U.S. patent application number 09/038117 was filed with the patent office on 2001-09-06 for method of forming thin copper film.
Invention is credited to FUKADA, TETSUO, HASEGAWA, MAKIKO, MORI, TAKESHI, TOYODA, YOSHIHIKO.
Application Number | 20010019847 09/038117 |
Document ID | / |
Family ID | 13108801 |
Filed Date | 2001-09-06 |
United States Patent
Application |
20010019847 |
Kind Code |
A1 |
MORI, TAKESHI ; et
al. |
September 6, 2001 |
METHOD OF FORMING THIN COPPER FILM
Abstract
Copper material is exposed on the surface of a TiN film (an
underlying film) formed in the main surface of a silicon substrate
with a silicon oxide film interposed. Subsequently, a thin copper
film is formed on TiN film. Thus, the thin copper film can be
formed on the film including metal with high melting point or
nitride thereof with high adhesion by means of CVD.
Inventors: |
MORI, TAKESHI; (HYOGO,
JP) ; FUKADA, TETSUO; (HYOGO, JP) ; HASEGAWA,
MAKIKO; (HYOGO, JP) ; TOYODA, YOSHIHIKO;
(HYOGO, JP) |
Correspondence
Address: |
MCDERMOTT WILL & EMERY
600 13TH STREET, N.W.
WASHINGTON
DC
20005-3096
US
|
Family ID: |
13108801 |
Appl. No.: |
09/038117 |
Filed: |
March 11, 1998 |
Current U.S.
Class: |
438/2 ;
257/E21.295 |
Current CPC
Class: |
C23C 16/0272 20130101;
H01L 21/76843 20130101; H01L 21/32051 20130101; C23C 16/18
20130101; H01L 21/76876 20130101; H01L 21/76858 20130101 |
Class at
Publication: |
438/2 |
International
Class: |
H01L 021/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 13, 1997 |
JP |
9-059279(P) |
Claims
What is claimed is:
1. A method of forming a thin copper film on an underlying film
including metal with high melting point or nitride thereof,
comprising: the step of exposing copper material to a surface of
said underlying film; and the step of forming the thin copper film
on said underlying film after the exposure of said copper
material.
2. The method of forming the thin copper film according to claim 1,
wherein said underlying film is formed on a substrate, and said
step of exposing said copper material is performed while
controlling variation in temperature of the surface of said
substrate within a range of .+-.4.degree. C.
3. The method of forming the thin copper film according to claim 1,
wherein said step of exposing said copper material is performed at
a temperature lower than that at which said thin copper film is
formed.
4. The method of forming the thin copper film according to claim 1,
wherein said step of exposing said copper material includes a step
of performing thermal treatment for said underlying film at a
temperature higher than that at which said thin copper film is
formed after the exposure of said copper material.
5. The method of forming the thin copper film according to claim 1,
wherein said step of exposing said copper material is repeated
several times.
6. A semiconductor device with a thin copper film, comprising: an
insulation film formed on a semiconductor substrate; the thin
copper film formed in said insulation film; and an underlying film
formed between said thin copper film and said insulation film in
tight contact with a surface of said thin copper film, and
including metal with high melting point or nitride thereof.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to methods of forming thin
copper films and semiconductor devices with thin copper films, and
particularly to a method of forming a thin copper film on an
underlying film including metal with high melting point or nitride
thereof by means of CVD (Chemical Vapor Deposition), and a
semiconductor device with the thin copper film.
[0003] 2. Description of the Background Art
[0004] Conventionally, material of Al with copper added thereto
having high resistance or electromigration resistance has generally
been used as interconnection material for an LSI (Large Scale
Integration). However, as LSIs are increasingly reduced in size to
achieve as small an interconnection width as about 0.15 .mu.m or
less, a problem associated with resistance or the like becomes
inevitable even if material of Al with copper added is employed for
interconnection.
