U.S. patent application number 10/133432 was filed with the patent office on 2002-09-05 for process for producing barrier film and barrier film thus produced.
This patent application is currently assigned to ULVAC INC.. Invention is credited to Harada, Masamichi.
Application Number | 20020123215 10/133432 |
Document ID | / |
Family ID | 26377222 |
Filed Date | 2002-09-05 |
United States Patent
Application |
20020123215 |
Kind Code |
A1 |
Harada, Masamichi |
September 5, 2002 |
Process for producing barrier film and barrier film thus
produced
Abstract
A thin nitride film having a low resistance is formed at a low
film-forming temperature. In the step of forming a thin nitride
film 24 of a high temperature-melting point metal by introducing a
feedstock gas having the high temperature-melting point metal and a
reductive nitrogen-containing gas having a nitrogen atom into a
vacuum atmosphere, an auxiliary reductive gas free from nitrogen is
also introduced. The high temperature-melting point metal deposited
due to the auxiliary reductive gas compensates for the deficiency
of the high temperature-melting point metal of the deposited
nitride and thus enable the growth of the thin nitride film 24
having a low resistance.
Inventors: |
Harada, Masamichi;
(Chigasaki-shi, JP) |
Correspondence
Address: |
ARMSTRONG,WESTERMAN & HATTORI, LLP
1725 K STREET, NW.
SUITE 1000
WASHINGTON
DC
20006
US
|
Assignee: |
ULVAC INC.
Kanagawa
JP
|
Family ID: |
26377222 |
Appl. No.: |
10/133432 |
Filed: |
April 29, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10133432 |
Apr 29, 2002 |
|
|
|
09504923 |
Feb 16, 2000 |
|
|
|
Current U.S.
Class: |
438/618 ;
257/E21.17; 257/E21.579; 257/E21.585; 438/627; 438/633 |
Current CPC
Class: |
H01L 21/76843 20130101;
H01L 21/76814 20130101; H01L 21/76877 20130101; H01L 21/28556
20130101; H01L 21/76807 20130101; C23C 16/34 20130101 |
Class at
Publication: |
438/618 ;
438/627; 438/633 |
International
Class: |
H01L 021/4763 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 17, 1999 |
JP |
HEI 11-38041 |
Jul 6, 1999 |
JP |
HEI 11-192026 |
Claims
What is claimed is:
1. A process for producing a barrier film which comprises the steps
of: providing a substrate in a vacuum atmosphere; introducing a
feedstock gas having a high temperature-melting point metal in its
structure and a reductive nitrogen-containing gas comprising a
nitrogen atom into said vacuum atmosphere; and forming a thin film
of the nitride of said high temperature-melting point metal on said
substrate; wherein a nitrogen-free auxiliary reductive gas is
introduced into said vacuum atmosphere.
2. The process for producing a barrier film according to claim 1,
which comprises a step of introducing said auxiliary reductive gas
together with said feedstock gas and said reductive
nitrogen-containing gas into said vacuum atmosphere.
3. The process for producing a barrier film according to claim 2,
which comprises a step of introducing said feedstock gas and said
reductive nitrogen-containing gas into said vacuum atmosphere
without introducing said auxiliary reductive gas.
4. The process for producing a barrier film according to claim 2,
wherein, in the step of introducing said auxiliary reductive gas
together with said reductive nitrogen-containing gas and said
feedstock gas; said reductive nitrogen-containing gas is introduced
at a flow rate once or more higher than the flow rate of said
feedstock gas, and said auxiliary reductive gas is introduced at a
flow rate once or more but not more than 10 times higher than the
flow rate of said reductive nitrogen-containing gas.
5. The process for producing a barrier film according to claim 1,
wherein, in the step of introducing said auxiliary reductive gas
together with said reductive nitrogen-containing gas and said
feedstock gas; said reductive nitrogen-containing gas is introduced
at a flow rate once or more but not more than 5 times higher than
the flow rate of said feedstock gas, and said auxiliary reductive
gas is introduced at a flow rate 2 times or more but not more than
10 times higher than the flow rate of said reductive
nitrogen-containing gas.
