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HYDROGEN CONFIGURATIONS IN MICROCRYSTALLIZED SPUTTERED AMORPHOUS SILICON. L.LUSSON, P. ELKAIM, M. CUNIOT, D. BALLUTAUD, R. RIZK* and J. DIXMIER, Laboratoire de Physique des Solides, CNRS, I Place Aristide Briand, 92195 Meudon Cedex (France). LERMAT, ISMRA, 6 Boulevard du Mardchal Juin, 14050 CAEN Cedex. ABSTRACT Successive deuterium diffusion and effusion experiments are performed on undoped microcrystalline silicon obtained from thermally crystallized sputtered amorphous silicon thin films. The effect of prior incorporation of deuterium during the amorphous film growth on the crystallization mechanism and on the microcrystalline film quality is probed by the use of the post hydrogenation procedure. In connection with the deuterium solubility as provided by secondary ion mass spectroscopy (SIMS) profiling, the analysis of the effusion spectra suggests the existence of large cavities in the crystallized a-Si:D films, containing most probably molecular hydrogen. They are absent in the corresponding crystallized non-deuterated a-Si films. Other deuterium configurations seem to be present in both kinds of samples such as weakly bonded deuterium in small clusters and at grain boundaries. INTRODUCTION Due to a higher carrier mobility, polysilicon thin film transistors (TFT) are expected to replace their amorphous counterparts in some electronic devices [1]. A usual way of preparing polysilicon thin films consists in the crystallization of hydrogenated (deuterated) amorphous silicon deposits. While the incorporation of hydrogen during amorphous silicon growth, as well as the post hydrogenation of polysilicon [2], have been shown to improve in both cases the electronic properties of the films, the presence of hydrogen in the original amorphous layer seems to compromise the quality of the microcrystallized material. In order to provide further information on the role of hydrogen in the crystallization, we report in this paper results obtained from successive deuterium diffusion and effusion experiments performed on microcrystalline silicon films prepared by thermal crystallization of deuterated or not deuterated sputtered amorphous silicon layers. EXPERIMENTAL Undoped amorphous silicon was deposited by RF sputtering on highly resistive silicon, using either pure argon (Ar) or a mixture of Ar + 15% D2 to produce a-Si or a-Si:D respectively. The substrate temperature T8 was equal to either 130"C or 250"C and the thicknesses of the layers were in the range 1 - 2 pm. Effusion spectra were measured by a quadrupole mass spectrometer coupled to an evacuated quartz tube (10-1o mbar) which contained the deuterated samples of same surface (1 cm2) submitted to a linear heating rate of 20 K/min between room temperature and 800- 1000"C. The post-deuteration was performed by RF plasma (pressure of I mbar, 0.12 W/cm" 2) during 15 min at 150'C and the deuterium profiles were obtained by Secondary Ion Mass Spectroscopy (SIMS) using a CAMECA IMS4f apparatus. The primary ion was Cs' and the absolute concentration was determined by calibration