U.S. patent application number 10/352628 was filed with the patent office on 2004-01-22 for porous low-dielectric constant materials for use in electronic devices.
Invention is credited to Hawker, Craig Jon, Hedrick, James L., Miller, Robert D., Volksen, Willi.
Application Number | 20040012076 10/352628 |
Document ID | / |
Family ID | 23754065 |
Filed Date | 2004-01-22 |
United States Patent
Application |
20040012076 |
Kind Code |
A1 |
Hawker, Craig Jon ; et
al. |
January 22, 2004 |
Porous low-dielectric constant materials for use in electronic
devices
Abstract
A novel dielectric composition is provided that is useful in the
manufacture of electronic devices such as integrated circuit
devices and integrated circuit packaging devices. The dielectric
composition is prepared by crosslinking a thermally decomposable
porogen to a host polymer via a coupling agent, followed by heating
to a temperature suitable to decompose the porogen. The porous
materials that result have dielectric constants of less than
2.4.
Inventors: |
Hawker, Craig Jon; (Los
Gatos, CA) ; Hedrick, James L.; (Pleasanton, CA)
; Miller, Robert D.; (San Jose, CA) ; Volksen,
Willi; (San Jose, CA) |
Correspondence
Address: |
REED & EBERLE LLP
800 MENLO AVENUE, SUITE 210
MENLO PARK
CA
94025
US
|
Family ID: |
23754065 |
Appl. No.: |
10/352628 |
Filed: |
January 27, 2003 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10352628 |
Jan 27, 2003 |
|
|
|
09892234 |
Jun 26, 2001 |
|
|
|
6541865 |
|
|
|
|
09892234 |
Jun 26, 2001 |
|
|
|
09441730 |
Nov 16, 1999 |
|
|
|
6342454 |
|
|
|
|
Current U.S.
Class: |
257/642 ;
257/643; 257/E21.273; 257/E21.581; 257/E23.077; 257/E23.144;
257/E23.167; 438/725; 438/82 |
Current CPC
Class: |
H01L 2924/0002 20130101;
Y10S 977/788 20130101; H01L 23/5222 20130101; H01L 23/5329
20130101; H05K 3/28 20130101; H05K 1/024 20130101; H01L 2924/00
20130101; H01L 2221/1047 20130101; H01L 21/02203 20130101; H01L
23/49894 20130101; Y10S 977/773 20130101; Y10T 428/12528 20150115;
Y10T 428/249953 20150401; Y10T 428/24504 20150115; H01L 2924/09701
20130101; H01L 21/7682 20130101; H01L 21/31695 20130101; H01L
21/02126 20130101; H01L 21/02216 20130101; H01L 2924/0002 20130101;
H01L 21/02282 20130101 |
Class at
Publication: |
257/642 ;
257/643; 438/82; 438/725 |
International
Class: |
H01L 021/00; H01L
023/58 |
Claims
1. A dielectric material comprised of a porous polymeric material
having closed cell pores less than about 200 .ANG. in diameter, a
void percentage in the range of approximately 5% to 35%, and a
dielectric constant of less than 2.4, wherein the polymeric
material comprises a host polymer that has a pre-process molecular
weight in the range of approximately 750 to 100,000 and a glass
transition temperature of at least about 400.degree. C.
2. The dielectric material of claim 1, wherein the host polymer is
an organic thermosetting polymer.
3. The dielectric material of claim 1, wherein the host polymer is
a crosslinked polymer.
4. The dielectric material of claim 1, wherein the host polymer is
silicon-containing.
5. The dielectric material of claim 4, wherein the host polymer is
selected from the group consisting of silsesquioxanes,
alkoxysilanes, organic silicates, orthosilicates, and combinations
thereof.
6. The dielectric material of claim 5, wherein the host polymer is
a silsesquioxane, and derivatives and combinations thereof.
7. The dielectric material of claim 6, wherein the silsesquioxane
is selected from the group consisting of hydrogen silsesquioxanes,
alkyl silsesquioxanes, aryl silsesquioxanes, and derivatives and
combinations thereof.
8. The dielectric material of claim 7, wherein the host polymer is
selected from the group consisting of hydrogen silsesquioxanes,
lower alkyl silsesquioxanes and phenyl silsesquioxanes.
9. The dielectric material of claim 1, wherein the host polymer is
a copolymer of a polyimide and a silsesquioxane.
10. The dielectric material of claim 1, wherein the host polymer is
a polyimide.
11. The dielectric material of claim 1, wherein the host polymer is
a polybenzocyclobutene.
12. The dielectric material of claim 1, wherein the host polymer is
a poly(arylene).
13. The dielectric material of claim 1, wherein the host polymer is
a poly(arylene ether).
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. Ser. No.
09/892,234, filed Jun. 26, 2001, which is a divisional of U.S. Ser.
No. 09/441,730, filed Nov. 16, 1999, now U.S. Pat. No. 6,342,454,
which was based on a common specification with application Ser. No.
09/441,728, also filed on Nov. 16, 1999, now U.S. Pat. No.
6,107,357.
TECHNICAL FIELD
[0002] This invention relates generally to dielectric materials and
their use in electronic devices such as integrated circuits. More
particularly, the invention pertains to novel dielectric materials
of foamed polymers and associated methods of preparation. The novel
dielectric materials are particularly useful in the fabrication of
electronic devices such as integrated circuit devices and
integrated circuit packaging devices.
BACKGROUND
[0003] As semiconductor devices are becoming smaller and on-chip
device density is correspondingly increasing, both signal delays
due to capacitive coupling and crosstalk between closely spaced
metal lines are increasing. These problems are exacerbated by the
need to keep conductor lines as short as possible in order to
minimize transmission delays, thus requiring multilevel wiring
schemes for the chip. The problems have been ameliorated to some
extent by the switch to copper metallurgy, but as feature sizes go
below 0.25 .quadrature.m, this alone will not provide a solution.
