U.S. patent application number 11/166582 was filed with the patent office on 2005-11-17 for porous materials.
This patent application is currently assigned to Shipley Company, L.L.C.. Invention is credited to Annan, Nikoi, Gallagher, Michael K., Gore, Robert H., You, Yujian.
Application Number | 20050255710 11/166582 |
Document ID | / |
Family ID | 35767871 |
Filed Date | 2005-11-17 |
United States Patent
Application |
20050255710 |
Kind Code |
A1 |
You, Yujian ; et
al. |
November 17, 2005 |
Porous materials
Abstract
Porous thermoset dielectric materials having low dielectric
constants useful in electronic component manufacture are provided
along with methods of preparing the porous thermoset dielectric
materials. Also provided are methods of forming integrated circuits
containing such porous thermoset dielectric material.
Inventors: |
You, Yujian; (Lansdale,
PA) ; Annan, Nikoi; (Willow Grove, PA) ;
Gallagher, Michael K.; (Hopkinton, MA) ; Gore, Robert
H.; (Southampton, PA) |
Correspondence
Address: |
S. Matthew Cairns
Edwards & Angell, LLP
P.O. Box 55874
Boston
MA
02205
US
|
Assignee: |
Shipley Company, L.L.C.
Marlborough
MA
|
Family ID: |
35767871 |
Appl. No.: |
11/166582 |
Filed: |
June 24, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11166582 |
Jun 24, 2005 |
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10106338 |
Mar 26, 2002 |
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60279541 |
Mar 28, 2001 |
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Current U.S.
Class: |
438/780 ;
257/E21.259; 257/E21.273; 257/E21.576; 257/E23.167 |
Current CPC
Class: |
H01L 21/312 20130101;
H01L 2924/00 20130101; H01L 23/5329 20130101; H01L 2924/09701
20130101; H01L 21/02282 20130101; H01L 21/31695 20130101; H01L
21/7682 20130101; H01L 21/02203 20130101; H01L 21/76801 20130101;
H01L 2924/0002 20130101; H01L 21/02118 20130101; H01L 2924/0002
20130101 |
Class at
Publication: |
438/780 |
International
Class: |
H01L 021/31 |
Claims
1-15. (canceled)
16. A composition comprising B-staged thermoset dielectric matrix
material and a plurality of cross-linked polymeric porogen
particles; wherein the thermoset dielectric material is selected
from the group consisting of benzocyclobutenes and polyarylenes;
wherein the porogen particles are substantially compatible with the
B-staged thermoset dielectric matrix material and wherein the
porogen particles comprise as polymerized units one or more
monomers selected from the group consisting of N-vinyl monomers and
heteroatom-substituted styrene monomers and at least one
(meth)acrylate cross-linking agent.
17. The composition of claim 16 wherein the (meth)acrylate
cross-linking agent is selected from the group consisting of
ethyleneglycol diacrylate, trimethylolpropane triacrylate, allyl
methacrylate, ethyleneglycol dimethacrylate, diethyleneglycol
dimethacrylate, propyleneglycol dimethacrylate, propyleneglycol
diacrylate, trimethylolpropane trimethacrylate, glycidyl
methacrylate, 2,2-dimethylpropane-1,3-diacrylat- e, 1,3-butylene
glycol diacrylate, 1,3-butylene glycol dimethacrylate,
1,4-butanediol diacrylate, diethylene glycol diacrylate, diethylene
glycol dimethacrylate, 1,6-hexanediol diacrylate, 1,6-hexanediol
dimethacrylate, tripropylene glycol diacrylate, triethylene glycol
dimethacrylate, tetraethylene glycol diacrylate, polyethylene
glycol 200 diacrylate, tetraethylene glycol dimethacrylate,
polyethylene glycol dimethacrylate, ethoxylated bisphenol A
diacrylate, ethoxylated bisphenol A dimethacrylate, polyethylene
glycol 600 dimethacrylate, poly(butanediol) diacrylate,
pentaerythritol triacrylate, trimethylolpropane triethoxy
triacrylate, glyceryl propoxy triacrylate, pentaerythritol
tetraacrylate, pentaerythritol tetranethacrylate, dipentaerythritol
monohydroxypentaacrylate, and mixtures thereof.
18. The composition of claim 16 wherein the N-vinyl monomers are
selected from the group consisting of vinylpyridines,
(C.sub.1-C.sub.8)alkyl substituted N-vinyl pyridines;
N-vinylcaprolactam; N-vinylbutyrolactam; N-vinylpyrrolidone; vinyl
imidazole; N-vinyl carbazole; N-vinyl-succinimide;
N-vinyl-oxazolidone; N-vinylphthalimide; N-vinyl-pyrrolidones;
vinyl pyrroles; vinyl anilines; and vinyl piperidines.
19. The composition of claim 16 wherein the N-vinyl monomers are
selected from the group consisting of N-vinylpyrrolidone and
N-vinylphthalimide.
20. The composition of claim 16 wherein the heteroatom-substituted
styrene monomers are selected from the group consisting of
vinylanisole, o-aminostyrene, m-aminostyrene, p-aminostyrene,
4-fluorostyrene, 3-fluorostyrene, and vinyldimethoxybenzene.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates generally to porous materials. In
particular, this invention relates to the preparation and use of
porous films containing thermoset materials and having a low
dielectric constant.
[0002] As electronic devices become smaller, there is a continuing
desire in the electronics industry to increase the circuit density
in electronic components, e.g., integrated circuits, circuit
boards, multichip modules, chip test devices, and the like without
degrading electrical performance, e.g., crosstalk or capacitive
coupling, and also to increase the speed of signal propagation in
these components. One method of accomplishing these goals is to
reduce the dielectric constant of the interlayer, or intermetal,
insulating material used in the components. A method for reducing
the dielectric constant of such interlayer, or intermetal,
insulating material is to incorporate within the insulating film
very small, uniformly dispersed pores or voids.
[0003] Porous dielectric matrix materials are well known in the
art. One known process of making a porous dielectric involves
co-polymerizing a thermally labile monomer with a dielectric
monomer to form a block copolymer, followed by heating to decompose
the thermally labile monomer unit. See, for example, U.S. Pat. No.
5,776,990. In this approach, the amount of the thermally labile
monomer unit is limited to amounts less than about 30% by volume.
If more than about 30% by volume of the thermally labile monomer is
used, the resulting dielectric material has cylindrical or lamellar
domains, instead of pores or voids, which lead to interconnected or
collapsed structures upon removal, i.e., heating to degrade the
thermally labile monomer unit. See, for example, Carter et. al.,
Polyimide Nanofoams from Phase-Separated Block Copolymers,
Electrochemical Society Proceedings, volume 97-8, pages 32-43
(1997). Thus, the block copolymer approach provides only a limited
reduction in the dielectric constant of the matrix material.
[0004] Another known process for preparing porous dielectric
materials disperses thermally removable particles in a dielectric
precursor, polymerizing the dielectric precursor without
substantially removing the particles, followed by heating to
substantially remove the particles, and, if needed, completing the
curing of the dielectric material. See, for example, U.S. Pat. No.
5,700,844. In the '844 patent, uniform pore sizes of 0.5 to 20
microns are achieved. However, this methodology is unsuitable for
such electronic devices as integrated circuits where feature sizes
are expected to go below 0.25 microns.
[0005] Copending U.S. patent application Ser. No. 09/460,326 (Allen
et al.), discloses porogen particles that are substantially
compatibilized with B-staged dielectric matrix materials. However,
this patent application does not broadly teach how to prepare
porous dielectric layers containing polyarylene materials.
[0006] Polyarylenes are well known dielectric materials. For
example, U.S. Pat. No. 6,093,636 (Carter et al.) discloses a method
for forming an integrated circuit containing a porous high
temperature thermoset, such as a polyarylene. Such porous
thermosets are prepared by using as pore forming material highly
branched aliphatic esters that have functional groups that are
further functionalized with appropriate reactive groups such that
the functionalized aliphatic esters are incorporated into, i.e.
copolymerized with, the vitrifying polymer matrix. Such
incorporation of the pore forming material into the matrix
restricts the mobility of the pore forming material, i.e.
incorporation prevents phase separation of the pore forming
material from the matrix. By restricting such mobility, the size of
the phase-separated domains is also restricted. Also, the '636
patent does not teach how to prepare porous thermoset dielectric
materials having a mean pore diameter.ltoreq.10 nm, such as a
diameter in the range of 0.75 to 8 nm.
[0007] International Patent Application WO 00/31183 (Bruza et al.)
discloses a porous cross-linked thermoset dielectric matrix
material, such as a polyarylene. This patent application discloses
a number of porogens, such as solvents and polymers, particularly
cross-linkable polymers. Suitable cross-linkable polymers are those
that react to copolymerize with the thermoset dielectric matrix
material. Suitable polymers useful as porogens include dendrimers,
hyperbranched polymer systems and cross-linked latex particles.
