NICKEL SILICIDE THERMAL-STABILITY ON POLYCRYSTALLINE AND SINGLE-CRYSTALLINE SILICON

The thermal stability of NiSi on polycrystalline silicon (poly-Si) or single crystalline silicon on sapphire (SOS) substrates has been inves tigated with scanning electron microscopy, transmission electron micro scopy, and in-situ resistance measurements. For NiSi on poly-Si, silic ide enhanced grain growth occurs in the poly-Si. The grain growth firs t occurs from the NiSi/poly-Si interface with poly-Si grains growing i nto the silicide, resulting in alternating grains of poly-Si and NiSi on the top surface. With further annealing, grain growth also occurs i n the bottom layer of the poly-Si, with NiSi moving to the bottom inte rface and consuming the small poly-Si grains, resulting in an inverted structure. Agglomeration of NiSi is observed for NiSi on SOS substrat es after high temperature annealing. The activation energies for inver sion and agglomeration are similar, (3.0 +/- 0.2 and 2.9 +/- 0.2 eV, r espectively) suggesting that the same mechanism is controlling both pr ocesses. The activation energy may correspond to that for adding a Si atom onto a growing Si grain, as suggested by L.H. Allen, K.N. Tu, L.C . Feldman, and J.W. Mayer, Phys. Rev. B, 41 (1990) 8213.