Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material
Reexamination Certificate
1998-03-11
2001-10-16
Whitehead, Jr., Carl (Department: 2822)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
To form ohmic contact to semiconductive material
C438S643000, C438S661000, C438S680000, C438S687000
Reexamination Certificate
active
06303495
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
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.
2. Description of the Background Art
Conventionally, material of A
1
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 &mgr;m or less, a problem associated with resistance or the like becomes inevitable even if material of A
1
with copper added is employed for interconnection.
Then, to cope with the interconnection width of about 0.15 &mgr;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.
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.
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.
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
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.
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.
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° C.
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.
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.
The step of exposing copper material is preferably repeated several times.
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.
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° 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.
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.
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.
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.
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.
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.
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.
REFERENCES:
pate
Fukada Tetsuo
Hasegawa Makiko
Mori Takeshi
Toyoda Yoshihiko
Brophy Jamie L.
Jr. Carl Whitehead
McDermott & Will & Emery
Mitsubishi Denki & Kabushiki Kaisha
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