The use of an insulator with a lower dielectric constant than the
currently used SiO.sub.2 (k=8.9-4.1) would also, clearly, improve
the situation. Current integration demands for insulators used
with, for example, Al(Cu) wiring, also require thermal stabilities
in excess of 450.degree. C., good mechanical properties, resistance
to crack generation and propagation, low defect densities, low
water uptake, chemical resistance, processability by
photolithographic techniques and gas phase etching procedures, and
capacity for planarization.
[0004] Accordingly, considerable attention has focused on the
replacement of silicon dioxide with new materials, particularly
materials having lower dielectric constants, since both capacitive
delays and power consumption depend on the dielectric constant of
the insulator. This is not a simple matter given the complexities
and demands of current semiconductor integration processes. Of the
existing materials with demonstrated ultra-low dielectric
constants, the highly fluorinated materials (e.g., Teflon.RTM.)
have the longest history. For example, attempts have been made to
reduce the dielectric constant of polyimides by incorporating
perfluoroalkyl-containing comonomers into the polymer structure
(see, e.g., Haidar et al. (1991) Mater. Res. Soc. Symp. Proc.
227:35; Critchlen et al. (1972) J. Polym. Sci. A-1 10:1789; and
Harris et al. (1991) Mater. Res. Soc. Symp. Proc. 227:3). The
synthesis of polyimides based on 9,9-disubstituted xanthene
dianhydrides, e.g., 6FXDA/6FDA
(9,9-bis(trifluoromethoxy)xanthenetetracarboxylic
dianhydride/2,2-bis(4-aminophenyl)-1,1,1,3,3,3-hexafluoropropane),
as well as polyimides based on the TFMOB monomer
(2,2-bis(trifluoromethyl)be- nzidine), has been reported. See
Muraka (March 1996) Solid State Tech 83 and Jang et al. (1994)
Mater. Res. Soc. Symp. Proc. 337:25. Although these alkane polymers
have the lowest dielectric constants of any homogeneous polymers,
there are many liabilities. Current integration requirements call
for exceptional thermal stability at temperatures in the range of
400-450.degree. C. This temperature region is a problem for most
organic polymers, and particularly for fluorocarbons. Also,
adhesion of fluorinated materials (self-adhesion, adhesion to
metals, dielectrics, ceramics, etc.) is a problem without some
prior surface pretreatment. Further, the stability of fluorinated
materials with metallurgy at elevated temperatures is problematic.
The mechanical properties of known fluorinated materials are not
ideal; they usually have large thermal expansion coefficients and
are intrinsically soft materials. The latter creates a problem for
chemical mechanical polishing (CMP) procedures. Finally, the
methodology to develop other highly fluorinated materials such as
fluorinated polyimides is limited by synthetic difficulties
associated with the incorporation of a substantial number of
pendant perfluoroalkyl groups.
[0005] Attempts have been made to reduce the dielectric constant of
such materials through the introduction of kinks and
conjugation-interrupting linkages in the polymer backbone to lower
molecular polarizability and reduce chain-chain interactions (St.
Clair et al. (1988) Proc. Amer. Chem. Soc. Div. Polym. Mater. Sci.
Eng. 59:28). A more viable approach, however, has been controlled
introduction of porosity into existing low dielectric constant
materials.
[0006] Generation of porous polymer foams substantially reduces the
dielectric constant of the material while maintaining the desired
thermal and mechanical properties of the base (or "host") polymer.
The reduction in dielectric constant is achieved by incorporating
air voids, as air has a dielectric constant of 1. The advantage of
a foam approach is illustrated in Hedrick et al. (1995) Polymer
36:2685, which illustrates in graph form a Maxwell-Garnett model of
composite structures based on a matrix polymer having an initial
dielectric constant of 2.8. Incorporation of a second phase of
dielectric constant 1.0, as with the introduction of air-filled
pores in a foam, causes a dramatic reduction in the dielectric
constant. However, foams provide a unique set of problems for
dielectric applications. The pore size must be much smaller than
both the film thickness and any microelectronic device features. In
addition, it is desired that the pores be closed cell, i.e. the
connectivity between the pores must be minimal to prevent the
diffusion of reactive contaminants. Finally, the volume fraction of
the voids must be as high as possible to achieve the lowest
possible dielectric constant. All of these features can alter the
mechanical properties of the film and affect the structural
stability of the foam.
[0007] An approach that has been developed for preparing a
dielectric polymer foam with pore sizes in the nanometer regime
involves the use of block copolymers composed of a high
temperature, high T.sub.g polymer and a second component which can
undergo clean thermal decomposition with the evolution of gaseous
by-products to form a closed-cell, porous structure. See, e.g.,
Hedrick et al. (1993) Polymer 34:4717, and Hedrick et al. (1995)
Polymer 36:4855. The process involves use of block copolymers that
can undergo thermodynamically controlled phase separation to
provide a matrix with a dispersed phase that is roughly spherical
in morphology, monodisperse in size and discontinuous. By using as
a host or matrix material a thermally stable polymer of low
dielectric constant and, as the dispersed phase, a labile polymer
that undergoes thermolysis at a temperature below the T.sub.g of
the matrix to yield volatile reaction products, one can prepare
foams with pores in the nanometer dimensional regime that have no
percolation pathway; they are closed structures with nanometer size
pores that contain air.
[0008] While the method has proved to be somewhat useful, the
inventors herein have found the formation of porous structures to
be problematic in several respects. That is, although the concept
was demonstrated in principle (see Hedrick et al. (1993); and
Hedrick et al. (1995)), processing was complicated by synthetic
difficulties and by the extremely small processing window. Also,
the thermal stability of the foam product was limited to about
350-375.degree. C. (Hedrick et al. (1996) J. Polym. Sci.; Polym.
