【作者】 王守国；

【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， 2004， 博士

【摘要】 碳化硅（SiC）材料具有热导率高、电子的饱和速度大、击穿电压高等优点，是制备高温、大功率、高频等半导体器件的理想材料。由于杂质在SiC中的扩散系数很小，离子注入掺杂是除了外延掺杂以外的唯一可行的方法，离子注入工艺的良好解决有助于SiC材料的进一步推广应用，使SiC器件的制备更加灵活。在高温肖特基二极管（SBD）器件和金属半导体场效应晶体管（MESFET）器件的制备方面，离子注入具有使制备工艺简单、降低成本等优点。目前，国内外在SiC材料的研制、器件的制备方面发展较快，一系列制约SiC材料应用的瓶颈问题正逐步得到解决，但是SiC材料的离子注入工艺仍然存在较多的问题，如注入缺陷的消除、激活率的提高等问题有待于研究解决。在理论方面，随着离子注入制备工艺的使用，器件特性的分析、模型的建立等问题急需加以解决，本研究对离子注入制备4H-SiC器件及其温度特性进行了系统的理论和实验研究，研究内容及结果如下。 由于界面层、表面态的存在，实际的SBD器件的势垒高度受界面层、表面态的影响很大。目前对这两个参数没有很好的提取方法，严重妨碍着对器件特性的分析和模型的建立。本研究在热电子发射模型的基础上，提出了一种简单提取4H-SiC SBD器件特性参数的理论模型，基于这个模型，对制备的Ti／4H-SiC SBD器件，可以计算得出理想因子、串联电阻、零电场势垒高度、表面态浓度、界面层电容、表面态中性能级等参数。本方法的特点是模型较为简单，可以计算出4H-SiC SBD器件的界面层电容，表面态中性能级等参数，这些参数的提取未见报道。 SiC材料是宽禁带半导体，杂质的电离能较大，在室温下杂质是非完全离化。对4H-SiC施主掺杂（掺氮）的非完全离化进行了研究，引入电场强度对杂质的离化率的影响（PF效应），通过计算给出了完全离化、非完全离化考虑PF效应和非完全离化不考虑PF效应等情况下的4H-SiC MESFET器件的夹断电压随温度的变化。给出了一种计算4H-SiC MESFET夹断电压的精确模型，考虑杂质的非完全离化、界面态、反向漏电流等的影响。给出了考虑非完全离化时的4H-SiC MESFET栅电容的C-V特性，并计算了温度的影响。 通过研究离子注入的理论和工艺特性，以及蒙特卡洛分析软件TRIM对氮离子注入4H-SiC的能量、深度和偏差等参数的分析，在注入层的能带理论分析的基础上，提出了计算离子注入4H-SiC MESFET器件的沟道深度的方法，以及离子注入工艺参数，包括能量、剂量的确定方法。给出了两种离子注入的设计方案，即三次、四次离子注入，以及欧姆接触区的离子注入设计。说明了注入掩膜层SiO₂离子注入制备4H一SIC器件及其温度特性研究的厚度的计算方法，并给出了各次离子注入的掩膜层厚度。设计了一种离子注入制备4H一SIC SBD器件、MESFET器件的版图，包括:SBD器件、MESFET器件、欧姆测试TLM图形、HALL图形、标记等。 在大量查阅文献并结合国内制备条件的基础上，确定本实验采用的欧姆接触和肖特基接触的制备方案。设计了离子注入制备4H一SIC器件的基本工艺流程。 在国内现有的条件下，研究了离子注入制备4H一SIC欧姆接触、SBD器件和MESFET器件，摸索出了可行的制备工艺条件和完整的用离子注入制备SIC器件的工艺流程。 运用欧姆接触测试图形TLM结构对欧姆接触进行了测试，得到了三次和四次离子注入的欧姆接触的比电阻、注入层的方块电阻。测试了SBD器件的I一V和C一V特性，得到三次和四次离子注入层上习4H一siC SBD的势垒高度、激活率。测试了离子注入MESFET器件的I一V特性。在分析实验结果和工艺条件的基础上，总结了实验的不足，并给出了改进的措施。 用热电子发射理论对T订4H一SIC SBD器件的I一V特性进行模拟，得到三次和四次离子注入层上T订4H一siC SBD的势垒高度、理想因子和串联电阻等参数。建立了离子注入层上制备的Ti/4H一siC SBD器件的C一V特性模型，理论模拟时考虑沟道的离子注入分布、器件的非完全离化、PF效应等的影响，得到了与实验曲线符合较好的模型。在分析物理模型的基础上，对离子注入4H一siC MESFET器件的I一v特性进行了理论分析，得到了器件的解析模型。用模型分析了激活率、衬底掺杂浓度、温度等因素对器件特性的影响。关键词:碳化硅金属半导体场效应晶体管肖特基二极管表面态 非完全离化退火离子注入半导体工艺更多还原

