Goos-Hänchen Correction for Autofocus Measurement Accuracy
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Solution Overview
Problem
Current autofocus systems in microlithography tools face challenges in accurately correcting Goos-Hänchen effects, which lead to errors in substrate height measurements due to variations in thin-film layers and patterns, and existing methods are inadequate for high-speed and high-accuracy corrections in microcircuit fabrication.
Innovation Solution
The method involves using a combination of GH-insensitive physical displacement sensors and GH-sensitive optical sensors to map displacements, determining Goos-Hänchen correction coefficients based on actual measurements, and applying these coefficients to correct for errors in substrate position measurements, thereby reducing the impact of Goos-Hänchen effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If optical sensors are used for high-speed substrate position measurement, then measurement speed is improved, but measurement precision deteriorates due to Goos-Hänchen effects and optical property variations
Solution Approach 1:
The patent introduces an intermediary correction process that uses reference measurements and Goos-Hänchen effect models to mediate between the fast optical sensor readings and the true physical position. The correction coefficients act as a mediator that transforms the distorted optical measurements into accurate position data, resolving the contradiction between speed and precision.
Solution Approach 2:
The patent changes the parameters of the measurement system by introducing correction coefficients that account for Goos-Hänchen effects. These coefficients are determined through reference measurements and are applied to transform the optical sensor readings, effectively changing the measurement parameters to compensate for the systematic errors introduced by the optical properties of the substrate and photoresist.
2Measurement precision
If Goos-Hänchen correction is applied to improve measurement precision, then position accuracy is improved, but device complexity increases due to additional correction calculations
Solution Approach 1:
The patent applies preliminary action by pre-determining the Goos-Hänchen correction coefficients through reference measurements before actual production measurements. This preliminary characterization of the system's optical properties allows the correction to be applied as a simple computational step during production, rather than requiring complex real-time corrections, thus improving precision without significantly increasing operational complexity.
3Measurement precision
If physical sensors are used instead of optical sensors, then measurement precision is improved by avoiding Goos-Hänchen effects, but productivity decreases due to slower measurement speed
Solution Approach 1:
The patent replaces the physical/mechanical sensing approach with an optical sensing system that can be corrected through computational methods. Instead of using slow physical sensors, the system uses fast optical sensors and substitutes the mechanical sensing limitation with optical measurement combined with Goos-Hänchen correction, achieving both high speed and high precision.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach provides more accurate and region-specific corrections for Goos-Hänchen effects, improving the accuracy of autofocus determinations and reducing errors in substrate height measurements, essential for high-volume manufacturing and microcircuit fabrication.
Implementation Method 1
The positions are usually determined based on a detected position of a beam of light reflected from the substrate surface
Implementation Method 2
One source of AF errors arises from some of the AF light (which may form images of 'slits' or 'fringes' on the substrate) reflecting from previously formed patterned thin films beneath the surface of the substrate
Data Source
AI summary
An exemplary method involves, in a system comprising a tool that performs a task on a workpiece, a method for determining displacement of the workpiece relative to the tool. Respective displacements of loci of at least a region of the workpiece are mapped using a Goos-Hänchen-insensitive (GH-insensitive) displacement sensor to produce a first set of physical displacement data for the region. Also mapped are respective displacements, from the tool, of the loci using a GH sensitive sensor to produce a second set of optical displacement data for the region. Goodness of fit (GOF) is determined of the second set of data with the first set. According to the GOF, respective GH-correction (GHC) coefficients are determined for at least one locus of the region. When measuring displacement of the at least one locus in the region relative to the tool, the respective GHC coefficient is applied to the measured displacement to reduce an error that otherwise would be present in the measured displacement due to a GH effect.