Thermal stability of thin PtSi films on silicon substrates

Abstract

The thermal stability of PtSi is an important parameter in large-scale integration processing schemes which involve postmetallization high-temperature operations. For this reason, the effect of annealing on various properties of PtSi has been studied over the temperature range 800–900°C, for 200- and 900-Å-thick PtSi films on single-crystal silicon substrates. The as-prepared films, produced by backsputter cleaning of Si surface followed by sputtering of Pt, in situ sintering at 700°C for 10 min, and etching to dissolve any unreacted Pt, were found to be single-phase PtSi. The 200-Å-thick PtSi films on (111) Si possess a strong degree of preferred orientation with grains which are triply positioned with (100) PtSi ∥ (111) Si and [010] PtSi ∥ 〈110〉 Si; the orientation remains unchanged upon further annealing. On going to higher thickness (900 Å), the preferred orientation of PtSi changes to (010) type and then to a partial (111) type on annealing at 900°C. Rapid grain growth is observed on annealing in the range 800–900°C; the grain size increases from 0.01–0.25 μ in the as-deposited film to several μ at 850°C. The grain growth is followed at 900°C by agglomeration, i.e., a changeover from continuous film to island-type microstructure. The final stage of agglomeration, which has been observed in 200-Å PtSi at 900°C, is associated with a drastic increase in resistivity. The resistivity of as-prepared PtSi films is estimated to be 15 (±5) μΩ cm. Partial agglomeration of 900-Å PtSi occurs at 900°C; it produces only a 10% increase in resistivity. It is concluded that for PtSi films 200–900 Å thick, 800°C is a safe upper-limit (and 850°C, absolute-limit) temperature below which there is no agglomeration, no change in crystallographic orientation, and grain growth is not excessive.