U.S. patent application number 09/820075 was filed with the patent office on 2001-09-13 for silicone polymer insulation film on semiconductor substrate and method for forming the film.
Invention is credited to Matsuki, Nobuo.
Application Number | 20010021590 09/820075 |
Document ID | / |
Family ID | 12511254 |
Filed Date | 2001-09-13 |
United States Patent
Application |
20010021590 |
Kind Code |
A1 |
Matsuki, Nobuo |
September 13, 2001 |
Silicone polymer insulation film on semiconductor substrate and
method for forming the film
Abstract
A siloxan polymer insulation film has a dielectric constant of
3.3 or lower and has --SiR.sub.2O-- repeating structural units. The
siloxan polymer has dielectric constant, high thermal stability and
high humidity-resistance on a semiconductor substrate. The siloxan
polymer is formed by directly vaporizing a silicon-containing
hydrocarbon compound expressed by the general formula
Si.sub..alpha.O.sub..beta.C.sub.xH.sub.y (.alpha., .beta., x, and y
are integers) and then introducing the vaporized compound to the
reaction chamber of the plasma CVD apparatus. The residence time of
the source gas is lengthened by reducing the total flow of the
reaction gas, in such a way as to form a siloxan polymer film
having a micropore porous structure with low dielectric
constant.
Inventors: |
Matsuki, Nobuo; (Tokyo,
JP) |
Correspondence
Address: |
KNOBBE MARTENS OLSON & BEAR LLP
620 NEWPORT CENTER DRIVE
SIXTEENTH FLOOR
NEWPORT BEACH
CA
92660
US
|
Family ID: |
12511254 |
Appl. No.: |
09/820075 |
Filed: |
March 28, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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09820075 |
Mar 28, 2001 |
|
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09243156 |
Feb 2, 1999 |
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Current U.S.
Class: |
438/780 ;
257/E21.26; 257/E21.261; 257/E23.12 |
Current CPC
Class: |
B05D 1/62 20130101; Y10S
257/914 20130101; H01L 2924/0002 20130101; C09D 4/00 20130101; C23C
16/30 20130101; H01L 21/3122 20130101; H01L 21/02274 20130101; H01L
21/02126 20130101; H01L 2924/12044 20130101; H01L 21/02216
20130101; H01L 23/296 20130101; C23C 16/401 20130101; H01L 21/3121
20130101; C09D 4/00 20130101; C08G 77/00 20130101; H01L 2924/0002
20130101; H01L 2924/00 20130101 |
Class at
Publication: |
438/780 |
International
Class: |
H01L 021/31 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 5, 1998 |
JP |
10-37929 |
Claims
What is claimed is:
1. A method for forming a siloxan polymer insulation film on a
semiconductor substrate by plasma treatment, comprising the steps
of: vaporizing a silicon-containing hydrocarbon compound to produce
a material gas for silicone polymer, said silicon-containing
hydrocarbon having the formula
Si.sub..alpha.O.sub..alpha.-1R.sub.2.alpha.-.beta.+2(O-
C.sub.nH.sub.2n+1), wherein .alpha. is an integer of 1-3, .beta. is
0, 1, or 2, n is an integer of 1-3, and R is C.sub.1-6 hydrocarbon
attached to Si; introducing the material gas into a reaction
chamber for plasma CVD processing wherein a semiconductor substrate
is placed; introducing an additive gas comprising an inert gas and
optionally an oxidizing gas, said oxidizing gas being used in an
amount less than the material gas; and forming a siloxan polymer
film having --SiR.sub.2O-- repeating structural units on the
semiconductor substrate by activating plasma polymerization
reaction in the reaction chamber where a reaction gas composed of
the material gas and the additive gas is present, while controlling
the flow of the reaction gas to lengthen a residence time, Rt, of
the reaction gas in the reaction chamber, wherein 100
msec.ltoreq.Rt,
Rt[s]=9.42.times.10.sup.7(Pr.multidot.Ts/Ps.multidot.Tr)r-
.sub.w.sup.2d/F wherein: Pr: reaction chamber pressure (Pa) Ps:
standard atmospheric pressure (Pa) Tr: average temperature of the
reaction gas (K) Ts: standard temperature (K) r.sub.w: radius of
the silicon substrate (m) d: space between the silicon substrate
and the upper electrode (m) F: total flow volume of the reaction
gas (sccm).
2. The method according to claim 1, wherein the residence time is
determined by correlating the dielectric constant with the
residence time.
3. The method according to claim 1, wherein the additive gas
comprises at least either argon (Ar) or Helium (He).
4. The method according to claim 1, wherein the flow of the
reaction gas is controlled to render the relative dielectric
constant of the silicone polymer film lower than 3.30.
5. The method according to claim 1, wherein the flow of the
reaction gas is controlled to render the dielectric constant of the
silicone polymer film no more than 3.1.
6. The method according to claim 1, wherein Rt is no less than 165
msec.
7. The method according to claim 1, wherein the additive gas is
exclusively an inert gas.
8. A method for forming a siloxan polymer insulation film on a
semiconductor substrate by plasma treatment, comprising the steps
of: vaporizing a silicon-containing hydrocarbon compound to produce
a material gas for silicone polymer, said silicon-containing
hydrocarbon having the formula
Si.sub..alpha.O.sub..alpha.-1R.sub.2.alpha.-.beta.+2(O-
C.sub.nH.sub.2n+1).beta. wherein .alpha. is an integer of 1-3,
.beta. is 0 or 1, n is an integer of 1-3, and R is C.sub.1-6
hydrocarbon attached to Si; introducing the material gas into a
reaction chamber for plasma CVD processing wherein a semiconductor
substrate is placed; introducing an additive gas comprising an
inert gas and an oxidizing gas, said oxidizing gas being used in an
amount less than the material gas; and forming a siloxan polymer
film having --SiR.sub.2O-- repeating structural units on the
semiconductor substrate by activating plasma polymerization
reaction in the reaction chamber where a reaction gas composed of
the material gas and the additive gas is present, while controlling
the flow of the reaction gas to lengthen a residence time, Rt, of
the reaction gas in the reaction chamber, wherein 100
msec.ltoreq.Rt, Rt[s]=9.42.times.10.sup.7(P-
r.multidot.Ts/Ps.multidot.Tr)r.sub.w.sup.2d/F wherein: Pr: reaction
chamber pressure (Pa) Ps: standard atmospheric pressure (Pa) Tr:
average temperature of the reaction gas (K) Ts: standard
temperature (K) r.sub.w: radius of the silicon substrate (m) d:
space between the silicon substrate and the upper electrode (m) F:
total flow volume of the reaction gas (sccm).
9. A siloxan polymer insulation film formed on a semiconductor
substrate by the method of claim 1, which has a dielectric constant
of 3.3 or lower and has --SiR.sub.2O-- repeating structural units
formed by plasma polymerization reaction from a silicon-containing
hydrocarbon having the formula
Si.sub..alpha.O.sub..alpha.-1R.sub.2.alpha.-.beta.+2(OC.sub.nH.su-
b.2n+1).beta. wherein .alpha. is an integer of 1-3, .beta. is 0, 1,
or 2, n is an integer of 1-3, and R is C.sub.1-6 hydrocarbon
attached to Si.
