Lossless Compression Algorithms for the REBL Direct-Write E-Beam Lithography System

Professor Borivoje Nikolic Second Reader Date 2 ABSTRACT Future lithography systems must produce microchips with smaller feature sizes, while maintaining throughputs comparable to those of today's optical lithography systems. This places stringent constraints on the effective input data rate of any maskless lithography system. In recent years, my research group has developed a datapath architecture for direct-write lithography systems, and has shown that compression plays a key role in reducing throughput requirements of such systems. The approach integrates a low complexity hardware-based decoder with the writers, in order to decompress a compressed data layer in real time on the fly. In doing so, we have developed a spectrum of lossless compression algorithms for integrated circuit layout data to provide a tradeoff between compression efficiency and hardware complexity, the latest of which was Block Golomb Context Copy Coding (Block GC3). This thesis presents two lossless compression techniques, which optimize compression efficiency for use with the REBL direct-write E-beam lithography system. The first method, called Block RGC3, is a modified version of Block GC3, specifically tailored to the REBL system; the second achieves compression using vector quantization. Two characteristic features of the REBL system are a rotary stage and E-beam correction prior to writing the data. The former results in arbitrarily-rotated layout imagery to be compressed, and as such, presents significant challenges to the lossless compression algorithms. The performance of Block RGC3 and vector quantization is characterized in terms of compression efficiency and encoding complexity on a number of rotated layouts and at various angles, and it is shown that they outperform existing lossless compression algorithms.