Research On Influence Of Crystal Anisotropy On The Surface Shape Deviation Of Sliced Wafer By Diamond Wire Sawing

Electroplated diamond wire saw is widely used in the slicing of crystal materials due to its advantages of small kerf loss,large gripping force of abrasive particles and high cutting efficiency.Diamond wire saw sawing technology is the mainstream technology for slicing various crystal materials.At present,research on diamond wire saw sawing mainly focuses on its material removal mechanism and the crack damage of the sliced wafer.However,crystals are usually anisotropic materials.The anisotropy of the crystal during sawing may cause the transverse force,which would lead to the deviation of the diamond wire saw in the direction of wafer thickness,resulting in the large surface shape deviation of sliced wafer.The surface shape deviation of sliced wafer would increase the cost of subsequent precision machining and affect the wafer orientation accuracy.Monocrystalline silicon and KDP crystal are research objects of this paper.The influence of crystal anisotropy on the sawing force of diamond wire saw was analyzed.The prediction of surface shape deviation of monocrystal line silicon and KDP crystal in different crystal planes and processing conditions was realized.The research work is of great significance to improve the surface shape accuracy of sliced wafer by diamond wire sawing.The main research work of this paper is summarized as follows:1)Considering the influence of crystal anisotropy,the sawing force of diamond wire saw was analyzed and calculated.A three-dimensional model of diamond wire saw was established.The cutting part of diamond abrasives were simplified as cones.The size of abrasives is in normal distribution,and the abrasives are distributed randomly on the surface of diamond wire saw.Expression of crystal orientation on the cross section of diamond wire saw was derived by coordinate transformation,and the anisotropic parameters such as elastic modulus,hardness,fracture toughness and critical depth of brittle plastic transition were obtained.In the condition that the(100)crystal plane of monocrystalline silicon is sliced and the feed angle of wire saw is 0°,the sawing forces were calculated,and the quantitative relationship between normal sawing force and process parameters was obtained by data fitting.The slicing experiments of(100)crystal plane of the monocrystalline silicon with different process parameters were carried out.The experimental values of sawing force were obtained by measuring the deflection of the wire saw.The relative error between the experimental values and the calculated values of sawing force is 1.0%?6.3%.2)Anisotropy properties of several crystal planes of monocrystalline silicon in slicing process were analysed.The sawing force and the surface shape deviation of monocrystalline silicon wafer caused by sawing force were studied.The influence of crystal anisotropy on the surface shape deviation of silicon wafer was obtained.In slicing of the(100),(110),(111),(112)and(120)crystal planes of monocrystalline silicon,expression of crystal orientation of the sliced silicon on the wire saw section was obtained by the coordinate change.Then the anisotropic properties of the silicon were analysed.The sawing force was calculated by the established sawing force calculation method considering crystal anisotropy.The spatial shape of diamond wire saw under sawing force was analyzed,and the influence of anisotropy of monocrystalline silicon on the surface shape deviation of sliced wafer was obtained.The conclusions are as follows:when the(100)and(110)crystal planes of silicon are sliced,the anisotropy of silicon would not affect the surface shape deviation.For the(111),(112)and(120)crystal planes,the anisotropy of silicon would affect the surface shape deviation of the wafer.However,the influence of anisotropy on the surface shape deviation can be minimized by selecting specific wire saw feed angles.The experiments of slicing monocrystalline silicon with different crystal planes and wire saw feed angles were carried out.The surface shape deviation of monocrystalline silicon wafer was measured experimentally.The maximum relative error between simulation and experiment results of the surface shape deviation is 8.57%.3)Coupling stress of the sawing force and heat in KDP crystal in slicing was studied,and the critical process parameters of no cracking failure in slicing were obtained.A finite element model of KDP crystal in diamond wire saw slicing was established by ABAQUS software,while the material removal process was simulated by the method of element birth and death.The sawing force of KDP crystal was obtained by the established sawing force calculation method.The distribution of sawing force and heat absorbing power in the saw seam area was derived and applied to the KDP crystal.Then the temperature field and the stress field of KDP crystal were obtained and the coupling stress of the sawing force and heat in KDP crystal in sawing was studied.The influence of sawing parameters on the coupling stress was studied.The failure criterion of maximum tensile stress was used to obtain the critical process parameters of KDP crystal in slicing without cracking.It was found that the stress caused by thermal stress is the main reason for the cracking of KDP crystal.The critical process parameters of KDP crystal without cracking were obtained,when the value of vf0.7940vs0.1912 is less than 0.9910,the KDP crystal would not crack in sawing.4)Anisotropic properties of three commonly used crystal planes of KDP crystal were analysed.The sawing force was calculated and the surface shape deviation of sliced wafer was predicted.The influence of the anisotropy of KDP crystal on the surface shape deviation of sliced wafer was obtained.In slicing of the three commonly used crystal planes of KDP crystal with any wire saw feed angle,crystal orientation expressions of the sliced KDP crystal on the wire saw section was obtained by the coordinate change.And the anisotropic properties of KDP crystal were analysed.The sawing force of KDP crystal was obtained by the established sawing force calculation method considering crystal anisotropy.The force model of diamond wire saw was established in ABAQUS.The spatial shape and three-dimensional trajectory of diamond wire saw cutting are obtained.The surface deviation of sliced wafer of KDP crystal was calculated,and the influence of anisotropy of KDP crystal on the surface shape deviation of wafer was obtained.It was found that,for the(001)crystal plane,the anisotropy of KDP crystal does not affect the surface shape deviation of the sliced wafer.For the double and the triple frequency crystal planes,the influence of anisotropy of KDP crystal on the surface shape deviation can be minimized by selecting certain feed angles of the wire saw.