Self-aligned MOSFET gate/source/drain salicide formation

DETAILED DESCRIPTION The present invention provides a method of fabricating a MOSFET device structure in a silicon substrate.
The MOSFET device structure includes planarized trench isolation field oxide regions formed in the substrate, a layer of gate oxide formed on the substrate to electrically insulate the polysilicon gate from the substrate, oxide sidewall spacers formed on sidewalls of the polysilicon gate and gate oxide, and LDD N- regions formed on the substrate adjacent the field oxide regions and beneath the sidewall spacers to define a channel region in the substrate beneath the polysilicon gate.
In accordance with the method of the invention, a layer of polysilicon is deposited on the abovedefined structure and a chemical mechanical polishing step is performed to define raised source/drain polysilicon regions that are self-aligned to the LDD N- regions.
N-type dopant is then implanted into the polysilicon gate and into the raised source/drain polysilicon regions.
A first rapid thermal processing step is then performed to activate the N-type dopant and to diffuse N-type dopant from the raised source/drain polysilicon regions into the underlying LDD N- regions to form shallow N+ junctions within the LDD N- regions.
A cleaning step is performed and a layer of cobalt is then deposited on the polysilicon gate and on the raised source/drain polysilicon regions.
The cobalt layer is then implanted with heavy ions to mix the cobalt and silicon at the interface of the cobalt layer and the underlying polysilicon.
A titanium nitride capping film is then formed on the cobalt layer to protect the film from nitrogen diffusion during RTP, which results in producing a highly uniform salicide layer due to the absence of foreign materials in the cobalt film.
The TiN film also results in reducing the RTP thermal budget.
The first salicidation RTP step is performed at low temperature (about 450 degrees C.
) to allow the cobalt to be the diffusing species into the underlying silicon.
By doing this, the lateral growth of the cobalt salicide is eliminated