Basic Research On CMP Of Silicon Wafer With Ice Fixed Abrasives

With the development of ultra large scale integration (ULSI), the integrated level of chips is becoming exigenter and exigenter, and the diameters of silicon wafer used as substrate materials are becoming larger and larger. The silicon wafers not only need to have very good flatness and low surface roughness but also have no surface damage or scratches. Silicon is a kind of hard material and easy to fail in a way of wear-out-failure because of brittle fracture, so it is difficult to machine it. Based on this background, a novel polishing technology with ice fixed abrasives pad for silicon wafer was proposed. A series of researches were carried on the mechanism of brittle-ductile transition of silicon wafer, the preparation of ice fixed abrasives pad and the polishing mechanism and technology. The work can provide a basis for the development and industrialization of this novel polishing technology. The main work is as follows:1. Mechanism of brittle-ductile transition of single silicon wafer at different temperatures. Formation, propagation and length of crack and hardness of single silicon wafer were invested at different temperatures by means of Vickers indentation. The effect of temperature on the mechanism of brittle-ductile transition of single silicon wafer was analyzed.2. Critical-depth-of-cut of single silicon wafer manchining at ductile mode. The scratch resistance of single silicon wafer at ambient temperature was measured by nanoscratching using nanoindenter. The mechanism of brittle-ductile transition of single silicon wafer at dynamic state was analyzed. The critical load and scratch depth was estimated from the scratch depth profile after the scratching and the friction profile. Based on the properties of silicon wafer obtained from the experiment, the formula of critical-depth-of-cut described by Bifnao was modified.3. Dispersion and stability ofα-Al2O3 and CeO2 nanopowders in water suspension. In the condition of the pH of the suspension was kept to 10~11, the optimal dispersing conditions ofα-Al2O3 and CeO2 nanopowders in water suspension were explored by selecting proper supersonic time and surfactant concentration. The work can guide to prepare polishing solution with high performance.4. Techniques for preparing ice fixed abrasives pad.The ice mold was designed and fabricated and then the ice fixed abrasives pad was fabricated by gradient freezing, laminar pouring and iceing. Using heat pressing, the ice fixed abrasives pad with grooves was fabricated.5. Simulation on the polishing trajectories of the ice fixed abrasives pad and their effects on the surface quality of silicon wafer. The effects of the eccentricity, ratio of transmission between the polishing pad and the workpiece and the number of grits on the trajectories were simulated, which can give an explanation of the changes of the surface roughness.6. Simulation study of the temperature field on polishing with ice fixed abrasives pad. The finite element model of temperature field of ice polishing was established. Effects of different processing parameters on temperature distribution and melting rate of the ice fixed abrasives pad were researched, which is theoretically useful for choosing the ambient temperature and the processing parameters.7. Technologic processes of IFA-CMP. Taguchi method and overall balance method were applied for optimization of the polishing conditions. Each processing parameter which affected the surface roughness and material removal rate in polishing silicon wafer was experimentally described in detail. The optimum processing parameter was obtained, which lay a basis for the application of IFA-CMP.8. Ice polishing mechanism of silicon wafer. The friction and wear behaviors of silicon wafer sliding against Al2O3 and agate at ambient air and low contact stress under unlubricated condition were studied using a UMT-2MT test rig. The results can provide experimental basis for the evaluation of sliding wear behavior and the study of ultra-precision finishing of silicon wafer. The friction tests of blanket silicon wafers against ice counterparts were carried out to investigate the friction effect and mechanism. The results showed that the removal of material was dominated by the coactions of ductile regime machining and chemical corrosion. A model of material removal of IFA-CMP was built.