Mechanisms of Extended Defect Nucleation During PVT Growth of Silicon Carbide

这个GOALI项目代表了卡内基梅隆大学、纽约州立大学(Stony Brook)和CAPE SIMULATIONS Inc.的研究人员与晶体生长公司Cree Research，Inc.，EPitronics，Inc.，Northrop Grumman Corp.，Airtron-Litton Corp.和II-VI，Inc.合作研究碳化硅中晶体缺陷的成核机制。该项目的目标是促进对碳化硅颗粒中扩展缺陷的形核和演化过程的理解。特别是，将研究基面和螺位错、层错、微管和低角度区域边界。该方法包括三个方面：(1)碳化硅物理气相输运生长的模拟，重点是不同生长阶段的热弹应力。在PVT生长中常见的小第二相夹杂物周围的局部应力场也将被模拟。(Ii)碳化硅PVT生长实验将在小规模的PVT系统中进行，在精心选择的条件下进行，以最大限度地减少缺陷形核。将调整关键工艺参数，以检验缺陷形核和扩散模型。生长将在不同的阶段中断(特别是早期播种阶段)，随后是非原位结构特征。(3)利用同步辐射白束X射线形貌术(SWBXT)、原子力显微镜(AFM)、透射电子显微镜、刻蚀和高分辨X射线衍射仪(HRXRD)对碳化硅晶体进行了结构表征。基面位错密度和基面总弯曲将被确定，并与宏观应力分布相关联。用X射线形貌术和透射电子显微镜观察生长早期螺位错的形核及其与堆积无序和夹杂物的关系。通过腐蚀揭示的跨低角度晶界的取向偏差成分将通过高分辨X射线衍射仪进行测量并解释其来源。%该项目致力于具有高潜在技术相关性的材料科学的热门领域的基础研究问题。这项研究将在基础水平上为块状晶体的生长贡献基础材料科学知识，这对电子学/光子学非常重要。从研究中获得的基本知识和理解有望有助于提高先进器件的成本、性能和稳定性。该计划的一个重要特点是通过在一个具有根本意义和技术意义的领域对学生进行培训，将研究和教育结合起来。参与这个项目的研究生将获得与团队成员合作的多方面经验。他们将使用和改进工艺模拟工具，生长和表征碳化硅晶体，参与技术转让，并将在学术和工业环境中工作。该项目由DMR/电子材料计划和MPS OMA(多学科活动办公室)共同支持。*

This GOALI project represents a collaborative effort between researchers at Carnegie Mellon University, SUNY (Stony Brook), and Cape Simulations Inc., together with crystal growth companies: Cree Research, Inc., Epitronics, Inc., Northrop Grumman Corp., Airtron-Litton Corp., and II-VI, Inc. to investigate nucleation mechanisms of crystalline defects in SiC. The objectives of the project are to advance the understanding of processes responsible for nucleation and evolution of extended defects in SiC boules. In particular basal plane and screw dislocations, stacking faults, micropipes, and low angle domain boundaries will be investigated. The approach consists of three thrusts:(i) Modeling of silicon carbide Physical Vapor Transport growth with emphasis on thermoelastic stresses at different stages of growth. Local stress fields around small second phase inclusions common in PVT growth will also be modeled. (ii) SiC PVT growth experiments will be performed in a small scale PVT system in carefully optimized conditions selected to minimize defect nucleation. Critical process parameters will be adjusted to test models of defect nucleation and multiplication. Growth will be interrupted at different stages (in particular early seeding stages), followed by ex situ structural characterization. (iii) Structural characterization of SiC crystals will be performed by synchrotron white beam x-ray topography (SWBXT), Atomic Force Microscopy (AFM), transmission electron microscopy, etching and high resolution x-ray diffraction (HRXRD). Density of basal plane dislocations and total bending of basal plane will be determined and correlated with macroscopic stress distributions. Nucleation of screw dislocations at early stages of growth and their association with stacking disorder and inclusions will be observed by x-ray topography and TEM. Misorientation components across low angle grain boundaries revealed by etching will be measured by HRXRD and their origin interpreted.%%%The project addresses basic research issues in a topical area of materials science having high potential technological relevance. The research will contribute basic materials science knowledge at a fundamental level to bulk crystal growth important to electronics/photonics. The basic knowledge and understanding gained from the research is expected to contribute to improving the cost, perform-ance and stability of advanced devices. An important feature of the program is the integration of research and education through the training of students in a fundamentally and technologically significant area. Graduate students participating in this project will gain multifaceted experience collaborating with team members. They will work with and improve process simulation tools, grow and characterize SiC crystals, take part in technology transfer, and will be exposed to work in both academic and industrial environments. The project is co-supported by the DMR/Electronic Materials program and the MPS OMA(Office of Multidisciplinary Activities).***