Finding the Optimum Chloride-Based Chemistry for Chemical Vapor Deposition of SiC

Abstract

Chemical vapor deposition of silicon carbide with a chloride-based chemistry can be done using several different silicon and carbon precursors. Here, we present a comparative study of SiCl 4 , SiHCl 3 , SiH 4 +HCl, C 3 H 8 , C 2 H 4 and CH 4 in an attempt to find the optimal precursor combination. We find that while the chlorinated silanes SiCl 4 and especially SiHCl 3 give higher growth rate than natural silane and HCl, SiH 4 +HCl gives better morphology at C/Si around 1 and SiCl 4 gives the best morphology at low C/Si. Our study shows no effect on doping incorporation with precursor chemistry. We suggest that these results can be explained by the number of reaction steps in the gas phase chemical reaction mechanisms for producing SiCl 2 , which is the most important Si species, and by formation of organosilicons in the gas phase. As carbon precursor, C 3 H 8 or C 2 H 4 are more or less equal in performance with a slight advantage for C 3 H 8 , CH 4 is however not a carbon precursor that should be used unless extraordinary growth conditions are For the last, approximately ten years, chloride-based chemistry has been studied for chemical vapor deposition (CVD) of electronic grade SiC.1 The addition of Cl to the gas mixture circumvents condensation of silicon droplets above the substrate since the stronger Si-Cl bond (400 kJ/mol or 4.15 eV) 2 prevents Si-Si bonds (226 kJ/mol or 2.34 eV) 2 to form. This allows a higher precursor concentration in the CVD gas mixture which enables higher growth rates of epitaxial SiC layers; growth rates exceeding 100 μm/h are common, compared to the 5-10 μm/h usually obtained for the standard, non-chlorinated chemistry based on silane (SiH 4 ) and small hydrocarbons like ethylene (C 2 H 4 ) or propane (C 3 H 8 ). Cl-based CVD chemistry is therefore seen as an enabler of SiC power device technology 1 , where approximately 100 μm thick, low doped (10 14 cm −3 ), epitaxial layers are required for devices capable of blocking voltages on the order of 10 kV.Addition of Cl can be done either through the addition of HCl to the standard precursors, by using a chlorinated silane molecule (SiH x Cl y ) instead of SiH 4 , by using a chlorinated hydrocarbon (CH x Cl y ) instead of C 3 H 8 /C 2 H 4 or by using a single molecule (SiH x C y Cl z ). All these approaches have been reported to be successful and capable of growth rates exceeding 100 μm/h. 1 However, the optimal precursor for Clbased CVD of SiC is still not identified, despite ten years of research on Cl-based CVD chemistry. The single molecule approach has been successful, 3 but the inherent locked C/Si ratio hinders an efficient control of the doping incorporation 4 in SiC. Thermochemical studies suggests that the use of CH x Cl y is not likely an optimal route since the C-Cl bond is found to break, allowing Si-Cl bonds to form.5 Thus the CH x Cl y approach is probably a chemical detour. There have been attempts to compare data from various groups 1,6 but these comparisons are hampered by the fact that the data are acquired in differ...

Brominated Chemistry for Chemical Vapor Deposition of Electronic Grade SiC

“…Brominated chemistry does not offer this wide range of options and is therefore perhaps less attractive at a first glance. However, in a recent study, we have shown that for a combination of both high growth rate and high-quality morphology, HCl addition to the standard precursors is the best chemical route for chlorinated chemistry . In the light of this study, brominated chemistry by HBr addition can be viewed as a solid alternative to HCl addition.…”

Precursors and defect control for halogenated CVD of thick SiC epitaxial layers

“…We have demonstrated that it is possible to use CH4 as carbon precursor in CVD of high quality epitaxial layers of SiC, by carefully optimizing the C/Si ratio to achieve a growth chemistry that is neither carbon nor silicon limited [105]. Also we have studied the use of silane (SiH4), trichlorosilane (SiHCl3) and tetrachlorosilane (SiCl4) as silicon precursors, and propane (C3H8), ethylene (C2H4) and methane (CH4) as carbon precursors [106]. It was found that the SiHCl3-based process using C3H8 shows the highest growth efficiency while the SiH4-based process using CH4 shows the lowest growth efficiency (Figure 12).…”

Controlled CVD Growth of Highly ⟨111⟩-Oriented 3C-SiC

“…The stronger Si−Cl bonds (400 kJ/mol) 3 can suppress the formation of weaker Si−Si bonds (226 kJ/mol). 3,4 In terms of the carbon precursor, small hydrocarbons such as ethylene or propane are often used because they can produce highquality SiC coatings and are available at high purities.…”

“…The addition of Cl to the SiC CVD processes has been reported to not only increase the growth rate but also prevent the formation of Si droplets in the gas phase. The stronger Si–Cl bonds (400 kJ/mol) can suppress the formation of weaker Si–Si bonds (226 kJ/mol). , In terms of the carbon precursor, small hydrocarbons such as ethylene or propane are often used because they can produce high-quality SiC coatings and are available at high purities.…”