Chemical vapour deposition of silicon carbide by pyrolysis of methylchlorosilanes
Chemical vapour deposition of silicon carbide by pyrolysis of methylchlorosilanes
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甲基氯硅烷热解化学气相沉积碳化硅
DOI：
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发表时间：
1997
期刊：
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通讯作者：
D. Kim
中科院分区：
文献类型：
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作者：
B. Choi;Dong;D. Kim
通过化学气相沉积（CVD）制备的碳化硅（SiC）对于结构[1，2]和电子[3，4]应用仍然很重要。在输入气体成分、温度和压力的广泛变化的条件下，各种气态前体已用于SiC沉积[5]。对于SiC的CVD，通常，载气鼓泡通过与另一载气流混合的含硅液体。所需的碳或者包含在氯硅烷中，或者通过引入烃来提供。甲基氯硅烷（MTS：CH 3SiCl 3）作为前体，是最有用的可用氯硅烷之一，因为它含有化学计量比的硅和碳[6]。因此，已经预期得到化学计量的SiC沉积。最近，从MTS H2气体系统中SiC的CVD的热力学研究[7，8]中，已经表明SiC是在宽的温度、压力和反应物浓度范围内存在的唯一稳定固相。然而，在实验工作中，文献[9，10]中有许多报告表明，过量的Si在较低温度下与SiC共沉积。此外，在我们以前的工作[11]中，在1000-1500 8 C的温度范围内使用MTS H2气体系统进行，我们总是在低于1400 8 C的温度下发现过量的Si沉积。为了获得化学计量的SiC沉积，我们最近报道了[12]将丙烷（C3 H8）作为过量碳源添加到MTS H2气体系统中，这导致化学计量的SiC的沉积。因此，可以想到的是，硅烷比碳氢化合物与衬底更具反应性，并且需要供应过量的碳以进行化学计量的SiC沉积。存在一些提供过量碳的前体，例如二甲基二氯硅烷（DDS：（CH 3）2SiCl 2）、三甲基氯硅烷（TCS：（CH 3）3SiCl）和四甲基硅烷（TS：（CH 3）4Si）。这些氯硅烷含有硅和碳，并且分子中的C/Si比分别为2、3和4。此外，DDS、TCS和TS分子比MTS更容易分解，并在基底上方提供足够的烃。本文的目的是通过添加DDS、TCS或TS作为反应物来制备化学计量比的SiC存款，并研究其微观结构的变化。SiC涂层是在1000-1500 ℃常压下在水平石英反应器中沉积的。用光学高温计测量温度，并根据先前用热电偶校准来校正以接近基板的温度。石墨板和SiC涂层石墨分别用作衬底和感受器。使用三种类型的甲基氯硅烷（DDS、TCS和TS），它们由来自蒸发器的保持在0 8 ℃的氢气携带。用氢气控制甲基氯硅烷的浓度。X（X DDS、TCS或TS）H2气体混合物的总流速保持恒定在1600标准立方厘米/分钟（sccm）。通过测量沉积期间的重量增加来估计生长速率。用X射线衍射仪（XRD）分析了涂层的晶体结构，用能谱仪（EDS）和俄歇电子能谱仪（AES）测定了涂层的硅含量。通过扫描电子显微镜（SEM）研究了涂层的表面形貌。实验程序的细节与先前报道的相似[11，12]。沉积速率对摩尔分数的依赖性如图1所示。还显示了在MTS H2系统中进行的先前工作[11]的结果以供比较。甲基硅烷的总流速为1600 sccm，石墨基底的温度为1300 ℃。如图1所示，沉积速率随着反应物浓度的增加而线性增加。Hunt和Stirl [13]已经表明，增长率r由表示为rcE的关系决定。P0 . TF，其中cE、P0和TF分别是实验工作中的沉积产率、反应物的分压和总系统压力。因此，摩尔分数（X/（X H2），X MTS，DDS，TCS或TS）的增加导致生长速率的线性增加。采用DDS（C/Si 2）时，生长速率较高，而采用TCS或TS时，生长速率下降。沉积速率的温度依赖性如图2所示。在MTS H2系统中，
Silicon carbide (SiC) prepared by chemical vapour deposition (CVD) remains of importance for both structural [1, 2] and electronic [3, 4] applications. A variety of gaseous precursors has been used for SiC deposition under widely varying conditions of input gas composition, temperature and pressure [5]. For CVD of SiC, in general, a carrier gas is bubbled through a silicon containing liquid mixed with another stream of carrier gas. The necessary carbon is either contained in the chlorosilane or supplied by introducing a hydrocarbon. Methylchlorosilane (MTS: CH3SiCl3), as a precursor, is one of the most useful of the available chlorosilanes because it contains silicon and carbon in stoichiometric proportions [6]. Accordingly, it has been expected to give stoichiometric SiC deposition. Recently, from thermodynamic studies on the CVD of SiC in the MTS H2 gas system [7, 8], it has been shown that SiC is the only stable solid phase present in a wide range of temperature, pressure and concentration of the reactant. In experimental works, however, there have been many reports in the literature [9, 10] showing that excess Si is codeposited with SiC at lower temperature. Furthermore, in our previous work [11] conducted with the MTS H2 gas system in the temperature range 1000–1500 8C, we always found excess Si