10. The siloxan polymer insulation film according to claim 9, which
has a dielectric constant of 3.1.
11. The siloxan polymer insulation film according to claim 10,
which has a dielectric constant of 2.8.
12. The siloxan polymer insulation film according to claim 9,
wherein the dielectric constant is stable as measured one hour
after being placed at 120.degree. C. and 100% humidity.
13. The siloxan polymer insulation film according to claim 9,
wherein said R in the repeating structural unit is C.sub.1
hydrocarbon.
14. A method for forming a siloxan polymer insulation film on a
semiconductor substrate by plasma treatment, comprising the steps
of: vaporizing a silicon-containing hydrocarbon compound to produce
a material gas for silicone polymer, said silicon-containing
hydrocarbon having the general formula
Si.sub..alpha.O.sub..beta.C.sub.xH.sub.y wherein .alpha., .beta.,
x, and y are integers; introducing the material gas into a reaction
chamber for plasma CVD processing wherein a semiconductor substrate
is placed; introducing an additive gas; and forming a siloxan
polymer film having --SiR.sub.2O-- repeating structural units on
the semiconductor substrate by activating plasma polymerization
reaction in the reaction chamber where a reaction gas composed of
the material gas and the additive gas is present, while controlling
the flow of the reaction gas to lengthen a residence time, Rt, of
the reaction gas in the reaction chamber, wherein 100
msec.ltoreq.Rt,
Rt[s]=9.42.times.10.sup.7(Pr.multidot.Ts/Ps.multidot.Tr)r.sub.w.sup.2d/F
wherein: Pr: reaction chamber pressure (Pa) Ps: standard
atmospheric pressure (Pa) Tr: average temperature of the reaction
gas (K) Ts: standard temperature (K) r.sub.w: radius of the silicon
substrate (m) d: space between the silicon substrate and the upper
electrode (m) F: total flow volume of the reaction gas (sccm).
15. The method according to claim 14, wherein the alkoxy present in
the silicon-containing hydrocarbon compound has 1 to 3 carbon
atoms.
16. The method according to claim 14, wherein the hydrocarbon
present in the silicon-containing hydrocarbon compound has 1 to 6
carbon atoms.
17. The method according to claim 14, wherein the
silicon-containing hydrocarbon compound has 1 to 3 silicon
atoms.
18. The method according to claim 14, wherein the
silicon-containing hydrocarbon compound has formula
Si.sub..alpha.O.sub..alpha.-1R.sub.2.alp-
ha.-.beta.+2(OC.sub.nH.sub.2n+1).beta. wherein .alpha. is an
integer of 1-3, .beta. is 0, 1, or 2, n is an integer of 1-3, and R
is C.sub.1-6 hydrocarbon attached to Si.
19. The method according to claim 14, wherein the additive gas
comprises at least either argon (Ar) or Helium (He).
20. The method according to claim 14, wherein the additive gas
comprises either an oxidizing agent or a reducing agent.
21. The method according to claim 19, wherein the additive gas
further comprises either an oxidizing agent or a reducing
agent.
22. The method according to claim 14, wherein the
silicon-containing hydrocarbon compound is selected from the group
consisting of: 14wherein R1 and R2 are independently CH.sub.3,
C.sub.2H.sub.3, C.sub.2H.sub.5, C.sub.3H.sub.7 or C.sub.6H.sub.5,
and m and n are any integer, 15wherein R1, R2 and R3 are
independently CH.sub.3, C.sub.2H.sub.3, C.sub.2H.sub.5,
C.sub.3H.sub.7 or C.sub.6H.sub.5, and n is any integer, 16wherein
R1, R2, R3 and R4 are independently CH.sub.3, C.sub.2H.sub.3,
C.sub.2H.sub.5, C.sub.3H.sub.7 or C.sub.6H.sub.5, and m and n are
any integer, 17wherein R1, R2, R3, R4, R5 and R6 are independently
CH.sub.3, C.sub.2H.sub.3, C.sub.2H.sub.5, C.sub.3H.sub.7 or
C.sub.6H.sub.5, if the additive gases are argon (Ar), Helium (He)
and either nitrogen oxide (N.sub.2O) or oxygen (O.sub.2), and
18wherein R1, R2, R3 and R4 are independently CH.sub.3,
C.sub.2H.sub.3, C.sub.2H.sub.5, C.sub.3H.sub.7 or C.sub.6H.sub.5,
if the additive gases are argon (Ar), Helium (He) and either
nitrogen oxide (N.sub.2O) or oxygen (O.sub.2).
23. The method according to claim 14, wherein the flow of the
reaction gas is controlled to render the relative dielectric
constant of the silicone polymer film lower than 3.30.
Description
[0001] This is a continuation of U.S. patent application Ser. No.
09/243,156, filed Feb. 2, 1999, which claims priority based on
Japanese patent application No. 37929/1998, filed Feb. 5, 1998. The
entire disclosure of the parent application is hereby incorporated
by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention relates generally to a semiconductor
technique and more particularly to a silicone polymer insulation
film on a semiconductor substrate and a method for forming the film
by using a plasma CVD (chemical vapor deposition) apparatus.
[0004] 2. Description of Related Art
[0005] Because of the recent rise in requirements for the
large-scale integration of semiconductor devices, a multi-layered
wiring technique attracts a great deal of attention. In these
multi-layered structures, however, capacitance among individual
wires hinders high-speed operations. In order to reduce the
capacitance it is necessary to reduce the dielectric constant
(relative permittivity) of the insulation film. Thus, various
materials having a relatively low dielectric constant have been
developed for insulation films.
[0006] Conventional silicon oxide films SiO.sub.x are produced by a
method in which oxygen O.sub.2 or nitrogen oxide N.sub.2O is added
as an oxidizing agent to a silicon material gas such as SiH.sub.4
or Si(OC.sub.2H.sub.5).sub.4 and then processed by heat or plasma
energy. Its dielectric constant is about 4.0.
[0007] Alternatively, a fluorinated amorphous carbon film has been
produced from C.sub.xF.sub.yH.sub.z as a material gas by a plasma
CVD method. Its dielectric constant .epsilon. is as low as
2.0-2.4.
[0008] Another method to reduce the dielectric constant of
insulation film has been made by using the good stability of Si--O
bond. A silicon-containing organic film is produced from a material
gas under low pressure (1 Torr) by the plasma CVD method. The
material gas is made from P-TMOS (phenyl trimethoxysilane, formula
1), which is a compound of benzene and silicon, vaporized by a
babbling method. The dielectric constant .epsilon. of this film is
as low as 3.1. 1
[0009] A further method uses a porous structure made in the film.
An insulation film is produced from an inorganic SOG material by a
spin-coat method. The dielectric constant .epsilon. of the film is
as low as 2.3.
[0010] However, the above noted approaches have various
disadvantages as described below.
