U.S. patent application number 11/512968 was filed with the patent office on 2006-12-28 for composition for forming porous film, porous film and method for forming the same, interlevel insulator film, and semiconductor device.
This patent application is currently assigned to Shin-Etsu Chemical Co., Ltd.. Invention is credited to Yoshitaka Hamada, Hideo Nakagawa, Masaru Sasago, Fujio Yagihashi.
Application Number | 20060289849 11/512968 |
Document ID | / |
Family ID | 33127841 |
Filed Date | 2006-12-28 |
United States Patent
Application |
20060289849 |
Kind Code |
A1 |
Yagihashi; Fujio ; et
al. |
December 28, 2006 |
Composition for forming porous film, porous film and method for
forming the same, interlevel insulator film, and semiconductor
device
Abstract
The invention includes a semiconductor device. Specifically
provided is a semiconductor device comprising a porous film
therein, the porous film being formable by a composition comprising
a surfactant, an aprotic polar solvent and a solution comprising a
polymer formed by hydrolysis and condensation of one or more silane
compounds represented by foramula (1) : R.sub.nSi(OR').sub.4-n.
Also provided is a method for manufacturing a porous film
comprising steps of applying said composition so as to form a film,
drying the film and transforming the dried film to a porous film by
removing said surfactant. The porous film obtained from the
composition for forming porous film is further provided.
Inventors: |
Yagihashi; Fujio;
(Niigata-ken, JP) ; Hamada; Yoshitaka;
(Niigata-ken, JP) ; Nakagawa; Hideo;
(Oumihachiman-shi, JP) ; Sasago; Masaru; (Osaka,
JP) |
Correspondence
Address: |
ALSTON & BIRD LLP
BANK OF AMERICA PLAZA
101 SOUTH TRYON STREET, SUITE 4000
CHARLOTTE
NC
28280-4000
US
|
Assignee: |
Shin-Etsu Chemical Co.,
Ltd.
Matsushita Electric Industrial Co., Ltd.
|
Family ID: |
33127841 |
Appl. No.: |
11/512968 |
Filed: |
August 29, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10810360 |
Mar 26, 2004 |
7119354 |
|
|
11512968 |
Aug 29, 2006 |
|
|
|
Current U.S.
Class: |
257/3 ;
257/E21.273; 257/E21.581 |
Current CPC
Class: |
H01L 21/02126 20130101;
H01L 21/02216 20130101; H01L 21/02203 20130101; H01L 21/31695
20130101; H01L 21/02282 20130101 |
Class at
Publication: |
257/003 |
International
Class: |
H01L 29/04 20060101
H01L029/04 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 9, 2003 |
JP |
2003-104774 |
Claims
1. A semiconductor device comprising a porous film therein, the
porous film being formable by a composition comprising a
surfactant, an aprotic polar solvent and a solution comprising a
polymer formed by hydrolysis and condensation of one or more silane
compounds represented by formula (1): R.sub.nSi(OR').sub.4-n (1)
wherein each R independently represents a linear or branched alkyl
group having 1 to 8 carbons or an aryl group, and when there are
two or more Rs, each may be the same or different; each R'
independently represents an alkyl group having 1 to 4 carbons, and
when there are two or more R's, each R' may be the same or
different; and n is an integer from 0 to 3.
2. The semiconductor device according to claim 1 wherein said
surfactant is a quaternary ammonium salt which can form a micelle
when dissolved.
3. The semiconductor device according to claim 2 wherein said
quaternary ammonium salt is an alkyltrimethylammonium salt
represented by formula (2): R''N+(CH.sub.3).sub.3X.sup.- (2)
wherein R'' represents a linear or branched alkyl group having 8 to
20 carbons and X represents an atom or functional group which can
form anion.
4. The semiconductor device according to claim 2 wherein said
aprotic polar solvent has a dielectric constant of 20 or more.
5. The semiconductor device according to claim 2 wherein said
aprotonic polar solvent is one or more selected from the group
consisting of acetonitrile, propionitrile, isobutyronitrile,
N-methylpyrrolidone, N, N-dimethylformamide, N,N-dimethylacetamide,
dimethylsulfoxide, hexamethylphosphortriamide, nitrobenzene and
nitromethane.
6. The semiconductor device according to claim 2 wherein said
porous film is between metal interconnections in a same layer of
multi-level interconnects or between upper and lower metal
interconnection layers.
7. The semiconductor device according to claim 1 wherein said
quaternary ammonium salt is an alkyltrimethylammonium salt
represented by formula (2): R''N.sup.+(CH.sub.3).sub.3X.sup.- (2)
wherein R'' represents a linear or branched alkyl group having 8 to
20 carbons and X represents an atom or functional group which can
form anion.
8. The semiconductor device according to claim 1 wherein said
aprotic polar solvent has a dielectric constant of 20 or more.
9. The semiconductor device according to claim 1 wherein said
aprotonic polar solvent is one or more selected from the group
consisting of acetonitrile, propionitrile, isobutyronitrile,
N-methylpyrrolidone, N, N-dimethylformamide, N,N-dimethylacetamide,
dimethylsulfoxide, hexamethylphosphortriamide, nitrobenzene and
nitromethane.
