U.S. patent application number 09/878152 was filed with the patent office on 2002-05-16 for controlled cleavage using patterning.
Invention is credited to Cheung, Nathan W., Henley, Francois J..
Application Number | 20020056519 09/878152 |
Document ID | / |
Family ID | 37944191 |
Filed Date | 2002-05-16 |
United States Patent
Application |
20020056519 |
Kind Code |
A1 |
Henley, Francois J. ; et
al. |
May 16, 2002 |
Controlled cleavage using patterning
Abstract
A technique for forming a film of material (12) from a donor
substrate (10). The technique has a step of introducing energetic
particles (22) in a selected manner through a surface of a donor
substrate (10) to form a pattern at a selected depth (20)
underneath the surface. The particles have a concentration
sufficiently high to define a donor substrate material (12) above
the selected depth. An energy source is directed to a selected
region of the donor substrate to initiate a controlled cleaving
action of the substrate (10) at the selected depth (20), whereupon
the cleaving action provides an expanding cleave front to free the
donor material from a remaining portion of the donor substrate.
Inventors: |
Henley, Francois J.; (Los
Gatos, CA) ; Cheung, Nathan W.; (Albany, CA) |
Correspondence
Address: |
TOWNSEND AND TOWNSEND AND CREW, LLP
TWO EMBARCADERO CENTER
EIGHTH FLOOR
SAN FRANCISCO
CA
94111-3834
US
|
Family ID: |
37944191 |
Appl. No.: |
09/878152 |
Filed: |
June 7, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09878152 |
Jun 7, 2001 |
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09026793 |
Feb 20, 1998 |
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60046276 |
May 12, 1997 |
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Current U.S.
Class: |
156/712 ;
156/750; 156/937; 216/58; 257/E21.568; 428/206; 438/455 |
Current CPC
Class: |
Y10T 156/1158 20150115;
Y10S 117/915 20130101; Y10T 428/249956 20150401; H01L 21/187
20130101; H01L 21/304 20130101; B81C 1/0038 20130101; H01L 21/2236
20130101; H01L 21/76254 20130101; H01L 21/7813 20130101; H01L
21/2658 20130101; Y10S 438/977 20130101; Y10T 428/24893 20150115;
B81C 2201/0191 20130101; H01L 21/26506 20130101; Y10T 156/11
20150115; Y10T 156/19 20150115; Y10S 438/974 20130101; B81C
2201/0192 20130101; Y10S 156/93 20130101; Y10T 428/21 20150115;
H01L 21/2007 20130101; H01L 21/7624 20130101 |
Class at
Publication: |
156/344 ;
428/206; 216/58; 438/455 |
International
Class: |
B32B 005/16 |
Claims
What is claimed is:
1. A process for forming a film of material from a substrate, said
process comprising steps of: introducing particles in a selected
manner through a surface of a substrate to a selected depth
underneath said surface, said particles being at a concentration at
said selected depth to define a substrate material to be removed
above said selected depth, said selected manner providing a
patterned distribution of particles at said selected depth to
enhance said controlled cleaving action; and providing energy to a
selected region of said substrate to initiate a controlled cleaving
action at said selected depth in said substrate, whereupon said
cleaving action is made using a propagating cleave front to free a
portion of said material to be removed from said substrate.
2. The process of claim 1 wherein said particles are derived from a
source selected from the group consisting of hydrogen gas, helium
gas, water vapor, methane, hydrogen compounds, and other light
atomic mass particles.
3. The process of claim 1 wherein said particles are selected from
the group consisting of neutral molecules, charged molecules,
atoms, and electrons.
4. The process of claim 1 wherein said particles are energetic.
5. The process of claim 4 wherein said energetic particles have
sufficient kinetic energy to penetrate through said surface to said
selected depth underneath said surface.
6. The process of claim 1 wherein said step of providing energy
sustains said controlled cleaving action to remove said material
from said substrate to provide a film of material.
7. The process of claim 1 wherein said step of providing energy
increases a controlled stress in said material and sustains said
controlled cleaving action to remove said material from said
substrate to provide a film of material.
8. The process of claim 1 further comprising a step of providing
additional energy to said substrate to sustain said controlled
cleaving action to remove said material from said substrate to
provide a film of material.
9. The process of claim 1 further comprising a step of providing
additional energy to said substrate to increases a controlled
stress in said material and sustains said controlled cleaving
action to remove said material from said substrate to provide a
film of material.
10. The process of claim 1 wherein said introducing step forms
damage selected from the group consisting of atomic bond damage,
bond substitution, weakening, and breaking bonds of said substrate
at said selected depth.
11. The process of claim 10 wherein said damage causes stress to
said substrate material.
12. The process of claim 10 wherein said damage reduces an ability
of said substrate material to withstand stress without a
possibility of a cleaving of said substrate material.
13. The process of claim 1 wherein said propagating cleave front is
selected from a single cleave front or multiple cleave fronts.
14. The process of claim 1 wherein said introducing step causes
stress of said material region at said selected depth by a presence
of said particles at said selected depth.
15. The process of claim 1 further comprising a step of increasing
an energy level of said substrate while substantially preventing a
possibility of cleaving said substrate.
16. The process of claim 15 wherein said step of introducing said
energy level is at a global substrate temperature that is below a
temperature of said introducing step.
17. The process of claim 1 further comprising a step of increasing
a stress of said substrate while substantially preventing a
possibility of cleaving said substrate at said selected depth.
18. The process of claim 17 wherein said step of introducing said
stress is maintained at a global substrate temperature that is
below a temperature of said introducing step.
19. The process of claim 15 wherein said step of increasing said
energy is performed while substantially preventing a possibility of
inducing a cleaving action between said film of material and said
substrate.
20. The process of claim 15 wherein said step of increasing said
energy increases stress between said portion of said film material
and said substrate at said selected depth while substantially
preventing a possibility of inducing a cleaving action between said
film of material and said substrate.
21. The process of claim 15 wherein said energy is provided by an
energy source selected from the group consisting of a thermal
source, a thermal sink, a mechanical source, a chemical source, and
an electrical source.
22. The process of claim 21 wherein said chemical source provides
particles, fluids, gases, or liquids.
23. The process of claim 21 wherein said chemical source includes a
chemical reaction.
24. The process of claim 21 wherein said chemical source is
selected from the group consisting of a flood source, a
time-varying source, a spatially varying source and a continuous
source.
25. The process of claim 21 wherein said mechanical source is
selected from the group consisting of a rotational source, a
translational source, a compressional source, an expansional
source, and an ultrasonic source.
26. The process of claim 21 wherein said mechanical source is
selected from the group consisting of a flood source, a
time-varying source, a spatially varying source and continuous
source.
27. The process of claim 21 wherein the electrical source is
selected from the group consisting of an applied voltage source and
an applied electromagnetic field source.
28. The process of claim 21 wherein said electrical source is
selected from the group consisting of a flood source, a
time-varying source, a spatially varying source, and a continuous
source.
29. The process of claim 21 wherein said thermal source or thermal
sink transfers heat to or from the substrate by radiation,
convection, or conduction.
30. The process of claim 24 wherein said thermal source is selected
from the group consisting of a photon beam, a fluid jet, a liquid
jet, a gas jet, an electro/magnetic field, an electron beam, a
thermoelectric heating, an oven, and a furnace.
31. The process of claim 29 wherein said thermal sink is selected
from the group consisting of a fluid jet, a liquid jet, a gas jet,
a cryogenic fluid, a super-cooled liquid, a thermoelectric cooling
means, and an electro/magnetic field.