Chem. 34, 2867). Furthermore, although dielectric constants of
2.3-2.4 were achieved at porosity levels less than about 20% (see
Hedrick et al. (1996)), the pore content could not be further
increased without compromising the small domain sizes and/or the
non-interconnectivity of the pore structure.
[0009] The present invention is addressed to the aforementioned
need in the art, and provides a novel method for preparing low
dielectric materials comprised of foamed polymer structures with a
significantly increased processing window, wherein the structures
contain non-interconnected, "closed cell" pores in the form of
sharply defined domains at most 200 .quadrature. in diameter,
wherein the structures have very low dielectric constants (on the
order of 3.0 or less), are thermally stable at temperatures in
excess of 450.degree. C., have good mechanical properties, are
resistant to crack generation and propagation, and are readily
processable by photolithographic techniques.
SUMMARY OF THE INVENTION
[0010] Accordingly, it is a primary object of the invention to
address the above-mentioned need in the art by providing novel
dielectric materials that are useful, inter alia, in electronic
devices.
[0011] It is another object of the invention to provide such
dielectric materials that are useful in integrated circuit devices.
It is still another object of the invention to provide such
dielectric materials in the form of a foam.
[0012] It is yet another object of the invention to provide methods
for manufacturing the present dielectric materials.
[0013] It is an additional object of the invention to provide an
integrated circuit device in which metallic circuit lines on a
substrate are electrically insulated from each other by a
dielectric material of the invention.
[0014] Still a further object of the invention is to provide an
integrated circuit packaging device (multichip module) that
incorporates a dielectric material of the invention.
[0015] Additional objects, advantages and novel features of the
invention will be set forth in part in the description which
follows, and in part will become apparent to those skilled in the
art upon examination of the following, or may be learned by
practice of the invention.
[0016] The invention thus provides, in one embodiment, a novel
dielectric material comprised of a porous material having closed
cell pores less than about 200 .ANG. in diameter, preferably less
than about 100 .ANG. in diameter, a void percentage in the range of
approximately 5% to 35%, and a dielectric constant of less than
3.0, wherein the polymeric material comprises a host polymer that
has a pre-process molecular weight in the range of approximately
750 to 100,000, and is thermally stable at temperatures of at least
about 400.degree. C., preferably temperatures of at least about
450.degree. C. Such dielectric materials are prepared using the
following process steps: (a) admixing, in a suitable solvent, (i) a
thermally labile porogen having a reactive site that enables
covalent attachment to another molecular moiety, (ii) a thermally
stable, low dielectric constant host polymer having a high glass
transition temperature T.sub.g, and (iii) a coupling agent
effective to covalently bind to both the reactive site of the
porogen and the host polymer; (b) heating the admixture to a
temperature T.sub.C effective to couple the porogen to the host
polymer via the coupling agent, whereby a polymeric matrix is
formed in which the porogen is present as a discrete phase within a
continuous phase formed by the host polymer; and (c) heating the
polymeric matrix to a temperature T.sub.D effective to degrade the
porogen without affecting the host polymer, leaving closed cell
"pores" behind, wherein T.sub.C<T.sub.D<T.sub.g.
[0017] In another embodiment of the invention, an integrated
circuit device is provided that comprises: (a) a substrate; (b)
individual metallic circuit lines positioned on the substrate; and
(c) a dielectric composition positioned over and/or between the
individual metallic circuit lines, the dielectric composition
comprising the novel dielectric material of the invention.
[0018] Still an additional embodiment of the invention relates to
an integrated circuit packaging device providing signal and power
current to an integrated circuit chip, the packaging device
comprising:
[0019] (i) a substrate having electrical conductor means for
connection to a circuit board,
[0020] (ii) a plurality of alternating electrically insulating and
conducting layers positioned on the substrate wherein at least one
of the electrically insulating layers is comprised of a dielectric
material as provided herein; and
[0021] (iii) a plurality of vias for electrically interconnecting
the electrical conductor, the conducting layers and the integrated
circuit chip.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 is a cross-sectional view of a portion of an
integrated circuit device fabricated using the novel dielectric
materials provided herein.
[0023] FIGS. 2-5 schematically illustrate a process for making an
integrated circuit device using the present dielectric
materials.
[0024] FIGS. 6-8 schematically illustrate an alternative process
for making an integrated circuit device using the present
dielectric materials.
DETAILED DESCRIPTION OF THE INVENTION
[0025] Overview and Definitions:
[0026] Before describing the present invention in detail, it is to
be understood that this invention is not limited to specific
compositions, components, or process steps, as such may vary. It is
also to be understood that the terminology used herein is for the
purpose of describing particular embodiments only, and is not
intended to be limiting.
[0027] It must be noted that, as used in this specification and the
appended claims, the singular forms "a," "and," and "the" include
plural referents unless the context clearly dictates otherwise.
Thus, for example, reference to "a porogen" includes mixtures of
porogens, a "host polymer" includes mixtures of host polymers, "a
solvent" includes mixtures of solvents, and the like.
[0028] In describing and claiming the present invention, the
following terminology will be used in accordance with the
definitions set out below.
[0029] The term "alkyl" as used herein refers to a branched or
unbranched saturated hydrocarbon group of 1 to approximately 24
carbon atoms, such as methyl, ethyl, n-propyl, isopropyl, n-butyl,
isobutyl, t-butyl, octyl, decyl, tetradecyl, hexadecyl, eicosyl and
tetracosyl, as well as cycloalkyl groups such as cyclopentyl and
cyclohexyl. The term "lower alkyl" intends an alkyl group of 1 to 6
carbon atoms.