10. The semiconductor device according to claim 1 wherein said
porous film is between metal interconnections in a same layer of
multi-level interconnects or between upper and lower metal
interconnection layers.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. application Ser.
No. 10/810,360, filed Mar. 26, 2004, which is hereby incorporated
herein in its entirety by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the invention
[0003] The present invention relates to a composition for film
formation which can be formed into a porous film which excels in
dielectric properties, adhesion, film uniformity and mechanical
strength, and has reduced moisture absorption; a porous film and a
method for forming the same; and a semiconductor device which
contains the porous film inside.
[0004] 2. Description of the related art
[0005] In the fabrication of semiconductor integrated circuits, as
the circuits are packed tighter, an increase in interconnection
capacitance, which is a parasitic capacitance between metal
interconnections, leads to an increase in interconnection delay
time, thereby hindering the enhancement of the performance of
semiconductor circuits. The interconnection delay time is called an
RC delay which is in proportion to the product of the electric
resistance of the metal interconnections and the static capacitance
between the interconnections. Reducing the interconnection delay
time requires reducing the resistance of metal interconnections or
the interconnection capacitance.
[0006] The reduction in resistance of the interconnection metal and
the interconnection capacitance can prevent a densely packed
semiconductor device from causing an interconnection delay, thereby
realizing a smaller and faster semiconductor device with reduced
power consumption.
[0007] In an attempt to reduce the resistance of metal
interconnections, in recent years, metallic copper interconnections
have been employed more than conventional aluminum interconnections
in the structure of a device. However, use of this structure alone
has limits in the enhancement of the performance, so the reduction
in interconnection capacitance is an urgent necessity for higher
performance of semiconductors.
[0008] One method for reducing interconnection capacitance is to
reduce the relative permittivity (dielectric constant) of an
interlevel insulator film disposed between metal interconnections.
As such an insulator film with a low relative permittivity, it has
been considered to use a porous film instead of a silicon oxide
film which has been used conventionally. A porous film can be said
to be the only practical film as a material with a relative
permittivity of 2.0 or less, and various methods for forming a
porous film have been proposed.
[0009] A first method for forming a porous film is as follows: a
precursor solution of a siloxane polymer containing a thermally
unstable organic component is synthesized; then the precursor
solution is applied on the substrate to form a coating film; and
later, a heat treatment is applied to decompose and volatilize the
organic component. The result is a number of micro-pores formed in
the film.
[0010] As a second method for forming a porous film, it is well
known to carry out processing as follows: a silica sol solution is
applied onto a substrate by coating or using a CVD method so as to
form a wet gel; and then the silica sol is subjected to a
condensation reaction while restricting volume reduction by
controlling the speed of the evaporation of the solvent from the
wet gel.
[0011] As a third method for forming a porous film, it is well
known that a silica micro-particle solution is applied on a
substrate to form a coating film, and then the coating film is
sintered to form a number of micro-pores between silica
micro-particles.
[0012] As a fourth method, Japanese Patent Provisional Publication
No. 2000-44875 proposes a composition for porous film formation
which is characterized by containing a compound having (A) a
component expressed by (R').sub.nSi(OR'').sub.4-n (R' and R'' are
univalent organic radicals, and m is an integer of 0 to 2); (B) a
metal chelate compound; and (C) a compound having a polyalkylene
oxide structure.
[0013] However, these methods have respective major drawbacks as
follows.
[0014] In the first method for forming a porous film, the synthesis
of the precursor solution of the siloxane polymer increases the
cost. In addition, the formation of the coating film by coating the
precursor solution increases the amount of silanol groups remaining
in the coating film, which causes a degassing phenomenon indicating
the evaporation of water and the like in the heat treatment process
that is conducted later and which also deteriorates the film
quality due to the porous film absorbing humidity.
[0015] In the second method for forming a porous film, the speed
control of the evaporation of the solvent from the wet gel requires
a special type of coating device, which increases the cost. In
addition, a significant amount of silanol remains on the surface of
the micro-pores which must be silanized because otherwise
hygroscopicity is high so that the film quality decreases. The
silanization makes the process more complicated. In the case where
a wet gel is formed by the CVD process, it is necessary to use a
special type of CVD device which is different from the plasma CVD
device generally used in the semiconductor process, thereby also
increasing the cost.
[0016] In the third method for forming a porous film, the diameter
of the micro-pores formed between the silica micro-particles, which
is determined by the accumulation structure A of the silica
micro-particles that are accumulated geometrically, becomes very
large. This makes it difficult to set the relative permittivity of
the porous film to 2 or below.
[0017] In the case of the fourth method, out of the three
components (A), (B), and (C), the metal chelate compound of (B) is
essential to increase the compatibility of the components (A) and
(C), and to make the thickness of the coating film uniform after
being hardened. However, it is not preferable because it makes the
manufacturing process complicated and increases the cost.
Therefore, it is desired to develop a material which enables a
homogeneous solution to be formed without a chelate component and
the coating film to be flat after being hardened.
