Fixed-Focus Low-NA Alignment for Warped Photolithography Substrates
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional alignment techniques in photolithography struggle with substrates that are warped or bowed, as high numerical aperture microscopes have a small depth of focus, making it difficult to accurately image fiducials at varied heights.
Innovation Solution
Employ a photolithography machine with a fixed-focus alignment system using low numerical aperture microscope cameras that can detect fiducials at various heights without adjusting focus, allowing for faster alignment by eliminating the need for individual camera focusing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high numerical aperture microscopes are used for alignment, then measurement precision is improved, but depth of focus deteriorates
Solution Approach 1:
The patent changes the numerical aperture parameter from high NA to low NA (0.05 or less) for the alignment microscope cameras. This parameter change sacrifices some resolution capability to gain a large depth of focus, enabling the system to image fiducials at varied heights without focus adjustment. The low NA cameras maintain sufficient precision for alignment while accommodating substrate warpage and bowing.
2Measurement precision
If individual focus adjustment is performed for each microscope camera, then measurement precision is improved, but productivity deteriorates
Solution Approach 1:
The patent performs focus adjustment in advance by pre-setting all microscope cameras to a fixed focus state during system setup. This preliminary action eliminates the need for individual focus adjustment during actual alignment operations, allowing all cameras to simultaneously image fiducials without time-consuming focus changes. The fixed focus is calibrated to accommodate the expected range of fiducial heights.
Solution Approach 2:
The low NA microscope cameras are designed to be self-sufficient regarding focus adjustment. Their optical characteristics inherently provide sufficient depth of focus to image fiducials at various heights without requiring active focus control. This self-service capability eliminates a complex control step and significantly speeds up the alignment process.
3Productivity
If low numerical aperture cameras with fixed focus are used, then productivity is improved, but measurement precision deteriorates
Solution Approach 1:
The patent segments the alignment system into multiple low NA microscope cameras, each dedicated to detecting fiducials in specific exposure regions. This segmentation allows parallel processing across multiple regions simultaneously. While each camera uses low NA optics, the combined system achieves high productivity through concurrent imaging, and sufficient precision is maintained through the collective data from multiple cameras.
Data Source
AI summary
Disclosed herein are examples of a photolithography machine with fast alignment. The machine may include a stage to hold and move a substrate and a projection system to project images on a plurality of exposure regions of the substrate. The machine may also include an alignment system positioned adjacent to the projection system. The alignment system may include a plurality of microscope cameras with a fixed focus, each microscope camera configured to detect a respective fiducial in a respective exposure region of the substrate.