7 (mA.multidot.cm.sup.-2)
[0305] Anodization solution: HF: H.sub.2O:
C.sub.2H.sub.5)H=1:1:1
[0306] Time: 11 (minute)
[0307] Thickness of the porous Si layer: 12 (.mu.m)
[0308] Porous Si was used to form a high-quality epitaxial Si layer
and as a separation layer.
[0309] This substrate was oxidized in an oxygen atmosphere at
400.degree. C. for one hour. The oxidization caused the inner wall
of the pores in the porous Si layer to be covered with a thermally
oxidized film. The surface of the porous Si layer was treated with
hydrofluoric acid to remove only the oxidized film on the surface
of the porous Si layer while leaving the oxidized film on the inner
wall of the pores, and the CVD was then used to allow single
crystal Si to epitaxially grow by 0.3 .mu.m on the porous Si layer.
The growth conditions are listed below.
[0310] Source gas: SiH.sub.2Cl.sub.2/H.sub.2
[0311] Gas flow rate: 0.5/180 1/min.
[0312] Gas pressure: 80 Torr
[0313] Temperature: 950.degree. C.
[0314] Growth speed: 0.3 .mu.m/min.
[0315] Furthermore, a 200 nm thick oxide film (an SiO.sub.2 layer)
was formed on the epitaxial Si layer as an insulating layer, using
thermal oxidation.
[0316] The surface of a separately prepared second Si substrate was
placed on the surface of the SiO.sub.2 layer to contact them
mutually. These substrates were then subjected to thermal treatment
at 1180.degree. C. for 5 minutes for bonding.
[0317] The bonded substrate formed in this manner was separated
using the apparatus shown in FIG. 4.
[0318] A bonded wafer 401 was allowed to stand in the vertical
direction.
[0319] The bonded wafer 401 was set so as to fit on a positioning
pin 413 and was sucked and held by a holder 404. After the bonded
wafer 401 was held in an accurate position so as to fit on the
positioning pin 413, the nozzle 402 was moved until it was located
perpendicularly to the top of the bonded wafer 401 and the distance
between the wafer 401 and the nozzle 402 was set at 15 mm. Then, a
holder 403 was moved forward (leftward in the figure) via a bearing
411 until it sucked and held the wafer 401.
[0320] Then, water without abrasive material grains was fed from a
water jet pump 414 to the nozzle 402 for a specified period of time
until the injected fluid was stabilized. Once the water had been
stabilized, a shutter 406 was opened to inject the high-pressure
pure water from the nozzle 402 against the thickness-wise center of
the side of the bonded wafer 401. At this point, a holder 404 was
rotated to rotate the bonded wafer 401 and holder 403. The
high-pressure water also entered the porous Si layer to extend the
bonded wafer 401, thereby enabling it to be finally separated into
two.
[0321] Subsequently, the porous Si layer transferred to the second
substrate was selectively etched by being stirred using a mixture
of 49% hydrofluoric acid and 30% hydrogen peroxide solution. The
single crystal Si layer remained without being etched, whereas the
porous Si layer was entirely removed by selective etching using the
single crystal Si layer as an etch stop material.
[0322] The single crystal Si layer of 0.2 .mu.m thickness was
formed on the Si oxide film. The single crystal Si layer was not
affected by the selective etching of the porous Si layer. When 100
points of the overall surface of the single crystal Si layer formed
were measured for thickness, the value obtained was 200 nm.+-.3
nm.
[0323] An observation of the cross section by the transmission
electron microscope indicated that new crystal defects did not
occur in the Si layer and that excellent crystallinity was
maintained.
[0324] Thermal treatment was further carried out in hydrogen at
1100.degree. C. for one hour and the surface roughness was
evaluated using the interatomic force microscope. The mean square
roughness of a 50-.mu.m square region was about 0.2 nm and was
similar to that of commercially available Si wafers.
