Thermal stability of thin PtSi films on silicon substrates

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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.