In situ study of the formation of silicide phases in amorphous Ni-Si mixed layers

Abstract

In this paper, we investigated Ni silicide phase formation when Si is added within an as deposited 50 nm Ni film. A series of 22 samples with a Si content varying from 0 to 50 at. % was prepared and systematically investigated with in situ x-ray diffraction. The inert oxide substrate was used to identify the phases which first crystallize in an amorphous Ni-Si mixture of a given concentration. The noncongruent silicides Ni3 Si and Ni3 Si2 are never observed to crystallize readily out of the mixture. A remarkable observation is the initial crystallization at low temperature of a hexagonal Ni-silicide, observed over a broad mixed layer composition [35-49%Si]; this hexagonal phase nucleates readily as a single phase [39-47%Si] or together with Ni2 Si [35-38%Si] or NiSi [49%Si]. This low-temperature phase is related to the high temperature θ -phase, but covers a wide composition range up to 47%Si. For the same Ni-Si films deposited on Si(100), the initial nucleation of the Ni(Si) mixture is similar as for the samples deposited on SiO2, such that the complex sequence of metal-rich Ni-silicide phases typically observed during Ni/Si reactions is modified. For samples containing more than 21%Si, a simpler sequential phase formation was observed upon annealing. From pole figures, the phase formation sequence was observed to have a significant influence on the texture of the technologically relevant NiSi phase. For mixture composition ranging from 38% to 43%Si, the initial transient θ -phase appears extremely textured on Si(100). The observed transient appearance of a hexagonal phase is of importance in understanding the phase formation mechanisms in the Ni-Si system. © 2009 American Institute of Physics.