Materials and device issues in the formation of sub-100-nm junctions

Abstract

This paper compares the materials and device issues associated with two alternative techniques for the formation of ultrashallow junctions: 1) the use of preamorphization and low energy dopant implantation, combined with rapid, low-temperature annealing; and 2) the use of metal suicides as a diffusion source (SADS) where dopants are implanted into CoSi 2 and subsequently diffused into silicon. For conventionally-formed, ultrashallow junctions, preamorphization with either silicon or germanium does not result in shallower junctions. The enhanced diffusion associated with the preamorphization implant damage compensates for the reduction in channeling. Preamorphization does, however, give low sheet resistance junctions and high dopant activation after recrystallization at 550°C. Considerable dopant motion (∼ 50 nm) is observed in the tail region, near the junction, after 10 s of annealing at a relatively low temperature (800°C). The SADS process is seen to produce low leakage n + and p + diodes with less than 10 nm of dopant diffusion beyond the silicide/silicon interface, using a very low thermal budget process. By confining the implantation to within the suicide, no crystal defects are created in the underlying silicon. With the SADS process, the limitation on scaling the junction depth lies in producing thin, stable suicide films. Agglomeration of the silicide and pullback along feature edges restrict the maximum thermal cycle and the minimum allowable film thickness.