This patent application does not teach how to prepare porous
thermoset dielectric materials having a mean pore
diameter.ltoreq.10 nm, such as a diameter in the range of 0.75 to 8
nm, nor how to prepare such porous materials where the porogens are
substantially free of aggregation or agglomeration and without
copolymerization with the dielectric matrix materials.
[0008] Other methods of preparing porous dielectric materials are
known, but suffer from broad distributions of pore sizes, too large
pore size, such as greater than 20 microns, or technologies that
are too expensive for commercial use, such as liquid extractions
under supercritical conditions.
[0009] There is thus a need for improved porous thermoset
dielectric matrix materials with substantially smaller pore sizes
and a greater percent by volume of pores for use in electronic
components, and in particular, as an interlayer, or intermetal,
dielectric material for use in the fabrication of integrated
circuits. There is also a need for porous thermoset dielectric
materials where the volume fraction of pores in the film is
equivalent to the volume fraction of pore forming material.
SUMMARY OF THE INVENTION
[0010] It has now been surprisingly found that certain polymeric
particles (or porogens) incorporated into thermoset dielectric
matrix provide porous films having a suitable dielectric constant
and sufficiently small pore size for use as insulating material in
electronic devices such as integrated circuits and printed wiring
boards. Such polymeric particles provide thermoset dielectric
matrix material having a greater percentage of pores by volume and
more uniformly dispersed pores than are available from known
approaches.
[0011] In a first aspect, the present invention is directed to a
method of preparing porous thermoset dielectric materials including
the steps of: a) dispersing a plurality of removable cross-linked
polymeric porogen particles in B-staged thermoset dielectric matrix
material; b) forming a film of the B-staged thermoset dielectric
matrix material; c) curing the B-staged thermoset dielectric matrix
material to form a thermoset dielectric matrix material; and d)
subjecting the thermoset dielectric matrix material to conditions
which at least partially remove the porogen particles to form a
porous thermoset dielectric material without substantially
degrading the thermoset dielectric material; wherein the thermoset
dielectric material is selected from the group consisting of
benzocyclobutenes and polyarylenes; wherein the porogen particles
are substantially compatible with the B-staged thermoset dielectric
matrix material and wherein the porogen particles include as
polymerized units one or more monomers selected from the group
consisting of N-vinyl monomers and heteroatom-substituted styrene
monomers and at least one (meth)acrylate cross-linking agent.
[0012] In a second aspect, the present invention is directed to
porous thermoset dielectric materials prepared by the method
described above.
[0013] In a third aspect, the present invention is directed to a
method of preparing an integrated circuit including the steps of:
a) depositing on a substrate a layer of a composition including
B-staged thermoset dielectric matrix material having a plurality of
cross-linked polymeric porogen particles dispersed therein; b)
curing the B-staged thermoset dielectric matrix material to form a
thermoset dielectric matrix material; c) subjecting the thermoset
dielectric matrix material to conditions which at least partially
remove the porogen particles to form a porous thermoset dielectric
material layer without substantially degrading the thermoset
dielectric material; d) patterning the thermoset dielectric layer;
e) depositing a metallic film onto the patterned dielectric layer;
and f) planarizing the film to form an integrated circuit; wherein
the thermoset dielectric material is selected from the group
consisting of benzocyclobutenes and polyarylenes; wherein the
porogen particles are substantially compatible with the B-staged
thermoset dielectric matrix material and wherein the porogen
particles include as polymerized units one or more monomers
selected from the group consisting of N-vinyl monomers and
heteroatom-substituted styrene monomers and at least one
(meth)acrylate cross-linking agent.
[0014] In a fourth aspect, the present invention is directed to an
integrated circuit prepared by the method described above.
[0015] In a fifth aspect, the present invention is directed to a
composition including B-staged thermoset dielectric matrix material
and a plurality of cross-linked polymeric porogen particles;
wherein the thermoset dielectric material is selected from the
group consisting of benzocyclobutenes and polyarylenes; wherein the
porogen particles are substantially compatible with the B-staged
thermoset dielectric matrix material and wherein the porogen
particles include as polymerized units one or more monomers
selected from the group consisting of N-vinyl monomers and
heteroatom-substituted styrene monomers and at least one
(meth)acrylate cross-linking agent.
DETAILED DESCRIPTION OF THE INVENTION
[0016] As used throughout this specification, the following
abbreviations shall have the following meanings, unless the context
clearly indicates otherwise: .degree. C.=degrees centigrade;
.mu.m=micron=micrometer; UV=ultraviolet; rpm=revolutions per
minute; nm=nanometer; cm=centimeter; g=gram; wt %=weight percent;
L=liter; mL=milliliter; STY=styrene; NVP=N-vinyl-pyrrolidone;
NVPIM=N-vinylphthalimide; TMPTA=trimethylolpropane triacrylate;
TMPTMA=trimethylolpropane trimethacrylate; 4FSTY=4-fluorostyrene;
and VAS=4-vinylanisole.
[0017] The term "(meth)acrylic" includes both acrylic and
methacrylic and the term "(meth)acrylate" includes both acrylate
and methacrylate. Likewise, the term "(meth)acrylamide" refers to
both acrylamide and methacrylamide. "Alkyl" includes straight
chain, branched and cyclic alkyl groups. The term "porogen" refers
to a pore forming material, that is a polymeric material or
particle dispersed in a dielectric material that is subsequently
removed to yield pores, voids or free volume in the dielectric
material. Thus, the terms "removable porogen," "removable polymer"
and "removable particle" are used interchangeably throughout this
specification. The terms "pore," "void" and "free volume" are used
interchangeably throughout this specification. "Cross-linker" and
"cross-linking agent" are used interchangeably throughout this
specification and refer to a monomer containing two or more
polymerizable sites, such as double or triple bonds. "Polymer"
refers to polymers and oligomers, and also includes homopolymers
and copolymers. The terms "oligomer" and "oligomeric" refer to
dimers, trimers, tetramers and the like. "Monomer" refers to any
ethylenically or acetylenically unsaturated compound capable of
being polymerized. Such monomers may contain one or more double or
triple bonds. "Halo" refers to fluoro, chloro, bromo and iodo.
Likewise, "halogenated" refers to fluorinated, chlorinated,
brominated and iodinated.
[0018] The term "B-staged" refers to uncured thermoset dielectric
matrix materials. By "uncured" is meant any thermoset material that
can be polymerized or cured to form higher molecular weight
materials, such as coatings or films. Such B-staged material may be
monomeric, oligomeric or mixtures thereof. B-staged material is
further intended to include mixtures of polymeric material with
monomers, oligomers or a mixture of monomers and oligomers.
"Polyarylene" as used herein is intended to describe a wide variety
of thermosetting resins or polymers having backbones containing
arylene units. Such polyarylenes include polyarylene ethers.
[0019] Unless otherwise noted, all amounts are percent by weight
and all ratios are by weight. All numerical ranges are inclusive
and combinable in any order, except where it is obvious that such
numerical ranges are constrained to add up to 100%.
[0020] The present invention relates to the synthesis, composition,
size, distribution and purity of polymer particles useful as
removable porogens, i.e., pore forming material. Such porogens are
useful for forming porous thermoset dielectric materials in the
fabrication of electronic and optoelectronic devices.
[0021] The present invention relates to a method of preparing
porous thermoset dielectric materials including the steps of: a)
dispersing a plurality of removable cross-linked polymeric porogen
particles in B-staged thermoset dielectric material to form
B-staged thermoset dielectric matrix material; b) forming a film of
the B-staged thermoset dielectric matrix material; c) curing the
B-staged thermoset dielectric matrix material to form a thermoset
dielectric matrix material; and c) subjecting the thermoset
dielectric matrix material to conditions which at least partially
remove the porogen particles to form a porous thermoset dielectric
material without substantially degrading the thermoset dielectric
material; wherein the thermoset dielectric material is selected
from the group consisting of benzocyclobutenes and polyarylenes;
wherein the porogen particles are substantially compatible with the
B-staged thermoset dielectric matrix material and wherein the
porogen particles include as polymerized units one or more monomers
selected from the group consisting of N-vinyl monomers and
heteroatom-substituted styrene monomers and at least one
(meth)acrylate cross-linking agent.
[0022] The porogens of the present invention are useful in reducing
the dielectric constant of thermoset dielectric materials,
particularly those materials having low dielectric constants ("k").
A low-k dielectric material is any material having a dielectric
constant less than about 4.
[0023] Thermoset dielectric materials useful in the present
invention include benzocyclobutenes, polyarylenes and mixtures
thereof. Polyarylenes include polyarylene ethers. Suitable
benzocyclobutenes include, but are not limited to, those disclosed
in U.S. Pat. Nos. 4,540,763 and 4,812,588. A particularly suitable
benzocyclobutene is
1,3-bis(2-bicyclo[4.2.0]octa-1,3,5trien-3-ylethynyl)-1,1,3,3-tetramethyld-
isiloxane, sold under the tradename CYCLOTENE by the Dow Chemical
Company (Midland, Mich.).
