Study On Laser Cutting Technology With Low Damage Under Thin Water Layer

Monocrystalline silicon is a kind of brittle semiconductor material,which is widely used in microelectronics industry.Traditional mechanical processing is difficult to meet the current market demand,while simple laser processing often results in a large amount of heat accumulation and slag deposit.Underwater laser processing technology can reduce the defects of recast layer and heat accumulation,but there are still problems such as water layer fluctuations,air bubbles and debris interference.Water-jet assisted laser processing technology can improve the processing effect to a certain extent.The cutting method in which the laser scanning direction is opposite to the direction of the water-jet is defined as reverse etching in this paper.This method can form a continuous and more stable thin water layer in the processing area,and this scanning method is rarely reported.In order to improve the laser processing quality and energy utilization,a thin water layer formed by water-jet impact is used to assist the laser cutting of single crystal silicon wafers,and the reverse etching method is used to explore the water jet assisted laser processing method and its processing effect.The specific research is as follows :(1)In this paper,the physical phenomena and mechanism of laser ablation of substrate underwater are discussed firstly,and the process of plasma shock and cavitation shock produced by laser ablation of substrate underwater is mainly analyzed.In addition,the wall jet area formed by water jet impinging on the wall is analyzed.The wall shear stress and average convective heat transfer coefficient of the wall jet area are studied,and the influence on laser processing is analyzed.(2)Fluent software is used to simulate the impact process of two kinds of water jet with grooves.The results show that the reverse etch model has a larger flow velocity at the laser irradiation point,while the same-direction etching has a greater internal velocity.Then,the effects of changes in water speed and target distance on wall pressure and wall shear stress without grooves are simulated and analyzed.The simulation results show that the wall pressure in the X direction and the wall shear stress in the Z direction increase significantly with increasing water speed,while the impact pressure on the bottom wall is less affected by the change of target distance.(3)The experimental study of reverse etching is carried out,and the results are compared with that of etching method in the same direction.The experimental resultsshow that there is no pit damage on the upper surface of the groove obtained by reverse etching,which has smaller roughness,neater groove edge line and larger depth-width ratio.Then,the influence of laser power,scanning speed,nozzle target distance and water jet speed on the groove shape is studied by using the control variable method.The difference between the two etching results caused by the change of process parameters is analyzed.The results show that the groove surface obtained by reverse etching has higher surface quality and energy utilization.(4)The prediction model of groove width and depth obtained from reverse etching is established,and the accuracy of the model is verified by variance analysis.The predicted results of the model are basically consistent with the experimental results,and the errors of the corresponding groove width and depth are 7.04% and2.61% respectively.