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Proceedings Paper

Enhancement Of Optical Registration Signals Through Digital Signal Processing Techniques
Author(s): Daniel R. Cote; Jeanne Lazo-Wasem
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Paper Abstract

Alignment and setup of lighography processes has largely been conducted on special test wafers. Actual product level optimization has been limited to manual techniques such as optical verniers. This is especially time consuming and prone to inconsistencies when the registration characteristics of lithographic systems are being measured. One key factor obstructing the use of automated metrology equipment on product level wafers is the inability to discern reliably, metrology features from the background noise and variations in optical registration signals. This is often the case for metal levels such as aluminum and tungsten. This paper discusses methods for enhancement of typical registration signals obtained from difficult semiconductor process levels. Brightfield and darkfield registration signals are obtained using a microscope and a 1024 element linear photodiode array. These signals are then digitized and stored on the hard disk of a computer. The techniques utilized include amplitude selective and adaptive and non-adaptive frequency domain filtering techniques. The effect of each of these techniques upon calculated registration values is analyzed by determining the positional variation of the center location of a two line registration feature. Plots of raw and processed signals obtained are presented as are plots of the power spectral density of ideal metrology feature signal and noise patterns. It is concluded that the proper application of digital signal processing (DSP) techniques to problematic optical registration signals greatly enhances the applicability of automated optical registration measurement techniques to difficult semiconductor process levels.

Paper Details

Date Published: 1 January 1988
PDF: 9 pages
Proc. SPIE 0921, Integrated Circuit Metrology, Inspection, and Process Control II, (1 January 1988); doi: 10.1117/12.968367
Show Author Affiliations
Daniel R. Cote, The Perkin-Elmer Corporation (United States)
Jeanne Lazo-Wasem, The Perkin-Elmer Corporation (United States)


Published in SPIE Proceedings Vol. 0921:
Integrated Circuit Metrology, Inspection, and Process Control II
Kevin M. Monahan, Editor(s)

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