AES and LEED studies of surface stoichiometry of palladium silicide epilayers on Si(111)

Abstract

The stability region of the (1×1) surface structure for ultrathin epitaxial Pd 2Si (0001) films grown on Si (111) under UHV conditions was studied by AES and LEED. It is shown that solid state epitaxy of a Pd 2Si layer (5–20nm thick) on Si causes Si-enrichment of the silicide, both its surface and the film. Monolayer Pd deposition on the silicide surface at room temperature and recording of Si L 2,3VV Auger line shape variation allows the stoichiometric Pd 2Si formation to be determined. At Pd deposition being carried on the two-phase Pd 2Si+Pd system is formed. At the metal atom concentration being critical the silicide is formed which is more Pd-rich than Pd 2Si. The stoichiometry thereof is yet not understood. This new compound is unstable and after being held in vacuum it transforms back into Pd 2Si+Pd or Pd 2Si depending on the relative Pd or Si concentration. For all the phase transitions found the only (1×1) surface structure having a different spot/background ratio in the diffraction pattern is characteristic.