Abstract
Transmission electron microscopy and Auger electron spectroscopy have been applied to investigate the effects of doping impurities and substrate crystallinity on the formation of nickel suicides at 200-280° C in nickel thin films on silicon. The systems investigated included samples with as-implanted BF 2 , B, F, As, and P and recrystallized (001) Si as well as P-doped low pressure chemical vapor deposited (LP-P) and B-doped plasma enhanced chemical vapor deposited (PE-B) amorphous silicon substrates. In samples annealed at 220-280° C, substantial amounts of epitaxial NiSi 2 were found to form on crystalline structure of BF 2 , B and F implanted samples to various extents at different temperatures. High resolution lattice imagings of cross-sectional samples showed that the epitaxial NiSi 2 /Si interfaces are coherent. No NiSi 2 was detected in all nickel thin films deposited on implantation-amorphous specimens. NiSi 2 epitaxy was found to be a sensitive function of annealing temperature. Good correlation was found between the atomic size factor and resulting stress and NiSi 2 epitaxy at low temperature. The formation of Ni 2 Si and NiSi was observed to be influenced by the dopant species and crystallinity of the substrates. The vast difference in inducing the formation of nickel suicides in implantation-amorphous and recrystallized samples is likely due to variations in initial structure and/or dopant distribution. The finding that both n-type and p-type dopants influenced the formation of Ni 2 Si and NiSi suggested that they may be related to the electrical activity of the doping species in recrystallized samples. NiSi, possessing one of the lowest resistivity among all metal silicides, was found to be the only phase formed in all implantation-amorphous as well as LP-P and PE-B amorphous silicon samples annealed at 280° C. Nickel thin film appears to be an attractive candidate for the metallization of amorphous silicon devices. © 1988 The Metallurgical of Society of AIME.