In-Situ Mass Spectroscopy of ECR Silane Plasmas for Amorphous and Microcrystalline Silicon Growth
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In-Situ Mass Spectroscopy of ECR Silane Plasmas for Amorphous and Microcrystalline Silicon Growth Young J. Song, Elena Guliants, Hak-Gyu Lee, and Wayne A. Anderson State University of New York at Buffalo, Department of Electrical Engineering, Amherst, NY 14260, U.S.A. ABSTRACT ECR silane plasmas for the deposition of a-Si:H and µc-Si films were investigated by in-situ mass spectroscopy (MS) using a quadrupole residual gas analyzer. The results showed that the intensities of ionic and neutral species (H, H2, He, Ar, Si and SiHx) in the 2 % SiH4/He plasma are strongly dependent on the deposition conditions such as chamber pressure, input power and hydrogen dilution. In all cases, the prevalence of Si ions was observed over SiH, SiH2 and SiH3 ions, suggesting a high decomposition rate of the silane in the plasma. In particular, the population of atomic hydrogen in the plasma seems to play a key role in the properties of both aSi:H and µc-Si films. For example, the increased intensity of atomic hydrogen, compared to that of molecular hydrogen, resulted in the better quality a-Si:H film, showing a higher photo and dark conductivity ratio of ~105. The intensity of the hydrogen species was especially sensitive to the chamber pressure. The correlation between MS spectra and film properties is presented. INTRODUCTION a-Si:H and microcrystalline silicon (µc-Si) thin films grown by plasma-assisted decomposition of SiH4 have become an important material for large-area applications such as solar cells and thin film transistors [1,2]. To improve the quality and reproducibility of the material, an understanding of plasma kinetics and its correlation to the electro-optical properties is essential. Early research groups made efforts to characterize the SiH4 discharge using various techniques, for example optical emission spectroscopy [3], vibrational spectroscopy [4] and mass spectroscopy (MS) [3,5]. However, the above studies focused primarily on the standard rf-driven plasma enhanced chemical vapor deposition (PECVD), and there have been very few reports on the alterative growth technique like electron cyclotron resonance CVD (ECR-CVD), which utilizes a high-frequency power for plasma excitation at a lower pressure without electrodes. Since the plasma properties are sensitive to the growth environment, the ECR SiH4 plasma is believed to be quite different from the standard one. In this paper, we studied the ECR 2%SiH4/He plasma by in-situ MS using a residual gas analyzer (RGA). Various deposition parameters such as chamber pressure, input power, and hydrogen dilution ratio were explored to find the relationship between MS profile and film properties. Particularly, the relative distribution of atomic and molecular species including impurities will be emphasized during the analysis of the MS spectra. Optimal growth conditions for a better quality film will be discussed based on the role of deposition parameters on the MS data.
A5.4.1
EXPERIMENT Fig. 1 illustrates the experimental set-up for MS of ECR SiH4 plasmas. A quadrupole re
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