Formation of silicided, ultra-shallow junctions using low thermal budget processing

Abstract

The tradeoffs involved in alternative processes for the formation of ultra shallow junctions are described. Low energy implantation, preamorphization to eliminate channeling and low thermal budget processing are adequate to form junctions that are 0.1 to 0.3μm deep. For junctions less than about 100 nm, however, the enhanced diffusion resulting from the amorphization implant reduces its benefits. Athermal diffusion can result in considerable junction motion even when low thermal budget processing is used. Junctions this shallow typically require silicide or metal cladding to reduce the sheet resistance; however, the dopant redistribution associated with siliciding pre-existing junctions increases the contact resistance which diminishes the potential benefit of silicidation. In addition, high leakage can result from excessive silicon consumption. While the use of silicide as a diffusion source can overcome some of the limitations of silicided junctions, this technique can be especially hindered by slow dopant diffusion or compound formation in the silicide and by the limited thermal stability of the silicide. One outstanding issue associated with silicide diffusion sources is understanding the seemingly enhanced diffusivity of dopant in the silicon.