Effects of process parameters on low-temperature silicon homoepitaxy by ultrahigh-vacuum electron-cyclotron-resonance chemical-vapor deposition

The effects of the process parameters on the low-temperature Si homoepitaxial growth in an ultrahigh-vacuum electron-cyclotron-resonance chemical-vapor-deposition (UHV-ECRCVD) system are examined by reflection high-energy electron diffraction and transmission electron microscopy (TEM). The substrate dc bias during plasma deposition drastically changes the crystal structure from polycrystalline silicon at negative bias to single crystalline at positive bias. The defect production during plasma deposition is mainly caused by the energetic ions impinging on the Si substrate, and it can be effectively suppressed by the proper control of the process parameters in the direction of minimizing the ion energy. The positive substrate dc bias is a prerequisite for better crystallinity of low-temperature Si, but additionally the other process parameters such as microwave power, distance of the ECR layer from the substrate, SiH₄ partial pressure, and total pressure should be definitely optimized to obtain dislocation-free Si epilayers. Dislocation-free Si epilayers are successfully grown at 560 °C at the positive dc bias greater than +10 V with the optimal control of the other process parameters. At temperatures below 470 °C, a high density of defects in the Si epilayers is observed by plan-view TEM, and the growth of the single-crystalline silicon is possible even without substrate heating but with a high density of defects. It is concluded that the substrate dc bias is a critical process parameter and the other process parameters do play a small but significant role as well in determining the crystallinity of the Si epilayers grown by UHV-ECRCVD.