U.S. patent application number 11/457567 was filed with the patent office on 2008-01-17 for laminate body, and method for manufacturing thin substrate using the laminate body.
This patent application is currently assigned to 3M Innovative Properties Company. Invention is credited to Larry D. Boardman, Carl R. KESSEL, Richard J. Webb.
Application Number | 20080014532 11/457567 |
Document ID | / |
Family ID | 38923562 |
Filed Date | 2008-01-17 |
United States Patent
Application |
20080014532 |
Kind Code |
A1 |
KESSEL; Carl R. ; et
al. |
January 17, 2008 |
LAMINATE BODY, AND METHOD FOR MANUFACTURING THIN SUBSTRATE USING
THE LAMINATE BODY
Abstract
Provided is a laminated body comprising a substrate to be ground
and a support, where the substrate may be ground to a very small
(thin) thickness and can then be separated from the support without
damaging the substrate. One embodiment is a laminated body
comprising a substrate to be ground, a curable silicone adhesive
layer in contact with the substrate to be ground, a photothermal
conversion layer comprising a light absorbing agent and a heat
decomposable resin, and a light transmitting support. After
grinding the substrate surface which is opposite that in contact
with the adhesive layer, the laminated body is irradiated through
the light transmitting layer and the photothermal conversion layer
decomposes to separate the substrate and the light transmitting
support.
Inventors: |
KESSEL; Carl R.; (St. Paul,
MN) ; Boardman; Larry D.; (Woodbury, MN) ;
Webb; Richard J.; (Inver Grove Heights, MN) |
Correspondence
Address: |
3M INNOVATIVE PROPERTIES COMPANY
PO BOX 33427
ST. PAUL
MN
55133-3427
US
|
Assignee: |
3M Innovative Properties
Company
|
Family ID: |
38923562 |
Appl. No.: |
11/457567 |
Filed: |
July 14, 2006 |
Current U.S.
Class: |
430/311 |
Current CPC
Class: |
H01L 2221/68381
20130101; B32B 2310/0806 20130101; B24B 7/228 20130101; H01L
21/6836 20130101; B32B 37/12 20130101; H01L 2221/68386 20130101;
B32B 2457/14 20130101; H01L 21/6835 20130101; H01L 2221/68327
20130101; Y10T 428/31663 20150401 |
Class at
Publication: |
430/311 |
International
Class: |
G03C 5/00 20060101
G03C005/00 |
Claims
1. A method for manufacturing a laminated body, the laminated body
comprising: a substrate to be ground; a joining layer in contact
with said substrate; a photothermal conversion layer comprising a
light absorbing agent and a heat decomposable resin disposed
beneath the joining layer; and a light transmitting support
disposed beneath the photothermal conversion layer, said method
comprising: coating on a light transmitting support a photothermal
conversion layer precursor containing a light absorbing agent and a
heat decomposable resin solution or a monomer or oligomer as a
precursor material of a heat decomposable resin; drying to solidify
or curing said photothermal conversion layer precursor to form a
photothermal conversion layer on said light transmitting support;
applying a curable silicone adhesive to the substrate to be ground
or the photothermal conversion layer; joining said substrate to be
ground and said photothermal conversion layer through said curable
silicone adhesive under reduced pressure, and curing to form a
laminated body.
2. The method of claim 1 wherein said curable silicone adhesive is
selected from addition curable silicones, condensation curable
silicones, free-radical curable silicones, and cationic curable
silicones.
3. The method of claim 2, wherein said curable silicone adhesive
further comprises a reinforcing agent.
4. The method of claim 1 wherein said substrate is a silicon
wafer.
5. The method of claim 1 wherein said support is glass.
6. The method of claim 2 wherein said curable silicone adhesive is
an addition curable silicone adhesive.
7. The method of claim 6 wherein said adhesive comprises an
ethylenically unsaturated functional group silicone, a hydride
functional silicone, and a hydrosilylation catalyst.
8. The method of claim 7, wherein said hydrosilylation catalyst is
a photohydrosilylation catalyst.
9. The method of claim 1, wherein said silicone adhesive is at
least one free radical-cure silicone adhesive comprising an
ethylenically unsaturated silicone.
10. The method of claim 1, wherein said silicone adhesive is at
least one condensation curable silicone.
11. The method of claim 1, wherein said silicone adhesive is at
least one cationic curable silicone.
12. The method of claim 11 wherein said cationic curable silicone
is an epoxy silicone.
13. The method of claim 1 wherein the curable silicone is cured by
exposure to actinic radiation.
14. A method for producing a semiconductor chip, comprising:
applying a photothermal conversion layer comprising a
light-absorbing agent and a heat decomposable resin on a
light-transmitting support, preparing a semiconductor wafer having
a circuit face with a circuit pattern and a non-circuit face on the
side opposite of said circuit face, laminating said semiconductor
wafer and said light-transmitting support through a curable
silicone adhesive by placing said circuit face and said
photothermal conversion layer to face each other, and irradiating
light through said light-transmitting support side to cure the
curable silicone adhesive layer, thereby forming a laminated body
having a non-circuit face on the outside surface, grinding the
non-circuit face of said semiconductor wafer until said
semiconductor wafer reaches a desired thickness, irradiating
radiation energy through said light-transmitting support side to
decompose said photothermal conversion layer, thereby causing
separation into semiconductor wafer having said adhesive layer and
a light-transmitting support, and removing said silicone adhesive
layer from said semiconductor wafer, and optionally dicing the
ground semiconductor wafer to cut it into a plurality of
semiconductor chips.
15. The method for producing a semiconductor chip of claim 14,
wherein a die bonding tape is affixed to the semiconductor wafer
before dicing the ground semiconductor wafer.
16. The method for producing a semiconductor chip of claim 14,
wherein laminating said semiconductor wafer and said
light-transmitting support through a curable silicone adhesive is
performed in a vacuum.
17. The method of claim 14, wherein said semiconductor wafer is
ground to a thickness of 50 .mu.m or less.
18. The method of claim 14 wherein said semiconductor wafer has
been partially sawn through on the circuit face.
19. A laminated body comprising: a substrate to be ground; a
curable silicone adhesive joining layer in contact with said
substrate; a photothermal conversion layer comprising a light
absorbing agent and a heat decomposable resin disposed beneath the
joining layer; and a light transmitting support disposed beneath
the photothermal conversion layer.
20. A method of providing a thin substrate comprising: a) providing
a laminated body comprising a substrate to be ground; a joining
layer comprising a cured silicone in contact with said substrate; a
photothermal conversion layer comprising a light absorbing agent
and a heat decomposable resin disposed beneath the joining layer;
and a light transmitting support disposed beneath the photothermal
conversion layer; b) grinding the face of said substrate to a
desired thickness, c) irradiating radiation energy through said
light-transmitting support side to decompose said photothermal
conversion layer, thereby causing separation into a thin substrate
having said adhesive layer and a light-transmitting support, and
optionally removing said cured silicone joining layer from said
ground substrate.
21. The method of claim 20 further comprising the step of dicing
the ground substrate into a plurality of ground substrates.
22. The method of claim 20 wherein said substrate to be ground
comprises a semiconductor wafer, said wafer having a circuit face
adjacent said joining layer and a non-circuit face.
23. The method of claim 20, wherein said substrate is ground to a
thickness of 50 .mu.m or less.
24. The method of claim 20 wherein said substrate has been
partially sawn through on the face adjacent the joining layer.
Description
TECHNICAL FIELD
[0001] The present invention relates to a laminated body where a
substrate to be ground, such as silicon wafer, fixed on a support
can be easily separated from the support, and also relates to a
method for manufacturing this laminated body and a method for
producing a thinned substrate.
BACKGROUND
[0002] In various fields, reducing the thickness of a substrate
often is critical. For example, in the field of quartz devices,
reducing the thickness of a quartz wafer is desired so as to
increase the oscillation frequency. Particularly, in the
semiconductor industry, efforts to further reduce the thickness of
a semiconductor wafer are in progress to respond to the goal of
reducing the thickness of semiconductor packages as well as for
high-density fabrication by chip lamination technology. Thickness
reduction is performed by so-called back side grinding of a
semiconductor wafer on the surface opposite that containing
pattern-formed circuitry. Usually, in conventional techniques of
grinding the back side, or surface, of a wafer and conveying it
while holding the wafer with only a backgrinding protective tape,
thickness reduction can be accomplished in practice only to a
thickness of about 150 micrometers (.mu.m) because of problems such
as uneven thickness of the ground wafer or warping of the wafer
with protective tape after grinding. For example, Japanese
Unexamined Patent Publication (Kokai) No. 6-302569 discloses a
method where a wafer is held on a ring-form frame through a
pressure-sensitive adhesive tape, the back surface of this wafer
held on the frame is ground and the wafer is conveyed to the next
step. However, this method has not yet attained a remarkable
improvement over the present level of wafer thickness that may be
obtained without encountering the aforementioned problems of
unevenness or warping.
