Chlorosilanes are used at high temperatures throughout the world's semiconductor industries primarily as a way to refine and deposit silicon and silicon containing materials. They are most prevalent in the manufacture of solar grade polycrystalline silicon; an industry that has historically used high cost alloys to effectively handle corrosive chlorosilane species. This study focused on understanding the corrosion behaviors of AISI 316L stainless steel, a low cost alloy, in chlorosilane environments at a variety of industrially-relevant times (0-200 hours), temperatures (500-700 • C), and hydrogen chloride (HCl) mole fractions (0.0-0.06). It was observed that AISI 316L can form either predominately metal chloride or metal silicide corrosion products depending on the mole fraction of HCl. Increasing temperatures tend to favor metal silicide formation, a trend predicted by thermodynamically generated predominance diagrams. Additionally, metal silicide surface layer growth appears to be diffusion controlled with an apparent parabolic rate at long times and high temperatures. There is also evidence for reaction-limited iron silicide formation at lower temperatures. Improved understanding of metals in high-temperature chlorosilane environments will help guide materials selection processes, and ultimately facilitate cost-competitive deployment of silicon-based photovoltaic systems. Chlorosilane species are used throughout the semiconductor, polycrystalline silicon, and fumed silica industries, primarily as a way to refine, deposit, and produce silicon and silicon containing materials. 1-4A typical chlorosilane gas stream usually contains some mixture of silicon tetrachloride (SiCl 4 , STC), trichlorosilane (HSiCl 3 , TCS), dichlorosilane (H 2 SiCl 2 , DCS), silane (SiH 4 ), hydrogen chloride (HCl), and hydrogen (H 2 ). The presence of both silicon-and chlorinecontaining species creates a unique corrosion environment for the metallic materials tasked with handling chlorosilane gas streams due to the propensity of many metals to form both metal-chlorides and metal-silicides.Metal-silicide and metal-chloride formation has been studied extensively for other applications. For example, metal chlorides have been studied due to the presence of chlorine in many industrial processes and metal silicides have been studied due to their use in electronics. It is generally considered that chloride formation is more problematic than silicide formation in industrial applications. This is because metal chlorides have high vapor pressures (at elevated temperatures) and can reactively evaporate 5 while metal silicides are potentially protective by forming dense, well-adhered surface layers. Consequently, for chlorosilane service, many industrial plants use alloys that resist chloride attack; however, the implementation of expensive corrosion resistant alloys comes at great cost. This is especially true in the polysilicon industry, where economic silicon refinement requires many large reactors and other process vessels. Because of process...
Chlorosilanes are used abundantly at high temperatures in the production of ultra-pure silicon and silicon containing materials. The presence of both chlorine and silicon presents a unique corrosion environment for the metallic materials that must handle these compounds. It is known that in chlorosilane environments, 316L can form either a protective metal silicide layer or a volatile metal chloride layer on the substrate. However, it is not known what dependence this surface reaction has on temperature, time, or gas composition. In this study, AISI 316L stainless steel was exposed to vaporized silicon tetrachloride (STC, SiCl4), pure hydrogen (H2), and anhydrous hydrogen chloride (HCl) at temperatures (>350°C), times (1-200 hours), and compositions relevant to industrial processes. Metal silicide and metal chloride formation was evaluated using surface and gravimetric analysis, with metal silicide formation causing a gain in sample mass and metal chloride formation causing a loss in sample mass. It was revealed that the transition between chloride and silicide formation depends on time of exposure, temperature, and mole fraction of HCl present in the gas stream. Lastly, some discussion is provided on the underlying mechanisms of silicide and chloride formation, and how to prevent excessive corrosion in industrial applications.
Chlorosilane species are commonly used at high temperatures in the manufacture and refinement of ultra-high purity silicon and silicon materials. They are highly corrosive in these processes, necessitating the use of high cost alloys for the construction of reactors, pipes, and vessels required to handle and produce them. In this study, iron, the primary alloying component of low cost metals, was exposed to a variety of silicon tetrachloride-hydrogen-hydrogen chloride vapor streams at industrially-relevant times (0-100 hours), temperatures (500-700°C), and compositions. Post exposure analyses including FE-SEM, EDS, XRD, and gravimetric analysis revealed formation and growth of stratified silicide and chloride surface layers, which vary as a function of time, temperature and gas composition. Additionally, there was evidence for various regimes of diffusion-limited and reaction-limited surface layer growth. Speculated mechanisms to explain these observations were supported by thermodynamic equilibrium simulations of experimental conditions. This study furthers the understanding of metals in chlorosilane environments, which is critically important for manufacturing the high purity silicon required for silicon-based electronic and photovoltaic devices.
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