deposition at temperatures below 1400 8C. In order to obtain stoichiometric SiC deposition, we recently reported [12] the addition of propane (C3H8) as an excess carbon source to the MTS H2 gas system, which resulted in the deposition of stoichiometric SiC. Therefore, it is conceivable that silanes are more reactive with the substrate than hydrocarbon and supplying excess carbon is needed for stoichiometric SiC deposition. There are some precursors that supply excess carbon, such as dimethyldichlorosilane (DDS: (CH3)2SiCl2), trimethylchlorosilane (TCS: (CH3)3SiCl) and tetramethylsilane (TS: (CH3)4Si). These chlrorosilanes contain both silicon and carbon, and the ratios of C/Si in the molecules are 2, 3 and 4, respectively. In addition DDS, TCS and TS molecules decompose more easily than MTS and supply sufficient hydrocarbon above the substrate. The purpose of the work reported here was thus to prepare stoichiometric SiC deposit by supplying DDS, TCS or TS as a reactant and to investigate the change of the microstructure. The SiC coatings were deposited in a horizontal quartz reactor at 1000–1500 8C and under atmospheric pressure. The temperatures were measured with an optical pyrometer and corrected to approximate the temperature of substrate in accordance with a previous calibration with a thermocouple. Graphite plates and SiC-coated graphite were used as substrate and susceptor, respectively. The three types of methylchlorosilane (DDS, TCS and TS) were used and they were carried by hydrogen from the evaporator maintained at 0 8C. The concentration of methylchlorosilane was controlled with hydrogen. The total flow rate of X (X DDS, TCS or TS) H2 gas mixture was kept constant at 1600 standard cubic centimetres per minute (sccm). The growth rate was estimated by measuring the weight increase during deposition periods. The crystal structure was analysed by X-ray diffractometry (XRD) and the silicon content of the coating layer was determined by energy dispersive spectrometry (EDS) and Auger electron spectroscopy (AES). The surface morphology of the coating layer was investigated by scanning electron microscopy (SEM). Details of the experimental procedure were similar to those reported previously [11, 12]. The molar fraction dependence of the deposition rate is shown in Fig. 1. The results of previous work [11], carried out in the MTS H2 system, are also shown for comparison. The total flow rate of methylsilane was 1600 sccm and the temperature of the graphite substrate was 1300 8C. As shown in Fig. 1, the deposition rate increased linearly with increasing reactant concentration. Hunt and Stirl [13] have shown that the growth rate r is determined by the relationship expressed as r cE . P0 . TF, where cE, P0 and TF are deposition yields in experimental work, partial pressure of reactants and total system pressure, respectively. Thus, increase of the molar fraction (X/(X H2), X MTS, DDS, TCS or TS) leads to linear increase in the growth rate. By using DDS (C/Si 2), a higher growth rate was achieved, while it decreased with TCS or TS. The temperature dependence of the deposition rate is shown in Fig. 2. In the MTS H2 system, as is