Stability and composition of Ni–germanosilicided Si1−xGex films

The stability and composition of the Ni–germanosilicided films formed on relaxed Si1−xGex alloy has been studied in the temperature range of 400–900 °C. During the solid phase thermal reaction between Ni and Si1−xGex, a nickel–germanosilicide Niy(Si1−wGew)1−y ternary phase (w⩽x and y≈0.5) and a Ge-rich Si1−zGez phase (z>x) have been found. In the lower annealing temperature range of 500 °C, the Ge composition in the nickel–germanosilicide phase is similar to that of the Si0.75Ge0.25 substrate. At the same time, germination of Si1−zGez (z>x) takes place within the germanosilicide film. At higher annealing temperatures, Ni thermodynamically prefers to react with Si compared to Ge, and as a result, Ge segregates out from the germanosilicide grains to enrich Ge in the formed Si1−zGez (z>x) grains in between the germanosilicide grains. On the other hand, the size of the germanosilicide grains increases almost linearly with annealing temperature while that for the Si1−zGez grains remains almost constant up to an annealing temperature of 700 °C, and above which it increases sharply. As a result, the Ge-rich Si1−zGez grains make the germanosilicide film discontinuous, leading to an increase in the sheet resistance of the germanosilicide film.