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 (approx imately 1 J/cm2) laser fluence. The recorded spectra have line and ban d structures, which originate from both W atoms and W ions produced af ter 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 s cattered laser light increased significantly. This is explained by W c luster formation in the gas phase which was facilitated by the presenc e of H-2. The intensity of a characteristic W line was measured for di fferent total pressures and different WF6 partial pressures for the WF 6/Ar mixture. Two linear regimes could be observed in both the pressur e 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 yiel ded such a high W concentration in the vapour that W clusters were nuc leated. The intensity of a characteristic W line had a strong nonlinea r dependence on the laser fluence. Model calculation was performed to explain this nonlinearity and the agreement with the experimental resu lts was good.