This paper presents the properties of the Sigma7300 which is a commercial DUV laser pattern generator based on spatial light modulator (SLM) technology designed to meet the requirements of the 65-nm technology node and below [1]. The introduction of spatial light modulators provides a possibility for optical mask writers to combine high resolution and accuracy with short write time making it possible to write most of the high end mask layers in a cost effective way. The Sigma7300 mask writer is developed by Micronic Laser Systems whereas the SLM, which is a combined MEMS and CMOS component with individually controllable movable micromirrors, is developed by the Fraunhofer-IPMS institute in Dresden. The SLM allows parallel writing of one million pixels with a frame rate of up to 2 kHz. The technology offers resolution enhancement advantages from stepper technology not available in other mask patterning tools [2].
We propose a brief overview of different techniques to implement complex-valued filters on binary spatial light modulators (SLMs), including encoding techniques at both pixel-and cell-(i.e. group of pixels) levels. We show that group-oriented methods offer extended coding domains, at the expense of a reduced space bandwidth product and spurious noise in the correlation plane. We propose the concept of a time multiplexing technique that combines at the pixel level the pseudorandom encoding method with the minimum Euclidean distance approach. This pixel-oriented method offers the advantage to keep the full space bandwidth of SLMs, and the possibility to very efficiently encode ternary filters {-1, 0, +1 }on binary phase {-1, +1 } SLMs. Tested on a sequence of images acquired with an JR sensor in a tracking scenario (1 target), encoded ternary filters have offered superior performance in terms of peak-to-clutter ratio than classical BPOF (+45% in the simulation, +35% inthe first optical experiments).
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