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22 March 2008 Lot acceptance sampling inspection plan for non-normal CD distribution
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The optimizing of sampling plans for process control and lot acceptance inspections is emerging as an important subject concerning the recent lithography process. With proper acceptance variables, one can reduce sample size using inspection by variables rather than inspection by attributes. The inspection by variables is cost-effective and desirable. However, it is difficult to apply to a non-normal population. Many cases exist where CD distribution cannot be regarded as normal. If one applies the acceptance sampling inspection with conventional acceptance variables@in those cases, the inspections become tighter or are reduced, which is contrary to expectations. The problem of non-normality, which is an essential property of CD distributions, should be treated extensively. We found that the above problem can be overcome by modifying the conventional acceptance variables through the inclusion of the 3rd moment. As a result, 50% reduction of sample size can be realized by introducing the lot acceptance sampling with new variables.
© (2008) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Takahiro Ikeda and Masafumi Asano "Lot acceptance sampling inspection plan for non-normal CD distribution", Proc. SPIE 6922, Metrology, Inspection, and Process Control for Microlithography XXII, 692214 (22 March 2008);

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