Investigation of Refractory Metal Gate on AlGaN/GaN HFET

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In order to achieve high-temperature operating AlGaN/GaN HFET or AlGaN/GaN HFET with self align gate structure, the formation process of gate and ohmic electrodes with refractory metals, the interface reaction, the electrical performance after thermal treatment should be investigated.In this work, Schottky contacts with normal metals like Ni, Cu, refractory metals like Ir, Pt, Rh, Ru, and metal nitrides like TaN, TiN, HfN, ZrN were fabricated. The films of the metal nitrides, which were obtained by reactive sputtering in nitrogen ambient, and the characteristics of the Schottky diodes were evaluated. High-temperature operation from mom temperature to 200℃ and thermal stability test were performed for all the samples. After annealed at 800℃,the performance of TiN diode had almost no degradation. The leakage current of ZrN diode was found to decease by two degrees after 800℃ annealing. The barrier height of this diode increased from 0.66 eV in room temperature to 0.77 eV after annealing. … More The ideality factor of this diode deceased from 1.16 eV in room temperature to 1.06 eV alter annealing.AlGaN/GaN HFET with ZrN and TN gate was also fabricated and evaluated The performances of the devices were found to have no obvious degradation after annealing at 850℃ for 30 seconds. The gate leakage deceased For the evaluation of self-align process, device with gate-first structure was fabricated After TiN or ZrN gate fabrication, Ohmic metals of TiAlTiAu were evaporated. After that, to form Ohmic contact in the drain and sauce region, the device was annealed at 850℃ for 30 seconds. Proper operation was confirmed for this gate-first device.Schottky contacts with refractory metals like W, WTi, WSi, Mo, MoSi and their nitrides were fabricated and evaluated. The leakage current was found to decrease, the barrier height was bind to increase fix the diode with metal nitrides. Especially Sr the diode with MoN Schottky contact, the leakage performance is similar to that of the diode with Ni contact Ideality factor of 1.03 and barrier height of 0.74 eV were obtained for the MoN diode, indicating a near ideal Schottky contact The sample was annealed at temperature from 300℃ to 800℃ with step of 100℃.After annealing, the leakage was found to increase gradually. But the increasing was very small compared with Ni contact. This indicates that the interface is much stable for the MoN-GaN interface. Wet etching of TiN was achieved. Based on the wet etching, self-align AlGaN/GaN HFET process was also tried.In conclusion, the achievements of this project can be considered to be the fundamental technologies in the development of heat-resistant devices and devices with self-align structure. Less