Microcrystalline Silicon by DC Magnetron Sputtering: Growth Mechanisms
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MICROCRYSTALLINE SILICON BY DC MAGNETRON SPUTrERING: GROWTH MECHANISMS G.F. Feng*, M. Katiyar, Y.H. Yang, J.R. Abelson, and N. Maley Coordinated Science Laboratory and Department of Materials Science and Engineering, University of Illinois, Urbana, IL 61801. ABSTRACT We have used real-time, in situ spectroscopic ellipsometry (SE) and infrared reflectance (IR) to study microcrystalline silicon (ptc-Si) formation in reactive magnetron sputtering (RMS). g.c-Si growth occurs at high hydrogen partial pressures and moderate substrate temperatures. We use IR studies and SE studies of film growth on rough surfaces, respectively, to show that these conditions lead to high hydrogen coverage of the film surface and high effective surface diffusivity. The interface region is amorphous and its thickness decreases with deposition rate. For a fixed growth flux, we observe a 30% decrease in the deposition rate of pgc-Si relative to the amorphous interface region.
This could be due to increased etching or decreased sticking
coefficients during microcrystalline growth.
I. INTRODUCTION Microcrystalline silicon (p.c-Si) thin films have been used in amorphous silicon (a-Si:H) based solar cells and have been actively investigated for thin film transistor materials in flat panel displays.l• The formation of gtc-Si by glow discharge plasma deposition has been extensively studied, and several mechanisms have been proposed, including hydrogen enhanced surface
diffusion 3 , weak-bond etching by hydrogen 4.5 , and sub-surface chemical annealing 6 . In last few years several groups, including ours, have reported g.c-Si growth by reactive magnetron sputtering (RMS). 7 -11 However, little is known about microcrystalline formation during magnetron sputtering. Here, we describe studies aimed at understanding pgc-Si formation in RMS using real-time, in situ spectroscopic ellipsometry (SE) and infrared reflectance.
II. EXPERIMENT Films were deposited in a dc magnetron sputtering chamber equipped with real-time in 12 In addition to commonly used substrate situ SE and IR reflectance, as previously described.
materials (Coming 7059 glass, c-Si), we used multilayer, absorption-enhancing substrates for IR reflectance,
13
and evaporated Cr films with controlled surface roughness for surface diffusivity
studies.
Present address: Applied Display Technology, Applied Materials Inc., 3050
Bowers Ave. Santa Clara, CA 95054 Mat. Res. Soc. Symp. Proc. Vol. 283. 01993 Materials Research Society
502
In a recent study, 11 we have shown that p.c-Si growth by RMS occurs at high hydrogen partial pressures, P(H 2 ) above 4 mTorr, and in a narrow substrate temperature range, Ts between 150 - 300 'C. Using real time in situ ellipsometry, we have also observed an amorphous layer at the film-substrate interface. The thickness of the interface layer depends on the substrate surface, and it decreases with film deposition rate. III. RESULTS We have carried out two sets of experiments to elucidate: (1) the effects of substrate temperature on surface hydrogen cover
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