U.S. patent application number 11/763253 was filed with the patent office on 2008-08-21 for high-temperature, spin-on, bonding compositions for temporary wafer bonding using sliding approach.
Invention is credited to Chenghong Li, Sunil K. Pillalamarri.
Application Number | 20080200011 11/763253 |
Document ID | / |
Family ID | 39283184 |
Filed Date | 2008-08-21 |
United States Patent
Application |
20080200011 |
Kind Code |
A1 |
Pillalamarri; Sunil K. ; et
al. |
August 21, 2008 |
HIGH-TEMPERATURE, SPIN-ON, BONDING COMPOSITIONS FOR TEMPORARY WAFER
BONDING USING SLIDING APPROACH
Abstract
New compositions and methods of using those compositions as
bonding compositions are provided. The compositions comprise a
polymer dispersed or dissolved in a solvent system, and can be used
to bond an active wafer to a carrier wafer or substrate to assist
in protecting the active wafer and its active sites during
subsequent processing and handling. The compositions form bonding
layers that are chemically and thermally resistant, but that can
also be softened to allow the wafers to slide apart at the
appropriate stage in the fabrication process.
Inventors: |
Pillalamarri; Sunil K.;
(Austin, TX) ; Li; Chenghong; (Cary, NC) |
Correspondence
Address: |
HOVEY WILLIAMS LLP
10801 Mastin Blvd., Suite 1000
Overland Park
KS
66210
US
|
Family ID: |
39283184 |
Appl. No.: |
11/763253 |
Filed: |
June 14, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60828572 |
Oct 6, 2006 |
|
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|
Current U.S.
Class: |
438/458 ;
257/E21.703 |
Current CPC
Class: |
H01L 2221/68327
20130101; Y10T 428/31678 20150401; B29B 17/02 20130101; Y10T
156/1153 20150115; H01L 2221/6834 20130101; B32B 38/10 20130101;
B32B 43/006 20130101; C09J 2301/502 20200801; H01L 21/6835
20130101; H01L 2924/30105 20130101; Y10T 156/1972 20150115; Y10T
156/19 20150115; Y10T 156/11 20150115; Y10T 156/1168 20150115; Y10T
156/1189 20150115 |
Class at
Publication: |
438/458 ;
257/E21.703 |
International
Class: |
H01L 21/30 20060101
H01L021/30 |
Goverment Interests
GOVERNMENT FUNDING
[0002] This invention was made with government support under
contract number W911 SR-05-C-0019 awarded by the United States Army
Research, Development, and Engineering Command. The United States
Government has certain rights in the invention.
Claims
1. A wafer bonding method comprising: providing a stack comprising
first and second substrates bonded together via a bonding layer
formed from a bonding composition comprising a polymer dissolved or
dispersed in a solvent system; subjecting said stack to a
temperature of at least about 190.degree. C. so as to soften said
bonding layer; and applying a force to at least one of said first
and second substrates while causing the other of said first and
second substrates to resist said force, said force being applied in
a sufficient amount so as to separate said first and second
substrates.
2. The method of claim 1, said stack having an axis that passes
through both the first and second substrates, said force being
applied in a generally transverse direction relative to said
axis.
3. The method of claim 1, said applying a force comprising lifting
the at least one first and second substrate in a direction
generally away from the other of said first and second
substrates.
4. The method of claim 1, further comprising thinning one of said
substrates prior to subjecting said stack to a temperature of at
least about 190.degree. C.
5. The method of claim 1, further comprising subjecting said stack
to a process selected from the group consisting of backgrinding,
metallizing, patterning, and combinations thereof prior to
subjecting said stack to a temperature of at least about
190.degree. C.
6. The method of claim 1, wherein said polymer is at least about
95% soluble in nonpolar solvents.
7. The method of claim 1, wherein said composition further
comprises an ingredient selected from the group consisting of
tackifiers, adhesion promoting agents, antioxidants, surfactants,
and mixtures of the foregoing.
8. The method of claim 1, wherein said first substrate has a first
surface and a second surface remote from said first surface and
comprising at least one active site and plurality of topographical
features, and said bonding layer is bonded to said second
surface.
9. The method of claim 8, wherein said second substrate comprises a
bonding surface that is bonded to said bonding layer.
10. The method of claim 9, wherein: said topographical features
present respective end surfaces remote from the first surface of
said first substrate, and at least one of the end surfaces is
further from the first surface of the first substrate than the
other of said end surfaces, said further end surface defining a
plane that is substantially parallel to said first surface; and the
distance from said plane to the bonding surface on said second
substrate varying by less than about 10% across said plane and
second substrate bonding surface.
11. The method of claim 1, wherein said first substrate: has a
first surface and a second surface remote from said first surface;
comprises at least one active site and plurality of topographical
features on said second surface; and is selected from the group
consisting of microelectromechanical system devices, display
devices, flexible substrates, compound semiconductors, low k
dielectric layers, dielectric layers, ion implant layers, and
substrates comprising silicon, aluminum, tungsten, tungsten
silicide, gallium arsenide, germanium, tantalum, tantalum nitrite,
SiGe, and mixtures of the foregoing.