[0030] The term "alkylene" as used herein refers to a difunctional
saturated branched or unbranched hydrocarbon chain containing from
1 to approximately 24 carbon atoms, typically 1 to approximately 12
carbon atoms, and includes, for example, methylene (--CH.sub.2--),
ethylene (--CH.sub.2--CH.sub.2--), propylene
(--CH.sub.2--CH.sub.2--CH.sub.2--), 2-methylpropylene
(--CH.sub.2--CH(CH.sub.3)--CH.sub.2--), hexylene
(_(CH.sub.2).sub.6--), and the like. "Lower alkylene" refers to an
alkylene group of 1 to 6, more preferably 1 to 4, carbon atoms.
[0031] The term "alkoxy" as used herein refers to a substituent
--O--R wherein R is alkyl as defined above. The term "lower alkoxy"
refers to such a group wherein R is lower alkyl, e.g., methoxy,
ethoxy and the like.
[0032] The term "aryl" as used herein, and unless otherwise
specified, refers to an aromatic moiety containing 1 to 5 aromatic
rings. For aryl groups containing more than one aromatic ring, the
rings may be fused or linked. Aryl groups are optionally
substituted with one or more inert, nonhydrogen substituents per
ring; suitable "inert, nonhydrogen" substituents include, for
example, halo, haloalkyl (preferably halo-substituted lower alkyl),
alkyl (preferably lower alkyl), alkenyl (preferably lower alkenyl),
alkynyl (preferably lower alkynyl), alkoxy (preferably lower
alkoxy), alkoxycarbonyl (preferably lower alkoxycarbonyl), carboxy,
nitro, cyano and sulfonyl. Unless otherwise indicated, the term
"aryl" is also intended to include heteroaromatic moieties, i.e.,
aromatic heterocycles. Generally, although not necessarily, the
heteroatoms will be nitrogen, oxygen or sulfur.
[0033] The term "halo" is used in its conventional sense to refer
to a chloro, bromo, fluoro or iodo substituent. In the reagents and
materials described and claimed herein, halo substituents are
generally fluoro or chloro. The terms "haloalkyl," "haloaryl" (or
"halogenated alkyl" or "halogenated aryl") refer to an alkyl or
aryl group, respectively, in which at least one of the hydrogen
atoms in the group has been replaced with a halogen atom.
[0034] The term "hydrocarbyl" is used in its conventional sense to
refer to a hydrocarbon group containing carbon and hydrogen, and
may be aliphatic, alicyclic or aromatic, or may contain a
combination of aliphatic, alicyclic and/or aromatic moieties. The
hydrocarbyl substituents herein generally contain 1 to 24 carbon
atoms, more typically 1 to 12 carbon atoms, and may be substituted
with various substituents and functional groups.
[0035] The term "polymer" is used to refer to a chemical compound
that comprises linked monomers, and that may or may not be linear,
crosslinked or thermosetting.
[0036] Process for Preparing the Novel Dielectric Material:
[0037] In a first embodiment, the invention provides a process for
preparing a low dielectric constant, foamed polymeric material
having numerous advantages. In contrast to prior processes, the
present method enables use of higher molecular weight polymers and
simplified procedures, resulting in a thermally and chemically
stable porous material with a high void percentage, on the order of
5% to 35%, and a dielectric constant less than 3.0, preferably less
than 2.8, and most preferably less than 2.5.
[0038] The process involves, at the outset, admixing (i) a
thermally labile porogen having a reactive site that enables
covalent attachment to another molecular moiety, (ii) a thermally
stable, low dielectric constant host polymer, and (iii) a coupling
or "crosslinking" agent effective to covalently bind to both the
reactive site of the porogen and the host polymer, in a suitable
solvent. The admixture is heated to a crosslinking temperature
T.sub.C to bring about coupling of the porogen to the host polymer
via the coupling agent. This crosslinking reaction results in
formation of a polymeric matrix in which the porogen is present as
a discrete phase within a continuous phase formed by the host
polymer. After formation of the matrix, the porogen is thermally
degraded, leaving closed cell pores present throughout. This latter
step involves heating the polymeric matrix to a temperature T.sub.D
effective to degrade the porogen without affecting the host
polymer, i.e., T.sub.D is less than the glass transition
temperature T.sub.g of the host polymer.
[0039] 1. The Host Polymer
[0040] As noted above, the present process allows use of high
molecular weight host polymers, i.e., host polymers having a
pre-processing molecular weight of at least about 750, and
preferably at least about 5,000. Generally, the host polymer will
have a pre-processing molecular weight in the range of
approximately 750 to 100,000. In addition, the host polymer should
have, after curing, a high glass transition temperature T.sub.g,
i.e., a T.sub.g of at least about 400.degree. C., most preferably
at least about 450.degree. C.
[0041] The host polymer is typically although not necessarily a
silicon-containing polymer, preferably organic polysilica. Organic
polysilica is a polymeric compound comprising silicon, carbon,
oxygen and hydrogen atoms. Suitable organic polysilica include (i)
silsesquioxanes, (ii) alkoxy silanes, preferably partially
condensed alkoxysilanes (e.g., partially condensed by controlled
hydrolysis of tetraethoxysilane having an Mn of about 500 to
20,000), (iii) organically modified silicates having the
composition RSiO.sub.3 and R.sub.2SiO.sub.2 wherein R is an organic
substituent, and (iv) orthosilicates, preferably partially
condensed orthosilicates having the composition SiOR.sub.4.
Silsesquioxanes are polymeric silicate materials of the type
(RSiO.sub.1.5).sub.n where R is an organic substituent.
[0042] Suitable organic polysilica for use in the present invention
are known to those skilled in the art. Preferably, the organic
polysilica is a silsesquioxane. Suitable silsesquioxanes for the
present invention include, but are not limited to, hydrogen
silsesquioxanes, alkyl (preferably lower alkyl, e.g., methyl)
silsesquioxanes, aryl (e.g., phenyl) or alkyl/aryl silsesquioxanes,
and copolymers of silsesquioxanes (e.g., copolymers of polyimides
and silsesquioxanes), all of which are commercially available
(e.g., GR950 from Techniglass, Perrysburg, Ohio). Other suitable
silsesquioxanes will be known to those skilled in the art and are
disclosed in the pertinent texts, patent documents and literature
references; see, e.g., U.S. Pat. No. 5,384,376, and Chem. Rev.
