Epitaxial growth is primarily a chemical process. The main gas sources used for silicon epitaxial growth are hydrogen and chlorosilanes, such as silicon tetrachloride (SiCl4), trichlorosilicon (SiHCl3), dichlorosilane (SiH2Cl2). In addition, in order to reduce the growth temperature, silane is often used as a source of air. The choice of which air source mainly depends on the growth conditions and epitaxial layer specifications, in which the growth temperature is an important factor to be considered when selecting air source. There is an important relationship between the growth rate of silicon epitaxial layer and the growth temperature. The graph shows two distinct growth regions. There is an index relationship between the growth rate and temperature of the silicon epitaxial layer. There is an index relationship between the low temperature zone (zone A) and the silicon epitaxial layer, indicating that they are controlled by surface reaction. In the high temperature zone (zone B), there is little direct relationship between their growth rate and temperature, indicating that they are subject to mass control or diffusion. It should be emphasized that the silicon film growing at low temperature is a polycrystalline layer. The formation temperature of the silicon epitaxial layer is higher than the turning point of each curve, and the temperature of the turning point changes with the change of the molar ratio of the reactant, the flow speed and the type. It can be inferred from this figure that the formation temperature of the silicon epitaxial layer is about 1100 ° C, and when SiH4 is used as the gas source, the formation temperature of the silicon epitaxial layer is about 900 ° C.

It is recommended to note that the reduction and corrosion processes are in competition with each other, which mainly depends on the molar ratio of the reacting object and the growth temperature. At atmospheric pressure, the boundary between corrosion and deposition is related to the growth temperature and the relationship between SiCl4 and H2, as well as SiCl4 and H2 as reaction objects at a total pressure intensity of 1.01×L05Pa (1 atmospheric pressure). In addition, the study provides a relationship between growth rate and temperature, as shown in Figure 2.2-31, when the reaction object is silicon epitaxial with SiCl4 and H2. As can be seen from the figure, what takes place at low and high temperatures is a corrosion process. Therefore, in this case, the epitaxial temperature is usually chosen at 1100~1300 ° C. In order to obtain a thicker extended layer, SiHCl3 is usually selected as the gas source, mainly because its deposition rate is faster than SiCl4.

The chemical reaction involved in SiH4 as an epitaxial gas source is not the same, and the thermal decomposition reaction is irreversible when using SiH4 gas source, and the point is to obtain the silicone epitaxial layer at a relatively low temperature. However, due to the homogeneous reaction of silanes, it is difficult to avoid the gas phase nuclei of silanes. As a result, silicon particles form during growth, resulting in rough surface shapes and even polycrystalline growth. Controlling the growing temperature or growing under low pressure can solve this problem. Silane is an easily oxidized and explosive gas, so it is not often used in traditional silane epitaxy. In addition, HCl is not present in the growth process with silane as the gas source, so there is no corrosion process, resulting in a high concentration of metal impurities in the epitaxial layer. Therefore, when using silane as a gas source, a careful pre-cleaning process is required.