26 May 1995 Improving the backend focus budget for 0.5-um lithography
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One of the biggest challenges for printing 0.6 micrometers metal lines (1.3 micrometers pitch) over 1.1 micrometers of topography is the shallow depth of focus. Total random errors, or, Built In Focus Errors (BIFE) for the class of steppers used in this study was determined to be 0.48 micrometers . When topography, and field curvature/astigmatism, are factored in, the required depth of focus to print the metal lines is approximately 2.18 micrometers . However, the 'Available' DOF (as determined from PROLITH simulations) is only 1.8 micrometers . The deficit between available DOF and required DOF grows bigger when there are multiple steppers. To overcome this deficiency, various techniques have been studied. Topography reduction by 0.4 micrometers was achieved by the use of Reverse Well technology. Effect of different resist chemistries, off-axis illumination, variation in numerical aperture and partial coherence, on the focus latitude are shown.
© (1995) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Satyendra S. Sethi, Satyendra S. Sethi, Alex Flores, Alex Flores, P. McHale, P. McHale, R. Booth, R. Booth, Steve W. Graca, Steve W. Graca, S. Frezon, S. Frezon, C. Fruga, C. Fruga, "Improving the backend focus budget for 0.5-um lithography", Proc. SPIE 2440, Optical/Laser Microlithography VIII, (26 May 1995); doi: 10.1117/12.209290; https://doi.org/10.1117/12.209290

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