U.S. patent application number 10/932319 was filed with the patent office on 2006-03-02 for composition for forming silica-based film, method of forming silica-based film, and electronic component provided with silica-based film.
Invention is credited to Koichi Abe, Haruaki Sakurai.
Application Number | 20060047034 10/932319 |
Document ID | / |
Family ID | 35944253 |
Filed Date | 2006-03-02 |
United States Patent
Application |
20060047034 |
Kind Code |
A1 |
Sakurai; Haruaki ; et
al. |
March 2, 2006 |
Composition for forming silica-based film, method of forming
silica-based film, and electronic component provided with
silica-based film
Abstract
The present invention provides a composition for forming a
silica-based film, the composition containing (a) a siloxane resin;
(b) an organic solvent including at least one species of aprotic
solvent; and (c) an onium salt.
Inventors: |
Sakurai; Haruaki;
(Hitachi-shi, JP) ; Abe; Koichi; (Hitachi-shi,
JP) |
Correspondence
Address: |
WESTERMAN, HATTORI, DANIELS & ADRIAN, LLP
1250 CONNECTICUT AVENUE, NW
SUITE 700
WASHINGTON
DC
20036
US
|
Family ID: |
35944253 |
Appl. No.: |
10/932319 |
Filed: |
September 2, 2004 |
Current U.S.
Class: |
524/236 |
Current CPC
Class: |
C08K 5/5415 20130101;
C08K 5/5415 20130101; C08L 83/04 20130101 |
Class at
Publication: |
524/236 |
International
Class: |
C08K 5/32 20060101
C08K005/32 |
Claims
1-12. (canceled)
13. A composition for forming a silica-based film comprising: (a) a
siloxane resin; (b) an organic solvent containing at least one
species of aprotic solvent; and (c) an onium salt.
14. A composition for forming a silica-based film comprising: (a) a
siloxane resin; (b) an organic solvent containing at least one
species of aprotic solvent; and (c) an onium salt, wherein the
organic solvent contains at least one species of aprotic solvent
selected from the group consisting of ether-based solvents and
ketone-based solvents.
15. A composition for forming a silica-based film comprising: (a) a
siloxane resin; (b) an organic solvent containing at least one
species of aprotic solvent; and (c) an onium salt, wherein the
organic solvent contains at least one species of aprotic solvent
excluding amide-based solvent.
16. A composition for forming a silica-based film comprising: (a) a
siloxane resin; (b) an organic solvent containing at least one
species of aprotic solvent; and (c) an onium salt, wherein the
onium salt contains at least an ammonium salt selected from the
group consisting of tetramethylammonium nitrate,
tetramethylammonium acetate, tetramethylammonium propionate,
tetramethylammonium maleate, and tetramethylammonium sulfate.
17. A composition for forming a silica-based film comprising: (a) a
siloxane resin; (b) an organic solvent containing at least one
species of aprotic solvent; and (c) an onium salt, wherein the
siloxane resin contains a siloxane resin including units derived
from tetraalkoxysilane and trialkoxysilane.
18. A composition for forming a silica-based film comprising: (a) a
siloxane resin; (b) an organic solvent containing at least one
species of aprotic solvent; and (c) an onium salt, wherein the
aprotic solvent contains at least one species of aprotic solvent
selected from the group consisting of alkylene glycol dialkyls,
alkylene glycol alkyl esters, alkylene glycol diesters, and cyclic
ketones.
19. A composition for forming a silica-based film comprising: (a) a
siloxane resin; (b) an organic solvent containing at least one
species of aprotic solvent; and (c) an onium salt, wherein the
aprotic solvent contains an aprotic solvent having a relative
permittivity of at least 10.
20. A composition for forming a silica-based film comprising: (a) a
siloxane resin containing a siloxane resin obtainable by
hydrolyzing and condensing a compound represented by the following
general formula (1): R.sup.1.sub.nSiX.sub.4-n wherein R.sup.1 is an
H or F atom, a group containing a B, N, Al, P, Si, Ge, or Ti atom,
or an organic group having a carbon number of 1 to 20; X is a
hydrolyzable group; and n is an integer of 0 to 2; R.sup.1 being
either identical or different when n is 2; X being either identical
or different when n is 0 to 2; (b) an organic solvent containing at
least one species of aprotic solvent; and (c) an onium salt,
wherein the total content of H, F, B, N, Al, P, Ge, Ti, and C atoms
in the siloxane resin with respect to 1 mol of Si atom is 0.65 mol
or less.
21. A composition for forming a silica-based film comprising: (a) a
siloxane resin; (b) an organic solvent containing at least one
species of aprotic solvent; and (c) an onium salt, further
comprising a pore forming compound which thermally decomposes or
evaporates at a heating temperature of 250.degree. to 500.degree.
C.
22. A composition for forming a silica-based film comprising: (a) a
siloxane resin; and (b) an organic solvent containing at least one
species of aprotic solvent; wherein the siloxane resin is
obtainable by hydrolyzing and condensing the compound in the
aprotic solvent.
23. A composition for forming a silica-based film comprising: (a) a
siloxane resin; and (b) an organic solvent containing at least one
species of aprotic solvent, wherein the aprotic solvent includes a
dialkylether of dihydric alcohol.
24. A composition for forming a silica-based film comprising: (a) a
siloxane resin; and (b) an organic solvent containing at least two
species of aprotic solvent.
25. A composition for forming a silica-based film comprising: (a) a
siloxane resin; and (b) an organic solvent containing at least one
species of aprotic solvent, wherein the siloxane resin is
obtainable by hydrolyzing and condensing the compound in the
presence of organic or inorganic acid.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a composition for forming a
silica-based film, a silica-based film, a method of making the
same, and an electronic component provided with the silica-based
film.
[0003] 2. Related Background Art
[0004] SiO.sub.2 films, formed by CVD, having a relative
permittivity of about 4.2, have conventionally been used as a
material for forming an interlayer insulating film. However, from
the viewpoint of reducing the capacity between wires in the device
so as to improve the operating speed of LSI, materials which can
exhibit a lower dielectric constant have been in demand.
[0005] For this demand, SiOF films, formed by CVD, having a
relative permittivity of about 3.5, have been developed. Further,
organic SOG (Spin On Glass), organic polymers, etc. have been
developed as insulating materials having a relative permittivity of
2.5 to 3.0. Also, as an insulating material having a relative
permittivity of 2.5 or less, porous materials having a pore in a
film have been considered effective, and they have vigorously been
under study and development so as to be employed in interlayer
insulating films for LSI.
[0006] As a method of forming such a porous material, one using
organic SOG has been proposed in Japanese Patent Application
Laid-Open Nos. HEI 11-322992 and HEI 11-310411. This method heats a
composition containing a hydrolytic condensate and a polymer having
a volatile or decomposing property, so as to form a film, and then
heats the film, so as to form a pore in the film, thereby yielding
a porous material.
SUMMARY OF THE INVENTION
[0007] In electronic device parts such as semiconductor devices
typified by LSI, increases in signal delay time due to increases in
the capacity between wires have been becoming problematic as wires
have become thinner because of higher integration. Therefore,
insulating materials for electronic device parts have been required
to attain not only heat resistance, mechanical characteristics,
etc., but also a lower relative permittivity and a shorter heating
step.
[0008] In general, the signal propagation velocity (v) of a wire
and the relative permittivity (.epsilon.) of an insulating material
in contact with a wiring material have a relationship represented
by the expression of v=k/ {square root over (.epsilon.)}, where k
is a constant. Namely, the signal propagation can be made faster if
the frequency region in use is made higher while the relative
permittivity (.epsilon.) of the insulating material is lowered.
[0009] The inventors studied the above-mentioned conventional
method in detail, and have found it necessary to introduce a quite
large amount of pore (void) into an insulating film in order to
achieve a low dielectric constant required for the insulating film.
Also, the inventors have found that a layer tends to further lower
its mechanical strength if the porosity increases in excess when
the mechanical film strength or film hardness of the organic SOG to
become a base material of the film is inherently insufficient.