[0005] Then, to cope with the interconnection width of about 0.15
.mu.m or less, which will be expected in future, employment of a
copper interconnection is considered. Copper is relatively easily
diffused, so that it might disadvantageously be diffused in the
underlying film by thermal treatment commonly performed in a
manufacturing process of the LSI. To avoid such diffusion, a common
practice would be to form a diffusion barrier film such as a TiN
film under the copper interconnection.
[0006] In view of the foregoing, a conventional method of forming a
thin copper film on a TiN film will now be described with reference
to FIGS. 10 and 11. FIGS. 10 and 11 are cross sectional views
showing first and second steps of the conventional method of
forming the thin copper film on the TiN film. FIGS. 10 and 11 show
a thin copper film 4 formed on a TiN film 3, which has been formed
on a silicon substrate 1 with a silicon oxide film 2
interposed.
[0007] Referring now to FIG. 10, silicon oxide film 2 and TiN film
3 are sequentially deposited on silicon substrate 1 by means of
CVD, for example. Then, as shown in FIG. 11, thin copper film 4 is
formed on the TiN film by means of CVD using for example Cu (hfac)
(tmvs) without any particular pretreatment. Here, hfac and tmvs are
abbreviations of hexafluoroacetylacetonate and
trimethylvinylsilane, respectively.
[0008] When thin copper film is formed on TiN film 3 using Cu
(hfac) (tmvs) by means of CVD without any pretreatment as mentioned
above, however, sufficient adhesion is not ensured between thin
copper film 4 and underlying TiN film 3 as pointed out in Advanced
Metalization for ULSI Applications, pp. 79-86, 1994.
SUMMARY OF THE INVENTION
[0009] The present invention is made to solve the aforementioned
problem. An object of the present invention is to provide a method
of forming a thin copper film on an underlying film including metal
with high melting point or nitride thereof with high adhesion by
means of CVD, and a semiconductor device with the thin copper
film.
[0010] In the method of forming the thin copper film in accordance
with the present invention, the thin copper film is formed on the
underlying film including metal with high melting point or nitride
thereof. To start with, copper material is kept in close contact
with or exposed to the surface of the underlying film. The exposure
of copper material is followed by film formation of the thin copper
film on the underlying film. It is noted that in the present
description, "exposure" is defined as a treatment for applying
material such as copper material on the underlying film while
avoiding reaction therewith. In addition, the above mentioned "film
formation" is defined as a process for forming a film such as the
thin copper film by reaction of material with the underlying
film.
[0011] It is noted that, preferably, the above mentioned underlying
film is formed on a substrate and the step of exposing copper
material is performed controlling variation in temperature of the
surface of the substrate within .+-.4.degree. C.
[0012] In addition, the step of exposing copper material is
preferably performed at a temperature which is lower than that at
which the thin copper film is formed.
[0013] Further, the step of exposing copper material preferably
includes a step of heat-treating the underlying film at a
temperature which is higher than that at which the thin copper film
is formed.
[0014] The step of exposing copper material is preferably repeated
several times.
[0015] As described above, in the method of forming the thin copper
film in accordance with the present invention, exposure treatment
of copper material is performed before formation of the thin copper
film. In the exposure treatment, the underlying film is exposed to
copper material in vapor phase at a prescribed temperature, so that
copper material can be applied on the entire surface of the
underlying film with almost uniform thickness. Thus, in forming the
thin copper film, nucleus of copper material can almost uniformly
be produced on the entire surface of the underlying film. As a
result, the thin copper film can be formed on the surface of the
underlying film with almost uniform thickness and high
adhesion.
[0016] In addition, when the above mentioned exposure treatment is
performed with the underlying film formed on the substrate and with
variation in temperature of the surface of the substrate maintained
within the range of about .+-.4.degree. C., copper material can
more uniformly be applied on the surface of the underlying film.
Thus, in addition to the above described effects, as shown in FIG.
6, the thin copper film can be formed on the substrate (a
semiconductor wafer 6 in FIG. 6) with almost uniform thickness. As
a result, the thin copper film with reduced surface roughness is
obtained.
[0017] In addition, when the above mentioned exposure treatment is
performed at a temperature which is lower than that at which the
thin copper film is formed, copper material can be applied on the
underlying film while avoiding reaction therewith. Thus, as
described above, the thin copper film can be formed on the
underlying film with high adhesion.