[0003] A method of grinding the back surface of a wafer and
conveying it while firmly fixing the wafer on a hard support
through an adhesive agent has also been proposed. This intends to
prevent the breakage of a wafer during the back surface grinding
and conveyance by supporting the wafer using such a support.
According to this method, a wafer can be processed to a lower
thickness level as compared with the above-described method,
however, the thin wafer cannot be separated from the support
without breaking the wafer and therefore, this method cannot be
practically used as a method of thinning a semiconductor wafer.
SUMMARY OF THE INVENTION
[0004] The present invention provides a laminated body in which a
substrate to be ground is fixed on a support, by means of a joining
layer (comprising a cured silicone adhesive), and the joining layer
can be easily peeled off from the substrate after grinding. The
present invention further provides a method for manufacturing the
laminated body, and a method for manufacturing a thin substrate
using the laminated body. In some preferred embodiments, the thin
substrate may comprise a semiconductor wafer.
[0005] The present method allows the laminated body to be subjected
to higher temperature processes than prior art methods. In the
manufacture of semiconductor wafers, the instant method allows
subsequent processing such as sputtering or dry etching, and still
allows the joining layer to be easily removed from the ground
substrate (wafer). In some embodiments the laminated body
comprising a cured silicone adhesive joining layer may be subjected
to temperatures in excess of 150.degree. C., preferably 200.degree.
C., and more preferably 250.degree. C.
[0006] The curable silicone adhesive may be a condensation-curable
silicone adhesive, addition-curable (hydrosilylation curable)
silicone adhesive, a free radical-cure silicone adhesive, or a
cationic-curable silicone adhesive. As used herein, a "curable"
silicone refers to one that is capable of polymerization and/or
crosslinking reactions including, for example, photopolymerization
reactions involving one or more compounds capable of curing.
Preferably the cure mechanism yields no gaseous or liquid
byproducts that could contaminate or damage the laminated body.
Preferably, the cure mechanism does not use agents, such as acidic
agents, that may compromise the functioning of the
semiconductor.
[0007] In one embodiment of the present invention, a laminated body
is provided, the laminated body comprising a substrate to be
ground; a joining layer (comprising a cured silicone adhesive) in
contact with said substrate to be ground; a photothermal conversion
layer (comprising a light absorbing agent and a heat decomposable
resin); and a light transmitting support. After grinding the
substrate surface that is opposite that in contact with the joining
layer, the laminated body can be irradiated through the
light-transmitting layer to decompose the photothermal conversion
layer and to separate the substrate and the light transmitting
support. In this laminate, the substrate ground to a very small
thickness can be separated from the support without breaking the
substrate.
[0008] A method for manufacturing the above-described laminated
body is also provided, the method comprising providing a
photothermal conversion layer on a light transmitting support,
applying a curable silicone adhesive to a substrate to be ground or
to the photothermal conversion layer, joining the substrate to be
ground and the photothermal conversion layer by means of the
curable silicone adhesive, under reduced pressure, curing the
silicone adhesive to form a joining and therefore form a laminated
body. The photothermal conversion layer may be provided by
providing a photothermal conversion layer precursor containing a
light absorbing agent and a heat decomposable resin solution, or a
monomer or oligomer as a precursor material of a heat decomposable
resin; and drying to solidify or cure the photothermal conversion
layer precursor to form a photothermal conversion layer on the
light transmitting support.
[0009] By joining the substrate to be ground and the light
transmitting support through the joining layer (comprising a cured
silicone adhesive) under reduced pressure, bubbles and dust
contamination are prevented from forming inside the laminated body,
so that a level surface can be formed and the substrate can
maintain the evenness of thickness after grinding.
[0010] In still another embodiment of the present invention, a
method for manufacturing a reduced thickness substrate is provided,
the method comprising preparing the above-described laminated body,
grinding the substrate to a desired thickness, irradiating the
photothermal conversion layer through the light transmitting
support to decompose the photothermal conversion layer and thereby
to separate the substrate from the light transmitting support after
grinding, and peeling the joining layer from the substrate after
grinding. In this method, a substrate can be ground to a desired
thickness (for example, 150 .mu.m or less, preferably 50 .mu.m or
less, more preferably 25 .mu.m or less) on a support and after
grinding, the support is separated from the substrate using
exposure to radiation energy, so that the joining layer remaining
on the substrate after grinding can be easily peeled off from the
substrate.
BRIEF DESCRIPTION OF DRAWINGS
[0011] FIG. 1 is a cross-sectional view showing a laminated body of
the present invention.
[0012] FIG. 2 is a cross-sectional view showing a vacuum adhesion
device useful in the present invention.
[0013] FIG. 3 is a partial cross-sectional view of a grinding
device useful in the method of the present invention.
[0014] FIG. 4 is a drawing showing the steps of separating the
support and peeling the joining layer.
[0015] FIG. 5 is a cross-sectional view of a laminated body fixing
device which can be used in the laser beam irradiation step.
[0016] FIG. 6 is a perspective view of a laser irradiation
device.
[0017] FIG. 7 is a schematic view of a pick-up used in the
operation of separating wafer and support.
[0018] FIG. 8 is a schematic view showing how the joining layer is
peeled from the wafer.
[0019] FIG. 9 is a schematic view of an apparatus for measuring the
adhesive strength of the joining layer.
DETAILED DESCRIPTION OF THE INVENTION
[0020] The laminated body features a cured silicone adhesive
joining layer for joining the substrate to be ground to a support.
In the laminated body 1 of FIG. 1, a substrate 2 to be ground, a
joining layer 3 (comprising a cured silicone adhesive), a
photothermal conversion layer 4 and a support 5 are shown. The
elements comprising the laminated body of the present invention are
described in greater detail below.
[0021] The joining layer, comprising a cured silicone adhesive, is
used for fixing the substrate to be ground to the support through a
photothermal conversion layer. After the separation of the
substrate and the support by the decomposition of the photothermal
conversion layer, a substrate having the joining layer thereon is
obtained. Therefore, the joining layer is desirably easily
separated from the substrate, such as by peeling. Thus, the joining
layer has an adhesive strength high enough to fix the substrate to
the support yet low enough to permit separation from the
substrate.
[0022] The adhesive layer comprises a curable silicone adhesive
selected from a condensation curable silicone adhesive, an
addition-curable (or hydrosilylation curable) silicone adhesive, a
free radical-cure silicone adhesive, or a cationic-curable silicone
adhesive. Curable silicone adhesives can provide long-term
durability and are useful over a wide range of temperature,
humidity and environmental conditions, and can be used effectively
to bond the laminated body of the invention. In some embodiments,
the curable silicones may be photocurable silicones, including UV
and visible light curable silicones. In some embodiments, the
curable silicone may further comprise a reinforcing agent such as a
silica, quartz, and/or MQ resin, which reinforces the cured
silicone. Such a reinforcing agent may be added in amounts up to 75
wt. % of the curable silicone composition.
[0023] General references regarding curable silicone polymers
include Kirk-Othmer Encyclopedia of Polymer Science and
Engineering, 2.sup.nd edition, Wiley-Interscience Pub., 1989,
volume 15, pp. 235-243; Comprehensive Organometallic Chemistry, Ed.
Geoffrey Wilkinson, Vol. 2, Chapter 9.3, F. O. Stark, J. R.
Falender, A. P. Wright, pp. 329-330, Pergamon Press: New York,
1982; Silicones and Industry: A Compendium for Practical Use,
Instruction, and Reference, A. Tomanek, Carl Hanser: Wacher-Chemie:
Munich, 1993; Siloxane Polymers, S. J. Clarson, Prentice Hall:
Englewood Cliffs, N.J., 1993; and Chemistry and Technology of
Silicones, W. Noll, Verlag Chemie: Weinheim, 1960.
[0024] The curable silicone adhesive can an addition-cure or
hydrosilylation cure silicone adhesive comprising an ethylenically
unsaturated (e.g. alkenyl or (meth)acryloyl) functional silicone
base polymer, a hydride functional cross-linking or chain extending
agent (e.g., SiH), and a hydrosilylation catalyst. The silicone
base polymer has ethylenically unsaturated (e.g., vinyl, propenyl,
higher alkenyl, (meth)acryloyl, etc.) groups which may be present
at the ends of the polymer (terminal) and/or pendent along the
polymer chain. Preferably the ethylenically unsaturated groups are
vinyl or higher alkenyl groups. It may be desirable for a
reinforcing agent to be included such as, for example, a silica,
quartz, and/or MQ resin containing alkenyl or SiH functional
groups. The hydrosilylation catalyst may be a Group VIII metal or
metal complex or supported metal catalyst, but is typically a noble
metal catalyst containing, for example, Pt or Rh.