However, the film strength tends to decrease as the relative
permittivity decreases, whereby there remains a large problem for
conventional processes to be applied thereto.
[0010] For hardening the coating film forming composition so as to
form a film, a high-temperature atmosphere at 450.degree. C. or
higher is necessary. Also, a long period of about 1 hour is likely
to be required until the hardening finally ends. Therefore, when
such a film is used as an interlayer insulating film, there is a
fear of the heat input amount (thermal budget) in the film forming
process deteriorating other layers, a wiring layer in particular.
Also, substrates may warp remarkably as the heat input amount
increases.
[0011] Further, as mentioned above, higher integration has been
accelerating the thinning of wires, whereby individual member
layers constituting semiconductor devices have been reducing their
thickness and increasing their number, while wiring layers and the
like have been changing their materials. The influence of the heat
input amount on the deterioration in materials of the layers is
expected to increase from now on, whereby there is an urgent need
to improve thermal histories by lowering thermal load in each
process.
[0012] It is an object of the present invention to provide a
composition for forming a silica-based film, which has an
excellently low dielectric property and a sufficient mechanical
strength while being curable at a lower temperature in a shorter
time as compared with conventional ones; a silica-based film
comprising such a composition, a method of forming the same, and an
electronic component provided with such a silica-based film.
[0013] For achieving the above-mentioned object, the inventors
conducted diligent studies from the viewpoint of material
components and their compositions for yielding a silica-based film
suitable for an insulating film and, as a result, have found that a
composition containing a specific component can eliminate various
conventional problems, thereby completing the present
invention.
[0014] The present invention provides a composition for forming a
silica-based film, the composition comprising (a) a siloxane resin;
(b) an organic solvent containing at least one species of aprotic
solvent; and (c) an onium salt.
[0015] Preferably, the siloxane resin in the present invention
contains a siloxane resin obtainable by hydrolyzing and condensing
a compound represented by the following general formula (1):
R.sup.1.sub.nSiX.sub.4-n (1)
[0016] In expression (1), R.sup.1 is an H or F atom, a group
containing a B, N, Al, P, Si, Ge, or Ti atom, or an organic group
having a carbon number of 1 to 20; X is a hydrolyzable group; and n
is an integer of 0 to 2. When n is 2, R.sup.1 may be either
identical or different. When n is 0 to 2, X may be either identical
or different.
[0017] The composition for forming a silica-based film in
accordance with the present invention contains a siloxane resin as
a film forming component, an aprotic solvent as an essential
component of an organic solvent component for dissolving the
siloxane resin, and an onium salt, and thus can form a silica-based
film having an excellently low dielectric property, in a
high-frequency region (of at least 100 kHz, e.g., 1 MHz) in
particular, and a sufficient mechanical strength, while being
curable at a lower temperature in a shorter time as compared with
conventional ones. Since the composition can be cured at a lower
temperature in a shorter time, the heat input amount in the film
forming process is reduced. Therefore, problems such as
deterioration in wiring layers and the like and warping of
substrates can be eliminated. Further, the uniformity in thickness
of the film can be improved. Such effects can be exhibited further
effectively and reliably if one obtainable by hydrolyzing and
condensing the compound represented by the above-mentioned general
formula (1) is employed as the siloxane resin.
[0018] Though causes of the above-mentioned effects are not
completely clear, it is presumed that the silica-based film attains
a low dielectric property and a sufficient mechanical strength
mainly because the siloxane resin and aprotic solvent are used
together, whereas the film is curable at a lower temperature in a
shorter time mainly because the aprotic solvent and onium salt are
used together. On the other hand, the uniformity in thickness of
the film seems to improve mainly because the aprotic solvent is
used.
[0019] The aprotic solvent preferably contains at least one species
of aprotic solvent selected from the group consisting of alkylene
glycol dialkyls, alkylene glycol alkyl esters, aklkylene glycol
diesters, and cyclic ketones; whereas at least one species of the
aprotic solvent is preferably a aprotic solvent having a relative
permittivity of at least 10. Preferably, the content of the aprotic
solvent having a relative permittivity of at least 10 is at least
50 mass % based on the weight of the organic solvent containing at
least one aprotic solvent.
[0020] In particular, the composition for forming a silica-based
film comprising a aprotic solvent having a relative permittivity of
at least 10 as an organic solvent component tends to narrow its
pore distribution when pores are formed while a pore forming
compound, which will be explained later, is contained therein.
[0021] Preferably, the total content of H, F, B, N, Al, P, Ge, Ti,
and C atoms in the siloxane resin with respect to 1 mol of Si atom
is 0.65 mol or less.
[0022] The composition for forming a silica-based film having the
configuration mentioned above restrains the adhesion and mechanical
strength between the silica-based film and other films (layers)
from decreasing. This can also prevent interfacial peeling from
occurring in the process of CMP (chemical mechanical polishing)
metal wiring layers made of Cu or the like coated on the
silica-based film.
[0023] Preferably, the onium salt is an ammonium salt. Thus
configured composition for forming a silica-based film can enhance
the stability of the composition and further improve electric and
mechanical characteristics of the silica-based film.
[0024] Preferably, the composition further contains a pore forming
compound which thermally decomposes or evaporates at a heating
temperature of 250.degree. to 500.degree. C. Thus configured
composition for forming a silica-based film can form a silica-based
film capable of achieving a lower dielectric constant while
restraining mechanical strength from remarkably decreasing.
[0025] In another aspect, the present invention provides a method
of forming a silica-based film on a substrate, the method
comprising the steps of forming a coating film by applying the
composition for forming a silica-based film in accordance with the
present invention onto the substrate; removing the organic solvent
contained in the coating film; and firing the coating film at a
heating temperature of 250.degree. to 500.degree. C. after the
removing step.
[0026] In still another aspect, the present invention provides a
silica-based film disposed on a substrate and formed by the
above-mentioned method of forming a silica-based film. Such a film
is useful, in particular, as one formed between conductive layers
arranged adjacent each other among a plurality of conductive layers
disposed on the substrate, i.e., an insulating film required to
sufficiently lower a leak current, e.g., an interlayer insulating
film.
[0027] In still another aspect, the present invention provides an
electronic component comprising a substrate and the silica-based
film in accordance with the present invention formed thereon. Such
an electronic component constitutes an electronic device such as a
semiconductor device.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] FIG. 1 is a schematic sectional view showing a preferred
embodiment of a multilayer wiring structure in accordance with the
present invention;
[0029] FIG. 2 is a schematic partial sectional view for explaining
a wiring forming step for forming a single-layer wire on a
transistor;
[0030] FIG. 3 is a schematic partial sectional view for explaining
the wiring forming step for forming the single-layer wire on the
transistor;
[0031] FIG. 4 is a schematic partial sectional view for explaining
the wiring forming step for forming the single-layer wire on the
transistor; and
[0032] FIG. 5 is a schematic partial sectional view for explaining
the wiring forming step for forming the single-layer wire on the
transistor.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0033] In the following, preferred embodiments of the present
invention will be explained in detail with reference to the
drawings when necessary. Among the drawings, constituents identical
to each other will be referred to with numerals identical to each
other without repeating their overlapping descriptions. Positional
relationships such as upper, lower, left, and right positions will
be based on those depicted unless otherwise specified. Ratios of
dimensions in the drawings are not limited to those depicted. In
the specification, "(meth)acrylate" refers to "acrylate" and its
corresponding "methacrylate".
[0034] While the composition for forming a silica-based film in
accordance with the present invention contains (a) to (c)
components, the characteristic feature of the present invention
lies in that the composition contains at least one species of
aprotic solvent, i.e., a polar solvent having a high relative
permittivity, as the (b) component. In the following, the
individual components of the composition for forming a silica-based
film in accordance with the present invention will be explained in
detail.