[0018] Further, when heat treatment is performed at a temperature
which is higher than that at which the thin copper film is formed
after the exposure treatment, a composite layer which is formed of
the material for the underlying film and copper can be obtained
between the above mentioned nucleus and the underlying film. When
the underlying film is formed, for example of TiN, in the composite
layer, copper exists between grain boundaries of TiN. The composite
layer still remains after formation of the thin copper film,
thereby further increasing adhesion between the thin copper film
and the underlying film after film formation.
[0019] When the exposure treatment is repeated several times,
copper material can be applied on the surface of the underlying
film more uniformly and closely. Thus, the nucleus is produced more
uniformly and closely on the surface of the underlying film after
application of copper material. This enables formation of the thin
copper film on the underlying film with high adhesion and uniform
thickness.
[0020] The semiconductor device with the thin copper film in
accordance with the present invention includes an insulation film
formed on the semiconductor substrate, a thin copper film formed in
the insulation film and an underlying film. The underlying film is
formed between the thin copper film and the insulation film in
tight contact with the surface of the thin copper film, and
includes metal with high melting point or nitride thereof.
[0021] If the thin copper film is formed by the above mentioned
method, nucleus density in forming the thin copper film can be
increased. Thus, any space between the underlying film and the thin
copper film is prevented. As a result, electromigration life time
for the thin copper film is increased to provide interconnection
with enhanced reliability.
[0022] The foregoing and other objects, features, aspects and
advantages of the present invention will become more apparent from
the following detailed description of the present invention when
taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIGS. 1 to 4 are cross sectional views showing first to
fourth steps in a method of forming a thin copper film in
accordance with a first embodiment of the present invention.
[0024] FIG. 5 is a cross sectional view related to the problem when
copper material is unevenly applied on the surface of an underlying
TiN film.
[0025] FIG. 6 is a diagram showing thickness distribution of a thin
copper film when it is formed on the surface of a semiconductor
wafer as a substrate in accordance with a method described in
conjunction with a second embodiment of the present invention.
[0026] FIGS. 7 and 8 are cross sectional views showing
characteristic first and second steps in a method of forming a thin
copper film in accordance with a fourth embodiment of the present
invention.
[0027] FIG. 9 is a cross sectional view showing an exemplary
semiconductor device (DRAM) to which the method of forming the thin
copper film in accordance with the present invention can be
applied.
[0028] FIGS. 10 and 11 are cross sectional views showing first and
second steps in a conventional method of forming a thin copper
film.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0029] Referring to FIGS. 1 to 9, embodiments of the present
invention will be described.
[0030] First Embodiment
[0031] Referring now to FIGS. 1 to 4, an embodiment of the present
invention will be described.
[0032] Referring to FIG. 1, a silicon oxide film 2 and a TiN film 3
are sequentially formed on a surface of a silicon substrate 1 by
means of CVD or the like. Silicon oxide film 2 and TiN film 3 have
thickness of for example about 500 nm and 10 nm, respectively.
[0033] Then, copper material 4a is exposed to the surface of TiN
film 3 as shown in FIG. 2. In other words, copper material 4a is
applied on the surface of TiN film 3 while avoiding reaction
therewith. The condition required at the time is specified in the
following Table 1.
1 TABLE 1 temperature of substrate 30.degree. C. pressure 18 Torr
material flow rate Cu (hfac) (tmvs) 0.5 g/min carrier flow rate
(H.sub.2) 500 sccm exposure time more than two minutes
[0034] It is noted that while the required temperature of the
substrate is about 30.degree. C. according to the above Table 1,
any other temperature may be employed so long as it allows copper
material 4a to be applied on an underlying film such as TiN film 3
while avoiding reaction therewith. For example, copper material 4a
can be applied on the surface of TiN film 3 while avoiding reaction
therewith at a temperature which is lower than that of the
substrate, which allows formation of the thin copper film as will
be later described.
