206 Applied Surface Science 46 (1990) 206-209 North-Holland Gas mixture dependence of the LCVD of SiO, films using an ArF laser T. Szijr&yi *, P. Gonzhlez, D. Fernhdez, J. Pou, B. Le6n and M. PCrez-Amor Departamen~o F&a Aplicada. zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Uniuer.sity of Vigo. P.O. Box 6-7, 36280 V~go, Spain Received 29 May 1990: accepted for publication 1 June 1990 Large-area silica films have been deposited on silicon wafers using silane. nitrous oxide and argon gas mixtures zyxwvutsrqponml and an ArF excimer laser in parallel configuration. An exhaustive study has been carried out on the role of the total and partial pressure of the various components of the gas mixture on the growth and the properties of silica films. Films are characterized by FT-IR spectroscopy and ellipsometry. 1. Introduction Microelectronic industry demands high-quality silica films as interlayer for multilevel metalliza- tion and as passivation layer, which ought to be deposited at low temperatures to minimize wafer warpage, doping profile redistribution and to make this processing step compatible to metallization steps based on aluminium and especially gold. For these purposes, among other low-temperature SiO, deposition techniques laser-induced CVD in paral- lel configuration may be a good candidate [l-4] since there is no interaction between the laser beam and the substrate (no photon impingement on the substrate). In this paper, SiH, and N,O have been used as reactants gases, with argon as window purging gas. Literature values of the ab- sorption cross sections of the precursors at X = 193 nm [5-71, allow as the fundamental processes to propose the photo-decomposition of the nitrous oxide and monosilane molecules and further radi- cal reaction yielding silicon oxide on the heated substrate. * Permanent address: Research Group on Laser Physics H- 6720, Szeged, D6m T&r 9. Hungary. 2. Experimental The experiments were conducted in a LCVD system consisting of an ArF excimer laser (h = 193 nm. maximum pulse energy of 250 mJ), a reaction chamber connected to the vacuum and gas supply system and several optical elements as shown in fig. 1. Substrates were single-crystal silicon wafers placed horizontally on a temperature-controlled sample holder zyxwvutsrqponmlkjihgfedcbaZYXWVU (T = 250” C), allowing the laser beam to pass parallel above the substrate surface at variable distance. The gas flows (UHP elec- tronic grade) were adjusted by electronic mass flow controllers and the total pressure was mea- sured by a capacitance manometer. Characteriza- tion of the samples was done by ellipsometry (thickness and refractive index) and transmission Fourier Transform IR spectroscopy. 3. Results A strong dependence of growth rate and film properties on nitrous oxide and silane partial pres- sure was found. In order to study this aspect. a series of samples was processed by changing the N,O flow rate and adjusting the total pressure to 0169-4332/90/$03.50 8 1990 - Elsevier Science Publishers B.V. (North-Holland)