Laser photochemical deposition of germanium-silicon alloy thin films

Thin films of Ge-Si alloys were deposited by 193 nm photolysis of GeH ₄/Si₂H₆ gas mixtures using an ArF laser. For substrate temperatures below 350 °C, deposition occurred only with the laser present, while for temperatures above 400 °C, film growth was little influenced by laser photolysis and resembled conventional chemical vapor deposition (CVD). The Si/Ge ratio in the films was about three times the P _Si2H₆/P_GeH4 ratio of reactant partial pressures for deposition in either the laser photolysis or the CVD regime. This result indicates that there is strong cross chemistry between silicon and germanium-bearing species in the gas phase. Film stoichiometry was measured by Auger analysis and Raman spectroscopy, with both methods leading to the same film composition.