Study On 4H-SiC Devices Fabricated By Ion Implantations And Their Temperature Characteristics

Silicon carbide (SiC) has outstanding properties such as high thermal conductivity, high saturated electron drift velocity and high electric breakdown field, and is a very promising material to fabricate high-temperature, high-power and high-frequency semiconductor devices. Because thermal diffusion rates of most dopants are very slow in SiC, ions implantation of dopants has been recognized as the only feasible method of selective area doping other than controlled doping during epitaxial-layer growth. Ion-implantation technique can make the fabrication processes of SiC devices more flexibility so that the application of SiC materials becomes a wider range. On the high-temperature devices such as Schottky Barrier Diode (SBD) and Metal Semiconductor Field Effect Transistor (MESFET), the utilizing of ion-implantation can make fabrication processes simpler and the expenses cheaper. At present, researches on SiC material and the fabrication of its devices increase rapidly at home and abroad, many troubles about the application of SiC material have been solved. But the technique of ion-implantation of SiC material still have a lot of problems, such as the removing of defaults after implantation and the increasing of ions activation rate, waiting to be solved. On the theory research, the analysis of characteristics of devices and the model for the ion-implanted devices are urgent to be solved with the utilizing of ion-implantation technique. This study gives a series researches on 4H-SiC devices fabricated by ion-implantation and their temperature characteristics theoretically and experimentally. The research areas and main contributions are as follows.An actual SBD is a metal-semiconductor contact with a thin film and surface states between them, which has an effect on the barrier height. At present no way can extract these two parameters, which has seriously hampered the analysis of characteristics of devices and the building of model. Based on the thermionic emission theory, a simple method to extract parameters of 4H-SiC SBD is given in this study. Using this model, the ideality factor, series resistance, zero-field barrier height, surface state density, interface oxide capacitance and the neutral level of the surface states of Ti/4H-SiC SBD fabricated can be extracted. The method has a character of simplicity and can calculate the interface oxide capacitance and the neutral level of the interface states, that aren't extracted as far as we know.SiC material is a wide bandgap semiconductor and the impurities have high value of ionization energies, so the impurities are not completely ionized at room temperature. The incomplete ionization of donors of nitrogen in 4H-SiC has been studied with theeffects of electric field on the ionization rate (PF effect). The pinch-off voltages of 4H-SiC MESFET under the conditions of complete ionization, incomplete ionization with and without the PF effect are calculated at different temperatures. A more precise model of the pinch-off voltage of 4H-SiC MESFET is given, with the effects of incomplete ionization of dopants, the interface states and the reverse current are considered. The C-V characteristics of gate capacitance of 4H-SiC MESFET are calculated with the effect of incomplete ionization and its temperature characteristics.From the analysis of theory and technique character of ion-implantation and the energies, the implant range and straggle of nitrogen ions in 4H-SiC calculated by TRIM, the method to calculate the channel depth of 4H-SiC MESFET is present based on the energy diagram's analysis of implanted layer. The method of determining parameters of ion-implantation, such as the energies and doses, are also given. Two designs of ion-implantation, such as 3 times and 4 times implantations and the implantation-range of Ohmic contact are given. The method to calculate the thickness of resist mask SiO₂ is given and the thickness of SiO₂ for every implantation is calculated. According the characteristics of ion-implantation and the parameters needed to be extracted, the layout...