Lithography Focus Calibration via Light Field Reconstruction
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Solution Overview
Problem
Conventional lithography apparatuses face challenges in accurately and efficiently calibrating the best focus position of a projection optical system due to variations in heat, atmospheric pressure, and temperature, leading to long measurement times and decreased accuracy when increasing driving speed.
Innovation Solution
A lithography apparatus that includes a projection optical system, an original holder, a substrate holder, a detector for generating refocusable light field image data, and a controller to reconstruct images at different focus positions, allowing for the adjustment of the original and substrate holders based on the reconstructed images to calibrate the best focus position without the need for step driving.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the substrate stage is driven to measure the best focus position, then the measurement can be performed, but the measurement time becomes long
Solution Approach 1:
The patent replaces the mechanical driving method with an optical field reconstruction method. Instead of physically moving the substrate stage to different positions to measure focus, the system captures a single light field image and computationally reconstructs multiple focus planes through image processing algorithms, eliminating mechanical movement while achieving the same measurement objective.
Solution Approach 2:
The patent creates virtual copies of the focus measurement process through computational imaging. By capturing one light field image and generating multiple reconstructed images at different focus positions, the system creates virtual measurements without physical movement, effectively copying the measurement information from a single capture event.
2Productivity
If the driving speed is increased to shorten measurement time, then the measurement speed improves, but measurement accuracy decreases due to vibration
Solution Approach 1:
The patent eliminates the need for mechanical driving by using optical field capture and computational reconstruction. This substitution removes the source of vibration entirely, allowing fast measurement without the accuracy penalty that would result from high-speed mechanical movement.
Solution Approach 2:
The patent performs preliminary capture of the light field image containing all focus information, then processes it computationally. This preliminary action captures all necessary data in a single static moment, avoiding the need for subsequent mechanical movements that would introduce vibration.
3Loss of time
If a non-driving focus alignment method is used, then measurement time is reduced, but spatial resolution in the focal direction becomes low
Solution Approach 1:
The patent replaces simple optical focusing methods with computational light field reconstruction. Instead of relying on optical systems alone to provide spatial resolution, the system uses mathematical algorithms to extract precise focus information from the light field data, achieving high resolution without mechanical or optical movement.
Solution Approach 2:
The patent transitions from two-dimensional image capture to four-dimensional light field capture (spatial x, spatial y, angular theta, angular phi). This additional dimensional information enables precise focus measurement through computational reconstruction, overcoming the resolution limitations of conventional optical methods.
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 significantly increases the speed of focus position calibration and maintains high measurement accuracy, reducing the impact of vibrations and environmental influences on the calibration process.
Implementation Method 1
a detector that detects an original-side mark image arranged in one of the original and the original holder, and a substrate-side mark image arranged in one of the substrate and the substrate holder via the projection optical system
Data Source
AI summary
A lithography apparatus includes a detector that detects an original-side mark image and a substrate-side mark image via a projection optical system, and a controller. The detector generates refocusable light field image data that includes the original-side mark image and the substrate-side mark image. The controller performs, based on the light field image data obtained from the detector, a refocus operation of reconstructing a plurality of images different in position in a focus direction and adjusts a position of at least one of the original holder and the substrate holder based on the plurality of images reconstructed by the refocus operation.