Photoemission study of interfacial reactions during annealing of ultrathin yttrium on SiO2/Si(1 0 0)

X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS) and work-function measurements have been used to investigate the Y/SiO2/Si(1 0 0) interfaces in situ as a function of annealing temperature. The results show that yttrium is very reactive with SiO2 and can react with SiO2 to form Y silicate and Y2O3 even at room temperature. Annealing leads to the continual growth of the Y silicate. Two distinctive reaction mechanisms are suggested for the annealing processes below and above 600 K. The reaction between metallic yttrium and SiO2 dominates the annealing processes below 600 K, while at annealing temperatures above 600 K, a reaction between the new-formed Y2O3 and SiO2 becomes dominant. No Y silicide is formed during Y deposition and subsequent annealing processes. UPS valence-band spectra indicate the silicate layer is formed at the top surface. After 1050 K annealing, a Y-silicate/SiO2/Si structure free of Y2O3 is finally formed.