Analytical Prediction Of Damage Layer Depth Of Ground Surface Of Monocrystalline Silicon Wafers Induced By Ultra-fine Grinding

Integrated circuit(IC)serves as the core device of the electronic information industry,which lays a solid foundation for the development of the information technology.Monocrystalline silicon is widely used in the manufacturing process of the integrated circuit.As a typical hard-and-brittle material,wire sawing,ultra-fine grinding,lapping and polishing are the common techniques to process hard-and-brittle materials,among which,lapping and polishing have low production efficiency and poor wafer thickness uniformity,which makes ultra-fine grinding act as the most suitable technique for the efficient manufacturing of hardand-brittle materials with high efficiency and good wafer thickness uniformity.Compared to the conventional straight surface grinding,wafer rotation grinding has the capability of producing better total thickness variation(TTV),and is easy to realize on-line measurement,which makes it widely used in the manufacture of integrated circuit.Grinding with diamond wheels will inevitably generate surface/subsurface damage,which can reduce the strength and performance of the machined parts.As a result,the prediction and control of grinding damage becomes the core issue in the ultra-fine grinding.Damage forms and depths can be judged by grain depth-of-cut,which plays an important part in the prediction of the transition point from brittle mode to ductile mode and also the subsurface damage depth in order to shorten optimization cycle of the grinding process,improve the quality of machined parts and reduce costs.However,predicted grain depth-of-cut based on existing models derived from wafer rotation grinding deviates obviously from experimental results with decreasing grain size and is too small to make physical sense,which neglect the influence of the effective cutting edge radius,the number of active grains,the minimum grain depth-of-cut and the springback of the workpiece.Moreover,existing analytical models of the subsurface damage depth usually aim at the brittle mode,while little analytical models of subsurface damage for ductile mode are reported.The main contents of this paper are as follows:(1)Based on wafer rotation grinding process,analytical model of grain depth-of-cut for ductile mode is proposed through comprehensively considering effective cutting edge radius,number of active grains,minimum grain depth-of-cut and workpiece springback.The influences of these parameters on the value and radial variation of grain depth-of-cut are also discussed.(2)Due to the difficulty of measuring nanoscale chips generated in the ultra-fine grinding,the relationship between grain depth-of-cut and surface roughness Ra has been used for model validation.The proposed grain depth-of-cut model is assessed through the comparison between the predicted surface roughness Ra and experimental results,which shows a good agreement.(3)The plastic zone size of the scratch groove is obtained by grain depth-of-cut,which is used for the prediction of the subsurface damage depth for ultra-fine grinding in this paper.The subsurface damage depths of ground silicon wafers are observed by transmission electron microscope and are compared with the predicted results,thus validating the analytical model of the subsurface damage.