Exploring the Plasma Chemistry in Microwave Chemical Vapor Deposition of Diamond from C/H/O Gas Mixtures
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- 作者：Mark W. Kelly ; James C. Richley ; Colin M. Western ; Michael N. R. Ashfold ; Yuri A. Mankelevich
- 刊名：The Journal of Physical Chemistry A
- 出版年：2012
- 出版时间：September 27, 2012
- 年：2012
- 卷：116
- 期：38
- 页码：9431-9446
- 全文大小：740K
- 年卷期：v.116,no.38(September 27, 2012)
- ISSN：1520-5215
文摘
Microwave (MW)-activated CH4/CO2/H2 gas mixtures operating under conditions relevant to diamond chemical vapor deposition (i.e., XC/危 = Xelem(C)/(Xelem(C) + Xelem(O)) 鈮?0.5, H2 mole fraction = 0.3, pressure, p = 150 Torr, and input power, P = 1 kW) have been explored in detail by a combination of spatially resolved absorption measurements (of CH, C2(a), and OH radicals and H(n = 2) atoms) within the hot plasma region and companion 2-dimensional modeling of the plasma. CO and H2 are identified as the dominant species in the plasma core. The lower thermal conductivity of such a mixture (cf. the H2-rich plasmas used in most diamond chemical vapor deposition) accounts for the finding that CH4/CO2/H2 plasmas can yield similar maximal gas temperatures and diamond growth rates at lower input powers than traditional CH4/H2 plasmas. The plasma chemistry and composition is seen to switch upon changing from oxygen-rich (XC/危 < 0.5) to carbon-rich (XC/危 > 0.5) source gas mixtures and, by comparing CH4/CO2/H2 (XC/危 = 0.5) and CO/H2 plasmas, to be sensitive to the choice of source gas (by virtue of the different prevailing gas activation mechanisms), in contrast to C/H process gas mixtures. CH3 radicals are identified as the most abundant C1Hx [x = 0鈥?] species near the growing diamond surface within the process window for successful diamond growth (XC/危 鈮?0.5鈥?.54) identified by Bachmann et al. (Diamond Relat. Mater.1991, 1, 1). This, and the findings of similar maximal gas temperatures (Tgas 2800鈥?000 K) and H atom mole fractions (X(H)5鈥?0%) to those found in MW-activated C/H plasmas, points to the prevalence of similar CH3 radical based diamond growth mechanisms in both C/H and C/H/O plasmas.