【作者】 夏杰；

【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， 2006， 硕士

【摘要】 碳化硅材料有着包括禁带宽、击穿电场大、电子饱和漂移速度快等等物理性质方面的优势,这决定了碳化硅材料在高温、高频、高辐射等这些相对极端的环境下发挥重要的作用。同时,埋沟MOSFET(在SiO2/SiC界面注入一层N型掺杂层)的出现很好地避免了SiC/SiO2界面对载流子输运的影响。为了更好地发挥碳化硅埋沟MOSFET在功率性能的优势和潜力,必须对器件的电学击穿特性进行较为深入的模拟研究。本文的主要工作有:研究了4H-SiC埋沟MOSFET的基本结构模型及其参数,其中主要包括迁移率模型及其参数、不完全电离模型和碰撞离化模型,验证了器件的工作机理,讨论了器件的基本特性,验证了埋沟MOSFET相对传统MOSFET的优势;研究了4H-SiC埋沟MOSFET的高温特性。为接下来讨论4H-SiC埋沟MOSFET的击穿特性奠定了基础。为正确地模拟4H-SiC埋沟MOSFET的击穿特性,合理地设置了器件的深度和漏区的宽度。介绍了4H-SiC埋沟MOSFET的基本击穿机理;比较了埋沟和传统MOSFET的击穿特性,埋沟器件的击穿电压大说明了它在高压器件方面具有一定的优势;讨论了4H-SiC埋沟MOSFET的各个结构参数对器件击穿特性的影响,包括埋沟沟道掺杂浓度、沟道深度、衬底掺杂浓度、氧化层厚度、场板等;最后,介绍了环境温度对器件击穿特性的影响等。结果表明:4H-SiC埋沟MOSFET击穿电压随着栅压、沟道掺杂浓度、埋沟深度、氧化层厚度增大而增大;随着衬底掺杂浓度增大而减小;随着场板的出现而增大;另外,击穿电压随着温度的升高而增大。这将对4H-SiC埋沟MOSFET在今后研究中起到指导作用。介绍了4H-SiC埋沟MOSFET研制的最新实验情况。实验测试表明所有器件的阈值电压都为正,说明器件都是增强型的;器件I-V特性都具有较好的线性区和饱和区;最高的有效迁移率约为90cm2/Vs。实验获得了较高的迁移率,但和文献报道还有较大的差距,提出了一些改进方案。由于实验条件所限,4H-SiC埋沟MOSFET的击穿特性测试实验工作还没有来得及进行。更多还原

【Abstract】 SiC-based devices will play more and more important role in the applications of the electronic system operated in some extreme environments, such as at high temperature and high radiation. The high breakdown electric field and high saturated electron drift velocity make SiC-based devices cater for high power and high frequency applications. To decrease the influence of interface state, Buried Channel MOSFET formed by implanted n-type layer near SiO2/SiC interface is developed. Simulation study on the electrical breakdown characteristics is needed to realize the potential of the promising high voltage device-4H-SiC BC MOSFET. The main tasks in this thesis are as follows:It has been done to develop the basic model and improved parameters of 4H-SiC BC-MOSFET for accurate simulation, such as mobility model and imcomplete ionization model. Operational modes of the buried-channel MOSFET are verified with these models. The I-V characteristics have been simulated at room temperature and high temperature, which prove the advantage of this novel device. All these establish a foundation for following study of breakdown characteristic of the device.To better analyze breakdown characteristics of 4H-SiC BC MOSFET, the depth of the device and the width of drain region should be increased in terms of the requirement of MEDICI. In this case, the mechanism of breakdown of 4H-SiC BC MOSFET is more understood. Simulated results show the breakdown voltage of 4H-SiC BC MOSFET is larger than surface channel MOSFET, which indicates the potential of BC MOSFET to act as power device. Also it is shown that the breakdown voltage of 4H-SiC BC MOSFET increases with gate bias, channel density, channel depth and oxide thickness, decreases with substrate doping concentration. And the breakdown voltage becomes larger with increasing temperature.Latest fabrication of 4H-SiC BC MOSFET is brought forward.It is indicated that the threshold voltages of each device are positive,so these devices are normally-off.The tested I-V characteristics show good linear and saturation characteristics.The maximum effective mobility is about 90cm2/Vs.The obtained effective mobility indicates the superiority of SiC BC MOSFET,which shows the feasibility of improving mobility with SiC BC MOSFET structure.But great difference between experimental and reported mobility still exists,further modificative scheme is suggested.更多还原