(a) Component
[0035] The siloxane resin used as the (a) component in the present
invention functions as a film forming component of a silica-based
film, which will be explained later. For exhibiting such a
function, it will be preferred if the composition for forming a
silica-based film in accordance with the present invention contains
a siloxane resin obtainable by hydrolyzing and condensing a
compound represented by the following general formula (1):
R.sup.1.sub.nSiX.sub.4-n (1)
[0036] In the above-mentioned expression (1), R.sup.1 is an H or F
atom; a group containing a B, N, Al, P, Si, Ge, or Ti atom; or an
organic group having a carbon number of 1 to 20 (preferably 1 to
12, more preferably 1 to 6).
[0037] The total amount (M) of H, F, B, N, Al, P, Si, Ge, Ti, and C
atoms (hereinafter referred to as "specific binding atom") combined
to one Si atom forming a siloxane bond of the siloxane resin is
preferably not greater than 0.65, more preferably not greater than
0.55, not greater than 0.50 in particular, quite preferably not
greater than 0.45. The lower limit for M is preferably about
0.20.
[0038] When the M value exceeds 0.65, the adhesion, mechanical
strength, etc. between the finally obtained silica-based film and
other films (layers) tend to deteriorate. When the M value is less
than 0.20, on the other hand, the film tends to deteriorate its
dielectric property when used as an insulating film. From the
viewpoint of improving the film forming property in the
silica-based film, it will be more preferred if the siloxane resin
contains at least one species of H, F, N, Si, Ti, and C atoms among
the specific binding atoms mentioned above. Among them, from the
viewpoint of improving dielectric characteristics and mechanical
strength, it will be more preferred if at least one species of H,
F, N, Si, and C atoms is contained.
[0039] The M value can be determined from the feeding amount of the
compound represented by the above-mentioned general formula (1),
which is a material for the siloxane resin. For example, it can be
calculated from the following expression:
M=[M.sub.1+(M.sub.2/2)+(M.sub.3/3)]/M.sub.Si wherein M.sub.1 is the
total number of atoms which are respectively combined with a single
(sole) Si atom in the specific binding atoms; M.sub.2 is the total
number of atoms which are respectively commonly owned by two
silicon atoms in the specific binding atoms; M.sub.3 is the total
number of atoms which are respectively commonly owned by three
silicon atoms in the specific binding atoms; and M.sub.Si is the
total number of Si atoms.
[0040] In the above-mentioned general formula (1), X is a
hydrolyzable group. Examples of X include alkoxy groups, aryloxy
groups, halogen atoms, acetoxy group, isocyanate group, and
hydroxyl group, among which alkoxy groups are preferred. When X is
an alkoxy group, the liquid stability, coating characteristics,
etc. of the composition become better.
[0041] Examples of the compound represented by the above-mentioned
general formula (1) in the case where the hydrolyzable group X is
an alkoxy group include tetraalkoxysilane, trialkoxysilane, and
dialkoxysilane, each of which may be substituted.
[0042] Examples of tetraalkoxysilane include tetramethoxysilane,
tetraethoxysilane, tetra-n-propoxysilane, tetra-iso-propoxysilane,
tetra-n-butoxysilane, tetra-sec-butoxysilane, and
tetra-tert-butoxysilane.
[0043] Examples of trialkoxysilane include trimethoxysilane,
triethoxysilane, tripropoxysilane, fluorotrimethoxysilane,
fluorotriethoxysilane, methyltrimethoxysilane,
methyltriethoxysilane, methyltri-n-propoxysilane,
methyltri-iso-propoxysilane, methyltri-n-butoxysilane,
methyltri-iso-butoxysilane, methyltri-tert-butoxysilane,
ethyltrimethoxysilane, ethyltriethoxysilane,
ethyltri-n-propoxysilane, ethyltri-iso-propoxysilane,
ethyltri-n-butoxysilane, ethyltri-iso-butoxysilane,
ethyltri-tert-butoxysilane, n-propyltrimethoxysi lane,
n-propyltriethoxysi lane, n-propyltri-n-propoxysilane,
n-propyltri-iso-propoxysilane, n-propyltri-n-butoxysilane,
n-propyltri-iso-butoxysilane, n-propyltri-tert-butoxysilane,
iso-propyltrimethoxysilane, iso-propyltriethoxysilane,
iso-propyltri-n-propoxysilane, iso-propyltri-iso-propoxysilane,
iso-propyltri-n-butoxysilane, iso-propyltri-iso-butoxysilane,
iso-propyltri-tert-butoxysilane, n-butyltrimethoxysilane,
n-butyltriethoxysilane, n-butyltri-n-propoxysilane,
n-butyltri-iso-propoxysilane, n-butyltri-n-butoxysilane,
n-butyltri-iso-butoxysilane, n-butyltri-tert-butoxysilane,
n-butyltriphenoxysilane, sec-butyltrimethoxysilane,
sec-butyltriethoxysilane, sec-butyltri-n-propoxysilane,
sec-butyltri-iso-propoxysilane, sec-butyltri-n-butoxysilane,
sec-butyltri-iso-butoxysilane, sec-butyltri-tert-butoxysilane,
t-butyltrimethoxysilane, t-butyltriethoxysilane,
t-butyltri-n-propoxysilane, t-butyltri-iso-propoxysilane,
t-butyltri-n-butoxysilane, t-butyltri-iso-butoxysilane,
t-butyltri-tert-butoxysilane, phenyltrimethoxysilane,
phenyltriethoxysilane, phenyltri-n-propoxysilane,
phenyltri-iso-propoxysilane, phenyltri-n-butoxysilane,
phenyltri-iso-butoxysilane, phenyltri-tert-butoxysilane,
trifluoromethyltrimethoxysilane, pentafluoroethyltrimethoxysilane,
3,3,3-trifluoropropyltrimethoxysilane, and
3,3,3-trifluoropropyltriethoxysilane.
[0044] Examples of dialkoxysilane include dimethyldimethoxysilane,
dimethyldiethoxysilane, dimethyldi-n-propoxysilane,
dimethyldi-iso-propoxysilane, dimethyldi-n-butoxysilane,
dimethyldi-sec-butoxysilane, methyldi-tert-butoxysilane,
diethyldimethoxysilane, diethyldiethoxysilane,
diethyldi-n-propoxysilane, diethyldi-iso-propoxysilane,
diethyldi-n-butoxysilane, diethyldi-sec-butoxysilane,
diethyldi-tert-butoxysilane, di-n-propyldimethoxysilane,
di-n-propyldiethoxysilane, di-n-propyldi-n-propoxysilane,
di-n-propyldi-iso-propoxysilane, di-n-propyldi-n-butoxysilane,
di-n-propyldi-sec-butoxysilane, di-n-propyldi-tert-butoxysilane,
di-iso-propyldimethoxysilane, di-iso-propyldiethoxysilane,
di-iso-propyldi-n-propoxysilane, di-iso-propyldi-iso-propoxysilane,
di-iso-propyldi-n-butoxysilane, di-iso-propyldi-sec-butoxysilane,
di-iso-propyldi-tert-butoxysilane, di-n-butyldimethoxysilane,
di-n-butyldiethoxysilane, di-n-butyldi-n-propoxysilane,
di-n-butyldi-iso-propoxysilane, di-n-butyldi-n-butoxysilane,
di-n-butyldi-sec-butoxysilane, di-n-butyldi-tert-butoxysilane,
di-sec-butyldimethoxysilane, di-sec-butyldiethoxysilane,
di-sec-butyldi-n-propoxysilane, di-sec-butyldi-iso-propoxysilane,
di-sec-butyldi-n-butoxysilane, di-sec-butyldi-sec-butoxysilane,
di-sec-butyldi-tert-butoxysilane, di-tert-butyldimethoxysilane,
di-tert-butyldiethoxysilane, di-tert-butyldi-n-propoxysilane,
di-tert-butyldi-iso-propoxysilane, di-tert-butyldi-n-butoxysilane,
di-tert-butyldi-sec-butoxysilane,
di-tert-butyldi-tert-butoxysilane, diphenyldimethoxysilane,
diphenyldiethoxysilane, diphenyldi-n-propoxysilane,
diphenyldi-iso-propoxysilane, diphenyldi-n-butoxysilane,
diphenyldi-sec-butoxysilane, diphenyldi-tert-butoxysilane,
bis(3,3,3-trifluoropropyl)dimethoxysilane, and
methyl(3,3,3-trifluoropropyl)dimethoxysilane.
