Pyramidal structural defects in erbium silicide thin films

TL;DR

This paper reports the discovery of pyramidal defects in epitaxial erbium disilicide thin films, which form due to strain-induced buckling and separation from the substrate during annealing.

Contribution

It identifies a new type of defect in erbium silicide films and links their formation to epitaxial strain and stress relief mechanisms.

Findings

Pyramidal defects are 5-8 microns wide and form during annealing.

Defects occur even in vacuum, indicating oxidation is not a cause.

Defects are absent on amorphous substrates, implicating epitaxial strain.

Abstract

A new pyramidal structural defect, 5 to 8 micron wide, has been discovered in thin films of epitaxial erbium disilicide formed by annealing thin Er films on Si(001) substrates at temperatures of 500 to 800C. Since these defects form even upon annealing in vacuum of TiN-capped films their formation is not due to oxidation. The pyramidal defects are absent when the erbium disilicide forms on amorphous substrates, which suggests that epitaxial strains play an important role in their formation. We propose that these defects form as a result of the separation of the silicide film from the substrate and its buckling in order to relieve the compressive, biaxial epitaxial stresses. Silicon can then diffuse through the silicide or along the interface to fully or partially fill the void between the buckled erbium disilicide film and the substrate.