LASER-INDUCED FLUORESCENCE SPECTROSCOPY OF WF6/M(M = H2, AR) GAS-MIXTURES DURING LCVD OF W AT A HIGH LASER ENERGY DENSITY

ArF excimer laser induced fluorescence spectroscopy has been performed for WF6, and for gas mixtures of WF6/H-2 and WF6/Ar at a high (approximately 1 J/cm2) laser fluence. The recorded spectra have line and band structures, which originate from both W atoms and W ions produced after photolysis of WF6. Light was also emitted for a wavelength shorter than the laser excitation wavelength. This was due to the excitation of and the emission from the W ions. There were no differences between the spectra obtained from pure WF6 and those obtained from the WF6/Ar mixture. However, using a WF6/H-2 gas mixture, the intensity of the scattered laser light increased significantly. This is explained by W cluster formation in the gas phase which was facilitated by the presence of H-2. The intensity of a characteristic W line was measured for different total pressures and different WF6 partial pressures for the WF6/Ar mixture. Two linear regimes could be observed in both the pressure dependence curves. For lower pressures (first part of the curve) the slope of the line was steep, while the second part (higher pressures) was less steep. This observation might be explained by the formation of W atoms in the vapour at low pressures, while higher pressures yielded such a high W concentration in the vapour that W clusters were nucleated. The intensity of a characteristic W line had a strong nonlinear dependence on the laser fluence. Model calculation was performed to explain this nonlinearity and the agreement with the experimental results was good.