[0325] Similar effects can be obtained by forming the oxide film on
the surface of the second substrate instead of the surface of the
epitaxial layer or forming it on both surfaces.
[0326] In addition, the porous Si layer remaining on the first
substrate was selectively etched by being stirred using a mixture
of 49% hydrofluoric acid and 30% hydrogen peroxide solution.
Subsequently, using hydrogen annealing or surface treatment such as
surface polishing, the first or second substrate could be reused to
repeat the above process.
[0327] Similar results were obtained by separating wafers in which
a separation layer was formed according to Examples 2 to 4.
EXAMPLE 8
Diagonal Injection
[0328] A first P-type single crystal Si substrate having a
resistivity of 0.01 .OMEGA..multidot.cm was subjected to
anodization in an HF solution.
[0329] The anodization conditions are listed below.
[0330] Current density: 7 (mA.multidot.cm.sup.-2)
[0331] Anodization solution: HF: H.sub.2O:
C.sub.2H.sub.5OH=1:1:1
[0332] Time: 11 (minute)
[0333] Thickness of the porous Si layer: 12 (.mu.m)
[0334] Porous Si was used to form a high-quality epitaxial Si layer
and as a separation layer.
[0335] The thickness of the porous Si layer is not limited to the
above value but may be between 0.1 to several hundred .mu.m.
[0336] This substrate was oxidized in an oxygen atmosphere at
400.degree. C. for one hour. The oxidization caused the inner wall
of the pores in the porous Si layer to be covered with a thermally
oxidized film. The surface of the porous Si layer was treated with
hydrofluoric acid to remove only the oxidized film on the surface
of the porous Si layer while leaving the oxidized film on the inner
wall of the pores, and the CVD was then used to allow single
crystal Si to epitaxially grow by 0.3 .mu.m on the porous Si layer.
The growth conditions are listed below.
[0337] Source gas: SiH.sub.2Cl.sub.2/H.sub.2
[0338] Gas flow rate: 0.5/180 1/min.
[0339] Gas pressure: 80 Torr
[0340] Temperature: 950.degree. C.
[0341] Growth speed: 0.3 .mu.m/min.
[0342] Furthermore, a 200 nm thick oxide film (an SiO.sub.2 layer)
was formed on the epitaxial Si layer as an insulating layer, using
thermal oxidation.
[0343] The surface of a separately prepared second Si substrate was
placed on the surface of the SiO.sub.2 layer to contact them
mutually. These substrates were then subjected to thermal treatment
at 1180.degree. C. for 5 minutes for bonding.
[0344] A bonded wafer was allowed to stand in the vertical
direction, and high-pressure pure water at 2,000 kgf/cm.sup.2 was
jetted from the 0.15-mm diameter nozzle of the water jet apparatus
located above the wafer against the bonding region in the bonded
wafer through the gap therein formed by bevelling, from a direction
inclined at an angle a from the bonding interface (surface).
[0345] The wafer was held by the apparatus shown in FIG. 4 and the
nozzle was disposed as shown in FIG. 8 to inject the fluid against
the side of the wafer.
[0346] Subsequently, the porous Si layer transferred to the second
substrate was selectively etched by being stirred using a mixture
of 49% hydrofluoric acid and 30% hydrogen peroxide solution. The
single crystal Si layer remained without being etched, whereas the
porous Si layer was entirely removed by selective etching using the
single crystal Si layer as an etch stop material.
[0347] The single crystal Si layer of 0.2 .mu.m thickness was
formed on the Si oxide film. The single crystal Si layer was not
affected by the selective etching of the porous Si layer. When 100
points of the overall surface of the single crystal Si layer formed
were measured for thickness, the value obtained was 201 nm.+-.4
nm.
[0348] An observation of the cross section by the transmission
electron microscope indicated that new crystal defects did not
occur in the Si layer and that excellent crystallinity was
maintained.
