Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material
Reexamination Certificate
1999-07-08
2001-10-30
Bowers, Charles (Department: 2813)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
To form ohmic contact to semiconductive material
C438S627000, C438S633000, C438S637000, C438S643000, C438S687000, C438S685000
Reexamination Certificate
active
06309964
ABSTRACT:
BACKGROUND OF INVENTION
1) Field of the Invention
This invention relates generally to fabrication of semiconductor devices and more particularly to a method for forming a copper damascene structure over a tungsten plug with improved adhesion, oxidation resistance and diffusion barrier properties by using nitridation of the tungsten plug.
2) Description of the Prior Art
The term Damascene is derived from a form of inlaid metal jewelery first seen in the city of Damascus. In the context of integrated circuits it implies a patterned layer imbedded on and in another layer such that the top surfaces of the two layers are coplanar.
As device dimensions shrink, the electrical conductivity of the conductive materials used for interconnections (or wiring) becomes increasingly important. Because of its excellent conductivity, copper has become the most attractive interconnect material. Damascene processes have become a common method of forming a copper line contacting underlying tungsten plugs (W-plugs).
However, the top surface of the W-plugs can be oxidized during an etching process to form a trench for a damascene structure, or even from exposure to air. Another problem with current damascene processes is that the oxidized tungsten or tungsten at the top of the W-plugs provide poor adhesion to other materials such as a TaN barrier layer. Also, the tungsten provides a poor diffusion barrier to copper from the damascene structure, allowing the xopper to diffuse into the W-plugs.
The importance of overcoming the various deficiencies noted above is evidenced by the extensive technological development directed to the subject, as documented by the relevant patent and technical literature. The closest and apparently more relevant technical developments in the patent literature can be gleaned by considering the following patents.
U.S. Pat. No. 5,744,376 (Chan et al.) teaches a Copper plug with a barrier layer.
U.S. Pat. No. 5,314,843 (Yu et al.) shows a WN
x
layer on a W layer before a CMP where the WNx layer is used as a CMP-resist layer.
U.S. Pat. No. 5,084,412 (Nakasaki) shows a W-plug covered by a chromium layer and a copper line. The copper line is covered with a nitride metal.
U.S. Pat. No. 5,691,235 (Meikle et al.) shows a method of depositing W-nitride.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method for forming a damascene structure over W-plugs using nitridation of the W-plugs to provide better oxidation resistance, thereby reducing the interconnect resistance.
It is another object of the present invention to provide a method for forming a damascene structure over W-plugs using nitridation of the W-plugs to provide better adhesion between the W-plugs and the overlying material.
It is yet another object of the present invention to provide a method for forming a damascene structure over W-plugs using nitridation of the W-plugs to provide a better diffusion barrier between the W-plugs and the overlying material, thereby preventing copper from the damascene structure from diffusing into the W-plugs.
To accomplish the above objectives, the present invention provides a method for forming a damascene structure over tungsten plugs using nitridation of said tungsten plugs to provide better oxidation resistance, better adhesion properties and better copper diffusion barrier proerties. The process begins by providing a substrate structure having at least one device layer thereon and having a first dielectric layer overlying the device layer. The dielectric layer has tungsten plugs therein providing a conductive path between the surface of the dielectric layer and the device layer. The tungsten plugs are nitridized to form a WN
x
layer on top of the tungsten plugs. A second dielectric layer is deposited over the WNx layer and the first dielectric layer. The second dielectric layer is patterned to form a trench in the second dielectric layer; whereby the WN
x
layer is exposed in the trench. A barrier layer is formed in the trench. A metal layer is formed over the barrier layer. The metal layer and the second dielectric layer are planarized to form a damascene structure.
The present invention provides considerable improvement over the prior art. The WN
x
layer (
40
) on top of the tungsten plugs (
30
) is more resistant to oxidation by the oxygen plasma than the tungsten plugs which are exposed in the current process. Another advantage is that the WN
x
layer (
40
) provide better adhesion for the barrier layer (
60
) than the tungsten plugs (
30
) without a WN
x
layer (
40
), particularly if the tungsten plugs are oxidized. Yet another advantage of the present invention is that the WN
x
layer (
40
) provides an improved diffusion barrier to copper migration, preventing copper migration into the tungsten plugs.
The present invention achieves these benefits in the context of known process technology. However, a further understanding of the nature and advantages of the present invention may be realized by reference to the latter portions of the specification and attached drawings.
REFERENCES:
patent: 5084412 (1992-01-01), Nakasaki
patent: 5314843 (1994-05-01), Yu et al.
patent: 5633200 (1997-05-01), Hu
patent: 5691235 (1997-11-01), Meikle et al.
patent: 5744376 (1998-04-01), Chan et al.
patent: 5780908 (1998-07-01), Sekiguchi et al.
patent: 5891513 (1999-04-01), Dubin et al.
patent: 5981377 (1999-11-01), Koyama
patent: 6037664 (2000-03-01), Zhao et al.
patent: 6110648 (2000-08-01), Jang
Shue Shaulin
Tsai Ming Hsing
Ackerman Stephen B.
Bowers Charles
Nguyen Thanh
Saile George O.
Stoffel William J.
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