[0024] A wide variety of polyarylenes and polyarylene ethers may be
used in the present invention. Suitable polyarylenes may be
synthesized from precursors such as ethynyl aromatic compounds of
the formula: 1
[0025] wherein each Ar is an aromatic group or inertly-substituted
aromatic group: each R is independently hydrogen, an alkyl, aryl or
inertly-substituted alkyl or aryl group; L is a covalent bond or a
group which links one Ar to at least one other Ar; n and m are
integers of at least 2; and q is an integer of at least 1. As such,
the ethynyl aromatic compounds of the invention typically have four
or more ethynyl groups (for example, tetraethynyl aromatic
compounds) and are useful as monomers in the preparation of
polymers, including their oligomeric precursors.
[0026] In another aspect, the polyarylenes used in the invention
may include a polymer including as polymerized units: 2
[0027] wherein Ar' is the residual of the reaction of product of
(C.ident.C).sub.n--Ar or Ar--(C.ident.C).sub.m moieties and R, L, n
and m are as defined above.
[0028] In another embodiment, the polyarylene copolymers of the
invention include as polymerized units a monomer having the
formula: 3
[0029] wherein Ar' and R are as defined above.
[0030] Exemplary polyarylenes include, but are not limited to,
those wherein Ar-L-Ar are: biphenyl; 2,2-diphenyl propane;
9,9'-diphenyl fluorene; 2,2-diphenyl hexafluoro propane; diphenyl
sulfide; oxydiphenylene; diphenyl ether;
bis(phenylene)diphenylsilane; bis(phenylene) phosphine oxide;
bis(phenylene)benzene; bis(phenylene)naphthalene;
bis(phenylene)enthracene; thiodiphenylene;
1,1,1-triphenyleneethane; 1,3,5-triphenylenebenzene;
1,3,5-(2-phenylene-2-propyl)benzene; 1,1,1-triphenylenemethane;
1,1,2,2-tetraphenylene-1,2-diphenylethane;
bis(1,1-diphenyleneethyl)benze- ne;
2,2'-diphenylene-1,1,1,3,3,3-hexafluoropropane;
1,1-diphenylene-1-phenylethane; naphthalene; anthracene; or
bis(phenylene)napthacene; more preferably biphenylene; naphthylene;
p,p'(2,2-diphenylene propane) (i.e.,
--C.sub.6H.sub.4--C(CH.sub.3).sub.2-- -C.sub.6H.sub.4--);
p,p'-(2,2-diphenylene-1,1,1,3,3,3hexafluoropropene) and
(--C.sub.6H.sub.4--C(CF.sub.3).sub.2--C.sub.6H.sub.4--).
[0031] Useful bis-phenyl derivatives include 2,2-diphenyl propane;
9,9'-diphenyl fluorene; 2,2-diphenyl hexafluoro propane; diphenyl
sulfide; diphenyl ether; bis(phenylene)diphenylsilane;
bis(phenylene)phosphine oxide; bis(phenylene)benzene;
bis(phenylene)naphthalene; bis(phenylene)anthracene; or
bis(phenylene)napthacene.
[0032] The ethynyl groups on each Ar are either on adjacent carbon
atoms or are vinylogously conjugated within the ring. It is
believed that they dimerize upon application of heat to form an
aromatic ring having a 1,4-diradical which serves to polymerize
and/or cross-link the compound. While not being bound by theory, it
is believed that this dimerization occurs via Bergman cyclization
such as disclosed by Warner, et al. in Science, 268, Aug. 11, 1995,
pp. 814-816.
[0033] The ethynyl aromatic monomer precursors to thermosetting
polyarylenes are preferably bis(o-diethynyl) monomers (also
referred to as BODA (bis(ortho-diacetylene)monomers)), which means
there are at least two sets of adjacent substituted or vinylogously
conjugated ethynyl groups on the monomer, that is, at least one set
of ethynyl groups on each Ar group. Preferably, the ethynyl
aromatic compound contains from 2 to 4, most preferably 2 or 3,
diethynyl sets, most preferably, except when additional
cross-linking is desired, two sets (i.e., four) of ethynyl
groups.
[0034] The polyarylene precursor monomers may be prepared by a
variety of methods known in the art, such as by: (a) selectively
halogenating, preferably in a solvent, a polyphenol (preferably a
bisphenol) to selectively halogenate, preferably brominate, each
phenolic ring with one halogen on one of the two positions ortho to
the phenolic hydroxyl group; (b) converting the phenolic hydroxyl
on the resulting poly(ortho-halophenol), preferably in a solvent,
to a leaving group such as a sulfonate ester (for example, a
trifluoromethanesulfonate ester prepared from
trifluoromethanesulfonyl halide or trifluoromethane sulfonic acid
anhydride) which is reactive with and replaced by terminal ethynyl
compounds; and (c) reacting the reaction product of step (b) with
an ethynyl-containing compound or an ethynyl synthon in the
presence of an aryl ethynylation, preferably palladium, catalyst
and an acid acceptor to simultaneously replace the halogen and the
trifluoromethylsulfonate with an ethynyl-containing group (for
example, acetylene, phenylacetylene, substituted phenylacetylene or
substituted acetylene). Further explanation of this synthesis is
provided in PCT patent application WO 97/10193 (Babb).
[0035] The ethynyl aromatic monomers of Formula (D are useful to
prepare polymers of either Formula (II) or (III). While not being
bound by theory, it is believed that the ethynyl groups,
specifically those of ortho orientation, on the aromatic ring
cyclize upon heating, forming a dehydro aromatic ring which reacts
to form a polymer chain. Monomers with more than two ortho ethynyl
groups (that is, more than one set of ethynyl groups) are used to
form thermoset polymers and depending on the concentration of
monomer having more than one set of ortho-ethynyl groups may
contain from almost none (that is, a polymer having essentially
repeat units of Formula (II) only to substantial segments of linear
polymer chain structure (that is, a polymer of Formula (III)).
[0036] Polymerization of the ethynyl aromatic monomers is well
within the ability of one skilled in the art. Typically,
polymerization is achieved thermally and will generally occur at a
temperature more than 150.degree. C., but polymerization
temperatures are preferably at least 180.degree. C., and more
preferably at least 210.degree. C. The polymerization temperature
preferably does not exceed that temperature which would result in
undesirable degradation of the resulting polymer, which means
polymerization is generally conducted at a temperature less than
300.degree. C. for monomers having benzylic hydrogen atoms, and,
for monomers not having a benzylic hydrogen, less than 450.degree.
C., preferably less than 400.degree. C., and more preferably less
than 350.degree. C. The polymerization temperature will vary with
Ar-L-Ar and R, with smaller R groups like H generally requiring
lower temperatures than larger R groups, and more conjugated Ar and
R (when aromatic) groups requiring lower temperatures than less
conjugated Ar and R groups. For example, when R or Ar is
anthracene, the polymerization is more advantageously conducted at
a lower temperature than when Ar or R is phenyl. Polymerization is
conveniently conducted at atmospheric pressure, but pressures
higher or lower than atmospheric pressure can be employed.
[0037] The polymerization may be conducted in the presence of
agents for controlling (accelerating) the cyclization reaction such
as free radical initiators, or the chlorides disclosed by Warner,
et al. in Science 269, pp. 814-816 (1995) can be employed in the
polymerization reaction. While the specific conditions of
polymerization are dependent on a variety of factors including the
specific ethynyl aromatic monomer(s) being polymerized and the
desired properties of the resulting polymer, in general, the
conditions of polymerization are detailed in PCT application WO
97/10193 (Babb).
[0038] Particularly suitable polyarylenes for use in the present
invention include those sold as SiLK.TM. Semiconductor Dielectric
(available from The Dow Chemical Company), FLARE.TM. dielectric
(available from Honeywell), and VELOX.TM. poly(arylene ether)
(available from Air Products/Shumacher). Other particularly
suitable polyarylenes include those disclosed in WO 00/31183, WO
98/11149; WO 97/10193, WO 91/09081, EP 755 957, and U.S. Pat. Nos.
5,115,082; 5,155,175; 5,179,188; 5,874,516; and 6,093,636, all
herein incorporated by reference to the extent they teach
polyarylene thermosets.
[0039] It will be appreciated that a mixture of dielectric
materials may be used in the present invention, such as two or more
thermoset dielectric materials or a mixture of a thermoset
dielectric material with one or more other dielectric materials,
i.e. not a thermoset dielectric material. Suitable other dielectric
materials include, but are not limited to, inorganic materials such
as organo polysilicas, carbides, oxides, nitrides and oxyfluorides
of silicon, boron, or aluminum; and organic matrix materials such
as poly(aryl esters), poly(ether ketones), polycarbonates,
polynorbornenes, poly(arylene ethers), poly(perfluorinated
hydrocarbons) such as poly(tetrafluoroethylene), and
polybenzoxazoles. Thus, the porogens of the present invention may
be combined with a thermoset/other dielectric material mixture to
form a thermoset/other dielectric matrix composite material.