[0045] Examples of the compound represented by the above-mentioned
general formula (1) in the case where the hydrolyzable group X is
an aryloxy group include tetraaryloxysilane, triaryloxysilane, and
diaryloxysilane, each of which may be substituted. An example of
tetraaryloxysilane is tetraphenoxysilane. Examples of
triaryloxysilane include triphenoxysilane, methyltriphenoxysi lane,
ethyltriphenoxysi lane, n-propyltriphenoxysilane,
iso-propyltriphenoxysilane, sec-butyltriphenoxysilane,
t-butyltriphenoxysilane, and phenyltriphenoxysilane. Examples of
diaryloxysilane include dimethyldiphenoxysilane,
diethyldiphenoxysilane, di-n-propyldiphenoxysilane,
di-iso-propyldiphenoxysilane, di-n-butyldiphenoxysilane,
di-sec-butyldiphenoxysilane, di-tert-butyldiphenoxysilane, and
diphenyldiphenoxysilane.
[0046] Examples of the compound expressed by the general formula
(1) in the case where X is a halogen atom (halogen group), i.e.
halogenated silane, include compounds in which alkoxy groups in the
alkoxysilane molecules mentioned above are substituted by halogen
atoms. Examples of the compound (acetoxysilane) expressed by the
general formula (1) in the case where X is an acetoxy group include
compounds in which alkoxy groups in the alkoxysilane molecules
mentioned above are substituted by acetoxy groups. Examples of the
compound (isocyanate silane) expressed by the general formula (1)
in the case where X is an isocyanate group include compounds in
which alkoxy groups in the alkoxysilane molecules mentioned above
are substituted by isocyanate groups. Examples of the compound
(hydroxysilane) expressed by the general formula (1) in the case
where X is a hydroxy group include compounds in which alkoxy groups
in the alkoxysilane molecules mentioned above are substituted by
hydroxyl groups.
[0047] The compounds represented by the above-mentioned formula (1)
may be used either singly or in combination of two or more.
[0048] Among these compounds, more preferred from the viewpoints of
liquid stability, film coating characteristics, etc. of the
composition itself is tetraalkoxysilane or organotrialkoxysilane,
tetraethoxysilane or methyltriethoxysilane in particular.
[0049] In the above-mentioned general formula (1), n is an integer
of 0 to 2. When n is 2, R.sup.1 may be either identical or
different. When n is 0 to 2, X may be either identical or
different. Preferably, n is 0 or 1. It will be preferred if a
compound represented by the above-mentioned formula (1) in which
n=0 and a compound represented by the above-mentioned formula (1)
in which n=1 are used in combination. When the respective compounds
whose n is 0 and 1 are combined together, the siloxane resin
includes a unit represented by SiO.sub.2 and a unit represented by
R.sup.1SiO.sub.3/2. Here, R.sup.1 is defined as above. This
siloxane resin is obtainable by hydrolyzing and co-condensing
polyfunctional tetraalkoxysilane and trialkoxysilane mentioned
above. The unit represented by SiO.sub.2 is one derived from
tetraalkoxysilane, whereas the unit represented by
R.sup.1SiO.sub.3/2 is one derived from trialkoxysilane. Since the
siloxane resin includes such units, its crosslinking density
improves, whereby its coating characteristics can be improved.
[0050] Examples of catalysts employed for accelerating the
hydrolytic condensation of the compound represented by the
above-mentioned general formula (1) include organic acids such as
formic acid, maleic acid, fumaric acid, acetic acid, propionic
acid, butanoic acid, pentanoic acid, hexanoic acid, heptanoic acid,
octanoic acid, nonanoic acid, decanoic acid, oxalic acid, adipic
acid, sebacic acid, butyric acid, oleic acid, stearic acid, linolic
acid, linoleic acid, salicylic acid, benzoic acid, p-aminobenzoic
acid, p-toluenesulfonic acid, phthalic acid, sulfonic acid,
tartaric acid, and trifluoromethanesulfonic acid; inorganic acids
such as hydrochloric acid, phosphoric acid, nitric acid, boric
acid, sulfuric acid, and hydrofluoric acid.
[0051] The amount of use of catalysts is preferably within the
range of 0.0001 to 1 mol with respect to 1 mole of the compound.
When the amount of use exceeds 1 mol, gelling tends to accelerate
at the time of hydrolytic condensation. When the amount of use is
less than 0.0001 mol, the reaction is less likely to proceed
substantially.
[0052] The alcohol generated as a byproduct upon the hydrolysis of
the compound represented by the above-mentioned general formula (1)
in the hydrolytic condensation reaction is a protonic solvent, and
is preferably eliminated by use of an evaporator or the like. The
amount of water used in the hydrolytic condensation reaction can be
determined as appropriate, and is preferably a value within the
range of 0.5 to 20 mol with respect to 1 mol of the compound
represented by the above-mentioned general formula (1). When the
amount of water is less than 0.5 mol or more than 20 mol, the film
forming property of the silica-based film tends to deteriorate, and
the composition itself is likely to lower its shelf stability.
[0053] From the viewpoints of solubility in solvents, mechanical
characteristics, formability, etc., the weight average molecular
weight (Mw) of the siloxane resin is preferably 500 to 20,000, more
preferably 1,000 to 10,000. When Mw is less than 500, the film
forming property of the silica-based film tends to deteriorate.
When Mw exceeds 20,000, on the other hand, the compatibility with
solvents tends to decrease. In the present invention, Mw refers to
the weight average molecular weight by gel permeation
chromatography (GPC) based on standard polystyrene.
[0054] As the siloxane resin, a single species or a combination of
two or more species may be used. When combining two or more
species, respective siloxane resins having different weight average
molecular weights, and respective siloxane resins in which
compounds (monomer components) to be hydrolyzed and condensed are
different, etc. may be combined, for example.
(b) Component
[0055] Preferably, the (b) component is an organic solvent which
can dissolve the siloxane resin, which is the (a) component, so as
to lower the viscosity thereof, thereby facilitating the handling
and the like thereof. The (b) component also functions to narrow
the distribution of pores included in the silica-based film by
causing the aprotic solvent to have a predetermined relative
permittivity or higher.
[0056] For exhibiting such a function, the composition for forming
a silica-based film in accordance with the present invention
contains preferably at least 80 mass %, more preferably at least 90
mass %, further preferably at least 95 mass % of the aprotic
solvent based on the weight of the (b) component. If the content of
the aprotic solvent in the (b) component is small, it may hinder
temperature from lowering and process time from shortening when
curing the composition. There is also a fear of increasing the
relative permittivity of the film and lowering its mechanical
strength.
[0057] Preferably, at least one species of aprotic solvent has a
relative permittivity of at least 10. Such a relative permittivity
tends to narrow the pore distribution in the film when forming
pores in the film containing a pore forming compound which will be
explained later. The relative permittivity in the present invention
refers to the value measured at 20.degree. C. The content of the
aprotic solvent having a relative permittivity of at least 10 in
the (b) component is preferably at least 50 mass %, more preferably
at least 60 mass %.
[0058] Examples of the aprotic solvent include ketone-based
solvents, ether-based solvents, ester-based solvents,
ether-acetate-based solvents, acetonitrile, amide-based solvents,
and sulfoxide-based solvents. Among them, ether-based solvents and
ketone-based solvents are preferable, alkylene glycol dialkyls,
alkylene glycol alkyl esters, aklkylene glycol diesters, and cyclic
ketones are more preferred, and diethylene glycol dimethylether and
cyclohexanone are preferred in particular. Among these preferred
aprotic solvents, from the viewpoints of compatibility with the
siloxane resin, mechanical strength of the silica-based film, etc.,
ketone-based solvents are preferred, among which cyclic ketones are
more preferred, and cyclohexanone is preferred in particular.
