Phosphorescence from tungsten clusters during laser-assisted chemical-vapor deposition of tungsten

Abstract

Phosphorescent light emission was investigated upon irradiation of WF6/H2/noble gas (Ar, Kr, Ne, Xe) mixtures by ArF excimer laser. The continuous, broadband phosphorescence emission originates from excited tungsten clusters. The phosphorescence ceased with increased Xe and H2 concentrations. Xe inhibits the formation of tungsten clusters and H2 quenches the phosphorescence. The H2 quenching rate and the unperturbed phosphorescence lifetime were determined to be 2.8×104 mbar−1 s−1 and 23 μs, respectively. The intensity dependence of phosphorescence on the WF6 partial pressure shows a rising part, then a declining part, and finally an increasing part again. It was shown that the declining part can be interpreted by scattering of the emitted phosphorescence. The phosphorescence intensity was dependent on the noble gas/H2 concentration ratio. This effect was explained in terms of the thermal conductivity of the WF6/H2/noble gas mixture, which influences the lifetime of the activated subfluorides and, thus, the cluster formation and growth rate. The intensity of the laser beam had a nonlinear effect on the phosphorescent light intensity due to the nonlinearly coupled photolytical steps of WF6 and of the subfluorides.