Abstract
We propose a novel excimer laser machining using a multiple imaging system employing a holographic optical element (HOE). The multiple imaging system can generate many images from one mask pattern. The HOEs that we used were com-puter generated phase holograms.
We calculated the HOE by with the following three-step optimization using a direct binary search algorithm, 1) high efficiency enhancement step, 2) uniforming step and 3) noise reduction step. By this optimization procedure, a diffraction efficiency over 60% was obtained, the uniformity errors were less than 2%, and noise peak was less than 5% of signal peaks. The optimized HOE pattern was 4-level, and the matrix size was 1024×1024 with 1 micron pixels. To obtain a large HOE area, we tiled the optimized HOE pattern, and manufactured 30×30mm HOEs on a quartz substrate by dry etching.
With the use of this HOE, the 95 holes whose diameter was 0.1mm were drilled in a 10×10mm area. The energy avalil-ability was 19.4%. When a conventional mask-projection system is used, the energy availability is usually less than 1% owing to the small rate of the mask open area, A multiple imaging system using HOE can machine small holes at an efficiency up to 20 times that of conventional mask-projection system.
