Phase-microstructure of Mo/Si nanoscale multilayer and intermetallic compound formation in interfaces

Abstract

Microstructural investigation of the Mo/Si nanoscale multilayers (MLs) is essential to design high-reflective nanomirrors. Raman spectroscopy showed existence of silicon layer in the amorphous structure. Small fraction of the nanocrystalline silicon (nc-Si) phase was found to be embedded in the amorphous silicon (a-Si) matrix. The disorder in a-Si is increased with the decrease in the thickness of silicon layer in the Mo/Si MLs, determined by the increased bond-angle deviation (ΔΘ) of the Si–Si network. The MLs exposed to high-temperature (HT) showed a decrease in the ΔΘ value, which signifies the relaxation of both molecular disorder and residual stress. X-ray diffraction analysis confirmed the polycrystalline bcc phase of Mo and the formation of intermetallic t-Mo5Si3 phase in the interfaces. This phase is more prominent for higher value of β (thickness ratio of high atomic weight (z) layer to ML period d, i.e. β = dMo/d). Intensity of the Mo (110) plane is decreased for the sample annealed at HT, which is directly related to the degree of amorphization and the formation of intermetallic phases. However, HT annealed Mo/Si showed the growth of Mo (220) planes for higher β value of MLs. Current findings revealed that the disorder in the a-Si and microstructure of the Mo and intermetallic phase depend on the annealing temperature and the β value. The analysis of the intermetallic phase is critical for the development of high reflective mirrors.