Today, haze and crystal growth on the reticle surface are still a primary concern of the microlithography industry. The crystals limit the reticle usage as they result in printable defects on the wafers. Numerous studies have been presented so far. The general belief is that different root causes can lead to crystal growth and haze formation, among them the contaminants on the mask surface from the clean processes.
In this paper we are investigating the potential of sulfate free clean processes based on ozonated and hydrogen water for the next generation of photomasks. Key parameters such as cleaning efficiency, as well as the impact of the chemistry on the mask optical properties will be presented. The potential of the chemistry will be discussed and compared to the standard cleaning processes.
Progress towards 65nm next-generation lithography requires unprecedented global CD uniformity, with the actual ITRS 2002 roadmap proposing 4.2nm 3σ (dense lines) for 65nm binary masks. Since resolution requirements are satisfied only by using chemically amplified resists (CARs), exposure and post-exposure bake (PEB) are key processes to successful mask making, both introducing global CD errors. Develop and etch processes potentially contribute further global CD errors. The global CD uniformity can be improved significantly by adaptive PEB, especially for CARs showing moderate to strong PEB sensitivity, like NEB22. With the 25-zone hotplate of the APB5500 bake system, facilitated through a novel calibration mask with 25 equidistant temperature sensors within the resist plane, an appropriate temperature profile can be applied during PEB. This temperature profile is automatically calculated by an adaptive optimization algorithm, based on 2-dimensional spline fitting of a CD measurement. A CD-uniformity improvement (dense lines) from 3.80nm 3σ to 3.06nm 3σ (~20%) is achieved on evaluation photomasks with an 11x11 CD measurement grid.
With shrinking feature sizes there is a growing demand for improved uniformity values and defect levels especially for aqueous develop during photomask processing. Standard nozzle systems with discrete dispense channels for applying the developer medium onto the photomask surface may cause non-uniformities. This results in characteristic imprints in CD-uniformity reflecting the nozzle design used during the develop process step. These can lead on the one hand to an increased number and various types of defects and on the other hand to variations in CD-uniformity. A new puddle nozzle design for the STEAG HamaTech's ASP5500 has been developed to address this issue. Instead of discrete dispense holes the developer medium is applied onto the substrate surface by a full-width film. This media film is applied uniform across the substrate and has low impact onto the photomask surface. By combining the new nozzle design with gas-less high volume dispense pumps a very uniform and defect-free dispense can be achieved. The uniformity and defect performance of the new film nozzle will be presented and compared to a standard dispense nozzle system. The study has been done on masks with Chemically Amplified Resist (CAR).
A new type of bake system for photomasks, APB5000, has been developed, using a dynamic and multiple zone approach, to enable more precise Post Exposure Bake (PEB) and Post Coat Bake (PCB) of conventional and chemically amplified resists (CAR). The principal equipment concept and the optimization strategies are presented. The baking performance of the APB5000 is demonstrated for several surface temperatures between 90 degree(s)C and 150 degree(s)C. The temperature uniformity ranges achieved at the resist plane are better than 0.25 degree(s)C after stabilization at the final temperature and better than 1.5 degree(s)C during the ramping period. The repeatability of the bake temperature is better than +/- 0.07 degree(s)C for the setpoint temperature.
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