||Exposure process plays an important role in high technology electric industry, and it is an inevitable trend that conventional mercury lamp will be replaced by UV LED (Ultraviolet Light-Emitting Diode). In the exposure process, the intensity and uniformity of light in the exposure area directly influence the precision of products. So how to improve the intensity of light without reducing the uniformity is the main direction. |
This article is based on the law of conservation of energy and law of refraction, by distributing the energy of emitting surface, a free form lens with uniform light field of main exposure area can be designed, and a TFMG is used as reflection layer, light outside the exposure area could be concentrated into the area to improve the intensity of light. The optical glass BK7 with high transmittance is applied as the material of lens and molding method is used to fabricating the lens. Al-base TFMG is coating around the lens by multi-gun sputtering method, the reflectance is about 80% at the UV wave band, it can improve the serious decay of reflectance of other pure metal such as Ag, Mg, Cu and their alloy at UV band wave. Beside, excellent scratch resistance and etch resistance could be achieved because of the unique amorphous structure.
This study used TracePro optical software to simulate and analysis the energy intensity and uniformity. According to the result of simulation, the compound lens can improve the average irradiance of exposure area for about 7.6 %, and maintain the uniformity at about 80%. According to the result of simulation, by using multi UV LED combined with light-uniform lens, 93% uniformity can be achieved. By the Polydimethylsiloxane (PDMS) lens, the uniformity measurement of UV LED exposure system can be increased from 69.49 % to 87.06 %. This result proves the effect of light uniform of the lens which we design. According to the measurement results of PDMS lens combined with reflective layer, while the coverage angle of reflective layer is 40°, the average irradiance can be improved by 6.61% and 83.7% uniformity can be obtained as well. After exposure process with PDMS lens, about 4% inaccuracy was obtained, comparing to 10% inaccuracy of general exposure system, it shows that using UV LED to replace conventional exposure lamp is available.