[0018] In comparison to the conventional method for forming a
porous film, it has been found that a porous member having a
channel structure of mesopore size (micro-pores with diameters of 2
to 50 nm) can be formed as follows: alumino silicate, silica, or
the like is condensed while using a micelle made from a
surface-active agent as a mold so as to form the structure, and
then the surface-active agent component is removed by sintering or
solvent extraction. For example, Inagaki et al. propose making
polysilicates react in water while using a surface-active agent as
a mold (J. Chem. Soc. Chem. Commun., p. 680, 1993). Furthermore,
Japanese Patent Provisional Publication No. 9-194298 discloses that
tetraalkoxysilane is reacted in acid conditions in water while
using a surface-active agent as a mold, and is applied onto the
substrate so as to form a silica porous film having micro-pores of
diameters of 1 to 2 nm.
[0019] However, these methods have problems as follows. In the
first method, the powdered porous member can be easily formed, but
it is impossible to form a porous film as a thin film on the
substrate which is used for the fabrication of semiconductor
devices. In the second method, a porous member can be formed into a
thin film, but it is impossible to control the orientation of
micro-pores, and it is also impossible to form a uniform thin film
in a wide area.
[0020] Japanese Patent Provisional Publication No. 2001-130911
discloses a method for forming a silica mesoporous thin film by
using a mixture of an acid hydrolysis condensate of a silicon
alkoxide and a surface-active agent after adjusting the mixture to
pH3 or below for stabilization.
[0021] However, in this method, too, the restriction of the solute
concentration makes it difficult to properly control the thickness
of a coating film, thereby making it difficult to apply it to a
practical semiconductor fabrication process. When this solution is
diluted with water, the thickness of the coating film becomes
controllable, but the speed of polycondensation of the silica
component increases to lose stability of the coating solution.
[0022] As mentioned above, the conventional materials have several
problems such as deterioration of the film quality during the heat
treatment step and high cost. Moreover, the formation of the porous
film results in pores having a large diameter so that it is
difficult to obtain the low dielectric constant. When the
conventional porous film is incorporated into the multi-level
interconnects of the semiconductor device as an insulator film,
there is a problem that the mechanical strength necessary for the
semiconductor device is not obtained.
[0023] Thus, when the dielectric constant of the porous film used
as an insulator film in the multi-level interconnects of the
semiconductor device is too high, the RC delay in the multi-level
interconnects of the semiconductor device is increased so that the
performance of the semiconductor device (high speed and low power
consumption) cannot be improved. This represents large problems.
Furthermore, a porous film with a low mechanical strength
deteriorates the reliability of the semiconductor device.
SUMMARY OF THE INVENTION
[0024] Considering the above problems, the object of the invention
is to provide a composition for forming a porous film having a
desirably controlled thickness, wherein the film can be easily
formed using the usual semiconductor process and the film has a
mesopore channel structure which excels in stability m is. Another
purpose of this invention is to provide a high-performing and
highly reliable semiconductor device which contains the porous film
inside.
[0025] The inventors have studied hard for the development of the
coating liquid for forming the above porous film and then found the
composition for forming porous film, which has a mesopore channel
structure, and the manufacturing method of the porous film, which
is applicable in the semiconductor manufacturing process. Thus, the
invention is completed.
[0026] According-to the invention, provided is a composition for
forming a porous film comprising a surfactant, an aprotic polar
solvent and a solution comprising a polymer formed by hydrolysis
and condensation of one or more silane compounds represented by
R.sub.nSi(OR').sub.4-n formula (1)
[0027] wherein R represents a linear or branched alkyl group having
1 to 8 carbons or an aryl group, and when there are two or more Rs,
the Rs may be independently same or different; R' represents an
alkyl group having 1 to 4 carbons, and when there are two or more
R's, the R's may be independently same or different; and n is an
integer from 0 to 3.
[0028] According to the invention, provided is a method for
manufacturing a porous film comprising steps of applying said
composition to a substrate so as to form a film thereon, drying the
film and transforming the dried film to a porous film by removing
said surfactant such as quarternary ammonium salt. A porous film
formable by said composition is provided.
[0029] The semiconductor device of the invention comprises a porous
film therein, the porous film being formed by a composition
comprising a surfactant, an aprotic polar solvent and a solution
comprising a polymer formed by hydrolysis and condensation of one
or more silane compounds represented by R.sub.nSi(OR').sub.4-n
formula (1)
[0030] wherein R represents a linear or branched alkyl group
having-1 to 8 carbons or an aryl group, and when there are two or
more Rs, the Rs may be independently same or different; R'
represents an alkyl group having 1 to 4 carbons, and when there are
two or more R's, the R's may be independently same or different;
and n is an integer from 0 to 3. Specifically, said porous film may
be used as an insulator film of the multi-level interconnects in
the semiconductor device.
[0031] Thus, keeping the mechanical strength of the semiconductor
device secured, the hygroscopic property of the porous film is
decreased. Hence, the semiconductor device with a built-in
insulator film having a low dielectric constant is obtained.
Because of lowering dielectric constant of the insulator film, the
parasitic capacitance of the area around the multi-level
interconnects is decreased, leading to the high-speed operation and
low power consumption of the semiconductor device.
[0032] Moreover, it is preferable for the semiconductor device of
the invention that said porous film is between metal
interconnections in a same layer of multi-level interconnects or
between upper and lower metal interconnection layers. This
arrangement can achieve a high-performing and highly reliable
semiconductor device.