[0025] Addition-cured silicones (e.g., hydrosilylation cured
silicones) are generally considered to be of higher quality and are
more dimensionally stable than condensation-cured silicones. Unlike
condensation-cured silicones, addition-cured silicones, e.g.,
hydrosilylation-cured silicones, do not produce potentially
detrimental byproducts during curing. Such silicones differ from
condensation-cured silicones in that the hydrosilylation-cured
composition typically contains 1) a polyethylenically unsaturated
silicone polymer or oligomer; 2) a "hydrosilane" component
containing two or more silane (Si--H) bonds; and 3) a
hydrosilylation catalyst such as a platinum catalyst. By
"polyethylenically unsaturated" it is meant a compound or component
having a plurality of ethylenically unsaturated groups, such as a
plurality of vinyl groups and (meth)acryloyl groups. The
ethylenically unsaturated groups and the Si--H groups may be
terminal or pendent. In some embodiments, the silicone may have
both Si--H bonds and vinyl groups.
[0026] A particularly preferred addition-cured silicone is formed
by reacting (1) a multiply-ethylenically unsaturated
group-containing organopolysiloxane with (2) an organopolysiloxane
containing a multiplicity of SiH bonds per molecule (hereinafter
"organohydropolysiloxane"). This reaction is typically facilitated
by the presence of (3) a platinum-containing catalyst.
[0027] The curable silicone composition can be prepared by
combining (e.g., mixing together) the polyethylenically unsaturated
organopolysiloxane, the organohydropolysiloxane, and the
hydrosilylation catalyst. In one embodiment, the components are
pre-mixed into preferably two parts prior to use. For example, part
"A" may contain the vinyl-containing organopolysiloxane, and the
catalyst, while part "B" may contain the organohydropolysiloxane
and optionally vinyl-containing organopolysiloxane. In another
embodiment, the components are provided in one part and further
contain an ingredient (e.g., a catalyst inhibitor) that inhibits
the cure reaction.
[0028] Numerous patents teach the use of various complexes of
cobalt, rhodium, nickel, palladium, or platinum as catalysts for
accelerating the thermally-activated addition reaction
(hydrosilylation) between a compound containing silicon-bonded
hydrogen and a compound containing aliphatic unsaturation. For
example, U.S. Pat. No. 4,288,345 (Ashby et al) discloses as a
catalyst for hydrosilylation reactions a platinum-siloxane complex.
Additional platinum-siloxane complexes are disclosed as catalysts
for hydrosilylation reactions in U.S. Pat. Nos. 3,715,334,
3,775,452, and 3,814,730 (Karstedt et al). U.S. Pat. No. 3,470,225
(Knorre et al) discloses production of organic silicon compounds by
addition of a compound containing silicon-bonded hydrogen to
organic compounds containing at least one non-aromatic double or
triple carbon-to-carbon bond using a platinum compound of the
empirical formula PtX.sub.2(RCOCR'COR'').sub.2 wherein X is
halogen, R is alkyl, R' is hydrogen or alkyl, and R'' is alkyl or
alkoxy. The catalysts disclosed in the foregoing patents are
characterized by their high catalytic activity. Other platinum
complexes for accelerating the aforementioned thermally-activated
addition reaction include: a platinacyclobutane complex having the
formula (PtCl.sub.2C.sub.3H.sub.6).sub.2 (U.S. Pat. No. 3,159,662,
Ashby); a complex of a platinous salt and an olefin (U.S. Pat. No.
3,178,464, Pierpoint); a platinum-containing complex prepared by
reacting chloroplatinic acid with an alcohol, ether, aldehyde, or
mixtures thereof (U.S. Pat. No. 3,220,972, Lamoreaux); a platinum
compound selected from trimethylplatinum iodide and
hexamethyldiplatinum (U.S. Pat. No. 3,313,773, Lamoreaux); a
hydrocarbyl or halohydrocarbyl nitrile-platinum (II) halide complex
(U.S. Pat. No. 3,410,886, Joy); a hexamethyl-dipyridine-diplatinum
iodide (U.S. Pat. No. 3,567,755, Seyfried et al); a platinum curing
catalyst obtained from the reaction of chloroplatinic acid and a
ketone having up to 15 carbon atoms (U.S. Pat. No. 3,814,731,
Nitzsche et al); a platinum compound having the general formula
(R')PtX.sub.2 where R' is a cyclic hydrocarbon radical or
substituted cyclic hydrocarbon radical having two aliphatic
carbon-carbon double bonds, and X is a halogen or alkyl radical
(U.S. Pat. No. 4,276,252, Kreis et al); platinum alkyne complexes
(U.S. Pat. No. 4,603,215, Chandra et al.); platinum
alkenylcyclohexene complexes (U.S. Pat. No. 4,699,813, Cavezzan);
and a colloidal hydrosilylation catalyst provided by the reaction
between a silicon hydride or a siloxane hydride and a platinum (0)
or platinum (II) complex (U.S. Pat. No. 4,705,765, Lewis).
[0029] Although these platinum complexes and many others are useful
as catalysts in processes for accelerating the thermally-activated
addition reaction between the compounds containing silicon-bonded
hydrogen and compounds containing aliphatic unsaturation, processes
for promoting the ultraviolet or visible radiation-activated
addition reaction between these compounds may be preferable in some
instances. Platinum complexes that can be used to initiate
ultraviolet radiation-activated hydrosilation reactions have been
disclosed, e.g., platinum azo complexes (U.S. Pat. No. 4,670,531,
Eckberg); (.eta..sup.4-cyclooctadiene)diarylplatinum complexes
(U.S. Pat. No. 4,530,879, Drahnak); and
(.eta..sup.5-cyclopentadienyl)trialkylplatinum complexes (U.S. Pat.
No. 4,510,094, Drahnak). Other compositions that are curable by
ultraviolet radiation include those described in U.S. Pat. Nos.
4,640,939 and 4,712,092 and in European Patent Application No.
0238033. U.S. Pat. No. 4,916,169 (Boardman et al) describes
hydrosilylation reactions activated by visible radiation. U.S. Pat.
No. 6,376,569 (Oxman et al.) describes a process for the actinic
radiation-activated addition reaction of a compound containing
silicon-bonded hydrogen with a compound containing aliphatic
unsaturation, said addition being referred to as hydrosilylation,
the improvement comprising using, as a platinum hydrosilylation
catalyst, an
(.eta..sup.5-cyclopentadienyl)tri(.sigma.-aliphatic)platinum
complex, and, as a reaction accelerator, a free-radical
photoinitiator capable of absorbing actinic radiation, i.e., light
having a wavelength ranging from about 200 nm to about 800 nm. The
process can also employ, as a sensitizer, a compound that absorbs
actinic radiation, and that is capable of transferring energy to
the aforementioned platinum complex or platinum
complex/free-radical photoinitiator combination, such that the
hydrosilylation reaction is initiated upon exposure to actinic
radiation. The process is applicable both to the synthesis of low
molecular weight compounds and to the curing of high molecular
weight compounds, i.e., polymers.
[0030] Sometimes it is useful to include in the composition
additives to improve the bath life or working time of the
hydrosilylation curable composition. Such hydrosilylation
inhibitors are well known in the art and include such compounds as
acetylenic alcohols, certain polyolefinic siloxanes, pyridine,
acrylonitrile, organic phosphines and phosphites, unsaturated
amides, and alkyl maleates. For example, an acetylenic alcohol
compound can inhibit certain platinum catalysts and prevent curing
from occurring at low temperatures. Upon heating, the composition
begins to cure. The amount of catalyst inhibitor can vary up to
about 10 times or more of the amount of catalyst, depending upon
the activity of the catalyst and the shelf life desired for the
composition.
[0031] The curable silicone adhesive can be at least one free
radical-cure silicone adhesive comprising a polysiloxane polymer or
oligomer having free-radically polymerizable, ethylenically
unsaturated groups such as vinyl, allyl, (meth)acryloyl, etc.
pendent from the polymer chain and/or the terminal ends. It is
desirable for a free radical catalyst to be included for initiating
free radical polymerization when the adhesive is to be thermally or
radiation (e.g., UV or photo) cured. Optionally, a small percentage
of a free radically polymerizable vinyl monomer can be included. In
addition, a free radically polymerizable cross-linking agent may
also be included.
[0032] Ethylenically unsaturated free radically polymerizable
silicones, including especially the acrylated polysiloxane
oligomers and polymers containing terminal and/or pendant
ethylenically unsaturated groups, such as acrylate or methacrylate
groups, can be prepared by a variety of methods, generally through
the reaction of chloro-, silanol-, aminoalkyl-, epoxyalkyl-,
hydroxyalkyl-, vinyl-, or silicon hydride-functional polysiloxanes
with a corresponding (meth)acryloyl-functional capping agent. These
preparations are reviewed in a chapter entitled "Photopolymerizable
Silicone Monomers, Oligomers, and Resins" by A. F. Jacobine and S.
