Interferometer Mirror Calibration via Object Rotation
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Solution Overview
Problem
Interferometer systems in lithographic apparatuses face challenges in accurately measuring object positions due to imperfect mirror surfaces, which hinder precise feature projection on substrates, especially as they fail to fully reconstruct asymmetrical mirror shapes using symmetrical position signals.
Innovation Solution
A method involving tilting the object to generate data sets from interferometer position signals at different rotational orientations, allowing for the determination of both symmetrical and asymmetrical mirror shapes by shifting measurement beam locations, thereby enabling full reconstruction of mirror shapes using multi-pass interferometers and linear least squares systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If interferometers are arranged at opposite sides of the object to measure position signals, then position measurement capability is provided, but only symmetrical mirror shape information can be obtained and asymmetrical shapes cannot be fully reconstructed
Solution Approach 1:
The patent applies the dynamics principle by rotating the object to different angular positions during measurement. Instead of static measurement from opposite sides, the system dynamically changes the object's orientation to capture mirror shape information from multiple perspectives, enabling reconstruction of both symmetrical and asymmetrical shape characteristics
Solution Approach 2:
The patent introduces a rotational dimension to the measurement process. By adding angular position as a new dimension of measurement, the system transforms the measurement from a simple 1D opposite-side arrangement to a multi-dimensional approach that captures comprehensive mirror shape information including asymmetrical features
2Productivity
If mirrors are used to direct measurement beams for position measurement, then position signals are generated, but imperfect mirror surfaces introduce disturbances and measurement errors
Solution Approach 1:
The patent implements feedback by measuring the actual position signals from the mirrors and using this information to calculate compensation values. The system continuously refines the measurement by comparing expected versus actual signals and adjusting the calibration data to compensate for mirror imperfections
Solution Approach 2:
The patent applies parameter changes by modifying the measurement approach through object rotation and multi-position measurement. By changing the angular parameters and measurement configurations, the system obtains additional data that enables calculation of compensation values to correct for mirror surface imperfections
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 allows for accurate calibration and adjustment of mirror shapes, enhancing the precision of position measurements and feature projection in lithographic processes, particularly in directions where asymmetrical shapes are critical.
Implementation Method 1
an interferometer system configured to measure a position of an object. The interferometer system comprises a first interferometer and a second interferometer. The first interferometer is arranged to provide a first position signal representative of a position of the object in X-direction by directing a first measurement beam on a first mirror
Data Source
AI summary
A method for calibrating a mirror of an interferometer system configured to measure a position of an object using two interferometers of the interferometer system that are arranged at opposite sides of the object and configured to measure the position of the object in the same X-direction, wherein two sets of measurements are obtained for different rotational orientations about an axis perpendicular to the X-direction to determine a shape of the mirror. There is also provided a position measuring method in which the obtained shape of the mirror is used to adjust measurements in the X-direction, a lithographic apparatus and a device manufacturing method making use of such a lithographic apparatus.