单晶碳化硅接触中亚表层损伤与破坏机理的原子尺度分析

Atomic Analysis of Contact-induced Subsurface Damage Behavior of Single Crystal SiC Based on Molecular Simulation

基于分子动力学的Vashishta势函数研究了碳化硅纳米压痕受载诱导产生的位错环演变特征、相变转化数额和接触力学性能,分析了极端使役温度对其亚表层损伤行为和接触力学性能的影响。结果表明:碳化硅材料亚表层损伤主要以位错形核、位错堆积和位错滑移方式发生塑性变形,接触时的位错环历经位错形核、位错环生成增大、位错环繁衍增殖和位错环脆断等四个阶段。较高的使役温度,使碳化硅材料的最大承载性、硬度、杨氏模量和接触刚度曲线呈类抛物线趋势下降。其主要原因是,温度越高碳化硅晶格点阵越容易摆脱原子键能的束缚而产生晶格点阵缺陷,位错的产生导致材料亚表层发生应力集中,最终使碳化硅材料接触时的力学性能大大降低。此外,亚表层应力集中也使碳化硅材料内相变结构由立方碳化硅向闪锌矿碳化硅类型转变。随着温度的升高立方碳化硅和闪锌矿碳化硅的相变结构随之增多。另外,半导体器件中的碳化硅受载时发生的相变对使役温度的依赖极为显著。温度升高引起碳化硅晶格相变和表面随机粗糙斑点的产生,是产生接触黏着的主要原因。

It is helpful to understand the microstructure evolution characteristics and mechanical properties of monocrystalline SiC semiconductor devices during contact from the perspective of atomic scale to understand the microscopic mechanism of subsurface damage behavior and phase transformation.Based on the Vashishta potential function of molecular dynamics,the microscopic evolution characteristics of the nano-indentation induced dislocation rings,the amount of phase transformation and the contact mechanical properties of the corresponding monocrystalline SiC surface were studied,and the effect of extreme service temperature on the subsurface damage behavior and the contact mechanical properties were analyzed.The results show that the plastic deformation of SiC subsurface damage is mainly caused by dislocation nucleation,dislocation accumulation and dislocation slip,whilst the dislocation ring goes through four evolution stages during contact,i.e.,dislocation nucleation,dislocation ring growth,dislocation ring reproduction and dislocation ring brittle break.Besides,with the increasing temperature,the maximum bearing capacity,hardness,Young's modulus and contact stiffness curves of silicon carbide materials show a parabolic trend of decline.The main reason is that the higher the temperature is,the SiC lattice is easy to get rid of the bondage of atomic bond energy,resulting in lattice defects,and easy to breed dislocation,which result in the enrichment of stress concentration on subsurface of materials at lastly.As a result,the mechanical properties of SiC materials are greatly reduced while being contacted.In addition,the subsurface stress concentration is also the fundamental reason for the phase transformation from cubic to sphalerite for SiC materials.With the increase of temperature,the amount of phase transformation increases.The dynamic contact plastic deformation and micro-structure evolution of SiC in semiconductor devices under loading,and the phase transformation are significantly dependent on the operating temperature.The rising temperature related change of crystal lattice and the generation of random rough spots on the surface are the main causes of contact adhesion.This study may provide a deeper understand on contact mechanical properties and sub-surface damage behavior at extreme service temperatures,and will also enrich the understanding of the contact failure mechanism of nano silicon carbide.