6. The process for producing a barrier film according to claim 2,
wherein, in the step of introducing said auxiliary reductive gas
together with said reductive nitrogen-containing gas and said
feedstock gas; said auxiliary reductive gas is introduced at a flow
rate once or more but not more than 15 times higher than the flow
rate of the feedstock gas having said high temperature-melting
point metal.
7. The process for producing a barrier film according to claim 1,
wherein, in the step of growing the thin film of the nitride of
said high temperature-melting point metal; a diluent gas not
reacting with said high temperature-melting point metal and a gas
having an oxygen atom in its chemical structure are introduced so
that the pressure of said vacuum atmosphere is regulated to 1 Pa or
more but not more than 100 Pa.
8. A process for producing a barrier film for forming a barrier
film made of a thin film of the nitride of a high
temperature-melting point metal on a substrate, wherein; the
surface of said substrate is exposed to a plasma of hydrogen gas
and a plasma containing at least one gas selected from among argon,
nitrogen and helium gases, and then the thin film of the nitride of
said high temperature-melting point metal is formed on the surface
of the substrate.
9. A barrier film comprising a thin nitride film of a high
temperature-melting point metal, wherein; said thin nitride film
has a content of said high temperature-melting point metal
exceeding the stoichiometric composition ratio thereof.
10. A barrier film comprising a thin nitride film of a high
temperature-melting point metal formed on a substrate and aiming at
preventing the diffusion of metals in an interconnecting thin film
formed on said thin nitride film, wherein; said thin nitride film
is free from silicon.
Description
FIELD OF THE INVENTION
[0001] This invention relates to the technical field of metal
interconnecting for semiconductor devices. More particularly, it
relates to a process for producing a barrier film which is to be
located between a copper interconnecting film and an insulation
film, a barrier film which is to be located between a film
containing Si, GaAs, etc. and a metal interconnecting for
preventing silicidation, and a barrier film which is to be located
between a highly dielectric film or a ferroelectric film and an
electrode.
BACKGROUND OF THE INVENTION
[0002] In recent years, it has been required to more and more speed
up the operations of semiconductor devices. To satisfy this
requirement, studies have been undertaken on low-resistant copper
interconnectings as a substitute for aluminum interconnectings.
[0003] However, copper occurs as an impurity in semiconductor
crystals. In addition, it suffers from a problem of having a large
diffusion coefficient in silicon crystals or silicon oxide.
Therefore, it has been a practice that a thin film comprising the
nitride of a high temperature-melting point metal (a thin tungsten
nitride film, etc.) is formed as a barrier film on the surface of a
silicon substrate or a thin silicon oxide film and then a copper
interconnecting film is formed on the surface of the barrier
film.
[0004] To form such a barrier film, the sputtering method, the heat
CVD method or the PE-CVD method is used. In the sputtering method,
a high temperature-melting point metal is employed as a target. In
the heat CVD method, a thin nitride film is formed by the following
reduction reactions. Formula (1) shows a case wherein tungsten is
used, while formula (2) shows another case wherein titanium is
used.
4WF.sub.6+8NH.sub.3.fwdarw.2W.sub.2N+24HF+3N.sub.2 (1)
TiCl.sub.4+NH.sub.3.fwdarw.TiN+2HCl+1/2H.sub.2 (2)
[0005] In case of forming a semiconductor device with multi-layered
interconnecting, it is needed to laminate copper interconnectings
while inserting interlayer insulation films between them. In a
semiconductor device to be operated at a high speed, the resistance
of the copper interconnectings as well as the capacity of the
interlayer insulation films and the resistance of the barrier films
should be lowered so as to minimize signal transfer delay. More
concretely speaking, a barrier film should have a resistance as low
as 200 to 300 .mu..OMEGA.cm.
[0006] Although a thin nitride film having a low resistance can be
formed by the sputtering method, only poor step coverage can be
achieved thereby. Thus, no uniform barrier film can be formed in a
viahole with a high aspect ratio by this method.
