Origin of the Laser-Induced Broad Band Luminescence from a WF 6 /H 2 /Ar Gas Mixture
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Origin of the Laser-Induced Broad Band Luminescence from a WFSH/Ar Gas Mixture P. Heszler*, P. Mogyor6si, J.O. Carlsson Thin Film and Surface Chemistry Group, Department of Chemistry, Uppsala University, Box 531, S-751 21 Uppsala, Sweden
Abstract The origin of the ArF excimer laser induced luminescence from a WFJH/Ar gas mixture was investigated. The experiments prove that the emission originates from excited W clusters with a size of about 10-20 nm. The influence of the H2 and Ar concentrations, the laser fluence and the repetition rate on the light intensity was studied.
Introduction A photolytic deposition process combines photochemical and chemical reaction steps occurring in the vapour as well as on the growing surface. In this investigation the experiments were designed in such a way that the photochemistry was induced in the vapour above the substrate surface. By separating the two reaction regions vapour and substrate/vapour interface, respectively, a deeper understanding of the growth mechanism and possibilities to control the growth process may be obtained. Optical spectroscopy has been used in this work to study the gas-phase photochemistry induced in a WF 6/H/JAr gas mixture by an ArF excimer laser. Luminescent light has been observed and explained by plasma formation during pyrolytic W deposition using Ar ion laser [1]. However, as far as the authors know this is the first optical spectroscopic study of this system.
Experimental The beam of an ArF laser, operating at the wavelength of 193 nm (FWHM 17 ns), entered through a quartz window a stainless steel reaction chamber, which was of the cold-wall type. The laser fluence was _ 0.1 J/cm 2. To avoid deposition on the window it was purged with Ar during the experiments. The experiments were performed at room temperature. The spectroscopic measurements were performed perpendicular to the laser beam. The emitted light was filtered using a glass plate to prevent the detector from the strong scattered UV laser light. Then the light was coupled into a quartz optical fibre which was connected to a 0.3 m long f/3.8 spectrograph equipped with an entrance slit of 25 [m. The grating used was 150 1/mm, blazed for 500 nm. The light was characterized by an EG&G OMA III (Optical Multichanel Analyzer) diode array. The exposure time of the detector was 2 s, the laser repetition rate was 25 Hz. The intensity values of the registered spectra were not corrected for the sensitivity of the detector. A mixture of WF 6, H2, and Ar was used for the experiments. The purities of the gases were 99.998%, 99.9999%, and 99.9997%, respectively.
" On leave from
the Research Group of Laser Physics of the Hungarian Academy of Sciences, Szeged, Hungary
Mat. Res. Soc. Symp. Proc. Vol. 236. ©1992 Materials Research Society
124
Results and Discussion The spectrum recorded during laser irradiation of a WF 6/H2/Ar 1:10:200 in an open CVD system is shown in Fig. 1.
4W0
Wavelength [nm] Fig. 1. Spectrum recorded from an excited WF 6/H2 /Ar gas mixture. The total pressure was 4 mbar.
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