[0011] First, the fluorinated amorphous carbon film has lower
thermal stability (370.degree. C.), poor adhesion with
silicon-containing materials and also lower mechanical strength.
The lower thermal stability leads to damage under high temperatures
such as over 400.degree. C. Poor adhesion may cause the film to
peel off easily. Further, the lower mechanical strength can
jeopardize wiring materials.
[0012] Oligomers that are polymerized using P-TMOS molecules do not
form a linear structure in the vapor phase, such as a siloxane
structure, because the P-TMOS molecule has three O--CH.sub.3 bonds.
The oligomers having no linear structure cannot form a porous
structure on a Si substrate, i.e., the density of the deposited
film cannot be reduced. As a result, the dielectric constant of the
film cannot be reduced to a desired degree.
[0013] In this regard, the babbling method means a method wherein
vapor of a liquid material, which is obtained by having a carrier
gas such as argon gas pass through the material, is introduced into
a reaction chamber with the carrier gas. This method generally
requires a large amount of a carrier gas in order to cause the
material gas to flow. As a result, the material gas cannot stay in
the reaction chamber for a sufficient length of time to cause
polymerization in a vapor phase.
[0014] Further, the SOG insulation film of the spin-coat method has
a problem in that the material cannot be applied onto the silicon
substrate evenly and another problem in which a cure system after
the coating process is costly.
[0015] Object of the Invention
[0016] It is, therefore, a principal object of this invention to
provide an improved insulation film and a method for forming
it.
[0017] It is another object of this invention to provide an
insulation film that has a low dielectric constant, high thermal
stability, high humidity-resistance and high adhesive strength, and
a method for forming it.
[0018] It is a further object of this invention to provide a
material for forming an insulation film that has a low dielectric
constant, high thermal stability, high humidity-resistance and high
adhesive strength.
[0019] It is a still further object of this invention to provide a
method for easily forming an insulation film that has a low
dielectric constant without requiring an expensive device.
SUMMARY OF THE INVENTION
[0020] One aspect of this invention involves a method for forming
an insulation film on a semiconductor substrate by using a plasma
CVD apparatus including a reaction chamber, which method comprises
a step of directly vaporizing a silicon-containing hydrocarbon
compound expressed by the general formula
Si.sub..alpha.O.sub..beta.C.sub.xH.sub.y (.alpha.,.beta., x, and y
are integers) and then introducing it to the reaction chamber of
the plasma CVD apparatus, a step of introducing an additive gas,
the flow volume of which is substantially reduced, into the
reaction chamber and also a step of forming an insulation film on a
semiconductor substrate by plasma polymerization reaction wherein
mixed gases made from the vaporized silicon-containing hydrocarbon
compound as a material gas and the additive gas are used as a
reaction gas. It is a remarkable feature that the reduction of the
additive gas flow also results in a substantial reduction of the
total flow of the reaction gas. According to the present invention,
a silicone polymer film having a micropore porous structure with
low dielectric constant can be produced.
[0021] The present invention is also drawn to an insulation film
formed on a semiconductor substrate, and a material for forming the
insulation film, residing in the features described above.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 is a schematic diagram illustrating a plasma CVD
apparatus used for forming an insulation film of this
invention.
[0023] FIG. 2 is a graph showing the relationship between
dielectric constant and the total flow of a reaction gas as well as
the relationship between residence time and the total flow of a
reaction gas, both in experiments using PM-DMOS as a material
gas.
[0024] FIG. 3 is a graph showing the relationship between the
residence time and dielectric constant in experiments using PM-DMOS
as a material gas.
[0025] FIG. 4 is a graph showing the thermal desorption spectra of
components having a molecular weight of 16 due to desorption of
CH.sub.4 from films (PM-DMOS, DM-DMOS) according to the present
invention in a thermal desorption test.
[0026] FIG. 5 is a graph showing changes in the degree of vacuum
corresponding to the number of total molecules dissociated from the
films (PM-DMOS, DM-DMOS), i.e., pressure raises due to gas
dissociated from the films in the thermal desorption test.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE
INVENTION
[0027] Basic Aspects
[0028] In the present invention, the silicon-containing hydrocarbon
compound expressed as the general formula
Si.sub..alpha.O.sub..beta.C.sub- .xH.sub.y (.alpha.,.beta., x, and
y are integers) is preferably a compound having at least one Si--O
bond, two or less O--C.sub.nH.sub.2n+1 bonds and at least two
hydrocarbon radicals bonded with silicon (Si). More specifically,
the silicon-containing hydrocarbon compound includes at least one
species of the compound expressed by the chemical formula (2) as
follows: 2
[0029] wherein R1 and R2 are one of CH.sub.3, C.sub.2H.sub.3,
C.sub.2H.sub.5, C.sub.3H.sub.7 and C.sub.6H.sub.5, and m and n are
any integer.
[0030] Except for the species indicated above, the
silicon-containing hydrocarbon compound can include at least one
species of the compound expressed by the chemical formula (3) as
follows: 3
[0031] wherein R1, R2 and R3 are one of CH.sub.3, C.sub.2H.sub.3,
C.sub.2H.sub.5, C.sub.3H.sub.7 and C.sub.6H.sub.5, and n is any
integer.
[0032] Except for those species indicated above, the
silicon-containing hydrocarbon compound can include at least one
species of the compound expressed by the chemical formula (4) as
follows: 4
[0033] wherein R1, R2, R3 and R4 are one of CH.sub.3,
C.sub.2H.sub.3, C.sub.2H.sub.5, C.sub.3H.sub.7 and C.sub.6H.sub.5,
and m and n are any integer.
[0034] Further, except for those species indicated above, the
silicon-containing hydrocarbon compound can include at least one
species of the compound expressed by the chemical formula (5) as
follows: 5
[0035] wherein R1, R2, R3, R4, R5 and R6 are one of CH.sub.3,
C.sub.2H.sub.3, C.sub.2H.sub.5, C.sub.3H.sub.7 and C.sub.6H.sub.5,
and the additive gases are argon (Ar), Helium (He) and either
nitrogen oxide (N.sub.2O) or oxygen (O.sub.2).
[0036] Furthermore, except for those species indicated above, the
silicon-containing hydrocarbon compound can include at least one
species of the compound expressed by the chemical formula (6) as
follows: 6
[0037] wherein R1, R2, R3 and R4 are one of CH.sub.3,
C.sub.2H.sub.3, C.sub.2H.sub.5, C.sub.3H.sub.7 and C.sub.6H.sub.5,
and the additive gases are argon (Ar), Helium (He) and either
nitrogen oxide (N.sub.2O) or oxygen (O.sub.2).
[0038] Still further, the material gas can include at least one of
said silicon-containing hydrocarbon compounds indicated above.
[0039] In accordance with another aspect of this invention, an
insulation film is formed on a substrate and the film is
polymerized with plasma energy in a plasma CVD apparatus by using a
material gas including a silicon-containing hydrocarbon compound
expressed by formula 2.
[0040] Additionally, the insulation film is formed on a substrate
and the film is polymerized with plasma energy in a plasma CVD
apparatus by using a material gas including a silicon-containing
hydrocarbon compound expressed by formula 3.