[0033] Use of the composition for forming a porous film of the
invention facilitates the formation of a porous film having a
stable mesoporous channel structure at a desirably controlled
thickness. The porous film has a low dielectric constant, and
excels in adhesion, film uniformity, and mechanical strength. In
addition, use of the porous film formed by the composition of the
invention as the insulator film of the multi-level interconnects
can produce a high-performing and highly reliable semiconductor
device.
BRIEF DESCRIPTION OF THE DRAWINGS
[0034] FIG. 1 is a schematic cross-sectional view of a
semiconductor device of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0035] The silane compound used in this invention is represented by
formula (1) wherein R represents a linear or branched alky group
having 1 to 8 carbons or aryl group and may have a substituent. The
R may include methyl, ethyl, propyl, isopropyl, butyl, isobutyl,
sec-butyl, tert-butyl, pentyl, sec-pentyl, neopentyl, hexyl,
2-ethylhexyl, heptyl, octyl, phenyl, o-tolyl, m-tolyl, p-tolyl,
xylyl and benzyl.
[0036] In formula (1), R' represents an alkyl group having 1 to 4
carbons. The R' may include methyl, ethyl, propyl, isopropyl and
butyl. In formula (1), n is an integer from 0 to 3.
[0037] The silane compound represented by formula (1) may include,
but are not limited to, tetramethoxysilane, tetraethoxysilane,
tetrapropoxysilane, tetrabutoxysilane, methyltrimethoxysilane,
methyltriethoxysilane, methyltripropoxysilane,
ethyltrimethoxysilane, propyltrimethoxysilane,
butyltrimethoxysilane, pentyltrimethoxysilane,
hexyltrimethoxysilane, 2-ethylhexyltrimethoxysilane,
phenyltrimethoxysilane, dimethyldimethoxysilane,
dimethyldiethoxysilane, trimethylmethoxysilane,
triethylmethoxysilane and butyldimethylmethoxysilane.
[0038] The silane compound solution becomes a polymer solution by
hydrolysis and condensation. The silane compound is preferably
subjected to hydrolysis and condensation in the present of water
under an acidic condition using acid as catalyst to yield a polymer
solution. The acid used in this case may include mineral acid such
as hydrochloric acid, sulfuric acid and nitric acid; sulfonic acid
such as methanesulfonic acid, benzenesulfonic acid,
p-toluenesulfonic acid and trifluoromethanesulfonic acid; organic
acid such as formic acid, acetic acid, propionic acid, oxalic acid,
malonic acid, fumaric acid, maleic acid, tartaric acid, citric acid
and malic acid; and phosphoric acid. The water for the hydrolysis
may be preferably 0.5 to 10 times, more preferably 1.0 to 4.0 times
the amount (mole) of water required to hydrolyze the silane
compound completely.
[0039] The polymer solution can be produced also under an alkali
condition. The base used in this case may include amines such as
ammonia, ethylamine, propylamine, diisopropylamine, triethylamine,
and triethanolamine; alkali metal hydroxide or alkali earth metal
hydroxides such as sodium hydroxide, potassium hydroxide and
calcium hydroxide.
[0040] The acid or alkali catalyst for the hydrolysis and
condensation should be selected carefully so that the surfactant
will not be decomposed in the presence of the acid or alkali
catalyst so as to allow the surfactant to work. For example, it is
necessary to avoid the decomposition of quarternary ammonium salt
in the presence of a strong base into amine. It is because the
decomposition of quarternary ammonium salt will prevent it from
functioning as a surfactant. The preferable combination may include
acid catalyst and quaternary ammonium salt which can produce
micelle as dissolved.
[0041] When the silane compound represented by formula (1) is
subjected to the hydrolysis and condensation to form a polymer
solution, solvent other than water may be added. The solvent may
include alcohol which corresponds to the alkoxy group of the silane
compound. The alcohol may include methanol, ethanol, isopropyl
alcohol, butanol, propylene glycol monomethyl ether, propylene
glycol monopropyl ether, propylene glycol monopropyl ether acetate,
ethyl lactate and cyclohexanone. The solvent other than water may
be added in the weight of preferably 0.1 to 10 times, more
preferably 0.5 to 2 times the weight of the silane compound.
[0042] The hydrolysis and condensation reaction of the silane may
be carried out in a usual condition of the conventional hydrolysis
and condensation reaction. The reaction temperature may be
typically from 0.degree. C. to a boiling point of the alcohol
generated by the hydrolysis and condensation, preferably from room
temperature to 60.degree. C.
[0043] The reaction time may not be especially limited. It may
typically take from 10 minutes to 18 hours, more preferably 30
minutes to about 3 hours.
[0044] The preferable weight-average molecular weight of the
polymer obtained from the silane compound represented by formula
(1) may be 500 to 50,000 based on polystyrene with Gel Permeation
Chromatography (GPC).
[0045] The polymer solution produced in the above manner may be
used as it is, or may be used as the solution to which a smaller
amount of one or more other components have been added. The other
component may include titanium oxide, aluminum oxide and zirconium
oxide and may be added in an amount of 0 to 20 wt % based on the
weight of the main component, the silane compound of formula
(1).