12. The method of claim 1, wherein said second substrate comprises
a carrier wafer comprising a material selected from the group
consisting of sapphire, ceramic, glass, quartz, aluminum, silver,
and silicon.
13. The method of claim 1, wherein said providing a stack
comprises: applying the bonding composition to one of the first and
second substrates to form a bonding composition-coated substrate
and a bonding composition-free substrate; and contacting the
bonding composition-free substrate with the bonding
composition-coated substrate so as to bond the substrates
together.
14. The method of claim 13, wherein said applying comprises
spincoating the bonding composition onto one of the first and
second substrates.
15. The method of claim 13, wherein said contacting comprises
applying pressure to the substrates.
16. An article comprising: a first substrate having a back surface
and an active surface, said active surface comprising at least one
active site and a plurality of topographical features; a second
substrate having a bonding surface; and a thermoplastic bonding
layer bonded to said active surface and to said bonding surface,
wherein: said topographical features present respective end
surfaces remote from the back surface of said first substrate, and
at least one of the end surfaces is further from the back surface
of the first substrate than the other of said end surfaces, said
further end surface defining a plane that is substantially parallel
to said first surface; and the distance from said plane to the
bonding surface on said second substrate varying by less than about
5% along said plane and second substrate bonding surface.
17. The article of claim 16, said bonding layer: having a thickness
defined as the distance from the active surface to the bonding
surface; and comprising the same composition across said
thickness.
18. The article of claim 16, wherein said bonding layer is formed
from a composition comprising a polymer dissolved or dispersed in a
solvent system.
19. The article of claim 18, wherein said polymer is at least about
95% soluble in nonpolar solvents.
20. The article of claim 18, wherein said composition further
comprises an ingredient selected from the group consisting of
tackifiers, adhesion promoting agents, antioxidants, surfactants,
and mixtures of the foregoing.
21. The article of claim 16, wherein said first substrate is
selected from the group consisting of microelectromechanical system
devices, display devices, flexible substrates, compound
semiconductors, low k dielectric layers, dielectric layers, ion
implant layers, and substrates comprising silicon, aluminum,
tungsten, tungsten silicide, gallium arsenide, germanium, tantalum,
tantalum nitrite, SiGe, and mixtures of the foregoing.
22. The article of claim 16, wherein said second substrate
comprises a material selected from the group consisting of
sapphire, ceramic, glass, quartz, aluminum, silver, and
silicon.
23. The article of claim 16, wherein said bonding layer has a
softening temperature of at least about 190.degree. C.
24. A composition comprising a polymer and a poly(pinene) dissolved
or dispersed in a solvent system, said polymer including recurring
monomers comprising cyclo-olefins.
25. The composition of claim 24, wherein said composition comprises
from about 5% to about 50% by weight of said polymer and from about
50% to about 95% of said pinene, based upon the total weight of the
composition taken as 100% by weight.
26. The composition of claim 24, wherein said pinene is selected
from the group consisting of .alpha.-pinene and .beta.-pinene.
27. The composition of claim 24, wherein said solvent system
comprises limonene, and said composition further comprising an
adhesion promoting agent.
28. A flowable, bonding composition comprising a tackifier and a
polymer including recurring monomers comprising cyclo-olefins, said
tackifier and polymer being dispersed or dissolved in a solvent
system, said composition comprising at least about 30% by weight
solvent system, based upon the total weight of the composition
taken as 100% by weight.
29. The composition of claim 28, wherein said tackifier is a
hydrocarbon resin.
30. The composition of claim 28, wherein said solvent system
comprises a solvent selected from the group consisting of limonene,
mesitylene, xylene, dodecene, propylene glycol monomethyl ether,
methyl isoamyl ketone, ethyl acetoacetate, and mixtures
thereof.
31. The composition of claim 28, wherein said composition further
comprises an ingredient selected from the group consisting of
antioxidants, surfactants, adhesion promoting agents, and mixtures
thereof.
32. The composition of claim 31, wherein said ingredient comprises
an antioxidant, and said antioxidant is selected from the group
consisting of phenolic antioxidants and phosphite antioxidants.
33. The composition of claim 28, wherein said composition is
essentially free of blowing, and foaming agents.
34. The composition of claim 28, wherein said composition is
essentially free of crosslinking agents.
35. The composition of claim 28, wherein said composition has a
Mooney viscosity of less than about 35 MU.
36. The composition of claim 28, wherein said composition has a
viscosity at 250.degree. C. of less than about 1,000 poise.
37. A flowable, bonding composition comprising: a tackifier; and a
compound selected from the group consisting of rubbers,
styrene-isoprene-styrene, styrene-butadiene-styrene, halogenated
butyl rubber, and mixtures thereof, said tackifier and compound
being dispersed or dissolved in a solvent system, said composition
comprising at least about 30% by weight solvent system, based upon
the total weight of the composition taken as 100% by weight.
38. The composition of claim 37, said composition further
comprising a polymer including recurring monomers comprising
cyclo-olefins.
39. The composition of claim 37, wherein said compound is a rubber
selected from the group consisting of ethylene-propylene
terpolymers, ethylene-propylene-diene monomers, and mixtures
thereof.