32. The process of claim 21 wherein said thermal source or sink is
selected from the group consisting of a flood source, a
time-varying source, a spatially varying source, and a continuous
source.
33. The process of claim 1 wherein said energy is provided by a
source selected from the group consisting of a thermal source, a
thermal sink, a mechanical source, a chemical source, and an
electrical source.
34. The process of claim 33 wherein said chemical source provides
particles.
35. The process of claim 33 wherein said chemical source includes a
chemical reaction.
36. The process of claim 33 wherein said chemical source is
selected from the group consisting of a flood source, a
time-varying source, a spatially varying source, and a continuous
source.
37. The process of claim 33 wherein said mechanical source is
selected from the group consisting of a rotational source, a
translational source, a compressional source, an expansional
source, and an ultrasonic source.
38. The process of claim 33 wherein said mechanical source is
selected from the group consisting of a flood source, a
time-varying source, a spatially varying source, and a continuous
source.
39. The process of claim 33 wherein electrical source is selected
from the group consisting of an applied voltage and an applied
electromagnetic means.
40. The process of claim 33 wherein said electrical source is
selected from the group consisting of a flood source, a
time-varying source, a spatially varying source, and a continuous
source.
41. The process of claim 33 wherein said thermal source transfers
heat to the substrate by radiation, convection, or conduction.
42. The process of claim 41 wherein said thermal source is selected
from the group consisting of a photon beam, a liquid jet, a gas
jet, an electron beam, a thermo-electric heating, an oven, and a
furnace.
43. The process of claim 41 wherein said thermal sink is selected
from the group consisting of a liquid jet, a gas jet, a cryogenic
fluid, a super-cooled liquid, a thermoelectric cooling means, and a
super-cooled gas.
44. The process of claim 33 wherein said thermal source is selected
from the group consisting of a flood source, a time-varying source,
a spatially varying source, and a continuous source.
45. The process of claim 1 wherein said substrate is maintained at
a temperature ranging between -200.degree. C. and 450.degree. C.
during said introducing step.
46. The process of claim 1 wherein said step of providing said
energy is maintained at a temperature below 400.degree. C.
47. The process of claim 1 wherein said step of providing said
energy is maintained at a temperature below 350.degree. C.
48. The process of claim 1 wherein said step of introducing is a
step(s) of beam line ion implantation.
49. The process of claim 1 wherein said step of introducing is a
step(s) of plasma immersion ion implantation.
50. The process of claim 1 further comprising a step of joining
said surface of said substrate to a surface of a target substrate
to form a stacked assembly.
51. The process of claim 50 wherein said joining step is provided
by applying an electrostatic pressure between said substrate and
said target substrate.
52. The process of claim 50 wherein said joining step is provided
by using an adhesive substance between said target substrate and
said substrate.
53. The process of claim 50 wherein said joining step is provided
by an activated surface between said target substrate and said
substrate.
54. The process of claim 50 wherein said joining step is provided
by an interatomic bond between said target substrate and said
substrate.
55. The process of claim 50 wherein said joining step is provided
by a spin-on-glass between said target substrate and said
substrate.
56. The process of claim 50 wherein said joining step is provided
by a polyimide between said target substrate and said
substrate.
57. The process of claim 1 wherein said substrate is made of a
material selected from the group consisting of silicon, diamond,
quartz, glass, sapphire, silicon carbide, dielectric, group III/V
material, plastic, ceramic material, and multi-layered
substrate.
58. The process of claim 1 wherein said surface is planar.
59. The process of claim 1 wherein said surface is curved.
60. The process of claim 1 wherein said substrate is a silicon
substrate comprising an overlying layer of dielectric material,
said selected depth being underneath said dielectric material.
61. The process of claim 60 wherein said dielectric material is
selected from the group consisting of an oxide material, a nitride
material, and an oxide/nitride material.
62. The process of claim 1 wherein said substrate includes an
overlying layer of conductive material.
63. The process of claim 62 wherein said conductive material is
selected from the group consisting of a metal, a plurality of metal
layers, aluminum, tungsten, titanium, titanium nitride, polycide,
polysilicon, copper, indium tin oxide, silicide, platinum, gold,
silver, and amorphous silicon.
64. The process of claim 1 wherein said step of introducing
provides a substantially uniform distribution of particles along a
plane of said material region at said selected depth.
65. The process of claim 64 wherein said substantially uniform
distribution is a uniformity of less than about 5%.
66. The process of claim 1 wherein said patterned distribution of
particles is in a pattern selected from the group consisting of a
checkerboard pattern, an annular ring pattern, a concentric circle
pattern, an annular pattern, a webbed pattern (e.g., dart board,
spider web), and spiral pattern defined on said top surface of said
substrate.
67. A substrate device comprising: a substrate with a patterned
layer of particles disposed within said substrate at a selected
depth between about 1-15 microns, said particles capable of
creating stress in said substrate to separate a portion of material
from said substrate.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority from the provisional patent
application entitled A CONTROLLED CLEAVAGE PROCESS AND RESULTING
DEVICE, filed May 12, 1997 and assigned Application No. 60/046,276,
the disclosure of which is hereby incorporated in its entirety for
all purposes.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to the manufacture of
substrates. More particularly, the invention provides a technique
including a method and device for cleaving a substrate in the
fabrication of a silicon-on-insulator substrate for semiconductor
integrated circuits using a patterning technique, for example. But
it will be recognized that the invention has a wider range of
applicability; it can also be applied to other substrates for
multi-layered integrated circuit devices, three-dimensional
packaging of integrated semiconductor devices, photonic devices,
piezoelectronic devices, microelectromechanical systems ("MEMS"),
sensors, actuators, solar cells, flat panel displays (e.g., LCD,
AMLCD), biological and biomedical devices, and the like.
[0003] Craftsmen or more properly crafts-people have been building
useful articles, tools, or devices using less useful materials for
numerous years. In some cases, articles are assembled by way of
smaller elements or building blocks. Alternatively, less useful
articles are separated into smaller pieces to improve their
utility. A common example of these articles to be separated include
substrate structures such as a glass plate, a diamond, a
semiconductor substrate, and others.
[0004] These substrate structures are often cleaved or separated
using a variety of techniques. In some cases, the substrates can be
cleaved using a saw operation. The saw operation generally relies
upon a rotating blade or tool, which cuts through the substrate
material to separate the substrate material into two pieces. This
technique, however, is often extremely "rough" and cannot generally
be used for providing precision separations in the substrate for
the manufacture of fine tools and assemblies. Additionally, the saw
operation often has difficulty separating or cutting extremely hard
and/or brittle materials such as diamond or glass.
[0005] Accordingly, techniques have been developed to separate
these hard and/or brittle materials using cleaving approaches. In
diamond cutting, for example, an intense directional
thermal/mechanical impulse is directed preferentially along a
crystallographic plane of a diamond material. This
thermal/mechanical impulse generally causes a cleave front to
propagate along major crystallographic planes, where cleaving
occurs when an energy level from the thermal/mechanical impulse
exceeds the fracture energy level along the chosen crystallographic
plane.
[0006] In glass cutting, a scribe line using a tool is often
impressed in a preferred direction on the glass material, which is
generally amorphous in character. The scribe line causes a higher
stress area surrounding the amorphous glass material. Mechanical
force is placed on each side of the scribe line, which increases
stress along the scribe line until the glass material fractures,
preferably along the scribe line. This fracture completes the
cleaving process of the glass, which can be used in a variety of
applications including households.
