Measuring Microscope Self-Calibration for Lithography Mask Surface Profiles
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Solution Overview
Problem
Current measuring microscopes in lithography struggle to achieve high accuracy in measuring structured elements, particularly in determining surface profiles, due to errors from the stage and the mask, which are difficult to separate and correct for.
Innovation Solution
A method and measuring microscope that utilize a self-calibration algorithm with a calibration mask having a known surface profile, combined with a device for determining the refractive index, to correct measurement errors and improve accuracy by accounting for gravitational bending and refractive index changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If self-calibration methods are used to improve measurement accuracy, then position errors can be separated from intrinsic apparatus errors, but it remains difficult to ascertain surface profiles of masks
Solution Approach 1:
The patent transitions from two-dimensional position measurement to three-dimensional surface profile measurement by incorporating focus variation analysis. The measuring microscope captures images at different focus positions (z-coordinates) and uses the focus variation to determine height information, enabling reliable surface profile ascertainment while maintaining the self-calibration approach for accurate position measurement.
2Ease of manufacture
If conventional self-calibration is performed without considering refractive index changes, then calibration can be completed with standard equipment, but measurement accuracy deteriorates due to uncorrected refractive index errors
Solution Approach 1:
The patent implements a feedback mechanism where the refractive index is continuously monitored during measurement and calibration processes. The measured refractive index values are fed back to correct the z-coordinate measurements in real-time, compensating for environmental changes and maintaining high measurement accuracy without requiring complex calibration procedures.
Solution Approach 2:
The patent accounts for changes in physical parameters, specifically the refractive index of air, which varies with temperature, pressure, and humidity. By measuring and compensating for these parameter changes, the system maintains accurate z-coordinate measurements despite environmental variations, bridging the gap between simple calibration and high precision requirements.
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 enables precise measurement of structured elements with reduced errors, allowing for reliable determination of z-coordinates and improved accuracy in the z-direction, even in non-exact structure positions, and facilitates accurate surface profile measurement.
Implementation Method 1
The position of the positioning stage and of the objective is ascertained by way of an interferometer
Implementation Method 2
coordinates ascertained subsequently in time and in the direction of the optical axis of the structured elements to be measured are corrected by way of a change in a refractive index
Data Source
AI summary
The present invention relates to a method for calibrating a measuring microscope which may be used to measure masks, in which a calibration mask is utilized in a self-calibration algorithm in order to ascertain error correction data of the measuring microscope, wherein, in the self-calibration algorithm, the calibration mask is imaged and measured in various positions in the measuring microscope in order to ascertain one or more portions of the error correction data, wherein the surface profile of the calibration mask is ascertained and utilized when determining the error correction. Moreover, the invention relates to a measuring microscope and a method for operating same.