[0046] The surfactant used in the invention may be preferably the
quaternary ammonium salt which can form micelle as dissolved.
[0047] Any quaternary ammonium salt may be used as long as the
quaternary ammonium salt can form micelle when it is added to the
polymer solution and dissolve therein. Any cationic surfactant can
be generally used.
[0048] It should be noted that the surfactant such as quaternary
ammonium salt can be added to a solution of the silane compound so
as to allow the polymerization reaction to take place in the
solution.
[0049] The quaternary ammonium salt used in the invention may be
preferably alkyltrimethylammonium salt represented by formula (2):
R''N+(CH3)3X- (2) Wherein R'' represents a linear or branched alkyl
group having 8 to 20 carbons and X represents an atom or a
functional group which can form an anion.
[0050] The particularly preferable quaternary ammonium salt may be
alkyltrimethylammonium salt where the alkyl group is a linear alkyl
group having 12 of 18 carbons. The examples may include, but are
not limited to, dodecyltrimethylammonium chloride,
dodecyltrimethylammonium bromide, dodecyltrimethylammonium iodide,
tetradecyltrimethylammonium chloride, tetradecyltrimethylammonium
bromide, tetradecyltrimethylammonium iodide,
hexadecyltrimethylammonium chloride, hexadecyltrimethylammonium
bromide, hexadecyltrimethylammonium iodide,
hexadecyltrimethylammonium formate, hexadecyltrimethylammonium
acetate, hexadecyltrimethylammonium oxalate,
hexadecyltrimethylammonium trifluoroacetate,
hexadecyltrimethylammonium methanesulfonate,
hexadecyltrimethylammonium trifluoromethanesulfonate,
hexadecyltrimethylammonium hydroxide, stearyltrimethylammonium
chloride and stearyltrimethylammonium bromide.
[0051] The surfactant such as the quaternary ammonium salt may be
dissolved uniformly in the silane solution or the polymer solution
only by mixing or stirring. However, the maximum amount of
surfactant which can be dissolved uniformly differs depending on
the type of surfactant such as the quaternary ammonium salt.
Accordingly, the amount of surfactant may be variable. The amount
of the surfactant may be typically from 0.01 to 0.5 mol % of the
amount (mole) of the silane compound (mole) of formula (1).
[0052] The solution containing the silicon polymer and the
surfactant such as quaternary ammonium salt is applied to a
substrate to form a film. Then the film is sintered so that the
surfactant will be removed off, thereby a porous film will be
obtained at the end. However, there is a problem that it is
difficult to control the film thickness during the coating because
the coating liquid contains alcohol and water as only solvents,
where the alcohol has been generated by the hydrolysis and
condensation of starting silane and corresponds to the alkoxy group
of the starting silane, and water has been added for the hydrolysis
and condensation.
[0053] To solve the above problem, the inventors have studied
keenly and found that a film having a desirable thickness can be
formed by controlling a concentration of a composition solution by
dilution with a certain kind of solvent and by controlling a
coating condition, and the film thus formed can become a porous
film having a mesopore channel structure by removing the surfactant
such as quaternary ammonium salt with heat or with solvent
extraction. Then, the invention is completed. The composition
obtained is also found to have higher storage stability in
comparison to a non-diluted composition.
[0054] When water is used as solvent to dilute the composition, the
condensation of polymers progresses rapidly so that gelling is
usually observed after the composition diluted with water is left
overnight at room temperature. When water or ethylene glycol is
used as solvent for the dilution, the stability is lowered and
gelling speed increases. On the other hand, when aprotic solvent is
used, the process of reaching a high molecular weight is suppressed
so that the stability increases.
[0055] The solvent for dilution may be aprotic polar solvent, which
is a polar solvent having no active hydrogen. The aprotic polar
solvent may preferably have a dielectric constant of 20 or more,
more preferably 20 to 50. When the dielectric constant is lower
than 20, it may be difficult for the surfactant such as quaternary
ammonium hydroxide to form micelle so that the channel structure
may not be formed. Consequently, the film may shrink during the
removal of the surfactant so that it may not become porous.
[0056] The solvent for dilution may preferably include (the figure
in parentheses indicates the dielectric constant) acetonitrile
(37.5), propionitrile (29.7), isobutyronitrile,
N-methylpyrrolidone, N,N-dimethylformamide (36.7),
N,N-dimethylacetamide (37.8), dimethylsulfoxide (48.8),
hexamethylphosphortriamide (29.6), nitrobenzene and nitromethane.
It may more preferably include acetonitrile, propionitrile,
isobutyronitrile and nitromethane.
[0057] Unsuitable solvent for dilution may include water (80.1),
ethylene glycol (37.7), ethyl acetate (6.02) and methyl isobutyl
ketone (13.1).
[0058] A film having a desirable thickness can be formed by
spin-coating an appropriately controlled concentration of the
coating liquid with an appropriate number of spin rotations. For
example, the actual film thickness of the film may be about 0.2 to
1 .mu.m, but not limited to this range. For example, by applying
the coating solution several times, the thickness of the thin film
can be increased. The method of coating other than spin coating may
include scan coating. The amount of the solvent for dilution may be
preferably 10 to 500% by volume, more preferably 20 to 300% by
volume based on the volume of solution before the dilution.