[0007] Although the techniques described above are satisfactory,
for the most part, as applied to cutting diamonds or household
glass, they have severe limitations in the fabrication of small
complex structures or precision workpieces. For instance, the above
techniques are often "rough" and cannot be used with great
precision in fabrication of small and delicate machine tools,
electronic devices, or the like. Additionally, the above techniques
may be useful for separating one large plane of glass from another,
but are often ineffective for splitting off, shaving, or stripping
a thin film of material from a larger substrate. Furthermore, the
above techniques may often cause more than one cleave front, which
join along slightly different planes, which is highly undesirable
for precision cutting applications.
[0008] From the above, it is seen that a technique for separating a
thin film of material from a substrate which is cost effective and
efficient is often desirable.
SUMMARY OF THE INVENTION
[0009] According to the present invention, an improved technique
for removing a thin film of material from a substrate using a
controlled cleaving action and a patterning technique is provided.
This technique allows an initiation of a cleaving process on a
substrate using a single or multiple cleave region(s) through the
use of controlled energy (e.g., spatial distribution) and selected
conditions to allow an initiation of a cleave front(s) and to allow
it to propagate through the substrate to remove a thin film of
material from the substrate.
[0010] In a specific embodiment, the present invention provides a
process for forming a film of material from a donor substrate using
a controlled cleaving process. The process includes a step of
introducing a pattern of energetic particles (e.g., charged or
neutral molecules, atoms, or electrons having sufficient kinetic
energy) through a surface of a donor substrate to a selected depth
underneath the surface, where the particles are at a relatively
high concentration to define a thickness of donor substrate
material (e.g., thin film of detachable material) above the
selected depth. To cleave the donor substrate material, the method
provides energy to a selected region of the donor substrate to
initiate a controlled cleaving action in the donor substrate,
whereupon the cleaving action is made using a propagating cleave
front(s) to free the donor material from a remaining portion of the
donor substrate.
[0011] The particles may be introduced in a single step, such as by
moving a beam of ions across the surface of the wafer in a
controlled fashion to form a pattern, or by directing a flux of
ions at the wafer through a stencil or patterned layer of masking
material (e.g. photoresist). The ion flux may be provided by a
conventional ion beam implanter, a plasma immersion ion implanter,
or ion shower device, among other sources. Alternatively, the
pattern of particles may be created by a combination of implanting
steps, such as a uniform implant followed by a patterned implant,
the final pattern being a combination of the two implanting steps.
The patterned layer of particles facilitates cleaving thin films
from a donor substrate while minimizing damage to the crystalline
structure of the thin film and while minimizing implantation time,
in some embodiments.
[0012] The present invention achieves these benefits and others in
the context of known process technology. However, a further
understanding of the nature and advantages of the present invention
may be realized by reference to the latter portions of the
specification and attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIGS. 1-11 are simplified diagrams illustrating a controlled
cleaving technique according to an embodiment of the present
invention;
[0014] FIGS. 12-20 are simplified diagrams of implanting particles
in patterns according to alternative aspects of the present
invention; and
[0015] FIGS. 21-27 are simplified cross-sectional view diagrams
illustrating a method of forming a silicon-on-insulator substrate
according to the present invention.
DESCRIPTION OF THE SPECIFIC EMBODIMENT
[0016] The present invention provides a technique for removing a
thin film of material from a substrate while preventing a
possibility of damage to the thin material film and/or a remaining
portion of the substrate. The thin film of material is attached to
or can be attached to a target substrate to form, for example, a
silicon-on-insulator wafer. The thin film of material can also be
used for a variety of other applications. The invention will be
better understood by reference to the FIGS. and the descriptions
below.
[0017] 1. Controlled Cleaving Techniques
[0018] FIG. 1 is a simplified cross-sectional view diagram of a
substrate 10 according to the present invention. The diagram is
merely an illustration and should not limit the scope of the claims
herein. As merely an example, substrate 10 is a silicon wafer which
includes a material region 12 to be removed, which is a thin
relatively uniform film derived from the substrate material. The
silicon wafer 10 includes a top surface 14, a bottom surface 16,
and a thickness 18. Substrate 10 also has a first side (side 1) and
a second side (side 2) (which are also referenced below in the
FIGS. ). Material region 12 also includes a thickness 20, within
the thickness 18 of the silicon wafer. The present invention
provides a novel technique for removing the material region 12
using the following sequence of steps.
[0019] In most embodiments, a cleave is initiated by subjecting the
material with sufficient energy to fracture the material in one
region, causing a cleave front, without uncontrolled shattering or
cracking. The cleave front formation energy (E.sub.t) must often be
made lower than the bulk material fracture energy (E.sub.mat) at
each region to avoid shattering or cracking the material. The
directional energy impulse vector in diamond cutting or the scribe
line in glass cutting are, for example, the means in which the
cleave energy is reduced to allow the controlled creation and
propagation of a cleave front. The cleave front is in itself a
higher stress region and once created, its propagation requires a
lower energy to further cleave the material from this initial
region of fracture. The energy required to propagate the cleave
front is called the cleave front propagation energy (E.sub.p). The
relationship can be expressed as:
E.sub.c=E.sub.p+[cleave front stress energy]
[0020] A controlled cleaving process is realized by reducing
E.sub.p along a favored direction(s) above all others and limiting
the available energy to be below the E.sub.p of other undesired
directions. In any cleave process, a better cleave surface finish
occurs when the cleave process occurs through only one expanding
cleave front, although multiple cleave fronts do work.
[0021] Selected energetic particles implant 22 through the top
surface 14 of the silicon wafer to a selected depth 24, which
defines the thickness 20 of the material region 12, termed the thin
film of material. A variety of techniques can be used to implant
the energetic particles into the silicon wafer. These techniques
include ion implantation using, for example, beam line ion
implantation equipment manufactured from companies such as Applied
Materials, Eaton Corporation, Varian, and others. Alternatively,
implantation occurs using a plasma immersion ion implantation
("PIII") technique. Examples of plasma immersion implantation
techniques are described in "Recent Applications of Plasma
Immersion Ion Implantation," Paul K. Chu, Chung Chan, and Nathan W.
Cheung, SEMICONDUCTOR INTERNATIONAL, pp. 165-172, June 1996, and
"Plasma Immersion Ion Implantation--A Fledgling Technique for
Semiconductor Processing,", P. K. Chu, S. Qin, C. Chan, N. W.
Cheung, and L. A. Larson, MATERIALS SCIENCE AND ENGINEERING
REPORTS: A REVIEW JOURNAL, pp. 207-280, Vol. R17, Nos. 6-7, (Nov.
30, 1996), which are both hereby incorporated by reference for all
purposes. Of course, techniques used depend upon the
application.
[0022] Depending upon the application, smaller mass particles are
generally selected to reduce a possibility of damage to the
material region 12. That is, smaller mass particles easily travel
through the substrate material to the selected depth without
substantially damaging the material region that the particles
traverse through. For example, the smaller mass particles (or
energetic particles) can be almost any charged (e.g., positive or
negative) and/or neutral atoms or molecules, or electrons, or the
like. In a specific embodiment, the particles can be neutral and/or
charged particles including ions such as ions of hydrogen and its
isotopes, rare gas ions such as helium and its isotopes, and neon.
The particles can also be derived from compounds such as gases,
e.g., hydrogen gas, water vapor, methane, and hydrogen compounds,
and other light atomic mass particles. Alternatively, the particles
can be any combination of the above particles, and/or ions and/or
molecular species and/or atomic species. The particles generally
have sufficient kinetic energy to penetrate through the surface to
the selected depth underneath the surface.
