The effect of oxygen impurity on growth of molybdenum disilicide and its distribution during rapid thermal annealing of co-sputtered MoSi_x thin films

Abstract

Thin films of MoSi_x (with and without oxygen) were deposited by co-sputtering of molybdenum and silicon targets. As-deposited films were annealed in argon environment in the temperature range 700-1150 °C for 15-120 s. Rapid thermal annealing of oxygen-contaminated films at low temperature (700-800 °C) in an argon environment results in evolution of a mixture of MoSi₂, Mo₃Si₃, polycrystalline silicon and amorphous phases. Subsequent annealing at higher temperature (above 800 °C) results in further growth of Mo₅Si₃, MoSi₂ and polycrystalline silicon. At 1150 °C, a 15-120 s annealing time produces successive growth of tetragonal MoSi₂ phase at the expense of Mo₅Si₃ and silicon. Auger electron spectroscopy depth profiles of annealed films indicate the accumulation of oxygen impurity at the MoSix-Si(crystalline) interface, which is initially distributed uniformly throughout the MoSix matrix. However, oxygen-free MoSix films do exhibit the growth of MoSi₂ (both tetragonal and hexagonal) during rapid thermal annealing up to 1050 °C. At higher temperature (1150 °C) a single-phase MoSi₂ (tetragonal) is observed. The surface morphology of oxygen-free annealed films reveals a uniform distribution of silicide grains as compared with oxygen-containing films. The sheet resistance of the finally annealed films (1150 °C and 120 s) was found to be 9.5 Ω/◊ for oxygen-contaminated films and 7.6 Ω/◊ for oxygen-free films.