Research On Dicing Of Glass/Silicon Multilayer Bonding Plate Based On Laser Induced Thermal-crack Propagation

The wafer level chip scale packaging(WLCSP)of multilayer silicon/glass using anodic bonding technology has gained widespread adoption in manufacturing the semiconductor devices used in the IC industry,MEMS and solar energy system.Dicing would account for one of the most significant manufacture procedures in the post-packaging process of the silicon/glass device.The conventional mechanical blade dicing method has low efficiency and tends to cause edge damages and pollution,and hence influencing the yield and the reliability.The laser stealth dicing and ultrafast laser dicing methods would induce numerous damages in the recast layer and the heat affected zone(HAZ)at the cutting edge,and require complex process flow and the high cost of ownership of a laser dicing system.Laser induced thermal-crack propagation(LITP)method using laser spot as a continuous moving local heat source to generate a tensile-compressive stress field which would induced the crack propagate and separate the material.The LITP method is an economic,environmental-friendly,high-efficiency and high-quality dicing method for brittle materials such as glass,silicon and ceramic.However,there exist few studies concerning dicing of multilayer silicon/glass anodic bonded plate using LITP technology.The industry commonly used semiconductor laser was introduced as the heat source,and the LITP dicing machine with double lasers was introduced as the experimental setup.LITP dicing of the silicon/glass double layer plate and glass/silicon/glass triple layer plate,was studied.The physical process of LITP dicing multilayer silicon/glass plate was analyzed theoretically.Reasonable assumptions were purposed,and the laser beam characters,material physical properties and environmental conditions were considered.The mathematical model of a combination of the volume heat source and the surface heat source was established.The heat transfer,thermal-elastic and fracture problems and its initial conditions and boundary conditions were defined.The three dimensional initial crack included finite element(FE)model was built for process analyzing of LITP dicing multilayer silicon/glass bonded plate.Temperature measuring experiment was carried out for FE model verification.The mechanism of LITP dicing silicon/glass double layer bonded plate,and the mechanism of LITP dicing glass/silicon/glass triple layer bonded plate using double laser beam,were studied through simulation and experiment.And the crack synchronous propagation process in the multilayer bonded plate was revealed.For the double layer plate,the temperature and thermal-stress distributions and the crack propagation status were calculated using the extended finite element method(XFEM).And the surface morphology on the specimen fracture surface at the steady crack propagation stage was analyzed.The influence of the differences between the physical properties of silicon and glass on the fracture process of the silicon/glass plate,was investigated.The mechanism of crack path deviation at the trailing edge was investigated,and the improvement method for the path deviation was studied.For triple layer plate,the temperature and thermal-stress distribution was calculated at three different stages of the crack propagation process,include the entrance stage,the stable crack propagation stage and the exit stage.And the crack front J-integral distribution under critical status was further investigated.The regularity for change of ripple lines of the edge structures on the fracture surface were obtained.The similarities and differences between LITP dicing mechanisms of the double and triple layer bonded plate were studied.Based on the theory of anisotropy thermal-elastic mechanics and crystal physics,the stiffness coefficient tensors under fixed coordinate system for different dicing directions on different types of wafer were calculated.Based on the Irwin's analytic solution of crack-tip stress field from classic fracture mechanics,the theoretical crack-tip stress angular distribution of the mixed-mode cracks were calculated,and set as comparison for crack-tip stress field analysis.The thermal-stress distribution was calculated,and the influence of dicing directions on the stress intensity factors ratio KII/KI and KIII/KI during LITP dicing of silicon/glass bonded plate was obtained.By examining the fracture surface gained from experiment,the influences of anisotropy of single crystal silicon on the dicing quality were investigated.The influence of dicing process parameters on temperature distribution was investigated,and the reasonable range of the process parameters was analyzed.Then,the influences of process parameters on crack initiation minimum condition,dicing quality at the leading/trailing edges,and fracture surface quality at the stable stage were analyzed through experiment.And the optimized process parameters were acquired.Furthermore,the experiment of LITP dicing silicon/glass wafer at 110mm/s dicing speed was performed,and the roughness of the obtained fracture surface is down to nanoscale.The temperature and thermal-stress distribution under high dicing speed,was calculated.By comparing the simulation results with the fracture surface morphology gained by experiment,the crack asynchronous propagation process under high dicing speed was revealed.Additionally,the temperature and thermal-stress distribution,the stress intensity factor,and the fracture surface morphology under asymmetric line dicing of the silicon/glass plate using LITP were studied,and the path deviation mechanism was studied.Experiments of asymmetric line dicing and curve dicing of glass/silicon/glass plate using LITP technology were performed,and the path deviation phenomenon was investigated.