40. The composition of claim 37, wherein said tackifier is a
hydrocarbon resin.
41. The composition of claim 37, wherein said solvent system
comprises a solvent selected from the group consisting of limonene,
mesitylene, xylene, dodecene, propylene glycol monomethyl ether,
methyl isoamyl ketone, ethyl acetoacetate, and mixtures
thereof.
42. The composition of claim 37, wherein said composition further
comprises an ingredient selected from the group consisting of
antioxidants, surfactants, adhesion promoting agents, and mixtures
thereof.
43. The composition of claim 42, wherein said ingredient comprises
an antioxidant, and said antioxidant is selected from the group
consisting of phenolic antioxidants and phosphite antioxidants.
44. The composition of claim 37, wherein said composition is
essentially free of blowing and foaming agents.
45. The composition of claim 37, wherein said composition is
essentially free of crosslinking agents.
46. The composition of claim 37, wherein said composition has a
Mooney viscosity of less than about 35 MU.
47. The composition of claim 37, wherein said composition has a
viscosity at 250.degree. C. of less than about 1,000 poise.
Description
RELATED APPLICATIONS
[0001] This application also claims the priority benefit of U.S.
Provisional Patent Application No. 60/828,572, entitled
HIGH-TEMPERATURE SPIN-ON ADHESIVES FOR TEMPORARY WAFER BONDING
USING SLIDING APPROACH, filed Oct. 6, 2006, the entire disclosure
of which is incorporated by reference herein.
BACKGROUND OF THE INVENTION
[0003] 1. Field of the Invention
[0004] The present invention is broadly concerned with novel
compositions and methods of using those compositions to form
bonding compositions that can support active wafers on a carrier
wafer or substrate during wafer thinning and other processing.
[0005] 2. Description of the Prior Art
[0006] Wafer (substrate) thinning has been used to dissipate heat
and aid in the electrical operation of the integrated circuits
(IC). Thick substrates cause an increase in capacitance, requiring
thicker transmission lines, and, in turn, a larger IC footprint.
Substrate thinning increases impedance while capacitance decreases
impedance, causing a reduction in transmission line thickness, and,
in turn, a reduction in IC size. Thus, substrate thinning
facilitates IC miniaturization.
[0007] Geometrical limitations are an additional incentive for
substrate thinning. Via holes are etched on the backside of a
substrate to facilitate frontside contacts. In order to construct a
via using common dry-etch techniques, geometric restrictions apply.
For substrate thicknesses of less than 100 .mu.m, a via having a
diameter of 30-70 .mu.m is constructed using dry-etch methods that
produce minimal post-etch residue within an acceptable time. For
thick substrates, vias with larger diameters are needed. This
requires longer dry-etch times and produces larger quantities of
post-etch residue, thus significantly reducing throughput. Larger
vias also require larger quantities of metallization, which is more
costly. Therefore, for backside processing, thin substrates can be
processed more quickly and at lower cost.
[0008] Thin substrates are also more easily cut and scribed into
ICs. Thinner substrates have a smaller amount of material to
penetrate and cut and therefore require less effort. No matter what
method (sawing, scribe and break, or laser ablation) is used, ICs
are easier to cut from thinner substrates. Most semiconductor
wafers are thinned after frontside operations. For ease of
handling, wafers are processed (i.e., frontside devices) at their
normal full-size thicknesses, e.g., 600-700 .mu.m. Once completed,
they are thinned to thicknesses of 100-150 .mu.m. In some cases
(e.g., when hybrid substrates such as gallium arsenide (GaAs) are
used for high-power devices) thicknesses may be taken down to 25
.mu.m.
[0009] Mechanical substrate thinning is performed by bringing the
wafer surface into contact with a hard and flat rotating horizontal
platter that contains a liquid slurry. The slurry may contain
abrasive media along with chemical etchants such as ammonia,
fluoride, or combinations thereof. The abrasive provides "gross"
substrate removal, i.e., thinning, while the etchant chemistry
facilitates "polishing" at the submicron level. The wafer is
maintained in contact with the media until an amount of substrate
has been removed to achieve a targeted thickness.
[0010] For a wafer thickness of 300 .mu.m or greater, the wafer is
held in place with tooling that utilizes a vacuum chuck or some
means of mechanical attachment. When wafer thickness is reduced to
less than 300 .mu.m, it becomes difficult or impossible to maintain
control with regard to attachment and handling of the wafer during
further thinning and processing. In some cases, mechanical devices
may be made to attach and hold onto thinned wafers, however, they
are subject to many problems, especially when processes may vary.
For this reason, the wafers ("active" wafers) are mounted onto a
separate rigid (carrier) substrate or wafer. This substrate becomes
the holding platform for further thinning and post-thinning
processing. Carrier substrates are composed of materials such as
sapphire, quartz, certain glasses, and silicon, and usually exhibit
a thickness of 1000 .mu.m. Substrate choice will depend on how
closely matched the coefficient of thermal expansion (CTE) is
between each material.
[0011] One method that has been used to mount an active wafer to a
carrier substrate comprises the use of a cured bonding composition.