[0349] Thermal treatment was further carried out in hydrogen at
1100.degree. C. for one hour and the surface roughness was
evaluated using the interatomic force microscope. The mean square
roughness of a 50-.mu.m square region was about 0.2 nm and was
similar to that of commercially available Si wafers.
[0350] Similar effects can be obtained by forming the oxide film on
the surface of the second substrate instead of the surface of the
epitaxial layer or forming it on both surfaces.
[0351] In addition, the porous Si layer remaining on the first
substrate was selectively etched by being stirred using a mixture
of 49% hydrofluoric acid and 30% hydrogen peroxide solution.
Subsequently, using hydrogen annealing or surface treatment such as
surface polishing, the first or second substrate could be reused to
repeat the above process.
[0352] Similar results were obtained by separating wafers in which
a separation layer was formed according to Examples 2 to 4.
EXAMPLE 9
A Plurality of Jets
[0353] A first P-type single crystal Si substrate having a
resistivity of 0.01 .OMEGA..multidot.cm was subjected to
anodization in an HF solution.
[0354] The anodization conditions are listed below.
[0355] Current density: 7 (MA.multidot.cm.sup.-2)
[0356] Anodization solution: HF: H.sub.2O:
C.sub.2H.sub.5OH=1:1:1
[0357] Time: 11 (minute)
[0358] Thickness of the porous Si layer: 12 (.mu.m)
[0359] Porous Si was used to form a high-quality epitaxial Si layer
and as a separation layer.
[0360] The thickness of the porous Si layer is not limited to the
above value but may be between 0.1 to several hundred .mu.m.
[0361] This substrate was oxidized in an oxygen atmosphere at
400.degree. C. for one hour. The oxidization caused the inner wall
of the pores in the porous Si layer to be covered with a thermally
oxidized film. The surface of the porous Si layer was treated with
hydrofluoric acid to remove only the oxidized film on the surface
of the porous Si layer while leaving the oxidized film on the inner
wall of the pores, and the CVD was then used to allow single
crystal Si to epitaxially grow by 0.3 .mu.m on the porous Si layer.
The growth conditions are listed below.
[0362] Source gas: SiH.sub.2Cl.sub.2/H.sub.2
[0363] Gas flow rate: 0.5/180 1/min.
[0364] Gas pressure: 80 Torr
[0365] Temperature: 950.degree. C.
[0366] Growth speed: 0.3 .mu.m/min.
[0367] Furthermore, a 200-nm oxide film (an SiO.sub.2 layer) was
formed on the epitaxial Si layer, using thermal oxidation.
[0368] The surface of a separately prepared second Si substrate was
placed on the surface of the SiO.sub.2 layer to contact them
mutually. These substrates were then subjected to thermal treatment
at 1180.degree. C. for 5 minutes for bonding.
[0369] The bonded substrate formed in this manner was separated
using the apparatus shown in FIG. 9.
[0370] A shown in FIG. 9, the wafer holder 708 was used to hold
both sides of the bonded wafer 701 so as to stand in the vertical
direction. High-pressure pure water at 2,000 kgf/cm.sup.2 was
jetted against the gap in the wafer 701 formed by bevelling,
through the 0.15 mm nozzles 702 to 704 of the three water jet
apparatuses located above or on the side of the wafer, from a
direction parallel with the bonding interface (surface) in the
bonded wafer. A plurality of nozzles were scanned in a direction in
which the high-pressure pure water moved along the gap formed by
bevelling.
[0371] This operation allowed the wafer to be separated into two
via the porous Si layer.
[0372] As a result, the SiO.sub.2 layer, the epitaxial Si layer,
and part of the porous Si layer which were originally formed on the
surface of the first substrate were transferred to the second
substrate. Only the remaining part of the porous Si layer remained
on the surface of the first substrate.
