Chemical vapor deposition of tungsten using...

Details Chemical vapor deposition of tungsten using... Chemical vapor deposition of tungsten using...

1998-02-10

2001-04-03

Bowers, Charles (Department: 2813)

Semiconductor device manufacturing: process

Coating with electrically or thermally conductive material

To form ohmic contact to semiconductive material

C438S681000, C438S685000

Reexamination Certificate

active

06211082

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to integrated circuit fabrication methods, and more particularly to methods of forming conductive layers on integrated circuits.
BACKGROUND OF THE INVENTION
As the integration density of integrated circuit devices continues to increase, it may become increasingly difficult to provide high density conductive interconnections between the active devices in the integrated circuit. In order to provide high performance interconnections, tungsten is often used as an interconnection material. The tungsten layer may be formed by Chemical Vapor Deposition (CVD). CVD tungsten can have high performance characteristics compared to aluminum or polycide.
Tungsten is generally chemical vapor deposited using a source gas containing tungsten and a reducing gas. A typical source gas used is tungsten hexafluoride (WF
6
). The reducing gas may be hydrogen and/or silane (SiH
4
). The deposition of tungsten may be obtained by the following reactions:
WF
6
+3H
2
→W+6HF
2WF
6
+3SiH
4
→2W+3SiF+6H
2
Unfortunately, a tungsten layer grown using the above CVD reactions may grow too rapidly. During this rapid growth, the tungsten may tend to grow in a crystalline manner, so that it grows preferentially in one direction compared to other directions. This rapid and/or preferential growth may cause the surface of the tungsten layer to be rough. The roughness of the tungsten surface may cause adhesion problems during subsequent microelectronic processing and may cause other problems that can also impact performance during subsequent processing.
One technique for reducing the surface roughness of tungsten is described in a publication by Tsai et al. entitled “
Layer Tungsten and Its Applications for VLSI Interconnects
”, IEDM Technical Digest, 1988, pp. 462-465. As described, tungsten grain growth is interrupted using a layer of thin silicon and the silicon layer is consumed during subsequent tungsten deposition, to thereby form tungsten films with fine grains. Unfortunately, this technique interrupts the tungsten deposition process with a silicon deposition process, and may thereby complicate processing.
It is also known to provide an antireflective coating to reduce the roughness of the surface of the tungsten layer. The antireflective coating may also increase the processing complexity.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide improved methods of forming tungsten layers on integrated circuit substrates.
It is another object of the present invention to provide tungsten layers with reduced roughness.
It is still another object of the present invention to provide reduced roughness tungsten layers without requiring interruption of the tungsten deposition process and without requiring the addition of antireflective layers.
These and other objects are provided according to the present invention, by chemical vapor depositing a tungsten layer on an integrated circuit substrate using a source gas containing tungsten, a reducing gas and a nitrogen-containing gas. The nitrogen-containing gas can act as a surface roughness reducing gas that reduces the roughness of the tungsten layer compared to a tungsten layer that is chemical vapor deposited using the source gas containing tungsten and the reducing gas, but without using the surface roughness reducing gas. Viewed in another way, the nitrogen-containing gas acts as a growth rate controlling gas that produces uniform growth of the tungsten layer in a plurality of directions compared to a tungsten layer that is deposited using the source gas containing tungsten and the reducing gas, but without using the growth rate controlling gas.
The reducing gas is preferably selected from the group consisting of SiH
4
, H
2
, SiH
2
Cl
2
, Si
2
H
6
, B
2
H
6
and SiH
2
F
2
. The source gas containing tungsten is preferably tungsten hexafluoride (WF
6
). The nitrogen-containing gas may be an organic compound or an inorganic compound containing nitrogen. An inorganic compound containing nitrogen is preferably selected from the group consisting of nitrogen gas (N
2
) and ammonia (NH
3
). An example of an organic compound containing nitrogen is methyl hydrazine (CH
6
N
2
).
Accordingly, tungsten is chemical vapor deposited by injecting a material containing nitrogen in addition to the source gas and reducing gas, to thereby reduce the roughness of the surface of the tungsten layer. Defects caused by excessive surface roughness can thereby be reduced or eliminated, without requiring interrupted tungsten deposition processes or requiring the formation of antireflective coating layers. It will also be understood that the use of nitrogen-containing gas can be used in other metal deposition processes wherein a metal source gas and a reducing gas are used.


REFERENCES:
patent: 4612257 (1986-09-01), Broadbent
patent: 5028565 (1991-07-01), Chang
patent: 5691235 (1997-11-01), Meikle
patent: 5888588 (1999-03-01), Nagabushnam
patent: 95-37760 (1995-10-01), None
Tsai et al., “Layer Tungsten and Its Applications for VLSI Interconnects”, IEDM Technical Digest, Dec. 11-14, 1988, pp. 462-465.

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