The Study Of SiC Wafer Plasma Cleaning Technology

The third-generation semiconductor-silicon carbide (SiC) has excellent characteristics, such as wide band gap, high critical breakdown field, high saturated electron mobility and high thermal conductivity, so it is widely used for high-frequency, high power, high temperature devices and integrated circuits. However, SiC substrates present high density of surface states because of surface defects, contaminations, irregular arrangement of surface atoms and so on, which impact device performance seriously, so developing a new wafer cleaning technology for getting clean surfaces is an important to improve the development and application of SiC as the first step of semiconductor process.In this paper, plasma wafer cleaning technology was studied. The plasma was generated by electron cyclotron resonance (ECR) plasma enhanced metal organic chemical vapor deposition system, with high purity hydrogen (99.99%) and high purity nitrogen (99.99%) as the source of hydrogen and nitrogen plasma. SiC wafers after the RCA cleaning were treated by low temperature hydrogen plasma and nitrogen hydrogen plasma respectively. The best treatment parameters like power, temperature, time and gas flow-rate were investigated, and the surface structures, chemical and electrical properties were analyzed by in-situ refection high energy electron diffraction (RHEED), X-ray photoelectron spectroscopy (XPS) respectively. The results indicated that the 4H-SiC films had the preferred orientation, smooth and unreconstructed surfaces free of chemical residues (oxide and carbon contamination) at the treatment temperature of 400℃for 3 minutes, which was stable against oxidation in air according to the XPS measurements. After low temperature (400℃) cleaning 8 minutes by nitrogen hydrogen plasma, the C, O contamination of SiC surface were also removed. And we found that the films were sensitive to the treatment time, so using a little nitrogen plasma in the hydrogen plasma could control the cleaning process better.The results showed that the hydrogen and nitrogen hydrogen plasma cleaning lead to clean, smooth, atomically ordered surfaces free of chemical residues and unreconstructed SiC surfaces, the density of surface states are decreased by saturating the dangling bond, forming stable Si-H bonding and Si-N bonding on the surface, resulting in chemically and electrically well passivated and stable against oxidation in air, which is significant for improving the properties of semiconductor devices.