[0023] Using hydrogen as the implanted species into the silicon
wafer as an example, the implantation process is performed using a
specific set of conditions. Implantation dose ranges from about
10.sup.15 to about 10.sup.13 atoms/cm.sup.2, and preferably the
dose is greater than about 10.sup.16 atoms/cm.sup.2. Implantation
energy ranges from about 1 KeV to about 1 MeV, and is generally
about 50 KeV. Implantation temperature ranges from about -200 to
about 600.degree. C., and is preferably less than about 400.degree.
C. to prevent a possibility of a substantial quantity of hydrogen
ions from diffusing out of the implanted silicon wafer and
annealing the implanted damage and stress. The hydrogen ions can be
selectively introduced into the silicon wafer to the selected depth
at an accuracy of about +/-0.03 to +/-0.05 microns. Of course, the
type of ion used and process conditions depend upon the
application.
[0024] Effectively, the implanted particles add stress or reduce
fracture energy along a plane parallel to the top surface of the
substrate at the selected depth. The energies depend, in part, upon
the implantation species and conditions. These particles reduce a
fracture energy level of the substrate at the selected depth. This
allows for a controlled cleave along the implanted plane at the
selected depth. Implantation can occur under conditions such that
the energy state of substrate at all internal locations is
insufficient to initiate a non-reversible fracture (i.e.,
separation or cleaving) in the substrate material. It should be
noted, however, that implantation does generally cause a certain
amount of defects (e.g., micro-detects) in the substrate that can
be repaired by subsequent heat treatment, e.g., thermal annealing
or rapid thermal annealing.
[0025] FIG. 2 is a simplified energy diagram 200 along a
cross-section of the implanted substrate 10 according to the
present invention. The diagram is merely an illustration and should
not limit the scope of the claims herein. The simplified diagram
includes a vertical axis 201 that represents an energy level (E)
(or additional energy) to cause a cleave in the substrate. A
horizontal axis 203 represents a depth or distance from the bottom
of the wafer to the top of the wafer. After implanting particles
into the wafer, the substrate has an average cleave energy
represented as E 205, which is the amount of energy needed to
cleave the wafer along various cross-sectional regions along the
wafer depth. The cleave energy (E.sub.t) is equal to the bulk
material fracture energy (E.sub.mat) in non-implanted regions. At
the selected depth 20, energy (E.sub.cz) 207 is lower since the
implanted particles essentially break or weaken bonds in the
crystalline structure (or increase stress caused by a presence of
particles also contributing to lower energy (E.sub.cz) 207 of the
substrate) to lower the amount of energy needed to cleave the
substrate at the selected depth. The present invention takes
advantage of the lower energy (or increased stress) at the selected
depth to cleave the thin film in a controlled manner.
[0026] Substrates, however, are not generally free from defects or
"weak" regions across the possible cleave front or selected depth
z.sub.0 after the implantation process. In these cases, the cleave
generally cannot be controlled, since they are subject to random
variations such as bulk material non-uniformities, built-in
stresses, defects, and the like. FIG. 3 is a simplified energy
diagram 300 across a cleave front for the implanted substrate 10
having these defects. The diagram 300 is merely an illustration and
should not limit the scope of the claims herein. The diagram has a
vertical axis 301 which represents additional energy (E) and a
horizontal axis 303 which represents a distance from side 1 to side
2 of the substrate, that is, the horizontal axis represents regions
along the cleave front of the substrate. As shown, the cleave front
has two regions 305 and 307 represented as region 1 and region 2,
respectively, which have cleave energies less than the average
cleave energy (E.sub.cz) 207 (possibly due to a higher
concentration of defects or the like). Accordingly, it is highly
likely that the cleave process begins at one or both of the above
regions, since each region has a lower cleave energy than
surrounding regions.
[0027] An example of a cleave process for the substrate illustrated
by the above FIG. is described as follows with reference to FIG. 4.
FIG. 4 is a simplified top-view diagram 400 of multiple cleave
fronts 401, 403 propagating through the implanted substrate. The
cleave fronts originate at "weaker" regions in the cleave plane,
which specifically includes regions 1 and 2. The cleave fronts
originate and propagate randomly as shown by the arrows. A
limitation with the use of random propagation among multiple cleave
fronts is the possibility of having different cleave fronts join
along slightly different planes or the possibility of forming
cracks, which is described in more detail below.
[0028] FIG. 5 is a simplified cross-sectional view 500 of a film
cleaved from a wafer having multiple cleave fronts at, for example,
regions 1 305 and 2 307. This diagram is merely an illustration and
should not limit the scope of the claims herein. As shown, the
cleave from region 1 joined with the cleave from region 2 at region
3 309, which is defined along slightly different planes, may
initiate a secondary cleave or crack 311 along the film. Depending
upon the magnitude of the difference 313, the film may not be of
sufficient quality for use in manufacture of substrates for
integrated circuits or other applications. A substrate having crack
311 generally cannot be used for processing. Accordingly, it is
generally undesirable to cleave a wafer using multiple fronts in a
random manner. An example of a technique which may form multiple
cleave fronts in a random manner is described in U.S. Pat. No.
5,374,564, which is in the name of Michel Bruel ("Bruel"), and
assigned to Commissariat A l'Energie Atomique in France. Bruel
generally describes a technique for cleaving an implanted wafer by
global thermal treatment (i.e., thermally treating the entire plane
of the implant) using thermally activated diffusion. Global thermal
treatment of the substrate generally causes an initiation of
multiple cleave fronts which propagate independently. In general,
Bruel discloses a technique for an "uncontrollable" cleaving action
by way of initiating and maintaining a cleaving action by a global
thermal source, which may produce undesirable results. These
undesirable results include potential problems such as an imperfect
joining of cleave fronts, an excessively rough surface finish on
the surface of the cleaved material since the energy level for
maintaining the cleave exceeds the amount required, and many
others. The present invention overcomes the formation of random
cleave fronts by a controlled distribution or selective positioning
of energy on the implanted substrate.
[0029] FIG. 6 is a simplified cross-sectional view of an implanted
substrate 10 using selective positioning of cleave energy according
to the present invention. This diagram is merely an illustration,
and should not limit the scope of the claims herein. The implanted
wafer undergoes a step of selective energy placement or positioning
or targeting which provides a controlled cleaving action of the
material region 12 at the selected depth. The impulse or impulses
are provided using energy sources. Examples of sources include,
among others, a chemical source, a mechanical source, an electrical
source, and a thermal sink or source. The chemical source can
include a variety such as particles, fluids, gases, or liquids.
These sources can also include chemical reaction to increase stress
in the material region. The chemical source is introduced as flood,
time-varying, spatially varying, or continuous. In other
embodiments, a mechanical source is derived from rotational,
translational, compressional, expansional, or ultrasonic energies.
The mechanical source can be introduced as flood, time-varying,
spatially varying, or continuous. In further embodiments, the
electrical source is selected from an applied voltage or an applied
electro-magnetic field, which is introduced as flood, time-varying,
spatially varying, or continuous. In still further embodiments, the
thermal source or sink is selected from radiation, convection, or
conduction. This thermal source can be selected from, among others,
a photon beam, a fluid jet, a liquid jet, a gas jet, an
electro/magnetic field, an electron beam, a thermo-electric
heating, a furnace, and the like. The thermal sink can be selected
from a fluid jet, a liquid jet, a gas jet, a cryogenic fluid, a
super-cooled liquid, a thermo-electric cooling means, an
electro/magnetic field, and others. Similar to the previous
embodiments, the thermal source is applied as flood, time-varying,
spatially varying, or continuous. Still further, any of the above
embodiments can be combined or even separated, depending upon the
application. Of course, the type of source used depends upon the
application.
