Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material
Reexamination Certificate
1998-06-09
2003-07-15
Quach, T. N. (Department: 2814)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
To form ohmic contact to semiconductive material
C438S656000, C438S660000, C438S659000
Reexamination Certificate
active
06593233
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the invention
The present invention relates to a semiconductor device and a method for manufacturing the same, and more specifically to a semiconductor device having a metal wiring layer and a method for manufacturing the same.
2. Description of related art
First, one example of the prior art will be described. As a technology for filling a connection hole such as a fine contact hole or a fine via-hole for interconnecting wiring conductors of different levels, a blanket tungsten chemical vapor deposition (blanket WCVD) has been reduced into practice, which is excellent in step coverage and low in resistance. In this blanket WCVD method, after a blanket tungsten film is formed, the blanket tungsten film is etched back by a dry etching so that the tungsten film of only a plug is caused to remain, and then, a film of a metal such as aluminum is formed thereon, and patterned to form a patterned wiring conductor.
Recently, a method has been proposed in which a wiring conductor itself is formed of the tungsten film, in order to omit the step of etching back the tungsten film. Now, this method will be described with reference to
FIGS. 1A
to
1
D.
First, as shown in
FIG. 1A
, a silicon oxide film
2
is formed on silicon substrate
1
, and a contact hole is formed in the silicon oxide film
2
. An adhesion layer
3
is deposited in the contact hole by a sputtering. The adhesion layer
3
is suitable to be formed of a double layer of composed of a titanium (Ti) film and a titanium nitride (TiN) film. Then, a tungsten film
4
is deposited by a chemical vapor deposition (CVD), as shown in FIG.
1
B. Furthermore, a photoresist pattern
5
for a possible wiring conductor is formed by a lithography, as shown in FIG.
1
C. The tungsten film
4
is etched by a dry etching using the photoresist pattern
5
as a mask, so that a desired wiring conductor
6
is completed as shown in FIG.
1
D.
Next, another example of the prior art will be described. In a semiconductor device having an upper level metal wiring conductor and a lower level metal wiring conductor which are separated by an interlayer insulator film such as a silicon oxide film but which are interconnected through a contact hole formed by selectively etching the interlayer insulator film, it was a conventional practice of forming the metal wiring layers by a relatively simple and inexpensive sputtering. However, because a diameter of the contact holes has become small with advanced microminiaturization, a void occurs in the contact hole if sputtering having a poor step coverage is used. A long term reliability of the wiring conductor is deteriorated because of the void. Therefore, the metal wiring conductors have been formed by a chemical vapor deposition having an excellent step coverage to prevent generation of the void. However, if the metal wiring conductors are formed by the chemical vapor deposition, it is disadvantageous because a silicon wafer is bowed from internal stress of the metal film. This often results in a suction failure in a next step performed in the same apparatus or in a vacuum suction robot feeding machine for feeding it to a next step.
In order to avoid the above problem, the conventional semiconductor device was formed as follows: As shown in
FIG. 2A
, an silicon oxide film
12
is formed on a silicon substrate
11
in which a desired circuit has been already formed. Then, a contact hole
13
is formed by selectively etching the silicon oxide film
12
, and a refractory metal layer
14
is deposited on a surface including the contact hole
13
, by a sputtering.
Thereafter, as shown in
FIG. 2B
, a tungsten film
15
is formed by a chemical vapor deposition using WF
6
and H
2
as a raw material, under a condition realizing an excellent step coverage, namely, a reaction rate controlling condition such as a WF
6
flow rate of 50 sccm to 100 sccm and a deposition temperature of 400° C. to 460° C.
Then, as shown in
FIG. 2C
, the tungsten film
15
is etched back so that the tungsten film
15
remains only in the inside of the contact hole
13
but the tungsten film
15
is completely removed from the upper surface of the refractory metal film
14
so as to expose the surface of the refractory metal film
14
.
Furthermore, as shown in
FIG. 2D
, an aluminum layer
17
is deposited by a sputtering, and then, is patterned to form a wiring conductor composed of the refractory metal film
14
and the aluminum wiring layer
17
which are connected to a lower level circuit in the contact hole
13
.
In the first example of the prior art as mentioned above, the tungsten film formed by the blanket WCVD is required to fill a fine contact hole having a diameter of not greater than 0.5 &mgr;m without occurrence of the void, and also to have a property which causes no problem in a process after the tungsten film deposition step. In the prior art, however, the tungsten film used for forming a tungsten plug can fill the fine contact hole with no void, but has the internal stress of 1×10
10
dyne/cm
2
or more, so that the wafer has a large bowing. Therefore, if the wiring conductors were formed of the tungsten film used for forming the tungsten plug, a problem is encountered in which, a feed trouble occurs in a feeding system of a semiconductor manufacturing machine for feeding it to a process after the tungsten film deposition step, particularly, a lithography step for forming the wiring pattern.
In order to lower the stress of the tungsten film, it is a general practice to form a film deposition under a supply rate controlling condition by lowering the WF
6
flow rate and/or by elevating the deposition or growth temperature.
As shown in
FIGS. 3A and 3B
, if the metal film were formed by changing the CVD film deposition condition of a tungsten film
16
to a condition for forming a film having a low internal stress, namely, to a supply rate controlling condition, the step coverage property is deteriorated, so that a void
18
occurs, and a problem such as a low long-term reliability of the wiring conductor and the others is generated.
As mentioned above, with the film deposition under the supply rate controlling condition, the step coverage of the tungsten film deteriorates, and it becomes difficult to fill a fine contact of not greater than 0.5 &mgr;m without generation of void.
Because of the problems mentioned above, it was difficult to use the tungsten film for the wiring conductor having small contacts.
In the second example of the prior art as mentioned above of the semiconductor device and the method for manufacturing the same, the manufacturing process becomes long and complicated, resulting in an increased manufacturing cost. In addition, in order to shorten the manufacturing process, if the metal wiring conductor is formed of a metal film formed by only the CVD process, there occurs the above mentioned problem caused by the high stress.
Thomas E. Clark, et al, “High Pressure Blanket CVD Tungsten”, Solid State Technology Japanese Edition, December 1989, pages 33-41 discloses a different WCVD process. However, the tungsten film formed in this process has a high internal stress, and therefore, cannot be used as the wiring conductor.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a semiconductor device and a method for manufacturing the same, which have overcome the above mentioned defects of the conventional ones.
Another object of the present invention is to provide a semiconductor device and a method for manufacturing the same, which have a tungsten plug and a tungsten wiring conductor, and which have a minimized wafer bowing and an excellent step coverage.
Still another object of the present invention is to provide a method for manufacturing a semiconductor device, which has a reduced number of manufacturing steps.
The above and other objects of the present invention are achieved in accordance with the present invention by a semiconductor device having a semiconductor substrate having a principal surface thereof, an interla
Miyazaki Kazuki
Shigehara Kazunobu
Zenke Masanobu
NEC Electronics Corporation
Quach T. N.
Whitham Curtis & Christofferson, PC
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