Surface characterization of excimer laser induced deposition of W on GaAs from WF6 and H2

Deposition of W thin films has been induced by a KrF excimer laser incident perpendicularly on a GaAs substrate placed in an ambient containing WF6, H2 and Ar. In-situ X-Ray Photoelectron Spectroscopy (XPS) shows evidence of a surface interaction between WF6 and GaAs under laser irradiation. At 50 mJ/cm2, fluorinated W species adsorbed on the GaAs substrate are partially dissociated by the laser beam, leading to a loss in stoichiometry and the formation of GaF3 on the surface. The generation of stable, non-volatile, GaF3 has been identified as a possible obstacle to the nucleation of metallic tungsten films on GaAs in CVD processes using WF6. At 67 mJ/cm2, the gas-substrate interaction is further enhanced, but the dissociation of WF6 into metallic W is achieved. However, at such laser energy densities, the substrate appears to be damaged. By using H2 as a reducing gas for WF6, 0.2 μm thick W deposits were obtained but the process was difficult to reproduce. Two competing phenomena, the fluorination of the GaAs surface and the nucleation of the metallic W films taking place simultaneously explain the difficulty in controlling the process. The Auger profiles show limited, but noticeable, As incorporation in the films resulting from the interaction between WF6 and GaAs under laser irradiation.