[0059] The film thus prepared may be heated preferably for several
minutes at 50.degree. C. to 150.degree. C. in a drying step
(generally called a pre-bake in the semiconductor process) so as to
remove the solvent.
[0060] The film thus formed will be made porous in the following
methods. In one method, the surfactant such as ammonium salt is
removed by decomposition, evaporation or sublimation thereof caused
by heating or calcinations at a high temperature so that spaces of
thin film where the surfactant has been occupied will become pores.
The temperature may be temperature sufficient for the surfactant
such as ammonium salt to decompose, evaporate or sublime and
typically 200 to 400.degree. C.
[0061] In another method, the surfactant such as quaternary
ammonium salt is dissolved in solvent so as to be removed. The
solvent may be any solvent as long as it can dissolve the
surfactant but does not dissolve the resin matrix. The solvent may
include, but are not limited to, methanol, ethanol, isopropanol,
acetone, methyl ethyl ketone, methyl isobutyl ketone, ether, ethyl
acetate, n-butyl acetate, isobutyl acetate, benzene, toluene,
xylene, anisole, N-methylpyrrolidone, N,N-dimethylformamide,
N,N-dimethylacetamide, dimethylsulfoxide,
hexamethylphosphortriamide, nitrobenzene and nitromethane. Although
the solvent may be used at room temperature, it can be also used
after being heated.
[0062] The film to which the surfactant such as quaternary ammonium
salt has been removed has a very large specific surface area,
typically 2,000 to 4,000 m.sup.2/g, according to the BET surface
area method using adsorption of a nitrogen gas. Consequently, a
film having a very small dielectric constant can be produced. For
example, the film of the invention may have dielectric constant of
1.5 to 2.5 of when measured with an automatic mercury probe.
[0063] Moreover, the porous film produced in the above method may
have an extremely narrow pore distribution, usually in the range of
1 to 3 nm and have almost no pores exceeding 3 nm. It can be
confirmed by the BET surface area measurement using gas
adsorption.
[0064] The obtained porous film has excellent mechanical strength
although the percentage of the pores in the entire film is
extremely high. It is because of uniform pore distribution in the
micro-pore channel structure. The film may typically have hardness
of 0.5 to 1.5 GPa and modulus of about 5.0 to 10 GPa when measured
with nanoindentation. This indicates that the obtained film has
much higher mechanical strength than the porous material produced
by adding a thermally decomposable polymer to siloxane resin and
thermally removing the polymer so as to form pores. It is because
the material has hardness of 0.05 to 2 GPa and modulus of about 1.0
to 4.0 GPa.
[0065] The porous film of the present invention is particularly
preferable as the interlevel insulator film of the interconnections
in a semiconductor integrated circuit. The semiconductor device is
required to reduce interconnection capacitance in order to prevent
interconnection delay when highly integrated. Various means have
been developed to achieve this, and one of them is to reduce the
relative permittivity of the interlevel insulator film disposed
between metal interconnections. When an interlevel insulator film
is prepared by using the composition for forming a porous film of
the present invention, the semiconductor device can be downsized
and faster and consume less power.
[0066] However, there is a conventional problem that when a porous
film is prepared by introducing pores in the film so as to lower
the dielectric constant, the mechanical strength of the film
decreases as the density of the material composing the film
decreases. The decrease in mechanical strength not only affects the
strength of the semiconductor device itself but also causes
exfoliation due to insufficient strength in a chemical mechanical
polishing process which is generally used in the fabrication
process. Particularly, when used as the interlevel insulator film
of a semiconductor, the porous film of the present invention with
high mechanical strength and low relative permittivity prevents
such exfoliation, thereby greatly improving the reliability of the
manufactured semiconductor device.
[0067] The embodiments of the semiconductor device of the present
invention will be described below. FIG. 1 shows an schematic
cross-sectional view of an example of the semiconductor device of
the present invention.
[0068] In FIG. 1, the substrate 1 is an Si semiconductor substrate
such as an Si substrate or an SOI (Si-on-insulator) substrate;
however, it can be a compound semiconductor substrate such as SiGe
or GaAs. The interlevel insulator films include the interlevel
insulator film 2 of the contact layer; the interlevel insulator
films 3, 5, 7, 9, 11, 13, 15, and 17 of the interconnection layers;
and the interlevel insulator films 4, 6, 8, 10, 12, 14, and 16 of
the via layers. The interconnection layers corresponding to the
lowermost interlevel insulator film 3 through the uppermost
insulator film 17 are abbreviated as M1, M2, M3, M4, M5, M6, M7,
and M8, respectively. The via layers corresponding to the lowermost
interlevel insulator film 4 through the uppermost insulator film 16
are abbreviated as V1, V2, V3, V4, V5, V6, and V7, respectively.
Although some of the metal interconnections are referred to with
the numbers 18 and 21 to 24, the other regions with the same
pattern not labeled with numbers indicate metal interconnections.