[0030] In a specific embodiment, the present invention provides a
controlled-propagating cleave. The controlled-propagating cleave
uses multiple successive impulses to initiate and perhaps propagate
a cleaving process 700, as illustrated by FIG. 7. This diagram is
merely an illustration, and should not limit the scope of the
claims herein. As shown, the impulse is directed at an edge of the
substrate, which propagates a cleave front toward the center of the
substrate to remove the material layer from the substrate. In this
embodiment, a source applies multiple pulses (i.e., pulse 1, 2, and
3) successively to the substrate. Pulse 1 701 is directed to an
edge 703 of the substrate to initiate the cleave action. Pulse 2
705 is also directed at the edge 707 on one side of pulse 1 to
expand the cleave front. Pulse 3 709 is directed to an opposite
edge 711 of pulse 1 along the expanding cleave front to further
remove the material layer from the substrate. The combination of
these impulses or pulses provides a controlled cleaving action 713
of the material layer from the substrate.
[0031] FIG. 8 is a simplified illustration of selected energies 800
from the pulses in the preceding embodiment for the
controlled-propagating cleave. This diagram is merely an
illustration, and should not limit the scope of the claims herein.
As shown, the pulse 1 has an energy level which exceeds average
cleaving energy (E), which is the necessary energy for initiating
the cleaving action. Pulses 2 and 3 are made using lower energy
levels along the cleave front to maintain or sustain the cleaving
action. In a specific embodiment, the pulse is a laser pulse where
an impinging beam heats a selected region of the substrate through
a pulse and a thermal pulse gradient causes supplemental stresses
which together exceed cleave formation or propagation energies,
which create a single cleave front. In preferred embodiments, the
impinging beam heats and causes a thermal pulse gradient
simultaneously, which exceed cleave energy formation or propagation
energies. More preferably, the impinging beam cools and causes a
thermal pulse gradient simultaneously, which exceed cleave energy
formation or propagation energies.
[0032] Optionally, a built-in energy state of the substrate or
stress can be globally raised toward the energy level necessary to
initiate the cleaving action, but not enough to initiate the
cleaving action before directing the multiple successive impulses
to the substrate according to the present invention. The global
energy state of the substrate can be raised or lowered using a
variety of sources such as chemical, mechanical, thermal (sink or
source), or electrical, alone or in combination. The chemical
source can include a variety such as particles, fluids, gases, or
liquids. These sources can also include chemical reaction to
increase stress in the material region. The chemical source is
introduced as flood, time-varying, spatially varying, or
continuous. In other embodiments, a mechanical source is derived
from rotational, translational, compressional, expansional, or
ultrasonic energies. The mechanical source can be introduced as
flood, time-varying, spatially varying, or continuous. In further
embodiments, the electrical source is selected from an applied
voltage or an applied electromagnetic field, which is introduced as
flood, time-varying, spatially varying, or continuous. In still
further embodiments, the thermal source or sink is selected from
radiation, convection, or conduction. This thermal source can be
selected from, among others, a photon beam, a fluid jet, a liquid
jet, a gas jet, an electro/magnetic field, an electron beam, a
thermoelectric heating, and a furnace. The thermal sink can be
selected from a fluid jet, a liquid jet, a gas jet, a cryogenic
fluid, a super-cooled liquid, a thermoelectric cooling means, an
electromagnetic field, and others. Similar to the previous
embodiments, the thermal source is applied as flood, time-varying,
spatially varying, or continuous. Still further, any of the above
embodiments can be combined or even separated, depending upon the
application. Of course, the type of source used also depends upon
the application. As noted, the global source increases a level of
energy or stress in the material region without initiating a
cleaving action in the material region before providing energy to
initiate the controlled cleaving action.
[0033] In a specific embodiment, an energy source elevates an
energy level of the substrate cleave plane above its cleave front
propagation energy but is insufficient to cause self-initiation of
a cleave front. In particular, a thermal energy source or sink in
the form of heat or lack of heat (e.g., cooling source) can be
applied globally to the substrate to increase the energy state or
stress level of the substrate without initiating a cleave front.
Alternatively, the energy source can be electrical, chemical, or
mechanical. A directed energy source provides an application of
energy to a selected region of the substrate material to initiate a
cleave front which self-propagates through the implanted region of
the substrate until the thin film of material is removed. A variety
of techniques can be used to initiate the cleave action. These
techniques are describes by way of the FIGS. below.
[0034] FIG. 9 is a simplified illustration of an energy state 900
for a controlled cleaving action using a single controlled source
according to an aspect of the present invention. This diagram is
merely an illustration, and should not limit the scope of the
claims herein. In this embodiment, the energy level or state of the
substrate is raised using a global energy source above the cleave
front propagation energy state, but is lower than the energy state
necessary to initiate the cleave front. To initiate the cleave
front, an energy source such as a laser directs a beam in the form
of a pulse at an edge of the substrate to initiate the cleaving
action. Alternatively, the energy source can be a fluid (e.g.,
liquid, gas) that directs a momentum transfer medium in the form of
a pulse at an edge of the substrate to initiate the cleaving
action. The global energy source maintains the cleaving action
which generally requires a lower energy level than the initiation
energy.
[0035] An alternative aspect of the invention is illustrated by
FIGS. 10 and 11. FIG. 10 is a simplified illustration of an
implanted substrate 1000 undergoing rotational forces 1001, 1003.
This diagram is merely an illustration, and should not limit the
scope of the claims herein. As shown, the substrate includes a top
surface 1005, a bottom surface 1007, and an implanted region 1009
at a selected depth. An energy source increases a global energy
level of the substrate using a light beam or heat source to a level
above the cleave front propagation energy state, but lower than the
energy state necessary to initiate the cleave front. The substrate
undergoes a rotational force turning clockwise 1001 on top surface
and a rotational force turning counterclockwise 1003 on the bottom
surface which creates stress at the implanted region 1009 to
initiate a cleave front. Alternatively, the top surface undergoes a
counter-clockwise rotational force and the bottom surface undergoes
a clockwise rotational force. Of course, the direction of the force
generally does not matter in this embodiment.
[0036] FIG. 11 is a simplified diagram of an energy state 1100 for
the controlled cleaving action using the rotational force according
to the present invention. This diagram is merely an illustration,
and should not limit the scope of the claims herein. As previously
noted, the energy level or state of the substrate is raised using a
global energy source (e.g., thermal, beam) above the cleave front
propagation energy state, but is lower than the energy state
necessary to initiate the cleave front. To initiate the cleave
front, a mechanical energy means such as rotational force applied
to the implanted region initiates the cleave front. In particular,
rotational force applied to the implanted region of the substrates
creates zero stress at the center of the substrate and greatest at
the periphery, essentially being proportional to the radius. In
this example, the central initiating pulse causes a radially
expanding cleave front to cleave the substrate.
[0037] The removed material region provides a thin film of silicon
material for processing. The silicon material possesses limited
surface roughness and desired planarity characteristics for use in
a silicon-on-insulator substrate. In certain embodiments, the
surface roughness of the detached film has features that are less
than about 60 nm, or less than about 40 nm, or less than about 20
nm. Accordingly, the present invention provides thin silicon films
which can be smoother and more uniform than pre-existing
techniques.