The major drawback with this approach is that the composition must
be chemically removed, typically by dissolving in a solvent. This
is very time-consuming, thus reducing throughput. Furthermore, the
use of the solvent adds to the cost and complexity of the process,
and it can be hazardous, depending upon the solvent required to
dissolve the bonding composition.
[0012] Another method for mounting an active wafer to a carrier
substrate is via a thermal release adhesive tape. This process has
two major shortcomings. First, the tapes have limited thickness
uniformity across the active wafer/carrier substrate interface, and
this limited uniformity is often inadequate for ultra-thin wafer
handling. Second, the thermal release adhesive softens at such low
temperatures that the bonded wafer/carrier substrate stack cannot
withstand many typical wafer processing steps that are carried out
at higher temperatures.
[0013] There is a need for new compositions and methods of adhering
an active wafer to a carrier substrate that can endure high
processing temperatures and that allow for ready separation of the
wafer and substrate at the appropriate stage of the process.
SUMMARY OF THE INVENTION
[0014] In one embodiment, the present invention is a wafer bonding
method wherein a stack comprising first and second substrates
bonded together via a bonding layer is preferably subjected to
various processing steps (e.g., wafer thinning). The processed
stack is then heated to a temperature of at least about 190.degree.
C., and a sliding force is applied to at least one of the
substrates while causing the other of the substrates to resist the
force, such as by securing the other substrate or subjecting it to
an opposing force. The force is applied in a sufficient amount so
as to separate the substrates.
[0015] In another embodiment, the invention provides an article
comprising: a first substrate having a back surface and an active
surface; a second substrate having a bonding surface; and bonding
layer bonded to the active and bonding surfaces.
[0016] In one embodiment, the bonding layer is formed of a
composition comprising a polymer (or polymer blend) and a tackifier
such as a pinene or poly(pinene) dissolved or dispersed in a
solvent system, with the polymer including recurring monomers
comprising cyclo olefins.
[0017] In another embodiment, the invention provides a flowable,
bonding composition comprising a tackifier and a polymer including
recurring monomers comprising cyclo-olefins. The tackifier and
polymer are dispersed or dissolved in a solvent system that makes
up at least about 30% by weight of the composition, based upon the
total weight of the composition taken as 100% by weight.
[0018] In one embodiment, a flowable, bonding composition
comprising a tackifier and a compound selected from the group
consisting of rubbers, styrene-isoprene-styrene,
styrene-butadiene-styrene, halogenated butyl rubber, and mixtures
thereof is provided. The tackifier and compound are dispersed or
dissolved in a solvent system that makes up at least about 30% by
weight of the composition, based upon the total weight of the
composition taken as 100% by weight.
BRIEF DESCRIPTION OF THE DRAWING FIGURES
[0019] Figure (FIG.) 1 illustrates the inventive method of thinning
and debonding two wafers according to the present invention;
[0020] FIG. 2 is a flow diagram showing the process steps followed
in the examples;
[0021] FIG. 3 is a graph depicting the rheological analysis results
of a bonding composition described in Example 1;
[0022] FIG. 4 is a graph depicting the rheological analysis results
of a bonding composition described in Example 2;
[0023] FIG. 5 is a graph depicting the rheological analysis results
of a bonding composition described in Example 3; and
[0024] FIG. 6 is a graph depicting the rheological analysis results
of a bonding composition described in Example 4.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0025] In more detail, the inventive compositions comprise a
polymer (which includes a polymer mixture) dispersed or dissolved
in a solvent system. The polymer is preferably present in the
composition at levels of from about 5% to about 50% by weight, more
preferably from about 5% to about 35% by weight, and even more
preferably from about 10% to about 35% by weight, based upon the
total weight of solids in the composition taken as 100% by
weight.
[0026] The preferred polymers are thermoplastic and preferably have
a weight average molecular weight of from about 500 Daltons to
about 1,000,000 Daltons, and more preferably from about 1,000
Daltons to about 500,000 Daltons. Preferred polymers preferably
have a softening point (ring and ball softening point) of at least
about 50.degree. C., more preferably at least about 100.degree. C.,
and even more preferably from about 100.degree. C. to about
200.degree. C.
[0027] Preferred polymers will be at least about 95%, preferably at
least about 98%, and even more preferably about 100% by weight
dissolved when allowed to sit at ambient temperatures in a solvent
such as limonene, mesitylene, xylene, methyl isoamyl ketone, ethyl
acetoacetate, and/or dodecene for a time period of about 1-24
hours.
[0028] Some preferred polymers that work in the present invention
include those selected from the group consisting of cellulose
polymers (such as cellulose acetate polymers), cyclo olefin
polymers (such as those sold under the name Zeonex), rubbers (e.g.,
ethylene-propylene terpolymers (EPM), ethylene-propylene-diene
monomers (EPDM)), styrene-isoprene-styrene,
styrene-butadiene-styrene, polyolefins, ethylene-vinyl acetate,
halogenated butyl rubber, and mixtures thereof.
[0029] The composition should comprise at least about 30% by weight
solvent system, preferably from about 50 to about 95% by weight
solvent system, more preferably from about 65-95% by weight solvent
system, and even more preferably from about 65-90% by weight
solvent system, based upon the total weight of the composition
taken as 100% by weight. The solvent system should have a boiling
point of from about 100-200.degree. C., and preferably from about
120-180.degree. C.