[0041] Further, the insulation film is formed on a substrate and
the film is polymerized with plasma energy in a plasma CVD
apparatus by using a material gas including a silicon-containing
hydrocarbon compound expressed by formula 4.
[0042] Furthermore, the insulation film is formed on a substrate
and the film is polymerized with plasma energy in a plasma CVD
apparatus by using a material gas including a silicon-containing
hydrocarbon compound expressed by formula 5.
[0043] Still further, the insulation film is formed on a substrate
and the film is polymerized with plasma energy in a plasma CVD
apparatus by using a material gas including a silicon-containing
hydrocarbon compound expressed by formula 6.
[0044] In accordance with a further aspect of this invention, a
material for forming an insulation film is supplied in a vapor
phase in the vicinity of a substrate and is treated in a plasma CVD
apparatus to form the insulation film on the substrate by chemical
reaction, and the material is further expressed by formula 2.
[0045] Additionally, a material for forming an insulation film is
supplied in a vapor phase in the vicinity of a substrate and is
treated in a plasma CVD apparatus to form the insulation film on
the substrate by chemical reaction, and the material is further
expressed by formula 3.
[0046] Further, a material for forming an insulation film is
supplied in a vapor phase in the vicinity of a substrate and is
treated in a plasma CVD apparatus to form the insulation film on
the substrate by chemical reaction, and the material is further
expressed by formula 4.
[0047] Furthermore, a material for forming an insulation film is
supplied in a vapor phase with either nitrogen oxide (N.sub.2O) or
oxygen (O.sub.2) as an oxidizing agent in the vicinity of a
substrate and is treated in a plasma CVD apparatus to form said
insulation film on said substrate by chemical reaction, and this
material can be the compound expressed by formula 5.
[0048] Still further, a material for forming an insulation film is
supplied in a vapor phase with either nitrogen oxide (N.sub.2O) or
oxygen (O.sub.2) as the oxidizing agent in the vicinity of a
substrate and is treated in a plasma CVD apparatus to form said
insulation film on said substrate by chemical reaction, and this
material further can be the compound expressed by formula 6.
[0049] Residence Time and Gas Flow
[0050] The residence time of the reaction gas is determined based
on the capacity of the reaction chamber for reaction, the pressure
adapted for reaction, and the total flow of the reaction gas. The
reaction pressure is normally in the range of 1-10 Torr, preferably
3-7 Torr, so as to maintain stable plasma. This reaction pressure
is relatively high in order to lengthen the residence time of the
reaction gas. The total flow of the reaction gas is important to
reducing the dielectric constant of a resulting film. It is not
necessary to control the ratio of the material gas to the additive
gas. In general, the longer the residence time, the lower the
dielectric constant becomes. The material gas flow necessary for
forming a film depends on the desired deposition rate and the area
of a substrate on which a film is formed. For example, in order to
form a film on a substrate [r(radius)=100 mm] at a deposition rate
of 300 nm/min, at least 50 sccm of the material gas is expected to
be included in the reaction gas. That is approximately
1.6.times.10.sup.2 sccm per the surface area of the substrate
(m.sup.2). The total flow can be defined by residence time (Rt).
When Rt is defined described below, a preferred range of Rt is 100
msec Rt, more preferably 200 msecRt5 sec. In a conventional plasma
TEOS, Rt is generally in the range of 10-30 msec.
Rt[s]=9.42.times.10.sup.7(Pr.multidot.Ts/Ps.multidot.Tr)r.sub.w.sup.2d/F
[0051] wherein:
[0052] Pr: reaction chamber pressure (Pa)
[0053] Ps: standard atmospheric pressure (Pa)
[0054] Tr: average temperature of the reaction gas (K)
[0055] Ts: standard temperature (K)
[0056] r.sub.w: radius of the silicon substrate (m)
[0057] d: space between the silicon substrate and the upper
electrode (m)
[0058] F: total flow volume of the reaction gas (sccm)
[0059] In the above, the residence time means the average period of
time in which gas molecules stay in the reaction chamber. The
residence time (Rt) can be calculated at Rt=.alpha.V/S, wherein V
is the capacity of the chamber (cc), S is the volume of the
reaction gas (cc/s), and .alpha. is a coefficient determined by the
shape of the reaction chamber and the positional relationship
between the inlet of gas and the outlet of exhaust. The space for
reaction in the reaction chamber is defined by the surface of the
substrate (.pi.r.sup.2) and the space between the upper electrode
and the lower electrode. Considering the gas flow through the space
for reaction, .alpha. can be estimated as 1/2. In the above
formula, .alpha. is 1/2.
[0060] Basic Effects
[0061] In this method, the material gas is, in short, a
silicon-containing hydrocarbon compound including at least one Si-O
bond, at most two O-C.sub.nH.sub.2n+1 bonds and at least two
hydrocarbon radicals bonded to the silicon (Si). Also, this
material gas is vaporized by a direct vaporization method. The
method results in an insulation film having a low dielectric
constant, high thermal stability and high humidity-resistance.
[0062] More specifically, the material gas vaporized by the direct
vaporization method can stay in the plasma for a sufficient length
of time. As a result, a linear polymer can be formed so that a
linear polymer having the basic structure (formula 7), wherein the
"n" is 2 or a greater value, forms in a vapor phase. The polymer is
then deposited on the semiconductor substrate and forms an
insulation film having a micropore porous structure. 7
[0063] wherein X1 and X2 are O.sub.nC.sub.mH.sub.p wherein n is 0
or 1, m and p are integers including zero.
[0064] The insulation film of this invention has a relatively high
stability because its fundamental structure has the Si-O bond
having high bonding energy therebetween. Also, its dielectric
constant is low because it has a micropore porous structure.
Further, the fundamental structure (--Si-O--).sub.n has, on both
sides, dangling bonds ending with a hydrocarbon radical possessing
hydrophobicity, and this property renders the humidity-resistance.
Furthermore, the bond of a hydrocarbon radical and silicon is
generally stable. For instance, both the bond with a methyl
radical, i.e., Si-CH.sub.3, and bond with benzene, i.e.,
Si-C.sub.6H.sub.5, have a dissociation temperature of 500.degree.
C. or higher. Since above semiconductor production requires thermal
stability to temperatures above 450.degree. C., that property of
the film is advantageous for production of semiconductors.
[0065] Further aspects, features and advantages of this invention
will become apparent from the detailed description of the preferred
examples which follows.
[0066] Outline of Example Structures
[0067] FIG. 1 diagrammatically shows a plasma CVD apparatus usable
in this invention. This apparatus comprises a reaction
gas-supplying device 12 and a plasma CVD device 1. The reaction
gas-supplying device 12 comprises plural lines 13, control valves 8
disposed in the lines 13, and gas inlet ports 14, 15 and 16. A flow
controller 7 is connected to the individual control valves 8 for
controlling a flow of a material gas of a predetermined volume. A
container accommodating liquid reacting material 18 is connected to
a vaporizer 17 that directly vaporizes liquid. The plasma CVD
device 1 includes a reaction chamber 6, a gas inlet port 5, a
susceptor 3 and a heater 2. A circular gas diffusing plate 10 is
disposed immediately under the gas inlet port. The gas diffusing
plate 10 has a number of fine openings at its bottom face and can
inject reaction gas to the semiconductor substrate 4 therefrom.