[0059] Examples of the ketone-based solvents include acetone,
methylethylketone, methyl-n-propylketone, methyl-iso-propylketone,
methyl-n-butylketone, methyl-iso-butylketone,
methyl-n-pentylketone, methyl-n-hexylketone, diethylketone,
dipropylketone, di-iso-butylketone, trimethylnanone, cyclohexanone,
cyclopentanone, methylcyclohexanone, 2,4-pentanedione, and
acetonylacetone.
[0060] Examples of ether-based solvents include dioxane,
dimethyldioxane, ethylene glycol dimethyl ether, ethylene glycol
diethyl ether, ethylene glycol dipropyl ether, ethylene glycol
dibutyl ether, diethylene glycol dimethyl ether, diethylene glycol
diethyl ether, diethylene glycol methyl ethyl ether, diethylene
glycol methyl mono-n-butyl ether, diethylene glycol di-n-butyl
ether, diethylene glycol methyl mono-n-hexyl ether, tetraethylene
glycol di-n-butyl ether, dipropylene glycol dimethyl ether,
dipropylene glycol methyl ethyl ether, dipropylene glycol diethyl
ether, tetrahydrofuran, and 2-methyltetrahydrofuran.
[0061] Examples of the ester-based solvent include methyl acetate,
ethyl acetate, n-propyl acetate, i-propyl acetate, n-butyl acetate,
i-butyl acetate, sec-butyl acetate, n-pentyl acetate, sec-pentyl
acetate, 3-methoxybutyl acetate, methylpentyl acetate, 2-ethylbutyl
acetate, 2-ethylhexyl acetate, benzyl acetate, cyclohexyl acetate,
methylcyclohexyl acetate, nonyl acetate, .gamma.-butyrolactone,
.gamma.-valerolactone, methyl acetoacetate, ethyl acetoacetate,
diethylene acetate glycol monomethyl ether, diethylene acetate
glycol monoethyl ether, diethylene acetate glycol mono-n-butyl
ether, dipropylene acetate glycol monomethyl ether, dipropylene
acetate glycol monoethyl ether, glycol diacetate, methoxytriglycol
acetate, ethyl propionate, n-butyl propionate, i-amyl propionate,
diethyl oxalate, and di-n-butyl oxalate.
[0062] Examples of the ether-acetate-based solvent include ethylene
glycol methyl ether propionate, ethylene glycol ethyl ether
propionate, acetate ethylene glycol methyl ether acetate, ethylene
glycol ethyl ether acetate, diethylene glycol methyl ether acetate,
diethylene glycol ethyl ether acetate, diethylene glycol-n-butyl
ether acetate, propylene glycol ethyl ether acetate, propylene
glycol propyl ether acetate, dipropylene glycol methyl ether
acetate, and dipropylene glycol ethyl ether acetate.
[0063] Examples of the amide-based solvent include
N,N-dimethylformamide and N,N-dimethylacetoamide, whereas an
example of the sulfoxide-based solvent is
N,N-dimethylsulfoxide.
[0064] Examples of the aprotic solvent having a relative
permittivity of at least 10 include ketone-based solvents,
acetonitrile, amide-based solvents, and sulfoxide-based solvents.
Examples of the ketone-based solvents having a relative
permittivity of at least 10 include acetone, methylethylketone,
methyl-n-propylketone, methyl-iso-propylketone,
methyl-n-butylketone, methyl-iso-butylketone,
methyl-n-pentylketone, methyl-n-hexylketone, diethylketone,
dipropylketone, di-iso-butylketone, trimethylnonanone,
cyclohexanone, cyclopentanone, methylcyclohexanone,
2,4-pentanedione, and acetonylacetone. Examples of the amide-based
solvents having a relative permittivity of at least 10 include
N,N-dimethylformamide and N,N-dimethylacetoamide. An example of the
sulfoxide-based solvents having a relative permittivity of at least
10 is N,N-dimethylsulfoxide.
[0065] They may be used either singly or in combination of two or
more.
[0066] Other protonic solvent components may further be contained
as the (b) component when necessary. Examples of such a protonic
solvent include alcohol-based solvents, ether-based solvents, and
ester-based solvents.
[0067] Examples of the alcohol-based solvents include methanol,
ethanol, n-propanol, i-propanol, n-butanol, i-butanol, sec-butanol,
t-butanol, n-pentanol, i-pentanol, 2-methylbutanol, sec-pentanol,
t-pentanol, 3-methoxybutanol, n-hexanol, 2-methylpentanol,
sec-hexanol, 2-ethylbutanol, sec-heptanol, n-octanol,
2-ethylhexanol, sec-octanol, n-nonyl alcohol, n-decanol,
sec-undecyl alcohol, trimethylnonyl alcohol, sec-tetradecyl
alcohol, sec-heptadecyl alcohol, phenol, cyclohexanol,
methylcyclohexanol, benzyl alcohol, ethylene glycol, 1,2-propylene
glycol, 1,3-butylene glycol, diethylene glycol, dipropylene glycol,
triethylene glycol, and tripropylene glycol.
[0068] Examples of the ether-based solvents include ethylene glycol
methyl ether, ethylene glycol ethyl ether, ethylene glycol
monophenyl ether, diethylene glycol monomethyl ether, diethylene
glycol monoethyl ether, diethylene glycol mono-n-butyl ether,
diethylene glycol mono-n-hexyl ether, ethoxytriglycol,
tetraethylene glycol mono-n-butyl ether, dipropylene glycol
monomethyl ether, dipropylene glycol monoethyl ether, and
tripropylene glycol monomethyl ether.
[0069] Examples of the ester-based solvents include methyl lactate,
ethyl lactate, n-butyl lactate, and n-amyl lactate.
[0070] They may be used either singly or in combination of two or
more together with the aprotic solvent.
(c) Component
[0071] The (c) component is presumed to function to enhance the
stability of the composition for forming a silica-based film and
further improve electric and mechanical characteristics of the
silica-based film. Also, this component seems to have a function of
accelerating the condensation reaction of the (a) component so that
the curing can be effected at a lower temperature in a shorter
time, and further restrain the mechanical strength from
lowering.
[0072] For exhibiting such functions, the composition for forming a
silica-based film in accordance with the present invention contains
an onium salt as the (c) component. Examples of the onium salt
include ammonium salts, phosphonium salts, arsonium salts,
stibonium salts, oxonium salts, sulfonium salts, selenonium salts,
stannonium salts, and iodonium salts. Among them, ammonium salts
are preferred because they are superior in terms of the stability
of the composition, and quaternary ammonium salts are more
preferred.
[0073] Examples of the ammonium salts include tetramethylammonium
oxide, tetramethylammonium chloride, tetramethylammonium bromide,
tetramethylammonium fluoride, tetrabutylammonium oxide,
tetrabutylammonium chloride, tetrabutylammonium bromide,
tetrabutylammonium fluoride, tetramethylammonium nitrate,
tetramethylammonium acetate, tetramethylammonium propionate,
tetramethylammonium maleate, and tetramethylammonium sulfate.
[0074] Preferred in particular among these ammonium salts from the
viewpoint of improving electric characteristics of the silica-based
film are ammonium salts such as tetramethylammonium nitrate,
tetramethylammonium acetate, tetramethylammonium propionate,
tetramethylammonium maleate, and tetramethylammonium sulfate.
[0075] Though not completely elucidated yet in detail, the effect
due to the onium salt contained in the composition is presumed to
be based on a mechanism in which the onium salt promotes the
condensation reaction, so as to increase the density of siloxane
bonds and reduce the number of remaining silanol groups, thereby
improving the mechanical strength and dielectric property. This
does not limit operations, however.
