Time resolved spectroscopy of the emission of fluorescent light upon UV laser assisted CVD of W from WF 6

Abstract

Time resolved spectroscopy of ArF excimer laser excited WF 6/H 2/Ar and WF 6/Ar gas mixtures during LCVD of W has been performed with a time resolution of 20 and 5 ns, respectively. Using a high laser energy density (∼J/cm 2 and a WF 6/Ar gas mixture, the recorded spectra have both line and band structures which originate from W atoms and W ions. The spectral intensity distribution followed the shape of the laser pulse (FWHM≈20 ns). This means that the lifetime of the excited states is much shorter than that of the laser pulse duration. A broad band emission spectrum was obtained from a WF 6/H 2/Ar gas mixture at a laser energy density of ∼100 mJ/cm 2. This originates from excited W clusters produced in the gas phase. Time resolved measurements of this radiation showed that the spectral intensity distribution did not change with time. This indicates that the emission process cannot be black body radiation. The time dependence of the intensity of the fluorescent light could be separated into two parts: a fast decay (life time ∼400 ns) and a slow decay (∼5.7μs). The fast decay was explained in terms of vibrational quenching. The slow decay was assumed to be due to the spontaneous lifetime of excited states of the W clusters.