Measurement And Evaluation For The Optical System In Excimer Laser Projection Lithography

With the wide applications of laser lithography in laser micro machining fields,measuring and evaluating optical system of laser lithography obtains intensive attentions. If the beam of exposure system is non-uniform, it will result in the mask graphic inconsistencies under same light mask of the same phase-stepped, causing the mask graphic around the middle part is greater than the amount of exposure, resulting in insufficient about the exposure or overexposed of the middle part. As to the problems of beam exposure system of energy utilization and a whole requirment by uniformity through laser projection system, all require some evaluation norm quantitatively:such as evaluation index of excimer laser beam uniformity,which including the processing window, energy fraction, top-hat factors, dynamic range and evaluation norm of the system: beam quality factor M2.Discusses a evaluating specification on the optical system of laser projection image lithography that can help our to define the optical system requirements and to compare the optical system. While this evaluating specification will not answer all questions about the optical system, it can be used as a figure of merit for the optical system. This paper begin with measuring the optical system, then discuss the various important characteristics of this evaluating specification on the optical system, and finally we conclude that the evaluating specification on optical system of laser lithography has some certain significance.Based on the system of a large-area laser projection image lithography using351nm XeF excimer laser, some optical properties of the system including the illumination system with numerical aperture (NA) value of0.02and the folded projection system with NA value of0.025are measured. According to the variation of energy and beam quality past through two cylindrical square lens and two micro lens array, some evaluating norm about excimer laser beam uniformity is partly adopted to evaluate this optical system. The energy distribution on different crucial areas of the optical system and the top-hat factor can be obtained. The results show that the micro lens array maintains the beam uniformity, whereas the energy utilization rate is suppressed due to the diffraction. Meanwhile, through the PCB and ITO lithography experiment, it shows that the designed double-telecentric confocal projection lithography system can meet the required resolution, provided the uniform-output energy is controlled to be in accord with the exposure dose.