Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material
Reexamination Certificate
1999-09-30
2001-12-04
Nguyen, Ha Tran (Department: 2812)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
To form ohmic contact to semiconductive material
C438S628000, C438S630000, C438S638000, C438S639000, C438S643000, C438S644000, C438S653000, C438S654000, C438S656000, C438S672000, C438S675000, C438S680000, C438S685000, C438S687000
Reexamination Certificate
active
06326297
ABSTRACT:
BACKGROUND
1. Field of Invention
The present invention relates to integrated circuit structures and fabrication methods, and in particular to enhancing tungsten nitride adhesion to an underlying dielectric.
2. Related Art
The semiconductor industry is moving toward copper interconnects to produce faster and less expensive integrated circuits. However, manufacturing fully integrated copper devices presents formidable technical challenges. One critical manufacturing aspect is the choice of barrier material. Copper readily diffuses into interlayer dielectrics, and the diffusion may result in line-to-line leakage and integrated circuit device damage.
Physical vapor deposited (PVD) tantalum (Ta) and tantalum nitride (TaN) liners have been experimented with as copper barriers for 0.25 &mgr;m and 0.18 &mgr;m device generations. These materials have a nearly amorphous texture that impedes copper diffusion. However, the drawback of the PVD techniques, including ionized PVD, is poor sidewall coverage in high aspect ratio, dual damascene features. The industry requires conformal, highly reliable copper barriers.
Tungsten nitride is a potential copper barrier. When deposited using plasma enhanced chemical vapor deposition (PECVD), tungsten nitride provides good conformal coverage in high aspect ratio features. Unfortunately, tungsten nitride is not thermally stable when deposited on dielectric materials such as silicon dioxide. During high temperature process steps (e.g., annealing after electrochemical plating of copper) following the tungsten nitride deposition, the tungsten nitride separates from the dielectric. What is required is a method to improve the tungsten nitride's thermal stability and adhesion to the underlying dielectric.
SUMMARY
In accordance with the invention, a layer of silicon is formed over the dielectric before the tungsten nitride is deposited. The invention may be used in various applications involving one or more layers of tungsten nitride. Such applications include, for example, dual damascene copper interconnect structures and electrically conductive gates for insulated gate transistors.
A conventional dielectric layer (e.g., silicon dioxide) is formed over a semiconductor substrate. In some embodiments the dielectric layer may be patterned to form, for example, a damascene structure. A thin layer of silicon is formed over the dielectric layer. In some embodiments the silicon layer is amorphous silicon. In other embodiments the layer of silicon may have a different physical structure. Tungsten nitride is formed over the silicon layer using plasma enhanced chemical vapor deposition (PECVD). During the deposition, tungsten hexafluorine (WF
6
) and nitrogen (N
2
) react to form the tungsten nitride layer. In addition, silicon in the silicon layer is consumed by reacting with the N
2
to form silicon nitride, and with the WF
6
to form tungsten silicide and silicon tetrafluoride. The silicon nitride and tungsten silicide remain between the dielectric and the tungsten nitride to form an adhesion layer. The volatile silicon tetrafluoride is carried away during the PECVD process.
REFERENCES:
patent: 5341016 (1994-08-01), Prall et al.
patent: 5888588 (1999-03-01), Nagabushnam et al.
patent: 5989623 (1999-11-01), Chen et al.
patent: 6066540 (2001-05-01), Yeom et al.
Allenby Christopher B.
Nguyen Ha Tran
Novellus Systems Inc.
Skjerven Morrill & MacPherson LLP
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