[0038] In a preferred embodiment, the present invention is
practiced at temperatures that are lower than those used by
preexisting techniques. In particular, the present invention does
not require increasing the entire substrate temperature to initiate
and sustain the cleaving action as pre-existing techniques. In some
embodiments for silicon wafers and hydrogen implants, substrate
temperature does not exceed about 400.degree. C. during the
cleaving process. Alternatively, substrate temperature does not
exceed about 350.degree. C. during the cleaving process.
Alternatively, substrate temperature is kept substantially below
implanting temperatures via a thermal sink, e.g., cooling fluid,
cryogenic fluid. Accordingly, the present invention reduces a
possibility of unnecessary damage from an excessive release of
energy from random cleave fronts, which generally improves surface
quality of a detached film(s) and/or the substrate(s). Accordingly,
the present invention provides resulting films on substrates at
higher overall yields and quality.
[0039] The above embodiments are described in terms of cleaving a
thin film of material from a substrate. The substrate, however, can
be disposed on a workpiece such as a stiffener or the like before
the controlled cleaving process. The workpiece joins to a top
surface or implanted surface of the substrate to provide structural
support to the thin film of material during controlled cleaving
processes. The workpiece can be joined to the substrate using a
variety of bonding or joining techniques, e.g., electrostatics,
adhesives, interatomic. Some of these bonding techniques are
described herein. The workpiece can be made of a dielectric
material (e.g., quartz, glass, sapphire, silicon nitride, silicon
dioxide), a conductive material (silicon, silicon carbide,
polysilicon, group III/V materials, metal), and plastics (e.g.,
polyimide-based materials). Of course, the type of workpiece used
will depend upon the application.
[0040] Alternatively, the substrate having the film to be detached
can be temporarily disposed on a transfer substrate such as a
stiffener or the like before the controlled cleaving process. The
transfer substrate joins to a top surface or implanted surface of
the substrate having the film to provide structural support to the
thin film of material during controlled cleaving processes. The
transfer substrate can be temporarily joined to the substrate
having the film using a variety of bonding or joining techniques,
e.g., electrostatics, adhesives, interatomic. Some of these bonding
techniques are described herein. The transfer substrate can be made
of a dielectric material (e.g., quartz, glass, sapphire, silicon
nitride, silicon dioxide), a conductive material (silicon, silicon
carbide, polysilicon, group III/V materials, metal), and plastics
(e.g., polyimide-based materials). Of course, the type of transfer
substrate used will depend upon the application. Additionally, the
transfer substrate can be used to remove the thin film of material
from the cleaved substrate after the controlled cleaving
process.
[0041] 2. Patterned Implanting Techniques
[0042] Although the embodiments in this specification are in terms
of general implanting techniques, controlled cleaving can be
enhanced by way of patterned implanting techniques according to the
present invention. Patterned implanting techniques are used to
selectively introduce impurities into the substrate using a desired
or selected pattern, which enhances the control for the cleaving
process. FIGS. 12-20 illustrate a few examples of implanting
techniques according to this embodiment of the present invention.
These FIGS. are merely illustrations and should not limit the scope
of the claims herein. One of ordinary skill in the art would
recognize other variations, alternatives, and modifications.
[0043] FIG. 12 is a simplified cross-sectional view diagram 1200 of
an implanting step using a patterned mask 1201 according to the
present invention. The patterned mask is merely an illustration and
should not limit the scope of the claims herein. Patterned mask
1201 is a shadow mask, but also can be others. The patterned
implanting step 1203 provides a patterned distribution 1205 of
particles at a selected depth (z.sub.0). For instance, the
patterned mask can be applied directly to the substrate using
photolithographic techniques. An example of numerous photographic
techniques are described in "Semiconductor Lithography, Principles,
Practices, and Materials," Wayne M. Moreau, Plenum Press (1988),
which is hereby incorporated by reference for all purposes.
[0044] Optionally, the present method uses a blanket implanting
step 1300 of the substrate surface after the patterned implanting
step described, as illustrated by FIG. 13. The blanket implanting
step provides a uniform distribution of particles through the
surface of the substrate to a selected depth (z.sub.0). An example
of a distribution of particles in the substrate after a two-step
implanting process using patterned and blanket implanting steps is
illustrated by the simplified diagram of FIG. 14. As shown, the
diagram 1400 has a vertical axis representing particle
concentration at the selected depth (z.sub.0), and has a horizontal
axis representing distance from side 1 of the substrate to side 2
of the substrate. Using the two-step process described above, which
includes a blanket implanting step and a patterned implanting step,
concentration distribution 1401 through the cleave plane from side
1 to side 2 of the substrate various periodically and spatially
from C.sub.1 to C.sub.2. Depending upon the technique for cleaving
the substrate, various patterns can be used, and are illustrated by
FIGS. 15-18.
[0045] FIG. 15 is a simplified top-view diagram 1500 of an annular
distribution of particles according to the present invention. This
distribution of particles includes a lower concentration region
1505 and a higher concentration region 1501. The higher
concentration region 1501 is defined in concentric annular patterns
around a center region 1503 of the substrate. As shown, the annular
patterns are defined symmetrically around the center of the
substrate and have a plurality of annular regions which are placed
next to each other in a constant spatial frequency. The annular
patterns tend to enhance the controlled cleaving action according
to some embodiments of the present invention.
[0046] Alternatively, the distribution of particles in the
substrate can be in a linear pattern 1600, as illustrated by FIG.
16. As shown, the substrate includes particles having higher and
lower concentrations in regions 1601 and 1603, respectively. The
linear pattern has regions (i.e., lines) of higher concentration.
The regions also have similar widths, but can include other widths.
Additionally, the linear pattern has regions (i.e., lines) of lower
concentration. The lower concentration regions have similar widths,
but also can include other widths. Again, this pattern is likely to
enhance the controlled cleaving action according to embodiments of
the present invention.
[0047] Alternatively, FIG. 17 is a simplified top-view diagram 1700
of a "checker board" pattern of particles according to an
alternative aspect of the present invention. The diagram 1700
illustrates a higher concentration region 1701 and a lower
concentration region 1705. Higher concentration regions include
vertical lines 102 and horizontal lines 1703, which are disposed at
a relatively constant spacial frequency. Of course, the use of this
pattern will depend upon the particular application.
[0048] Alternatively, FIG. 18 is a simplified top-view diagram 1800
of a "webbed" or "dart board" pattern of particles according to yet
an alternative embodiment of the present invention. This pattern
1800 includes concentric annular regions 1801 of higher
concentration, and other higher concentration regions 1803 (i.e,
lines) which intersect the annular regions. Lower concentration
regions 1805 are also shown. The annular regions have a spatial
frequency that is relatively constant, but can also be others, i.e.
non-constant. Again, the use of this particular embodiment will
depend upon the application.
[0049] FIGS. 19-20 are simplified top-view diagrams 1900, 2000 of
still further particle distributions according to the present
invention. These distributions of particles do not have features of
constant spatial frequency. In particular, the diagram 1900 of FIG.
19 has a higher concentration region 1901 which has a higher
density of particles on one side 1903 of the substrate as compared
to the other side 1905 of the substrate. The higher concentration
region 1903 includes a plurality of lines, which have different
sized widths (but can also be similar). Additionally, lower to
initiate a controlled cleaving action at the selected depth;
[0050] (7) Provide additional energy to the bonded substrates to
sustain the controlled cleaving action to free the thickness of
silicon film from the silicon wafer (optional);
[0051] (8) Complete bonding of donor silicon wafer to the target
substrate; and
[0052] (9) Polish a surface of the thickness of silicon film.