[0035] Then, the temperature of silicon substrate 1 is increased,
for example, to about 180.degree. C. Thus, a nucleus 4b including
copper material 4a is formed on the surface of TiN film 3 as shown
in FIG. 3. After the formation of nucleus 4b, thin copper film 4 is
formed under the condition shown in the following Table 2.
2 TABLE 2 temperature of substrate 180.degree. C. pressure 18 Torr
material flow rate Cu (hfac) (tmvs) 0.2 g/min carrier flow rate
(H.sub.2) 500 sccm
[0036] As shown in Table 2 above, the temperature of the substrate
is maintained at a temperature which is higher than that at which
copper material 4a is exposed. In this example, the temperature of
the substrate is shown as maintained at about 180.degree. C. Other
temperatures may also be employed as long as it allows production
and growth of nucleus 4b by reaction of copper material 4a. In
addition, flow rate of copper material 4a in forming thin copper
film 4, shown in Table 2, is lower than that in exposing copper
material 4a. Thus, by suitably controlling flow rate of copper
material 4a in accordance with the treatment, larger amount of
copper material 4a can be applied on the surface of underlying TiN
film 3 to promote production of nucleus 4b, thereby facilitating
growth of thin copper film 4.
[0037] After forming thin copper film 4 in a manner as described
above, silicon substrate 1 is cooled down to a prescribed
temperature. Then, silicon substrate 1 is removed from a CVD
furnace. Through the process hereinbefore, thin copper film 4 is
formed on silicon substrate 1 with TiN film 3 interposed.
[0038] The inventor of the present invention evaluated adhesion
strength between thin copper film 4 and TiN film 3 after thin
copper film 4 was formed in accordance with the above described
method. The evaluation result is shown in the following Table 3. It
is noted that in the evaluation, two types of thin copper films 4,
which had been formed on TiN films 3 with or without the exposure
treatment in accordance with the present invention, were prepared,
and adhesive tapes were attached to each of thin copper films 4.
Then, by taking off the tapes, evaluation was made as to if thin
copper film also came off from TiN film 3.
3TABLE 3 exposure treatment test with tape performed .largecircle.
not performed X
[0039] As shown in Table 3, it was verified that thin copper film 4
remained on TiN film 3 after the adhesive tape was removed from
thin copper film 4 with the exposure treatment performed in
accordance with the present invention. This means that formation of
thin copper film 4 by the above described method can increase
adhesion strength between thin copper film 4 and TiN film 3.
[0040] It is noted that a similar result would be obtained even if
other kind of metal with high melting point, including W, Ta, Ti,
Cr, Mo, or nitride thereof is employed instead of the above
mentioned TiN film 3. In addition, the above or later described
film formation method may also be applicable in forming a
conductive layer other than copper film 4.
[0041] Second Embodiment
[0042] Referring to FIGS. 5 and 6, a second embodiment of the
present invention will now be described. FIG. 5 is a cross
sectional view showing a problem concerned when variation in
temperature of the surface of the substrate is significant during
exposure treatment.
[0043] Referring to FIG. 5, copper material 4a is not uniformly
applied when there is a variation in temperature of the surface of
the substrate which is beyond the prescribed range during the
exposure treatment. Thus, nucleus 4b will also unevenly be formed
on the surface of TiN film 3 after application of copper material
4a. Referring to FIG. 5, the resulting thin copper film 4 has
portions respectively having relatively small and large thicknesses
t1 and t2, whereby surface roughness of thin copper film 4 is
increased. As a result, characteristics of the thin copper film
when used as interconnection or the like may deteriorate.
[0044] Accordingly, silicon substrate 1 is controlled so that
variation in temperature of the surface thereof is within the
prescribed range. More specifically, a heater for heating a
substrate, for example of a hot plate type, is prepared and silicon
substrate 1 is pressed against the hot plate for heating (cooling).
Here, heating (cooling) for middle and periphery portions of the
hot plate can be independently controlled, and a contact portion
between the hot plate and silicon substrate 1 is provided with
increased heat uniformity by employing an aluminum member. In
addition, gas is introduced into the back surface of silicon
substrate 1 for heating by heat conduction. It is noted that
cooling is performed by circulating cooled He using a chiller.
