Silicon Recrystallization in Sipos Material Obtained by Disilane
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ABSTRACT Conventional and Rapid Thermal Annealing of Semi-Insulating Polycrystalline Silicon layers obtained by Low Pressure Chemical Vapor Deposition (LPCVD) from disilane Si 2H6 have been performed in order to determine the structural
modifications induced on the layers by these thermal treatments. The study of these modifications has been carried out by several analysis methods like FTIR, XPS, TEM, RAMAN and ellipsometry. The results obtained are presented, contrasted and discussed in this work.
INTRODUCTION SIPOS (Semi Insulating POlycrystalline Silicon) is the generic name for a non-stoichiometric silicon oxide SiO,, with x varying between 0 and 2. Depending on the oxygen content of the material, its electrical properties vary between those of polycrystalline silicon (x=O) and those of silicon oxide (x =2). Thus, SIPOS has a wide range of technological applications like electrical passivation of high voltage planar devices [1,2,31, CMOS Integrated Circuits [4], emitters in heterojunction transistors or solar cells. SIPOS is typically obtained by LPCVD from silane SiH 4 and nitrous oxide N 20 [4,9,10,11] at temperatures between 600 and 650 0C. The oxygen content of the material obtained, and hence its conductivity, is then controlled by flux ratio -ys=Q(N 20)/Q(SiH 4) of the gas mixture fixed during the deposition process. However, this usual process presents obstacles like a deposition rate inhibited when -y.increases, or required temperatures of deposition being too high to be used in low thermal budget processes. An alternative recently studied to palliate these disadvantages is the use of disilane Si 2H 6 instead of silane [12]. Disilane has been found to allow higher deposition rates with lower thermal budgets. Similar results were found in the past for the deposition of in situ doped polysilicon [13]. The structural and physical properties of SIPOS layers are closely dependent of the oxygen content, the process and post-process parameters of these layers. A first study of the influence of rapid thermal annealing and conventional annealing of SIPOS layers obtained from disilane has been performed and recently published [13]. The results of this study are 351 Mat. Res. Soc. Symp. Proc. Vol. 403 01996 Materials Research Society
in agreement with a model previously proposed by other authors [14,15] for SIPOS deposited from silane. Nevertheless, up to now no studies of the kinetics of recrystallisation of SIPOS obtained from disilane have been reported. In the present paper, we report a study by TEM, RAMAN, FTIR and XPS of the
structural behaviour of SIPOS films obtained from disilane with different oxygen contents, after several times of rapid thermal annealing at 10501C. From the analysis of these results
we deduce the evolution of the structure of the material from the as-grown layers to the maximun crystallization.
EXPERIMENTAL PROCEDURE SIPOS layers were obtained by pyrolysis of a mix
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