对称极化掺杂增强型功率GaN HFET机理与工艺实现研究

In view of the key issues how to realize the enhancement mode (E-mode), high breakdown voltage (BV) and low leakage current in GaN power devices research, the following 3 items researches will be implemented: 1. Mechanism and novel structure of symmetrically polarization-doped E-mode power GaN HFET is proposed. Four novel mechanisms are included: ① The mechanism that the polarization-doped improves the output current is given as follows: The three-dimensional electron gas (3DEG) is induced in the linear variation doping AlGaN layer due to the polarization effect, which improves electron density and broadens the electron transport path. ② The mechanism that the hole gas realizes the E-mode is given as follows: Hole gas blocks the vertical channel and thus realizes the E-mode with a trench MIS gate. The proposed HFET maintains both high threshold voltage and large output current. ③ The mechanism that the polarization junction and source field plate enhance the BV is given as follows: Polarization junction formed by positive and negative polarization charges modulates the electric field distribution; and the source and drain locate at the same side of the gate and the source acts as a field plate, improving the BV and decreasing the device size; ④ The mechanism that the MIS recessed gate suppresses the leakage current is given as follows: the MIS recessed gate is used to suppress the leakage current and increase the gate voltage swing. The BV of the proposed HFET is more than 200 V, threshold voltage is at least 1 V, output current is more than 15 A and on-resistance is less than 30 mΩ. 2. The epitaxy technology of the back-to-back symmetrically polarization doping and high quality gate dielectric growth technique are developed. 3. The leakage current physics mechanism caused by defects are studied, and supressed-leakage current and the reliability reinforcement methods are developed accordingly. This project has frontier innovative significance and practical value.

针对GaN功率器件研发中增强型、耐压、漏电等关键问题，进行 3 项研究：1. 提出对称极化掺杂增强型功率GaN HFET新机理与结构。含4项机理 ① 对称极化掺杂提高开态电流：Al组分的线性渐变产生极化效应，形成三维电子气，提升器件电子面密度并拓宽电子输运路径。② 空穴气实现增强型：利用空穴气阻断纵向沟道实现增强型，兼具高阈值电压和高输出电流。③ 极化结和源场板增强阻断耐压：正、负极化电荷构建极化结，调制电场分布；源、漏极位于栅极同侧并构成源极场板，提高耐压且缩小器件尺寸。④ MIS凹栅抑制漏电：MIS凹槽栅抑制泄漏电流，并增大栅压摆幅。新器件耐压达200 V，阈值电压达1 V，输出电流达15 A，导通电阻不超过30 mΩ。2. 开发对称极化掺杂外延生长和高质量栅介质生长技术。3. 研究缺陷引起漏电的物理机制，提出漏电抑制技术和可靠性加固技术。项目乃前沿性基础创新研究，具有实用价值。

GaN材料具有宽禁带、高电子饱和速度及高临界击穿电场等特点，加上GaN异质结具有高浓度二维电子气（2DEG），使得GaN功率器件在高压、大功率及低功耗方面独具优势。针对如何实现高耐压、低导通电阻、增强型和高可靠性等关键问题，对高质量栅介质生长、低阻欧姆接触、低损伤刻蚀以及界面处理等关键工艺进行攻关，提出 2 种渐变极化掺杂高压GaN功率器件新结构，提出并研制 2 种具有极化结的高压GaN器件新结构，研制出 3 种具渐变氟离子终端AlGaN/GaN HEMT器件，提出并优化设计双栅增强型翻转AlGaN/GaN HEMT器件新结构，均具有优良的电学性能。提出的对称渐变极化掺杂高压GaN器件，构建了对称极化结和纵向沟道结构，由三维空穴气（3DHG）和三维电子气（3DEG）构成的极化结优化漂移区电场，实现高压；空穴气阻断源极3DEG的纵向沟道，实现增强型。基于极化理论和能带工程，建模仿真其工作机理，为工程设计提供理论指导。对称渐变极化掺杂增强型AlGaN/GaN HFET的开启电压为2.19 V，比导通电阻为0.31 mΩ·cm2，器件耐压达919 V；具有背势垒层的渐变极化增强型HEMT的开启电压为3.2 V，比导通电阻为0.34 mΩ·cm2，器件耐压达860 V。具有极化结的增强型RC-HEMT导通电阻为11.6 Ω·mm，击穿电压为721 V，反向开启电压为0.68 V；具有极化结的高压肖特基二极管阈值电压为0.68 V，漂移区长度11 μm时，击穿电压为1109 V，比导通电阻为1.17 mΩ·cm2，在200 V的应力电压下，动态电阻仅增大了20 %。具有多三角形渐变F-终端的AlGaN/GaN HEMT、多矩形渐变F-终端的AlGaN/GaN HEMT和梯形渐变F-终端的AlGaN/GaN HEMT在漂移区长度为7.5μm时，击穿电压分别为447 V、416 V和430 V，比导通电阻分别为0.56 mΩ·cm2、0.60 mΩ·cm2和0.73 mΩ·cm2，BFOM值分别为357 MW/cm2、288 MW/cm2和253 MW/cm2。以该项目研究成果为主要支撑内容发表论文 12 篇，获授权中国发明专利 5 项，获授权美国发明专利 1 项，已受理中国发明专利申请 17 项。