[0007] By the heat CVD method, on the other hand, a uniform barrier
thin film can be formed in a viahole. However, the upper limit of
the film-forming temperature in the heat CVD method resides in 400
to 500.degree. C., since the dielectric constants of interlayer
insulation films with low dielectric constants would be increased
when exposed to a high temperature exceeding 500.degree. C. At such
a low film-forming temperature, the resistivity of, for example, a
thin tungsten nitride film attains several thousand .mu..OMEGA.cm,
which makes it impossible to give barrier films with low
resistance.
[0008] With respect to the CVD methods, barrier films with low
resistance can be formed at a low temperature by the MOCVD method
with the use of organometallic compounds or the plasma CVD method.
However, the organometallic compounds are expensive, while the
plasma CVD method has a problem of achieving only poor step
coverage. Thus, these methods are not usable in practice.
SUMMARY OF THE INVENTION
[0009] The present invention, which has been made to overcome the
above-described troubles encountering in the conventional art, aims
at providing a barrier film having a value of low resistivity and
good step coverage.
[0010] The present inventors analyzed thin films of high
temperature-melting point metal nitrides formed by the conventional
heat CVD method and, as a result, found that the high
temperature-melting point metal atoms were provided only in an
insufficient amount. In the case of tungsten, for example, a
tungsten nitride in the conventional art fails to establish the
stoichiometric composition (W.sub.2N) but shows a composition
W.sub.xN wherein x ranges from about 1.5 to 1.6. It is assumed that
such insufficient supply of metal atoms in a nitride might worsen
the crystallinity of the thin nitride film, thereby elevating the
value of the resistance.
[0011] In the present invention which has been completed based on
the above-described finding, attempts are made to approximate the
composition of the nitride of a high temperature-melting point
metal closely to the stoichiometric level. To achieve this object,
the present invention relates to a process for producing a barrier
film which comprises the steps of providing a substrate in a vacuum
atmosphere, introducing a feedstock gas having a high
temperature-melting point metal in its structure and a reductive
nitrogen-containing gas having a nitrogen atom into said vacuum
atmosphere, and forming a thin film of the nitride of said high
temperature-melting point metal on said substrate, wherein a
nitrogen-free auxiliary reductive gas is introduced into said
vacuum atmosphere.
[0012] The present invention relates to the process for producing a
barrier film, which involves the step of introducing said auxiliary
reductive gas together with said feedstock gas and said
nitrogen-containing gas into said vacuum atmosphere.
[0013] The present invention relates to the process for producing a
barrier film, which involves the step of introducing said feedstock
gas and said nitrogen-containing gas into said vacuum atmosphere
without introducing said auxiliary reductive gas.
[0014] The present invention relates to the process for producing a
barrier film, wherein, in the step of introducing said auxiliary
reductive gas together with said reductive nitrogen-containing gas
and said feedstock gas, said reductive nitrogen-containing gas is
introduced at a flow rate once or more higher than the flow rate of
said feedstock gas, and said auxiliary reductive gas is introduced
at a flow rate once or more but not more than 10 times higher than
the flow rate of said reductive nitrogen-containing gas.
[0015] The present invention relates to the process for producing a
barrier film, wherein, in the step of introducing said auxiliary
reductive gas together with said reductive nitrogen-containing gas
and said feedstock gas, said reductive nitrogen-containing gas is
introduced at a flow rate once or more but not more than 5 times
higher than the flow rate of said feedstock gas, and said auxiliary
reductive gas is introduced at a flow rate 2 times or more but not
more than 10 times higher than the flow rate of said reductive
nitrogen-containing gas.
[0016] The present invention relates to the process for producing a
barrier film, wherein, in the step of introducing said auxiliary
reductive gas together with said reductive nitrogen-containing gas
and said feedstock gas, said auxiliary reductive gas is introduced
at a flow rate once or more but not more than 15 times higher than
the flow rate of the feedstock gas having said high
temperature-melting point metal.
