p-GaN在不同掩膜和刻蚀气体中的ICP刻蚀

Inductively Coupled Plasma Etching of p-GaN Using Different Masks and Etching Gases

p-GaN栅沟槽侧壁与AlGaN表面特性直接影响栅注入（GIT）型AlGaN/GaN HEMT器件的输出特性及击穿特性。对比研究了两种刻蚀气体（SF6/BCl3和Cl2/N2/O2）及不同的刻蚀掩膜层（SiO2,Si3N4和光刻胶）对AlGaN上p-GaN的选择性刻蚀结果,利用原子力显微镜（AFM）对刻蚀沟槽的表面形貌进行表征,并通过I-V测试其电学性能。结果显示,以Cl2/N2/O2为刻蚀气体,且体积流量为18,10和2 cm^3/min时,p-GaN刻蚀速率稳定且与AlGaN的刻蚀选择比较高（约30）,并且可使p-GaN刻蚀自动停止在AlGaN界面处。此外,以Si3N4作为刻蚀掩膜,可以获得表面光滑、无微沟槽且侧壁垂直度较好的沟槽结构。采用上述刻蚀工艺制备的GIT结构器件的漏端关态电流相比肖特基栅降低约2个量级,阈值电压约为0.61 V,峰值跨导为36 m S/mm。

The sidewall of p-GaN gate trench and AlGaN surface directly affect the output and breakdown characteristics of gate-injected（ GIT） AlGaN/GaN HEMT devices. The selective etching results of pGaN on AlGaN by using two types of etching gas（ SF6/BCl3 and Cl2/N2/O2 mixed gas） combined with different etching masks（ SiO2,Si3N4 and photoresist） were compared. The surface morphology of the etched trench was characterized by the atomic force microscopy（ AFM）,and its electrical properties were tested by I-V measurement. The results show that with the etching gas of Cl2/N2/O2 and the flow rate of 18,10,2 cm^3/min,a stable etching rate can be achieved and the etching selectivity of p-GaN and AlGaN is relatively higher（ about 30）. In addition,p-GaN etching can automatically stop at the AlGaN interface. By using Si3N4 as an etch mask,a trench structure with smooth microgroove-less surface and good sidewall perpendicularity can be obtained. Compared to the Schottky gate HEMT,the leakage current of the GIT structure device prepared by the above mentioned etching process is reduced by about 2 orders of the magnitude with a threshold voltage of about 0. 61 V and the peak transconductance of 36 mS/mm.