Hydrogenated Amorphous Silicon Thin-Film Deposition by Direct Photo-Enhanced Decomposition of Silane Using an Internal H
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HYDROGENATED AMORPHOUS SILICON THIN-FILM DEPOSITION BY DIRECT PHOTO-ENHANCED DECOMPOSITION OF SILANE USING AN INTERNAL HYDROGEN DISCHARGE LAMP.
P.A. ROBERTSON AND W.I. MILNE Cambridge University Engineering Department, Trumpington Street, Cambridge CB2 1PZ, England. ABSTRACT Hydrogenated amorphous silicon (a-Si:H) thin films have been deposited The from silane using a novel photo-enhanced decomposition technique. system comprises a hydrogen discharge lamp contained within the reaction this unified approach allows high energy photon excitation of the vessel; silane molecules without absorption by window materials or the need for The film growth rates (exceeding 4 R/s) and mercury sensitisation. material properties obtained are comparable to those of films produced by The reduction of energetic charged plasma-enhanced CVD techniques. particles in the film growth region should enable the fabrication of cleaner semiconductor/insulator interfaces in thin-film transistors.
INTRODUCTION Until recently, the photochemical deposition of a-Si:H has either required mercury sensitisation [1,21 and/or the use of a high power UV lamp The deposition rates are low due to the [3j outside the reaction vessel. absorption of the UV radiation by the window material and the coating of The effect of this is a-Si:H which tends to form on its inner surface. less severe when using disilane as the reaction gas [4,5], since the lower energy UV light required for decomposition suffers less attenuation. However, in our opinion none of these techniques are suited to the growth of thick a-Si:H films or continuous deposition processes which may be required for a production line. A unified deposition system was recently demonstrated by Tarui et al. However, [6] using an argon discharge lamp within the reaction vessel. significantly lower the deposition rates obtained (n 0.2 R/s) were still than the typical value for plasma-enhanced CVD (% 4 R/s) [7]. This paper describes the electrical and optical properties of a-Si:H films deposited using a novel system, incorporating a low power hydrogen The absence of any window discharge lamp within the reaction chamber. material obviates the UV light attenuation problems experienced with an external lamp and deposition rates exceeding 4 R/s have been achieved with Our preliminary results indicate that the electrical and this method. optical properties of a-Si:H films grown are comparable to those of films produced by plasma-enhanced CVD.
EXPERIMENTAL Deposition System The deposition system comprises a low power hydrogen discharge lamp Hydrogen is contained within a recess in the vacuum vessel top plate. admitted to the chamber through an inlet tube between the lamp electrodes. The hydrogen discharge produces short wavelength UV radiation (< 125 nm) The substrates rest on a which couples directly into the silane molecules. heated carrier plate, close to a feed pipe which introduces undiluted silane into the vessel.
Mat. Res. Soc. Symp. Proc. Vol. 70.
1986 Materials Retsearch Society
32
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