Alignment Mark Measurement Correction for Lithography
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Solution Overview
Problem
The accuracy of position measurement for small alignment marks and those with internal structures is compromised due to overfilling and sensitivity to scanning path errors in lithographic processes, leading to reduced precision in intra-field alignment.
Innovation Solution
A method that involves determining positions in multiple directions, calculating scan offsets, and using correction data sets to correct measurement errors, allowing for improved accuracy by accounting for both x and y-direction offsets, and potentially using two-dimensional correction maps to refine measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If small fine alignment marks are used to minimize the area needed, then the area occupied by alignment marks is reduced, but the measurement accuracy deteriorates due to overfilling where the spot size of the measurement beam is large compared with the size of the alignment mark
Solution Approach 1:
The patent applies preliminary action by measuring the alignment mark at multiple positions (first position and second position) before final calculation. The measurement beam is scanned at different locations across the alignment mark, and the results are combined to determine a corrected position that compensates for the overfilling effect, allowing small marks to be measured accurately despite the large spot size
Solution Approach 2:
The patent introduces an intermediary correction mechanism that uses scan offset data as a mediator between the raw measurement results and the final position determination. The scan offset, derived from the difference between expected and actual measurement positions, acts as a correction factor that mediates the relationship between the overfilled measurement signal and the true alignment mark position
2Measurement precision
If alignment marks with internal structure are used to improve position determination accuracy, then the measurement accuracy is improved, but the sensitivity to scanning path location increases making measurements more difficult
Solution Approach 1:
The patent performs preliminary measurements at multiple scan positions (first and second positions) before calculating the final corrected position. By pre-measuring at different locations and using the scan offset between expected and actual positions, the system compensates for the internal structure's sensitivity to scanning path variations
Solution Approach 2:
The patent implements feedback by using the scan offset information (the difference between expected and actual measurement positions) to correct the measured position. This feedback loop continuously refines the position determination by adjusting for the sensitivity introduced by the internal structure, thereby reducing the difficulty of accurate measurement
3Measurement precision
If multiple alignment marks are provided to improve position determination, then the measurement accuracy is improved, but the device complexity increases
Solution Approach 1:
The patent makes the alignment mark configuration universal by using the same correction methodology applicable to all alignment marks regardless of their specific arrangement. The scan offset correction technique can be applied consistently across different alignment mark types and positions, simplifying the overall system complexity while maintaining high measurement accuracy through standardized processing
Data Source
AI summary
The invention provides a method of measuring an alignment mark or an alignment mark assembly, wherein the alignment mark comprises grid features extending in at least two directions, the method comprising: measuring the alignment mark or alignment mark assembly using an expected location of the alignment mark or alignment mark assembly, determining a first position of the alignment mark or alignment mark assembly in a first direction, determining a second position of the alignment mark or alignment mark assembly in a second direction, wherein the second direction is perpendicular to the first direction, determining a second direction scan offset between the expected location of the alignment mark or alignment mark assembly in the second direction and the determined second position, and correcting the first position on the basis of the second direction scan offset using at least one correction data set to provide a first corrected position.