In Situ Diagnostics of Methane/Hydrogen Plasma Interactions with Si(100)
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ABSTRACT
Methane/hydrogen plasmas have been reported to be sources both for a-C:H film deposition and for compound semiconductor etching. In this work, an in situ diagnostic study of methane/hydrogen plasma interactions with a silicon surface is carried out, focusing on the effect of hydrogen dilution. A remote electron cyclotron resonance (ECR) plasma using a H2/Ar
mixture excites methane gas near a Si(l 00) substrate. In situ multiple internal reflection Fourier transform infrared (MIR-FTIR) spectroscopy is used to probe the surface species at different hydrogen dilution ratios. We find that at low methane pressure without hydrogen dilution, a-C:H films are deposited. With H 2 dilution, the results suggests that some sputter/etching of the silicon surface occurs. Hence, methyl groups are identified as potential etchants for silicon materials. The data suggest that there is a competition between etching and deposition chemistry which depends strongly upon the methane pressure and hydrogen ratio in the plasma. INTRODUCTION Plasma processing plays a key role in semiconductor device fabrication, with plasma reactors accounting for approximately 30% of all process equipment in a typical wafer fabrication facility [1,2] The increasing demands placed on the development of plasma technology strongly motivates a better scientific understanding of the interaction of plasmas with solid surfaces. In situ studies of plasma-surface interactions are particularly important in this regard. Although model studies of well-defined and well-characterized surfaces reveal important information, the lower pressures (-~10-10 Torr) commonly used in such studies is a significant departure from typical plasma reactor conditions (namely mTorr-Torr), and hence the chemistry may be altered. On the other hand, most standard surface analytical techniques which provide molecular level detail in UHV cannot be applied under the higher pressures. Fortunately, optical methods provide an important exception to this rule. Using optical spectroscopies, surface and gaseous intermediates can be probed in a plasma environment [3]. Multiple internal reflection Fourier transform infrared (MIR-FTIR) spectroscopy has proven to be a powerful technique for monitoring the surface during plasma-surface interactions [4-6]. In this study, we use MIR-FTIR spectroscopy to investigate methane/hydrogen plasma interactions with Si(1 00), a system which has been studied extensively by other techniques in the context of a-C:H or diamond film deposition [7-11 ]. Previous studies have looked at issues such as deposition rate, mechanical and optical properties of deposited films, and the early stages of growth [7-11]. Less is known about the mechanisms and reaction pathways of the plasmasurface interaction Furthermore, there is still debate over the processes occurring during initial stages of a-C:H and diamond deposition. For example, recent hot-wire chemical vapor deposition studies indicate that some etching of silicon occurs during the initial nucleation stage of the de
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