[0040] The porogen polymers of the present invention are
cross-linked particles and have a molecular weight or particle size
suitable for use as a modifier in advanced interconnect structures
in electronic devices. Typically, the useful mean particle size
range for a plurality of these particles for such applications is
up to about 1,000 nm, such as that having a mean particle size in
the range of about 0.75 to about 1000 nm. It is preferred that the
mean particle size is in the range of about 0.75 to about 200 nm,
more preferably from about 0.75 to about 50 nm, and most preferably
from about 1 nm to about 20 nm. An advantage of the present process
is that the size of the pores formed in the dielectric matrix are
substantially the same size, i.e., dimension, as the size of the
removed porogen particles used. Thus, the porous dielectric
material made by the process of the present invention has
substantially uniformly dispersed pores with substantially uniform
pore sizes having a mean pore size in the range of from 0.75 to
1000 nm, preferably 0.75 to 200 nm, more preferably 0.75 and 50 nm
and most preferably 1 to 20 nm. Particularly suitable pore sizes
are .ltoreq.10 nm, such as .ltoreq.5 nm, .ltoreq.3 nm and .ltoreq.2
nm.
[0041] The cross-linked polymeric porogens include as polymerized
units at least one monomer selected from N-vinyl monomers and
heteroatom-substituted styrene monomers. N-vinyl monomers suitable
for use in the present invention include, but are not limited to:
vinylpyridines such as 2-vinylpyridine or 4-vinylpyridine;
(C.sub.1-C.sub.8)alkyl substituted N-vinyl pyridines such as
2-methyl-5-vinyl-pyridine, 2-ethyl-5-vinylpyridine,
3-methyl-5-vinylpyridine, 2,3-dimethyl-5-vinyl-pyridine, and
2-methyl-3-ethyl-5-vinylpyridine; N-vinylcaprolactam;
N-vinylbutyrolactam; N-vinylpyrrolidone; vinyl imidazole; N-vinyl
carbazole; N-vinyl-succinimide; N-vinyl-oxazolidone;
N-vinylphthalimide; N-vinyl-pyrrolidones such as
N-vinyl-thio-pyrrolidone, 3-methyl-1-vinyl-pyrroli done,
4-methyl-1-vinyl-pyrroli done, 5-methyl-1-vinyl-pyrrolidone,
3-ethyl-1-vinyl-pyrrolidone, 3-butyl-1-vinyl-pyrrolidone,
3,3-dimethyl-1-vinyl-pyrrolidone, 4,5-dimethyl-1-vinyl-pyrrolidone,
5,5-dimethyl-1-vinyl-pyrrolidone,
3,3,5-trimethyl-1-vinyl-pyrrolidone, 4-ethyl-1-vinyl-pyrrolidone,
5-methyl-5-ethyl-1-vinyl-pyrrolidone and
3,4,5-trimethyl-1-vinyl-pyrrolid- one; vinyl pyrroles; vinyl
anilines; and vinyl piperidines. Preferred N-vinyl monomers are
N-vinylpyrrolidone and N-vinylphthalimide.
[0042] Heteroatom-substituted styrene monomers useful in the
present invention are any styrene monomers having one or more of
the aromatic hydrogens replaced with a heteroatom-containing
substituent. Suitable heteroatom-containing substituents include,
but are not limited to, (C.sub.1-C.sub.10)alkoxy, halo, amino,
(C.sub.1-C.sub.10)alkylamino, di(C.sub.1-C.sub.10)alkylamino,
nitro, cyano, carboxy, halo(C.sub.1-C.sub.10)alkyl,
carb(C.sub.1-C.sub.10)alkoxy and the like. Exemplary
heteroatom-substituted styrene monomers include, but are not
limited to, vinylanisole, o-, m-, or p-aminostyrene,
4-fluorostyrene, 3-fluorostyrene, vinyldimethoxybenzene, and the
like. Preferred heteroatom substituted styrene monomers are
vinylanisole, and o-, m-, or p-aminostyrene, and more preferably
vinylanisole.
[0043] The amount of N-vinyl monomers or heteroatom-substituted
styrene monomers of the present invention is typically from about 1
to about 99% wt, based on the total weight of the monomers used. It
is preferred that these monomers are present in an amount of from 1
to about 90% wt, and more preferably from about 5 to about 90% wt.
It will be appreciated that a mixture of N-vinyl monomers and
heteroatom-substituted styrene monomers may be used in the present
porogens.
[0044] In addition to the N-vinyl monomers or
heteroatom-substituted styrene monomers, the present porogens may
further contain as polymerized units one or more ethylenically or
acetylenically unsaturated monomers, including, but not limited to,
(meth)acrylic acid, (meth)acrylamides, alkyl (meth)acrylates,
alkenyl (meth)acrylates, aromatic (meth)acrylates, vinyl aromatic
monomers, nitrogen-containing compounds, substituted ethylene
monomers, and poly(alkylene oxide) monomers.
[0045] Typically, the alkyl (meth)acrylates useful in the present
invention are (C.sub.1-C.sub.24)alkyl (meth)acrylates. Suitable
alkyl (meth)acrylates include, but are not limited to, "low cut"
alkyl (meth)acrylates, "mid cut" alkyl (meth)acrylates and "high
cut" alkyl (meth)acrylates.
[0046] "Low cut" alkyl (meth)acrylates are typically those where
the alkyl group contains from 1 to 6 carbon atoms. Suitable low cut
alkyl (meth)acrylates include, but are not limited to: methyl
methacrylate ("MMA"), methyl acrylate, ethyl acrylate, propyl
methacrylate, butyl methacrylate ("BMA"), butyl acrylate ("BA"),
isobutyl methacrylate ("IBMA"), hexyl methacrylate, cyclohexyl
methacrylate, cyclohexyl acrylate and mixtures thereof.
[0047] "Mid cut" alkyl (meth)acrylates are typically those where
the alkyl group contains from 7 to 15 carbon atoms. Suitable mid
cut alkyl (meth)acrylates include, but are not limited to:
2-ethylhexyl acrylate ("EHA"), 2-ethylhexyl methacrylate, octyl
methacrylate, decyl methacrylate, isodecyl methacrylate ("IDMA",
based on branched (C.sub.10)alkyl isomer mixture), undecyl
methacrylate, dodecyl methacrylate (also known as lauryl
methacrylate), tridecyl methacrylate, tetradecyl methacrylate (also
known as myristyl methacrylate), pentadecyl methacrylate and
mixtures thereof. Particularly useful mixtures include
dodecyl-pentadecyl methacrylate ("DPMA"), a mixture of linear and
branched isomers of dodecyl, tridecyl, tetradecyl and pentadecyl
methacrylates; and lauryl-myristyl methacrylate ("LMA").
[0048] "High cut" alkyl (meth)acrylates are typically those where
the alkyl group contains from 16 to 24 carbon atoms. Suitable high
cut alkyl (meth)acrylates include, but are not limited to:
hexadecyl methacrylate, heptadecyl methacrylate, octadecyl
methacrylate, nonadecyl methacrylate, cosyl methacrylate, eicosyl
methacrylate and mixtures thereof. Particularly useful mixtures of
high cut alkyl (meth)acrylates include, but are not limited to:
cetyl-eicosyl methacrylate ("CEMA"), which is a mixture of
hexadecyl, octadecyl, cosyl and eicosyl methacrylate; and
cetyl-stearyl methacrylate ("SMA"), which is a mixture of hexadecyl
and octadecyl methacrylate.
[0049] The mid-cut and high-cut alkyl (meth)acrylate monomers
described above are generally prepared by standard esterification
procedures using technical grades of long chain aliphatic alcohols,
and these commercially available alcohols are mixtures of alcohols
of varying chain lengths containing between 10 and 15 or 16 and 20
carbon atoms in the alkyl group. Examples of these alcohols are the
various Ziegler catalyzed ALFOL alcohols from Vista Chemical
company, i.e., ALFOL 1618 and ALFOL 1620, Ziegler catalyzed various
NEODOL alcohols from Shell Chemical Company, i.e. NEODOL 25L, and
naturally derived alcohols such as Proctor & Gamble's TA-1618
and CO-1270. Consequently, for the purposes of this invention,
alkyl (meth)acrylate is intended to include not only the individual
alkyl (meth)acrylate product named, but also to include mixtures of
the alkyl (meth)acrylates with a predominant amount of the
particular alkyl (meth)acrylate named.
[0050] The alkyl (meth)acrylate monomers useful in the present
invention may be a single monomer or a mixture having different
numbers of carbon atoms in the alkyl portion. Also, the
(meth)acrylamide and alkyl (meth)acrylate monomers useful in the
present invention may optionally be substituted. Suitable
optionally substituted (meth)acrylamide and alkyl (meth)acrylate
monomers include, but are not limited to:
hydroxy(C.sub.2-C.sub.6)alkyl (meth)acrylates,
dialkylamino(C.sub.2-C.sub- .6)alkyl (meth)acrylates,
dialkylamino(C.sub.2-C.sub.6)alkyl (meth)acrylamides.
