The Effect of Ni:Si Ratio on Microstructural Properties of Ni/Si Ohmic Contacts to Sic

Detailed microstructural studies were performed on Ni/Si ohmic contacts to silicon carbide in order to investigate the effect of initial Ni:Si ratio in as-deposited structures on the occurrence of characteristic defects in Ni silicide layers, such as voids, layer discontinuities, rough surface or rough interface. The chosen range of investigated Ni:Si ratios corresponded to delta-Ni2Si as a dominant phase after complete annealing sequence. Strong effect of the initial stoichiometry on the ohmic contact's microstructure was observed. The highest Ni concentration significantly lowered the temperature at which roughening of the surface and the interface occurred. The middle value of investigated concentrations resulted in the rough interface after high temperature annealing, while the lowest investigated Ni content preserved smooth interface but introduced large voids and layer discontinuities. After the first annealing step, gamma-Ni31Si12 and/or delta-Ni2Si phases were detected. In the ohmic contacts (after two-step annealing sequence), beside delta-Ni2Si, the metastable, high temperature phase theta-Ni2Si was detected (also referred to as Ni3Si2 center dot h). This phase can exist within a relatively broad range of Ni:Si stoichiometry. The stoichiometry change toward higher Si content, which occurs during high temperature annealing, was realized through this phase. Superstructures were detected in theta-Ni2Si (Ni3Si2 center dot h) and in-gamma-Ni31Si12 grains. The effect of the stoichiometry change on the morphology of the Ni silicide layers is discussed. (C) 2016 Elsevier B.V. All rights reserved.