The via plug 19 is made from a metal. In the case of copper
interconnection, copper is generally used. The regions having the
same pattern as the via plug 19 represent via plugs although they
are not labeled with numbers in the drawing. The contact plug is
connected to the gate of the transistor (not illustrated) formed on
the top surface of the substrate 1 or to the substrate. Thus, the
interconnection layers and the via layers are alternately stacked,
and multi-level interconnections generally indicate M1 and regions
higher than Ml. In general, M1 to M3 are called local
interconnections, M4 and M5 are called intermediate
interconnections or semi-global interconnections, and M6 to M8 are
called global interconnections.
[0069] In the semiconductor device of the present invention, the
porous film of the present invention is used as one or more of the
interlevel insulator films 3, 5, 7, 9, 11, 13, 15, and 17 of the
interconnection layers or the insulator films 4, 8, 10, 12, 14, and
16 of the via layers.
[0070] For example, when the porous film of the present invention
is used for the interlevel insulator film 3 of the interconnection
layer (M1), the interconnection capacitance between the metal
interconnection 21 and the metal interconnection 22 can be greatly
reduced. When the porous film of the present invention is used for
the interlevel insulator film 4 of the via layer (Vl), the
interconnection capacitance between the metal interconnection 23
and the metal interconnection 24 can be greatly reduced. Using the
porous film with a low relative permittivity of the present
invention as an interconnection layer can greatly reduce the metal
interconnection capacitance in the same layer. On the other hand,
using the porous film with a low relative permittivity of the
present invention as a via layer can greatly reduce the interlevel
capacitance between the vertical metal interconnections.
[0071] Therefore, using the porous film of the present invention
for all of the interconnection layers and the via layers can
greatly reduce the parasitic capacitance of the interconnections.
Hence, the use of the porous film of the present invention as
insulator films of the interconnections prevents a conventional
problem, that is, an increase in the dielectric constant resulting
from the porous film absorbing humidity while multi-level
interconnections are formed by stacking porous films. Consequently,
the semiconductor device can perform high-speed and low-power
operations.
[0072] The porous film of the present invention enables a
semiconductor device to have higher mechanical strength by its high
mechanical strength, thereby greatly improving the yield of the
fabrication and the reliability of the semiconductor device.
[0073] The present invention will be described specifically through
the following examples and comparative examples, but is not limited
to the examples.
EXAMPLES 1-6
[0074] The mixture of 30.4 g tetramethoxysilane and 8.0 g water was
stirred at room temperature, while 0.2 ml hydrochloric acid was
added thereto all at once. After stirred for a few minutes, the
reacting solution generated heat and became a uniform solution. It
was stirred 1 hour further at room temperature, producing a
slightly viscous solution. According to the analysis with a gel
permeation chromatography using tetrahydrofuran as a moving bed,
the siloxane produced had weight-average molecular weight of 1,250
and number average molecular weight of 822 based on polystylene.
The 6.82 g trimethyloctadecylammonium chloride was added to this
solution and stirred to produce a uniform solution. Then an
additional one hour of agitation produced a transparent and
colorless solution.
[0075] This was used as a stock solution. The composition for
forming porous film was obtained by diluting the stock solution
with a prescribed quantity of solvent as shown in Table 1, wherein
DMF is N,N-dimethylformamide, DMAc is N,N-dimethylacetamide, HMPA
is hexamethylphosphortriamide and DMSO is dimethyl-sulfoxide.
COMPARATIVE EXAMPLES 1-4
[0076] The above stock solution was diluted with a prescribed
amount of water, ethylene glycol, ethyl acetate or ethyl isobutyl
ketone as shown in Table 1 to produce the compositions.
TABLE-US-00001 TABLE 1 stock solution solvent for dilution
stability weight Solvent weight for storage Example 1 5 g
acetonitrile 5 g Stable*1 Example 2 5 g Propionitrile 5 g Stable*1
Example 3 5 g DMF 5 g Stable*1 Example 4 5 g DMAc 5 g Stable*1
Example 5 5 g HMPA 5 g Stable*1 Example 6 5 g DMSO 5 g Stable*1
Comp. Ex. 1 5 g Water 5 g unstable*2 Comp. Ex. 2 5 g ethylene
glycol 5 g unstable*2 Comp. Ex. 3 5 g ethyl acetate 5 g Stable*1
Comp. Ex. 4 5 g Methyl isobutyl ketone 5 g Stable*1 *1No gellation
even after one week at room temperature. *2Gellation in one day at
room temperature.
[0077] As shown in Table 1, the solutions of Comparative Examples
1-2 was gelled and insoluble in solvent after being left at room
temperature for one day. However, the solutions in Examples 1-6 and
Comparative Examples 3-4 were not gelled and showed almost no
increase of molecular weight even after being left at room
temperature for one week.
EXAMPLES 7-13
[0078] The mixture of 15.2 g tetramethoxysilane, 13.6 g
methyltrimethoxysilane and 7.0 g water was stirred, while 0.2 ml of
1N hydrochloric acid solution was added all at once thereto. After
stirred for a few minute, the reacting solution generated heat and
became a uniform solution. It was stirred 1 hour further at room
temperature, and the resulting solution was analyzed with a gel
permeation chromatography. It had weight-average molecular weight
of 1,872 and number average molecular weight of 839 based on
polystylene. The 6.4 g trimethylhexadecylammonium chloride was
added to this solution and stirred further for one hour produced a
transparent and colorless solution.
