垂直结构氮化镓电力电子器件研制中的关键材料制备工艺研究

The development of high quality power devices is the fundamental task to improve the competitive power of energy saving technology in our country. Wide bandgap semiconductor GaN is one of the best materials to develop high quality power electronic devices. Although the vertical GaN power electronic devices based on homoepitaxy exhibit better performance than the silicon and SiC based devices, its high cost and low yield make it hard to practical application. In this project, we focus mainly on the three most critical aspect of the material growth. First, the proper stress modulation structure will be studied to realize low stress, dislocation density, and high yield HVPE-GaN single crystalline thick films, in order to eliminate the impact of residual stress of HVPE-GaN substrates on the device yield and performance. Second, The HVPE reactor well be improved to obtain high purity and smooth GaN films, and subsequently improve the device performance and product efficiency by substituting MOCVD. Third, the weak-bond buffer layer will be studied to realize the complete, large area separation and transference of GaN based power electronic devices from the GaN single crystalline substrates, which can be reused to further decrease the device fabrication cost. Our project is very important to realize the independent intellectual property rights and commercialization of high quality GaN power electronic devices.

我国发展节能高技术提升竞争力亟需高端电力电子器件为支撑。宽禁带半导体氮化镓是当前研制高端电力电子器件性能最优材料，尽管同质外延垂直结构GaN电力电子器件已展现优于现有Si和SiC器件性能，却因器件成品率低制备成本高而难以实用化应用。本项目重点开展三方面最关键材料制备工艺研究。一是通过探索合适应力调控结构，实现HVPE-GaN单晶厚膜衬底低应力低位错密度高成品率复制，解决HVPE-GaN衬底残余应力对器件成品率和性能的影响；二是通过改进HVPE反应室设计提升降速HVPE工艺生长的GaN材料纯度及膜层均匀平整度，进而替代常规MOCVD工艺实现器件性能和制备效率提升；三是通过探索合适弱键合解耦合结构，实现垂直结构GaN电力电子器件薄膜化制备与完整大面积剥离转移，剥离下来的GaN单晶衬底重复利用又进一步降低器件制备成本。为发展自主知识产权且适合产业化推广的高端GaN电力电子器件制备生产技术奠定基础

我国发展节能高技术提升竞争力亟需高端电力电子器件为支撑。宽禁带半导体氮化镓（GaN）是当前研制高端电力电子器件性能最优材料，尽管同质外延垂直结构GaN电力电子器件已展现优于现有Si和SiC器件性能，却因器件成品率低制备成本高而难实用化应用。本项目重点开展三方面研究工作：（1）HVPE-GaN单晶厚膜材料制备研究。为了克服HVPE-GaN衬底残余应力对器件成品率和性能影响，通过设计制备合适应力调控结构实现HVPE-GaN单晶厚膜材料低应力低位错密度高成品率复制，并将位错密度降至3乘10的6次方每平方厘米、RMS降至0.1nm；为了实现n¯-GaN漂移层高效高纯制备，通过改进HVPE反应室结构设计和优化HVPE生长工艺制备得到背景载流子浓度4乘10的16次方每立方厘米的高纯且表面均匀平整GaN单晶厚膜材料。还通过研究分析影响背景载流子浓度各种因素，探明了提升GaN外延材料纯度及生长质量新技术途径。（2）大尺寸HVPE反应室优化改进研究。为了推进GaN电力电子器件实用化进程，采用数值计算模拟仿真和材料生长实验，在不增加太大出气口与衬底托盘间距条件下，仅通过提升垂直结构HVPE反应室的外侧隔离吹扫保护气体氮气流速并引入合适环形低温区，或仅通过提升水平三层流水平结构HVPE反应室的顶层隔离吹扫保护气体氮气流速和设计合适倾斜角度的倾转区，就可实现大尺寸6英寸HVPE反应室流场和热场均匀分布及稳定。该创新改进和设计不仅为大尺寸HVPE设备设计建造提供技术指导，还为垂直结构GaN电力电子器件制备生产工艺改进提供参考。（3）GaN器件欧姆接触电极制作新工艺研究。通过对比研究发现过渡族难熔金属Hf和Zr替代金属Ti制作势垒层金属具有更好的欧姆接触电极性能，但如要有效克服界面反应和成分互扩散还需引入合适厚度的HfN和ZrN作为阻挡层。通过改进磁控溅射工艺实现a-Hf和a-Zr及其氮化物HfN和ZrN高质量单一择优取向生长，探索出了ZrN薄膜的MOCVD单晶生长工艺。既为发展GaN器件欧姆接触电极制作新工艺奠定了材料和工艺基础，还开辟了过渡族难熔金属及其氮化物在半导体领域应用的新方向。