UV Photon-Assisted Refractory Metal Deposition
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UV PHOTON-ASSISTED REFRACTORY METAL DEPOSITION G. A. KOVALL,"* J. C. MATTHEWS,* and R. SOLANKI**
Corporation, Rockville, MD20855 "Fusion Systems ** Department of Applied Physics and Electrical Engineering, Oregon Graduate
Center, Beaverton, OR 97006-1999 ABSTRACT We have been investigating deposition of tungsten and molybdenum films at lover temperatures than conventional CVD processes with the aid of ultraviolet photons. The photon source is a high intensity, medium-pressure mercury lamp. V and Mo films have been deposited from their respective hexacarbonyls. W films have also been obtained by photon enhanced reduction of tungsten hexafluoride. In all cases films were deposited over 75 mm diameter substrates, which included quartz, silicon dioxide, and silicon wafers. The deposition system, conditions and the properties of the photodeposited films are presented. INTRODUCTION It is well recognized that the current trend in microelectronics towards increased device density and reduced feature size is placing stringent requirements on traditional electronic materials, especially those used for metallization. The most widely used materials for gates, interconnects and contacts have been aluminum and its alloys. However, to meet the demands of this current trend, tungsten and molybdenum have been investigated as alternatives to aluminum [1,2]. Besides thermal stability, these refractory metals have several advantages over aluminum, e.g. they have approximately the same thermal expansion coefficient as silicon, reduced contact resistance, absence of hillock formation, and are less susceptible to electromigration [3-6]. Below we present results of our investigation of depositing Mo and W films using a low temperature process which utilizes ultraviolet (UV) radiation. Several groups, including us, have previously reported Here we will photodeposition of refractory metals using UV lasers [7-11]. present our initial results of deposition of Mo and W, over 3 inch diameter substrates, using a mercury lamp. This report consists of the experimental procedure for this process and the properties of the films deposited. UV PHOTODEPOSITION UV photodeposition involves use of ultraviolet radiation to induce a photolytic reaction which results in deposition of a thin film. It is essential that at least a portion of the absorption spectrum (electron absorption band) of the parent gas overlaps the emission spectrum of the UV source, otherwise no detectable film will be deposited. The photochemical reactions that lead to the film deposition involve the reactant molecules in the gas phase, as well as adsorbed to the surface of the substrate. However, due to space limitations these mechanisms will not be discussed here. EXPERIMENTAL APPROACH We have examined several donor gases for photodeposition of Mo and W based on two criteria: relatively high vapor pressures and at least a partial overlap between their absorption spectra and our UV lamp. Here we Mat. Res. Soc. Symp. Proc. Vol. 75. t1987 Materials Research Society
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