Excimer Laser Photofragmentation of TMA on Aluminum: Identification of Photoproduct Desorption Dynamics
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EXCIMER LASER PHOTOFRAGMENTATION OF TMA ON ALUMINUM: IDENTIFICATION OF PHOTOPRODUCT DESORPTION DYNAMICS T.E. ORLOWSKI AND D.A. MANTELL Xerox Webster Research Center, 800 Phillips Rd., Webster, NY 14580 ABSTRACT New mechanistic details regarding aluminum deposition by ArF excimer laser photodecomposition of trimethylaluminum (TMA) adsorbed on aluminum covered SiO 2 /Si substrates have been obtained using a time-of-flight quadrupole mass spectrometer. CH3 radicals and AI-(CH3)n (n = 1,2,3) species are efficiently photoejected from the surface with up to 0.22 eV of translational energy. Experiments at various TMA dosing levels reveal differences in desorbed fragment translational energy presumably associated with variations in surface site binding energy. No direct evidence is found for desorption of Al from the surface indicating that Al is more tightly bound than methyl-aluminum fragments. By carefully monitoring changes in fragment translational energy as an Al deposit forms on the clean Si0 2/Si substrate, we examine how the surface influences the onset of Al growth. No evidence of ethane or methane desorption from the sample surface is found implying that radical recombination and hydrogen abstraction are primarily secondary gas phase reactions which are not surface initiated. INTRODUCTION Recognition of the potential impact of laser based techniques upon the processing of semiconductor materials for microelectronic devices has been increasing over the past several years. Among the advantages laser processing offers are high spatial resolution for maskless patterning, selective photochemistry through choice of photon energy and low temperature alternatives to conventional thermal processing1. A process of great technological importance and one investigated in many laboratories recently is the patterned laser photodecomposition of organometallics to deposit metals on various surfaces (for a review see Ref. 2). Although it is generally accepted that high spatial resolution requires the photodissociation reactions to be confined to surface species 3 , many fundamental mechanistic issues remain unresolved including the origin of carbon incorporation in the deposited metal film and the role of surface/adsorbate interactions in the photodecomposition process. In this study, we examine the photodecomposition of trimethylaluminum (TMA) adsorbed upon an aluminum covered SiO 2/Si substrate using a time-of-flight (TOF) mass spectroscopic technique. We identify products created on the surface during the photodecom position process and obtain fragment desorption dynamics under various processing conditions. Some new aspects of the role surface/adsorbate interactions play in the photodissociation process are discovered. EXPERIMENTS AND RESULTS The apparatus used to obtain photofragment time-of flight data is described 4 elsewhere. Sample substrates [Si, p-type, 8-12 ohm-cm, (100)] were oxidized at 1000 0C in dry 02 to create a thin (-300A) SiO 2 layer. After cooling, rinsing with deionized water and alcohol, they were mounted
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