16 July 2002 Novel implementations of scatterometry for lithography process control
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Lithography process control is one of the greatest challenges of modern semiconductor manufacturing. Due to the complexity of the overall lithography process, the number of process elements that can contribute to the process yield is large. One area of chief concern ins the control of focus on the lithography tool. Determination of the center of focus for a fixed dose during the photoresist development step in wafer processing is critical. Furthermore, dose variations can compound the difficulty in determining this center of focus. The lenses that are used in steppers have a very limited depth of focus, so utmost precision is necessary. Lense that are in focus will yield sharper printed photoresist images, and lack of focus will result in improperly developed photoresist features. Being at the center of focus also improves process repeatability. Scatterometry is a technology well-suited for lithography inspection and process control because it provides rapid measurement data and can be used for the measurement of resist line profiles. In this research we will report on several different methods for lithography focus control, including approaches that use conventional scatterometry models as well as a model-less algorithm. Comparisons will be drawn between commanded focus offsets, stage tilts and the focus response from the scatterometer. Use of the focus control techniques to map illumination modes and field non- linearity will also be shown.
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Michael E. Littau, Michael E. Littau, Christopher J. Raymond, Christopher J. Raymond, Christopher J. Gould, Christopher J. Gould, Christy Gambill, Christy Gambill, } "Novel implementations of scatterometry for lithography process control", Proc. SPIE 4689, Metrology, Inspection, and Process Control for Microlithography XVI, (16 July 2002); doi: 10.1117/12.473490; https://doi.org/10.1117/12.473490

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