Process to fabricate ultra-short channel mosfets with self-aligned silicide contact

Abstract

The method of the present invention includes the following steps. First, a gate oxide layer is formed on the substrate. An undoped polysilicon layer is formed over the gate oxide layer. Then, a first dielectric layer is formed over the undoped polysilicon layer. A photoresist layer is formed over the first dielectric layer. Next, the photoresist layer is patterned to define a gate region. An etching process is performed to the photoresist layer to narrow the gate region. Portions of the first dielectric layer are etched using the residual photoresist layer as a mask. The undoped polysilicon layer is etched using the residual photoresist layer and the residual first dielectric layer as a mask. Then, a PSG is layer deposited over the residual first dielectric layer and the substrate. Subsequently, the PSG layer is etched back to form side-wall spacers to serve as ion diffusion source. A noble or refractory metal layer is deposited on all areas of the substrate. Next, a high dose arsenic or phosphorus ion implantation is performed through the metal layer to form first doped regions to serve as source and drain regions of the transistor. Finally, the two-step RTP annealing process is used to form self-aligned silicided contact of nMOSFETs.