FEM Analysis And Experimental Research On Lapping/Polishing Of Single-Crystal Silicon

IC (Integrated Circuit) technology as a kind of new technology, increasingly becomes themain power to promote the national economy and social informationization development.Silicon material as the main semiconductor materials is used in Integrated Circuitmanufacturing process. At present, there are a lot of new type of semiconductor material toappear constantly, but single-crystal silicon is still as the substrate material in most of thesemiconductor devices and circuits. Silicon wafer through lapping/polishing with highquality is the most important basic functional materials in chip manufacturing and integratedcircuit development. So the silicon wafer used in integrated circuits should have minimumsurface roughness and high surface flatness and surface integrity. And grinding and polishingis the last process to obtain silicon wafer with nanoscale super smooth surface and no damage,so to research the silicon wafer surface material removal mechanism becomes very important.Researching the lapping/polishing process through the experimental method is often limitedby experimental conditions and the cost is expensive, so the way to combine the experimentalmethod and simulation method is very effective to study the mechanism and optimize theprocess of lapping/polishing.Firstly, in order to research the lapping/polishing process, this essay based on the finiteelement software MSC. Marc establishes three dimensional contact model of the siliconwafer and polishing pad and the polishing disk from the macro scale to study the effects ofthe contact pressure between silicon wafer and polishing pad on the material removal rate andthe flatness, and study how to make use of the keep ring to eliminate the non-uniformity ofmaterial removal rate across silicon wafer, especially in silicon wafer diameter field. The bestdistance between keep ring and silicon diameter is6mm~10mm is confirmed through thesimulation, in other words, when the distance between keep ring and silicon diameter is6mm~10mm, the non-uniformity of material removal rate can be reduced even eliminated by adjusting the pressure on the wafer and keep ring. At the same time, to polish thesingle-crystal silicon and to obtain the experimental data by making use of the profilemeasuring instrument. By changing the pressure on the wafer and keep ring to obtain the twoexperimental data, the wafer profile of first experiment is better than that of secondexperiment. Then to compare the experimental results and simulation results, and find thatthe contact pressure variation of wafer silicon is related very well to variation of wafer profile,so confirm the correctness of the simulation. The purpose of simulation and experiment is torealize the uniformity of material removal rate across the silicon wafer, then to polish thesilicon wafer with high flatness.Secondly, to study the interaction between grinding grain and silicon wafer from themicroscale and effects of the abrasive size and shape as well as movement of abrasive onsurface scratch of silicon wafer. For sphere grain, when grinding grains cut into silicon wafersurface at the same Angle, grinding grain sizes will produce very large influence on normalforce, and the normal force will increase with the increase of the radius of abrasive, but theeffect of grinding grain radius size on tangential force is very small, and smaller grindinggrain radius is, bigger the residual scratch deep and pile-up of scratch are. For the triangularbody abrasive, during the process of abrasive cutting into silicon material, normal force onabrasive has undergone rapid increase, basic constant, increase again, and the normal forceand tangential force will change with the changes of rotational speed. When rotation speed ofgrinding grain is smaller, there exists an high Von-Mises stress area near the contact betweenabrasive and silicon material, and the high Von-Mises stress area extends from the effectivegrinding edge to the root of wear debris. When rotational speed of the triangular bodyabrasive speed is larger, higher Von-Mises stress area is divided into two areas, one area isnear the effective grinding edge and extends basically along the direction perpendicular to thefront outspread of the triangular body abrasive, another area is near the root of wear debris.For four edge body abrasive, there also exists an high Von-Mises stress area near the contactbetween abrasive and silicon material, however, abrasive wear debris shape caused by byfour edge body abrasive and triangular body abrasive is significantly different. Finally, to sum up the whole thesis and project the further simulation work planning,meanwhile put forward some improvement measures according to the present simulation andexperiments.