[0045] In accordance with the above described method of controlling
temperature of silicon substrate 1, for example, variation in
temperature of the surface of silicon substrate 1 is maintained
within the range of about .+-.4.degree. C. FIG. 6 shows thickness
distribution of the thin copper film obtained for exposure
treatment with the temperature of silicon substrate 1 maintained
within such temperature range, subsequently followed by formation
of thin copper film 4. It is noted that FIG. 6 is related to thin
copper film 4 formed on the surface of semiconductor wafer 6 of six
inches, which is used as the above mentioned silicon substrate
1.
[0046] As a result, thin copper film 4 had average thickness
d.sub.av of 4190.5 .ANG. and uniformity (.sigma./d.sub.av) of 6.6%.
It is apparent that controlling variation in temperature of the
surface of the substrate, i.e., of semiconductor wafer 6 in FIG. 6,
within the range of about .+-.4.degree. C. for exposure treatment
not only provides enhanced adhesion with the underlying film but
also enables formation of thin copper film 4 with reduced surface
roughness. Consequently, interconnection with enhanced
characteristics is obtained if thin copper film 4 thus formed is
used as interconnection.
[0047] Third Embodiment
[0048] Now, a third embodiment of the present invention will be
described. While temperature of the substrate is set at 30.degree.
C. in the above first embodiment, there may be a suitable range for
temperature of the substrate. Then, the preferred range for
temperature of the substrate during exposure treatment is discussed
in the present third embodiment.
[0049] In the exposure treatment in accordance with the present
invention, copper material 4a is applied on the surface of the
underlying film while avoiding reaction therewith as described
above. Thus, exposure treatment is preferably performed within the
range of the temperature at which copper material 4a stably exists
without liquefying and reaction between copper material 4a and the
underlying film (for example, TiN film 3) is avoided. Therefore,
exposure treatment is preferably performed within the range of
temperature of the substrate between about 5.degree. C. and about
30.degree. C. Most preferably, it is performed within the range
between about 5.degree. C. and about 20.degree. C. Thus, copper
material 4a can most effectively be applied on the surface of the
underlying film.
[0050] It is noted that the condition for exposure treatment in the
present third embodiment is shown in the following Table 4.
4TABLE 4 temperature of substrate more than 5.degree. C. and less
than 20.degree. C. pressure 18 Torr material flow rate Cu (hfac)
(tmvs) 0.5 g/min carrier flow rate (H.sub.2) 500 sccm exposure time
more than two minutes
[0051] Fourth Embodiment
[0052] Referring now to FIGS. 7 and 8, a fourth embodiment of the
present invention will be described. FIGS. 7 and 8 are cross
sectional views showing the characteristic first and second steps
in a method of forming thin copper film 4 in accordance with the
fourth embodiment of the present invention.
[0053] According to the fourth embodiment, a process for copper
material 4a proceeds up to the exposure treatment in a similar
manner as in the above described first embodiment. Then, thermal
treatment at the temperature for example of about 200.degree. C. to
about 450.degree. C. is performed for copper material 4a and TiN
film 3 after exposure treatment. It is noted that the thermal
treatment needs to be performed at a temperature which is higher
than that for forming the thin copper film 4 (for example of about
180.degree. C.), which will be later described. As shown in FIG. 7,
the thermal treatment under such temperature forms nucleus 4b
including copper material 4a, and a composite layer 5 of copper and
TiN is formed between nucleus 4b and TiN film 3. Composite layer 5,
where copper atoms exist between grain boundaries of TiN, can
provide enhanced adhesion strength between TiN film 3 and thin
copper film 4, which will be later formed.
[0054] After thermal treatment for forming composite layer 5 as
described above, thin copper film 4 is formed under a similar
condition as in the first embodiment. As a result, a structure
shown in FIG. 8 is obtained.
