Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material
Reexamination Certificate
1995-03-10
2001-08-07
Quach, T. N. (Department: 2814)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
To form ohmic contact to semiconductive material
C438S630000, C438S633000, C438S663000
Reexamination Certificate
active
06271120
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to semiconductor processing, and, more particularly, to improving the electrical integrity of contacts comprising metals deposited by physical vapor deposition (PVD) or chemical vapor deposition (CVD) during processing of sub-half micrometer semiconductor devices.
BACKGROUND ART
The present integrated circuit devices comprise a silicon substrate, doped regions in the semiconductor to which source or drain connections are made, separated by a gate control region. Metal connections to the source, gate, and drain electrodes are made by multilayer interconnects, which are supported over the substrate by an interlayer dielectric. To make electrical connection between different layers, the dielectric is sequentially patterned and etched to form contact openings. These opening are filled with plugs of an electrically conductive material such as aluminum. Some plugs contact a polysilicon layer which is formed over a thin oxide gate layer and these plugs become gate electrodes. Other plugs contact previously-doped regions in the semiconductor substrate and become source or drain contacts.
In the case where source and drain contacts are to be made, a titanium silicide layer is formed on the doped regions by use of a rapid thermal anneal. To support multilayer interconnects, an interlayer dielectric comprising of oxide is deposited on the surface and contact openings are etched in the interlayer dielectric.
The current practice in the industry is to deposit a Ti/TiN layer onto the titanium silicide layer after the contact openings are formed. The Ti/TiN layer serves as a barrier TiN layer that protects the junctions below. The formation of a barrier TiN layer is needed to prevent junction spiking caused by diffusion of metal from the plugs into the junctions. The minimum thickness of the barrier TiN layer depends on the device. Presently, physical vapor deposition (PVD) or chemical vapor deposition (CVD) is employed to deposit the barrier TiN layer.
What is needed is an improved process for forming a barrier TiN layer at the bottom of the contact opening.
DISCLOSURE OF INVENTION
In accordance with the invention, the top portion of the titanium silicide layer is converted into a barrier TiN layer of sufficient thickness. No additional mask is required to form the barrier TiN layer.
The process of forming a barrier TiN layer comprises converting the top portion of a titanium silicide layer into a layer of titanium nitride by exposing the titanium silicide layer to a rapid thermal anneal in a nitrogen-containing atmosphere.
In the case where source and drain contacts are to be made, contact openings are etched in the interlayer dielectric down to doped regions in the semiconductor (i.e., polysilicon or doped regions in the substrate). As described above, these doped regions have a titanium silicide layer on top. The barrier TiN layer on the bottom of the contact openings is provided by a rapid thermal anneal in a nitrogen-containing atmosphere which converts the top portion of the titanium silicide layer in the contact openings into a barrier TiN layer. This nitrogen-containing atmosphere contains a nitrogen-containing species (e.g., N
2
, NH
3
, N
2
O) that reacts with titanium silicide to form TiN under the conditions provided by a rapid thermal anneal.
Typically, the formation of the barrier TiN layer is followed by high temperature aluminum sputtering, regular aluminum sputtering followed by high temperature reflow, or chemical vapor deposition of aluminum. (High temperature reflow of aluminum involves a high temperature anneal (>450° C.) to flow the aluminum into the contact opening.) The aluminum plug is then formed by chemical-mechanical polishing or etchback.
Plugs comprised of other metals may also be used in place of aluminum. Examples of such metals include CVD metals, i.e., CVD-copper, CVD-gold and CVD-tungsten.
Other objects, features, and advantages of the present invention will become apparent upon consideration of the following detailed description and accompanying drawings, in which like reference designations represent like features throughout the Figures.
REFERENCES:
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patent: 4994410 (1991-02-01), Sun et al.
patent: 5124780 (1992-06-01), Sandhu et al.
patent: 5141897 (1992-08-01), Manocha et al.
patent: 5258333 (1993-11-01), Shappir et al.
patent: 5266521 (1993-11-01), Lee et al.
patent: 5272666 (1993-12-01), Tsang et al.
Cheung Robin W.
Huang Richard J.
Advanced Micro Devices , Inc.
Quach T. N.
Sawyer Law Group LLP
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