As photomask pattern complexity continues to increase, it becomes more challenging to control write times of shaped ebeam tools. This raises the related concerns of increased mask costs and extended mask cycle times. A strategy for sub-100 nm technology nodes is to use high-speed DUV laser pattern generators for as many layers as possible, reserving ebeam tools for only the most critical layers. With 248 nm optics and high-NA partially coherent imaging, the Sigma7500 increases the application space available to laser pattern generators. Image profiles are steepened with phase shifting methods, and pattern fidelity is improved with on-line corner enhancement. In the Sigma architecture, mask patterns are imaged with full fidelity and addressability in each writing pass. Because of this, the Sigma7500 provides additional means to improve write time by reducing the number of exposure passes. Platform improvements have resulted in a 2-pass writing accuracy that meets the 4-pass specification of the previous system. Write time is typically under two hours in 2-pass mode, compared to approximately three hours for 4-pass. The Sigma7500 can generally be used for all binary mask layers at the 90 nm technology node, and for about half the layers at 45 nm. The ProcessEqualizer TM function addresses long range CD errors arising from mask process effects. Mask data is sized in real time to compensate for process errors related to local pattern density, and also to correct for static process CD signatures. With a through-thelens alignment system and both grid matching and pattern matching capabilities, the tool is also suited to 2 nd layer patterning for advanced phase shifting mask (PSM) applications down to 45 nm, with extendibility to 32 nm. Process integration is facilitated by the use of standard FEP-171 chemically amplified resist (CAR).
With each new technology generation, photomask manufacturing faces increasing complexity due to shrinking designs and accelerating use of reticle enhancement techniques. Denser and more complex patterns on the mask result in lower yields and long write and turn-around times, important factors for the rapidly increasing mask related costs in IC manufacturing.Laser pattern generators operating at DUV wavelengths were recently introduced to provide cost effective alternatives to electron-beam systems for printing of high-end photomasks. DUV wavelengths provide the required resolution and pattern fidelity. Optical tools that use raster writing principles and massively parallel printing ensure short and predictable write times for photomasks almost independent of pattern complexity.One such high-volume production system, the Sigma7300, uses spatial light modulator (SLM) technology and a 248 nm excimer laser for printing. Partially coherent imaging and multi-pass printing as in a lithography scanner further increases resolution and pattern accuracy. With four-pass printing the system provides resolution and pattern accuracy meeting mask requirements for critical layers at the 90-nm node and sub-critical layers at the 65-nm node and beyond.The paper discusses how mask layout can be optimized to take full advantage of the speed potential provided by the SLM-based writer. It shows how flexible use of the writing principle can provide cost effective writing solutions for many layers in high-end mask sets. Resolution and pattern accuracy results from the Sigma7300 will be presented together with write times for different types of designs.
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