Deuterium Incorporation into Glow-Discharge Deposited Deuterated-Hydrogenated Amorphous Silicon
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DEUTERATED-HYDROGENATED AMORPHOUS SILICON
L. S. Sidhu, F. Gaspari, S. K. O'Leary, and S. Zukotynski Department of Electrical and Computer Engineering, University of Toronto, Toronto, Ontario, Canada M5S 1A4.
ABSTRACT We investigate deuterium incorporation into deuterated-hydrogenated amorphous silicon grown by the saddle-field glow-discharge of deuterium and silane. The presence of HD and SiH3 D in the discharge suggests strong gas phase mixing. The dominant process of deuterium incorporation into the growing film appears to be the direct reaction between deuterium and the growth surface.
INTRODUCTION High quality hydrogenated amorphous silicon (a-Si:H) may be prepared by the glowdischarge decomposition of silane [1][2]. This deposition technique involves the generation of radicals through the dissociation of silane, followed by radical diffusion and reaction processes with the growth surface. To further improve this deposition process, a detailed understanding of the growth mechanisms are desired. While much has been done [1-31, there are still many aspects which are not fully understood. In particular, there are questions regarding the mechanism of hydrogen incorporation into the growing film. Is it through direct interaction between hydrogen in the plasma and the growing film or is hydrogen introduced into the film in the form of silane radicals? In this paper, we present the results of an isotopic study of the glow-discharge growth of deuterated-hydrogenated amorphous silicon. In particular, the hydrogen isotope deuterium is used to identify the species present in both plasma and film. We do this by performing mass spectrometry on the plasma, followed by infrared (IR) spectroscopy and secondary ion mass spectrometry (SIMS) on the deposited films.
EXPERIMENT To produce the plasma, a mixture of silane and molecular deuterium was allowed to flow through the growth chamber at constant rates. These gases were dissociated in a dc glowdischarge, excited using the saddle-field electrode configuration [4]. A VG 300 plasma sampling quadropole mass spectrometer, operated in the neutral mode, was used to monitor the plasma. Films were grown on 10 Qcm p-type silicon wafers (Czochralski grown, (100) orientation, with both sides polished), mounted on a heated and electrically grounded substrate holder, exposed to the plasma at steady state. Infrared spectra of the deposited films were taken in the range 3504000 cm1, using a Perkin Elmer 2000 Fourier transform infrared spectrometer, purged with dry air. A silicon substrate was used as a reference for these IR measurements. SIMS analysis of the films was performed using a Cameca IMS 3f. Table I summarizes the preparation conditions of our deuterated films. To help resolve the influence of deuterium on both plasma and film, we also grew films under identical conditions, but with hydrogen replacing deuterium in the gas mixture.
87 Mat. Res. Soc. Symp. Proc. Vol. 377 ©1995 Materials Research Society
Table I. Summary of the preparation conditions. The deposition temperatures
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