Study On Mechanism Of Laser Backside Wet Etching Sapphire Substrate Based On Metal Salt Solution

Sapphire’s excellent optical,physical and chemical properties make it widely used in high-end smartphones,tablet computers,flat-panel television and other electronic display industries,aerospace industry,chemical technology and many other fields of equipment.Laser induced backside wet etching（LIBWE）,as a new processing technology,has been widely studied for its high quality transparent brittle material processing.At present,there are mainly three kinds of working solutions used in LIBWE,such as metal salt solution,organic solution and mixed solution containing metal particles.Because of the introduction of working solutions,the processing is unstable and the mechanism of processing becomes more complex.Many researchers used different working fluids to study its processing mechanism,and put forward some deposition theory and physical adsorption theory.However,these theories can not fully explain the observed phenomena,so the research on the mechanism of LIBWE using a single clear and non-toxic metal salt solution is conducive to more clearly observe and analyze the changes of its processing process,thus explaining and supplementing its processing mechanism.At the same time,according to its research mechanism,it has certain guiding significance on how to select parameters for high quality processing and efficient cutting of materials.In this paper,metal salt solution is used as working fluid to study the laser induced backside wet etching sapphire theoretically and experimentally,which provides theoretical guidance for obtaining high efficiency and high quality processing technology.Firstly,the relationship between the properties of the solution and the etching effect in different inorganic metal salts solution is analyzed.Secondly,the change of decomposition temperature and process of sapphire during LIBWE was obtained by component analysis.The influence of decomposition temperature on the etching results was studied by analyzing the etching results of organic compounds in aqueous solution.Finally,a high-speed photographic platform was set up to observe the dynamic characteristics of cavitation in different solutions during LIBWE,and the dynamic characteristics of cavitation under different laser energy density and laser repetition frequency.Based on the analysis of the etching rate of sapphire at different frequencies,the influence of incubation effect,i.e.laser repetition frequency,on the processing efficiency was studied.The sapphire was cut efficiently and etched with high quality in combination with the optimized process parameters.The main research methods and conclusions are as follows:（1）A system of LIBWE is constructed,which consists of a pulsed fiber laser（wavelength 1064 nm）,a high-speed camera system and a computer control system.The metal-salt solution such as CuSO₄,CuCl₂,FeSO₄,FeCl₃,NiSO₄ and NiCl₂ with concentration of 1 mol/L were prepared.The six metal salts were used as working fluids for LIBWE of sapphire.The transmittance and absorbance of the six solutions were measured by ultraviolet,visible and near infrared spectrophotometer,and the etching effect in different solutions was compared with the absorbance at 1064 nm.The results show that under the same conditions and parameters,the etching rate of sapphire decreases from CuSO₄,FeSO₄,NiSO₄,CuCl₂,NiCl₂ to FeCl₃ in turn,while the absorbance of solution decreases from CuCl₂,CuSO₄,NiCl₂,FeSO₄ to FeCl₃ in turn.In conclusion,the absorbance of the solution has little effect on the etching effect.（2）The products in the process of LIBWE were collected and dried in a constant temperature chamber at 40℃.The powder material was analyzed by EDS,XRD and XPS components,and the material removal mechanism and process were studied.The results show that when the working medium is CuSO₄ solution,the products consist of cuprous oxide and cuprous oxide.When the working medium is CuCl₂ solution,the products consist of cuprous chloride.According to the decomposition equation,the decomposition temperature of copper sulfate is low,and the micro-nano particles such as copper oxide and cuprous oxide produced during the decomposition process enhance the absorption of laser,thus enhancing the etching effect.However,the decomposition temperature of copper chloride is high,and the decomposition of copper chloride in the process produces less cuprous chloride,so the processing effect is weak.At the same time,in order to prove the influence of decomposition temperature on the etching effect,polyethylene glycol and anhydrous ethanol were added to copper sulfate and copper chloride solution respectively for LIBWE.The results show that the etching effect of inorganic substances with low decomposition temperature in solution is stronger than that without organic substances.Therefore,the decomposition temperature of solution is the main factor affecting the etching effect.（3）A high-speed photographic system was set up to observe the dynamic behavior of cavitation in the process of LIBWE of sapphire in different solutions.The effects of laser energy density and laser repetition frequency on the dynamic characteristics of cavitation were studied,and the etching rate of sapphire at different frequencies was analyzed.The results show that the bigger the laser energy density,the bigger the cavitation,the stronger the etching effect;the higher the laser repetition frequency,the bigger the cavitation,the stronger the etching effect and the more obvious the inoculation effect.The etching rate is determined by the size of the cavitation.The key to improve the etching rate is to increase the laser repetition frequency.（4）The process of LIBWE of sapphire was studied.The effects of laser energy density,scanning speed and scanning times on the quality and depth of sapphire etching were studied by single factor experiment.Finally,the sapphire can be cut efficiently and etched with high quality by optimizing laser processing parameters.