Substrate Alignment via Out-of-Focus Image Filtering
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Solution Overview
Problem
Existing alignment technologies struggle to achieve high accuracy when alignment marks on two substrates cannot be simultaneously brought into focus due to the limited depth of field of the imaging system, especially when the substrates need to be closer together to maintain focus, and variations in substrate dimensions and deflection cause alignment marks to be out of focus.
Innovation Solution
An alignment method that images both alignment marks within the same field of view, focuses on one mark while the other is out of focus, and uses image filtering to detect the center of gravity of the out-of-focus mark, allowing for precise positional adjustment without requiring both marks to be within the depth of field.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the magnification of the imager is increased to improve alignment accuracy, then the depth of field is reduced, making it difficult to simultaneously focus on both alignment marks
Solution Approach 1:
The patent divides the alignment mark detection into two separate processes: one for the first alignment mark and another for the second alignment mark. The first alignment mark is detected when it is in focus, and the second alignment mark is detected when it is in focus, allowing each mark to be imaged at optimal focus conditions even though they cannot be simultaneously in focus due to reduced depth of field.
Solution Approach 2:
The patent performs preliminary actions by detecting the first alignment mark before the second alignment mark. The system detects the first alignment mark when it is in focus, then adjusts the focus to detect the second alignment mark. This sequential preliminary detection allows both marks to be accurately positioned without requiring them to be simultaneously in focus.
2Reliability
If the substrates are brought closer together to maintain focus within depth of field, then alignment marks can be simultaneously in focus, but dimensional variations and deflection make it difficult to maintain proper alignment
Solution Approach 1:
The patent employs dynamic focus adjustment between detecting the first alignment mark and the second alignment mark. The focus position is dynamically changed to first focus on the first alignment mark, then adjusted to focus on the second alignment mark. This dynamic adjustment compensates for dimensional variations and deflection of substrates, maintaining alignment precision even when substrates are brought close together.
Solution Approach 2:
The system uses feedback from detecting the first alignment mark to adjust the focus position before detecting the second alignment mark. The detection result of the first alignment mark provides feedback that guides the focus adjustment, ensuring that the second alignment mark can be accurately detected even when the substrates are in close proximity with dimensional variations.
3Measurement precision
If individual imaging of two alignment marks is performed by successive focusing, then both marks can be detected, but optical axis variation during focusing reduces alignment accuracy
Solution Approach 1:
The patent segments the alignment mark detection into distinct first and second detection processes. The first alignment mark is detected in a first imaging state, and the second alignment mark is detected in a second imaging state. This segmentation allows each mark to be detected under controlled focus conditions, minimizing optical axis variation impact on overall alignment accuracy.
Solution Approach 2:
The patent performs preliminary detection of the first alignment mark before detecting the second alignment mark. By completing the first detection action first, the system establishes a reference point that minimizes the impact of subsequent focus adjustments on the overall alignment accuracy, reducing errors from optical axis variation.
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 high-accuracy alignment of substrates even when alignment marks are not simultaneously in focus, ensuring precise positioning and accurate transfer of patterns or thin films between substrates.
Implementation Method 1
a distance in an optical axis direction of the imager between the alignment mark formed surface of the first substrate and that of the second substrate is longer than the depth of field of the imager and the imager is focused on the alignment mark formed surface of the second substrate
Implementation Method 2
a filtering process of removing high spatial frequency components from the image is performed and a center of gravity position of the first alignment mark is detected from the image after filtering
Data Source
AI summary
A carrier and a substrate are aligned even if an imager cannot be simultaneously focused on alignment marks formed on both the carrier and the substrate. Center of gravity positions G1m of an alignment pattern element AP1 on a substrate and G2m of an alignment pattern element AP2 on a transparent blanket are calculated by image processing from an image IM imaged via the blanket by a CCD camera. The position of the center of gravity Gm2 is specified by a process associated with edge extraction from the image imaged with the alignment pattern element AP2 on the blanket being in focus. High spatial frequency components are removed and low frequency components are extracted for the alignment pattern element AP1 on the substrate imaged out of focus to have a blurred outline, and the position of the center of gravity G1m is specified from an extraction result.