T. Nakos in Radiation Curing Science and Technology (1992), Plenum:
N.Y., pp. 200-214. Preferred acrylated polysiloxane oligomers
include those acryl-modified polydimethylsiloxane resins
commercially available from Goldschmidt under the TEGO RC
designation and those acrylamido-terminated monofunctional and
difunctional polysiloxanes described in U.S. Pat. No. 5,091,483
(Mazurek et al.).
[0033] The curable silicone adhesive can be at least one
condensation-cure silicone adhesive. Condensation-curable silicones
usually comprise pendent or terminal groups such as, for example,
hydroxysilane (i.e., silanol), alkoxysilane or acyloxysilane
functional groups that react in the presence of moisture to form
cured (i.e., crosslinked) materials. Condensation-curable
compositions comprising alkoxysilane or acyloxysilane functionality
typically cure in two reactions. In the first reaction, the
alkoxysilane or acyloxysilane groups hydrolyze in the presence of
moisture and a catalyst to form compounds having silanol groups. In
the second reaction, the silanol groups condense with other
silanol, alkoxysilane, or acyloxysilane groups in the presence of a
catalyst to form --Si--O--Si-- linkages. The two reactions occur
essentially simultaneously upon generation of the
silanol-functional compound. Commonly used catalysts for the two
reactions include Bronsted and Lewis acids and are described in the
Encyclopedia of Polymer Science and Engineering, 2nd Edition,
Volume 15, page 252, (1989). A single material may catalyze both
reactions.
[0034] A variety of approaches have been used for providing
condensation-curable compositions that have acceptable cure rates
without processing and storage difficulties. For example, U.S. Pat.
No. 2,843,555 describes a two-part system, one part comprising a
functional polymer and the other part comprising a catalyst with
the two parts being mixed just prior before use. U.S. Pat. No.
5,286,815 discloses an ammonium salt catalyst that is inactive
until heated sufficiently to liberate an acid compound that
initiates the moisture curing reaction. Alternatively, the
condensation-curing agent can be a multifunctional cross-linking
agent (e.g., an aminosilane) that serves as both catalyst and
cross-linker.
[0035] U.S. Pat. No. 6,204,350 (Liu et al.), incorporated herein by
reference, describes cure-on-demand, moisture-curable compositions
of one or more compounds comprising molecules having reactive
silane functional groups and an acid generating material are taught
therein. The acid generating material releases an acid upon
exposure to heat, ultraviolet light, visible light, electron beam
irradiation or microwave irradiation to initiate and accelerate the
crosslinking reaction.
[0036] The curable silicone adhesive can be at least one
cationic-cure silicone adhesive. Cationic-curable silicones usually
comprise pendent or terminal groups such as, for example, epoxy,
alkenyl ether, oxetane dioxolane, and/or carbonate functional
groups that react in the presence of a cationic catalyst to form
cured (i.e., crosslinked) materials. If desired, the cationic
curable silicone may further comprise a MQ resin to improve the
strength of the cured silicone (joining layer).
[0037] The epoxysilicones may be prepared by many methods known in
the art such as the chloroplatinic acid catalyzed addition reaction
of hydride functional silicones with aliphatically unsaturated
epoxy compounds, or the epoxidation of vinyl or like unsaturated
siloxanes and Grignard type reactions as for example described by
E. P. Plueddemann and G. Fanger, J. Am. Chem. Soc. 81, 2632-35
(1959). A convenient method is the hydrosiloxane addition reaction
of unsaturated aliphatic epoxy compounds with hydride-functional
silicone oligomers. When this method is used, it is preferred that
essentially complete reaction of the SiH sites are accomplished
although small amounts of hydrogen attached to silicon can be
present. It is also preferred for best results that the
epoxysilicone is essentially free from low molecular weight
components such as cyclic siloxanes, since their presence in the
final cured coating could adversely affect the adhesion property of
the adhesive (resulting in adhesive loss or buildup).
[0038] U.S. Pat. No. 5,409,773 (Kessel et al.) describes one or
more epoxysilicones having cycloaliphatic and non-cycloaliphatic
epoxy groups in a total number which is about 5 to 50% of the total
number of siloxane units, the ratio of the total number of
cycloaliphatic epoxy groups to the total number of
non-cycloaliphatic epoxy groups being from about 1:10 to 2:1, the
epoxypolysiloxane(s) being cured in the presence of a catalytically
effective amount of a cationic epoxy curing catalyst.
[0039] An article entitled "Cationic Photopolymerization of
Ambifunctional Monomers" (J. V. Crivello et al., Macromolekular
Symposia, 95, 79-89, (1995)) describes the photopolymerization of
"ambifunctional" monomers (i.e., monomers bearing two chemically
different reactive functional groups within the same molecule)
using cationic catalysts. In one example, an ambifunctional monomer
having both epoxycyclohexyl and trimethoxysilyl reactive functional
groups is prepared and then subsequently UV irradiated in the
presence of a cationic triarylsulfonium catalyst.
[0040] The cured silicone is conveniently obtained by mixing the
cationic curable silicone and catalyst and optionally the
epoxy-terminated silane in a solvent, coating the solution on the
substrate and heating at a suitable curing temperature depending on
the effectiveness of the catalyst and heat sensitivity of the
substrate. Alternatively, the cationic curable silicone may be
cured by means of a photoacid generator, which generates one or
more molecules of a Bronsted or Lewis acid on exposure to UV or
visible light, and without the application of heat. Mixtures of the
epoxypolysiloxanes or mixtures of the epoxysilanes may be used.
[0041] Curing of the cationic curable silicone can be effected by
mixing with conventional cationic epoxy curing catalysts activated
by actinic radiation and/or heat. Catalysts activated by actinic
radiation are preferred. Examples of suitable photoinitiators are
onium salts of a complex halogen acid, particularly the
polyaromatic iodonium and sulfonium complex salts having SbF.sub.6,
SbF.sub.5 OH, PF.sub.6, BF.sub.4, or AsF.sub.6 anions, as are
disclosed in U.S. Pat. No. 4,101,513, incorporated herein by
reference. Preferred photoinitiators are the iodonium and sulfonium
salts most preferably having the SbF.sub.6 anion. Also useful
photoinitiators are organometallic complex salts that are disclosed
in U.S. Pat. No. 5,089,536, and supported photoinitiators for the
actinic radiation activated polymerization of
cationically-polymerizable compounds described in U.S. Pat. No.
4,677,137, both of which are incorporated herein by reference.
Suitable heat-activated cationic catalysts which may be used
include the heat-activated sulfonic and sulfonylic catalysts
described in U.S. Pat. No. 4,313,988, incorporated herein by
reference.
[0042] The substrate to be ground, such as a silicon wafer,
generally has asperities such as circuit patterns on one side. For
the joining layer to fill in the asperities of the substrate to be
ground and rendering the thickness of the joining layer uniform,
the silicone adhesive used for the joining layer is preferably in a
liquid state during coating and laminating and preferably has a
viscosity of less than 10,000 centipoise (cps) at the temperature
(for example, 25.degree. C.) of the coating and laminating
operations. This liquid silicone adhesive is preferably coated by a
spin coating method among various methods known in the art. As such
an adhesive, a UV-curable or a visible light-curable silicone
adhesive are particularly preferred, because the thickness of the
joining layer can be made uniform and moreover, the processing
speed is high.
[0043] The thickness of the joining layer is not particularly
limited as long as it can ensure the thickness uniformity required
for the grinding of the substrate to be ground and the tear
strength necessary for the peeling of the joining layer from the
wafer after removing the support from the laminated body, and can
sufficiently absorb the asperities on the substrate surface. The
thickness of the joining layer is typically from about 10 to about
150 .mu.m, preferably from about 25 to about 100 .mu.m. If desired,
the substrate may be partially sawn through on the face adjacent
the joining layer (circuit face), prior to assembling the laminated
body.
[0044] The substrate may be, for example, a brittle material
difficult to thin by conventional methods. Examples thereof include
semiconductor wafers such as silicon and gallium arsenide, a rock
crystal wafer, sapphire and glass.
[0045] The light transmitting support is a material capable of
transmitting radiation energy, such as a laser beam used in the
present invention, and the material is required to keep the ground
body in a flat state and not cause it to break during grinding and
conveyance. The light transmittance of the support is not limited
as long as it does not prevent the transmittance of a practical
intensity level of radiation energy into the photothermal
conversion layer to enable the decomposition of the photothermal
conversion layer. However, the transmittance is preferably, for
example, 50% or more. Also, in order to prevent the ground body
from warping during grinding, the light transmitting support
preferably has a sufficiently high stiffness and the flexural
rigidity of the support is preferably 2.times.10.sup.-3 (Pam.sup.3)
or more, more preferably 3.times.10.sup.-2 (Pam.sup.3) or more.