[0053] The above sequence of steps provides a step of initiating a
controlled cleaving action using an energy applied to a selected
region(s) of a multi-layered substrate structure to form a cleave
front(s) according to the present invention. This initiation step
begins a cleaving process in a controlled manner by limiting the
amount of energy applied to the substrate. Further propagation of
the cleaving action can occur by providing additional energy to
selected regions of the substrate to sustain the cleaving action,
or using the energy from the initiation step to provide for further
propagation of the cleaving action. This sequence of steps is
merely an example and should not limit the scope of the claims
defined herein. Further details with regard to the above sequence
of steps are described in below in references to the FIGS.
[0054] FIGS. 21-27 are simplified cross-sectional view diagrams of
substrates undergoing a fabrication process for a
silicon-on-insulator wafer according to the present invention. The
process begins by providing a semiconductor substrate similar to
the silicon wafer 2100, as shown by FIG. 21. Substrate or donor
includes a material region 2101 to be removed, which is a thin
relatively uniform film derived from the substrate material. The
silicon wafer includes a top surface 2103, a bottom surface 2105,
and a thickness 2107. Material region also includes a thickness
(z.sub.0), within the thickness 2107 of the silicon wafer.
Optionally, a dielectric layer 2102 (e.g., silicon nitride, silicon
oxide, silicon oxynitride) overlies the top surface of the
substrate. The present process provides a novel technique for
removing the material region 2101 using the following sequence of
steps for the fabrication of a silicon-on-insulator wafer.
[0055] Selected energetic particles 2109 implant through the top
surface of the silicon wafer to a selected depth, which defines the
thickness of the material region, termed the thin film of material.
As shown, the particles have a desired concentration 2111 at the
selected depth (z.sub.0). A variety of techniques can be used to
implant the energetic particles into the silicon wafer. These
techniques include ion implantation using, for example, beam line
ion implantation equipment manufactured from companies such as
Applied Materials, Eaton Corporation, Varian, and others.
Alternatively, implantation occurs using a plasma immersion ion
implantation ("PIII") technique. Of course, techniques used depend
upon the application.
[0056] Depending upon the application, smaller mass particles are
generally selected to reduce a possibility of damage to the
material region. That is, smaller mass particles easily travel
through the substrate material to the selected depth without
substantially damaging the material region that the particles
traversed through. For example, the smaller mass particles (or
energetic particles) can be almost any charged (e.g., positive or
negative) and/or neutral atoms or molecules, or electrons, or the
like. In a specific embodiment, the particles can be neutral and/or
charged particles including ions of hydrogen and its isotopes, rare
gas ions such as helium and its isotopes, and neon. The particles
can also be derived from compounds such as gases, e.g., hydrogen
gas, water vapor, methane, and other hydrogen compounds, and other
light atomic mass particles. Alternatively, the particles can be
any combination of the above particles, and/or ions and/or
molecular species and/or atomic species.
[0057] The process uses a step of joining the implanted silicon
wafer to a workpiece or target wafer, as illustrated in FIG. 22.
The workpiece may also be a variety of other types of substrates
such as those made of a dielectric material (e.g., quartz, glass,
silicon nitride, silicon dioxide), a conductive material (silicon,
polysilicon, group n/v materials, metal), and plastics (e.g.,
polyimide-based materials). In the present example, however, the
workpiece is a silicon wafer.
[0058] In a specific embodiment, the silicon wafers are joined or
fused together using a low temperature thermal step. The low
temperature thermal process generally ensures that the implanted
particles do not place excessive stress on the material region,
which can produce an uncontrolled cleave action. In one aspect, the
low temperature bonding process occurs by a self-bonding process.
In particular, one wafer is stripped to remove oxidation therefrom
(or one wafer is not oxidized). A cleaning solution treats the
surface of the wafer to form O--H bonds on the wafer surface. An
example of a solution used to clean the wafer is a mixture of
H.sub.2O.sub.2--H.sub.2SO.sub.4. A dryer dries the wafer surfaces
to remove any residual liquids or particles from the wafer
surfaces. Self-bonding occurs by placing a face of the cleaned
wafer against the face of an oxidized wafer.
[0059] Alternatively, a self-bonding process occurs by activating
one of the wafer surfaces to be bonded by plasma cleaning. In
particular, plasma cleaning activates the wafer surface using a
plasma derived from gases such as argon, ammonia, neon, water
vapor, and oxygen. The activated wafer surface 2203 is placed
against a face of the other wafer, which has a coat of oxidation
2205 thereon. The wafers are in a sandwiched structure having
exposed wafer faces. A selected amount of pressure is placed on
each exposed face of the wafers to self-bond one wafer to the
other.
[0060] Alternatively, an adhesive disposed on the wafer surfaces is
used to bond one wafer onto the other. The adhesive includes an
epoxy, polyimide-type materials, and the like. Spin-on-glass layers
can be used to bond one wafer surface onto the face of another.
These spin-on-glass ("SOG") materials include, among others,
siloxanes or silicates, which are often mixed with alcohol-based
solvents or the like. SOG can be a desirable material because of
the low temperatures (e.g., 150 to 250.degree. C.) often needed to
cure the SOG after it is applied to surfaces of the wafers.
[0061] Alternatively, a variety of other low temperature techniques
can be used to join the donor wafer to the target wafer. For
instance, an electro-static bonding technique can be used to join
the two wafers together. In particular, one or both wafer
surface(s) is charged to attract to the other wafer surface.
Additionally, the donor wafer can be fused to the target wafer
using a variety of commonly known techniques. Of course, the
technique used depends upon the application.
[0062] After bonding the wafers into a sandwiched structure 2300,
as shown in FIG. 23, the method includes a controlled cleaving
action to remove the substrate material to provide a thin film of
substrate material 2101 overlying an insulator 2305 the target
silicon wafer 2201. The controlled-cleaving occurs by way of
selective energy placement or positioning or targeting 2301, 2303
of energy sources onto the donor and/or target wafers. For
instance, an energy impluse(s) can be used to initiate the cleaving
action. The impulse (or impulses) is provided using an energy
source which include, among others, a mechanical source, a chemical
source, a thermal sink or source, and an electrical source.
[0063] The controlled cleaving action is initiated by way of any of
the previously noted techniques and others and is illustrated by
way of FIG. 23. For instance, a process for initiating the
controlled cleaving action uses a step of providing energy 2301,
2303 to a selected region of the substrate to initiate a controlled
cleaving action at the selected depth (z.sub.0) in the substrate,
whereupon the cleaving action is made using a propagating cleave
front to free a portion of the substrate material to be removed
from the substrate. In a specific embodiment, the method uses a
single impulse to begin the cleaving action, as previously noted.
Alternatively, the method uses an initiation impulse, which is
followed by another impulse or successive impulses to selected
regions of the substrate. Alternatively, the method provides an
impulse to initiate a cleaving action which is sustained by a
scanned energy along the substrate. Alternatively, energy can be
scanned across selected regions of the substrate to initiate and/or
sustain the controlled cleaving action.
