【作者】 戴振清；

【导师】 杨克武； 杨瑞霞；

【作者基本信息】 河北工业大学 ， 微电子学与固体电子学， 2007， 博士

【摘要】 SiC以其优异的材料特性,在高温、大功率和抗辐射器件电子学应用方面显示出明显的优势。另外,在化合物半导体中唯有SiC存在本征氧化物SiO2,因此SiC基MOSFET的研究引起高度关注和极大兴趣。本文主要围绕SiC材料和SiC基MOS器件开展了系列研究。在p型SiC中杂质激发态的影响很大,但目前这方面的研究还很少。本文集中研究了激发态对杂质电离、n-MOSFET反型层电荷和MOS电容的影响。激发态的影响与温度、掺杂浓度以及杂质能级深度存在密切的关系。在杂质激发态的作用下,n-MOSFET的反型层电荷面密度降低,激发态主要影响亚阈值区。对于MOS电容的C-V特性曲线,其在平带附近的Kink效应因激发态的影响而减弱,且曲线产生一小的平移。在SiC中存在显著的基态施主能级分裂现象,但目前的电子分布函数并不包含能级分裂因素。在本文中,通过引进基态施主分裂能级的平均能量增量和平均配分函数,得到了包含此因素的分布函数。并研究了在不同条件下基态施主能级分裂对杂质电离、p-MOSFET反型层电荷和MOS电容的影响。在基态施主能级分裂的作用下,p-MOSFET的反型层电荷面密度降低,MOS电容C-V特性曲线平带附近的Kink效应被减弱。为了使电路设计师能够充分利用SiC基MOSFET的优势,必须构建精确有效的器件集约模型(compact model)。在集约模型的构建过程中,高温沟道电子迁移率模型的建立至关重要。本文在考虑到各种现有因素并引进新因素的条件下,建立了比较合理的高温沟道迁移率模型。同时,在这部分中提出了采用与温度—阈值电压实验曲线拟合,来确定界面态参数和固定氧物电荷的新方法。表面势基MOSFET的集约模型中,表面势的显性表达式占有重要地位。目前已有的Si基MOSFET的表面势显性式,没有考虑界面陷阱电荷并认为杂质完全电离,因此它不适用于SiC基MOSFET。本文在Si基MOSFET的表面势显性表达式的基础上,并考虑到杂质不完全电离和界面态这两种因素,推导出了适用于SiC基MOSFET的从积累到强反型区的表面势显性表达式。总之,本文围绕SiC材料和SiC基MOS器件主要进行了四个方面的研究,其中重点研究了MOS器件。更多还原

【Abstract】 ii Silicon carbide shows the advantage in the application of device electronics which include high temperature, high power and radio resistance devices. In addition, silicon carbide is the only one among the compound semiconductors having the native oxide of silicon dioxide. Thus, silicon carbide based metal-oxide-semiconductor field effect transistor (MOSFET) has draw considerable attention and excited great interest. This dissertation aimed at the study of the material characteristics of silicon carbide and silicon carbide based MOS devices.In p-type silicon carbide, the excited states of dopants play an important role, but they are given a little attention. In this dissertation, the effect of excited states on ionization of dopants, inversion-layer charge density of n-channel MOSFET and MOS capacitor is investigated. The influence of excited states relates to temperature, the doping concentration and the depth of energy level of dopants. Under the effect of excited states, the inversion-layer charge density of n-channel MOSFET is lowered,and the impact of excited states are important under the threshold voltage. Under the influence of excited states, the kink effect of the C-V characteristic curve of the MOS capacitor round the flatband is weakened, and the curve produces a small horizontal displacement.There has remarkable valley-orbit splitting in n-type silicon carbide. However, the established distribution function for electrons did not include it. In this dissertation, a new distribution function for electrons is obtained by introducing the average increment and average partition function of all split levels. The influence of the valley-orbit splitting on ionization of dopants, inversion-layer charge density of p-channel MOSFET and MOS capacitor is investigated.Under the effect of the valley-orbit splitting, the inversion-layer charge density of p-channel MOSFET is lowered and the kink effect of the C-V characteristic curve of the MOS capacitor round the flatband is weakened.In order to utilize the advantage of silicon carbide for IC designer, the sufficient and accurate compact model of MOSFET has to be set up. During establishing the compact model, the temperature-dependent channel-electron mobility model is very important. In this dissertation, it is established by considering the existed and new factors. In addition, a new method extracting interface state parameters and fixed oxide charge density by simulating with the experimental temperature-threshold voltage curves is introduced.An explicit expression of surface potential is essential to the surface-potential-based MOSFET compact model. In the existed expression which suits silicon based MOSFET, interface trapped charge was not included, and dopants were considered to be ionized completely. However, it was not true for silicon carbide based MOSFET. High density interface states lie at SiC/SiO2, and freeze-out effect exists in silicon carbide. In this dissertation, we obtain the explicit expression of surface potential suitable to silicon carbide based MOSFET under the consideration of the two factors mentioned above.On the whole, this dissertation investigated four aspects around material characteristics of silicon carbide and silicon carbide based MOS devices. The most important part is about MOS devices.更多还原