A thermodynamic and kinetic study of chemical vapor deposition of tungsten from WF6 and GeH4

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Abstract
In this paper a thermodynamic and kinetic study of the deposition of tungsten on silicon (100) from tungsten hexafluoride (WF6) and germane (GeH4) is presented. Thermodynamic calculations, as well as experiments with a closed reactor, indicate that the reaction occurring during deposition is WF6+3GeH4→W+3GeF2+6H2. The growth rate as a function of process parameters is obtained for depositions in the temperature range from 600 to 800 K and a total pressure range from 150 to 1000 mTorr. Experiments show that the germane reduction of tungsten hexafluoride is of 0.9 order in WF6, −0.2 order in GeH4, and zero order in H2. The activation energy is 34 kJ/mol. The deposition rate does not change when SiH4 is added to the GeH4/WF6 mixture, while, on the contrary, a small amount of GeH4 reduces the growth rate from a SiH4/WF6 mixture considerably. The kinetic data indicate that the formation of GeF2 might be the rate‐limiting step.