Study On Process And Mechanism Of Ductile-Mode Machining For Silicon Wafer With Iced Fixed-Abrasives

The material for Integrated Circuit (IC) are consists of silicon, germanium, arsenic gallium. Among them, the proportion of single crystal silicon used in IC industry is over 90 percent. As we known, silicon is a typical hard brittle material which is difficult to be machined, while the diameter of wafer trends to be larger because of the fast development of IC manufacturing technology. It is a big challenge to get a high surface quality of wafer. Based on this background, first, a new method was proposed on ductile-mode machining for silicon wafer with Iced Fixed-Abrasive (IFA), and the mechanism of this method was studied. Then, the research was carried out on the preparation technique of IFA and the polishing performance.The main work and results are as follows:1. A low temperature cooling tester was designed, and the microhardness experiment of single crystal silicon at different temperature was carried out, the variation rule of microhardness and crack size with temperature at different loads were found.2. The mould of IFA was designed and prepared. By using this tool, experiment research was carried out on the preparation of IFA pad. At the same time, some approaches were used to solve the problems in the icing process such as air bubble, crack, sedimentation of abrasives. The IFA pads with uniformly distributed nano-SiO₂ and nano-Al₂O₃ abrasives were prepared successfully.3. A kinematics geometry model of silicon wafer polishing was established, by the model, the cutting trajectories of single-grit and multi-grits were found. Computer simulation results reveal of the effect of the eccentricity, different ratio of polishing pad rotating speed to workpiece rotating speed and different number of grits on the trajectories. The results provide a explanation of surface roughness.4. In order to create a suitable machining environment, a low temperature cooling system was built up. The different polishing behavior of nano-SiO₂, nano-Al₂O₃ abrasives under the same condition were discussed by Atomic Force Microscopy (AFM), including topography and surface roughness. The polishing results shows that nano-SiO₂ IFA has a better polishing result than nano-Al₂O₃, after 60 minutes polishing, the surface roughness of silicon wafer drops from Ra0.98nm to Ra0.40nm. But the surface roughness of total workpiece is ununiform.