Inhomogeneous Reaction between Epitaxial Al and Si(111) Revealed by Scanning Internal Photoemission Microscopy (IPEM)

Abstract

Aluminum is one of the most important materials for the Si LSI metallization. An epitaxial growth of Al films on Si can be achieved since the lattice constant ratio between Al and Si is approximately given by 3 to 4. It is expected that epitaxial Al films are highly stable against thermal annealing. However, epitaxial-Al/Si contacts have sometimes shown a significant change in Schottky barrier height (SBH) and interface structure upon annealing. The objective of this paper is to clarify the relation between the SBH inhomogeneity and the thermally induced reaction between Al and Si through grain boundaries. The microscopic SBH distribution was measured by using scanning internal- photoemission microscopy (IPEM).Epitaxial Al layers were deposited on n-Si(l11) by electron beam evaporation at substrate temperatures of 220°C and 250°C. In the as-deposited state, the Al film fabricated at 220°C consisted mainly of “type-A”- and partially of “type-”"-orientated interfaces (referred to as a mixed phase: MP-AS), while that deposited at 250°C consisted only of “type-B” (referred to as a single phase: SP-AS). The samples were annealed for 1 hour at temperatures between 450-550°C and then quenched.