Surface Spectroscopic Studies of the Initial Stages of Diamond Growth on Si(100)
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SURFACE SPECTROSCOPIC STUDIES OF THE INITIAL STAGES OF DIAMOND GROWTH ON Si(100) RICHARD B. JACKMAN%, LYE HING CHUA* and JOHN S. FOORD** *Electronic and Electrical Engineering, University College London,
Torrington Place, London, WClE 7JE, UK "**Physical Chemistry Laboratory, University of Oxford, South Parks Road, Oxford, OXI 3QZ, UK
ABSTRACT The interaction of hot filament "activated" methane and hydrogen with Si(100) surfaces has been probed in situ for the first time, using Auger electron and thermal desorption spectroscopies. It is shown that hot filament activation of methane results in the
chemisorption of acetylene and ethylene on Si (100). Atomic hydrogen drives a range of surface reactions within the adsorbed phases formed. In particular hydrogen abstraction is observed which results in the efficient conversion of ethylene to adsorbed
acetylene, and further reactions take place between atomic hydrogen, acetylene and C1 species, resulting in the formation of C3 hydrocarbon species. The implications of this work for diamond film growth are considered, and the results are used to develop a model to describe the growth of sp 3 hybridised hydrocarbon chains on the Si surface.
1. INTRODUCTION Impressive progress over the last five years has been made in the development of low pressure CVD processes for thin film diamond growth [1,2]. Particular attention has
now begun to focus on understanding the underlying growth mechanisms, since it is important to identify the factors which are at present limiting the quality of the films produced [3]. Although there has been considerable speculation concerning the reaction mechanisms [4-9], no direct experimental observations on the surface chemistry involved at a molecular level have yet been reported. It is very clear from the extensive literature that numerous detailed reaction models can be suggested, which are
chemically feasible and consistent with the extensive macroscopic data available on diamond film growth. Identification of the actual reaction mechanisms does not appear to be possible however without further experimental study of the surface chemistry giving rise to thin film formation at a molecular level. We have therefore initiated such a study and in this paper report results for the very first stage of hot filament diamond growth, namely the interaction of "hot filament" activated methane/hydrogen mixtures with a clean Si (100) surface.
2. EXPERIMENTAL METHODS All experiments were carried out inside a stainless steel ultra-high vacuum (UHV) chamber equipped with a four grid retarding field analyser, used for low energy electron diffraction (LEED) and Auger electron spectroscopy (AES), and a 1-300amu quadrupole mass spectrometer for thermal desorption spectroscopy (TDS). The Si(100) wafer (P doped, ca. 5 Q cm) was cleaned by annealing in vacuo at
temperatures up to 1500K to generate an atomically clean and ordered Si(100)(2xl) surface as verified by LEED and AES. TDS was achieved using a linear heating rate of 40Ks- 1 . Methane and hydrogen gas (Ai
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