Examples of useful supports include glass plates and acrylic
plates. Furthermore, in order to enhance the adhesive strength to
an adjacent layer such as photothermal conversion layer, the
support may be surface-treated with a silane coupling agent or the
like, if desired. In the case of using a UV-curable photothermal
conversion layer or joining layer, the support preferably transmits
ultraviolet radiation.
[0046] The support is sometimes exposed to heat generated in the
photothermal conversion layer when the photothermal conversion
layer is irradiated or when a high temperature is produced due to
frictional heating during grinding. Also, for the purpose of
forming a metal film on the substrate a process such as vapor
deposition, plating or etching may be additionally provided before
separating the ground substrate from the support. Particularly, in
the case of a silicon wafer, the support is sometimes subjected to
a high-temperature process to form an oxide film. Accordingly, a
support having heat resistance, chemical resistance and a low
expansion coefficient is selected. Examples of support materials
having these properties include borosilicate glass available as
Pyrex.TM. and Tenpax.TM. and alkaline earth boro-aluminosilicate
glass such as Corning.TM. #1737 and #7059.
[0047] To obtain the desired thickness uniformity after grinding of
the substrate, the thickness of the support is preferably uniform.
For example, for grinding a silicon wafer to 50 .mu.m or less and
attaining evenness of .+-.10% or less, the variability in the
thickness of the support should be reduced to .+-.2 .mu.m or less.
In the case where the support is repeatedly used, the support also
preferably has scratch resistance. For repeatedly using the
support, the wavelength of the radiation energy and the support may
be selected to suppress the damage to the support by the radiation
energy. For example, when Pyrex glass is used as the support and a
third harmonic generation YAG laser (355 nm) is employed, the
separation of the support and the substrate can be performed,
however, such a support exhibits low transmittance at the
wavelength of this laser and absorbs the radiation energy, as a
result, the support is thermally damaged and cannot be reused in
some cases.
[0048] The photothermal conversion layer contains a light absorbing
agent and a heat decomposable resin. Radiation energy applied to
the photothermal conversion layer in the form of a laser beam or
the like is absorbed by the light absorbing agent and converted
into heat energy. The heat energy generated abruptly elevates the
temperature of the photothermal conversion layer and the
temperature reaches the thermal decomposition temperature of the
heat decomposable resin (organic component) in the photothermal
conversion layer resulting in heat decomposition of the resin. The
gas generated by the heat decomposition is believed to form a void
layer (such as air space) in the photothermal conversion layer and
divide the photothermal conversion layer into two parts, whereby
the support and the substrate are separated.
[0049] The light-absorbing agent absorbs radiation energy at the
wavelength used. The radiation energy is usually a laser beam
having a wavelength of 300 to 11,000 nanometers (nm), preferably
300 to 2,000 nm and specific examples thereof include a YAG laser
which emits light at a wavelength of 1,064 nm, a second harmonic
generation YAG laser at a wavelength of 532 nm, and a semiconductor
laser at a wavelength of 780 to 1,300 nm. Although the light
absorbing agent varies depending on the wavelength of the laser
beam, examples of the light absorbing agent which can be used
include carbon black, graphite powder, microparticle metal powders
such as iron, aluminum, copper, nickel, cobalt, manganese,
chromium, zinc and tellurium, metal oxide powders such as black
titanium oxide, and dyes and pigments such as an aromatic
diamino-based metal complex, an aliphatic diamine-based metal
complex, an aromatic dithiol-base metal complex, a
mercaptophenol-based metal complex, a squarylium-based compound, a
cyanine-based dye, a methine-based dye, a naphthoquinone-based dye
and an anthraquinone-based dye. The light-absorbing agent may be in
the form of a film including a vapor deposited metal film. Among
these light-absorbing agents, carbon black is particularly useful,
because the carbon black significantly decreases the force
necessary for separating the substrate from the support after the
irradiation and accelerates the separation.
[0050] The concentration of the light-absorbing agent in the
photothermal conversion layer varies depending on the kind,
particle state (structure) and dispersion degree of the light
absorbing agent but the concentration is usually from 5 to 70 vol.
% in the case of general carbon black having a particle size of
approximately from 5 to 500 nm. If the concentration is less than 5
vol. %, heat generation of the photothermal conversion layer may be
insufficient for the decomposition of the heat decomposable resin,
whereas if it exceeds 70 vol. %, the photothermal conversion layer
becomes poor in the film-forming property and may readily cause
failure of adhesion to other layers. In the case where the adhesive
used as the joining layer is a UV-curable adhesive, if the amount
of carbon black is excessively large, the transmittance of the
ultraviolet ray for curing the adhesive decreases. Therefore, in
the case of using a UV-curable silicone adhesive as the joining
layer, the amount of carbon black should be 60 vol. % or less. In
order to reduce the force at the time of removing the support after
irradiation and thereby prevent abrasion of the photothermal
conversion layer during grinding (such as abrasion due to abrasive
in wash water), carbon black is preferably contained in the
photothermal conversion layer in an amount of 20 to 60 vol. %, more
preferably from 35 to 55 vol. %.
[0051] Examples of the heat decomposable resin which can be used
include gelatin, cellulose, cellulose ester (e.g., cellulose
acetate, nitrocellulose), polyphenol, polyvinyl butyral, polyvinyl
acetal, polycarbonate, polyurethane, polyester, polyorthoester,
polyacetal, polyvinyl alcohol, polyvinylpyrrolidone, a copolymer of
vinylidene chloride and acrylonitrile, poly(meth)acrylate,
polyvinyl chloride, silicone resin and a block copolymer comprising
a polyurethane unit. These resins can be used individually or in
combination of two or more thereof. The glass transition
temperature (Tg) of the resin is preferably room temperature
(20.degree. C.) or more so as to prevent the re-adhesion of the
photothermal conversion layer once it is separated due to the
formation of a void layer as a result of the thermal decomposition
of the heat decomposable resin, and the Tg is more preferably
100.degree. C. or more so as to prevent the re-adhesion. In the
case where the light transmitting support is glass, in order to
increase the adhesive force between the glass and the photothermal
conversion layer, a heat decomposable resin having within the
molecule a polar group (e.g., --COOH, --OH) capable of
hydrogen-bonding to the silanol group on the glass surface can be
used. Furthermore, in applications requiring a chemical solution
treatment such as chemical etching, in order to impart chemical
resistance to the photothermal conversion layer, a heat
decomposable resin having within the molecule a functional group
capable of self-crosslinking upon heat treatment, a heat
decomposable resin capable of being crosslinked by ultraviolet or
visible light, or a precursor thereof (e.g., a mixture of monomers
and/or oligomers) may be used. For forming the photothermal
conversion layer as an adhesive photothermal conversion layer as
shown in FIG. 1(e), an adhesive polymer formed from
poly(meth)acrylate or the like, as may be used for the heat
decomposable resin, is employed.
[0052] The photothermal conversion layer may contain a transparent
filler, if desired. The transparent filler acts to prevent the
re-adhesion of the photothermal conversion layer once it is
separated due to the formation of a void layer as a result of the
thermal decomposition of the heat decomposable resin. Therefore,
the force required for the separation of the substrate and the
support, after grinding of the substrate and subsequent
irradiation, can be further reduced. Furthermore, since the
re-adhesion can be prevented, the latitude in the selection of the
heat decomposable resin is broadened. Examples of the transparent
filler include silica, talc and barium sulfate. Use of the
transparent filler is particularly advantageous when a UV or
visible-curable adhesive is used as the joining layer. Further
information regarding the use of transparent fillers may be had
with reference to Assignee's published application U.S.
2005/0233547 (Noda et al.), incorporated herein by reference, and
WO 2005057651.
[0053] The photothermal conversion layer may contain other
additives, if desired. For example, in the case of forming the
layer by coating a heat decomposable resin in the form of a monomer
or an oligomer and thereafter polymerizing or curing the resin, the
layer may contain a photo-polymerization initiator. Also, the
addition of a coupling agent (integral blend method, i.e., the
coupling agent is used as an additive in the formulation rather
than as a pre-surface-treatment agent) for increasing the adhesive
force between the glass and the photothermal conversion layer, and
the addition of a crosslinking agent for improving the chemical
resistance are effective for their respective purposes.