[0051] Useful substituted alkyl (meth)acrylate monomers are those
with one or more hydroxyl groups in the alkyl radical, especially
those where the hydroxyl group is found at the .beta.-position
(2-position) in the alkyl radical. Hydroxyalkyl (meth)acrylate
monomers in which the substituted alkyl group is a
(C.sub.2-C.sub.6)alkyl, branched or unbranched, are preferred.
Suitable hydroxyalkyl (meth)acrylate monomers include, but are not
limited to: 2-hydroxyethyl methacrylate ("HEMA"), 2-hydroxyethyl
acrylate ("HEA"), 2-hydroxypropyl methacrylate,
1-methyl-2-hydroxyethyl methacrylate, 2-hydroxy-propyl acrylate,
1-methyl-2-hydroxyethyl acrylate, 2-hydroxybutyl methacrylate,
2-hydroxybutyl acrylate and mixtures thereof.
[0052] Other substituted (meth)acrylate and (meth)acrylamide
monomers useful in the present invention are those with a
dialkylamino group or dialkylaminoalkyl group in the alkyl radical.
Examples of such substituted (meth)acrylates and (meth)acrylamides
include, but are not limited to: dimethylaminoethyl methacrylate,
dimethylaminoethyl acrylate, N,N-dimethylaminoethyl methacrylamide,
N,N-dimethyl-aminopropyl methacrylamide, N,N-dimethylaminobutyl
methacrylamide, N,N-di-ethylaminoethyl methacrylamide,
N,N-diethylaminopropyl methacrylamide, N,N-diethylaminobutyl
methacrylamide, N-(1,1-dimethyl-3-oxobutyl) acrylamide,
N-(1,3-diphenyl-1-ethyl-3-oxobuty- l) acrylamide,
N-(1-methyl-1-phenyl-3-oxobutyl) methacrylamide, and 2-hydroxyethyl
acrylamide, N-methacrylamide of aminoethyl ethylene urea,
N-methacryloxy ethyl morpholine, N-maleimide of
dimethylaminopropylamine and mixtures thereof.
[0053] Other substituted (meth)acrylate monomers useful in the
present invention are silicon-containing monomers such as
.gamma.-propyl tri(C.sub.1-C.sub.6)alkoxysilyl (meth)acrylate,
.gamma.-propyl tri(C.sub.1-C.sub.6)alkylsilyl (meth)acrylate,
.gamma.-propyl di(C.sub.1-C.sub.6)alkoxy(C.sub.1-C.sub.6)alkylsilyl
(meth)acrylate, .gamma.-propyl
di(C.sub.1-C.sub.6)alkyl(C.sub.1-C.sub.6)alkoxysilyl
(meth)acrylate, vinyl tri(C.sub.1-C.sub.6)alkoxysilyl
(meth)acrylate, vinyl
di(C.sub.1-C.sub.6)alkoxy(C.sub.1-C.sub.6)alkylsilyl
(meth)acrylate, vinyl
(C.sub.1-C.sub.6)alkoxydi(C.sub.1-C.sub.6)alkylsily- l
(meth)acrylate, vinyl tri(C.sub.1-C.sub.6)alkylsilyl
(meth)acrylate, and mixtures thereof.
[0054] The vinylaromatic monomers useful as unsaturated monomers in
the present invention include, but are not limited to: styrene
("STY"), .alpha.-methylstyrene, vinyltoluene, p-methylstyrene,
ethylvinylbenzene, vinylnaphthalene, vinylxylenes, and mixtures
thereof.
[0055] Substituted ethylene monomers useful as unsaturated monomers
is in the present invention include, but are not limited to: vinyl
acetate, vinyl formamide, vinyl chloride, vinyl fluoride, vinyl
bromide, vinylidene chloride, vinylidene fluoride and vinylidene
bromide.
[0056] Suitable poly(alkylene oxide) monomers include, but are not
limited to, poly(propylene oxide) monomers, poly(ethylene oxide)
monomers, poly(ethylene oxide/propylene oxide) monomers,
poly(propylene glycol) (meth)acrylates, poly(propylene glycol)
alkyl ether (meth)acrylates, poly(propylene glycol) phenyl ether
(meth)acrylates, poly(propylene glycol) 4-nonylphenol ether
(meth)acrylates, poly(ethylene glycol) (meth)acrylates,
poly(ethylene glycol) alkyl ether (meth)acrylates, poly(ethylene
glycol) phenyl ether (meth)acrylates, poly(propylene/ethylene
glycol) alkyl ether (meth)acrylates and mixtures thereof. Preferred
poly(alkylene oxide) monomers include trimethoylolpropane
ethoxylate tri(meth)acrylate, trimethoylolpropane propoxylate
tri(meth)acrylate, poly(propylene glycol) methyl ether acrylate,
and the like. Particularly suitable poly(propylene glycol) methyl
ether acrylate monomers are those having a molecular weight in the
range of from about 200 to about 2000. The poly(ethylene
oxide/propylene oxide) monomers useful in the present invention may
be linear, block or graft copolymers. Such monomers typically have
a degree of polymerization of from about 1 to about 50, and
preferably from about 2 to about 50.
[0057] Typically, the amount of such additional monomers useful in
the porogen particles of the present invention is from about 1 to
about 99% wt, based on the total weight of the monomers used. The
amount of such additional monomers is preferably from about 2 to
about 90% wt, and more preferably from about 5 to about 80% wt.
[0058] The porogen particles of the present invention also contain
as polymerized units one or more cross-linking agents. At least one
cross-linking agent is a (meth)acrylate cross-linking agent.
Suitable (meth)acrylate cross-linkers useful in the present
invention include di-, tri-, tetra- or higher multi-functional
(meth)acrylate unsaturated monomers. Examples of (meth)acrylate
cross-linkers useful in the present invention include, but are not
limited to: ethyleneglycol diacrylate, trimethylolpropane
triacrylate, allyl methacrylate ("ALMA"), ethyleneglycol
dimethacrylate ("EGDMA"), diethyleneglycol dimethacrylate
("DEGDMA"), propyleneglycol dimethacrylate, propyleneglycol
diacrylate, trimethylolpropane trimethacrylate ("TMPTMA"), glycidyl
methacrylate, 2,2-dimethylpropane-1,3-diacrylate, 1,3-butylene
glycol diacrylate, 1,3-butylene glycol dimethacrylate,
1,4-butanediol diacrylate, diethylene glycol diacrylate, diethylene
glycol dimethacrylate, 1,6-hexanediol diacrylate, 1,6-hexanediol
dimethacrylate, tripropylene glycol diacrylate, triethylene glycol
dimethacrylate, tetraethylene glycol diacrylate, polyethylene
glycol 200 diacrylate, tetraethylene glycol dimethacrylate,
polyethylene glycol dimethacrylate, ethoxylated bisphenol A
diacrylate, ethoxylated bisphenol A dimethacrylate, polyethylene
glycol 600 dimethacrylate, poly(butanediol) diacrylate,
pentaerythritol triacrylate, trimethylolpropane triethoxy
triacrylate, glyceryl propoxy triacrylate, pentaerythritol
tetraacrylate, pentaerythritol tetramethacrylate, dipentaerythritol
monohydroxypentaacrylate, and mixtures thereof.
[0059] One or more additional cross-linking agents may be combined
with the (meth)acrylate cross-linking agent. A wide variety of
cross-linking agents may suitable be combined with the
(meth)acrylate cross-linker. Such additional cross-linking agents
include, but are not limited to, trivinylbenzene, divinyltoluene,
divinylpyridine, divinylnaphthalene, divinylxylene,
diethyleneglycol divinyl ether, trivinylcyclohexane, divinyl
benzene, divinylsilane, trivinylsilane, dimethyldivinylsilane,
divinylmethylsilane, methyltrivinylsilane, diphenyldivinylsilane,
divinylphenylsilane, trivinylphenylsilane,
divinylmethylphenylsilane, tetravinylsilane,
dimethylvinyldisiloxane, poly(methylvinylsiloxane),
poly(vinylhydrosiloxane), poly(phenylvinylsiloxane),
tetraallylsilane, 1,3-dimethyl tetravinyldisiloxane, 1,3-divinyl
tetramethyldisiloxane and mixtures thereof.
[0060] The (meth)acrylate cross-linking agents and additional
cross-linking agents may be used in a wide range of amounts, such
as from 1 to 99%, based on the total weight of monomers and
cross-linking agents. It is preferred that the amount of
cross-linking agent is from 5 to 95%, more preferably from 8 to
90%, and still more preferably from 10 to 50%.
