Diffraction Grating Displacement Measurement for Lithography
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional precision sensors in lithographic apparatuses, such as interferometers, are limited by air disturbances like turbulence and thermal variations, leading to reduced accuracy and increased costs due to the need to minimize these disturbances, which in turn reduces the throughput of the apparatus.
Innovation Solution
A displacement measurement system using diffraction gratings that measures the phase difference between first and negative first order diffracted radiation beams to determine the relative displacement of the gratings, with the beams being linearly polarized in orthogonal directions to enhance accuracy and reduce sensitivity to environmental variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional interferometers are used for displacement measurement, then accurate position measurements can be obtained, but the accuracy is limited by air disturbances such as turbulence and thermal variations
Solution Approach 1:
The patent uses diffraction gratings as intermediary elements that modulate the radiation beam to encode position information. The gratings convert linear displacement into phase differences of diffracted beams, allowing measurement without direct long-path radiation traversal through disturbed air, thus mitigating the harmful effect of air disturbances while maintaining measurement precision
Solution Approach 2:
The patent replaces the conventional interferometric mechanical/optical system with a diffraction-based system. Instead of using interferometer components that are sensitive to air disturbances, the invention uses diffraction gratings and phase detection to achieve position measurement, substituting the measurement mechanism to reduce sensitivity to environmental factors
2Measurement precision
If air disturbances are minimized by introducing delays to allow turbulence to decrease and temperature to settle, then measurement accuracy improves, but the throughput of the lithographic apparatus is reduced
Solution Approach 1:
The patent replaces the time-consuming environmental stabilization approach with an instantaneous diffraction-based measurement system. The diffraction gratings and phase detection method provide real-time position feedback without requiring delays for air turbulence to settle or temperature to stabilize, thus maintaining measurement accuracy while preserving apparatus throughput
Solution Approach 2:
The patent changes the measurement parameter from intensity-based interferometry to phase-based diffraction. This parameter change allows the system to be less sensitive to air disturbances and eliminates the need for environmental stabilization delays, thereby maintaining both accuracy and productivity
3Volume of moving object
If a measurement system is designed to occupy limited volume space within the lithographic apparatus, then space efficiency is improved, but this constrains the available configuration options for the measurement system
Solution Approach 1:
The patent merges the diffraction grating elements with the lithographic apparatus components themselves. The gratings are positioned on existing moving components (such as the substrate table or projection system), eliminating the need for separate measurement system housings and reducing overall volume occupation while simplifying configuration
Solution Approach 2:
The diffraction grating system serves multiple functions: it acts as both a positioning measurement element and integrates with the existing lithographic components. This multi-functionality reduces the need for dedicated measurement system space and simplifies the overall configuration within the apparatus
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
The system provides improved precision in displacement measurement with reduced sensitivity to air disturbances, maintaining high accuracy while minimizing space occupation within the lithographic apparatus, thus enhancing throughput and reducing costs.
Implementation Method 1
a first beam of radiation input to the measurement system is divided into first and negative first order diffracted radiation beams by the first diffraction grating
Implementation Method 2
the first and negative first order diffracted radiation beams are further diffracted by the second diffraction grating and subsequently recombined to form a second beam of radiation
Implementation Method 3
the measurement system further includes a sensor configured to determine the relative displacement of the first and second gratings from a determination of the phase difference between a first component of the second beam, derived from the first order diffracted radiation beam, and a second component of the second beam, derived from the negative first order diffracted radiation beam
Implementation Method 4
the measuring system further includes at least one linear polarizer configured such that the first and second components of the second beam of radiation are linearly polarized, oriented in mutually orthogonal directions
Data Source
AI summary
A displacement measurement system configured to provide measurement of the relative displacement of two components in six degrees of freedom with improved consistency and without requiring excessive space.