Study On The Processing Mechanism And Technological Rule Of Sapphire Substrate By Laser-Induced Backside Wetting Etching

Sapphire is characterized by high wear resistance, high hardness, high brittleness, chemical stability and so on. It is the most important commercial substrate for blue LED, window material in industrial and national defense field and bearing material. The traditional mechanical dicing method has the inherent disadvantages of chipping, crack and tool wear. Dry and wet chemical etching method is difficult to process this kind material. Furthermore, the regelation layer and thermal destruction phenomenon easily emerge during the process of laser dry etching sapphire. Laser induced backside wet etching method (LIBWE) can effectively avoid this flaws with advantages of no regelation layer, less micro crack and small heat affected zone, less in transparent material precision cutting, groove and other processing, Therefore, it is of great significance researching on LIB WIE in numerous aspects such as cutting the transparent material precision, machining micro flow channel and other microstructure.1. In this article, using the inorganic salt solution-CUSO4solution-as working fluid assisting pulse infrared laser induced backside etching method processed sapphire. Using high speed photography experimentally observed the laser-induced cavitation bubble’s growth, compression and collapse process, and using the Rayleigh-Plessent equation numerical calculation the internal pressure change, the pressure inside cavitation bubble can reach up to high pressure, and the high strength of shock wave is formed in the liquid. The shock wave formed during cavitation expansion process and the micro-jet and reverse jet generated during cavitation collapse process lead to the liquid flowing. Under the action of the confined plate, two annular backflow zone are formed between the sapphire and the limiting layer, increasing the pressure of liquid and enhancing the capability of overflow along the groove.2. The grooves processed using various processing methods and their edge areas is detected by EDS, finding that the copper amount at the the groove bottom is greater than at the edge areas. Employing a one-dimensional heat conduction equation analyzed the temperature field at the laser and material interaction region, discovering the liquid temperature at the solid-liquid interface does not reach the melting point of sapphire. Therefore, it can be deduced that CUSO4solution produced photochemical reaction after absorbing the laser energy, generating photochemical deposition including copper element on the rear sapphire surface. The deposition enhances the absorption rate of1064nm laser and then increases sapphire etching rate; Because of the restrictions of the confined plate, the liquid capability of overflow along the groove increased, so the copper amount at the the groove bottom is greater than at the edge areas.3. The main effect factors during laser processing sapphire were analyzed, a series of single factor experiments have been conducted to explore the effects of pulse energy, scanning speed, and scans times, liquid concentration and liquid film thickness on the groove size and quality. The following conclusions are drawn:(1) groove depth and width increases with the increasing pulse energy, At this time, groove bottom and edge become neat, avoiding the machining defects caused by small laser energy.(2) with the increasing scan numbers, the groove depth and width increase, besides, when the scanning number is small, the photochemical deposition displaying a asymmetric distribution, the groove quality is poor, with the increasing scanning frequency, the grooving quality is improved significantly;(3) Under the action of laser, the CUSO4liquid with a low concentration produce a uneven photochemical deposition, the groove quality is poor, the groove quality increase with the increasing liquid concentration,(4) The width and depth of the groove increase when the scan times increases, and the quality of groove improve;(5) with the increase of liquid film thickness, a groove depth first increased and then decreased, when the thickness of liquid film is less than the diameter of the cavitation, emerging instability processing phenomenon, in the contrary case, there is a micro jet enhancement effect.