[0061] In general, suitable B-staged thermoset dielectric materials
useful in the present invention have a molecular weight of less
than or equal to about 100,000. Preferably, the molecular weight of
the B-staged thermoset dielectric material is from about 1000 to
about 50,000, and more preferably from 1000 to 35,000. As the
molecular weight of the B-staged dielectric material increases
above about 35,000, it becomes increasingly difficult for the
porogen particles to be compatible with the dielectric material. In
cases where the molecular weight is greater than about 35,000,
particularly greater than or equal to 50,000, it is preferred that
the N-vinyl monomers or heteroatom-substituted styrene monomers be
present in the porogen particles in an amount of at least 20% based
on the total weight of the monomers and cross-linker, and more
preferably greater than 20%, such as 25%, 30%, 35%, 40% and most
preferably at least 45%. For B-staged thermoset dielectric
materials having molecular weights greater than about 35,000, it is
preferred that the porogen particles include N-vinylpyrrolidone as
polymerized units. In addition, for such thermoset materials one or
more different monomers may also be required to compatiblize the
porogen. Such monomers include, but are not limited to, vinyl
benzoate, vinyl naphthalene, vinyl biphenyl and
4-allyl-2-methoxyphenol. In such cases, a (meth)acrylate
cross-linking agent is still used. In an alternate embodiment, when
the B-staged dielectric material is benzocyclobutene, it is
preferred that the porogen particles include vinylanisole as
polymerized units.
[0062] The polymers useful as porogen particles in the present
invention may be prepared by a variety of polymerization
techniques, such as solution polymerization or emulsion
polymerization, and preferably by solution polymerization. The
solution polymers useful in the present invention may be copolymers
or homopolymers and are cross-linked.
[0063] The solution polymers of the present invention may be
prepared by a variety of methods, such as those disclosed in U.S.
Pat. No. 5,863,996 (Graham) and U.S. patent application Ser. No.
09/460,326, both of which are hereby incorporated by reference to
the extent they teach the preparation of such polymers. The
solution polymers of the present invention are generally prepared
in a non-aqueous solvent. Suitable solvents for such
polymerizations are well known to those skilled in the art.
Examples of such solvents include, but are not limited to:
hydrocarbons, such as alkanes, fluorinated hydrocarbons, and
aromatic hydrocarbons, ethers, ketones, esters, alcohols and
mixtures thereof. Particularly suitable solvents include dodecane,
mesitylene, xylenes, diphenyl ether, gamma-butyrolactone, ethyl
lactate, propyleneglycol monomethyl ether acetate, caprolactone,
2-hepatanone, methylisobutyl ketone, diisobutylketone,
propyleneglycol monomethyl ether, decanol, and t-butanol.
[0064] The solution polymer porogen particles of the present
invention typically have a weight average molecular weight in the
range of 5,000 to 1,000,000, preferably in the range of 10,000 to
500,000 and more preferably in the range of 10,000 to 100,000.
These solution polymer porogen particles typically have a particle
size up to about 1,000 nm, such as in the range of 0.75 to 1000 nm.
It is preferred that the mean particle size of a plurality of these
particles is in the range of about 0.75 to about 100 nm, more
preferably from about 0.75 about 50 nm, and most preferably from
about 1 nm to about 20 nm. Particularly useful porogen particles
are those having a mean particle size of .ltoreq.10 nm,
particularly .ltoreq.5 nm, such as 1 nm, 2 nm or 3 nm. The
polydispersity of these solution polymers is in the range 1 to 20
and more preferably in the range of 1.001 to 15 and most preferably
in the range of 1.001 to 10.
[0065] The emulsion polymers useful in the present invention are
generally prepared the methods described in U.S. patent application
Ser. No. 09/460,326, described above. Controlled polymerization of
the monomers in these droplets produces small polymer particles,
i.e. .ltoreq.100 nm, and preferably extremely small polymer
particles, i.e. .ltoreq.50 nm in size. Emulsion polymers having
other suitable mean particle sizes, such as .ltoreq.45 nm,
.ltoreq.40 nm, .ltoreq.35 nm, and .ltoreq.30 nm, may be produced
according to the present invention. Such polymer particles
typically have a lower mean particle size of about 1 nm. Thus, the
present polymer particles have a mean particle size range of from
0.75 to 100 nm, and preferably from 1 to 50 nm. The particle size
polydispersity of these emulsion polymer particles is in the range
1.0001 to 10, more preferably 1.001 to 5, and most preferably 1.001
to 2.5.
[0066] It is preferred that the polymers of the present invention
are prepared using anionic polymerization or free radical
polymerization techniques. It is also preferred that the polymers
useful in the present invention are not prepared by step-growth
polymerization processes.
[0067] The porogen particles of the present invention may be
directly added to the B-staged thermoset dielectric material as is
or may be first purified to remove impurities that might effect the
electrical or physical properties of electronic devices.
Purification of the porogen particles may be accomplished either by
precipitation of the porogen particles or adsorption of the
impurities.
[0068] In general, the cross-linked particles of the present
invention useful as porogens must be dispersible, miscible or
otherwise substantially compatible with the host B-staged
dielectric matrix material in solution and in the thin film. Thus,
the porogen particles must be soluble in the same solvent or mixed
solvent system as the host B-staged thermoset dielectric matrix
material. Also, the porogen particles must be present within this
solution as substantially discrete, substantially non-aggregated or
substantially non-agglomerated particles in order to achieve the
desired benefit of this invention, namely substantially uniformly
dispersed pores with a size comparable to that of the porogen's
size. This is accomplished by modifying the porogen particle
composition such that it is "compatible" with the host B-staged
thermoset dielectric matrix material.
[0069] It has been surprisingly found that when the present porogen
particles include as polymerized units at least one monomer
selected from N-vinyl monomers and heteroatom-substituted styrene
monomers and at least one (meth)acrylate cross-linking agent, that
such porogen particles are substantially compatible with B-staged
thermoset dielectric matrix materials. Such porogen particles, when
added to B-staged thermoset dielectric materials, remain as
substantially discrete, substantially non-aggregated or
substantially non-agglomerated particles. In this way, porous
materials are obtained containing pores having a mean pore diameter
substantially equal to the mean pore diameter of the porogen
particles used. Thus, very large pores, such as so-called "killer
defects or pores" obtained upon agglomeration or aggregation of
porogens, are substantially reduced or eliminated according to the
present invention. Thus, the present invention provides porous
thermoset dielectric materials having much smaller pores, more
uniformly sized pores and more uniformly dispersed pores than
conventional methods.
[0070] An advantage of the present invention is that the porogen
particles are substantially compatible, and preferably fully
compatible, with the dielectric material used. By "compatible" is
meant that a composition of B-staged thermoset dielectric matrix
material and a plurality of porogen particles are optically
transparent to visible light. It is preferred that a solution of
B-staged thermoset dielectric matrix material and porogen
particles, a film or layer including a composition of B-staged
thermoset dielectric material and porogen particles, a composition
including B-staged thermoset dielectric matrix material having
porogen particles dispersed therein, and the resulting porous
dielectric material after removal of the porogen particles are all
optically transparent to visible light. By "substantially
compatible" is meant that a composition of B-staged polyimide
dielectric matrix material and a plurality of porogen particles is
slightly cloudy or slightly opaque. Preferably, "substantially
compatible" means at least one of a solution of B-staged thermoset
dielectric matrix material and porogen particles, a film or layer
including a composition of B-staged thermoset dielectric matrix
material and porogen particles, a composition including B-staged
thermoset dielectric matrix material having porogen particles
dispersed therein, and the resulting porous thermoset dielectric
material after removal of the porogen particles is slightly cloudy
or slightly opaque.
[0071] To be compatible, the porogen particles must be soluble or
miscible in the B-staged thermoset dielectric matrix material, in
the solvent used to dissolve the B-staged thermoset dielectric
matrix material or both. When a film or layer of a composition
including the B-staged thermoset dielectric material, a plurality
of porogen particles and solvent is cast, such as by spin casting,
much of the solvent evaporates. After such film casting, the
porogen particles must be soluble in the B-staged thermoset
dielectric matrix material so that it remains substantially
uniformly dispersed. If the porogen particles are not compatible,
phase separation of the porogen particles from the B-staged
thermoset dielectric matrix material occurs and large domains or
aggregates form, resulting in an increase in the size and
non-uniformity of pores. Such compatible porogen particles provide
cured dielectric materials having substantially uniformly dispersed
pores having substantially the same sizes as the porogen
particles.
[0072] The compatibility of the porogen particles and B-staged
thermoset dielectric matrix material is typically determined by a
matching of their solubility parameters, such as the Van Krevelen
parameters of delta h and delta v. See, for example, Van Krevelen
et al., Properties of Polymers. Their Estimation and Correlation
with Chemical Structure, Elsevier Scientific Publishing Co., 1976;
Olabisi et al., Polymer-Polymer Miscibility, Academic Press, NY,
1979; Coleman et al., Specific Interactions and the Miscibility of
Polymer Blends, Technomic, 1991; and A. F. M. Barton, CRC Handbook
of Solubility Parameters and Other Cohesion Parameters, 2.sup.nd
Ed., CRC Press, 1991. Delta h is a hydrogen bonding parameter of
the material and delta v is a measurement of both dispersive and
polar interaction of the material. Such solubility parameters may
either be calculated, such as by the group contribution method, or
determined by measuring the cloud point of the material in a mixed
solvent system consisting of a soluble solvent and an insoluble
solvent. The solubility parameter at the cloud point is defined as
the weighted percentage of the solvents. Typically, a number of
cloud points are measured for the material and the central area
defined by such cloud points is defined as the area of solubility
parameters of the material.