95:1409.sub.--1430 (1995).
[0043] Other suitable host polymers include without limitation high
temperature polymers and thermosetting network resins such as
polyimide, polybenzocyclobutene, and polyarylenes such as
polyphenylenes, poly(phenylquinoxalines) and poly(arylene ethers).
Polyimides, as known in the art, are formed by imidization of a
poly(amic acid) or poly(amic acid ester), preferably a poly(amic
acid ester), which is in turn synthesized from a diamine and a
diester diacyl halide comprising the reaction product of a
tetracarboxylic dianhydride and a lower alkanol. Suitable
dianhydrides for preparing poly(amic acid esters) that can be
imidized to give polyimides useful herein include, but are not
limited to, the following: pyromellitic dianhydride (PMDA);
benzophenone dianhydride (BPDA); 2,2-bis(3,4-dicarboxyphenyl)
propane dianhydride; 3,3',4,4'-biphenyl-tetracarboxylic acid
dianhydride; bis(3,4-dicarboxyphenyl) ether dianhydride;
bis(3,4-dicarboxy-phenyl) thioether dianhydride; bisphenol-A
bisether dianhydride;
2,2-bis(3,4-dicarboxylphenyl)-hexafluoropropane dianhydride;
2,3,6,7-naphthalenetetra-carboxylic acid dianhydride;
bis(3,4-dicarboxyphenyl) sulfone dianhydride; 1,2,5,6-naphthalene
tetracarboxylic dianhydride; 2,2',3,3'-biphenyl tetracarboxylic
dianhydride; 9,9-bis-(trifluoromethyl) xanthenetetracarboxylic
dianhydride (6FXDA); 9-trifluoromethyl-9-phenyl
xanthenetetracarboxylic dianhydride; 3,4,3',4'-benzophenone
tetracarboxylic dianhydride; and terphenyldianhydride.
Correspondingly, suitable diamines for preparing poly(amic acid
ester) precursors that can be imidized for use herein include
without limitation: p-phenylene diamine (PDA);
4,4'-diamino-diphenylamine; benzidine; 4,4'-diamino-diphenyl ether
(ODA); 1,5-diamino-naphthalene; 3,3'-dimethyl-4,4'diamino-biphenyl;
3,3'-dimethoxybenzidine; 1,4-bis(p-aminophenoxy) benzene;
1,3-bis(p-aminophenoxy) benzene;
2,2-bis[4-aminophenyl]hexafluoropropane (6FDA);
1,1-bis(4-aminophenyl)-1-phenyl-2,2,2-trifluoroethane (3FDA); and
9,9-bis(4-aminophenyl) fluorene (FDA). Particularly preferred
polyimides for use herein are formed by imidization of a poly(amic
acid ester) formed from a dianhydride selected from the group
consisting of PMDA, BPDA and 6FXDA and a diamine selected from the
group consisting of PDA, ODA and 6FDAM. Examples of such preferred
structures are as follows: 1
[0044] 2. The Porogen
[0045] The porogen is a thermally degradable material, which, upon
heating to the material's decomposition temperature T.sub.D,
decomposes quantitatively into non-reactive species that can
readily diffuse through the host polymer matrix. The temperature at
which decomposition occurs should be sufficiently high to permit
standard film preparation and solvent removal yet below the T.sub.g
of the host polymer to avoid collapse of the foam matrix. Porogens
thus have a decomposition temperature T.sub.D that is at least
about 250.degree. C., preferably 30020 C.
[0046] Suitable porogens are generally decomposable polymers,
including not only linear, branched and crosslinked polymers and
copolymers, but also crosslinked polymeric nanoparticles with
reactive surface functionality. Linear polymers are preferred, and
vinyl-based polymers and polyethers are most preferred. Optimally,
the porogen is a polymer comprised of monomer units selected from
the group consisting of styrene, halogenated styrene,
hydroxy-substituted styrene, lower alkyl-substituted styrene,
acrylic acid, acrylamide, methacrylic acid, methyl acrylate, ethyl
acrylate, butyl acrylate, ethylene oxide, propylene oxide, and
combinations thereof, with poly(methyl methacrylate) (PMMA),
polystyrene and poly(-methyl styrene) preferred. Additional
polymers that may serve as the porogen herein include, but are not
limited to: aliphatic polycarbonates such as poly(propylene
carbonate) and poly(ethylene carbonate); polyesters; polysulfones;
polylactides; polylactones. The porogen may be a homopolymer, or it
may be a copolymer comprised of any of the foregoing monomeric
materials, e.g., poly(styrene-co-methyl styrene),
poly(styrene-ethylene oxide), poly(ether-lactones),
poly(ester-carbonates), and poly(lactone-lactides).
[0047] In order to couple the porogen to the host polymer, the
porogen must have at least one reactive site capable of reacting
with the coupling agent. The reaction may involve nucleophilic
substitution, electrophilic substitution, free radical
substitution, Diels Alder reactions, elimination, or any other
mechanism capable of resulting in the formation of a new covalent
bond. When the coupling reaction involves nucleophilic
substitution, the porogen may be functionalized so as to contain a
reactive site comprised of a nucleophilic moiety, e.g., --OH,
--NH.sub.2 or the like; alternatively, the porogen may be
functionalized so as to contain a reactive site capable of reaction
with such a nucleophilic moiety. Introduction of reactive sites can
be carried out using conventional methods, known to those skilled
in the art and/or described in the pertinent literature. For
example, monohydroxyl-terminated porogen polymers may be prepared
by anionic, ring opening, or group transfer polymerization methods;
if desired, the hydroxyl terminus may then be converted to an amino
end group, e.g., by reaction with 4-nitrophenyl chloroformate,
followed by catalytic hydrogenation to the desired amine. See
Hedrick et al. (1993) Polymer 34:4717; and Hedrick et al. (1995)
Polymer 36:4855. Alternatively, a reactive site can be introduced
in free radical processes through the use of a "masked" or
protected initiator. For example, an amino-functionalized
polystyrene can be prepared by using a living free radical
polymerization process employing an appropriately functionalized
AIBN initiator and 2,2,6,6-tetramethylpiperdinyloxy. Removal of the
t-butoxycarbonyl protecting group leads to monoamino-terminated
poly(styrene). The porogen polymer may also be end-functionalized
with a Diels-Alder dienophile such as maleimide, acryloyl chloride,
cinnamic acid or the like.