Furthermore, in order to promote the separation by the
decomposition of the photothermal conversion layer, a
low-temperature gas generator may be contained. Representative
examples of the low-temperature gas generator that can be used
include a foaming agent and a sublimating agent. Examples of the
foaming agent include sodium hydrogencarbonate, ammonium carbonate,
ammonium hydrogencarbonate, zinc carbonate, azodicarbonamide,
azobisisobutylonitrile, N,N'-dinitrosopentamethylenetetramine,
p-toluenesulfonylhydrazine and
p,p-oxybis(benzenesulfonylhydrazide). Examples of the sublimating
agent include 2-diazo-5,5-dimethylcyclohexane-1,3-dione, camphor,
naphthalene, borneol, butyramide, valeramide, 4-tert-butylphenol,
furan-2-carboxylic acid, succinic anhydride, 1-adamantanol and
2-adamantanone.
[0054] The photothermal conversion layer can be formed by mixing
the light absorbing agent such as carbon black, the heat
decomposable resin and a solvent to prepare a precursor coating
solution, coating this solution on the support, and drying it.
Also, the photothermal conversion layer can be formed by mixing the
light absorbing agent, a monomer or an oligomer as a precursor
material for the heat decomposable resin and, optionally, additives
such as photo-polymerization initiator, and a solvent, if desired,
to prepare a precursor coating solution in place of the heat
decomposable resin solution, coating the solution on the support,
drying and polymerizing/curing it. For the coating, a general
coating method suitable for coating on a hard support, such as spin
coating, die coating, and roll coating, can be used.
[0055] In general, the thickness of the photothermal conversion
layer is not limited as long as it permits the separation of the
support and the substrate, but it is usually 0.1 .mu.m or more. If
the thickness is less than 0.1 .mu.m, the concentration of the
light-absorbing agent required for sufficient light absorption
becomes high and this deteriorates the film-forming property, and
as a result, adhesion to the adjacent layer may fail. On the other
hand, if the thickness of the photothermal conversion layer is 5
.mu.m or more while keeping constant the concentration of the
light-absorbing agent required to permit the separation by the
thermal decomposition of the photothermal conversion layer, the
light transmittance of the photothermal conversion layer (or a
precursor thereof) becomes low. As a result, when a photo-curable,
for example, an ultraviolet (UV)-curable photothermal conversion
layer, and a joining layer are used, the curing process is
sometimes inhibited to the extent that a sufficiently cured product
cannot be obtained. Therefore, in the case where the photothermal
conversion layer is, for example, ultraviolet-curable, in order to
minimize the force required to separate the substrate from the
support after irradiation and to prevent the abrasion of the
photothermal conversion layer during grinding, the thickness of the
photothermal conversion layer is preferably from about 0.3 to about
3 .mu.m, more preferably from about 0.5 to about 2.0 .mu.m.
[0056] Since the substrate to be ground of the laminated body of
the present invention can be a wafer having formed thereon a
circuit, the wafer circuit may be damaged by radiation energy such
as a laser beam reaching the wafer through the light transmitting
support, the photothermal conversion layer and the joining layer.
To avoid such circuit damage, a light absorbing dye capable of
absorbing light at the wavelength of the radiation energy or a
light reflecting pigment capable of reflecting the light may be
contained in any of the layers constituting the laminated body or
may be contained in a layer separately provided between the
photothermal conversion layer and the wafer. Examples of light
absorbing dyes include dyes having an absorption peak in the
vicinity of the wavelength of the laser beam used (for example,
phthalocyanine-based dyes and cyanine-based dyes). Examples of
light reflecting pigments include inorganic white pigments such as
titanium oxide.
[0057] The laminated body of the present invention may comprise
additional layers other than the substrate to be ground, the
joining layer in contact with the substrate to be ground, the
photothermal conversion layer and the light transmitting support.
Examples of the additional layer include a first intermediate layer
(not shown) between the joining layer 3 and the photothermal
conversion layer 4, and/or a second intermediate layer (not shown)
provided between the photothermal conversion layer 4 and the
support 5. The second intermediate layer is preferably joined to
the support 5 through a joining layer 3.
[0058] In the case where the first intermediate layer is provided,
the laminated body 1 is separated at the photothermal conversion
layer 4 after the irradiation and a laminated body of first
intermediate layer/joining layer 3/substrate 2 is obtained.
Therefore, the first intermediate layer acts as a backing during
the separation of the joining layer 3 from substrate 2 and enables
the easy separation of the two. The first intermediate layer is
preferably a multilayer optical film. Also, the first intermediate
layer is preferably a film which selectively reflects the radiation
energy used to enable the separation, such as YAG laser (near
infrared wavelength light). This film is preferred because when the
first intermediate layer does not transmit but reflects radiation
energy, the radiation energy is prevented from reaching the wafer
surface, where circuitry is present, and this eliminates the
possibility of damage to the circuitry.
[0059] In the case of using a photocurable silicone adhesive as the
joining layer 3, a film having a sufficiently high transmittance
for curing light such as ultraviolet light is preferred.
Accordingly, the multilayer optical film is preferably transmissive
to ultraviolet light and selectively reflects near infrared light.
The preferred multilayer optical film which is transmissive to
ultraviolet light and reflects near infrared light is available as
3M.TM. Solar Reflecting Film (3M Company, St. Paul, Minn.). The
first intermediate layer functions as a substrate for the removal
of joining layer 3 from substrate 2 by peeling and therefore,
preferably has a thickness of 20 .mu.m or more, more preferably 30
.mu.m or more, and a breaking strength of 20 MPa or more, more
preferably 30 MPa or more, still more preferably 50 MPa or
more.
[0060] In the case where the above-described second intermediate
layer is provided, a laminated body of second intermediate
layer/joining layer 3/light transmitting support 5 is obtained
after the irradiation of the laminated body 1. Therefore, the
second intermediate layer acts as a backing during the separation
of the joining layer 3 and support 5 and enables the easy
separation of the two. As such, by providing a second intermediate
layer, the photothermal conversion layer 4 or the joining layer 3
(curable silicone adhesive) is prevented from remaining on the
light transmitting support 5, and the support 5 can be easily
recycled. In order to enable the removal of joining layer 3 from
support 5 by peeling them apart after the laser irradiation and
without rupturing, the second intermediate layer preferably has a
thickness of 20 .mu.m or more, more preferably 30 .mu.m or more,
and a breaking strength of 20 MPa or more, more preferably 30 MPa
or more, still more preferably 50 MPa or more. In some cases, the
resin of the second intermediate layer permeates into the
photothermal conversion layer 4, such as when the second
intermediate layer is coated as a mixture of photocurable oligomer
and monomer and cured with UV (e.g., when the sheet is produced by
coating photothermal conversion layer on the film substrate,
coating the second intermediate layer on photothermal conversion
layer and curing it, and coating the joining layer on the second
intermediate layer). In such cases, in order to prevent re-adhering
of the surface separated with a space formed by the laser
irradiation, the Tg of the resin (in the case of a photocurable
resin, the Tg of the cured resin) may be 40.degree. C. or more.
[0061] In the manufacture of the laminated body, it is important to
prevent undesirable foreign substances such as air from entering
between layers. For example, if air enters between layers, the
thickness uniformity of the laminated body is prevented and the
substrate to be ground cannot be ground to a thin substrate. In the
case of manufacturing a laminated body shown in FIG. 1, the
following method, for example, may be considered. First, the
precursor coating solution of the photothermal conversion layer is
coated on the support by any one of the methods known in the art,
dried and cured by irradiating with ultraviolet light or the like.
Thereafter, the curable silicone adhesive is coated on either one
or both of the surface of the cured photothermal conversion layer
and the surface of the substrate in the non-ground side. The
photothermal conversion layer and the substrate are attached
through the curable silicone adhesive, which is then cured to form
the joining layer, for example, by irradiating with ultraviolet
light from the support side, whereby a laminated body can be
formed. The formation of such a laminated body is preferably
performed under vacuum to prevent air from entering between layers.
This can be attained by, for example, by modifying a vacuum
adhesion device such as that described in Japanese Unexamined
Patent Publication (Kokai) No. 11-283279.
[0062] The laminated body is preferably designed such that it is
free from the invasion of water used during grinding of the
substrate, has an adhesive strength between layers so as not to
cause dropping off of the substrate, and has an abrasion resistance
so as to prevent the photothermal conversion layer from being
abraded by the water flow (slurry) containing dusts of the ground
substrate.
[0063] A thinned substrate can be manufactured by the method
comprising preparing a laminated body formed as above, grinding the
substrate, to a desired thickness, applying radiation energy to the
photothermal conversion layer through the light transmitting
support to decompose the photothermal conversion layer and thereby
to separate the ground substrate from the light transmitting
support, and peeling the joining layer from the substrate.
[0064] In one aspect, the method of the present invention is
described below by referring to the drawings. In the following, a
laser beam is used as the radiation energy source and a silicon
wafer is used as the substrate to be ground, however, the present
invention is not limited thereto.