[0073] When the solubility parameters of the porogen particles and
B-staged thermoset dielectric matrix material are substantially
similar, the porogen particles will be compatible with the
dielectric matrix material and phase separation and/or aggregation
of the porogen particles is less likely to occur. It is preferred
that the solubility parameters, particularly delta h and delta v,
of the porogen particles and B-staged thermoset dielectric matrix
material are substantially matched. It will be appreciated by those
skilled in the art that the properties of the porogen particles
that affect the particles' solubility also affect the compatibility
of these particles with the B-staged thermoset dielectric matrix
material. It will be further appreciated by those skilled in the
art that porogen particles may be compatible with one thermoset
dielectric matrix material, but not another. This is due to the
difference in the solubility parameters of the different B-staged
thermoset dielectric matrix materials.
[0074] To be useful as porogen particles in forming porous
dielectric materials, the porogens of the present invention must be
at least partially removable under conditions which do not
adversely affect the dielectric matrix material, preferably
substantially removable, and more preferably completely removable.
By "removable" is meant that the polymer depolymerizes or otherwise
breaks down into volatile components or fragments which are then
removed from, or migrate out of, the dielectric material yielding
pores or voids. Any procedures or conditions which at least
partially remove the porogen without adversely affecting the
dielectric matrix material may be used. It is preferred that the
porogen is substantially removed. Typical methods of removal
include, but are not limited to, exposure to heat or radiation,
such as, but not limited to, UV, x-ray, gamma ray, alpha particles,
neutron beam or electron beam. It is preferred that the matrix
material is exposed to heat or UV light to remove the porogen.
[0075] The porogen particles of the present invention can be
thermally removed under vacuum, nitrogen, argon, mixtures of
nitrogen and hydrogen, such as forming gas, or other inert or
reducing atmosphere. The porogen particles of the present invention
may be removed at any temperature that is higher than the thermal
curing temperature of the B-staged thermoset matrix material and
lower than the thermal decomposition temperature of the thermoset
dielectric material. Typically, the porogen particles of the
present invention may be removed at temperatures in the range of
150.degree. to 500.degree. C. and preferably in the range of
250.degree. to 450.degree. C. Typically, the porogen particles of
the present invention are removed upon heating for a period of time
in the range of 1 to 120 minutes. An advantage of the porogens of
the present invention is that 0 to 20% by weight of the porogen
remains after removal from the thermoset dielectric material.
[0076] In one embodiment, when a porogen of the present invention
is removed by exposure to radiation, the porogen polymer is
typically exposed under an inert atmosphere, such as nitrogen, to a
radiation source, such as, but not limited to, visible or
ultraviolet light. The porogen fragments generated from such
exposure are removed from the matrix material under a flow of inert
gas. The energy flux of the radiation must be sufficiently high to
generate a sufficient number of free radicals such that porogen
particle is at least partially removed. It will be appreciated by
those skilled in the art that a combination of heat and radiation
may be used to remove the porogens of the present invention.
[0077] In preparing the dielectric matrix materials of the present
invention, the porogen particles described above are first
dispersed within, or dissolved in, a B-staged thermoset dielectric
material. Any amount of porogen particles may be combined with the
B-staged thermoset dielectric matrix materials according to the
present invention. The amount of porogen particles used will depend
on the particular porogen employed, the particular B-staged
thermoset dielectric matrix material employed, and the extent of
dielectric constant reduction desired in the resulting porous
dielectric material. Typically, the amount of porogen particles
used is in the range of from 1 to 90 wt %, based on the weight of
the B-staged thermoset dielectric matrix material, preferably from
10 to 80 wt %, more preferably from 15 to 60 wt %, and still more
preferably from 15 to 30 wt %. A particularly useful amount of
porogen is in the range of form about 1 to about 60 wt %.
[0078] The porogen particles of the present invention may be
combined with the B-staged thermoset dielectric material by any
methods known in the art. Typically, the B-staged thermoset
material is first dissolved in a suitable solvent, such as, but not
limited to, methyl isobutyl ketone, diisobutyl ketone, 2-heptanone,
.gamma.-butyrolactone, .epsilon.-caprolactone, ethyl lactate
propyleneglycol monomethyl ether acetate, propyleneglycol
monomethyl ether, diphenyl ether, anisole, n-amyl acetate, n-butyl
acetate, cyclohexanone, N-methyl-2-pyrrolidone,
N,N'dimethylpropyleneurea, mesitylene, xylenes, or mixtures
thereof, to form a solution. The porogen particles are then
dispersed or dissolved within the solution. The resulting
dispersion is then deposited on a substrate by methods known in the
art, such as spin coating, spray coating or doctor blading, to form
a film or layer.
[0079] After being deposited on a substrate, the B-staged thermoset
dielectric matrix material is then substantially cured to form a
film, layer or coating. The dielectric matrix material is typically
cured by heating at a temperature below that required for removal
of the porogen. Suitable cure temperatures for the B-staged
thermoset dielectric matrix material vary across a wide range but
are generally from about 150.degree. to about 455.degree. C.,
preferably from about 200.degree. to about 400.degree. C.
[0080] Once the B-staged thermoset dielectric matrix material is
cured, the film is subjected to conditions which remove the porogen
particles without substantially degrading the polyimide dielectric
material, that is, less than 5% by weight of the dielectric
material is lost. Typically, such conditions include exposing the
film to heat and/or radiation. It is preferred that the material is
exposed to heat or light to remove the porogen. To remove the
porogen particles thermally, the dielectric material can be heated
by oven heating or microwave heating. Under typical thermal removal
conditions, the polymerized dielectric material is heated to about
300.degree. to about 450.degree. C. It will be recognized by those
skilled in the art that the particular removal temperature of a
thermally labile porogen will vary according to composition of the
porogen. The choice of porogen particles will depend upon the
thermal degradation temperature of the thermoset dielectric
material. Upon removal, the porogen polymer depolymerizes or
otherwise breaks down into volatile components or fragments which
are then removed from, or migrate out of, the dielectric matrix
material yielding pores or voids, which fill up with the carrier
gas used in the process. Thus, a porous thermoset dielectric
material having voids is obtained, where the size of the voids is
substantially the same as the particle size of the porogen. The
resulting dielectric material having voids thus has a lower
dielectric constant than such material without such voids.
[0081] The compatible, i.e., optically transparent, compositions of
the present invention do not suffer from agglomeration or long
range ordering of porogen materials, i.e. the porogen particles are
substantially uniformly dispersed throughout the B-staged thermoset
dielectric matrix material. Thus, the porous thermoset dielectric
materials resulting from removal of the porogen particles have
substantially uniformly dispersed pores. Such substantially
uniformly dispersed, very small pores are very effective in
reducing the dielectric constant of the dielectric materials.
[0082] A further advantage of the present invention is that low
dielectric constant materials are obtained having uniformly
dispersed voids, a higher volume of voids than known dielectric
materials and/or smaller void sizes than known dielectric
materials. These voids are on the order of 0.75 to 1000 nm,
preferably 0.75 to 200 nm, more preferably 0.75 to 50 nm, and most
preferably 1 to 20 nm. Particularly suitable are pores having a
mean pore size of .ltoreq.10 nm, .ltoreq.5 nm, .ltoreq.3 nm, and
.ltoreq.2 nm. Further, the void size can be adjusted, from 1 to
1000 nm and above, by varying the size of the removable porogen
particles. The resulting porous theromoset dielectric material has
low stress, less brittleness, low dielectric constant, low
refractive index, improved toughness and improved compliance during
mechanical contacting to require less contact force during
compression. The porogens of the present invention also act as
impact modifiers for the thermoset materials and improve thermoset
film formation as well as film properties.
[0083] The porogens of the present invention are compatible with
B-staged thermoset material without the need for further
functionalization of the porogen. It is preferred that the present
porogens are not further functionalized, and particularly that they
are not further surface functionalized. Also, the present porogens
are not incorporated into the vitrifying polymer, i.e. the porogens
are not copolymerized with the B-staged thermoset dielectric
material. The present porogen particles are compatibilized with the
B-staged thermoset matrix material by appropriate choice of
monomer, cross-linking agent or both. The present porogens can be
mixed or blended with the B-staged thermoset material without
macroscopic phase separation. Phase separation typically results in
a visually detectable second layer, i.e. the compositions are
opaque. The compositions of the present invention containing
porogen particles in a thermoset dielectric matrix material are
substantially non-phase separated and preferably are not phase
separated. Surprisingly, phase separation of the porogens is
prevented according to the present invention by compatibilizing the
porogens with the thermoset dielectric matrix material. Such
compatibilization, which is based on solubility, is achieved by
choice of monomers used to prepare the porogen, not by immobilizing
(i.e. copolymerizing) the porogen in the matrix polymer.