Optional Component
[0076] Preferably, the composition for forming a silica-based film
in accordance with the present invention further contains a pore
forming compound adapted to thermally decompose or evaporate at a
heating temperature of 250.degree. to 500.degree. C. as an optional
component (hereinafter referred to as "(d) component"). The (d)
component seems to have a function of gradually forming micropores
(voids or pores) in the silica-based film, thereby further thinning
pores and homogenizing their forms when finally cured. For
exhibiting such a function, the decrease ratio of the (d) component
in a nitrogen gas atmosphere at a temperature of 250.degree. to
500.degree. C. is preferably at least 95 mass %, more preferably at
least 97 mass %, further preferably at least 99 mass %. When the
decrease ratio is less than 95 mass %, the decomposition or
evaporation of the compound tends to become insufficient at the
time of heating the composition for forming a silica-based film.
Namely, the (d) component, a part of the (d) component, or a
reaction product derived from the (d) component may remain in the
finally obtained silica-based film. This may result in the
deterioration of electric characteristics of the silica-based film,
such as an increase in the relative permittivity.
[0077] The "decrease ratio" of the (d) component in the present
invention is a value determined by the following apparatus under
the following condition. Namely, the "decrease ratio" is measured
by a differential scanning calorimeter (TG/DTA6300 manufactured by
Seiko Instruments Inc.) under the condition where 10 mg of the
above-mentioned polymer are heated at a heating rate of 10.degree.
C./min from a heating start temperature of 50.degree. C. with a
nitrogen (N.sub.2) gas flow rate of 200 mL/min. .alpha.-alumina is
used as a reference, whereas a .phi.5 open sample pan made of
aluminum (manufactured by Seiko Instruments Inc.) is used as a
sample container.
[0078] The standard mass of the (d) component before starting the
decomposition is the mass at a temperature of 150.degree. C. in the
process of heating. This is because the decrease in mass at a
temperature of 150.degree. C. or lower is presumed to be caused by
elimination of absorbed moisture or the like without substantially
decomposing the (d) component itself. When the (d) component cannot
directly be weighed alone because it is dissolved in a solution,
etc., for example, about 2 g of the solution containing the (d)
component are collected in a metal petri dish, and are dried for 3
hours at 150.degree. C. in an air at normal pressure, and thus
obtained residue is used as a sample.
[0079] Examples of the (d) component include vinyl-ether-based
compounds, compounds having a polyalkylene unit such as vinyl-based
compounds or polymers having a polyoxyalkylene unit such as a
polyoxyethylene unit or polyoxypropylene unit, vinyl-pyridine-based
compounds, styrene-based compounds, alkyl-ester-vinyl-based
compounds, (meth)acrylate-based compounds, polycarbonate,
polyester, and polyanhydride. As the (d) component, from the
viewpoint of decomposition characteristics and film mechanical
strength, polymers having a polyoxyalkylene unit are preferred,
those having a polyoxypropylene unit in particular.
[0080] Examples of the polyoxyalkylene unit include
polyoxyethylene, polyoxypropylene, polyoxytetramethylene, and
polyoxybutylene units. More specific examples of the compounds
having a polyoxyalkylene unit include ether-based compounds such as
polyoxyethylene alkyl ether, polyoxyethylene sterol ether,
polyoxyethylene lanolin derivatives, ethylene oxide derivatives of
alkyl phenol formalin condensates, polyoxyethylene polyoxypropylene
block copolymer, polyoxypropylene alkyl ether, and polyoxyethylene
polyoxypropylene alkyl ether; ether-ester-based compounds such as
polyoxyethylene glycerin fatty acid ester, polyoxyethylene sorbitol
fatty acid ester, and polyoxyethylene fatty acid alkanolamide
sulfate; ether-ester-based compounds such as polyethylene glycol
fatty acid ester, ethylene glycol fatty acid ester, fatty acid
monoglyceride, polyglycerin fatty acid ester, sorbitan fatty acid
ester, and propylene glycol fatty acid ester; and glycol-based
compounds such as ethylene glycol, diethylene glycol, triethylene
glycol, propylene glycol, polyethylene glycol, and polypropylene
glycol.
[0081] Examples of (meth)acrylate-based compounds include alkyl
acrylate ester, alkyl methacrylate ester, alkoxyalkyl acrylate
ester, and alkoxyalkyl methacrylate ester. Examples of alkyl
acrylate ester include alkyl esters having a carbon number of 1 to
6 such as methyl acrylate, ethyl acrylate, n-propyl acrylate,
isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, pentyl
acrylate, and hexyl acrylate. Examples of alkyl methacrylate
include alkyl esters having a carbon number of 1 to 6 such as
methyl methacrylate, ethyl methacrylate, n-propyl methacrylate,
isopropyl methacrylate, n-butyl methacrylate, isobutyl
methacrylate, pentyl methacrylate, and hexyl methacrylate. Examples
of alkoxyalkyl acrylate ester include methoxymethyl acrylate and
ethoxyethyl acrylate. Examples of alkoxyalkyl methacrylate ester
include methoxymethyl methacrylate and ethoxyethyl
methacrylate.
[0082] As a (meth)acrylate-based compound, copolymers with
compounds having a hydroxyl group can be used. Specific examples of
the compound include 2-hydroxyethyl acrylate, diethylene glycol
acrylate, 2-hydroxypropyl acrylate, dipropylene glycol acrylate,
methacrylic acid, 2-hydroxyethyl methacrylate, diethylene glycol
methacrylate, 2-hydroxypropyl methacrylate, and dipropylene glycol
methacrylate.
[0083] Examples of polyester include polycondensates of
hydroxycarboxylic acid, ring-opening polymers of lactone, and
polycondensates of aliphatic polyol and aliphatic polycarboxylic
acid.
[0084] Examples of polycarbonate include polycondensates of
carboxylic acid and alkylene glycol, such as polyethylene
carbonate, polypropylene carbonate, polytrimethylene carbonate,
polytetramethylene carbonate, polypentamethylene carbonate, and
polyhexamethylene carbonate.
[0085] Examples of polyanhydride include polycondensates of
dicarboxylic acid, such as polymalonyl oxide, polyadipoyl oxide,
polypimelyl oxide, polysuberoyl oxide, polyazelayl oxide, and
polysebacoyl oxide.
[0086] From the viewpoints of solubility in solvents, compatibility
with siloxane resins, film mechanical characteristics, film
formability, etc., Mw of the (d) component is preferably 200 to
10,000, more preferably 300 to 5,000, further preferably 400 to
2,000. When Mw exceeds 10,000, the compatibility with siloxane
resins tends to decrease. When Mw is less than 200, on the other
hand, the forming of pores tends to become insufficient.
[0087] Respective contents of the components in the composition for
forming a silica-based film in accordance with the present
invention will now be explained. The content of the (a) component
in the composition for forming a silica-based film in accordance
with the present invention is preferably 3 to 25 mass %. When the
content of the (a) component exceeds 25 mass %, the amount of the
organic solvent tends to become so small that the film forming
property of the silica-based film deteriorates and the stability of
the composition itself lowers. When the content of the (a)
component is less than 3 mass %, on the other hand, the amount of
the solvent tends to become so large that a silica-based film
having a desirable thickness is hard to form.
[0088] The content of the (c) component is preferably 0.001 mass
ppm to 5 mass %, more preferably 0.01 mass ppm to 1 mass %, further
preferably 0.1 mass ppm to 0.5 mass %, based on the total weight of
the composition for forming a silica-based film in accordance with
the present invention. When the content is less than 0.001 mass
ppm, electrical and mechanical characteristics of the finally
obtained silica-based film tend to deteriorate. When the content
exceeds 5 mass %, on the other hand, the stability, film forming
property, etc. of the composition tend to deteriorate, and electric
characteristics and process adaptability of the silica-based film
are likely to lower. The onium salt, which is the (c) component,
can be added to the composition so as to yield a desirable
concentration after being dissolved in or diluted with water or a
solvent when necessary.
[0089] The content of the (d) component is preferably 0.1 to 10
mass %, more preferably 1 to 5 mass %, based on the total weight of
the composition for forming a silica-based film in accordance with
the present invention. When the content is less than 0.1 mass %,
the forming of pores tends to become insufficient. When the content
exceeds 10 mass %, the film strength may decrease.