There is an exhaust port 11 at the bottom of the reaction chamber
6. This exhaust port 11 is connected to an outer vacuum pump (not
shown) so that the inside of the reaction chamber 6 can be
evacuated. The susceptor 3 is placed in parallel with and facing
the gas diffusing plate 10. The susceptor 3 holds a semiconductor
substrate 4 thereon and heats it with the heater 2. The gas inlet
port 5 is insulated from the reaction chamber 6 and connected to an
outer high frequency power supply 9. Alternatively, the susceptor 3
can be connected to the power supply 9. Thus, the gas diffusing
plate 10 and the susceptor 3 act as a high frequency electrode and
generate a plasma reacting field in proximity to the surface of the
semiconductor substrate 4.
[0068] A method for forming an insulation film on a semiconductor
substrate by using the plasma CVD apparatus of this invention
comprises a step of directly vaporizing silicon-containing
hydrocarbon compounds expressed by the general formula
Si.sub..alpha.O.sub..beta.C.sub.xH.sub.y (.alpha.,.beta., x, and y
are integers) and then introducing it to the reaction chamber 6 of
the plasma CVD device 1, a step of introducing an additive gas,
whose flow is substantially reduced, into the reaction chamber 6
and also a step of forming an insulation film on a semiconductor
substrate by plasma polymerization reaction wherein mixed gases,
made from the silicon-containing hydrocarbon compound as a material
gas and the additive gas, are used as a reaction gas. It is a
remarkable feature that the reduction of the additive gas flow also
renders a substantial reduction of the total flow of the reaction
gas. This feature will be described in more detail later.
[0069] Material Gas and Additive Gas
[0070] In this regard, the silicon-containing hydrocarbon compound
expressed as the general formula
Si.sub..alpha.O.sub..beta.C.sub.xH.sub.y (.alpha.,.beta., x, and y
are integers) is preferably a compound having at least one Si-O
bond, two or less O-C.sub.nH.sub.2+1 bonds and at least two
hydrocarbon radicals bonded with silicon (Si). More specifically,
it is a compound indicated by (A) chemical formula: 8
[0071] wherein R1 and R2 are one of CH.sub.3, C.sub.2H.sub.3,
C.sub.2H.sub.5, C.sub.3H.sub.7 and C.sub.6H.sub.5, and m and n are
any integers;
[0072] a compound indicated by (B) chemical formula: 9
[0073] wherein R1, R2 and R3 are one of CH.sub.3, C.sub.2H.sub.3,
C.sub.2H.sub.5, C.sub.3H.sub.7 and C.sub.6H.sub.5, and n is any
integer;
[0074] a compound indicated by (C) chemical formula: 10
[0075] wherein R1 ,R2, R3 and R4 are one of CH.sub.3,
C.sub.2H.sub.3, C.sub.2H.sub.5, C.sub.3H.sub.7 and C.sub.6H.sub.5,
and m and n are any integer;
[0076] a compound indicated by (D) chemical formula: 11
[0077] wherein R1, R2, R3, R4, R5 and R6 are one of CH.sub.3,
C.sub.2H.sub.3, C.sub.2H.sub.5, C.sub.3H.sub.7 and C.sub.6H.sub.5,
and a mixture of the compound with nitrogen oxide (N.sub.2O) or
oxygen (O.sub.2) as an oxidizing agent; or a compound indicated by
(E) chemical formula: 12
[0078] wherein R1, R2, R3 and R4 are one of CH.sub.3,
C.sub.2H.sub.3, C.sub.2H1, C3H.sub.7 and C.sub.6H.sub.5, and a
mixture of the compound with nitrogen oxide (N.sub.2O) or oxygen
(O.sub.2) as an oxidizing agent.
[0079] Further, it should be noted that the silicon-containing
hydrocarbon compound can be any combinations of these compounds and
mixtures.
[0080] The additive gases used in this embodiment, more
specifically, are argon gas and helium gas. Argon is principally
used for stabilizing plasma, while helium is used for improving
uniformity of the plasma and also uniformity of thickness of the
insulation film.
[0081] In the method described above, the first step of direct
vaporization is a method wherein a liquid material, the flow of
which is controlled, is instantaneously vaporized at a vaporizer
that is preheated. This direct vaporization method requires no
carrier gas such as argon to obtain a designated amount of the
material gas. This differs greatly with the babbling method.
Accordingly, a large amount of argon gas or helium gas is no longer
necessary and this reduces the total gas flow of the reaction gas
and then lengthens the time in which the material gas stays in the
plasma. As a result, sufficient polymerizing reactions occur in the
vapor so that a linear polymer can be formed and a film having a
micropore porous structure can be obtained.
[0082] In FIG. 1, inert gas supplied through the gas inlet port 14
pushes out the liquid reacting material 18, which is the
silicon-containing hydrocarbon compound, to the control valve 8
through the line 13. The control valve 8 controls the flow of the
liquid reacting material 18 with the flow controller 7 so that it
does not exceed a predetermined volume. The reduced
silicon-containing hydrocarbon compound 18 goes to the vaporizer 17
to be vaporized by the direct vaporization method described above.
Argon and helium are supplied through the inlet ports 15 and 16,
respectively, and the valve 8 controls the flow volume of these
gases. The mixture of the material gas and the additive gases,
which is a reaction gas, is then supplied to the inlet port 5 of
the plasma CVD device 1. The space between the gas diffusing plate
10 and the semiconductor substrate 4, both located inside of the
reaction chamber 6 which is already evacuated, is charged with high
frequency RF voltages, which are preferably 13.4 MHz and 430 kHz,
and the space serves as a plasma field. The susceptor 3
continuously heats the semiconductor substrate 4 with the heater 2
and maintains the substrate 4 at a predetermined temperature that
is desirably 350-450.degree. C. The reaction gas supplied through
the fine openings of the gas diffusing plate 10 remains in the
plasma field in proximity to the surface of the semiconductor
substrate 4 for a predetermined time.
[0083] If the residence time is short, a linear polymer cannot be
deposited sufficiently so that the film deposited on the substrate
does not form a micropore porous structure. Since the residence
time is inversely proportional to the flow volume of the reaction
gas, a reduction of the flow volume of the reaction gas can
lengthen its residence time.
[0084] Extremely reducing the total volume of the reaction gas is
effected by reducing the flow volume of the additive gas. As a
result, the residence time of the reaction gas can be lengthened so
that a linear polymer is deposited sufficiently and subsequently an
insulation film having a micropore porous structure can be
formed.
