The Effect of Metal Atoms and Ligand Combinations in Organometallics on Excimer Laser Photoproducts and Yields
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The Effect of Metal Atoms and Ligand Combinations in Organometallics on Excimer Laser Photoproducts and Yields Y. Zhang and M. Stuke Max-Planck-Institut fir biophysikalische Chemie Postfach 2841, D-3400 Gdttingen, F.R. Germany ABSTRACT A systematic study to find the role of different metal atoms and ligand combinations on the yield of the photoproducts generated upon irradiation of gas phase organometallics (i.e. metalalkyls) by uv excimer laser radiation was performed using laser ionization mass spectrometry. INTRODUCTION In laser induced chemical vapor deposition (laser-CVD), various volatile organometallics have been used as precursors of metals [1,2]. Different organometallics for a given metal have been studied to reduce carbon incorporation that results in poor conductors and to give highly conductive metal films. Recent experiments [3,4] demonstrated that replacing trimethylaluminum (TMA) [5] by dimethylaluminumhydride (DMAH) can improve the conductivity of deposited aluminum films. Triisobutylaluminum (TIBA) [1] was found to give highly conductive aluminum films, but TIBA has a low vapor pressure. Fig. 1(a) shows the resistivity of the deposited conductors made from TMA, DMAH and TIBA, respectively. The explanation of this relation is unknwon and carbon incorporation from organic ligands has been mentioned without giving any details. For this, a systematic study was performed to find the role that different metal atoms and ligand combinations have on the yield of photoproducts generated upon irradiation of gas phase organometallics by uv excimer laser radiation.
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TMA
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TMA
DMAH
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Fig. 1: (a) The resistivity of the aluminum films made from TMA [5], DMAH [3,4] and TIBA [II with Laser-CVD processes, where the dashed line indicates that of bulk aluminum [4]; (b) The distribution of the AlCH3/AI yields from ArF laser dissociation of TMA, DMAH and TIBA, respectively. Mat. Res. Soc. Symp. Proc. Vol. 131. '1989 Materials Research Society
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EXPERIMENT The technique used for analysis is laser photoionization mass spectrometry [6]. The main system studied is the isolated gas phase metal-alkyls [7] of the Al, Ga and Te series with different ligands (CH3, C2H5 and i-C4H9) and ligand combinations (CH3, H and Cl) under collision-free conditions (10-6-10-5 mbar), since most of them have widely been used in Laser-CVD processes (see Ref.[1-6]). The laser system used for photolysis is a uv excimer laser (ArF at 193 nm, KrF at 248 nm and XeCI at 308 nm) at 0.1- 10 mJ/cm 2 . RESULTS 1.Detection of photoproducts: In order to understand carbon incorporation in the metal film grown in laser-CVD processes. it is neccessary to find out the photofragments produced from uv laser dissociation of organometallics in detail. Using laser photoionization mass spectrometry, neutral photofragments can not only be detected directly by a single shot of the probe laser in the time-of-flight (TOF) mass spectrum [8,9], but also be identified by the mul
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