【作者】 郭辉；

【导师】 张义门；

【作者基本信息】 西安电子科技大学 ， 微电子学与固体电子学， 2007， 博士

【摘要】 碳化硅(SiC)是近十几年来迅速发展起来的宽禁带半导体材料之一。与广泛应用的半导体材料Si,Ge以及GaAs相比,SiC材料具有宽禁带、高击穿电场、高载流子饱和漂移速率、高热导率、高功率密度等等许多优点,是制备高温、大功率、高频器件的理想材料,但是在SiC器件的制造工艺中仍然存在很多问题和困难,严重制约了SiC器件发展。对于器件的欧姆接触,低比接触电阻和高稳定性是决定器件性能的两个重要因素。因此为了充分的发挥碳化硅材料的优势,在其器件工艺中欧姆接触的制作工艺具有非常重要的位置。而目前碳化硅材料的欧姆接触存在着种种问题:(1)接触金属层成分和厚度不确定;(2)形成欧姆接触的合金化退火工艺的时间、温度、氛围等工艺参数相差很大;(3)得到的欧姆接触比接触电阻结果参差不齐,可重复性差;(4)欧姆接触形成的机理及物理模型还不够清楚等。大量的研究工作都是着眼于在对比实验结果的基础上进行工艺的优化,而较少的从形成欧姆接触的理论和机理角度进行研究并在其基础上对改进工艺进行指导。即使是对于相对应用广泛n型SiC材料的Ni基欧姆接触和p型SiC材料的Al-Ti金属欧姆接触,其形成欧姆接触的机理和物理模型也是众说纷纭,没有定论。本研究对SiC材料器件的欧姆接触工艺进行了系统的理论和实验研究,主要研究内容和创新性成果如下:1)研究了用于SiC材料欧姆接触重掺杂的离子注入理论和工艺特性。通过蒙特卡罗模拟软件TRIM对P、N、Al离子注入SiC中形成欧姆接触高掺杂区的能量,深度,偏差和杂质浓度分布等参数进行了分析,并对离子注入工艺参数(能量和剂量)进行了设计。设计了离子注入后杂质激活退火的温度,时间,氛围,密封剂等工艺条件,设计制作了具有多晶SiC内衬的退火用高纯石墨坩锅。提出了一种可行的高温退火掩膜(密封剂)方案,经表面测试对比证明,能够很好地改进了高温退火后SiC表面情况。得到了较好的离子注入激活率和较低的注入层的方块电阻值,为进一步进行器件的制备作好了工艺研究基础。2)研究了N型Ni基金属SiC材料欧姆接触形成的机理,提出在高温合金化退火时,Ni基金属和SiC的互相反应可以导致C原子外扩散,在接触金属层下的区域形成大量的C空位( )。因为起施主的作用,会导致接触下面电子浓度的增加,电子输运的耗尽层宽度减薄,隧穿效应大大增强,从而导致了比接触电阻的降低,是Ni基n型SiC欧姆接触形成的主要原因。在机理的研究基础上给出了Ni基n型SiC欧姆接触的界面区能带图,提出了比接触电阻构成模型。在此模型指导下对Ni基n型SiC欧姆接触的工艺进行了改进,利用两种Ni硅化物(NiSiVC VC2和NiSi)来制作n型SiC的欧姆接触,得到了接近国际最好值的比接触电阻结果。3)精确求解一维定态薛定谔方程得到电子通过三角形势垒的隧穿几率,并更多还原

【Abstract】 Silicon Carbide (SiC) is an attractive semiconductor material for high-power and high temperature electron devices because it has excellent physical properties such as a wide bandgap, high breakdown voltage, high thermal conductivity, and high saturation electron drift velocity. However, there are many difficulties and problems in the process, which restrict the development of the SiC devices.When SiC devices operate at the high temperature and high power, thermodynamically stable ohmic contacts with low specific contact resistance are important, since parasitic resistances generally limit or even jeopardize device operation. To utilize the excellent properties of SiC in an electronic device, ohmic contact technology should be one of the most important process for SiC. There are several problems in ohmic contacts to SiC at present: (1) The component and thickness are not confirmed completely; (2) Time, temperature, ambience of the metallization annealing are full of the variety; (3) There is a considerable variation in the results of specific contact resistance with lack of reproducibility; (4) The physical mechanism and model of ohmic contacts to SiC are not clear.Although many groups have successfully demonstrated ohmic specific contact resistance about 10?6 ?cm2, most of them pay attention to the process parameters optimization based on a lot of experiments, and few focus on the physical mechanism and model of ohmic contacts which can be used to direct the process parameters optimization. Even for Nickel, which is the most widely used metal for fabrication of ohmic contacts to n-type SiC, the physical mechanism is still not very clear.Furthermore it is same to Al-Ti metallization which is used to form ohmic contacts to p-type SiC popularly.This study gives a series researches on ohmic contacts to SiC theoretically and experimentally. The research areas and main contributions are as follows. The theory and technique of ion-implantation to form the heavy doped regions in the SiC surface for ohmic contacts are studied. The energies, depth,deviation and distribution of P, N, Al ion-implantation for forming high doping region used for ohmic contact are simulated by MC simulator TRIM, also the process parameters such as energies and doses are designed. The parameters of ion-implantation (for N+, P+, Al+), the temperature, time, ambience, and cap of post-implantation annealing are designed. The crucible coated by poly-SiC is designed and fabricated which is used in post-implantation annealing. The Carbon cap for the SiC surface protection during更多还原