[0017] The present invention relates to the process for producing a
barrier film, wherein, in the step of growing the thin film of the
nitride of said high temperature-melting point metal, a diluent gas
not reacting with said high temperature-melting point metal and a
gas having an oxygen atom in its chemical structure are introduced
so that the pressure of said vacuum atmosphere is regulated to 1 Pa
or more but not more than 100 Pa.
[0018] The present invention relates to a process for producing a
barrier film which comprising the steps of forming a barrier film
made of a thin nitride film of a high temperature-melting point
metal on a substrate, wherein the surface of said substrate is
exposed to a plasma of hydrogen and a plasma of at least one gas
selected from among argon, nitrogen and helium gases and then the
thin film of the nitride of said high temperature-melting point
metal is formed on the surface of the substrate.
[0019] The invention relates to a barrier film having a thin film
of the nitride of a high temperature-melting point metal, wherein
said thin nitride film has a content of said high
temperature-melting point metal exceeding the stoichiometric
composition ratio thereof.
[0020] The invention relates to a barrier film having a thin
nitride film a high temperature-melting point metal formed on a
substrate and aiming at preventing the diffusion of metals in a
thin interconnecting film formed on said thin nitride film, wherein
said thin nitride film is free from silicon.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIGS. 1(a) to (e) show the first half of a flow chart
illustrating the process of the present invention.
[0022] FIGS. 2(f) to (h) show the second half of a flow chart
illustrating the process of the present invention.
[0023] FIGS. 3(i) to (j) show the latter half of a flow chart
illustrating the process of the present invention.
[0024] FIG. 4 shows an example of a CVD apparatus by which the
process of the present invention can be embodied.
[0025] FIG. 5 is a graph which shows relationships between the
resistivity of a thin tungsten nitride film formed by the process
of the present invention and the flow rates of the feedstock gas,
the reductive nitrogen-containing gas and the auxiliary reductive
gas.
[0026] FIG. 6 is a graph which shows a change in the elemental
content of a thin tungsten nitride film formed by the process of
the present invention depending on the SiH.sub.4/WF.sub.6 flow
rate.
[0027] FIG. 7 is a graph which shows the composition of tungsten
nitride formed by the process of the present invention in the depth
direction.
[0028] FIG. 8 is a graph which shows the composition of tungsten
nitride of the conventional art in the depth direction.
[0029] In these drawings, each numerical symbol has the following
meaning:
[0030] 20: substrate
[0031] 24, 33: thin nitride films (barrier films)
[0032] 25: thin metal film
[0033] 27, 35: interconnecting films.
DETAILED DESCRIPTION OF THE INVENTION
[0034] In the present invention which has the above-described
constitution, a feedstock gas having a high temperature-melting
point metal atom and a reductive nitrogen-containing gas are
introduced into a vacuum atmosphere and the feedstock gas is thus
reduced by the reductive nitrogen-containing gas to deposit the
nitride of the high temperature-melting point metal, wherein a
nitrogen-free auxiliary reductive gas is also introduced into the
vacuum atmosphere so as to allow the deposition of the high
temperature-melting point metal too.
[0035] Further, a diluent gas and a gas having an oxygen atom in
its structure (oxygen gas, etc.) are simultaneously introduced. As
a result, it becomes possible to form a nitride film having
improved barrier performance and further lowered resistivity,
compared with a case where no oxygen atom-containing gas is
introduced.
[0036] When the nitride of the high temperature-melting point metal
is deposited at a low temperature, the high temperature-melting
point metal in the thin nitride film becomes deficient. However,
the high temperature-melting point metal atoms deposited by the
auxiliary reductive gas compensate for the deficiency. Thus, the
obtained thin nitride film has a composition wherein the content of
the high temperature-melting point metal exceeds the stoichiometric
level thereof.
[0037] The amount of the deposited metal may be smaller than the
amount of the deposited nitride. However, the auxiliary reductive
gas should be introduced in a somewhat larger amount than the
deposition level, since the auxiliary reductive gas is inferior in
the reactivity to the reductive nitrogen-containing gas.
