【作者】 张发生；

【导师】 李欣然；

【作者基本信息】 湖南大学 ， 电气工程， 2010， 博士

【摘要】 4H-SiC材料和高压4H-SiC肖特基二极管(SBD)器件具有优越的性能,在国民经济和军事等诸多领域有着广泛的应用前景,例如电力电子领域就是最具代表性的工程应用领域之一。高质量的厚外延层4H-SiC材料是制造高压SBD器件基础。但毋庸讳言,无论从4H-SiC外延材料生长还是高压SBD器件的制造中依然存在很多问题和困难,严重制约了高压4H-SiC SBD器件发展。国内4H-SiC单晶外延材料制备和4H-SiC SBD器件研制起步较晚,对4H-SiC宽禁带半导体和4H-SiC SBD器件关键理论问题缺乏深入、细致和系统的研究,使得我国的整体水平与国际先进水平尚存明显差距,主要存在以下问题:(1)高质量4H-SiC外延薄膜的生长机理和关键工艺尚未完全搞清;(2)没有一套系统完整4H-SiC单晶同质外延的表征测量方法;(3)高压SiC SBD器件所采用的结终端结构缺乏准确数据;(4)4H-SiC SBD器件关键制造工艺还未解决。在此背景下,本文针对上述主要问题进行了系统研究。主要的研究成果如下:1、在理论分析的基础上,对化学气相淀积(CVD)法4H-SiC同质外延生长的关键工艺进行了实验研究,得出影响这些材料参数的主要因素。确定了关键参数变化趋势,制定了完整的工艺流程。2、对4H-SiC同质外延薄膜进行了检测。提出了一种简易测试外延厚度的方法,即利用叶变换红外光谱(Fourier Transform Infrared Spectromtry)FTIR反射谱对4H-SiC同质外延半导体薄膜的质量进行评价,完善了用干涉条纹的频率和强弱的方法来计算外延薄膜的厚度。用汞(Hg)探针C-V测试获取4H-SiC同质外延纵向杂质浓度分布的信息,并通过多点测试,得到外延片的掺杂浓度均匀性。借助扫描电子显微镜SEM和原子力显微镜AFM等显微技术对4H-SiC同质外延薄膜样品表面形貌进行了定性和定量的测试分析。3、提出了高压4H-SiC SBD器件反向击穿电压与4H-SiC半导体材料临界电场、外延层的掺杂浓度、外延层的厚度之间定量关系,研究了室温下金属碳化硅接触的肖特基势垒高度Фb、串联电阻Ron和金属与4H-SiC紧密接触形成欧姆接触,并给出了它们的计算公式。证明了在温度不太高的范围(300K-500K)内,正向伏安特性符合热电子发射理论。提出了一种计算反向电流密度的理论模型,模型的计算结果与实验数据的比较表明,隧道效应是常温下反向电流的主要输运机理。但在温度较高时,反向热电子发射电流和耗尽层中复合中心产生电流都大大增加,不能再忽略不计。4、阐述了高压4H-SiC SBD结终端技术的必要性,原因是高压4H-SiC SBD结终端存在电场集中导致电压下降。提出了平面结终端技术:场板技术、保护环技术、腐蚀造型技术、场限环技术和结终端延伸技术等。介绍了数字模拟软件ISE-TCAD10.0特点、模拟运行的过程、并对带有场限环和结终端延伸的结终端技术的高压4H-SiC SBD进行了耐压特性模拟。通过模拟得到衬底掺杂浓度、厚度和结终端结构等参数对器件耐压的影响关系,为高压4H-SiC SBD的设计和研制做好准备5、研究了欧姆接触和肖特基接触,它们是高压4H-SiC SBD器件研制的基础和关键工艺。根据模拟结果,结合实际工艺条件,本文分别研制了具有结终端场限环保护的高压Mo/4H-SiC SBD和Ni/4H-SiC SBD器件及具有结终端延伸保护的高压Ni/4H-SiC SBD器件。根据实验结果指出此两种平面结终端保护结构是很有效的。这为今后进一步研制高性能的高压4H-SiC SBD器件奠定了实验基础。最后根据初步实验结果分析提出了今后改进设想。更多还原

