Ion-induced phase formation in metal-metal and metal-silicon thin film structures

Abstract

The phase formation in metals by using ion mixing techniques has been studied and compared with silicide formation. Upon irradiation of AlPt, AlNi and AlPd thin films, only the simplest intennetallic compounds of NiAl and PdAl were formed in crystalline structure, while the amorphous phase has been observed over a large range of composition. Ion mixing of AuCu bilayers resulted in the formation of substitutional solid solutions with no trace of ordered compounds. The formation of the ordered compound CuAu was achieved either by irradiation of bilayers with Ar ions at elevated substrate temperature or by irradiation of the mixed layers with He ions at relatively low temperature. In the AuAl system several crystal compounds existed in the as-deposited samples. These phases remained crystalline or transformed into other equilibrium compounds upon ion irradiation. The results suggest that the phase formation by ion mixing is dependent on the high quench rate in the collision cascade region and the atomic mobility at the irradiation temperature. The argument can be applied to silicide forming systems. With near-noble metals, the mixed atoms are mobile and form metallurgically distinct phases. With refractory metals, no equilibrium compounds are formed due to the lack of atomic mobility.