[0084] The porous thermoset dielectric material made by the process
of the present invention is suitable for use in any application
where a low refractive index or low dielectric constant material
may be used. When the porous dielectric material of the present
invention is a thin film, it is useful as insulators,
anti-reflective coatings, sound barriers, thermal breaks,
insulation, optical coatings and the like. The porous thermoset
dielectric materials of the present invention are preferably useful
in electronic and optoelectronic devices including, but not limited
to, the fabrication of multilevel integrated circuits, e.g.
microprocessors, digital signal processors, memory chips and band
pass filters, thereby increasing their performance and reducing
their cost.
[0085] The porous thermoset dielectric materials of the present
invention are particularly suitable for use in integrated circuits,
optoelectronic devices and wireless devices such as mobile
telephones. The present porous thermosets are suitable used on a
variety of substrates, such as, but not limited to, gallium
arsenide, silicon-germanium, silicon-on-insulator, silicon,
alumina, aluminum-nitride, printed wiring boards, flexible
circuits, multichip modules, flip chips, copper, copper alloys,
aluminum, high dielectric materials, low dielectric materials,
resistors, barrier layers such as titanium or tantalum nitride,
etch stop or cap layers such as silicon nitride, silicon oxide or
silicon oxycarbide, and the like. It will be appreciated that an
overlayer may be applied to such porous thermosets in certain
applications.
[0086] In one embodiment of integrated circuit manufacture, as a
first step, a layer of a composition including B-staged thermoset
dielectric matrix material having a plurality of cross-linked
polymeric porogen dispersed or dissolved therein and optionally a
solvent is deposited on a substrate. Suitable deposition methods
include spin casting, spray casting and doctor blading. Suitable
optional solvents include, but are not limited to: methyl isobutyl
ketone, diisobutyl ketone, 2-heptanone, .gamma.-butyrolactone,
.epsilon.-caprolactone, ethyl lactate propyleneglycol monomethyl
ether acetate, propyleneglycol monomethyl ether, diphenyl ether,
anisole, n-amyl acetate, n-butyl acetate, cyclohexanone,
N-methyl-2-pyrrolidone, N,N'-dimethylpropyleneurea, mesitylene,
xylenes or mixtures thereof. Suitable substrates include, but are
not limited to: silicon, silicon dioxide, silicon oxycarbide,
silicon germanium, silicon-on-insulator, glass, silicon nitride,
ceramics, aluminum, copper, gallium arsenide, plastics, such as
polycarbonate, circuit boards, such as FR-4 and polyimide, and
hybrid circuit substrates, such as aluminum nitride-alumina. Such
substrates may further include thin films deposited thereon, such
films including, but not limited to: metal nitrides, metal
carbides, metal suicides, metal oxides, and mixtures thereof. In a
multilayer integrated circuit device, an underlying layer of
insulated, planarized circuit lines can also function as a
substrate.
[0087] In a second step in the manufacture of integrated circuits,
the B-staged thermoset matrix material is cured to form a thermoset
dielectric matrix material. In a third step, the resulting cured
thermoset dielectric matrix material is then subjected to
conditions such that the porogen particles contained therein is
substantially removed without adversely affecting the dielectric
material to yield a porous thermoset dielectric material.
[0088] The porous thermoset dielectric material is then
lithographically patterned to form vias and/or trenches in
subsequent processing steps. The trenches generally extend to the
substrate and connect to at least one metallic via. Typically,
lithographic patterning involves (i) coating the dielectric
material layer with a positive or negative photoresist, such as
those marketed by Shipley Company (Marlborough, Mass.); (ii)
imagewise exposing, through a mask, the photoresist to radiation,
such as light of appropriate wavelength or e-beam; (iii) developing
the image in the resist, e.g., with a suitable developer; and (iv)
transferring the image through the dielectric layer to the
substrate with a suitable transfer technique such as reactive ion
beam etching. Optionally, an antireflective composition may be
disposed on the dielectric material prior to the photoresist
coating. Such lithographic patterning techniques are well known to
those skilled in the art.
[0089] A metallic film is then deposited onto the patterned
dielectric layer to fill the trenches. Preferred metallic materials
include, but are not limited to: copper, tungsten, gold, silver,
aluminum or alloys thereof. The metal is typically deposited onto
the patterned dielectric layer by techniques well known to those
skilled in the art. Such techniques include, but are not limited
to: chemical vapor deposition ("CVD"), plasma-enhanced CVD,
combustion CVD ("CCVD"), electro and electroless deposition,
sputtering, or the like. Optionally, a metallic liner, such as a
layer of nickel, tantalum, titanium, tungsten, or chromium,
including nitrides or silicides thereof, or other layers such as
barrier or adhesion layers, e.g. silicon nitride or titanium
nitride, is deposited on the patterned and etched dielectric
material.
[0090] In a fifth step of the process for integrated circuit
manufacture, excess metallic material is removed, e.g. by
planarizing the metallic film, so that the resulting metallic
material is generally level with the patterned dielectric layer.
Planarization is typically accomplished with chemical/mechanical
polishing or selective wet or dry etching. Such planarization
methods are well known to those skilled in the art.
[0091] It will be appreciated by those skilled in the art that
multiple layers of dielectric material, including multiple layers
of thermoset dielectric material, and metal layers may subsequently
be applied by repeating the above steps. The above steps in the
manufacture of an electronic device may further include one or more
other steps, such as, but not limited to, the application of etch
stops, cap layers, barrier layers, seed layers and the like. It
will be further appreciated by those skilled in the art that the
compositions of the present invention are useful in any and all
methods of integrated circuit manufacture.
[0092] The following examples are presented to illustrate further
various aspects of the present invention, but are not intended to
limit the scope of the invention in any aspect.
EXAMPLE 1
[0093] A vinylanisole containing cross-linked porogen was prepared
by polymerizing the monomers
vinylanisole/styrene/trimethylolpropane triacrylate in a weight
ratio of 45/45/10.
[0094] Approximately 2 mL of a 35 wt % solids solution of a
commercially available B-staged benzocyclobutene ("BCB") in
mesitylene and 2 mL of a 15 wt % solids solution of the porogen in
mesitylene were combined in a 20 mL vial and mixed thoroughly. The
resultant pale yellow transparent solution contained 70% BCB and
30% porogen with a total solids content of 25%. 2 mL of the
solution was disposed by a pipette onto a stationary 4 inch (ca. 10
cm) wafer on a spin coater. The wafer was then spun at 2500 rpm for
30 seconds and the wafer was removed and the film visually
examined. The BCB/porogen film was clear and free of visible
defects, striations or haze. The wafer was then heated to
150.degree. C. on a brass hot plate for 1 minute to remove excess
solvent. The film was then again visually examined and was clear
and free of visible defects, striations or haze. Thus, the porogen
was compatible with the B-staged BCB dielectric material.
EXAMPLE 2
[0095] The following porogen samples were prepared by polymerizing
the monomers in the amounts reported in Table 1.
1TABLE 1 Porogen Sample Monomer A Monomer B Cross-linker C A/B/C A
STY NVP TMPTA 45/45/10 B NVP -- TMPTA 90/10 C STY NVP TMPTA
80/10/10 D STY VAS TMPTA 45/45/10 E STY NVPIM TMPTA 45/45/10 F STY
4FSTY TMPTA 80/10/10 G STY VAS TMPTA 80/10/10
EXAMPLE 3
[0096] The compatibility of a number of porogen samples from
Example 2 in B-staged polyarylene ether dielectric materials in
cyclohexanone was determined. The B-staged polyarylene ether
material was either VELOX A poly(arylene ether) ("Polyarylene ether
A") or VELOX N poly(arylene ether) ("Polyarylene ether N"), both
available from Air Products/Shumacher. Both commercially available
B-staged materials had a molecular weight of approximately 50,000.
Compatibility determinations were performed by visually inspecting
a film of the B-staged polyarylene ether dielectric material and
porogen that was spun cast on a silicon wafer at 1000 rpm. The
porogen was loaded into the B-staged polyarylene dielectric
material at ca. 50% by weight with a total solids content of ca.
20%. The film thicknesses were from 0.9 to 2 .mu.m. All visual
inspections were by naked-eye under daylight. Film compatibility of
the porogen in the polyarylene ether dielectric material was
determined after removal of the solvent, but before removal of the
porogen. The compatibility results are reported in Table 2.
2 TABLE 2 Polyarylene Porogen Solution Film Ether Sample
Compatibility Compatibility A A clear clear B clear clear C cloudy
-- N A clear clear B clear clear C cloudy --
[0097] From these data, it can be clearly seen that Porogen Samples
A and B were compatible with both polyarylene ether samples.
Porogen Sample C, which contained the same components as Porogen
Sample A, did not contain a sufficient amount of NVP to
compatiblize the porogen with the high molecular weight (ca.
50,000) B-staged polyarylene ether.
* * * * *