Computer-assisted system for sintering of nanoceramics at high pressure

摘要

The nanocrystalline structure and mechanical properties of TaSi_2 films deposited by sputtering of TaSi_2 target have been investigated by x-ray diffraction, cross-sectional transmission electron microscopy (TEM), four-point electrical resistance measurement and cyclic depth-sensitive nanoindentation. The purpose of the work is to research the formation of nanocrystalline structure in TaSi_2 films on a silicon substrate. As revealed, a decrease in the deposition rate leads to an increase in the O and C impurities' content in films. Contamination of the film by O and C atoms during a low-rate deposition causes the formation of an amorphous phase in deposited films. Upon annealing, the amorphous structures crystallize into mixtures of disilicide and a small amount of polysilicide, i.e., TaSi_2 and Ta_5Si_3, respectively. After annealing at 970 K, the formation of nanocrystalline structure with a grain size about 10 nm takes place in the film produced at a deposition rate of 0.2 nm/sec. The formation of nanocrystalline structure changes drastically the mechanical properties of the film. The nanohardness and elastic modulus increase significantly, the film becomes brittle and overstressed. After deposition in the film produced at the 1 nm/sec deposition rate mainly Ta-disilicide and the amorphous phase are observed. After annealing the amorphous phase near the Si-substrate coexists with column-shape grains of Ta-disilicide of size 150 x 500 nm. The annealed thin film became nonuniform in thickness. The nanohardness and elastic modulus increase.