[0373] Subsequently, the porous Si layer transferred to the second
substrate was selectively etched by being stirred using a mixture
of 49% hydrofluoric acid and 30% hydrogen peroxide solution. The
single crystal Si layer remained without being etched, whereas the
porous Si layer was entirely removed by selective etching using the
single crystal Si layer as an etch stop material.
[0374] The single crystal Si layer of 0.2 .mu.m thickness was
formed on the Si oxide film. The single crystal Si layer was not
affected by the selective etching of the porous Si layer. When 100
points of the overall surface of the single crystal Si layer formed
were measured for thickness, the value obtained was 201 nm.+-.4
nm.
[0375] An observation of the cross section by the transmission
electron microscope indicated that new crystal defects did not
occur in the Si layer and that excellent crystallinity was
maintained.
[0376] Thermal treatment was further carried out in hydrogen at
1100.degree. C. for one hour and the surface roughness was
evaluated using the interatomic force microscope. The mean square
roughness of a 50-.mu.m square region was about 0.2 nm and was
similar to that of commercially available Si wafers.
[0377] Similar effects can be obtained by forming the oxide film on
the surface of the second substrate instead of the surface of the
epitaxial layer or forming it on both surfaces.
[0378] In addition, the porous Si layer remaining on the first
substrate was selectively etched by being stirred using a mixture
of 49% hydrofluoric acid and 30% hydrogen peroxide solution.
Subsequently, using hydrogen annealing or surface treatment such as
surface polishing, the first or second substrate could be reused to
repeat the above process.
[0379] Similar results were obtained by separating wafers in which
a separation layer was formed according to Examples 2 to 4.
[0380] The bonded wafer could also be separated efficiently by
using a plurality of nozzles in the water jet injection methods
according to Examples 5 to 8.
EXAMPLE 10
Slit Jet
[0381] A first P-type single crystal Si substrate having a
resistivity of 0.01 .OMEGA..multidot.Q cm was subjected to
anodization in an HF solution.
[0382] The anodization conditions are listed below.
[0383] Current density: 7 (mA.multidot.cm.sup.-2)
[0384] Anodization solution: HF: H.sub.2O:
C.sub.2H.sub.5OH=1:1:1
[0385] Time: 11 (minute)
[0386] Thickness of the porous Si layer: 12 (.mu.m)
[0387] Porous Si was used to form a high-quality epitaxial Si layer
and as a separation layer.
[0388] The thickness of the porous Si layer is not limited to the
above value but may be between 0.1 to several hundred .mu.m.
[0389] This substrate was oxidized in an oxygen atmosphere at
400.degree. C. for one hour. The oxidization caused the inner wall
of the pores in the porous Si layer to be covered with a thermally
oxidized film. The surface of the porous Si layer was treated with
hydrofluoric acid to remove only the oxidized film on the surface
of the porous Si layer while leaving the oxidized film on the inner
wall of the pores, and the CVD was then used to allow single
crystal Si to epitaxially grow by 0.3 .mu.m on the porous Si layer.
The growth conditions are listed below.
[0390] Source gas: SiH.sub.2Cl.sub.2/H.sub.2
[0391] Gas flow rate: 0.5/180 1/min.
[0392] Gas pressure: 80 Torr
[0393] Temperature: 950.degree. C.
[0394] Growth speed: 0.3 .mu.m/min.
[0395] Furthermore, a 200 nm thick oxide film (an SiO.sub.2 layer)
was formed on the epitaxial Si layer as an insulating layer, using
thermal oxidation.
[0396] The surface of a separately prepared second Si substrate was
placed on the surface of the SiO.sub.2 layer to contact them
mutually. These substrates were then subjected to thermal treatment
at 1180.degree. C. for 5 minutes for bonding.
[0397] The bonded substrate formed in this manner was separated
using the apparatus shown in FIGS. 10A and 10B.
