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17 March 2009 Full-chip characterization of compression algorithms for direct-write maskless lithography systems
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Future lithography systems must produce more dense microchips with smaller feature sizes, while maintaining throughput comparable to today's optical lithography systems. This places stringent data-handling requirements on the design of any maskless lithography system. Today's optical lithography systems transfer one layer of data from the mask to the entire wafer in about sixty seconds. To achieve a similar throughput for a direct-write maskless lithography system with a pixel size of 22 nm, data rates of about 12 Tb/s are required. Over the past 8 years, we have proposed a datapath architecture for delivering such a data rate to a parallel array of writers. Our proposed system achieves this data rate contingent on two assumptions: consistent 10 to 1 compression of lithography data, and implementation of real-time hardware decoder, fabricated on a microchip together with a massively parallel array of lithography writers, capable of decoding 12 Tb/s of data. To address the compression efficiency problem, in the past few years, we have developed a new technique, Context Copy Combinatorial Coding (C4), designed specifically for microchip layer images, with a low-complexity decoder for application to the datapath architecture. C4 combines the advantages of JBIG and ZIP, to achieve compression ratios higher than existing techniques. We have also devised Block C4, a variation of C4 with up to hundred times faster encoding times, with little or no loss in compression efficiency. While our past work has focused on characterizing the compression efficiency of C4 and Block C4 on samples of a variety of industrial layouts, there has been no full chip performance characterization of these algorithms. In this paper, we show compression efficiency results of Block C4 and competing techniques such as BZIP2 and ZIP for the Poly, Active, Contact, Metal1, Via1, and Metal2 layers of a complete industry 65 nm layout. Overall, we have found that compression efficiency varies significantly from design to design, from layer to layer, and even within parts of the same layer. It is difficult, if not impossible, to guarantee a lossless 10 to 1 compression for all blocks within a layer, as desired in the design of our datapath architecture. Nonetheless, on the most complex Metal1 layer of our 65 nm full chip microprocessor design, we show that a average lossless compression of 5.2 is attainable, which corresponds to a throughput of 60 wafer layers per hour for a 1.33 Tb/s board-to-chip communications link. As a reference, state-of-the-art HyperTransport 3.0 offers 0.32 Tb/s per link. These numbers demonstrate the role lossless compression can play in the design of a maskless lithography datapath.
© (2009) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Avideh Zakhor, Vito Dai, and George Cramer "Full-chip characterization of compression algorithms for direct-write maskless lithography systems", Proc. SPIE 7271, Alternative Lithographic Technologies, 72711H (17 March 2009); doi: 10.1117/12.813589;

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