[0030] Suitable solvents include those selected from the group
consisting of limonene (particularly D-limonene), mesitylene,
xylene, dodecene, propylene glycol monomethyl ether, methyl isoamyl
ketone, ethyl acetoacetate, and mixtures thereof.
[0031] In other embodiments, the composition could include a number
of optional ingredients, including surfactants, adhesion promoting
agents, tackifiers, plasticizer, and antioxidants.
[0032] When a surfactant is utilized, it is preferably present in
the composition at a level of from about 0.1% to about 3% by
weight, and more preferably from about 0.1% to about 1% by weight,
based upon the total weight of the solids in the composition taken
as 100% by weight. Examples of suitable surfactants include alcohol
ethoxylates such as octyl phenol ethoxylate (sold under the name
Triton X-100.RTM.).
[0033] When an adhesion promoting agent is utilized, it is
preferably present in the composition at a level of from about 0.1%
to about 3% by weight, and preferably from about 0.1% to about 1%
by weight, based upon the total weight of the solids in the
composition taken as 100% by weight. Examples of suitable adhesion
promoting agent include those selected from the group consisting of
bis(trimethoxysilylethyl)benzene, aninopropyl tri(alkoxy silanes)
(e.g., aminopropyl tri(methoxy silane), aminopropyl tri(ethoxy
silanes), N-phenyl aminopropyl tri(ethoxy silane)), and other
silane coupling agents.
[0034] When a tackifier is utilized, it is preferably present in
the composition at a level of from about 50% to about 95% by
weight, and preferably from about 75% to about 95% by weight, based
upon the total weight of the solids in the composition taken as
100% by weight. The tackifier is preferably a hydrocarbon resin
(polymeric and/or monomeric) and preferably has an M.sub.w of from
about 300-10,000 Daltons, and more preferably from about 500-5,000
Daltons. Preferred hydrocarbon resins have a softening point (ring
and ball softening point) of at least about 80.degree. C., and more
preferably from about 120-200.degree. C. Furthermore, it is
preferred that the hydrocarbon resin have a Brookfield viscosity at
190.degree. C. of from about 2,500-3,500 cP, preferably from about
2,800-3,200 cP, and even more preferably about 2,900-3,100 cP.
Suitable tackifiers include all aliphatic hydrocarbon resins,
aromatic hydrocarbon resins, and aliphatic/aromatic hydrocarbon
resins as well as those selected from the group consisting of
rosins (e.g., terpene rosins), poly(a-pinene), poly(.beta.-pinene),
and mixtures thereof. Particularly preferred hydrocarbon resins are
sold under the names EASTOTAC, PICCOTAC, and REGALREZ, all
available from Eastman Chemical Company.
[0035] When an antioxidant is utilized, it is preferably present in
the composition at a level of from about 0.01% to about 3% by
weight, more preferably from about 0.01% to about 1.5% by weight,
and even more preferably from about 0.01% to about 0.1% by weight,
based upon the total weight of the solids in the composition taken
as 100% by weight. Examples of suitable antioxidants include those
selected from the group consisting of phenolic antioxidants (such
as pentaerythritol
tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate sold under
the name Irganox.RTM. 1010 by Ciba) and phosphite antioxidants
(such as tris(2,4-ditert-butylphenyl)phosphite sold under the name
Irgafos.RTM. 168 by Ciba).
[0036] The inventive compositions are formed by simply mixing the
polymer and other ingredients with the solvent system, preferably
at temperatures of from about 20-80.degree. C. for time periods of
from about 1-24 hours. The final composition should be
thermoplastic (i.e., noncrosslinkable). Thus, the composition will
be essentially free (less than about 0.1% by weight and preferably
about 0% by weight) of crosslinking agents.
[0037] Furthermore, it is preferred that the final composition
undergo little or no (i.e., less than about 3%) expansion or change
in volume during exposure to different temperatures. To accomplish
this, the composition is preferably essentially free (less than
about 0.1% by weight and preferably about 0% by weight) of blowing
agents and foaming agents. Blowing and foaming agents are compounds
that will decompose and release substantial amounts gas under
certain conditions (e.g., exposure to high temperatures).
[0038] The final compositions will preferably have a Mooney
Viscosity (ML (1+4) 125.degree. C.; as determined by ISO289/ASTM D
1646) of less than about 35 MU, preferably less than about 30 MU,
and even more preferably from about 5 to about 25 MU.
[0039] The viscosity of the final composition will preferably be
less than about 1,000 poise, more preferably less than about 500,
and even more preferably from about 30 to about 100 poise. For
purposes of these measurements, the viscosity is determined via
rheological dynamic analysis (TA Instruments, AR-2000, two
parallel-plate configuration where the plates have a diameter of 25
mm). Furthermore, this viscosity is determined at 250.degree. C.
and there is preferably less than about 3% by weight, and more
preferably less than about 2% by weight, loss of the composition.
In other words, very little to no thermal decomposition occurs in
the composition at this temperature, as determined by
thermogravimetric analysis (TGA).