[0398] A shown in FIGS. 10A and 10B, the bonded wafer was allowed
to stand in the vertical direction, and high-pressure pure water at
800 kgf/cm.sup.2 was jetted against the gap in the wafer formed by
bevelling, through a slit-like nozzle of 0.15 mm width and 50 mm
length of the water jet apparatus located above or on the side of
the wafer, from a direction parallel with the bonding interface
(surface) in the bonded wafer. The slit was located parallel with
the bonding interface (surface) in the bonded wafer and a linear
flow of water was injected accurately against the gap in the wafer
formed by bevelling. A plurality of nozzles were scanned in a
direction in which the high-pressure pure water moved along the gap
formed by bevelling.
[0399] This operation allowed the wafer to be separated into two
via the porous Si layer.
[0400] As a result, the SiO.sub.2 layer, the epitaxial Si layer,
and part of the porous Si layer which were originally formed on the
surface of the first substrate were transferred to the second
substrate. Only the remaining part of the porous Si layer remained
on the surface of the first substrate.
[0401] Subsequently, the porous Si layer transferred to the second
substrate was selectively etched by being stirred using a mixture
of 49% hydrofluoric acid and 30% hydrogen peroxide solution. The
single crystal Si layer remained without being etched, whereas the
porous Si layer was entirely removed by selective etching using the
single crystal Si layer as an etch stop material.
[0402] The single crystal Si layer of 0.2 .mu.m thickness was
formed on the Si oxide film. The single crystal Si layer was not
affected by the selective etching of the porous Si layer. When 100
points of the overall surface of the single crystal Si layer formed
were measured for thickness, the value obtained was 201 nm.+-.4
nm.
[0403] An observation of the cross section by the transmission
electron microscope indicated that new crystal defects did not
occur in the Si layer and that excellent crystallinity was
maintained.
[0404] Thermal treatment was further carried out in hydrogen at
1100.degree. C. for one hour and the surface roughness was
evaluated using the interatomic force microscope. The mean square
roughness of a 50-.mu.m square region was about 0.2 nm and was
similar to that of commercially available Si wafers.
[0405] Similar effects can be obtained by forming the oxide film on
the surface of the second substrate instead of the surface of the
epitaxial layer or forming it on both surfaces.
[0406] In addition, the porous Si layer remaining on the first
substrate was selectively etched by being stirred using a mixture
of 49% hydrofluoric acid and 30% hydrogen peroxide solution.
Subsequently, using hydrogen annealing or surface treatment such as
surface polishing, the first or second substrate could be reused to
repeat the above process.
[0407] Similar results were obtained by separating wafers in which
a separation layer was formed according to Examples 2 to 4.
EXAMPLE 11
Quartz Substrate
[0408] A light-transmissive substrate of quartz was prepared as a
second substrate.
[0409] N.sub.2 plasma processing was applied to the surface of the
quartz prior to bonding and thermal treatment was carried out at
400.degree. C. for 100 hours. Then, thermal treatment under
hydrogen for flattening the SOI surface after separation was
carried out at less than 1000.degree. C., in this case, 970.degree.
C. for 4 hours.
[0410] The other process is the same as in Examples 1 to 10.
[0411] If a transparent substrate of an insulating material is used
as the second substrate, the oxide film (the insulating layer)
formed on the surface of the epitaxial Si layer in Examples 1 to 10
is not necessarily important. However, to space the epitaxial Si
layer on which elements such as transistors will subsequently be
formed, from the bonding interface to reduce the effects of
impurities in the interface, the oxide film (the insulating layer)
is preferably formed.
EXAMPLE 12
GaAs on Si
[0412] Examples 1 to 10 could be similarly implemented by forming
the epitaxial layer of a compound semiconductor represented by
GaAs.
[0413] In this case, the pressure of the water jet was maintained
at 500 to 3,500 kgf/cm.sup.2 and the nozzle had a diameter of 0.1
mm or more (half that of the total bonded wafer thickness).