[0048] 3. The Coupling Agent
[0049] The coupling agent which links the porogen to the host
polymer in the first step of the present method is a compound
having one or more functional group at each terminus, the first
functional group capable of covalently binding to the reactive site
of the porogen, and the second functional group capable of
covalently binding to the host polymer. Thus, the molecular
structure of the coupling agent may be represented as
R.sup.1--L--R.sup.2 wherein R.sup.1 is a functional group that
enables covalent binding to the reactive site of the porogen, L is
a hydrocarbylene linker containing at least two carbon atoms, and
R.sup.2 is a functional group that enables covalent binding to the
host polymer.
[0050] As explained in the preceding section, the coupling agent
may bind to the porogen via any chemical mechanism that results in
covalent attachment. For coupling to porogens which contain
nucleophilic sites, R.sup.1 is a functional group, e.g., an
isocyanate, a ketene, cyano, an imino ether, a carbodiimide, an
aldehyde, a ketone, or the like, that enables covalent binding to a
nucleophilic moiety. Conversely, R.sup.1 may itself be a
nucleophilic moiety and the reactive site of the porogen may be an
isocyanate, a ketene, cyano, or the like.
[0051] R.sup.2 is selected to enable covalent attachment to the
host polymer. For polymers containing free OH or COOH moieties,
then, R.sup.2 will be a group that enables covalent binding to
molecular moieties containing hydroxyl or carboxyl groups, e.g.,
terminal Si--OH moieties in silsesquioxanes and other siloxane
polymers. Preferred R.sup.2 moieties, when the host polymer is a
silicon containing polymer such as a silsesquioxane, have the
structural formula --SiX.sub.3 wherein the X substituents may be
the same or different, and either leaving groups or inert
hydrocarbyl moieties, with the proviso that at least one of the X
substituents must be a leaving group. Typically, the leaving groups
are hydrolyzable so as to form a silanol linkage with a hydroxyl
group present on the host polymer. Examples of suitable leaving
groups include, but are not limited to, halogen atoms, particularly
chloro, and alkoxy moieties, particularly lower alkoxy moieties.
When all three X substituents are leaving groups, then, the moiety
R.sup.2 will then be, for example, trichlorosilyl, trimethoxysilyl,
triethoxysilyl, or the like. If an inert hydrocarbyl substituent is
present, it is generally a lower alkyl group, e.g., methyl, ethyl,
isopropyl, n-propyl, t-butyl, etc. Thus, R.sup.2 may also be
diisopropylchlorosilyl, dimethylchlorosilyl, ethyldichlorosilyl,
methylethylchlorosilyl, or the like. Other R.sup.2 moieties will be
appropriate for other host polymers, as will be appreciated by
those skilled in the art. For example, when the host polymer is
poly(benzocyclobutene), R.sup.2 is benzocyclobutene. Also, like
R.sup.1, R2 may also be a functional group that enables covalent
binding to a nucleophilic moiety present on the host polymer; that
is, R.sup.2 may be, for example, an isocyanate, a ketene, cyano, an
imino ether, a carbodiimide, an aldehyde, a ketone, or the like.
Conversely, as with R.sup.1, R2 may be a nucleophilic moiety and
the reactive site of the host polymer may be an isocyanate, a
ketene, cyano, or the like.
[0052] The linker L between R.sup.1 and R.sup.2 is hydrocarbylene,
typically C.sub.2-C.sub.24 hydrocarbylene, including, but not
limited to, alkylene, arylene, and alkyl ether linkages, optionally
substituted with one or more, typically one or two, lower alkyl,
halogen, aryl, or other substituents. Particularly preferred L
moieties are unsubstituted C.sub.2-C.sub.12 alkylene linkages, with
C.sub.2-C.sub.6 alkylene linkages most preferred, and n-propylene
and n-butylene being particularly optimal.
[0053] 4. Crosslinking and Thermolysis
[0054] The crosslinking reaction is conducted in a suitable solvent
as noted above, generally a high boiling point solvent such as
N-methylpyrrolidone, dimethylacetamide, dimethylformamide,
dimethylphenyl urea, cyclohexanone, -butyrolactone, or the like,
with all reagents present in predetermined amounts. The coupling
agent and porogen are optimally present in an approximately 1:1
molar ratio, and the solids content of the solution is typically
about 10 wt. % to 60 wt. %, preferably about 30 wt. % to 40 wt. %.
In order to effect crosslinking, the reaction mixture is heated to
a temperature in the range of approximately 150.degree. C. to
250.degree. C., typically in the range of approximately 200.degree.
C. to 250.degree. C., for up to 2 hours, preferably up to 1 hour,
and most preferably up to about 30 minutes. The crosslinking
temperature, or T.sub.C, must be below the decomposition
temperature T.sub.D of the porogen. Generally, although not
necessarily, the reaction is conducted on a substrate, for example
following deposition of the reaction mixture as a thin film on a
substrate surface using spin-coating or the like.
