16 June 2003 Understanding particle defect transport in an ultra clean sputter coating process
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Abstract
Low-defect mask blanks remain a key technical challenge to Extreme Ultraviolet Lithography (EUVL). The mask blank is ion-beam sputter-coated with an 81-layer Mo/Si multilayer stack for high reflectance at l = 13.4nm. The current mask coating process can achieve a median added defect level of 0.05 defects/cm2 (12 added defects 90nm or larger on a 200mm Si-wafer test substrate), but this must be reduced by about a factor of 10 to meet mask cost requirements for EUVL. To further reduce the particle defect level, we have studied pathways for particle transport, using test particles and particles native to the coating process, and combined the results into a computational model of particle transport in an ion-beam sputter system. At process pressure, gas drag is negligible for particles above 100nm, so particles travel ballistically until they hit a surface. Bounce from chamber walls allows particles to reach all surfaces in the chamber if they have initial velocities above ~100m/s. The ion beam has sufficient momentum to entrain slower particles and accelerate them toward the sputter target, where some can bounce to the substrate. The model shows preliminary agreement with experimental defect distributions on witness wafers at various positions within the coating chamber.
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Christopher C. Walton, Christopher C. Walton, Patrick A. Kearney, Patrick A. Kearney, James A. Folta, James A. Folta, Donald W. Sweeney, Donald W. Sweeney, Paul B. Mirkarimi, Paul B. Mirkarimi, "Understanding particle defect transport in an ultra clean sputter coating process", Proc. SPIE 5037, Emerging Lithographic Technologies VII, (16 June 2003); doi: 10.1117/12.484970; https://doi.org/10.1117/12.484970
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