薄势垒增强型AlGaN/GaN HEMT及可靠性研究

The project will study the fabrication and reliability of the enhancement-mode AlGaN/GaN HEMT devices with thin barrier layer. Based on previous theoretical and experimental researches, we will improve the saturation current by introducing the AlN layer and adjusting device surface passivation layer, avoid etching damage and simplify the process by adopting "self-aligned” method, and obtain devices with stable characteristics. By studying the generation mechanism of traps by the thin barrier tunneling current and the effect of traps on the related reliability problems such as the gate leakage current, breakdown voltage of the above devices under high field/high temperature stress systematically and deeply, we will explore the related physical mechanism and rules, and focus on the correlation between traps and the reliability problems. Furthermore, we will establish the trap related life prediction model, obtaining the structure, process and stress parameters which can influence the device characteristics, and provide references for improving the device reliability. On the basis of the above research, considering the correlation between the reliability problems, we will put forward relevant measures to improve the reliability of the devices while characteristic parameters of device not degenerating, and further correct relevant theories and models by the testing results of the improved devices. Through this project, we expect to obtain the thin barrier enhancement-mode AlGaN/GaN HEMT devices with good performance and high reliability, so as to lay a foundation for its application and promotion in practice.

本课题将致力于薄势垒增强型AlGaN/GaN HEMT器件制备及可靠性研究。在前期研究的基础上，通过引入AlN层、调整表面钝化层等方法改善器件饱和电流，采用“自对准”工艺避免器件刻蚀损伤简化工艺流程，得到特性稳定的器件；通过研究上述器件在高场高温应力下的薄势垒隧穿电流产生陷阱物理机制及陷阱对栅泄漏电流、击穿特性等相关可靠性问题的影响，探索相关退化机制及规律，重点关注陷阱与各可靠性问题间的相关性研究，建立陷阱相关的寿命预测模型，得到器件结构、工艺参数、应力条件等对器件特性的影响，为提高器件可靠性提供参考；在上述研究的基础上，综合考虑各可靠性问题间的相关性，提出改善器件可靠性的相关措施，同时保障增强型器件的特性参数，并根据改进后样品测试结果进一步修正相关理论及模型。通过本课题的研究，旨在得到特性良好、可靠性高的薄势垒增强型AlGaN/GaN HEMT器件，从而为其在实际中的应用和推广奠定基础。

增强型AlGaN/GaN高电子迁移率晶体管（HEMT）在大规模微波射频、数字、混合等电路中的应用意义重大，因此其制备及可靠性的研究十分重要。本课题根据AlN插入层可显著增加导带不连续性和压电极化作用及SiN钝化层对AlGaN/AlN/GaN薄势垒沟道二维电子气的调制作用，采用薄势垒异质结材料代替常规势垒厚度异质结材料制备增强型器件，具有很好的直流和频率特性，但阈值电压较低。采用薄势垒与F注入相结合的方法，用F等离子体对薄势垒增强型器件进行处理，实现了较大的饱和电流和较高的阈值电压。器件的直流特性及频率特性较以往的GaN基增强型器件有较大提高，而击穿特性保持不变。本课题针对该类增强型器件进行了可靠性研究：利用Silvaco TCAD仿真软件探索了薄势垒增强型AlGaN/GaN HEMT器件的仿真方法，验证了“F离子碰撞电离”较“F离子迁移”在薄势垒增强型HEMT器件高场应力退化中更为合理；研究了薄势垒增强型HEMT器件的栅泄漏相关可靠性，针对AlGaN/GaN 肖特基二极管（SBD）进行了正向和反向电压应力下的栅泄漏研究，发现反向应力后SBD器件的阈值电压和正、反向电流均出现退化，而正向应力后器件基本无退化。通过分析应力下载流子的输运过程，发现反向应力后器件的退化与薄势垒层中F离子的碰撞电离以及新陷阱的产生有关，并且通过C-V电导法对应力前后器件界面态进行了测试，测试结果及器件异质结界面势垒的计算结果都验证了此分析；研究了高场电应力对薄势垒增强型AlGaN/GaN HEMT器件性能的影响。开态应力后器件阈值电压发生退化，分析发现器件阈值电压的退化与薄势垒层中F离子的碰撞电离有关，且退化程度与偏置应力电压密切相关；关态应力后器件栅源之间的泄漏电流减小而栅漏之间的泄漏电流增大，结合Frenkel-Poole模型分析了这些电流的变化情况，发现应力作用过程中器件薄势垒层中发生了F离子的碰撞电离和逆压电现象。另外，关态应力后器件的阈值电压也出现退化，分析可得改善GaN中F离子的分布对提高器件可靠性具有显著意义。通过对器件的可靠性分析，得出了相关可靠性的物理机制及原因，更好的改进了器件性能，为后续的增强型器件的实际应用奠定了一定的基础。