SURFACE CHARACTERIZATION OF EXCIMER-LASER INDUCED DEPOSITION OF W ON GAAS FROM WF6 AND H-2

Deposition of W thin films has been induced by a KrF excimer laser inc ident perpendicularly on a GaAs substrate placed in an ambient contain ing WF6, H-2 and Ar. In-situ X-Ray Photoelectron Spectroscopy (XPS) sh ows evidence of a surface interaction between WF6 and GaAs under laser irradiation. At 50 mJ/cm(2), fluorinated W species absorbed on the Ga As substrate are partially dissociated by the laser beam, leading to a loss in stoichiometry and the formation of GaF3 on the surface. The g eneration of stable, nonvolatile, GaF3 has been identified as a possib le obstacle to the nucleation of metallic tungsten films on GaAs in CV D processes using WF6. At 67 mJ/cm(2), the gas-substrate interaction i s further enhanced, but the dissociation of WF6 into metallic W is ach ieved. However, at such laser energy densities, the substrate appears to be damaged. By using H-2 as a reducing gas for WF6, 0.2 mu m thick W deposits were obtained by the process was difficult to reproduce. Tw o competing phenomena, the fluorination of the GaAs surface and the nu cleation of the metallic W films taking place simultaneously explain t he difficulty in controlling the process. The Auger profiles show limi ted, but noticeable, As incorporation in the films resulting from the interaction between WF6 and GaAs under laser irradiation.