NiSi$_2$ as seed layer for epitaxial growth of NiAl and Cr on Si(001)

Abstract

In general, metal layers cannot be grown epitaxially on Si due to the tendency of metals to react and form a silicide. Even in case the metal layer has a matching lattice symmetry and atomic distance, the Si/metal interface is disturbed by the silicide thus preventing epitaxial growth. One exception is NiAl which is known to grow epitaxially when deposited on Si(001). During the growth, NiAl reacts with Si to form NiSi$_2$. In this work, epitaxial NiAl is grown and significant silicidation is observed in accordance with previous reports. However, the role that this silicide plays as a template for the epitaxial growth of NiAl has not been clear to this date. We hypothesize that NiSi$_2$ acts as a necessary seed layer between the Si substrate and the NiAl layer. Additionally, NiSi$_2$ can be used as a seed layer for the epitaxial growth of other metals besides NiAl. This was tested by growing NiSi$_2$ seperately and replacing the NiAl layer with Cr. Growing Cr directly on Si(001) produced a polycrystalline layer. When NiSi$_2$ was used as a seed layer, the Cr layer was found to be a single crystal with Si(001)//Cr(001) and Si(100)//Cr(100). NiSi was also tried as seed layer for Cr and was found to produce a polycrystalline Cr layer. Using NiSi$_2$ as a seed layer could enable the growth of various epitaxial materials for industrial semiconductor applications.