[0079] This was used as a stock solution. The composition for
forming porous film was obtained by diluting the stock solution
with a prescribed quantity of solvent as shown in Table 2.
COMPARATIVE EXAMPLES 5-7
[0080] The above stock solution was diluted with a prescribed
amount of solvent as shown in Table 2 so that the compositions were
obtained. TABLE-US-00002 TABLE 2 stock solution solvent for
dilution stability weight solvent weight for storage Example 7 5 g
nitromethane 5 g stable*1 Example 8 5 g acetonitrile 5 g stable*1
Example 9 5 g propionitrile 5 g stable*1 Example 10 5 g DMF 5 g,
stable*1 Example 11 5 g DMAc 5 g stable*1 Example 12 5 g HMPA 5 g
stable*1 Example 13 5 g DMSO 5 g stable*1 Comp. Ex. 5 5 g water 5 g
unstable*2 Comp. Ex. 6 5 g ethyl acetate 5 g stable*1 Comp. Ex. 7 5
g Methyl isobutyl ketone 5 g stable*1 *1No gellation even after one
week at room temperature. *2Gellation in one day at room
temperature.
[0081] As shown in Table 2, the solution of Comparative Example 5
was gelled and insoluble in solvent after being left at room
temperature for one day. However, the solutions in Examples 7-13
and Comparative Examples 6-7 were not gelled and showed almost no
increase of molecular weight even after being left at room
temperature for one week.
COATING EXAMPLE 1
[0082] The solution in Example 1 was applied on an 8 inch wafer
with a spin coater at 2,000 rpm for 1 minute to produce a film on
the wafer. The film was heated on a hot plate at 100.degree. C. for
1 minute. Then, the film had thickness of 12,600 .ANG.. After the
film was further heated at 150.degree. C. for 1 minute, it was
heated at 400.degree. C. for 1 hour in a nitrogen atmosphere in a
clean oven. The obtained film had thickness of 10,200 .ANG.. The
dielectric constant of the coated film had 1.8 in a CV method using
an automatic mercury probe. Moreover, it had specific surface area
of 3,100 m.sup.2/g according to the method of gas adsorption. A
central value of the pore diameters was 2.0 nm and it was confirmed
that the pores having pore size of more than 3.0 nm did not
substantially existed. The film had modulus of 8.5 GPa according to
the measurement of a Nanoindenter.
COATING EXAMPLES 2-8
[0083] Each solution in Examples 2-8 and 10-11 was used as a
coating liquid and processed in the same manner as Coating Example
1. The dielectric constant and modulus obtained are shown in Table
3.
COMPARATIVE COATING EXAMPLE 3
[0084] The solution of Comparative Example 3 was applied on an 8
inch wafer with a spin coater at 1,500 rpm for 1 minute to produce
a film on the wafer. The film was heated on a hot plate at
100.degree. C. for 1 minute. Then, the film had thickness of 13,500
.ANG.. After the film was further heated at 150.degree. C. for 1
minute, it was heated at 400.degree. C. for 1 hour in a nitrogen
atmosphere in a clean oven. The obtained film had thickness of
7,300 .ANG.. The dielectric constant of the coated film had 4.2 in
a CV method using an automatic mercury probe. Moreover, it had
specific surface area of 50 m.sup.2/g according to the method of
gas adsorption. Thus, it was found that the film was not
porous.
COMPARATIVE COATING EXAMPLE 4
[0085] The solution of Comparative Example 4 was processed in the
same manner as Coating Example 1. The obtained film had dielectric
constant of 4.0 and specific surface area of 70 m.sup.2/g. Thus, it
was found that the film was not porous.
COMPARATIVE COATING EXAMPLE 7
[0086] The solution in Comparative Example 7 was processed in the
same manner as Coating Example 1. The obtained film had dielectric
constant of 4.4 and specific surface area of 80 m.sup.2/g. Thus, it
was found that the film was not porous. TABLE-US-00003 TABLE 3
specific coating surface dielectric modulus liquid area (m.sup.2/g)
constant (GPa) Coating Ex. 1 Ex. 1 3,100 1.8 8.5 Coating Ex. 2 Ex.
2 -- 1.9 7.2 Coating Ex. 3 Ex. 3 -- 2.0 8.0 Coating Ex. 4 Ex. 4 --
1.9 9.1 Coating Ex. 5 Ex. 5 -- 1.8 7.0 Coating Ex. 6 Ex. 6 -- 1.9
7.5 Coating Ex. 7 Ex. 7 -- 2.0 7.2 Coating Ex. 8 Ex. 8 -- 2.0 7.9
Coating Ex. 10 Ex. 10 -- 2.1 8.0 Coating Ex. 11 Ex. 11 -- 1.9 8.2
Comp. Coating Ex. 3 Comp. 50 4.2 -- Ex. 3 Comp. Coating Ex. 4 Comp.
70 4.0 -- Ex. 4 Comp. Coating Ex. 7 Comp. 80 4.4 -- Ex. 7
* * * * *