[0038] When the auxiliary reductive gas is introduced at an
excessively high rate, on the other hand, the content of the high
temperature-melting point metal becomes unnecessarily large and, as
a result, the thin film exhibits properties close to the properties
of the high temperature-melting point metal rather than those of
the nitride. When an auxiliary reductive gas containing Si is
employed, there arises a problem that the content of Si in the thin
nitride film is increased. Therefore, the reductive
nitrogen-containing gas, the auxiliary reductive gas, the diluent
gas and the gas having an oxygen atom in its structure should be
introduced each at an adequate rate.
[0039] For example, ammonia gas (i.e., the reductive
nitrogen-containing gas) is introduced at rates 1.0, 2.6 and 5.0
times higher than that of tungsten hexafluoride (i.e., the
feedstock gas) and the ratio of silane gas (i.e., the auxiliary
reductive gas) to the ammonia gas is varied.
[0040] FIG. 5 shows the results wherein the abscissa indicates the
introduction rate of the silane gas expressed by referring the
introduction rate of the ammonia gas as to 1 while the ordinate
indicates the resistivity of the thin tungsten nitride film thus
formed.
[0041] As this graph shows, it is preferable that the reductive
nitrogen-containing gas is introduced at a rate amount once or more
larger than the introduction rate of the feedstock gas, while the
auxiliary reductive gas is introduced at a rate 2 times or more but
not more than 10 times larger than the introduction rate of the
reductive nitrogen-containing gas.
[0042] The practically available resistivity of a barrier film
ranges from about 200 to 300 .mu..OMEGA.cm. Thus, it can be
understood from this graph that the reductive nitrogen-containing
gas is introduced preferably at a flow rate 1 time or more but not
more than 5 times higher than the flow rate of the feedstock gas
and the auxiliary reductive gas is introduced preferably at a flow
rate 2 times or more but not more than 5 times higher than the flow
rate of the reductive nitrogen-containing gas.
[0043] FIG. 6 shows the elemental content of each high
temperature-melting point metal nitride at various ratios of the
flow rate of the feedstock gas to the flow rate of the auxiliary
reductive gas in the step of forming high temperature-melting point
metal nitrides. In this case, WF.sub.6 is used as the feedstock gas
and SiH.sub.4 is used as the auxiliary reductive gas. Oxygen gas is
introduced at 1.5 sccm.
[0044] As this graph shows, the high temperature-melting point
metal nitride (WN in this case) contains Si when the ratio
SiH.sub.4/WF.sub.6 attains 15 or more. This graph also shows that
W.sub.xN thin films are formed within the scope of the ratio
SiH.sub.4/WF.sub.6 of 1 to 15 time.
[0045] FIG. 7 shows the results of Auger spectrochemical analysis
of a thin tungsten nitride film formed at a film forming
temperature of 400.degree. C. wherein the sputtering time given in
the abscissa indicates the depth from the surface. As this graph
shows, much tungsten is contained therein (about 4.0 tungsten atoms
per nitrogen atom), thereby indicating the effect of the
introduction of the auxiliary reductive gas.
[0046] Since the barrier film is oxidized when it is taken out into
the atmosphere, oxygen is observed on the film surface. Although
silicon is seemingly contained in the film, the content thereof is
less than the detection limit, i.e., a measurement error.
[0047] Thus, the resistivity can be lowered by using the high
temperature-melting point metal in the thin nitride film at a level
exceeding the stoichiometric composition ratio thereof while
sustaining the barrier performance.
[0048] In the CMP process, a thin nitride film should be adhered
closely to the surface of a substrate. When the surface of the
substrate is cleaned with a plasma of at least one gas selected
from among argon, nitrogen and helium gases, the plasma and the
plasma of hydrogen gas, and a plasma of mixed nitrogen, the thin
nitride film formed on this surface would not peel off even under a
load of 1 kg/cm.sup.2, thereby achieving an adhesiveness usable in
the CMP process.
[0049] When the thin nitride film contains silicon, the silicon
reacts with the high temperature-melting point metal (tungsten,
etc.) at a high temperature to form a silicon compound such as
tungsten silicide to thereby increase the resistivity. Since the
thin nitride film of the present invention is free form silicon, no
silicon compound is formed and thus the resistivity can be
stabilized at a low level.
