SiC基反向开关晶体管关键技术及应用基础研究

Through researching into the plasma effect in the solid-state SiC based reversely switched dynistor(RSD) in the condition of high electric field, combined with the NPNP four-layer structure proposed according to the SiC material performance, the physical model fit to SiC RSD characteristics is established. Explore to solve the localization in the turn-on process in principle, and optimize the critical parameters such as the width and dopant concentration for the graded P base and the thick epitaxial drift N base, the characteristic size of the alternate multi-cell P+ and N+ emitter region at anode, etc, so as to make the SiC RSD turn on uniformly and simultaneously over the whole chip area with a low residual voltage at the front edge of current commutation, and the total power dissipation of the switch reduce to 50% of that for Si RSD at the same voltage range. Through exploring the several key process of the device, such as the growth of the thick epitaxial layer, the selective ion injection and anneal for the multi-cell at anode, the formation of the reliable ohmic contact electrodes, the dry etching and passivation for the mesa, etc. The prototype sample of the SiC RSD with the maximum repetitive peak direct voltage above 4kV and the maximum pulse current density of 10 kA/cm2 with the pulse width of 50 μs is developed, and the characteristics evaluation methods are proposed. The experimental accordance and serial technology is provided for the design, manufacture and application of the SiC RSD device.

通过研究强电场条件下固态SiC基反向开关晶体管RSD(reversely switched dynistor)中的等离子体效应，结合依据SiC材料性能提出的NPNP四层结构，建立适应SiC RSD特点的物理模型，探索从原理上解决导通过程局部化问题，进行包括缓变P基区和厚外延漂移N基区宽度及杂质浓度分布、阳极P+和N+发射区交替多元胞特征尺寸等关键参数优化设计，以实现SiC RSD在芯片全面积均匀同步开通、换流前沿残余电压小，同等电压等级下开关的总损耗降为Si RSD的50%。通过探索器件芯片的若干关键工艺技术，包括厚外延层生长、阳极多元胞选择性离子注入及退火、稳定可靠欧姆接触电极的制备、干法刻蚀台面造型及表面钝化等，研制出断态重复峰值电压不低于4kV、50μs脉宽下最大脉冲电流密度10 kA/cm2 的SiC RSD原型样品，并提出特性评价方法，为其设计、制造及应用提供试验依据和系列技术。

为突破Si基脉冲功率开关反向开关晶体管RSD(reversely switched dynistor)的参数极限，首次提出采用宽禁带半导体材料SiC制备RSD器件，以期获得更好的阻断特性与开关特性的折中以及更好的重复频率性能。.在考虑载流子迁移率模型、SRH复合、俄歇复合、碰撞电离效应和禁带变窄效应等物理模型与效应的基础上，建立了SiC RSD器件的二维数值模型，分析了其断态和开关特性，具体讨论了其开通过程。通过预充使得RSD基区中积累的剩余等离子体足够高，使其在导通阶段不会耗尽，提供类似晶闸管触发门极的作用，是器件正常工作的关键。.根据可获得的单晶材料和加工工艺设计了NPNP型SiC RSD器件结构，选取N型漂移区配合台面结终端，阴极不设置短路点。优化设计了器件的纵向杂质分布剖面和横向元胞特征尺寸，综合讨论了包括P基区宽度、载流子寿命等器件参数以及预充电压、工作温度等外部条件对开通过程的影响，分析了不同正斜角台面下表面电场分布。.探索了包括选择性刻蚀、选择性掺杂、欧姆电极制备以及台面终端造型等在内的多步SiC RSD器件的关键工艺，采用氟基气体ICP(inductively coupled plasma)刻蚀得到了合适的刻蚀速率、表面粗糙度及形貌，采用多次氮离子注入及高温退火完成选择性掺杂，采用Ni基金属配合适当退火温度完成欧姆电极制备，采用机械切割斜角完成台面终端造型并进行钝化，最终获得最高2820V的阻断电压，达到4kV理论设计值的70%以上。