[0055] At this point in the process, after crosslinking, a
polymeric matrix has been synthesized in which the porogen is
present as a discrete phase within a continuous phase comprised of
the host polymer. The size of the porogen domains is generally less
than about 20 nm in diameter, typically less than about 10 nm in
diameter; the size of the domains is due to controlled phase
separation and is governed by the selection of materials and
processing conditions, as will be understood by those of ordinary
skill in the art. The aforementioned polymeric matrix represents a
novel composition of matter herein.
[0056] In the next step of the process, the polymeric matrix
(whether or not present as a coating on a substrate surface) is
heated to a temperature, which is at minimum equal to T.sub.D, the
decomposition temperature of the porogen. The decomposition
temperature, as alluded to earlier herein, will generally be at
least about 300.degree. C., but will be below the glass transition
temperature T.sub.g of the host polymer. The porogen thus
decomposes to volatile fragments, which diffuse out of the rigid
host matrix, leaving voids behind. The pore size in the "foamed" or
porous material so prepared will generally correspond to the size
of the domains of the decomposable polymer (thus, pore size can be
altered by varying the molecular weight of the decomposable
polymer).
[0057] The Novel Dielectric Material:
[0058] The dielectric composition prepared using the methodology
described in the preceding section is thus a porous polymeric
material with a number of advantageous properties. The material has
a dielectric constant of less than 3.0, preferably less than 2.8,
most preferably less than 2.5, at 25.degree. C. In addition, the
composition has closed cell pores generally less than about 20 nm
(i.e., less than about 200 .ANG.), preferably less than about 10 nm
(i.e., less than about 100 .ANG.) in diameter, and a void
percentage in the range of approximately 5% to 35%, resulting in
enhanced mechanical toughness and crack resistance and improved
isotropic optical properties. The novel dielectric composition also
has a low thermal expansion coefficient at elevated temperatures
(e.g., less than about 100 ppm, preferably less than about 40 ppm,
more preferably less than about 30 ppm), which assists in avoiding
film cracking during thermal processing. Further, the dielectric
composition has mechanical properties that enable it to be
chemically/mechanically planarized to facilitate lithographic
formation of multiple circuit levels in multilevel integrated
circuit devices. The dielectric composition is optically clear and
adheres well to substrates.
[0059] Integrated Circuit Devices:
[0060] A primary use of the novel dielectric compositions is in the
manufacture of electronic devices, particularly integrated circuit
devices. An integrated circuit device according to the present
invention is exemplified in FIG. 1, wherein the device is shown as
comprising substrate 2, metallic circuit lines 4, and a dielectric
material 6 of the present invention. The substrate 2 has vertical
metallic studs 8 formed therein. The circuit lines function to
distribute electrical signals in the device and to provide power
input to and signal output from the device. Suitable integrated
circuit devices generally comprise multiple layers of circuit lines
that are interconnected by vertical metallic studs.
[0061] Suitable substrates 2 comprise silicon, silicon dioxide,
silicon-germanium, glass, silicon nitride, ceramics, aluminum,
copper, and gallium arsenide. Suitable circuit lines generally
comprise a metallic, electrically conductive material such as
copper, aluminum, tungsten, gold or silver, or alloys thereof.
Optionally, the circuit lines may be coated with a metallic liner
such as a layer of nickel, tantalum or chromium, or with other
layers such as barrier or adhesion layers (e.g., SiN, TiN, or the
like).
[0062] The invention also relates to processes for manufacturing
integrated circuit devices containing a dielectric composition as
described and claimed herein. Referring to FIG. 2, the first step
of one process embodiment involves disposing on a substrate 2 a
layer 10 of an admixture of (i) a porogen, (ii) a host polymer,
(iii) a coupling agent, and (iv) a solvent (the solids content of
the admixture is generally in the range of about 10 wt. % to 60 wt.
%, preferably about 40 wt. % to 50 wt. %), all as described in
detail earlier herein. The admixture is applied to the substrate by
art known methods such as spin or spray coating or doctor blading.
The film is heated to a temperature effective to crosslink the
porogen and host polymer, followed by a further heating step to
bring about thermal decomposition of the porogen and conversion of
layer 10 to a dielectric composition of the invention.
[0063] Referring to FIG. 3, the third step of the process involves
lithographically patterning the layer 10 of dielectric composition
to form trenches 12 (depressions) therein. The trenches 12 shown in
FIG. 3 extend to the substrate 2 and to the metallic studs 8.
Lithographic patterning generally involves: (i) coating the layer
10 of the dielectric composition with a positive or negative
photoresist such as those marketed by Shipley or Hoechst Celanese,
(AZ photoresist); (ii) imagewise exposing (through a mask) the
photoresist to radiation such as electromagnetic, e.g., UV or deep
UV; (iii) developing the image in the resist, e.g., with suitable
basic developer; and (iv) transferring the image through the layer
10 of dielectric composition to the substrate 2 with a suitable
transfer technique such as reactive ion blanket or beam etching
(RIE). Suitable lithographic patterning techniques are well known
to those skilled in the art such as disclosed in Introduction to
Microlithography, 2nd Ed., eds. Thompson et al. (Washington, D.C.:
American Chemical Society, 1994).
[0064] Referring to FIG. 4, in the fourth step of the process for
forming an integrated circuit of the present invention, a metallic
film 14 is deposited onto the patterned dielectric layer 10.
Preferred metallic materials include copper, tungsten, and
aluminum. The metal is suitably deposited onto the patterned
dielectric layer by art-known techniques such as chemical vapor
deposition (CVD), plasma-enhanced CVD, electro and electroless
deposition (seed-catalyzed in situ reduction), sputtering, or the
like.
[0065] Referring to FIG. 5, the last step of the process involves
removal of excess metallic material by "planarizing" the metallic
film 14 so that the film is generally level with the patterned
dielectric layer 10. Planarization can be accomplished using
chemical/mechanical polishing or selective wet or dry etching.