[0050] For comparison, FIG. 8 shows the results of Auger
spectrochemical analysis of a thin tungsten nitride film formed by
the CVD method of the conventional art at a film forming
temperature of 400.degree. C. This thin film contains about 1.7
tungsten atoms per nitrogen atom, i.e., showing a smaller tungsten
content. It also shows a high resistivity of 1000 .mu..OMEGA.cm or
more.
[0051] In the step of the formation of the thin nitride film of the
high temperature-melting point metal, it is preferable to regulate
the pressure to 1 Pa or more but not more than 10000 Pa, still
preferably 1 Pa or more but not more than 100 Pa.
DESCRIPTION OF THE EMBODIMENTS OF THE INVENTION
[0052] Now, embodiments of the present invention will be described
by reference to the attached drawings.
[0053] FIGS. 1(a) to (d) show a flow chart which shows an example
of the embodiment of the present invention. In FIG. 1(a), the
numerical symbol 20 shows a substrate to be treated. This substrate
20 has a semiconductor substrate 21 made of single silicon crystal
on the surface of which a primary coat film 22 and an insulation
film 23 made of silicon oxide are formed. The primary film 22 and
the insulation film 23 are provided with a hole 31. The surface of
semiconductor substrate 21 is exposed at a bottom 32 of the hole
31.
[0054] A barrier film is to be formed on the surface of this
substrate 20.
[0055] In FIG. 4, the numerical symbol 50 shows a CVD apparatus
whereby the present invention can be embodied. This CVD apparatus
50 has a vacuum chamber 51 which is connected to a transport room
(not shown). The vacuum chamber 51 is provided with a substrate
holder 53 in the bottom side and an electrode 55 in the top
side.
[0056] When a barrier film is to be formed on the substrate 20 by
using this CVD apparatus 50, the substrate 20 is first brought into
the transport room and the transport room and the vacuum chamber 51
are evacuated. Next, a gate valve 52 between the vacuum chamber 51
and the transport room is opened and then the substrate 20 is
brought into the CVD apparatus 50.
[0057] The substrate holder 53 is provided with a substrate
elevator unit 54 with which the substrate brought into the vacuum
chamber 51 is placed on the substrate holder 53. In FIG. 4, the
substrate 20 is thus placed on the substrate holder 53.
[0058] Subsequently, the heater in the substrate holder 53 is
switched on and thus the substrate 20 is heated to a temperature of
not lower than 300.degree. C. but not higher than 400.degree.
C.
[0059] The vacuum chamber 51 is provided with a gas inlet system 57
through which argon gas and ammonia gas are introduced into the
vacuum chamber 51 each at a prescribed flow rate. By applying a
high-frequency voltage between the substrate holder 53 and the
electrode 55, ionized nitrogen and hydrogen are liberated from the
ammonia gas. In this step, the ionized argon gas serving as a
diluent gas is mixed with the ionized nitrogen and hydrogen to give
a plasma.
[0060] The insulation film 23 on the surface of the substrate 20 is
faced closely to the electrode 55. As the plasma is formed, the
surface of the insulation film 23 and the surface of the
semiconductor substrate 21 at the bottom of the hole 31 are exposed
to the plasma and the organic deposits are decomposed (i.e.,
cleaning).
[0061] The cleaning is performed at an ammonia gas flow rate of 75
sccm, an argon gas flow rate of 240 sccm, under a pressure of 40 Pa
and at a high-frequency electrical power of 100 W. After cleaning
for about 50 seconds, the application of the high-frequency voltage
is stopped to thereby extinguish the plasma. Although argon (Ar)
gas is used in this case, it can be substituted by nitrogen
(N.sub.2) gas, helium (He) gas or a mixture thereof.
[0062] Next, the flow rates of the ammonia gas and the argon gas
are changed and, at the same time, tungsten hexafluoride (WF.sub.6)
gas, silane gas and oxygen gas are introduced into the vacuum
chamber 51 through the gas inlet system 57 together with the
ammonia gas and the argon gas.
