Investigation On The Surface Stress Relaxation By Hydrodyanmic Suspension Polishing

Nano-film is extensively used in microelectronics,optics and biology for its special characteristics in mechanics,optics and electromagnetism.The ultra-smooth surface of the substrate is the basement for the fabrication of the nano-film that would affect the quality of nano-film as well,particularly,the residual stress on the surface.Therefore,to reduce the residual stress on the surface would have a significance effect on improving the quality of the nano-film.The key purpose of the hydrodynamic suspension polishing(HSP)process is to reduce the residual stress on the target surface and then obtain the ultra-smooth surface,so that in this thesis the investigation on the surface stress relaxation by the HSP process has been conducted as follows:(1)According to the theory of the fluid dynamics,the numerical model of the abrasive flow field during the HSP process was first developed in FLUENT,and then it was used to study the particle impact velocities and impact angles on the target surface with respect to different rotation speed of the polishing plate and the abrasive concentration in the pre-mixed abrasive slurry.The developed model was finally verified by the Particle Image Velocimetry(PIV)experiments,and it has been found that abrasive particles possessing relatively small impact angles and low impact velocities would impact the target surface.(2)Copper was selected as the target in this study.The finite element model of the particle impact the target surface was developed with ABAQUS as well by using the particle impact velocities and impact angles obtained from the previous simulation as discussed above.The single and multiple particle impacts have been simulated respectively,and it is found that the residual stress on the surface can be reduced by increasing the number of the particle impacts,and to increase the rotation speed of the polishing plate would decrease the residual stress in a given condition.(3)A comparison of the residual stress on the copper surface before and after the HSP process has been conducted experimentally.Using the XRD tests to measure the stress on the target surface found that the residual stress has been significantly reduced after the HSP process which verifies the numerical results from the ABAQUS as well.Moreover,the theory of the stress relaxation induced by the HSP process has been concluded,which could provide the theoretical guidance for the improvement of surface quality.In this paper,using the numerical and experimental studies the particle impact velocities and impact angles on the target surface have been obtained and then the effect of the particle impacts on the residual stress on the surface has been analyzed as well,and it is found that the HSP process can realize the stress relaxation.