Study On The Trajectory And Planarity During Polishing Of Sapphire Substrate

The sapphire single crystal has excellent optical,mechanical,chemical and electrical properties.The characteristics of high hardness,high strength,high temperature resistance and good light permeability make it has more and more extensive application in the field of photoelectron,communication,national defense and so on.As such,sapphire has a stable chemical and physical mechanical properties,which greatly increased the difficulty of the processing of sapphire.Not only requires high machining efficiency,but also requires high surface accuracy and low surface and sub-surface damage with the development of optics and microelectronics and related technology,so the manufacturing technology of sapphire wafer is facing great challenge.As a typical hard and brittle material,the processing technology of sapphire is not mature.Single crystal sapphire processing technology in the west is extremely confidential because of sapphire have a special purpose in aerospace,deep space exploration and other military areas.In order to realize the high efficiency,high precision and high quality of the single crystal sapphire,the lapping and polishing technology has emerged.Grinding is aimed at remove the micro convex and ensure the flatness of the wafer part of the chip surface by means of the micro cutting of abrasive particles.Polishing is mainly to reduce the surface roughness of the wafer and reduce the wafer surface and sub surface damage,so that the super smooth surface can be obtained.Lapping and polishing is a systematic project,which requires a high stability of the process conditions,and the mechanism of material removal and the formation mechanism of non-uniformity of materials are not perfect.Study on grinding and polishing process by test method is high-cost and restricted by various physical conditions,so combining experiment and simulation method is an effective method to study lapping and polishing mechanism and optimize machining process.Firstly,the relative motion model between the workpiece and the polishing disc is established in this paper.The particle motion trajectory equation is derived based on the principle of kinematics and coordinate transformation,and then the formula of track length and the formula of curve curvature are obtained.The influence of rotational speed ratio,eccentricity,particle radial distance and initial angle on the trajectory shape and curve curvature during in the grinding and polishing process were analyzed using MATLAB software.In this paper,we analyze the non-uniformity of track length,the non-uniformity of the velocity and the non-uniformity of the pressure distribution by introducing the variation coefficient.And the uniform wear equation can be obtained based on the principle of calculus.The effects of the speed of the polishing disc,the rotational speed of the workpiece,the eccentricity and the size of the particle radial distance on the wear factor are analyzed in order to satisfy the condition of uniform wear of workpiece.In this paper,the three-dimensional model between the workpiece,polishing pad,polishing pad and retaining ring is established by using the commercial finite element software Abaqus in order to explore the stress change of workpiece in the process of lapping and polishing.The effects of the pressure,the polishing pad thickness,the elastic modulus of the polishing pad,Poisson's ratio,the friction coefficient between the workpiece and the polishing pad on the contact stress distribution and the stress distribution are analyzed.On the basis of the above theoretical and simulation results,this paper will study the grinding and polishing of sapphire substrate through experiments.Study on the different pressure,the speed of polishing disc and the speed of polishing head,polishing pad and other parameters on the removal rate and surface roughness in chemical mechanical polishing of sapphire by means of single factor experiment.The processing technology can be improved combining theoretical demonstration and simulation experiments,which provided a theoretical guide for understanding the mechanism of lapping and polishing and the design of the polishing machine.