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1 June 1992 Overlay and field-by-field leveling in wafer steppers using an advanced metrology system
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Steppers suitable for resolutions down to 0.35 micrometers are now available for the development and production of 64 mb DRAMs. At these small feature sizes, the depth of focus approaches one micron and the machine to machine overlay requirements are decreased to below 150 nm. This paper reports on the design and characterization of focus, alignment, and stage metrology in a wafer stepper which can meet the aggressive feature size demands. The characteristics of a new broad band field-by-field leveling sensor system with an enhanced process tolerance compared to conventional systems is described. Furthermore, this leveling system has been combined with a multi-axis interferometer system to support a high throughput global alignment strategy with field-by-field leveling. Wafer stepper performance results are presented including depth of focus improvements and global alignment overlay with and without field-by-field leveling. The dependency of focus on wafer structure- and resist thickness-variation is also shown. The total metrology system makes possible a two point global alignment overlay performance below 30 nm, a focus repeatability of 25 nm, and a tilt repeatability of 2 (mu) rad.
© (1992) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Martin A. van den Brink, Judon M. D. Stoeldraijer, and Henk F.D. Linders "Overlay and field-by-field leveling in wafer steppers using an advanced metrology system", Proc. SPIE 1673, Integrated Circuit Metrology, Inspection, and Process Control VI, (1 June 1992);


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