[0040] Although the composition could be applied to either the
carrier substrate or active wafer first, it is preferred that it be
applied to the active wafer first. A preferred application method
involves spin-coating the composition at spin speeds of from about
300-3,500 rpm (more preferably from about 500-1,500 rpm), at
accelerations of from about 500-15,000 rpm/second, and for spin
times of from about 30-300 seconds. It will be appreciated that the
application steps can be varied to achieve a particular
thickness.
[0041] After coating, the substrate can be baked (e.g., on a hot
plate) to evaporate the solvents. Typical baking would be at
temperatures of from about 150-275.degree. C., and preferably from
about 150-225.degree. C. for a time period of from about 2-15
minutes, and more preferably from about 3-10 minutes. The film
thickness (on top of the topography) after bake will typically be
at least about 5 .mu.m, and more preferably from about 5-50
.mu.m.
[0042] After baking, the desired carrier wafer is contacted with,
and pressed against, the layer of inventive composition. The
carrier wafer is bonded to this inventive composition by heating at
a temperature of from about 150-250.degree. C., and preferably from
about 180-220.degree. C. This heating is preferably carried out
under vacuum and for a time period of from about 1-10 minutes,
under a bond force of from about 1 to about 15 kilonewtons.
[0043] FIG. 1(a) shows an exemplary stack 10 comprising active
wafer 12 and carrier wafer or substrate 14. Active wafer 12
comprises a back surface 16 and an active surface 18. Active
surface 18 can comprise one or more active sites (not shown) as
well as a plurality of topographical features (raised features or
lines as well as holes, trenches, or spaces) such as, for example,
those designated as 20a-d. Feature 20d represents the "highest"
feature on active surface 18. That is, the end portion or surface
21 is further from back surface 16 of wafer 12 than the respective
end portions of any other topographical feature on wafer 12.
[0044] Typical active wafers 12 can include any microelectronic
substrate. Examples of some possible active wafers 12 include those
selected from the group consisting of microelectromechanical system
(MEMS) devices, display devices, flexible substrates (e.g., cured
epoxy substrates, roll-up substrates that can be used to form
maps), compound semiconductors, low k dielectric layers, dielectric
layers (e.g., silicon oxide, silicon nitride), ion implant layers,
and substrates comprising silicon, aluminum, tungsten, tungsten
silicide, gallium arsenide, germanium, tantalum, tantalum nitrite,
SiGe, and mixtures of the foregoing.
[0045] Carrier substrate 14 has a bonding surface 22. Typical
carrier substrates 14 comprise a material selected from the group
consisting of sapphire, ceramic, glass, quartz, aluminum, silver,
and silicon.
[0046] Wafer 12 and carrier substrate 14 are bonded together via
bonding composition layer 24. Bonding layer 24 is formed of the
polymer compositions described above, and has been applied and
dried as also described above. As shown in the FIG. 1(a), bonding
layer 24 is bonded to active surface 18 of wafer 12 as well as to
bonding surface 22 of substrate 14. Unlike prior art tapes, bonding
layer 24 is a uniform (chemically the same) material across its
thickness. In other words, the entire bonding layer 24 is formed of
the same composition.
[0047] It will be appreciated that, because bonding layer 24 can be
applied to active surface 18 by spincoating, the bonding
composition flows into and over the various topographical features.
Furthermore, the bonding layer 24 forms a uniform layer over the
topography of active surface 18. To illustrate this point, FIG. 1
shows a plane designated by dashed line 26, at end portion 21 and
substantially parallel to back surface 16. The distance from this
plane to bonding surface 22 is represented by the thickness "T."
The thickness T is the total thickness variation, and it will vary
by less than about 8%, preferably by less than about 5%, more
preferably by less than about 2%, and even more preferably by less
than about 1% across the length of plane 26 and substrate 14.
[0048] The wafer package can then be subjected to subsequent
thinning (or other processing) of the substrate as shown in FIG.
1(b), where 12' presents the wafer 12 after thinning. It will be
appreciated that the substrates can be thinned to thicknesses of
less than about 100 .mu.m, preferably less than about 50 .mu.m, and
more preferably less than about 25 .mu.m. After thinning, typical
backside processing, including photolithography, via etching, and
metallization, may be performed.
[0049] Advantageously, the dried layers of the inventive
compositions possess a number of highly desirable properties. For
example, the layers will exhibit low outgassing for vacuum etch
processes. That is, if a 15-.mu.m thick film of the composition is
baked at 200.degree. C. for 2 minutes, the solvents will be driven
from the composition so that subsequent baking at 200.degree. C.
for 60 minutes results in a film thickness change of less than
about 5%, preferably less than about 2%, and even more preferably
less than about 1% or even 0% (referred to as the "Film Shrinkage
Test"). Thus, the dried layers can be heated to temperatures of up
to about 190.degree. C., preferably up to about 200.degree. C.,
more preferably up to about 220.degree. C., and even more
preferably up to about 240.degree. C. without physical changes or
chemical reactions occurring in the layer. For example, the layers
will not soften below these temperatures. In some embodiments, the
layers can also be exposed to polar solvents (e.g., NMP, PGME) at a
temperature of 85.degree. C. for 90 minutes without reacting.