[0414] The method for allowing the GaAs epitaxial layer to grow on
the porous Si layer is not limited to the CVD method but may be
implemented by various methods such as the MBE, sputtering, and
liquid phase growth methods. The thickness of this layer is between
several nm and several-hundred .mu.m.
[0415] In each of these examples, the selective etching liquid for
the ion implantation layer or porous layer is not limited to the
mixture of 49% hydrofluoric acid and 30% hydrogen peroxide
solution, but due to its enormous surface area, the porous Si layer
can be etched using the following liquids:
[0416] Hydrofluoric acid;
[0417] Hydrofluoric acid+alcohol;
[0418] Hydrofluoric acid+alcohol+hydrogen peroxide solution;
[0419] Buffered hydrofluoric acid;
[0420] Buffered hydrofluoric acid+alcohol;
[0421] Buffered hydrofluoric acid+hydrogen peroxide solution;
[0422] Buffered hydrofluoric acid+alcohol+hydrogen peroxide
solution; a mixture of hydrofluoric, nitric, and acetic acids.
[0423] The other steps are not limited to the conditions in these
examples but various other conditions can be used.
EXAMPLE 13
Rotation of the Wafer
[0424] A disc-like P-type single crystal Si wafer having a
resistivity of 0.01 .OMEGA..multidot.cm was prepared as a first Si
substrate and had its surface subjected to anodization in an HF
solution.
[0425] The anodization conditions are listed below.
[0426] Current density: 7 (mA.multidot.cm.sup.-2)
[0427] Anodization solution: HF: H.sub.2O:
C.sub.2H.sub.5OH=1:1:1
[0428] Time: 11 (minute)
[0429] Thickness of the porous Si layer: 12 (.mu.m)
[0430] This wafer was oxidized in an oxygen atmosphere at
400.degree. C. for one hour. The oxidization caused the inner wall
of the pores in the porous Si layer to be covered with a thermally
oxidized film. The surface of the porous Si layer was treated with
hydrofluoric acid to remove only the oxidized film on the surface
of the porous Si layer while leaving the oxidized film on the inner
wall of the pores, and the CVD was then used to allow single
crystal Si to epitaxially grow by 0.3 .mu.m on the porous Si layer.
The growth conditions are listed below.
[0431] Source gas: SiH.sub.2C1.sub.2/H.sub.2
[0432] Gas flow rate: 0.5/180 1/min.
[0433] Gas pressure: 80 Torr
[0434] Temperature: 950.degree. C.
[0435] Growth speed: 0.3 .mu.m/min.
[0436] Furthermore, a 200 nm thick oxide film (an SiO.sub.2 layer)
was formed on the epitaxial Si layer as an insulating layer, using
thermal oxidation.
[0437] Besides the first substrate formed in this manner, a
disc-like Si wafer was prepared as a second Si substrate.
[0438] The surface of the second Si substrate was placed on the
surface of the SiO.sub.2 layer of the first Si substrate to contact
them mutually. These substrates were then subjected to thermal
treatment at 1180.degree. C. for 5 minutes for bonding.
[0439] Next, preparations were made to separate the composite
member consisting of the bonded wafer using the apparatuses shown
in FIGS. 14, 15, and 17 to 20.
[0440] The wafer, which is the composite member, was located so as
to stand in the vertical direction while fitting on the notch in
the positioning base 35.
[0441] Pressurized air was supplied from the tubes 52 and 54 to the
pressurizing passage 56, and the holding sections 45a and 46a were
moved forward to the front and rear surfaces of the wafer,
respectively, in order to abut the front and rear surfaces of the
wafer with the holding surface of the holding sections 45a and 46a
each having an opening op, respectively, as shown in FIG. 18.
[0442] Using the tubes 51 and 53, the wafer was sucked and fixed to
the holding sections 45a and 46a. The supply of pressurized air was
stopped and tension was supplied to the wafer in the opposite
normal directions of the front and rear surfaces of the wafer using
the springs 47 and 48.
