Enhancement Of Optical Registration Signals Through Digital Signal Processing Techniques

Daniel R. Cote; Jeanne Lazo-Wasem

doi:10.1117/12.968367

1 January 1988 Enhancement Of Optical Registration Signals Through Digital Signal Processing Techniques

Daniel R. Cote, Jeanne Lazo-Wasem

Proceedings Volume 0921, Integrated Circuit Metrology, Inspection, and Process Control II; (1988) https://doi.org/10.1117/12.968367
Event: Santa Clara Symposium on Microlithography, 1988, Santa Clara, CA, United States

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.

Citation Download Citation

Daniel R. Cote and Jeanne Lazo-Wasem "Enhancement Of Optical Registration Signals Through Digital Signal Processing Techniques", Proc. SPIE 0921, Integrated Circuit Metrology, Inspection, and Process Control II, (1 January 1988); https://doi.org/10.1117/12.968367

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