Expeirmental Study On Material Removal Mechanism In Chemical Mechanical Polishing

Since1960s, the chemical mechanical polishing has been applied in the semiconductorindustry. From that time, the chemical mechanical polishing technology has been developingwith the development of the semiconductor industry, especially with the development ofintegrated circuit in the microelectronics industry. Currently, the chemical mechanicalpolishing technology has been widely used for precision polishing of many different materials,for example, hard and fragile material like: semiconductor material, jewel, optic glass withsuper cleanness requirements for special utilization. However, the research in this area by nowdoes not fully recognize the material removal mechanism of the chemical mechanicalpolishing, the relationship between the nanoscale sized abrasive particle, the micro-andnano-scale frictional and wear properties of single crystal silicon wafer and the materialremoval mechanism is not clearly understood, the related research is still in the beginningphase. Study on material removal mechanism in chemical mechanical polishing, study on thefunctions of these parameters of polishing load, speed, slurry chemical compositions, abrasiveparticles in the slurry, helps best select the polishing parameters, helps understand on thepolishing process deeply, it is conducive to well control and use this technology, to obtainhigh clean and non-damaged surface.Firstly, this paper built the mathematic model on material removal with consideration ofthe deformation of abrasive particle. Through calculation of the deformation of the abrasiveparticle, it is possible to calculate more precisely the depth of the abrasive particle embeddinginto the surface of the silicon wafer. With this depth, the removed material per unit time by theabrasive particle can be obtained. Simultaneously, the depth of the abrasive particleembedding into the surface of the silicon wafer determines the surface quality of the polishedsilicon wafer. Further study on the elements which are influencing the deformation of theabrasive particle, like: the size of the particle, its hardness, its elastic Young's modulus, etc.The following results can be achieved:?using the new model, the material removal ratecan be more precisely predicted, it is very close to the material removal rate obtained from theexperiments in this paper;?in the nanometer sized material removal research, the sizes ofthe particle itself is in nanoscale, its deformation can't be neglected;?the particle which isin a less hardness is more easily deformed by the outside force, the ploughed groove on thepolished surface is more shallow, it means that the roughness of polished surface is more less.Secondly, this paper studies the material removal mechanism of chemical mechanicalpolishing of single crystal silicon wafer under different lubrication conditions. By means ofnanoscale scratching experiments, the relationship between the polishing load and frictioncoefficient and the relationship between the polishing speed and the friction coefficient havebeen studied. The material removal rate is able to be obtained by calculation of the length,width and depth of the scratched groove, in this way, the relationship between the polishedload and the material removal rate and the relationship between the polishing speed and thematerial removal rate are obtained. The results from the experimental studies show that, in the nanoscale the material removal rate is direct proportional to the polishing load, but theincreasing of the polishing speed does not means that a higher material removal rate is surelyto be reached. At the same time, the different lubrication conditions in the polished interfacesinduce different material removal mechanisms: in the dry frictional condition, the singlecrystal silicon wafer presents a kind of material removal mechanism of adhesion wear in thechemical mechanical polishing; under the hydrogen peroxide lubrication, the materialremoval is a kind of material spalling which is induced by the micro cracks; under thedeionized water lubrication, the smallest scratching depth is0.0063nanometer in thenanoscale scratching experiments, it proves that the material removal mechanism is amolecular-scale material removal.Moreover, the reseach work of this paper also explored a novel research method forstudy on the surface and subsurface damage of polished single crystal silicon wafer. Byutilizing the modern devices and equipments in Suzhou Nano Science and TechnologyResearch Institute of China Academy of Sciences, the specimen of the single crystal siliconwafer with the nanoscale scratching from the nanoscale scratching experiments aresuccessfully prepared for the further study by the Transmission Electron Microscopy, and thestudy in a high resolution scope has been successfully carried out. Through this study, the lawof the damages and disfigurements like aberration and phase changing of crystal lattice etc.which are caused in the nanoscale scratching experiments in the surface and subsurface ofsingle crystal silicon wafer under different loads and speeds in the deionized water lubricationand hydrogen peroxide lubrication conditions has been mastered.Further study on the crystal structure of the nanoscale scratched surface and subsurfaceunder deionized water lubrication and hydrogen peroxide lubrication by comparison, reachesthat the chemical composition in the slurry reacts with the polishing surface material, thechemical features of the surface have been changed, the surface material becomes easy to beremoved by the mechanical effects; but, excessive chemical reactions will easily bring surfacedamage and subsurface damage also. The research results have proven that the synergiceffects of mechanical function and chemical function in the chemical mechanical polishing,and its influence to the outcome of the chemical mechanical polishing by the evolvement ofthe synergy of mechanical effects and chemical effects. In the nanoscale scratchingexperiments with deionized water lubrication and hydrogen peroxide lubrication, thefrictional chemical reactions happened in the frictional interface, and generate lubricatingfilms when the sliding speed unchanging and the load is between30mN and70mN. Hence,under this condition, mechanical effects can accelerate, or in other words, can expedite thechemical effects. Thus, the consumption of total energy and material will reach the minimumand the material removal rate may reach the maximum, no surface damage and no subsurfacedamage, less or no chemical pollution when the balance of mechanical energy and chemicaleffects, mechanical energy accelerating chemical effects, mechanical effects controlling thechemical effects are realized.Through the adjustment of mechanical and chemical parameters in the chemicalmechanical polishing processes, the mechanical effects dominating chemical effects may berealized. This research result in this dissertation built the foundation of less/non chemical pollution, green, undamaged and precise polishing technology, and the results providedsupplied the theoretical and experimental foundation for the clean mechanical effectsdominated high efficient green precise polishing so as to obtain the ideal surface from thechemical mechanical polishing.