Lithographic Reticle Alignment via Segmented Scanning
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Solution Overview
Problem
Current lithographic apparatuses face challenges in reticle alignment due to low frequency noise disturbances and resonance frequency noise contributions, which impair image sensor performance during the alignment process.
Innovation Solution
The implementation of a scanning scheme that increases the temporal separation of image sensor passes through the central portion of the target volume, replacing a single continuous scan with multiple shorter scans, each covering a portion of the volume, and allowing for overlapping and pseudo-randomized scan paths to reduce noise impact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single continuous scan is performed through the target volume, then the alignment measurement can be completed quickly, but the image sensor passes through the central portion multiple times within a short time period causing correlated measurements and increased sensitivity to low frequency noise
Solution Approach 1:
The single continuous scan is divided into multiple separate scans, each covering a portion of the target volume. This segmentation ensures that the image sensor passes through the central portion at different time periods, reducing temporal correlation between measurements and minimizing the impact of low frequency noise disturbances on alignment accuracy.
Solution Approach 2:
The scanning process is performed periodically with temporal separation between passes through the central portion. By introducing time delays between successive measurements at the central position, the system reduces sensitivity to low frequency noise while maintaining measurement completeness through multiple periodic scans.
2Object-affected harmful factors
If multiple separate scans are performed to reduce noise impact, then the temporal separation increases and noise sensitivity decreases, but the total scan time increases and productivity decreases
Solution Approach 1:
The scan volume is divided into multiple portions, with each scan covering a specific portion. This allows the image sensor to pass through the central portion at different times with temporal separation, reducing noise sensitivity while limiting the total scan time by not requiring complete coverage of the entire volume in each scan.
Solution Approach 2:
Instead of performing multiple complete scans through the entire target volume, the system performs multiple partial scans covering only the necessary portions. This partial action approach reduces the total time required while still achieving sufficient temporal separation to minimize noise impact on alignment measurements.
3Measurement precision
If discrete sampling is used during the scan, then the measurement points can be correlated and noise can be reduced, but the scan must be performed at high speed to maintain productivity
Solution Approach 1:
The scan is divided into multiple discrete sampling points distributed across different time periods and spatial locations. This segmentation allows for correlated measurements at different times, improving the signal-to-noise ratio while maintaining scan speed by not requiring continuous high-speed scanning through the entire volume.
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 reticle alignment accuracy by minimizing the impact of low frequency noise and resonance frequency noise contributions, resulting in improved image sensor performance and reduced noise sensitivity.
Implementation Method 1
a projection system for projecting the radiation beam, said apparatus being operable to impart the radiation beam through the projection system onto said alignment structure so as to obtain a resultant aerial image
Implementation Method 2
The light intensity detected by the photosensitive device is dependent on the relative position of the grating (and therefore the reticle), relative to the photosensitive device (and therefore the substrate)
Data Source
AI summary
Disclosed is a device manufacturing method and associated apparatus, the method comprising transferring a pattern from a patterning device onto a substrate. The method relates to the alignment of said patterning device and said substrate, and comprises imparting a radiation beam onto an alignment structure on said patterning device so as to obtain a resultant aerial image; scanning an image sensor in accordance with a scanning scheme, through a target volume containing said resultant aerial image, the relative positions of said image sensor and said substrate being known or subsequently determined; and measuring features of said image and thereby determining of the location of the alignment structure relative to the image sensor; wherein an alternative scanning scheme is used in which, for example two or more scans through the whole target volume are performed, having a total duration the same as a conventional single continuous scan.