[0085] In order to adjust the reaction in the vapor phase, it is
effective to add a small amount of an inert gas, an oxidizing
agent, or a reducing agent to the reaction chamber. Helium (He) and
Argon (Ar) are inert gases and have different first ionization
energies of 24.56 eV and 15.76 eV, respectively. Thus, by adding
either He or Ar singly or both in combination in predetermined
amounts, the reaction of the material gas in the vapor phase can be
controlled. Molecules of the reaction gas undergo polymerization in
the vapor phase, thereby forming oligomers. The oligomers are
expected to have a O:Si ratio of 1:1. However, when the oligomers
form a film on the substrate, the oligomers undergo further
polymerization, resulting in a higher oxygen ratio. The ratio
varies depending on the dielectric constant or other
characteristics of a film formed on the substrate (e.g., in Example
5 described later, the ratio was 3:2).
[0086] The remaining oxygen, which is derived from the material gas
and is not incorporated into the film, is dissociated from the
material compound and floats in plasma. The ratio of Si:O in the
material gas varies depending upon the compound. For example, in
formulae 2-6 above, the ratio of O:Si is 2:1, 1:1, 3:2, 1:2, and
0:1, respectively. If the material gas having a high ratio of O:Si
(e.g., 3/2 or higher) is used, the quantity of oxygen floating in
plasma increases. When the quantity of oxygen increases, the
organic groups, which are directly bound to Si and necessary to
form a film, are oxidized, and as a result, deterioration of the
film is likely to occur. In the above, by adding a reducing agent
such as H.sub.2 and CH.sub.4 to the reaction chamber, the oxygen
partial pressure in plasma is reduced, thereby preventing the above
oxidization of the organic groups. In contrast, when the O:Si ratio
is low (e.g., 3/2 or lower), it is necessary to supply oxygen for
forming a film by adding an oxidizing agent such as N.sub.2O and
O.sub.2. The appropriate amount of a reducing agent or an oxidizing
agent can be evaluated in advance based on preliminary experiment
in which the composition of a formed film is analyzed by FT-IR or
XRS, and its dielectric constant is also analyzed. Accordingly, by
selecting the appropriate type of additive gas such as He, Ar, a
reducing agent, and an oxidizing agent, and by controlling the
quantity of each gas to be added, a film having the desired quality
can be produced.
[0087] Other Aspects
[0088] In the above, the silicon-containing hydrocarbon compound to
produce a material gas for silicone polymer has preferably two
alkoxy groups or less or having no alkoxy group. The use of a
material gas having three or more alkoxy groups interferes with
formation of linear silicone polymer, resulting in relatively high
dielectric constant of a film. In the above, one molecule of the
compound preferably contains one, two, or three Si atoms, although
the number of Si atoms is not limited (the more the Si atoms, the
vaporization becomes more difficult, and the cost of synthesis of
the compound becomes higher). The alkoxy group may normally contain
1-3 carbon atoms, preferably one or two carbon atoms. Hydrocarbons
bound to Si have normally 1-12 carbon atoms, preferably 1-6 carbon
atoms. A preferable silicon-containing hydrocarbon compound has
formula:
Si.sub..alpha.O.sub..alpha.-1R.sub.2.alpha.-.beta.+2(OC.sub.nH.sub.2n+1).s-
ub..beta.
[0089] wherein .alpha. is an integer of 1-3, .beta. is 0, 1, or 2,
n is an integer of 1-3, and R is C.sub.1-6 hydrocarbon attached to
Si. The use of an oxidizing agent or a reducing agent is determined
depending on the target dielectric constant (3.30 or less,
preferably 3.10 or less, more preferably 2.80 or less) of a
silicone polymer film and other characteristics such as stability
of dielectric constant and thermal stability. The O:Si ratio in the
material gas is also considered to select an oxidizing agent or a
reducing agent, as described above. Preferably, if the ratio is
lower than 3:2, an oxidizing agent is used, whereas if the ratio is
higher than 3:2, a reducing agent is used. Further, an inert gas
such as Ar and He is for controlling plasma reaction, but is not
indispensable to form a silicone polymer film. The flow of material
gas and the flow of additive gas can also vary depending on the
plasma CVD apparatus. The appropriate flow can be determined by
correlating the dielectric constant of the silicone polymer film
with the residence time of the reaction gas (composed of the
material gas and the additive gas). The longer the residence time,
the lower the dielectric constant becomes. A reduction rate of
dielectric constant per lengthened residence time is changeable,
and after a certain residence time, the reduction rate of
dielectric constant significantly increases, i.e., the dielectric
constant sharply drops after a certain residence time of the
reaction gas. After this dielectric constant dropping range, the
reduction of dielectric constant slows down. This is very
interesting. In the present invention, by lengthening residence
time until reaching the dielectric constant dropping range based on
a predetermined correlation between the dielectric constant of the
film and the residence time of the reaction gas, it is possible to
reduce the dielectric constant of the silicone polymer film
significantly.
EXAMPLES
[0090] Some preferred results in the experiments are described
below. In these experiments, PM-DMOS (phenylmethyl dimethoxysilane,
formula 1), DM-DMOS (dimethyl dimethoxysilane, formula 8), and
P-TMOS were used as the material gas. An ordinary plasma CVD device
(EAGLE-10.TM., ASM Japan K. K.) was used as an experimental device.
The conditions for forming the film are as follows;
[0091] Additive gas: Ar and He
[0092] RF power supply: 250W (use the frequency made from 13.4 MHz
and 430 kHz by synthesizing them with each other)
[0093] Substrate temperature: 400.degree. C.
[0094] Reacting pressure: 7 Torr
[0095] Vaporizing method: direct vaporization
[0096] The residence time (Rt) is defined with the following
formula.
Rt[s]=9.42.times.10.sup.7(Pr.multidot.Ts/Ps.multidot.Tr)r.sub.w.sup.2d/F
[0097] In this formula, each abbreviation indicates the following
parameter.
[0098] Pr: reaction chamber pressure (Pa)
[0099] Ps: standard atmospheric pressure (Pa)
[0100] Tr: average temperature of the reaction gas (K)
[0101] Ts: standard temperature (K)
[0102] r.sub.w: radius of the silicon substrate (m)
[0103] d: space between the silicon substrate and the upper
electrode (m)
[0104] F: total flow volume of the reaction gas (sccm)
[0105] Individual parameters were fixed at the following values;
only the flow volume was varied so as to find out the relationship
between the flow volume and the dielectric constant.
[0106] Pr=9.33.times.10.sup.2 (Pa)
[0107] Ps=1.01.times.10.sup.5 (Pa)
[0108] Tr=273+400=673 (K)
[0109] Ts=273 (K)
[0110] r.sub.w=0.1 (m)
[0111] d=0.014 (m)
[0112] Table 1 lists comparative examples and present invention's
examples.
1 TABLE 1 Material Reaction Gas Gas Total Flow Ar He Flow Rt
Dielectric (sccm) (sccm) (sccm) (sccm) (msec) constant .epsilon.
C.Ex. 1 100 1000 1000 2100 24 3.38 (P-TMOS) C.Ex. 2 100 10 10 120
412 3.42 (P-TMOS) C.Ex. 3 100 775 775 1650 30 3.41 (PM- DMOS) C.Ex.