【Abstract】 Silicon carbide （SiC） has outstanding properties such as high thermal conductivity, high saturated electron drift velocity and high electric breakdown field, and is a very promising material to fabricate high-temperature, high-power and high-frequency semiconductor devices. Because thermal diffusion rates of most dopants are very slow in SiC, ions implantation of dopants has been recognized as the only feasible method of selective area doping other than controlled doping during epitaxial-layer growth. Ion-implantation technique can make the fabrication processes of SiC devices more flexibility so that the application of SiC materials becomes a wider range. On the high-temperature devices such as Schottky Barrier Diode （SBD） and Metal Semiconductor Field Effect Transistor （MESFET）, the utilizing of ion-implantation can make fabrication processes simpler and the expenses cheaper. At present, researches on SiC material and the fabrication of its devices increase rapidly at home and abroad, many troubles about the application of SiC material have been solved. But the technique of ion-implantation of SiC material still have a lot of problems, such as the removing of defaults after implantation and the increasing of ions activation rate, waiting to be solved. On the theory research, the analysis of characteristics of devices and the model for the ion-implanted devices are urgent to be solved with the utilizing of ion-implantation technique. This study gives a series researches on 4H-SiC devices fabricated by ion-implantation and their temperature characteristics theoretically and experimentally. The research areas and main contributions are as follows.An actual SBD is a metal-semiconductor contact with a thin film and surface states between them, which has an effect on the barrier height. At present no way can extract these two parameters, which has seriously hampered the analysis of characteristics of devices and the building of model. Based on the thermionic emission theory, a simple method to extract parameters of 4H-SiC SBD is given in this study. Using this model, the ideality factor, series resistance, zero-field barrier height, surface state density, interface oxide capacitance and the neutral level of the surface states of Ti/4H-SiC SBD fabricated can be extracted. The method has a character of simplicity and can calculate the interface oxide capacitance and the neutral level of the interface states, that aren’t extracted as far as we know.SiC material is a wide bandgap semiconductor and the impurities have high value of ionization energies, so the impurities are not completely ionized at room temperature. The incomplete ionization of donors of nitrogen in 4H-SiC has been studied with theeffects of electric field on the ionization rate （PF effect）. The pinch-off voltages of 4H-SiC MESFET under the conditions of complete ionization, incomplete ionization with and without the PF effect are calculated at different temperatures. A more precise model of the pinch-off voltage of 4H-SiC MESFET is given, with the effects of incomplete ionization of dopants, the interface states and the reverse current are considered. The C-V characteristics of gate capacitance of 4H-SiC MESFET are calculated with the effect of incomplete ionization and its temperature characteristics.From the analysis of theory and technique character of ion-implantation and the energies, the implant range and straggle of nitrogen ions in 4H-SiC calculated by TRIM, the method to calculate the channel depth of 4H-SiC MESFET is present based on the energy diagram’s analysis of implanted layer. The method of determining parameters of ion-implantation, such as the energies and doses, are also given. Two designs of ion-implantation, such as 3 times and 4 times implantations and the implantation-range of Ohmic contact are given. The method to calculate the thickness of resist mask SiO₂ is given and the thickness of SiO₂ for every implantation is calculated. According the characteristics of ion-implantation and the parameters needed to be extracted, the layout更多还原