[0065] FIG. 2 shows a cross-sectional view of a vacuum adhesion
device suitable for the production of the laminated body of one
embodiment of the present invention. A vacuum adhesion device 20
comprises a vacuum chamber 21; a supporting part 22 provided in the
vacuum chamber 21, on which either one of a substrate 2 to be
ground (silicon wafer) or a support 5 is disposed; and
holding/releasing means 23 provided in the vacuum chamber 21 and
movable in the vertical direction at the upper portion of the
supporting part 22, which holds the other one of the support 5 or
the silicon wafer 2. The vacuum chamber 21 is connected to a
pressure reducing device 25 via pipe 24, so that the pressure
inside the vacuum chamber 21 can be reduced. The holding/releasing
means 23 has a shaft 26 movable up and down in the vertical
direction, a contact surface part 27 provided at the distal end of
the shaft 26, leaf springs 28 provided in the periphery of the
contact surface part 27, and holding claws 29 extending from each
leaf spring 28. As shown in FIG. 2(a), when the leaf springs are in
contact with the upper surface of the vacuum chamber 21, the leaf
springs are compressed and the holding claws 29 are directed toward
the vertical direction to hold the support 5 or the wafer 2 at
peripheral edges. On the other hand, as shown in FIG. 2(b), when
the shaft 26 is pressed down and the support 5 or the wafer 2 is in
close proximity to the wafer 2 or the support 5 respectively
disposed on the supporting part, the holding claws 29 are released
together with the leaf springs 28 to superimpose the support 5 and
the wafer 2.
[0066] Using this vacuum adhesion device 20, the laminated body can
be manufactured as follows. First, as described above, a
photothermal conversion layer is provided on a support 5.
Separately, a wafer to be laminated is prepared. On either one or
both of the wafer 2 and the photothermal conversion layer of the
support 5, an adhesive for forming a joining layer is applied. The
thus-prepared support 5 and wafer 2 are disposed in the vacuum
chamber 21 of the vacuum adhesion device 20 as shown in FIG. 2(a),
the pressure is reduced by the pressure reducing device, the shaft
26 is pressed down to laminate the wafer as shown in FIG. 2(b) and
after opening to air, the adhesive is cured, if desired, to obtain
a laminated body.
[0067] FIG. 3 shows a partial cross-sectional view of a grinding
device useful in an embodiment of the invention. The grinding
device 30 comprises a pedestal 31 and a grinding wheel 33 rotatably
mounted on the bottom end of a spindle 32. A suction port 34 is
provided beneath the pedestal 31 and the suction port 34 is
connected to a pressure reducing device (not shown), whereby a
material to be ground is suctioned and fixed on the pedestal 31 of
the grinding device 30. The laminated body 1 of the present
invention as shown in FIG. 1 is prepared and used as a material to
be ground. The support side of the laminated body 1 is mounted on
the pedestal 31 of the grinding device 30 and fixed by suction
using a pressure-reducing device. Thereafter, while feeding a fluid
flow (such as water or any solution known useful in wafer
grinding), the grinding wheel 33 under rotation is brought into
contact with the laminated body 1, thereby performing the grinding.
The grinding can be performed to a thin level of 150 .mu.m or less,
preferably 50 .mu.m or less, more preferably 25 .mu.m or less.
[0068] After grinding to the desired level, the laminated body 1 is
removed and conveyed to subsequent steps, where the separation of
the wafer and the support by irradiation with a laser beam and the
peeling of the joining layer from the wafer are performed. FIG. 4
shows a drawing of the steps of separating the support and peeling
of the joining layer. First, by taking account of the final step of
dicing, a die bonding tape 41 is disposed, if desired, on the
ground surface of the wafer side of the laminated body 1 (FIG.
4(a)) or the die bonding tape 41 is not disposed (FIG. 4(a')), and
thereafter, a dicing tape 42 and a dicing frame 43 are disposed
(FIG. 4(b)). Subsequently, a laser beam 44 is irradiated from the
support side of the laminated body 1 (FIG. 4(c)). After the
irradiation of the laser beam, the support 5 is picked up to
separate the support 5 from the wafer 2 (FIG. 4(d)). Finally, the
joining layer 3 is separated by peeling to obtain a thinned silicon
wafer 2 (FIG. 4(e)).
[0069] Usually, a semiconductor wafer such as silicon wafer is
subjected to chamfering called beveling so as to prevent edges from
damage due to impact. That is, the corners at edge parts of a
silicon wafer are rounded. When a liquid adhesive is used as the
joining layer and coated by spin coating, the joining layer is
spread to the edge parts and the adhesive is exposed to edge parts
of the grinding surface. As a result, in disposing a dicing tape,
not only the ground wafer but also the exposed adhesive come into
contact with the pressure-sensitive adhesive of the dicing tape.
When the adhesion of the dicing tape used is strong, the joining
layer is sometimes difficult to separate. In such a case, it is
preferred to previously remove a part of the exposed adhesive
before disposing a dicing tape and a dicing frame. For the removal
of the exposed adhesive at edge parts, using radiation energy or a
CO.sub.2 laser (wavelength of 10.6 .mu.m) which the adhesive can
sufficiently absorb.
[0070] FIG. 5 shows a cross-sectional view of a laminated body
fixing device which can be used, for example, in the step of
irradiating, such as with a laser beam in one aspect of the
invention. The laminated body 1 is mounted on a fixing plate 51
such that the support comes as the upper surface with respect to
the fixing device 50. The fixing plate 51 is made of a porous metal
such as sintered metal or a metal having surface roughness. The
pressure is reduced from the lower part of the fixing plate 51 by a
vacuum device (not shown), whereby the laminated body 1 is fixed by
suction onto the fixing plate 51. The vacuum suction force is
preferably strong enough not to cause dropping in the subsequent
steps of separating the support and peeling of the joining layer. A
laser beam is used to irradiate the laminated body fixed in this
manner. For emitting the laser beam, a laser beam source having an
output high enough to cause decomposition of the heat decomposable
resin in the photothermal conversion layer at the wavelength of
light absorbed by the photothermal conversion layer is selected, so
that a decomposition gas can be generated and the support and the
wafer can be separated. For example, a YAG laser (wavelength of
1,064 nm), a second harmonic YAG laser (wavelength: 532 nm) and a
semiconductor laser (wavelength: from 780 to 1,300 nm) can be
used.
[0071] As the laser irradiation device, a device capable of
scanning a laser beam to form a desired pattern on the irradiated
surface and capable of setting the laser output and the beam moving
speed is selected. Also, in order to stabilize the processing
quality of the irradiated material (laminated body), a device
having a large focus depth is selected. The focus depth varies
depending on the dimensional precision in the design of device and
is not particularly limited but the focus depth is preferably 30
.mu.m or more. FIG. 6 shows a perspective view of a laser
irradiation device which can be used in the present invention. The
laser irradiation device 60 of FIG. 6(a) is equipped with a
galvanometer having a biaxial configuration composed of the X axis
and the Y axis and is designed such that a laser beam oscillated
from a laser oscillator 61 is reflected by the Y axis galvanometer
62, further reflected by the X axis galvanometer 63 and irradiated
on the laminated body 1 on the fixing plate. The irradiation
position is determined by the directions of the galvanometers 62
and 63. The laser irradiation device 60 of FIG. 6(b) is equipped
with a uniaxial galvanometer or a polygon mirror 64 and a stage 66
movable in the direction orthogonal to the scanning direction. A
laser beam from the laser oscillator 61 is reflected by the
galvanometer or polygon 64, further reflected by a hold mirror 65
and irradiated on the laminated body 1 on the movable stage 66. The
irradiation position is determined by the direction of the
galvanometer or polygon 64 and the position of the movable stage
66. In the device of FIG. 6(c), a laser oscillator 61 is mounted on
a movable stage 66 which moves in the biaxial direction of X and Y,
and a laser is irradiated on the entire surface of the laminated
body 1. The device of FIG. 6(d) comprises a fixed laser oscillator
61 and a movable stage 66 which moves in the biaxial direction of X
and Y. The device of FIG. 6(e) has a constitution such that a laser
oscillator 61 is mounted on a movable stage 66' which can move in
the uniaxial direction and a laminated body 1 is mounted on a
movable stage 66'' which can move in the direction orthogonal to
the movable stage 66'.
[0072] When there is concern about damaging the wafer of the
laminated body 1 by the laser irradiation, a top hat form (see FIG.
6(f)) having a steep energy distribution and very reduced leakage
energy to the adjacent region is preferably formed. The beam form
may be changed by any known method, for example, by (a) a method of
deflecting the beam by an acousto-optic device, a method of forming
a beam using refraction/diffraction, or (b) a method of cutting the
broadening portion at both edges by using an aperture or a
slit.
[0073] The laser irradiation energy is determined by the laser
power, the beam scanning speed and the beam diameter. For example,
the laser power that can be used is, but not limited to, from 0.3
to 100 watts (W), the scanning speed is from 0.1 to 40
meters/second (m/s), and the beam diameter is from 5 to 300 .mu.m
or more. In order to increase the speed of this step, the laser
power is enhanced and thereby the scanning speed is increased.