[0443] With the shutter 61 closed, pure water without abrasive
grains was fed forcefully from the pump 62 to the nozzle of 0.15 mm
diameter and the pump 62 was operated to inject water at a pressure
of about 200 kgf/cm.sup.2.
[0444] The positioning base 35 was moved to its standby position,
and the power to the motor 32 was turned on to transmit rotational
drive force via the shaft 31 and belts 27 and 28 in order to rotate
the holders 21 and 22.
[0445] Since the wafer was sucked by the holding sections 45a and
46a, it started to rotate simultaneously with the holders 21 and 22
at the same angular speed in the same direction.
[0446] The shutter 61 was opened to inject the water jet against
the separation portion in the side of the wafer, as shown in FIG.
19.
[0447] Water from the water jet apparatus entered the pores in the
separation portion to separate the wafer around the porous layer
that is the separation portion.
[0448] As the injection of the water jet and the rotation of the
wafer continue, the gap formed by separation gradually grew from
the periphery of the wafer toward its rotational center and the
wafer could be finally separated as shown in FIG. 20.
[0449] Since the wafer was subjected to forces in the directions
shown arrows TA and TB in FIG. 20, the wafer was separated as shown
in FIG. 20, simultaneously with the final separation of the
rotational center of the wafer.
[0450] Subsequently, the forced feeding of water was stopped and
the separated wafer was removed from the holding sections 45a and
46a.
[0451] Subsequently, the remaining porous Si layer transferred to
the second substrate was selectively etched by being stirred using
a mixture of 49% hydrofluoric acid and 30% hydrogen peroxide
solution. The transferred single crystal Si layer under the porous
layer remained without being etched, whereas the porous Si layer
was entirely removed by selective etching using the single crystal
Si layer as an etch stop material, thereby exposing the thin single
crystal Si layer.
[0452] Thus, a first SOI substrate having the single crystal Si
layer of 0.2 .mu.m thickness on the Si oxide film of the second
substrate was obtained. The single crystal Si layer was not
affected by the selective etching of the porous Si layer. When 100
points of the overall surface of the single crystal Si layer formed
were measured for thickness, the value obtained was 201 nm.+-.2
nm.
[0453] An observation of the cross section by the transmission
electron microscope indicated that new crystal defects did not
occur in the Si layer and that excellent crystallinity was
maintained.
[0454] Thermal treatment was further carried out in hydrogen at
1100.degree. C. for 50 minutes and the surface roughness was
evaluated using the interatomic force microscope. The mean square
roughness of a 50-.mu.m square region was about 0.2 nm.
[0455] In addition, the porous Si layer remaining on the first
substrate was selectively etched by being stirred using a mixture
of 49% hydrofluoric acid and 30% hydrogen peroxide solution.
Subsequently, surface treatment such as polishing was carried
out.
[0456] The first substrate, which had been polished, was again
subjected to anodization to form a porous Si layer and nonporous
single crystal Si was allowed to grow thereon. The surface of the
nonporous single crystal Si layer, which had grown epitaxially, was
oxidized. Then, the surface of a separately prepared Si wafer that
was a third substrate was bonded on the oxidized surface of the
single crystal Si layer of the first substrate.
[0457] The conditions for the above process were the same as those
for the first bonded-wafer production.
[0458] The wafer was again separated in the same manner as in the
first separation method described above to obtain a second SOI
substrate having the single crystal Si layer on the insulating
surface of the third substrate.
[0459] The above process was repeated to recycle the first
substrate in order to fabricate a third and a fourth SOI
substrates.
[0460] As described above, this invention enables a composite
member having a separation region inside to be separated into a
plurality of smaller members around the separation region without
damaging or destructing those portions other than the separation
region. Therefore, this invention enables semiconductor substrates
with higher quality than the conventional ones to be fabricated
easily and reliably with a high yield.
* * * * *