[0064] Optionally, an energy or stress of the substrate material is
increased toward an energy level necessary to initiate the cleaving
action, but not enough to initiate the cleaving action before
directing an impulse or multiple successive impulses to the
substrate according to the present invention. The global energy
state of the substrate can be raised or lowered using a variety of
sources such as chemical, mechanical, thermal (sink or source), or
electrical, alone or in combination. The chemical source can
include particles, fluids, gases, or liquids. These sources can
also include chemical reaction to increase stress in the material
region. The chemical source is introduced as flood, time-varying,
spatially varying, or continuous. In other embodiments, a
mechanical source is derived from rotational, translational,
compressional, expansional, or ultrasonic energies. The mechanical
source can be introduced as flood, time-varying, spatially varying,
or continuous. In further embodiments, the electrical source is
selected from an applied voltage or an applied electromagnetic
field, which is introduced as flood, time-varying, spatially
varying, or continuous. In still further embodiments, the thermal
source or sink is selected from radiation, convection, or
conduction. This thermal source can be selected from, among others,
a photon beam, a fluid jet, a liquid jet, a gas jet, an
electro/magnetic field, an electron beam, a thermoelectric heating,
and a furnace. The thermal sink can be selected from a fluid jet, a
liquid jet, a gas jet, a cryogenic fluid, a super-cooled liquid, a
thermoelectric cooling means, an electro/magnetic field, and
others. Similar to the previous embodiments, the thermal source is
applied as flood, time-varying, spatially varying, or continuous.
Still further, any of the above embodiments can be combined or even
separated, depending upon the application. Of course, the type of
source used depends upon the application. As noted, the global
source increases a level of energy or stress in the material region
without initiating a cleaving action in the material region before
providing energy to initiate the controlled cleaving action.
[0065] In a preferred embodiment, the method maintains a
temperature which is below a temperature of introducing the
particles into the substrate. In some embodiments, the substrate
temperature is maintained between -200 and 450.degree. C. during
the step of introducing energy to initiate propagation of the
cleaving action. Substrate temperature can also be maintained at a
temperature below 400.degree. C. In preferred embodiments, the
method uses a thermal sink to initiate and maintain the cleaving
action, which occurs at conditions significantly below room
temperature.
[0066] A final bonding step occurs between the target wafer and
thin film of material region according to some embodiments, as
illustrated by FIG. 24. In one embodiment, one silicon wafer has an
overlying layer of silicon dioxide, which is thermally grown
overlying the face before cleaning the thin film of material. The
silicon dioxide can also be formed using a variety of other
techniques, e.g., chemical vapor deposition. The silicon dioxide
between the wafer surfaces fuses together thermally in this
process.
[0067] In some embodiments, the oxidized silicon surface from
either the target wafer or the thin film of material region (from
the donor wafer) are further pressed together and are subjected to
an oxidizing ambient 2401. The oxidizing ambient can be in a
diffusion furnace for steam oxidation, hydrogen oxidation, or the
like. A combination of the pressure and the oxidizing ambient fuses
the two silicon wafers together at the oxide surface or interface
2305. These embodiments often require high temperatures (e.g.,
700.degree. C.).
[0068] Alternatively, the two silicon surfaces are further pressed
together and subjected to an applied voltage between the two
wafers. The applied voltage raises temperature of the wafers to
induce a bonding between the wafers. This technique limits the
amount of crystal defects introduced into the silicon wafers during
the bonding process, since substantially no mechanical force is
needed to initiate the bonding action between the wafers. Of
course, the technique used depends upon the application.
[0069] After bonding the wafers, silicon-on-insulator has a target
substrate with an overlying film of silicon material and a
sandwiched oxide layer between the target substrate and the silicon
film, as also illustrated in FIG. 24 The detached surface of the
film of silicon material is often rough 2404 and needs finishing.
Finishing occurs using a combination of grinding and/or polishing
techniques. In some embodiments, the detached surface undergoes a
step of grinding using, for examples, techniques such as rotating
an abrasive material overlying the detached surface to remove any
imperfections or surface roughness therefrom. A machine such as a
"back grinder" made by a company called Disco may provide this
technique.
[0070] Alternatively, chemical mechanical polishing or
planarization ("CMP") techniques finish the detached surface of the
film, as illustrated by FIG. 25. In CMP, a slurry mixture is
applied directly to a polishing surface 2501 which is attached to a
rotating platen 2503. This slurry mixture can be transferred to the
polishing surface by way of an orifice, which is coupled to a
slurry source. The slurry is often a solution containing an
abrasive and an oxidizer, e.g., H.sub.2O.sub.2, KIO.sub.3, ferric
nitrate. The abrasive is often a borosilicate glass, titanium
dioxide, titanium nitride, aluminum oxide, aluminum trioxide, iron
nitrate, cerium oxide, silicon dioxide (colloidal silica), silicon
nitride, silicon carbide, graphite, diamond, and any mixtures
thereof. This abrasive is mixed in a solution of deionized water
and oxidizer or the like. Preferably, the solution is acidic.
[0071] This acid solution generally interacts with the silicon
material from the wafer during the polishing process. The polishing
process preferably uses a polyurethane polishing pad. An example of
this polishing pad is one made by Rodel and sold under the
tradename of IC-1000. The polishing pad is rotated at a selected
speed. A carrier head which picks up the target wafer having the
film applies a selected amount of pressure on the backside of the
target wafer such that a selected force is applied to the film. The
polishing process removes about a selected amount of film material,
which provides a relatively smooth film surface 2601 for subsequent
processing, as illustrated by FIG. 26.
[0072] In certain embodiments, a thin film of oxide 2406 overlies
the film of material overlying the target wafer, as illustrated in
FIG. 24. The oxide layer forms during the thermal annealing step,
which is described above for permanently bonding the film of
material to the target wafer. In these embodiments, the finishing
process is selectively adjusted to first remove oxide and the film
is subsequently polished to complete the process. Of course, the
sequence of steps depends upon the particular application.
[0073] In a specific embodiment, the silicon-on-insulator substrate
undergoes a series of process steps for formation of integrated
circuits thereon. These processing steps are described in S. Wolf,
Silicon Processing for the VLSI Era (Volume 2), Lattice Press
(1990), which is hereby incorporated by reference for all purposes.
A portion of a completed wafer 2700 including integrated circuit
devices is illustrated by FIG. 27. As shown, the portion of the
wafer 2700 includes active devices regions 2701 and isolation
regions 2703. The active devices are field effect transistors each
having a source/drain region 2705 and a gate electrode 2707. A
dielectric isolation layer 2709 is defined overlying the active
devices to isolate the active devices from any overlying
layers.
[0074] Although the above description is in terms of a silicon
wafer, other substrates may also be used. For example, the
substrate can be almost any monocrystalline, polycrystalline, or
even amorphous type substrate. Additionally, the substrate can be
made of III/V materials such as gallium arsenide, gallium nitride
(GaN), and others. The multi-layered substrate can also be used
according to the present invention. The multi-layered substrate
includes a silicon-on-insulator substrate, a variety of sandwiched
layers on a semiconductor substrate, and numerous other types of
substrates. Additionally, the embodiments above were generally in
terms of providing a pulse of energy to initiate a controlled
cleaving action. The pulse can be replaced by energy that is
scanned across a selected region of the substrate to initiate the
controlled cleaving action. Energy can also be scanned across
selected regions of the substrate to sustain or maintain the
controlled cleaving action. One of ordinary skill in the art would
easily recognize a variety of alternatives, modifications, and
variations, which can be used according to the present
invention.
[0075] While the above is a full description of the specific
embodiments, various modifications, alternative constructions and
equivalents may be used. Therefore, the above description and
illustrations should not be taken as limiting the scope of the
present invention which is defined by the appended claims.
* * * * *