Study On The Thickness Of Sliced Single Crystal Silicon Wafer Sawn By Resin Bonded Diamond Wire Saw Based On The Fracture Strength Of Wafer

The thickness of the integrated circuit chip only accounts for 5%of the thickness of the sliced silicon wafer,and the rest is all removed during the process of wafer thinning.Besides that,the electronic structure of chip utilizes only 1%of the silicon wafer thickness,while the remaining 99%is only used for guaranteeing the required mechanical strength and stiffness during the manufacturing process of chip.With the development of semiconductor technology,the thickness of sliced silicon wafer decreases gradually.The improvement of production of silicon wafers,reduction of amount of subsequent processing and the optoelectronics industry production costs can be achieved by reducing the sliced wafer thickness.For this purpose,this thesis focus on the sliced thickness of single-crystal silicon wafer during resin bonded diamond wire sawing to study the strategy of reduce wafer thickness.The sliced wafer thickness is determined based on the fracture strength under a certain breakage ratio.Therefore,the cutting depth of abrasives,surface layer crack damage of sliced silicon wafer,fracture strength of sliced silicon wafers and the maximum stress of silicon wafer during wire sawing are studied.The results of this thesis can be used to providing the basis of reduction wafer thickness and promoting application and development of the technology of the fixed diamond wire sawing.The main research works in this thesis are summarized as follows.1)The models of resin bonded diamond wire saw and cutting depth of abrasives were established,which can be used to describe the shape,size,protrusion height,and location distribution of abrasives.The influences of processing parameters on cutting depth of abrasive were studied.After that,the mathematical relationship between the cutting force and the processing parameters was established by fitting the numerical results.The experimental parameters using for slicing silicon ingot were determined according to the bow angle of wire,which matched with the cutting ability of diamond wire.And also,the normal cutting force was obtained by measuring the bow angle of wire,which was used to be compared with the numerical results.The research showed that the main way of material removal was brittle fracture for resin bonded diamond wire saw.The quantitative relationship between normal cutting force and processing parameters was FN= 0.141vf0.728Ds1.017l0.975/vs0.656,and the ratio of normal cutting force to tangential cutting force was 1.2.The bow angle of wire measured by experiment was about 3°,which was close to the designed bow angle.It showed the correctness of the experimental parameter determination method which can be used to determine different wire sawing process parameters for different diamond wire saw.The maximum relative error between experimental and theoretical results was 8.07%indicating the correctness of numerical model of this paper.2)The median crack damage depth model for silicon wafers sliced by resin bonded diamond wire saw was established based on the cutting depth of abrasive.And the influence of processing parameters on crack damage depth was analyzed.The condition increasing cutting efficiency and ensuring smaller crack damage depth at the same time was obtained.The surface layer crack damage in sliced wafer was characterized by the method of cross-section microscopy.The morphology of sub-surface crack damage and the distribution of crack depth were analyzed by counting 200 cracks.At last,the distribution of surface cracks in the slice wafer was studied.The results showed that the abrasive particles generating median crack damage were mainly located between 57°and 90° of the cross-sectional of the wire saw.And the abrasive generating the maximum median crack damage depth was 78°,while the abrasives with the angle between 0° and 57° mainly realized the material removal.The median crack damage depth decreased with the increase of wire drawing speed and increased with the increase of feed rate,while it changed little when these two parameters increased proportionally.The sub-surface crack damage was formed by median cracks and transverse cracks,while the surface cracks crossed each other to form more complicated crack morphology.The distribution of surface cracks showed a certain distribution along both sides of the groove.The experimental results showed that most of the cracks had a depth between 5?m and 12 ?m,and the number of cracks with depth between 7 ?m and 9 ?m was largest.The number of cracks increased firstly and then decreased with the increase of crack depth.The depth distribution of surface crack obeyed Gaussian distribution.The maximum relative error between experimental and theoretical results of median crack damage depth was 10.36%.3)The numerical model of the fracture strength of sliced silicon wafers was established based on the experimental results of slice surface crack damage and the theory of the probability fracture strength of brittle material.The Weibull distribution of the fracture strength for silicon wafer was analyzed,and the influence of crack parameters on the fracture strength was also studied.The common characterization methods for fracture strength of brittle materials were compared and analyzed,and the fracture strength characterization method for single crystal silicon was determined.The load-displacement curve before fragmentation was measured and the theoretical and experimental results of fracture strength of single crystal silicon were compared and analyzed.The results showed that the fracture strength of silicon wafers distributed between 60 MPa and 300 MPa,and most of the fracture strength was between 80 MPa and 220 MPa,which were far smaller than the theoretical strength of silicon.The fracture strength of the silicon wafer tended to decrease first and then increase with the increase of the crack angle,The fracture strength distribution shifted to the right as a whole when the crack angle was larger than 45°.The Weibull distributions of the fracture strength obtained by the theory and experiment were very close,and the scale parameters obtained by the two methods were 157.4 MPa and 124.7 MPa respectively,indicating the correctness of the theoretical model.4)The forced vibration model of sliced silicon wafer was set up and the steady state solution of the forced vibration of the silicon wafer was obtained by using the thin plate theory and the integral transform method.The maximum stress of single crystal silicon wafer during the sawing process was analyzed,and the breakage rates for different thickness of sliced wafer at different sawing depths were obtained.The mathematical relationship between wafer thickness and breakage rate was established based on the fracture strength of silicon wafer.After that,two methods for determining the wafer thickness using the maximum stress and breakage rate were proposed.At last,the thickness of 450 mm silicon wafer and 156 mm×156 mm silicon wafer were determined.The results showed that the amplitude,maximum stress and breakage rate of silicon wafer during wire sawing increased with the increase of sawing depth,and increased with the decrease of slice thickness.Based on the thickness of 300 mm silicon wafer,the thickness of the 450 mm silicon wafer was determined which was 0.92 mm.When the silicon wafer breakage rate was 1%,the thickness of the 450 mm silicon wafer was 0.88 mm.The thicknesses of the 450 mm wafer determined by these both methods were according with the 0.925 mm prescribed by the SEMI.The thickness of 156 mm×156 mm silicon wafer was 0.197 mm determined based on the size of 125 mm×125 mm×0.18 mm silicon wafer,which breakage rate was 2.8%.