4 100 550 550 1200 41 3.41 (PM- DMOS) C.Ex. 5 100 430 430 960 51
3.40 (PM- DMOS) C.Ex. 6 100 310 310 720 68 3.35 (PM- DMOS) Ex. 1
100 140 140 480 103 3.10 (PM- DMOS) Ex. 2 100 100 100 300 165 2.76
(PM- DMOS) Ex. 3 100 70 70 240 206 2.64 (PM- DMOS) Ex. 4 100 10 10
120 412 2.45 (PM- DMOS) Ex. 5 100 10 10 120 412 2.58 (DM- DMOS) Ex.
6 25 3 0 28 1764 2.51 (DM- DMOS) Ex. 7 25 0 5 30 1647 2.50 (DM-
DMOS) Additive H.sub.2 CH.sub.4 Gas (sccm) (sccm) Change Ex. 8 100
20 0 120 412 2.52 (DM- DMOS) Ex. 9 25 5 0 30 1647 2.49 (DM- DMOS)
Ex. 10 25 0 5 30 1647 2.67 (DM- DMOS)
Comparative Example 1
[0113] Material gas: P-TMOS (100 sccm)
[0114] Additive gases: Ar (1000 sccm) and He (1000 sccm)
[0115] Total flow volume of reaction gas: 2100 sccm
[0116] Other conditions and devices used for forming the film are
given above. The calculated value of the residence time Rt was 24
msec. The conditions in this example reduced the dielectric
constant .epsilon. of the insulation film to 3.38.
Comparative Example 2
[0117] Material gas: P-TMOS (100 sccm)
[0118] Additive gases: Ar (10 sccm) and He (10 sccm)
[0119] Total flow volume of reaction gas: 120 sccm
[0120] Other conditions and devices used for forming the film are
given above. The calculated value of the residence time Rt was 412
msec. The conditions in this example reduced the dielectric
constant .epsilon. of the insulation film to 3.42.
Comparative Example 3
[0121] Material gas: PM-DMOS (100 sccm)
[0122] Additive gases: Ar (775 sccm) and He (775 sccm)
[0123] Total flow volume of reaction gas: 1650 sccm
[0124] Other conditions and devices used for forming the film are
given above. The calculated value of the residence time Rt was 30
msec. The conditions in this example reduced the dielectric
constant .epsilon. of the insulation film to 3.41.
Comparative Example 4
[0125] Material gas: PM-DMOS (100 sccm)
[0126] Additive gases: Ar (550 sccm) and He (550 sccm)
[0127] Total flow volume of reaction gas: 1200 sccm
[0128] Other conditions and devices used for forming the film are
given above. The calculated value of the residence time Rt was 41
msec. The conditions in this example reduced the dielectric
constant .epsilon. of the insulation film to 3.41.
Comparative Example 5
[0129] Material gas: PM-DMOS (100 sccm)
[0130] Additive gas: Ar (430 sccm) and He (430 sccm)
[0131] Total flow volume of reaction gas: 960 sccm
[0132] Other conditions and devices used for forming the film are
given above. The calculated value of the residence time Rt was 51
msec. The conditions in this example reduced the dielectric
constant .epsilon. of the insulation film to 3.40.
Comparative Example 6
[0133] Material gas: PM-DMOS (100 sccm)
[0134] Additive gases: Ar (310 sccm) and He (310 sccm)
[0135] Total flow volume of reaction gas: 720 sccm
[0136] Other conditions and devices used for forming the film are
given above. The calculated value of the residence time Rt was 68
msec. The conditions in this example reduced the dielectric
constant .epsilon. of the insulation film to 3.35.
Example 1
[0137] Material gas: PM-DMOS (100 sccm)
[0138] Additive gases: Ar (140 sccm) and He (140 sccm)
[0139] Total flow volume of reaction gas: 480 sccm
[0140] Other conditions and devices used for forming the film are
given above. The calculated value of the residence time Rt was 103
msec. The conditions in this example reduced the dielectric
constant .epsilon. of the insulation film to 3.10.
Example 2
[0141] Material gas: PM-DMOS (100 sccm)
[0142] Additive gases: Ar (100 sccm) and He (100 scem)
[0143] Total flow volume of reaction gas: 300 scem
[0144] Other conditions and devices used for forming the film are
given above. The calculated value of the residence time Rt was 165
msec. The conditions in this example reduced the dielectric
constant .epsilon. of the insulation film to 2.76.
Example 3
[0145] Material gas: PM-DMOS (100 sccm)
[0146] Additive gases: Ar (70 sccm) and He (70 sccm)
[0147] Total flow volume of reaction gas: 240 sccm
[0148] Other conditions and devices used for forming the film are
given above. The calculated value of the residence time Rt was 206
msec. The conditions in this example reduced the dielectric
constant .epsilon. of the insulation film to 2.64.
Example 4
[0149] Material gas: PM-DMOS (100 sccm)
[0150] Additive gases: Ar (10 sccm) and He (10 sccm)
[0151] Total flow volume of reaction gas: 120 sccm
[0152] Other conditions and devices used for forming the film are
given above. The calculated value of the residence time Rt was 412
msec. The conditions in this example reduced the dielectric
constant .epsilon. of the insulation film to 2.45.
[0153] Hereinafter, the results given above will be examined with
reference to FIGS. 2 and 3. FIG. 2 is a graph showing the
relationship between the dielectric constant .epsilon. and the
total flow volume of the reaction gas as well as the relationship
between the residence time Rt and the total flow volume of the
reaction gases, in the experiments using PM-DMOS as a material gas.
FIG. 3 is a graph showing the relationship between the residence
time Rt and the dielectric constant .epsilon. in the experiments
using PM-DMOS as a material gas.
[0154] First, the relationship between the flow volume of the
PM-DMOS gases and the dielectric constant .epsilon. of the
insulation film will be examined. FIG. 2 shows that the dielectric
constant .epsilon. is almost constantly 3.4 while the flow volume
is about 700 sccm. However, the dielectric constant .epsilon.
begins to fall with the decrease of the flow volume, i.e., at
approximately 700 sccm or less. Further, as the flow volume falls
to under 500 sccm, the residence time Rt rises drastically and the
dielectric constant .epsilon. falls drastically. Meanwhile, FIG. 3
shows that the dielectric constant .epsilon. begins to decrease
when the residence time Rt increases from approximately 70 msec.
When the residence time Rt is greater than 400 msec, the dielectric
constant .epsilon. falls to 2.45.
[0155] Thus, these present invention's examples apparently indicate
that if the total flow of the reaction gas of the PM-DMOS gas and
the additive gas is controlled so that Rt is more than 100 msec the
dielectric constant .epsilon. can be controlled to be less than
3.1.
Example 5
[0156] DM-DMOS (formula 8) was then tested. 13
[0157] Material gas: DM-DMOS (100 sccm)
[0158] Additive gases: Ar (10 sccm) and He (10 sccm)
[0159] Total flow volume of reaction gas: 120 sccm
[0160] Other conditions and devices used for forming the film are
given above. The calculated value of the residence time Rt was 412
msec. The conditions in this example reduced the dielectric
constant .epsilon. of the insulation film to 2.58.