[0063] Since the ammonia gas is superior in the reactivity to the
silane gas, the tungsten hexafluoride serves as the feedstock gas
and the ammonia gas serves as the reductive nitrogen-containing
gas. Thus, the reaction of reducing the feedstock gas proceeds.
Since the ammonia gas contains nitrogen, tungsten nitride is
deposited on the surface of the insulation film 23 and on the
surface of the semiconductor substrate 21 in the hole 31 due to the
reduction reaction represented by the above formula (1).
[0064] Although the silane gas introduced into the vacuum chamber
51 also has reductive properties, it is inferior in reactivity to
the ammonia gas and, therefore, serves as the auxiliary reductive
gas. Since the silane gas has no nitrogen atom, the feedstock gas
is reduced thereby in accordance with the following formula (3) and
thus metal tungsten is deposited.
WF.sub.6+({fraction (3/2)})SiH.sub.4.fwdarw.W+({fraction
(3/2)})SiF.sub.4+3H.sub.2 (3)
[0065] When metal tungsten is deposited, it is incorporated into
the thin tungsten nitride film under growing. That is to say, metal
tungsten is supplied during the growth of the thin tungsten nitride
film. When the thin tungsten nitride film grows at a low
temperature, the deficiency of tungsten is thus compensated for and
a barrier film (a thin tungsten nitride film) having a composition
close to the stoichiometric composition or one having a high
temperature-melting point metal content exceeding the
stoichiometric level can be formed.
[0066] The thin tungsten nitride film may grow under, for example,
the following conditions; substrate temperature: 380.degree. C.;
feedstock gas flow rate: 5 sccm; reductive nitrogen-containing gas
flow rate: 13 sccm; auxiliary reductive gas flow rate: 39 sccm;
argon gas flow rate: 240 sccm; oxygen gas introduction rate: 1.5
sccm; pressure: 40 Pa.
[0067] When the feedstock gas is subjected to the reduction
reaction by the reductive nitrogen-containing gas and the auxiliary
reductive gas for a prescribed period of time, a thin tungsten
nitride film is formed on the surface of insulation film 23 and on
the surface of the semiconductor substrate 21, as shown in FIG.
1(b) 24.
[0068] Next, the supply of the reductive nitrogen-containing gas is
ceased and the flow rate of the auxiliary reductive gas is
increased. Thus, the feedstock gas is reduced by the auxiliary
reductive gas and metal tungsten is deposited. In FIG. 1(c), the
numerical symbol 25 shows a thin metal tungsten film growing on the
surface of the thin nitride film 24.
[0069] The thin metal tungsten film may be formed under, for
example, the following conditions; substrate temperature:
380.degree. C.; feedstock gas flow rate: 20 sccm; auxiliary
reductive gas flow rate: 5 sccm; diluent (argon) gas introduction
rate: 240 sccm; pressure: 40 Pa.
[0070] Although the thin nitride film 24 has a favorable barrier
performance against copper, it has a higher resistivity than that
of the high temperature-melting point metal. On the other hand, the
film of the high temperature-melting point metal (for example, thin
metal tungsten film, etc.) has a poor barrier performance against
copper but has a much lower resistivity than that of the thin
nitride film 24.
[0071] When a thin nitride film 24 is formed as a barrier film and
a thin high temperature-melting point metal film is laminated
thereon as in the above-described case, the resistivity can be
lowered while sustaining the favorable barrier performance against
copper.
[0072] On the contrary, a thin nitride film may be formed on a high
temperature-melting point metal film or the thin nitride film may
be formed as a single layer.
[0073] After allowing the thin tungsten film 25 to grow for 20 to
30 seconds under the above-described conditions, the substrate 20
is taken out from the CVD apparatus 50. Then a thin copper film is
grown on the surface of the thin high temperature-melting point
metal film 25 by the metal plating method, the sputtering method,
etc. In FIG. 1(d), the numerical symbol 26 shows this thin copper
film 26.