[0050] The bond integrity of the dried layers can be maintained
even upon exposure to an acid or base. That is, a dried layer of
the composition having a thickness of about 15 .mu.m can be
submerged in an acidic media (e.g., concentrated sulfuric acid) or
base (e.g., 30 wt. % KOH) at 85.degree. C. for about 45 minutes
while maintaining bond integrity. Bond integrity can be evaluation
by using a glass carrier substrate and visually observing the
bonding composition layer through the glass carrier substrate to
check for bubbles, voids, etc. Also, bond integrity is maintained
if the active wafer and carrier substrate cannot be separated by
hand.
[0051] The bonding compositions are also thermally stable. When
subjected to the thermogravimetric analysis (TGA) test described
herein, the bonding compositions will exhibit a % weight loss
(after 200.degree. C. for 60 min) of less than about 4%, preferably
less than about 2%, and even more preferably less than about
1%.
[0052] After the desired processing has occurred, the active wafer
or substrate can be separated from the carrier substrate by heating
to temperatures of at least about 190.degree. C., preferably at
least about 200.degree. C., more preferably at least about
220.degree. C., and even more preferably at least about 240.degree.
C. These temperature ranges represent the preferred softening
points of the bonding composition layer. This heating will cause
the bonding composition layer to soften and form softened bonding
composition layer 24' as shown in FIG. 1(c), at which point the two
substrates can be separated by sliding apart. FIG. 1(c) also shows
an axis 28, which passes through both of wafer 12 and substrate 14,
and the sliding forces would be applied in a direction generally
transverse to axis 28. Alternatively, sliding may not be necessary,
and instead wafer 12 or substrate 14 can be lifted upward (i.e., in
a direction that is generally away from the other of wafer 12 or
substrate 14) to separate the wafer 12 from the substrate 14.
[0053] It will be appreciated that separation can be accomplished
by simply sliding and/or lifting one of wafer 12 or substrate 14
while maintaining the other in a substantially stationary position
so as to resist the sliding or lifting force (e.g., by applying
simultaneous opposing sliding forces to wafer 12 and substrate 14).
This can all be accomplished via conventional equipment.
[0054] Any bonding composition remaining in the device areas can be
easily removed using the original solvent that was part of the
composition prior to drying as well as using solvents such as
xylene, benzene, and limonene. Any composition remaining behind
will be completely dissolved (at least about 98%, preferably at
least about 99%, and more preferably about 100%) after 5-15 minutes
of exposure to the solvent. It is also acceptable to remove any
remaining bonding composition using a plasma etch, either alone or
in combination with a solvent removal process. After this step, a
clean, bonding composition-free wafer 12' and carrier substrate 14
(not shown in their clean state) will remain.
EXAMPLES
[0055] The following examples set forth preferred methods in
accordance with the invention. It is to be understood, however,
that these examples are provided by way of illustration and nothing
therein should be taken as a limitation upon the overall scope of
the invention.
Example 1
[0056] Formulations were made by dissolving various cellulose
derivatives (obtained from Eastman Chemical Company, Kingsport,
Tenn.) in appropriate solvents. The exact materials and quantities
used are reported in Table I.
TABLE-US-00001 TABLE I Bonding Composition Formulations from
Cellulose Materials. SAMPLE SAMPLE SAMPLE SAMPLE 1.1 1.2 1.3 1.4
INGREDIENTS (g) (g) (g) (g) Cellulose acetate (29.5%) 20 0 0 0
butyrate (17%) Cellulose acetate 0 18 0 0 trimelliate Cellulose
acetate (2%) 0 0 25 0 butyrate (52%) Cellulose acetate (18.5%) 0 0
0 25 butyrate (31%) Propylene glycol 0 82 0 0 monomethyl ether
Methyl isoamyl ketone 50 0 75 50 Ethyl acetoacetate 30 0 0 25
Example 2
Cycloolefin Resin and Poly(.alpha.-Pinene) Blend
[0057] Formulations were made by dissolving Zeonex 480R resin
(obtained from Zeon Chemicals, Louisville, Ky.) and/or
poly(.alpha.-pinene) (obtained from Aldrich, Milwaukee, Wis.)
and/or poly(.beta.-pinene) (obtained from Aldrich, Milwaukee, Wis.)
in D-limonene (obtained from Florida Chemical Company).
Bis(trimethoxysilylethyl)benzene (obtained from Aldrich, Milwaukee,
Wis.) was added as an adhesion promoter. The exact compositions of
the formulations are reported in Table II.
