| The third-generation semiconductor material,gallium nitride,has excellent physical and chemical properties and has attracted extensive attention from researchers.However,due to its high hardness and chemical inertness,the precision machining time is long and the machining efficiency is low.Gallium nitride is prone to microcrack initiation and expansion during diamond precision machining,causing damage to the crystal surface and subsurface,increasing material removal amount in subsequent finishing process,and ultimately affecting the performance and life of gallium nitride semiconductor devices.Therefore,it is very important to study the initiation and propagation of microcrack of gallium nitride during diamond precision machining.The nucleation and propagation of microcrack depends on the distribution of the total stress field in precision machining.In this paper,the subsurface total stress field mathematical model of single-crystal gallium nitride of single scratching by diamond particles is established,and the initial load of the median crack is analyzed and studied.The mathematical model of radial crack for scribing gallium nitride is established,and the nanomechanical testing system(Bruker Hysitron TI980)was used to carry out the diamond gradual loading single scribing experiment on gallium nitride wafer.The lateral crack mathematical model is established,and the influence of the distance between scratches on the initiation load of lateral crack and median crack is studied separately under the conditions of simultaneous double scratching and continuous double scratching of single crystal gallium nitride.The main content is:(1)The mathematical model of anisotropic subsurface total stress field of diamond scratching single crystal gallium nitride is established by superimposing elastic stress field and residual stress field.The initiation load judgment basis of median crack initiation in gallium nitride wafer is proposed when the tensile stress σ22 at the edge of the plastic domain in the x2=0 plane reaches the maximum stress value under the corresponding load greater than the allowable fracture strength value of gallium nitride,and verified by the experimental results.At the same time,the variation law of the stress field under the condition of different diamond tip half cone angles was studied.(2)The surface total stress field for scribing gallium nitride is calculated and analyzed by superposing the boussinesq field,cerruti field and sliding blister field which have been led-in anisotropy parameters.Then on the basis of the distribution of the maximum tensile stress on the scribing surface,the nucleation and initial spread angle of radial cracks are analyzed,and verified by the experimental results.A diamond conical indenter with the cone angle of 60°and a tip arc radius of 5 μm is used to perform the gradual loading scribing experiments on gallium nitride(0001)crystal plane along the[11-20]crystal orientation,and the microscopic mechanism of material removal during gallium nitride scribing was studied.The radial crack model is used to analyze other hexagonal crystal structure materials,and the calculated results are consistent with the experimental values in the literature.(3)Based on the residual stress field,the mathematical model of lateral crack of diamond scratching single crystal gallium nitride is established.On the base of the established mathematical models of lateral crack and median crack,the mutual influence law of the distance between two scratches on the initial load of lateral crack and median crack is studied in the case of simultaneous double scratching.The influence law of the residual stress field of first scratch on the lateral crack and median crack initiation load of second scratch at different separation distance is also studied during continuous double scratching. |
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