[0074] After the formation of the thin copper film 26, the surface
is abraded by the CMP method to thereby eliminate the thin copper
film 26, the thin nitride film 24 and the thin metal film 25 on the
insulation film 23. Thus, a interconnecting film 27 made of the
thin copper film 26 is formed in the hole 31. The thin nitride film
24 is located between the interconnecting film 27 and the
semiconductor substrate 21 and between the interconnecting film 27
and the insulation film 23 so as to prevent copper from
diffusion.
[0075] Next, primary films 41 and 43 and insulation films 42 and 44
are laminated alternately and the surface of the interconnecting
film 27 is windowed to form a hole or a groove, as shown in FIG.
2(g). In FIG. 2(g), the numerical symbol 38 shows the groove or
hole. The interconnecting film 27 is exposed on the bottom of this
groove or hole 38.
[0076] Then the substrate 20 is brought into the CVD apparatus 50
and a thin nitride film (a thin tungsten nitride film) is formed
under the same conditions as in forming the thin nitride film shown
in FIG. 1(b).
[0077] The numerical symbol 33 in FIG. 2(h) shows the thus formed
thin nitride film which covers the inner face of the groove or hole
38 and the surface of the insulation film 44 and the surface of the
interconnecting film 27.
[0078] Subsequently, the thin copper film 34 is grown by the metal
plating method or the sputtering method, as shown in FIG. 3). Thus,
the groove or hole 38 is filled with the thin copper film 34.
[0079] Finally, the surface is abraded by the CMP method. Thus, an
interconnecting film 35 is formed by the thin copper film 34 filled
into the groove or hole 38, as shown in FIG. 3(j).
[0080] Since the barrier film 33 is located between the
interconnecting film 35 and the insulation films 42 and 44, the
diffusion of copper into the insulation films 42 and 44 can be
prevented.
[0081] In the above-described case, a thin tungsten nitride film is
formed by using tungsten as the high temperature-melting point
metal, ammonia gas as the reductive nitrogen-containing gas and
silane gas as the auxiliary reductive gas. Although tungsten
hexafluoride is used as the feedstock gas in the above case, it is
also possible to use W(CO).sub.6 gas therefor.
[0082] Moreover, the present invention involves in its scope cases
where barrier films are produced by using high temperature-melting
point metals other than tungsten and forming thin films of the
nitrides thereof. When titanium (Ti) is used as the high
temperature-melting point metal, titanium halide gases (TiF.sub.4,
TiCl.sub.4, etc.) are usable as the feedstock gas. When tantalum
(Ta) is used as the high temperature-melting point metal, tantalum
halide gases (TaCl.sub.5, etc.) are usable as the feedstock gas. It
is also possible to use halides of Mo or Nb as the feedstock
gas.
[0083] As the reductive nitrogen-containing gas containing a
nitrogen atom, use can be made of N.sub.2H.sub.4 gas, NF.sub.3 gas,
N.sub.20 gas, etc. in addition to NH.sub.3 gas.
[0084] As the nitrogen-free auxiliary reductive gas, use can be
made of H.sub.2 gas, Si.sub.2H.sub.6 gas, PH.sub.3 gas,
B.sub.2H.sub.6 gas etc. in addition to SiH.sub.4 gas.
[0085] As the diluent gas, it is also possible to use argon gas,
nitrogen gas, helium gas or a mixture of these gases.
[0086] The cleaning conditions as described above are given merely
by way of example. Therefore, the cleaning may be performed under
different conditions. For example, similar effects can be achieved
by carrying out the cleaning for 60 seconds at an argon gas flow
rate of 100 sccm, under a pressure of 1.0 Pa at a high-frequency
electric power of 150W.
[0087] After completing the cleaning under such conditions,
additional cleaning may be performed by adding ammonia gas to the
argon gas.
[0088] According to the present invention, a barrier film (a thin
film of the nitride of a high temperature-melting point metal)
having a low resistance can be formed by the CVD method at a
temperature of 500.degree. C. or lower, in particular, from 350 to
450.degree. C. Therefore, interlayer insulation films are not
damaged thereby.
[0089] Furthermore, the thin nitride film is formed by the heat CVD
method, which makes it possible to achieve good step coverage.
* * * * *