Agglomeration-Free Nanoscale Cobalt Silicide Film Formation Via Substrate Preamorphization

Abstract

We have used preamorphization of silicon substrates as a process modification to suppress agglomeration during cobalt disilicide film formation. Planar, continuous and low resistivity (<21 μΩ-cm) silicide films less than 35 nm thick have been produced both on single crystal silicon and polysilicon. Nanoscale(<35 nm) silicide films are more susceptible to islanding phenomena since agglomeration is dependent onthe ratio of grain size to film thickness. Preamorphization prior to silicidation favorsa large increase in silicide nucleation rate, as well as reduction in critical nuclei size, both of which aid the formation of silicide with small grains. The resulting small grain silicides enable nanoscale films to remain below the critical grain size to thickness ratio for which thin films become morphologically unstable. An interphase void band which occurs between CoSi and CoSi₂ layers, acts as a convenient diffusion marker and aids interpretation of the complex stability issues. Preamorphization prior to silicidation was also extended to heavily doped substrates to study the applicability of this approach for junctions and gate contacts. Silicidation of amorphized heavily boron doped substrates produces non uniform layers due to the collision of the advancing silicidation and SPE interfaces. A comparision of concurrent processing, i.e. simulatneous dopant activation and silicide formation, with conventional silicidation of Si+ preamorphized heavily doped(B) substrates is also presented.