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ON CONTROL OF RESIST FILM UNIFORMITY IN THE MICROLITHOGRAPHY PROCESS
Ho Weng Khuen1, Lee Lay Lay1 and Charles Schaper2
1 Department of Electrical and Computer Engineering,
National University of Singapore,
10 Kent Ridge Crescent, Singapore (119260)
2 Department of Electrical Engineering
Stanford University, Packard 278
350 Serra Mall, Stanford, CA 94305-9510
A new approach to improve resist thickness uniformity through the softbake process is proposed. Using in-situ thickness measurements, a multi-zone bakeplate and sliding mode control algorithm, the temperature distributions of the bakeplate is manipulated in real-time to reduce the resist thickness non-uniformity. Constraints on the bakeplate temperature are imposed to prevent decomposition of the photoactive compound in the resist. Hence the sliding mode control is implemented in a cascaded control structure. The resist thickness non-uniformity is reduced to less than 10 angstroms across individual wafers and from wafer-to-wafer.
Keywords: Sliding mode control, temperature distributions, uniformity, cascade control, constraints
Session slot T-Tu-M11: Control of Industrial Processes/Area code 7a : Chemical Process Control
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