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Proceedings Paper

In-process image detection technique for determination of overlay and image quality for ASM-L wafer stepper
Author(s): Rainer Pforr; Stefan Wittekoek; Roland Van Den Bosch; Luc Van den Hove; Rik M. Jonckheere; Theo Fahner; Rolf Seltmann
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Paper Abstract

The possibilities of in-process blue image sensing by using only the implemented darkfield TTL alignment system of a stepper are investigated. It is shown, that all overlay related parameters of a PAS5000/50 and /70 stepper such as red-blue, magnification, rotation and translation can be measured from an enhanced latent image in a special dyed resist but also with some reduction in accuracy in a pure resist only. Results of overlay measurements on typical technological layers and of similar experiments based on latent image sensing in dyed and in pure resist are given, indicating the capability of in-situ overlay control and correction on process wafers. A new alignment target sensing (ATS) technique of focus measurement using the alignment detection system of the stepper for both daily focus control and correction as well as for focus setting on process wafers with typical technological layers is introduced. The method uses special designed alignment markers containing lines and spaces at the working resolution. Results are given for sensing the developed resist pattern as well as the latent image for an i-line and a DUV stepper. The applicability is demonstrated by measuring the influence of varying resist layer thickness and of varying oxide layer thickness of various film stacks of technological layers on optimum focus. The validity of these results is proven by comparisons to other focus measurement techniques such as chessboard and SEM linewidth measurements. A mathematical model based on the diffraction theory of thin gratings has been developed to support the marker design as well as to calculate the Image Quality Signal (IQS) vs. focus/exposure curves of developed images. The model has been verified by experiments.

Paper Details

Date Published: 1 June 1992
PDF: 15 pages
Proc. SPIE 1674, Optical/Laser Microlithography V, (1 June 1992); doi: 10.1117/12.130355
Show Author Affiliations
Rainer Pforr, Interuniv. Micro-Elektronica Centrum vzw (Belgium)
Stefan Wittekoek, ASM Lithography BV (Netherlands)
Roland Van Den Bosch, Interuniv. Micro-Elektronica Centrum vzw (Belgium)
Luc Van den Hove, Interuniv. Micro-Elektronica Centrum vzw (Belgium)
Rik M. Jonckheere, Interuniv. Micro-Elektronica Centrum vzw (Belgium)
Theo Fahner, ASM Lithography BV (Netherlands)
Rolf Seltmann, Fraunhofer Institut fuer Mikroelektronische Schaltungen und System (Germany)

Published in SPIE Proceedings Vol. 1674:
Optical/Laser Microlithography V
John D. Cuthbert, Editor(s)

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