基于原位等离子体氮化及低压化学气相沉积-Si_3N_4栅介质的高性能AlGaN/GaN MIS-HEMTs器件的研究

通过对低压化学气相沉积(LPCVD)系统进行改造,实现在沉积Si_3N_4薄膜前的原位等离子体氮化处理,氮等离子体可以有效地降低器件界面处的氧含量和悬挂键,从而获得了较低的LPCVD-Si_3N_4/GaN界面态,通过这种技术制作的MIS-HEMTs器件,在扫描栅压范围V_(G-sweep)=(-30 V,+24 V)时,阈值回滞为186 mV,据我们所知为目前高扫描栅压V_(G+)(20 V)下的最好结果.动态测试表明,在400 V关态应力下,器件的导通电阻仅仅上升1.36倍(关态到开态的时间间隔为100μs).

High-performance AlGaN/GaN MIS-HEMT device based on in situ plasma nitriding and low power chemical vapor deposition Si3N4 gate dielectrics

Gallium nitride (GaN)-based high electron mobility transistor (HEMT) power devices have demonstrated great potential applications due to high current density, high switching speed, and low ON-resistance in comparison to the established silicon (Si)-based semiconductor devices. These superior characteristics make GaN HEMT a promising candidate for next-generation power converters. Many of the early GaN HEMTs are devices with Schottky gate, which suffer a high gate leakage and a small gate swing. By inserting an insulator under gate metal, the MIS-HEMT is highly preferred over the Schottky-gate HEMT for high-voltage power switche, owing to the suppressed gate leakage and enlarged gate swing. However, the insertion of the gate dielectric creates an additional dielectric/(Al) GaN interface that presents some great challenges to AlGaN/GaN MIS-HEMT, such as the threshold voltage (V_th) hysteresis, current collapse and the reliability of the devices. It has been reported that the poor-quality native oxide (GaO_x) is detrimental to the dielectric/(Al) GaN interface quality that accounted for the V_th instability issue in the GaN based device. Meanwhile, it has been proved that in-situ plasma pretreatment is capable of removing the surface native oxide. On the other hand, low power chemical vapor deposition (LPCVD)-Si₃N₄ with free of plasma-induced damage, high film quality, and high thermal stability, shows great potential applications and advantages as a choice for the GaN MIS-HEMTs gate dielectric and the passivation layer. In this work, an in-situ pre-deposition plasma nitridation process is adopted to remove the native oxide and reduce surface dangling bonds prior to LPCVD-Si₃N₄ deposition. The LPCVD-Si₃N₄/GaN/AlGaN/GaN MIS-HEMT with a high-quality LPCVD-Si₃N₄/GaN interface is demonstrated. The fabricated MIS-HEMT exhibits a very-low V_th hysteresis of 186 mV at V_G-sweep=(-30 V, +24 V), a high breakdown voltage of 881 V, with the substrate grounded. The hysteresis of our device at a higher positive end of gate sweep voltage (V_{G +}>20 V) is the best to our knowledge. Switched off after an off-state V_DS stress of 400 V, the device has a dynamic on-resistance R_on only 36% larger than the static R_on.