Patterning Device Surface Mapping With Chromatic Confocal Sensing
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Solution Overview
Problem
Current methods for characterizing patterning devices in lithographic apparatuses are limited by the inability to accurately measure surface and geometric properties within the exposure field, particularly due to environmental sensitivity and the need for in-situ position information, which can lead to lithographic errors such as critical dimension uniformity and overlay issues.
Innovation Solution
A measurement system using a chromatic lens to illuminate the patterning device with multiple wavelengths, allowing for spectral analysis to determine surface parameters, including optical properties and shape, and compensate for heating effects by adjusting lens settings to correct for shape changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If interferometric measurement systems are used to obtain shape information within the exposure field, then measurement capability is improved, but sensitivity to environmental variations increases causing measurement errors
Solution Approach 1:
The patent replaces the interferometric measurement system with a chromatic confocal measurement system. This substitution eliminates the sensitivity to environmental variations while maintaining the capability to obtain shape information within the exposure field. The chromatic confocal system uses chromatic aberration of light through a lens to achieve axial distance measurements without the interference patterns that are sensitive to environmental changes.
Solution Approach 2:
The patent changes the measurement parameter from interferometric phase information to spectral intensity information at different focal planes. By using a chromatic lens to focus different wavelengths at different axial positions and measuring intensity spectra, the system achieves reliable shape measurements that are not affected by environmental variations.
2Measurement precision
If sensors are arranged at the stage to obtain position information, then position measurement is enabled, but measurement coverage is limited to areas close to the four edges of the patterning device
Solution Approach 1:
The patent transitions from edge-based position sensing to full-field shape measurement by introducing axial distance measurement as a new dimension. The chromatic confocal system measures the axial distance across the entire exposure field, providing comprehensive surface topology information rather than limited edge position data.
Solution Approach 2:
The chromatic confocal measurement system provides universal measurement capability across the entire exposure field, replacing the specialized edge-only sensors. It can obtain shape information at any location within the exposure field, making the measurement system universally applicable to the full patterning device surface.
3Manufacturing precision
If the patterning device surface is non-flat, then manufacturing variations occur, but accurate control over the projected pattern becomes difficult
Solution Approach 1:
The patent performs preliminary measurement of the patterning device surface shape using the chromatic confocal system before lithographic exposure. By obtaining the surface topology information in advance, the system can compensate for non-flatness effects and achieve accurate pattern control during the actual lithographic process.
Solution Approach 2:
The patent implements a feedback mechanism where the measured surface shape information from the chromatic confocal system is used to adjust and compensate for pattern placement errors. The measured axial distances across the exposure field provide feedback data that enables correction of lithographic errors caused by non-flat surfaces.
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
Enables accurate, real-time characterization and compensation of patterning device shape and optical changes, reducing lithographic errors and improving critical dimension uniformity and overlay control.
Implementation Method 1
a chromatic lens is configured to illuminate an area of the patterning device with the provided radiation, and wherein the chromatic lens is configured to collect at least a portion of the radiation reflected by the patterning device; a detector is configured to detect at least a portion of the collected radiation and to provide an intensity signal as a function of wavelength
Data Source
AI summary
A method is provided for determining surface parameters of a patterning device, comprising the steps of: positioning the patterning device with respect to a path of an exposure radiation beam using a first measurement system, providing the patterning device at a first focal plane of a chromatic lens arranged in a second measurement system, illuminating a part of a surface of the patterning device with radiation through the chromatic lens, wherein the radiation comprises a plurality of wavelengths, determining a position of the illuminated part of the patterning device in a first and second direction, collecting at least a portion of radiation reflected by the patterning device through the chromatic lens, measuring an intensity of the collected portion of radiation as a function of wavelength, to obtain spectral information of the illuminated area, and determining the surface parameters of the patterning device at the determined position from the spectral information.