The Research Of Micro-crack Propagation Under Indentation For Single Crystal Silicon

Single crystal silicon is an important functional material in the large scale integrated circuit, microelectronics, MEMS, optical devices, etc.It becomes new and high technology in the information technology, military technology, space technology and laser technology application for many countries.However,because of single crystal silicon belongs to hard brittle materials,it will inevitably bring about micro scratches, micro cracks, residual stress and other damage in the single crystal silicon surface during the manufacturing process.The damage will severely influence the quality and device performance of single crystal silicon.At present, the study of micro-crack damage of the surface layer of single crystal silicon is not perfect, therefore, it is extremely important to investigate the mechanical properties and micro crack propagation law of single crystal silicon for improving the performance and service life of Single crystal silicon.This topic is a part of the project "The research of multi-scale coupling analysis method of contact mechanical behavior of friction pair in MEMS ", which is supported by the National Natural Science Foundation of China.In this paper, Firstly analyze the basic theory and method of fracture mechanics, then we have done the contact experiment to the Single crystal silicon by nanoindentation testing technology. The hardness and the elastic modulus of single crystal silicon are gained from the load-penetration depth curve through the MTALB,hardness values showed significant size effect.Microscopic failure mechanism of Si (100) single crystal is studied by atomic force microscopy (AFM),the material showed only elastic-plastic deformation and no crack at the maximum load of 30mN,this proves the presence of a plastic deformed region of Si (100) single crystal.Material bulk and surface ridge is obvious with the increase of the maximum load,the cracks are generated below the center of the head, plastic-brittle transition of Single crystal silicon is occurred and it forms radial cracks along the edges of indentation,the material has noticeable cracks even partially broken, the crack length gradually increases along with the maximum load is increased.When the load is further increased in the material, at the maximum load of 230mN,chipping will be occurred for the further expansion of radial cracks.At last, use the linear elastic fracture mechanics approach to study micro indentation crack growth law of the regional stress field for the different load and the conditions under radius distribution by computer simulation. The results show that under the same pressure radius, with increasing pressure load, the stress intensity factor changes relatively flat, but with the increase in pressure radius, the stress intensity factor increases quickly, and the maximum of stress intensity factor exceeds the literature mono-crystalline material fracture limit of crack propagation, and the crack extensions was based I type, maximum stress in the material near the crack tip is 15.4GPa, about 3.1 times of the yield strength of the material.Form the graph of pressure load-stress intensity factor for circular arc and sharp indenter can be seen:when R<60nm, the stress intensity factor of circular arc slightly larger than Sharp indenter,when R>60nm,the stress intensity factor of sharp indenter is significantly greater than circular arc indenter,when R=60nm, the graph of pressure load-stress intensity factor for circular arc and sharp indenter almost complete coincidence.In addition, use the von Mises criterion to proved material to meet the linear elastic fracture mechanics of small scale yielding conditions, and thus the text to compare the crack extension is justified by the law of the stress intensity factor of the material.