Exploring the plasma chemistry in microwave chemical vapor deposition of diamond from C/H/O gas mixtures.
Exploring the plasma chemistry in microwave chemical vapor deposition of diamond from C/H/O gas mixtures.
复制标题
DOI：
10.1021/jp306190n
复制
发表时间：
2012-09
期刊：
影响因子：
--
通讯作者：
Mark Kelly;James C. Richley;C. Western;M. Ashfold;Y. Mankelevich
中科院分区：
文献类型：
--
作者：
Mark Kelly;James C. Richley;C. Western;M. Ashfold;Y. Mankelevich
微波（MW）激活的CH（4）/CO（2）/H（2）气体混合物在与金刚石化学气相沉积相关的条件下操作（即，X（C/O2）= X（elem）（C）/（X（elem）（C）+ X（elem）（O））= 0.5，H（2）摩尔分数= 0.3，压力p = 150 Torr，输入功率P = 1 kW）已通过空间分辨吸收测量的组合被详细探索（CH，C（2）（a），和OH自由基和H（n = 2）原子）内的热等离子体区域和同伴2维建模的等离子体。CO和H（2）被确定为等离子体核心中的优势物种。这种混合物的较低导热率（参见图1）。在大多数金刚石化学气相沉积中使用的富H（2）等离子体）解释了以下发现：CH（4）/CO（2）/H（2）等离子体可以在比传统CH（4）/H（2）等离子体更低的输入功率下产生类似的最大气体温度和金刚石生长速率。通过比较CH（4）/CO（2）/H（2）（X（C/CH 3）= 0.5）和CO/H（2）等离子体，可以看出等离子体化学和组成在从富氧（X（C/CH 3）0.5）源气体混合物改变时切换，与C/H工艺气体混合物相比，对源气体的选择敏感（由于不同的主要气体活化机制）。CH（3）自由基被鉴定为在用于成功金刚石生长的工艺窗口内生长金刚石表面附近最丰富的C（1）H（x）[x = 0-3]物质（X（C/H）= 0.5-0.54），其由Bachmann等人（Diamond Relat. 1991，1，1）。这一点，以及与MW活化的C/H等离子体中发现的那些相似的最大气体温度（T（气体）~2800-3000 K）和H原子摩尔分数（X（H）~5-10%）的发现，指出在C/H和C/H/O等离子体中类似的基于CH（3）自由基的金刚石生长机制的普遍性。
Microwave (MW)-activated CH(4)/CO(2)/H(2) gas mixtures operating under conditions relevant to diamond chemical vapor deposition (i.e., X(C/Σ) = X(elem)(C)/(X(elem)(C) + X(elem)(O)) ≈ 0.5, H(2) 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, C(2)(a), and OH radicals and H(n = 2) atoms) within the hot plasma region and companion 2-dimensional modeling of the plasma. CO and H(2) are identified as the dominant species in the plasma core. The lower thermal conductivity of such a mixture (cf. the H(2)-rich plasmas used in most diamond chemical vapor deposition) accounts for the finding that CH(4)/CO(2)/H(2) plasmas can yield similar maximal gas temperatures and diamond growth rates at lower input powers than traditional CH(4)/H(2) plasmas. The plasma chemistry and composition is seen to switch upon changing from oxygen-rich (X(C/Σ) 0.5) source gas mixtures and, by comparing CH(4)/CO(2)/H(2) (X(C/Σ) = 0.5) and CO/H(2) 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. CH(3) radicals are identified as the most abundant C(1)H(x) [x = 0-3] species near the growing diamond surface within the process window for successful diamond growth (X(C/Σ) ≈ 0.5-0.54) identified by Bachmann et al. (Diamond Relat. Mater.1991, 1, 1). This, and the findings of similar maximal gas temperatures (T(gas) ~2800-3000 K) and H atom mole fractions (X(H)~5-10%) to those found in MW-activated C/H plasmas, points to the prevalence of similar CH(3) radical based diamond growth mechanisms in both C/H and C/H/O plasmas.