论文摘要
AlGaN/GaN异质结高电子迁移率晶体管（HEMT）在高温大功率方面有非常好的应用前景。但是,AlGaN/GaN HEMT的工艺技术还不成熟,干法刻蚀、肖特基接触、欧姆接触、钝化、空气桥技术等多个关键工艺技术还有待优化和提高。AlGaN/GaN HEMT结构的优化及器件温度特性和可靠性问题还需要更多的分析研究工作。本文即在此背景下对AlGaN/GaN HEMT的几个关键工艺技术,以及器件特性与工艺、结构、温度、应力的关系进行了广泛而且较深入的研究。主要研究工作和成果如下：1.利用自主产权的MOCVD系统成功的生长出了高特性的AlGaN/GaN异质结材料；对材料在变温条件下特性的变化进行了研究;生长出了不同层结构的AlGaN/GaN异质结材料,得到了最有利于提高器件特性的层结构。2.对自行研制的GaN、AlGaN材料进行了感应耦合等离子体（ICP）干法刻蚀研究；对刻蚀速率与上电极功率、自偏压、反应室压力、反应气体配比的关系进行了摸索,更好的控制了刻蚀过程；在保证刻蚀速率的前提下优化刻蚀工艺条件,并采用SiO2做掩模材料得到了最佳的有源区形貌；进行了GaN/Al0.27Ga0.73N选择性刻蚀研究,为AlGaN/GaN HEMT的槽栅刻蚀提供了依据；研究了表面氧化层造成的刻蚀延迟现象,提高刻蚀自偏压能有效的减小刻蚀延迟；采用AFM研究了刻蚀损伤现象,在相同刻蚀参数下Cl2/N2和Cl2/Ar两种刻蚀气体中Cl2/N2气体获得了较小的刻蚀粗糙度。3.对自行研制的AlGaN/GaN异质结材料上Ni/Au肖特基接触进行研究,得到了高特性的肖特基接触,满足了AlGaN/GaN HEMT栅肖特基的特性要求；采用I-V法和C-V法对GaN上的Ni/Au肖特基势垒高度和理想因子进行了计算；研究了采用不同条件的O2等离子体和不同溶液表面处理对AlGaN/GaN异质结肖特基特性的影响效果；得到了提高AlGaN/GaN异质结肖特基特性的最佳退火条件；结合表面处理和退火两个因素,得到了进一步提高AlGaN/GaN异质结肖特基特性的工艺条件,并采用变频C-V进行了验证；对表面氧化层和介质层对肖特基特性的影响进行了研究；分析了20-200℃之间AlGaN/GaN异质结肖特基特性的变化规律。4.研究并给出了完整的AlGaN/GaN HEMT工艺流程,对光刻、剥离、金属淀积、钝化、电镀等重要的工艺步骤进行了工艺条件优化,制造出了具有良好特性的蓝宝石衬底和SiC衬底AlGaN/GaN HEMT;优化了器件的层结构,采用i-AlGaN或i-GaN帽层结构提高了栅肖特基特性;研究了不同衬底器件的自热效应,SiC衬底器件在较大漏偏压下只有很小的饱和电流下降；研究了器件截止频率的影响因素,减小栅长、接触电阻、寄生电容能得到更好的频率特性。设计了多栅指的大尺寸AlGaN/GaN HEMT器件,对空气桥跨接工艺进行了摸索,成功实现了空气桥互连。5.对自行研制出的AIGaN/GaN HEMT的温度稳定性进行了研究,器件的输运特性退化主要原因是材料迁移率下降,采用变温C-V及TLM测量研究了器件特性退化原因;研究了N2气氛中不同退火温度和时间下器件主要参数的变化,得到了热退火对AlGaN/GaN HEMT栅肖特基特性提高的最优退火条件；研究了不同偏置高场应力下AlGaN/GaN HEMT特性退化情况,并与直流扫描电流崩塌现象进行了对比,直流扫描电流崩塌现象在紫外光照后立即恢复,而高场应力后器件特性的退化无法恢复。综上所述,本文在研制出高质量的AlGaN/GaN异质结材料的基础上,系统的解决了刻蚀、肖特基接触、钝化、电镀空气桥等关键工艺技术,成功的研制出了具有良好特性的AlGaN/GaN HEMT,并对器件的温度特性、高场应力可靠性进行了分析研究,取得了满意的结果。
论文目录
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标签：氮化镓论文; 异质结论文; 高电子迁移率晶体管论文; 感应耦合等离子体论文; 肖特基接触论文; 温度特性论文; 高场应力论文;