TABLE-US-00002 TABLE II Bonding Composition Formulations from
Poly(cycloolefin) and Pinene Materials. SAMPLE SAMPLE SAMPLE SAMPLE
2.1 2.2 2.3 2.4 INGREDIENTS (g) (g) (g) (g) Zeonex 480R 120 55.9
46.05 20 Poly(.alpha.-pinene) 0 14.3 30.7 0 Poly(.beta.-pinene) 0 0
0 5 D-limonene 280 144.8 138.15 74.875 Bis(trimethoxysilyl- 0.5
0.268 0.268 0.125 ethyl)benzene
Example 3
Cycloolefin Resin and Rosin Ester Blend
[0058] The formulations were made by dissolving Zeonex 480R resin
and Eastotac H142W (obtained from Eastman Chemicals, Kingsport,
Tenn.) in a suitable solvent. Irganox 1010 and Irgafos 168
(obtained from Ciba Specialty Chemicals, Tarrytown, N.Y.) were
added to one of the formulations to prevent thermal oxidation at
high temperatures. Triton X-100 (obtained from Aldrich, Milwaukee,
Wis.) was added to reduce de-wetting problems, and
bis(trimethoxysilylethyl)benzene was added to promote adhesion. The
exact compositions of the formulations are reported in Table M.
TABLE-US-00003 TABLE III Bonding Composition Formulations Based on
Poly(cycloolefin) and Rosin Ester Blends. SAMPLE SAMPLE SAMPLE
SAMPLE 3.1 3.2 3.3 3.4 INGREDIENTS (g) (g) (g) (g) Zeonex 480R 3 5
g 7 40 Eastotac H142W 7 5 3 160 D-limonene 12 30 30 60 Mesitylene 0
0 0 140 Irganox 1010 0 0 0 2 Irgafos 168 0 0 0 1 Triton X-100 0 0 0
1 Bis(trimethoxysilyl- 0 0 0 1 ethyl)benzene
Example 4
EPDM Rubber and Rosin Ester Blend
[0059] The formulations were made by dissolving different grades of
ethylene propylene diene monomer rubber (EPDM rubber: Buna EP
T6250, obtained from Lanxess, Inc., Pittsburgh, Pa.; and Vistalon
2504, Exxon-Mobil Chemical, Houston, Tex.) and Eastotac H142W in a
suitable solvent. The antioxidant Irganox 1010 was added to three
of the four formulations. The exact compositions of the
formulations are reported in Table TV.
TABLE-US-00004 TABLE IV Bonding Composition Formulations Based on
EPDM Rubber and Rosin Ester Blends. SAMPLE SAMPLE SAMPLE SAMPLE 4.1
4.2 4.3 4.4 INGREDIENTS (g) (g) (g) (g) Buna EPT 6250 0.6 1 0 0
Vistalon 2504 0 0 3.7 19.425 Zeonex 480R 3.4 3 0 0 Eastotac H142W
16 16 11.1 91.575 D-limonene 20 20 25 189 Irganox 1010 0.2 0.2 0
1.11
Example 5
Application, Bonding, and Debonding
[0060] The formulations from Examples 1-4 were spin-coated onto
various substrate wafers. After baking to evaporate the solvent and
allowing the bonding composition to reflow, a second wafer was
bonded to each coated wafer by applying pressure. The procedure for
temporary wafer bonding using these bonding compositions is
illustrated in the flow diagram shown in FIG. 2. The bonded wafers
were tested for mechanical strength, thermal stability, and
chemical resistance. The wafers were tested for debonding by
manually sliding them apart at acceptable temperatures.
Example 6
Analysis of the Bonding Compositions
[0061] From a rheological analysis, the compositions of Samples
1.4, 2.2, 3.4, and 4.4 were identified as the preferred materials
for temporary wafer bonding. FIGS. 3, 4, 5, and 6 shows these
results for Samples 1.4, 2.4, 3.4, and 4.4, respectively. The
viscosity and modulus values of these materials are reported in
Table V, and these materials were successfully tested for
debonding. Further studies on thermal stability and chemical
resistance were also carried out on these four compositions as
described below.
[0062] Thermogravimetric analysis (TGA) was carried out on a TA
Instruments thermogravimetric analyzer. The TGA samples were
obtained by scraping the spincoated and baked bonding composition
samples listed in examples. The samples were heated at a rate of
10.degree. C./minute, up to 200.degree. C., and kept constantly at
200.degree. C. for longer periods of time to determine the thermal
stability of the particular bonding composition. All of these
compositions possessed the required thermal stability at
200.degree. C. and exhibited minimal outgassing (see Table VI).
[0063] To determine chemical resistance, two silicon wafers were
bonded using the particular bonding composition to be tested. The
bonded wafers were put into chemical baths of NMP or 30 wt. % KOH
at 85.degree. C., and concentrated sulfuric acid at room
temperature to determine chemical resistance. The bond integrity
was visually observed after 45 minutes, and the stability of the
bonding composition against the respective chemical was determined.
All bonding compositions, except for Sample 1.4, retained the bond
integrity.
TABLE-US-00005 TABLE V Storage Modulus and Viscosity Values of
Bonding Compositions Sample Number G' (dynes/cm.sup.2) at
200.degree. C. h at 200.degree. C. (poise) 1.4 270 244 2.2 2026
1782 3.4 736.5 847 4.4 463 210
TABLE-US-00006 TABLE VI Isothermal Thermogravimetric Results -
Thermal Stability of Bonding Compositions. Sample Number % Weight
loss (200.degree. C./60 min) Example 1.4 0.23 Example 2.2 0.35
Example 3.4 1.5 Example 4.4 2
* * * * *