[0090] The content of the (b) component is the residue left when
the total amount of the (a) component, (b) component, (c)
component, (d) component, and other additives added if necessary is
subtracted from the weight of the composition.
[0091] Preferably, the composition for forming a silica-based film
in accordance with the present invention contains neither alkali
metal nor alkaline earth metal. Even when the composition contains
such a metal, the metal ion concentration in the composition is
preferably 100 mass ppb or less, more preferably 20 mass ppb or
less. When the metal ion concentration exceeds 100 mass ppb, metal
ions are more likely to flow into semiconductor devices having a
silica-based film obtained by the above-mentioned composition,
whereby device performances themselves may adversely be affected.
Therefore, it will be effective if alkali metals and alkaline earth
metals are eliminated from within the composition by use of an
ion-exchange filter or the like when necessary.
Method of Forming Silica-Based Film, Silica-Based Film, and
Electronic Component
[0092] Preferred embodiments of the method of forming a
silica-based film, silica-based film, and electronic component in
accordance with the present invention will now be explained.
[0093] Using the composition for forming a silica-based film in
accordance with the present invention, the silica-based film in
accordance with the present invention can be formed by spin
coating, which will be explained in the following, for example. The
spin coating is suitable for forming the silica-based film in
accordance with the present invention, because of its excellent
film formability and film homogeneity.
[0094] First, the composition for forming a silica-based film is
spin-coated onto a substrate such as silicon wafer preferably at
500 to 5,000 rpm, more preferably at 1,000 to 3,000 rpm, so as to
form a coating film. Here, the film homogeneity tends to
deteriorate when the rotating speed is less than 500 rpm. When the
rotating speed exceeds 5,000 rpm, on the other hand, the film
forming property may deteriorate.
[0095] Subsequently, the organic solvent is removed from within the
coating film by a hot plate or the like preferably at 50.degree. to
350.degree. C., more preferably 1000 to 300.degree. C. When the
drying temperature at the time of removal is less than 50.degree.
C., the removal of the organic solvent tends to become
insufficient. When the drying temperature exceeds 350.degree. C.,
on the other hand, the (d) component for forming pores may
thermally decompose before the siloxane resin sufficiently forms a
siloxane skeleton, so that the amount of evaporation may increase
to a disadvantageous extent, whereby the silica-based film having a
desirable mechanical strength and low dielectric property may be
harder to obtain.
[0096] Subsequently, the coating film having removed the organic
solvent therefrom is fired at a heating temperature of 250.degree.
to 500.degree. C., so as to be finally cured. This forms a
silica-based film (Low-k film) which can exhibit a low dielectric
constant even in a high frequency region of 100 kHz or more. The
"relative permittivity" in the present invention refers to a value
measured in an atmosphere at 23.degree. C..+-.2.degree. C. with a
relative humidity of 40%+10%, and is preferably 2.5 or less. The
relative permittivity can be determined by measuring the electric
charge capacity between Al metal and an N-type low resistivity
substrate (Si wafer), for example. The silica-based film of the
present invention has a sufficient mechanical strength and can be
cured at a lower temperature in a shorter time as compared with
conventional ones. Preferably, the final curing is carried out in
an inert atmosphere such as nitrogen, argon, and helium, for
example. In this case, it will be preferred if the oxygen
concentration is 1,000 ppm or less. When the heating temperature at
the time of curing is less than 250.degree. C., curing is less
likely to be achieved sufficiently, and the
decomposition/evaporation of the (d) component is less likely to be
promoted sufficiently. When the heating temperature exceeds
500.degree. C., on the other hand, the heat input amount may
increase if there is a metal wiring layer, thereby deteriorating
the wiring metal.
[0097] The heating time for curing is preferably 2 to 60 minutes,
more preferably 2 to 30 minutes. When the heating time exceeds 60
minutes, the heat input amount may increase so much that the wiring
metal deteriorates. Preferably used as a heating apparatus are heat
processing apparatus such as silica tube furnaces and other
furnaces, hot plates, and rapid thermal annealing (RTA)
furnaces.
[0098] The thickness of thus formed silica-based film is preferably
0.01 to 40 .mu.m, more preferably 0.1 to 2.0 .mu.m. When the film
thickness exceeds 40 .mu.m, stresses are likely to generate cracks.
When the film thickness is less than 0.01 .mu.m in the case where a
metal wiring layer exists between upper and lower layers of the
silica-based film, leak characteristics between respective wires of
the upper and lower layers tend to deteriorate.
[0099] Examples of the electronic component using thus formed
silica-based film include electronic devices having a silica-based
film such as semiconductor devices and multilayer wiring boards.
The silica-based film in accordance with the present invention can
be used, for example, as a surface protection film (passivation
film), buffer coating film, or interlayer insulating film in a
semiconductor device. In a multilayer wiring board, on the other
hand, the film can favorably be used as an interlayer insulating
film. The silica-based film in accordance with the present
invention can also be used as a liquid crystal display part, an
optical waveguide part, etc.
[0100] Specific examples of the semiconductor device include
discrete semiconductor devices such as diodes, transistors,
compound semiconductors, thermistors, varistors, and thyristors;
storage devices such as DRAM (dynamic random access memory), SRAM
(static random access memory), EPROM (erasable programmable
read-only memory), mask ROM (mask read-only memory), EEPROM
(electrical erasable programmable read-only memory), and flash
memory; logic circuit devices such as microprocessors, DSP, and
ASIC; integrated circuit devices such as compound semiconductors
typified by MMIC (monolithic microwave integrated circuit); and
photoelectric converter devices such as hybrid integrated circuit
(hybrid IC), light-emitting diode, and charge-coupled device. An
example of the multilayer wiring board is a high-density wiring
board such as MCM.
[0101] FIG. 1 is a schematic sectional view showing an embodiment
of the multilayer wiring structure in accordance with the present
invention. FIG. 1 shows a multilayer (three-layer) wiring structure
100 formed on a transistor, which is made, for example, as follows.
First, on a transistor in which a device separating structure 2, an
impurity diffusing layer 3, a gate electrode 4, a first interlayer
insulating film 5, and a contact plug 6 are disposed on a silicon
substrate 1, a second insulating film 7, a silica-based film 8 in
accordance with the present invention, and a protective insulating
film 9 are laminated in succession, so as to form a structure 200
shown in FIG. 2. Subsequently, a resist film having a predetermined
form, for example, is formed on the protective insulating film 9
shown in FIG. 2, and the part of protective insulating film 9 not
covered with the resist film and the part of silica-based film 8
and interlayer insulating film 7 thereunder are removed by etching
or the like, and then the resist film is removed, so as to form a
first wiring groove 10 shown in FIG. 3.
[0102] Subsequently, a barrier metal layer 11 is formed so as to
cover the transistor and the exposed interlayer insulating film 7,
silica-based film 8, and protective insulating film 9, and a copper
film 12 is further laminated thereon, so as to yield a structure
400 shown in FIG. 4. Then, the copper film 12 and barrier metal
layer 11 are partly removed, for example, by chemical mechanical
polishing (CMP), so as to form a structure 500 shown in FIG. 5,
whose surface on the side opposite from the transistor is
flattened. This yields a structure in which a single layer of
wiring (first layer wire) is disposed on the transistor.
[0103] Then, a barrier insulating film 13 is formed on the first
layer wire, and second and third layer wires are successively
laminated thereon by forming or partly removing the silica-based
film 8 in accordance with the present invention, protective
insulating film 9, barrier metal layer 11, and copper film 12 by
the same method as that mentioned above. This yields the multilayer
(three-layer) wiring structure on the transistor shown in FIG. 1.
However, this does not restrict the multilayer wiring structure in
accordance with the present invention.