Example 6
[0161] Material gas: DM-DMOS (25 sccm)
[0162] Additive gases: Ar (3 sccm) and He (0 sccm)
[0163] Total flow volume of reaction gas: 28 sccm
[0164] Other conditions and devices used for forming the film are
given above. The calculated value of the residence time Rt was 1764
msec. The conditions in this example reduced the dielectric
constant .epsilon. of the insulation film to 2.51.
Example 7
[0165] Material gas: DM-DMOS (25 sccm)
[0166] Additive gases: Ar (0 sccm) and He (5 sccm)
[0167] Total flow volume of reaction gas: 30 sccm
[0168] Other conditions and devices used for forming the film are
given above. The calculated value of the residence time Rt was 1647
msec. The conditions in this example reduced the dielectric
constant .epsilon. of the insulation film to 2.50.
Example 8
[0169] Material gas: DM-DMOS (100 sccm)
[0170] Additive gases: H.sub.2 (20 sccm) and CH.sub.4 (0 sccm)
[0171] Total flow volume of reaction gas: 120 sccm
[0172] Other conditions and devices used for forming the film are
given above. The calculated value of the residence time Rt was 412
msec. The conditions in this example reduced the dielectric
constant .epsilon. of the insulation film to 2.52.
Example 9
[0173] Material gas: DM-DMOS (25 sccm)
[0174] Additive gases: H.sub.2 (5 sccm) and CH.sub.4 (0 sccm)
[0175] Total flow volume of reaction gas: 30 sccm
[0176] Other conditions and devices used for forming the film are
given above. The calculated value of the residence time Rt was 1647
msec. The conditions in this example reduced the dielectric
constant .epsilon. of the insulation film to 2.49.
Example 10
[0177] Material gas: DM-DMOS (25 sccm)
[0178] Additive gases: H.sub.2 (0 sccm) and CH.sub.4 (5 sccm)
[0179] Total flow volume of reaction gas: 30 sccm
[0180] Other conditions and devices used for forming the film are
given above. The calculated value of the residence time Rt was 1647
msec. The conditions in this example reduced the dielectric
constant .epsilon. of the insulation film to 2.67.
[0181] Thus, the above reveals that, in the material gas of formula
2, both compounds (PM-DMOS having C.sub.6H.sub.5 at R1 and CH.sub.3
at R2 and DM-DMOS having CH.sub.3 at R1 and CH.sub.3 at R2) can
produce insulation films having a very low dielectric constant
(.epsilon.<3.1).
[0182] The following will examine if the P-TMOS gas replacing the
PM-DMOS gas can render the same results. Comparative Examples 1 and
2 both are the results obtained in the experiments using the P-TMOS
as a material gas. These examples indicate that the dielectric
constant does not decrease even when the total flow of the reaction
gas is reduced to 5.7%. Thus, the relationship between the flow
volume and the dielectric constant that is effected with PM-DMOS
does not come into effect with P-TMOS.
[0183] Further, the following will examine differences of
dielectric constant when using different material gases. Comparing
Comparative Example 2 with the present invention's Example 4,
although the flow volumes and other conditions are identical, the
dielectric constant .epsilon. of P-TMOS is 3.42 while the
dielectric constant .epsilon. of PM-DMOS is 2.45. Such a large
difference between the dielectric constant values resides in the
difference in the molecular structures of the material gases. That
is, PM-DMOS has a pair of relatively unstable O-CH.sub.3 bonds
which are prone to separation so that that polymerization reactions
occur and a linear polymer (formula 7) forms in a gaseous state.
This polymer is deposited on a semiconductor substrate, forming a
micropore porous structure and subsequently the dielectric constant
of the insulation film decreases. In contrast, because P-TMOS has
three O-CH.sub.3 bonds, its polymer is not deposited linearly even
though the residence time is lengthened. Accordingly, the deposited
film does not have the micropore porous structure nor such a low
dielectric constant.
[0184] These experiments have revealed that it is preferable that
the silicon-containing hydrocarbon compounds used as the material
gases should have not only the Si-O bonds but also at most two
O-C.sub.nH.sub.2n+1 bonds and, further, at least two hydrocarbon
radicals bonded to the silicon (Si).
[0185] Film stability characteristics of low dielectric constant
films formed according to the present invention were evaluated by
preparing low dielectric constant films according to Example 4,
wherein PM-DMOS was used, and Example 5, wherein DM-DMOS was used,
thereby evaluating their stability of dielectric constant and their
thermal stability. (1) Stability of Dielectric constant
[0186] Changes in dielectric constant of the films were measured
upon heating and humidifying the PM-DMOS film and the DM-DMOS film
in a pressure cooker. That is, each film was formed on a Si wafer
at a thickness of 1 .mu.m, and its dielectric constant was measured
upon formation of the film and after being placed at 120.degree. C.
and 100% humidity for one hour. The results are shown below. No
change in dielectric constant of each film was detected, i.e.,
indicating high stability characteristics.
2TABLE 2 Dielectric constant One Hour at High Material Gas Upon
Formation Temp. and Humid. Example 4 PM-DMOS 2.45 2.45 Example 5
DM-DMOS 2.58 2.58
[0187] (2) Thermal Stability
[0188] Based on a thermal desorption test, thermal stability of
film structures was evaluated. That is, the samples of PM-DMOS
formed on the Si wafer and DM-DMOS formed on the Si wafer were
placed in a vacuum and subjected to rising temperature at a rate of
10.degree. C. per minute, thereby measuring the amount of molecules
dissociated from the film. FIG. 4 is a graph showing the thermal
desorption spectra of components having a molecular weight of 16
due to desorption of CH.sub.4 during the temperature rise. FIG. 5
is a graph showing changes in the degree of vacuum corresponding to
the number of total molecules dissociated from the film. In both
experiments, no desorption was detected in either film at a
temperature of 400.degree. C. or lower. Desorption began at
approximately 450.degree. C. in PM-DMOS and at approximately
500.degree. C. in DM-DMOS. Thermal stability required for low
dielectric constant films is generally for 400.degree. C. to
450.degree. C. Therefore, it was proved that both the PM-DMOS film
and the DM-DMOS film had high thermal stability.
[0189] As described above, the method of this invention using the
silicon-containing hydrocarbon compounds of this invention as the
material gases produces an insulation film that has high thermal
stability, high humidity-resistance and a low dielectric constant.
Additionally, it is found that controlling the residence time of
the reaction gas can effectively and easily control the dielectric
constant of the film. Further, the method of this invention
actualizes easy production of insulation films without using
expensive devices.
[0190] Although this invention has been described in terms of
certain examples, other examples apparent to those of ordinary
skill in the art are within the scope of this invention.
Accordingly, the scope of the invention is intended to be defined
only by the claims that follow.
[0191] It will be understood by those of skill in the art that
numerous and various modifications can be made without departing
from the spirit of the present invention. Therefore, it should be
clearly understood that the forms of the present invention are
illustrative only and are not intended to limit the scope of the
present invention.
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