Suitable methods for chemical/mechanical polishing are known to
those skilled in the art.
[0066] Referring to FIGS. 6-8, there is shown an alternative
process for making an integrated circuit device of the invention.
The first step of the process in this embodiment involves
depositing a metallic film 16 onto a substrate 18. Substrate 18 is
also provided with vertical metallic studs 20. Referring to FIG. 7,
in the second step of the process, the metallic film is
lithographically patterned through a mask to form trenches 22.
Referring to FIG. 8, in the third step of the process, a layer 24
of a reaction mixture comprising the porogen, the host polymer, the
coupling agent, and the selected solvent is deposited onto the
patterned metallic film 16. In the last step of the process, the
mixture is heated to crosslink the porogen and the host polymer,
followed by heating to a higher temperature effective to decompose
the porogen. Optionally, the dielectric layer so provided may then
be planarized, if necessary, for subsequent processing in a
multilayer integrated circuit.
[0067] The invention additionally relates to an integrated circuit
packaging device (multichip module) for providing signal and power
current to one or more integrated circuit chips comprising: (i) a
substrate having electrical conductor means for connection to a
circuit board; (ii) a plurality of alternating electrically
insulating and conducting layers positioned on the substrate
wherein at least of the layers comprises a film of a dielectric
material of the present invention; and (iii) a plurality of vias
for electrically interconnecting the electrical conductor means,
conducting layers and integrated circuit chips.
[0068] The integrated circuit packaging device represents an
intermediate level of packaging between the integrated circuit chip
and the circuit board. The integrated circuit chips are mounted on
the integrated circuit packaging device, which is in turn mounted
on the circuit board.
[0069] The substrate of the packaging device is generally an inert
substrate such as glass, silicon or ceramic; suitable inert
substrates also include epoxy composites, polyimides, phenolic
polymers, high temperature polymers, and the like. The substrate
can optionally have integrated circuits disposed therein. The
substrate is provided with electrical conductor means such as
input/output pins (I/O pins) for electrically connecting the
packaging device to the circuit board. A plurality of electrically
insulating and electrically conducting layers (layers having
conductive circuits disposed in an dielectric insulating material)
are alternatively stacked up on the substrate. The layers are
generally formed on the substrate in a layer-by-layer process
wherein each layer is formed in a separate process step.
[0070] The packaging device also comprises receiving means for
receiving the integrated circuit chips. Suitable receiving means
include pinboards for receipt of chip I/O pins or metal pads for
solder connection to the chip. Generally, the packaging device also
comprises a plurality of electrical vias generally vertically
aligned to electrically interconnect the I/O pins, the conductive
layers and integrated circuit chips disposed in the receiving
means. The function, structure and method of manufacture of such
integrated circuit packaging devices are well known to those
skilled in the art, as disclosed, for example in U.S. Pat. Nos.
4,489,364, 4,508,981, 4,628,411 and 4,811,082.
[0071] It is to be understood that while the invention has been
described in conjunction with the preferred specific embodiments
thereof, that the foregoing description as well as the examples
which follow are intended to illustrate and not limit the scope of
the invention. Other aspects, advantages and modifications within
the scope of the invention will be apparent to those skilled in the
art to which the invention pertains.
[0072] All patents, patent applications, and publications mentioned
herein are hereby incorporated by reference in their
entireties.
[0073] Experimental:
[0074] The following examples are put forth so as to provide those
of ordinary skill in the art with a complete disclosure and
description of how to prepare and use the oligomers and polymers
disclosed and claimed herein. Efforts have been made to ensure
accuracy with respect to numbers (e.g., quantities, temperature,
etc.) but some errors and deviations should be accounted for.
Unless indicated otherwise, parts are parts by weight, temperature
is in .degree. C. and pressure is at or near atmospheric.
Additionally, all starting materials were obtained commercially or
synthesized using known procedures.
EXAMPLE 1
[0075] Amino-terminated poly(methyl methacrylate) (Mn of 7-500),
methyl silsesquioxane, and 1-isocyanato-3-trimethoxysilyl-propane
(molar ratio 1:7.5:1) are dissolved in dimethylphenylurea to
provide a coating solution (45 wt. % solids content). The coating
is cast by spin coating onto silicon wafers to form films from 1 to
10 microns thick. Crosslinking is effected by heating the film for
1.5 hr at 200.degree. C. The temperature is then increased to
350.degree. C. to bring about decomposition of the porogen. The
porous material that results has a dielectric constant of less than
about 3.0 (at 25.degree. C.).
EXAMPLE 2
[0076] The process of Example 1 is repeated substituting
amino-substituted polystyrene for amino-substituted poly(methyl
methacrylate) as the porogen. Substantially the same results are
expected.
EXAMPLE 3
[0077] The process of Example 1 is repeated substituting
amino-substituted poly(propylene oxide) for amino-substituted
poly(methyl methacrylate) as the porogen. Substantially the same
results are expected.
EXAMPLE 4
[0078] The process of Example 1 is repeated substituting
poly(arylene) for the silsesquioxane "host polymer," and
4-(phenylethynyl)benzoyl chloride for
1-isocyanato-3-trimethoxysilyl-propane as the coupling agent.
Substantially the same results are expected.
EXAMPLE 5
[0079] The process of Example 1 is repeated substituting
polybenzocyclobutene for the silsesquioxane "host polymer."
Substantially the same results are expected.
EXAMPLE 6
[0080] The process of Example 1 is repeated substituting
3-isocyanatopropylbenzoyclobutane for
1-isocyanato-3-trimethoxysilyl-prop- ane as coupling agent.
Substantially the same results are expected.
EXAMPLE 7
[0081] The process of Example 1 is repeated substituting
1-cyano-3-trichlorosilyl-propane for
1-isocyanato-3-trimethoxysilyl-propa- ne as coupling agent.
Substantially the same results are expected.
* * * * *