[0055] Fifth Embodiment
[0056] A fifth embodiment of the present invention will now be
described. The fifth embodiment is characterized in that the
exposure treatment in accordance with the present invention is
repeated several times. By repeating exposure treatment several
times, copper material 4a can be more closely applied on the
surface of TiN film 3.
[0057] Thus, nucleus 4b is closely produced, thereby allowing
efficient formation of thin copper film 4. In addition, copper
material 4a can be applied on the surface of underlying TiN film 3
more uniformly, so that nucleus 4b is more uniformly produced. As a
result, efficient formation of thin copper film 4 as well as
enhanced adhesion strength between thin copper film 4 and TiN film
3 is achieved.
[0058] It is noted that exposure treatment may be repeated several
times either under the same or different conditions. In addition,
when thermal treatment is performed after exposure treatment as in
the above described fourth embodiment, both treatments may be
repeated several times. After thus repeating exposure treatment
several times, thin copper film 4 is formed in a similar manner as
described in each of the above embodiments.
[0059] Referring now to FIG. 9, an application of the present
invention will be described. FIG. 9 is a cross sectional view
showing a DRAM (Dynamic Random Access Memory) to which the method
of forming thin copper film 4 in accordance with the present
invention is applicable.
[0060] Referring to FIG. 9, impurity diffusion regions 14a and 14b
are formed spaced apart in the main surface of a silicon substrate
10. A gate electrode 16 is formed on a channel region defined by
impurity diffusion regions 14a and 14b with a gate insulation film
15 interposed. Trenches 11a and 11b for insulation of elements are
formed in the main surface of silicon substrate 10. Polysilicon
films 13a and 13b are formed in trenches 11a and 11b with
insulation films 12a and 12b interposed, respectively.
[0061] Formed to cover the main surface of silicon substrate 10 is
an interlayer insulation film 18a, in which contact holes 11c and
11d are formed which are respectively continuous to impurity
diffusion regions 14a and 14b. Plug electrodes 17a and 17c of for
example W are formed in contact holes 11c and 11d,
respectively.
[0062] An interlayer insulation film 18b is formed to cover
interlayer insulation film 18a, and a via hole 11e is formed in
interlayer insulation film 18b. A TiN film 19a is formed in via
hole 11c which functions as a barrier. A copper interconnection 20a
is formed on TiN film 19a. Thus, the method of forming the thin
copper film in accordance with the present invention can be applied
in forming copper interconnection 20a on TiN film 19a.
[0063] Thus, nucleus density in forming copper interconnection 20a
is increased, so that any space between underlying TiN film 19a and
copper interconnection 20a can be prevented. As a result,
reliability (electromigration life time) of copper interconnection
20a is increased.
[0064] An interlayer insulation film 18c is formed to cover
interlayer insulation film 18b, and a trench 11f is formed in
interlayer insulation film 18c. A copper interconnection 20b is
formed in trench 11f with a TiN film 19b interposed. An interlayer
insulation film 18d is further formed to cover interlayer
insulation film 18c, and a trench 11d is also formed in interlayer
insulating film 18d. In addition, a copper interconnection 20c is
formed in trench 11g with a TiN film 19c interposed. The
passivation film 21 is formed to cover copper interconnection 20c
and interlayer insulation film 18d. The method of forming the thin
copper film in accordance with the present invention may also be
applicable to formation of the above mentioned copper
interconnections 20c and 20b.
[0065] It is noted that in FIG. 9, while copper interconnections
20a, 20b and 20c are disclosed as being formed through a damascene
process contemplated for forming a copper interconnection of
submicron level, the present invention may also be applied to other
applications. The above mentioned damascene process is described,
for example, in "Interconnection Process Employing Damascene
Method" published in monthly magazine Semiconductor World,
December, 1995.
[0066] As in the foregoing, although the embodiments or application
of the present invention has been described, it is considered that
the present invention may be applied to formation of a conductive
film other than the thin copper film. In addition, the embodiment
disclosed herein are all by way of illustration and example only
and is not to be taken by way of limitation. The scope of the
present invention is limited only by the terms of the appended
claims, and any alteration in the meaning and scope equivalent to
the appended claims is included.
* * * * *