Lithography Inspection Apparatus Polarization Beam Splitter
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Solution Overview
Problem
Current scatterometry methods do not accurately measure phase differences and amplitude ratios between polarization directions of radiation beams diffracted from substrates across a full range of azimuthal angles, limiting the precision of substrate property determination.
Innovation Solution
An inspection apparatus and method that splits a radiation beam into four components with different polarization orientations, allowing simultaneous detection of angle-resolved spectra to determine phase differences and amplitude ratios between polarization orientations, enabling precise measurement across all azimuthal angles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a phase modulator system is used to measure polarization parameters, then certain parameters of orthogonally polarized beams can be measured, but the system becomes dependent on wavelength and requires recalibration for different radiation types
Solution Approach 1:
The patent removes the phase modulator from the optical path entirely, extracting the wavelength-dependent component that caused the recalibration problem. Instead of modifying the beam's phase, the invention directly measures polarization states using polarizing beam splitters and detectors, eliminating the need for wavelength-specific calibration while maintaining measurement capability.
Solution Approach 2:
The patent replaces the mechanical phase modulator system with a direct polarization analysis system using polarizing beam splitters and photodetectors. This substitution eliminates moving parts and wavelength-dependent phase modulation, creating a more robust system that works across different wavelengths without recalibration.
2Loss of information
If elliptically polarized radiation reflects from a substrate surface, then polarization information can be obtained, but information is only available at specific azimuthal angles (45° and 135°)
Solution Approach 1:
The patent segments the polarization measurement into four distinct linear polarization components (0°, 45°, 90°, 135°) using multiple polarizing beam splitters. This segmentation allows simultaneous measurement of all polarization states at any azimuthal angle, rather than being limited to specific angles, thereby capturing complete polarization information across the full angular range.
Solution Approach 2:
The patent transitions from measuring only at specific azimuthal angles to measuring polarization states across all azimuthal angles by introducing a fourth dimension of measurement - the ability to resolve linear polarization orientations at any angle. This is achieved through the combination of polarizing beam splitters and photodetectors that can capture polarization information in any orientation.
3Productivity
If only the intensity of scattered radiation is measured, then the measurement is quick, but precision is limited due to not accounting for polarization behavior
Solution Approach 1:
The patent maintains the quick measurement capability by using direct detection of polarization components without sequential modulation or complex processing. All four polarization components are measured simultaneously through the beam splitter network, preserving measurement speed while continuously capturing complete polarization information for precise substrate property determination.
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 enhances the precision of substrate property measurement by providing comprehensive data across all azimuthal angles, increasing the signal-to-noise ratio and reducing measurement time, while being independent of wavelength and having fewer moving components.
Implementation Method 1
a beam splitter system configured to split the radiation beam once reflected from the substrate into at least four components, each with a different polarization orientation
Implementation Method 2
a detector configured to detect simultaneously angle-resolved spectra of the four components of the radiation beam
Data Source
AI summary
Four separately polarized beams are simultaneously measured upon diffraction from a substrate (W) to determine properties of the substrate. Linearly, circularly or elliptically polarized radiation is transmitted through a first beam splitter (N-PBS) and split into two polarized beams. These two beams are further split into two further beams using two further beam splitters, the further beam splitters (32,34) being rotated by 45° with respect to each other. The plurality of polarizing beam splitters enables the measurement of the intensity of all four beams and thus the measurement of the phase modulation and amplitude of the combined beams to give the features of the substrate. Algorithms are used to compare the four intensities of each of the polarized angles to give rise to the phase difference between the polarization directions and the ratio between the two main polarization direction amplitudes of the original polarized beam.