Study On The Material Removal Mechanism And Process Of Sapphire Substrate By Laser Induced Plasma Assisted Ablation

Sapphire is widely used in optoelectronics,information communication and industry due to its unique lattice structure and excellent comprehensive material properties.Since sapphire is a transparent,hard and brittle material that is difficult to process,traditional machining methods cannot meet the processing requirements of contemporary sapphire high-precision devices for miniaturization and low damage.Using non-contact processing methods such as ion beam processing sapphire surface damage is small but inefficient,while using laser direct writing sapphire has high efficiency but large surface damage.In this paper,a new low-damage and high-efficiency processing technology,namely Laser-Induced Plasma-Assisted Ablation(LIPAA),is used to realize the processing of sapphire microstructure,and its processing mechanism and process rules are deeply analyzed.Finally,the preparation of high-quality microstructures is achieved.In this paper,the experimental results of laser-induced plasma processing and infrared laser direct writing of sapphire were compared,and the feasibility of laser-induced plasma processing of sapphire was explored.The anisotropy of sapphire and the influence of metal target on the results of laser-induced plasma processing of sapphire were studied.The molecular dynamics simulation was used to assist theoretical analysis to reveal the mechanism and material removal mechanism of laser-induced plasma processing of sapphire.At the same time,the influence of process parameters such as laser parameters and target-to-substrate distance on the processing results was systematically studied,and a complete process solution was obtained from workpiece material to processing technology,and high-quality sapphire patterned microstructures were successfully prepared.The main research contents and conclusions are as follows:(1)Firstly,the experimental results of infrared nanosecond laser-induced copper plasma processing sapphire and infrared nanosecond laser direct writing processing sapphire were compared,which proved the feasibility of laser-induced plasma processing of sapphire.Compared with infrared laser direct writing processing,LIPAA processing sapphire has the advantages of lower energy threshold,lower damage,thinner recast layer and smaller heat affected zone,and has higher processing stability,and there are no micro-cracks on the surface of microgrooves.The surface quality and integrity of the microgrooves have been greatly improved.(2)Experiments were carried out on the main influencing factors of LIPAA processing,namely the influence of the anisotropy of sapphire and metal targets on the processing results.The material removal rate of sapphire during LIPAA for different crystal directions decreased sequentially from the C-plane to the M-plane,the A-plane,and the R-plane.According to the experimental results and theoretical analysis,it was deduced that laser-induced plasma processing of sapphire conforms to the material removal mechanism of thermal ablation,and material removal is peeled atomic layer by atomic layer.The material is mainly amorphized(that is,melted at high temperature)to form ablation products in the form of thermal ablation,and the ablation products are assisted by ion mechanical bombardment.Due to the difference in thermal conductivity and reflectivity of materials,when pure iron is used as the target of LIPAA,the material removal rate is significantly higher than that of pure copper,which is 3～4.5 times that of pure copper.Through the non-contact temperature measurement method,the average maximum temperature of the processing area of pure iron as the target reached 630 °C(430 °C for pure copper).Compared with pure copper as a metal target,the micro-grooves processed by pure iron are larger in size,thinner recast layers on both sides of the groove,clearer groove contours,and neat groove edges.The surface roughness of the groove bottom is lower,and the machining morphology,quality and contour sharpness have been greatly improved.(3)Molecular dynamics simulation-assisted analysis was introduced,combined with experimental and theoretical analysis results,the processing mechanism and material removal mechanism of laser-induced plasma processing of sapphire were mainly analyzed.In the process of laser-induced plasma processing,combined with the anisotropic results of sapphire,it was believed that thermal ablation dominates the sapphire material removal process.Combined with the analysis of the experimental results of the surface morphology of microgrooves processed under different targets,it could be inferred that the sapphire material is removed in layers by thermal ablation.Finally,the mechanism and material removal mechanism of infrared nanosecond laser-induced plasma processing of sapphire were revealed.(4)The effects of process parameters such as laser single pulse energy,scanning speed,repetition frequency,scanning times and target-to-substrate distance on the size and quality of microgrooves in laser-induced iron plasma machining were systematically studied through single factor experiments.The microgrooves and patterned sapphire substrates with neat edges,no cracks and chipping,and less recast layers were fabricated by using suitable process parameters and processing conditions,which proved the reliability of the laser-induced plasma processing of sapphire.