Since the number of scans can be further reduced as the beam
diameter becomes larger, the beam diameter may be increased when
the laser power is sufficiently high.
[0074] The heat decomposable resin in the photothermal conversion
layer is decomposed by the laser irradiation to generate a gas that
creates cracks inside the layer to separate the photothermal
conversion layer itself. If air enters in between the cracks,
re-adhesion of the cracks can be prevented. Therefore, in order to
facilitate the entering of air, it is desirable to perform the beam
scanning from the edge part of the laminated body to the interior
of the laminated body.
[0075] As described above, the glass transition temperature (Tg) of
the photothermal conversion layer is preferably room temperature
(20.degree. C.) or more. This is because the separated cracks may
re-adhere to one another during the cooling of the decomposed resin
and make the separation impossible. The re-adhesion is considered
to occur due to the fact that the cracks of the photothermal
conversion layer become attached with each other under the weight
of the support. Therefore, the re-adhesion can be prevented when
the irradiation process is contrived not to impose the weight of
the support, for example, by performing the laser irradiation in
the vertical direction from the lower part to the upper part
(namely, by performing the laser irradiation in a configuration
such that the support comes to the bottom side) or by inserting a
hook between the wafer and the photothermal conversion layer from
the edge part and lifting the layer.
[0076] To employ a laser beam from the edge part of the laminated
body, a method of applying the laser beam while linearly
reciprocating it from the edge part to the tangential direction of
wafer or, alternatively, a method of spirally irradiating the laser
beam from the edge part to the center like a phonograph record may
be used.
[0077] After the laser irradiation, the support is separated from
the wafer and for this operation a general pick-up using a vacuum
is used. The pick-up is a cylindrical member connected to a vacuum
device having a suction device at the distal end. FIG. 7 shows a
schematic view of a pick-up for use in the separation operation of
the wafer and the support. In the case of FIG. 7(a), the pick-up 70
is in the center of the support 5 and picked up in the vertical
direction, thereby peeling off the support. Also, as shown in FIG.
7(b), the pick-up 70 is at the edge part of the support 5 and by
peeling while blowing a compressed air (A) from the side to enter
air between the wafer 2 and the support 5, the support can be more
easily peeled off.
[0078] After removing the support, the joining layer on the wafer
is removed. FIG. 8 is a schematic view showing how the joining
layer is peeled. For the removal of the joining layer 3,
preferably, an adhesive tape 80 for removing the joining layer,
which can create a stronger adhesive bond with joining layer 3 than
the adhesive bond between the wafer 2 and the joining layer 3, can
be used. Such an adhesive tape 80 is placed to adhere onto the
joining layer 3 and then peeled in the arrow direction, whereby the
joining layer 3 is removed.
[0079] Finally, a thinned wafer remains in the state of being fixed
to a dicing tape or a die frame with or without a die bonding tape.
This wafer is diced in a usual manner, thereby completing a chip.
However, the dicing may be performed before the laser irradiation.
In such a case, it is also possible to perform the dicing step
while leaving the wafer attached to the support, then subject only
the diced region to the laser irradiation and separate the support
only in the diced portion. The present invention may also be
applied separately to a dicing step without using a dicing tape, by
re-transferring through a joining layer the ground wafer onto a
light transmitting support having provided thereon a photothermal
conversion layer.
[0080] The present invention is effective, for example, in the
following applications.
1. Laminated CSP (Chip Size Package) for High-Density Packaging
[0081] The present invention is useful, for example, with a device
form called system-in-package where a plurality of Large Scale
Integrated (LSI) devices and passive parts are housed in a single
package to realize multifunction or high performance, and is called
a stacked multi-chip package. According to the present invention, a
wafer of 25 .mu.m or less can be reliably manufactured in a high
yield for these devices.
2. Through-Type CSP Requiring High Function and High-Speed
Processing
[0082] In this device, the chips are connected by a through
electrode, whereby the wiring length is shortened and the
electrical properties are improved. To solve technical problems,
such as formation of a through hole for forming a through electrode
and embedding of copper in the through hole, the chip may be
further reduced in the thickness. In the case of sequentially
forming chips having such a configuration by using the laminated
body of the present invention, an insulating film and a bump
(electrode) may be formed on the back surface of the wafer and the
laminated body needs resistance against heat and chemicals. Even in
this case, when the above-described support, photothermal
conversion layer and joining layer are selected, the present
invention can be effectively applied.
3. Thin Compound Semiconductor (e.g. GaAs) Improved in Heat
Radiation Efficiency, Electrical Properties and Stability
[0083] Compound semiconductors such as gallium arsenide are being
used for high-performance discrete chips, laser diode and the like
because of their advantageous electrical properties (high electron
mobility, direct transition-type band structure) over silicon.
Using the laminated body of the present invention and thereby
reducing the thickness of the chip increases the heat dissipation
efficiency thereof and improves performance. At present, the
grinding operation for thickness reduction and the formation of an
electrode are performed by joining a semiconductor wafer to a glass
substrate as the support using a grease or a resist material.
Therefore, the joining material may be dissolved by a solvent for
separating the wafer from the glass substrate after the completion
of processing. This is accompanied with problems that the
separation requires more than several days time and the waste
solution should be treated. These problems can be solved when the
laminated body of the present invention is used.
4. Application to Large Wafer for Improving Productivity
[0084] In the case of a large wafer (for example, a 12
inch-diameter silicon wafer), it is very important to separate the
wafer and the support easily. The separation can be easily
performed when the laminated body of the present invention is used,
and therefore, the present invention can be applied also to this
field.
5. Thin Rock Crystal Wafer
[0085] In the field of rock crystal wafer, the thickness reduction
of a wafer is required to increase the oscillation frequency. The
separation can be easily performed when the laminated body of the
present invention is used, and therefore, the present invention can
be applied also to this field.
EXAMPLES
[0086] These examples are merely for illustrative purposes only and
are not meant to be limiting on the scope of the appended claims.
All parts, percentages, ratios, etc. in the examples and the rest
of the specification are by weight, unless noted otherwise.
Solvents and other reagents used were obtained from Sigma-Aldrich
Chemical Company; Milwaukee, Wis. unless otherwise noted.
TABLE-US-00001 Table of Abbreviations Abbreviation or Trade
Designation DESCRIPTION VQM-135 Mixture of vinyl-terminated
polydimethylsiloxane with about 20 25% by weight vinyl-functional
silicate resin commercially available from Gelest, Morrisville, PA.
DMS-V31 Vinyl-terminated polydimethylsiloxane commercially
available from Gelest, Morrisville, PA. VQX-221 Vinyl-modified Q
silica resin 50% solution in xylenes commercially available from
Gelest, Morrisville, PA. SYL-OFF 7678 Silane-functional
polydimethylsiloxane commercially available from Dow Corning,
Midland, MI. Catalyst
(.eta..sup.5-methylcyclopentadienyl)trimethylplatinum(IV)
(MeCpPtMe.sub.3) commercially available from Alfa Aesar, Ward Hill,
MA. LTHC glass A glass plate of 1 millimeter thickness that has an
LTHC (light-to-heat- conversion) coating on it.
Example 1
[0087] A mixture of 100.0 grams of VQM-135, 7.2 grams of SYL-Off
7678, and 4.4 milligrams of Catalyst was prepared in an amber
bottle. Using a notch bar coater, a 75 micrometer thick layer of
this adhesive composition was coated onto the polyimide passivation
layer of a silicon wafer. A piece of LTHC glass was placed on the
adhesive with the LTHC layer facing the wafer. This sandwich was
passed under a UV processor (Fusion D bulb, low power, exposure
time approximately 15 seconds). The UV illumination passed through
the glass and cured the adhesive. Upon prying the glass off of the
wafer, the adhesive layer remained adhered to the glass and removed
cleanly from the polyimide surface.
Example 2
[0088] A mixture of 56.0 grams of VQM-135, 42.0 grams of DMS-V31
and 140.0 grams of VQX-221 was prepared in a glass bottle. The
xylenes solvent was removed using a rotary evaporator attached to a
vacuum pump. To the resulting mixture was added 17.5 grams of
SYL-Off 7678, and 7.7 milligrams of Catalyst. Using a notch bar
coater, a 75-micrometer thick layer of this adhesive composition
was coated onto the polyimide passivation layer of a silicon wafer.
A piece of LTHC glass was placed on the adhesive with the LTHC
layer facing the wafer. This sandwich was passed under a UV
processor (Fusion D bulb, low power, exposure time approximately 15
seconds). The UV illumination passed through the glass and cured
the adhesive. Upon prying the glass off of the wafer, the adhesive
layer remained adhered to the glass and removed cleanly from the
polyimide surface.
* * * * *