[0104] The electronic component exemplified above or the like
allows the silica-based film to have a relative permittivity
sufficiently lower than that conventionally available, thereby
being able to sufficiently shorten the wiring delay time in signal
propagation and realize a high reliability. This can also improve
the yield in production of electronic components and the like, and
the process tolerance. Further, the above-mentioned excellent
characteristics of the silica-based film made of the composition
for forming a silica-based film in accordance with the present
invention make it possible to provide electronic components and the
like having a high density, a high quality, and an excellent
reliability.
EXAMPLES
[0105] In the following, preferred examples of the present
invention will be explained in further detail. However, the present
invention is not limited to these examples.
Example 1
Making of Composition for Forming Silica-Based Film
[0106] Into a solution formed by dissolving 154.6 g of
tetraethoxysilane and 120.6 g of methyltriethoxysilane in 543.3 g
of cyclohexanone, 80.98 g of an aqueous solution containing 0.525 g
of 70% nitric acid dissolved therein were fed dropwise for 30
minutes while being stirred. Their reaction was carried out for 5
hours after the completion of dropwise feeding, and then thus
generated ethanol and cyclohexanone were partly evaporated under
reduced pressure in a warm bath, whereby 583.7 g of a polysiloxane
solution were obtained. The weight average molecular weight of
polysiloxane determined by GPC was 1,350.
[0107] Subsequently, into 553.9 g of the polysiloxane solution,
24.86 g of polypropylene glycol (PPG-725 manufactured by Aldrich
Co.), which was a pore forming compound, 498.7 g of cyclohexanone,
17.89 g of 2.38% tetramethylammonium nitrate aqueous solution (pH
3.6), and 5.5 g of 1% diluted maleic acid aqueous solution were
added and dissolved while being stirred for 30 minutes at room
temperature, so as to prepare a composition for forming a
silica-based film in accordance with the present invention. The
weight reduction ratio of polypropylene glycol (PPG-725
manufactured by Aldrich Co.) used as the pore forming compound was
99.9% at 350.degree. C.
Example 2
[0108] Into a solution formed by dissolving 154.6 g of
tetraethoxysilane and 120.6 g of methyltriethoxysilane in 543.3 g
of cyclohexanone, 80.98 g of an aqueous solution containing 0.525 g
of 70% nitric acid dissolved therein were fed dropwise for 30
minutes while being stirred. Their reaction was carried out for 5
hours after the completion of dropwise feeding, and then thus
generated ethanol and cyclohexanone were partly evaporated under
reduced pressure in a warm bath, whereby 598.2 g of a polysiloxane
solution were obtained. The weight average molecular weight of
polysiloxane determined by GPC was 1,280.
[0109] Subsequently, into 514.5 g of the polysiloxane solution,
22.60 g of polypropylene glycol (PPG-725 manufactured by Aldrich
Co.), which was a pore forming compound, 441.6 g of diethylene
glycol dimethyl ether, 16.26 g of 2.38% tetramethylammonium nitrate
aqueous solution (pH 3.6), and 5.0 g of 1% diluted maleic acid
aqueous solution were added and dissolved while being stirred for
30 minutes at room temperature, so as to prepare a composition for
forming a silica-based film in accordance with the present
invention. The weight reduction ratio of polypropylene glycol
(PPG-725 manufactured by Aldrich Co.) used as the pore forming
compound was 99.9% at 350.degree. C.
Comparative Example 1
[0110] Into a solution formed by dissolving 154.6 g of
tetraethoxysilane and 120.6 g of methyltriethoxysilane in 543.3 g
of ethanol, 80.98 g of an aqueous solution containing 0.525 g of
70% nitric acid dissolved therein were fed dropwise for 30 minutes
while being stirred. Their reaction was carried out for 5 hours
after the completion of dropwise feeding, whereby 819.0 g of a
polysiloxane solution were obtained. The weight average molecular
weight of polysiloxane determined by GPC was 1,170.
[0111] Subsequently, into 774.0 g of the polysiloxane solution,
22.60 g of polypropylene glycol (PPG-725 manufactured by Aldrich
Co.), which was a pore forming compound, 182.1 g of ethanol, 16.26
g of 2.38% tetramethylammonium nitrate aqueous solution (pH 3.6),
and 5.0 g of 1% diluted maleic acid aqueous solution were added and
dissolved while being stirred for 30 minutes at room temperature,
so as to prepare a composition for forming a silica-based film in
accordance with the present invention. The weight reduction ratio
of polypropylene glycol (PPG-725 manufactured by Aldrich Co.) used
as the pore forming compound was 99.9% at 350.degree. C.
Example 3
Making of Interlayer Insulating Film
[0112] The compositions for forming a silica-based film obtained by
Examples 1 and 2 and Comparative Example 1 were applied onto
silicon wafers in a rotational fashion, so as to form coating
films. For forming each coating film, the rotating speed was
adjusted so as to form a film having a thickness of 0.50.+-.0.05
.mu.m after curing. Subsequently, the organic solvent in the
coating films was eliminated over 3 minutes at 250.degree. C., and
then the coating films having the organic solvent removed therefrom
were finally cured over 30 minutes at 400.degree. C. by using a
silica tube furnace in which O.sub.2 concentration was controlled
so as to become about 100 pm, whereby silica-based films to become
interlayer insulating films were made. Thus obtained silica films
were irradiated with He--Ne laser light with wavelength of 633 nm.
The film thickness determined by an ellipsometer (Ellipsometer
L116B manufactured by Gaertner Scientific Corporation) from the
phase difference generated upon the light irradiation at a
wavelength of 633 nm was 0.504 .mu.m in Example 1, 0.498 .mu.m in
Example 2, and 0.501 .mu.m in Comparative Example 1.
[0113] Subsequently, using a vapor deposition apparatus, Al metal
was deposited in vacuum on each silica-based film so as to form a
circle having a diameter of 2 mm with a thickness of about 0.1
.mu.m. As a result, interlayer insulating films having a structure
in which a silica-based film is disposed between Al metal and a
silicon wafer (low resistivity substrate) were made.
Measurement of Relative Permittivity
[0114] Using an apparatus in which a dielectric test fixture
(HP16451B manufactured by Yokogawa Electric Corporation) was
connected to an LF impedance analyzer (HP4192A manufactured by
Agilent Technologies Inc.), the electric charge capacity of each of
thus obtained interlayer insulating films was measured under the
condition with a temperature of 23.degree. C..+-.2.degree. C., a
relative humidity of 40%.+-.10%, and a frequency in use of 1
MHz.
[0115] Then, thus measured value of electric charge capacity was
put into the following expression: <relative permittivity of
interlayer insulating
film>=3.597.times.10.sup.-2.times.<electric charge capacity
(pF)>. .times.<interlayer insulating film thickness
(.mu.m)>whereby the relative permittivity of the interlayer
insulating film was calculated. Employed as the interlayer
insulating film thickness was the value obtained by the
above-mentioned measurement of the silica-based film thickness.
Measurement of Modulus of Elasticity
[0116] Using a nanoindenter SA2 (DCM manufactured by MTS Systems
Corporation), the modulus of elasticity of each interlayer
insulating film was measured (at a temperature of 23.degree.
C..+-.2.degree. C. and a frequency of 75 Hz within an elasticity
measurement range not greater than 1/10 of the interlayer
insulating film thickness without fluctuating dependent on the
indentation depth).
[0117] Table 1 shows results of measurement of electric
characteristic and modulus of elasticity (film strength) of the
interlayer insulating films obtained by Example 3. TABLE-US-00001
TABLE 1 Example 1 Example 2 Co. Exam. 3 Relative permittivity 2.3
2.3 2.7 Modulus of elasticity 6.6 6.6 5.8 (GPa)
[0118] As explained in the foregoing, the present invention
provides a composition for forming a silica-based film, which can
exhibit a low dielectric property of 2.5 or less even in a high
frequency region of 100 kHz or more and a sufficient mechanical
strength while being curable at a lower temperature in a shorter
time as compared with conventional ones. The present invention also
provides a silica-based film comprising such a composition, a
method of forming the same, and an electronic component provided
with such a silica-based film.
* * * * *