Study of freeform lens for UV-LEDs exposure system with reflector for uniform irradiance

In this study, UV-LED (ultraviolet light emitting diode) is developed for photolithography industry. Since the accuracy of the degree of cross linking and sidewall profile could be affected by intensity of UV light dosage, this research proposes optical design and fabrication of freeform lens with reflector coated on the light source element of UV-LED for exposure systems. Based on the law of conservation of energy and Snell´s law method, a free-form lens is designed in the study. The optical distribution intensity of the freeform lens with reflector layer was determined by using commercial optical simulation FRED software. The experimental results show that the average irradiance and uniformity on the target plane with 60 degree reflector layer were 8.7mW/cm² and 86.9%, respectively. The irradiance and uniformity were higher than that of freeform lens without reflector, 7.8mW/cm² and 87%, respectively. Therefore, the results show that the freeform lens with reflector was demonstrated to obtain 97.5% average normalized cross correlation (NCC) between the simulation and experimental measurement of UV-LEDs exposure system. Through this design of reflection of UV-LED light source, the intensity and uniformity can be enhanced significantly.