【Abstract】 4H-Silicon carbide (SiC) material and its High Voltage SBD devices have shown the attractive prospects for wide range applications to the various field of social economy because of their excellent physical and electrical properties, one of which is the application in power electronic engineering. The high quality 4H-SiC single crystal material is the base for achieving 4H-SiC SBD devices with high performance. Needless to say, both 4H-SiC epitaxial material growth or manufacture of high-voltage SBD devices still exist many problems and difficulties,Seriously restricted the development of high-voltage SBD device.It led still the Significant difference between our country’s overall level and international advanced level to lack the in-depth, detailed and systematic study on 4H-SiC wide bandgap semiconductor and 4H-SiC SBD devices key theoretical problems because domestic 4H-SiC single crystal epitaxial material preparation and 4H-SiC SBD device development started late. There are following problems: (1) high-quality 4H-SiC epitaxial film growth mechanism and key technologies have not yet been clearly understood; (2) the lack of a series of test and characterization methods for characteristics of 4H-SiC homoepitaxial layers; (3) there are the lacks of the accurate junction terminal data for high voltage SiC SBD device; (4) the SiC SBD device key technologies are yet unresolved.In this dissertation, the main problem mentioned above is studied systematicly. The main studies and contributions of this dissertation are as follows.1. The key processes of growth are studied by experiments based on the theoretical analyse, and the major factors to affect the key processes are obtained. The trend of parameters and process are achieved.2. 4H-SiC homoepitaxial layers are tested. The quality of 4H-SiC homoepitaxial layers is evaluated and the depth is calculated using the intensity and frequency of interference fringes in FTIR spectrum. The surface topography and element of 4H-SiC homoepitaxial layers are qualitatively and quantitatively analysed by SEM, AFM.3. The quantitative relationship between high-voltage 4H-SiC SBD reverse breakdown voltage with the SiC semiconductor material critical electric field, the doping concentration and the thickness of epitaxial layer is proposed. The Schottky barrier height, series resistance and ohmic contacts under room temperature are analyzed, and their relative formulas are obtained. Then it is demonstrated that the current conduction mechanism follows the thermionic emission theory at the temperature range from 300K to 500K under forward biased conditions. A theoretical model used in calculating reverse current density is proposed considering several current transport mechanisms. The comparison of theoretical results with experimental data indicates that tunneling effect is the dominant mechanism under room temperature, but the thermionic emission current and the generation current in the depletion region will increase greatly when temperature becomes high so that they are no longer negligible.4. The necessity of junction termination technique for high-voltage 4H-SiC SBD is described because of the premature breakdown voltage occuring with electrical field crowding at the device edge. Some common plane termination extension techniques are put forward including field plate, guard ring, etch contour, field limiting ring and, junction termination extension technique, etc.. The digital simulation software ISE-TCAD characteristics and simulation operation process are introduced. The breakdown voltage characteristics of high-voltage 4H-SiC SBDs with field limiting rings and junction termination extension techniques are simulated respectively. The influence relations on the high voltage 4H-SiC SBD breakdown voltage obtained by the simulation substration doping concentration, thickness and junction termination structure will contribute to the design and development for high voltage 4H-SiC SBD.5. The ohmic contact and Schottky contact are studied because they are basis and key process of the farbrication for high-voltage 4H-SiC SBD device. According to the simulations results and our actual process conditions, the high-voltage Mo/4H-SiC SBD with field limiting ring and the high-voltage Ni/4H-SiC SBD with junction termination extension are farbricated respectively. The experimental results show that the protections of the two planar junction termination structures are very effective. This will provide for the experiment foundation for high-performance 4H-SiC SBD farbrication in the future.Finally, the ideas for future improvement are presented according to the preliminary experimental results.更多还原