Study Of Mechanical Properties Of Porous Silicon By Photo-mechanics Method And Numerical Simulation

Porous silicon (PS) is a new kind of nanometer semiconductor material with excellent mechanical, thermical, optical and electrical properties. It is extensively applied to MEMS technology. The mechanical properties of PS film have been paid considerable attentions in resent years because of potential technology applications and theoretical significance. The dimension effect is observed at a range of modulation periods. Hence the properties of the micro- and nano-scale material is greatly different to that of the macro-material. At the same time a lot of conventional test means and device are not applicable to PS film. It is imperative to set up a new data model and to develop new testing technology. The elastic modulus and residual stress of PS film has been deeply explored and studied from numerical simulation and experiment observation.The mechanical proterty of this material has direct connection to the structure of the atomy and electron. The balanced lattice parameter of the porous film is different to that of the general single silicon. An atomistic-based continuum theory is proposed by incorporating atomistic level simulation method with finite element method. The constitutive relation of the solid phase of the porous silicon film is obtained and the composite constitutive model consisting of include porosity and solid phase is built. A high-fidelity unified macro- , micro- and nano-mechanics constitutive model and its applications for porous composites are studied to meet the needs of analyzing mechanical behaviors of porous silicon and structures on macroscopic and microscopic scales. A multi-scale finite element simulation method corresponding to the constitutive model is developed to predict the mechanical behavior of porous silicon material. The results show the accuracy of this method to the properties of the porous silicon material.We are the first ones to use bulge testing method to measure porous silicon film in our country. We designed and manufactured experiment apparatus according to the theory of bulge testing method. We measured the mechanical properties of the porous silicon film sample, and calculated the elastic modulus. The facts prove that the outcomes of experiment are right and it is feasible to use the bulge method to test the mechanical properties of porous silicon film. The success will promote the use of the diamond film. An optical apparatus based on substrate curvature method was developed for stress measurement of thin films, which offered a lot of advantages as overall field, non-contact, high precision, nondestructive, easy operation and quick response. Using the apparatus, the residual stress in porous silicon (PS) layers prepared by electrochemical etching using a solution of HF/ethanol in a composition ratio of 1:1 on heavily or gently doped (100) silicon as a function of the electric current density were obtained. It is found that the residual tensile stress tends to increase with the porosity increasing and the doping concentration of the silicon wafer increasing. The results show that there is a deep connection between the micro-structure PS and the residual stress distribution.Calculation of the residual stress in the PS film due to the difference of electron densities of the film and the substrate was performed based on the modified TFD electron theory and elastic mechanics model. The electron densities of the PS film are deduced based on electron densities theory. The effect of the doped strength of the P-type silicon substrate to the PS film is analyzed in theory. The calculated results are comparable with those of experiments, which indicates that the main resource of the internal stress in the PS film is the interfacial electron transfer.