Lithographic Mask Placement Error Evaluation via Reference Point Distance
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Solution Overview
Problem
As lithography technology advances and feature sizes shrink, precise measurement of placement errors becomes crucial, especially in sub-45 nm nodes, where overlay errors impact the critical dimension (CD) budget, and existing methods struggle to accurately measure these errors between different locations on masks or between masks.
Innovation Solution
A method and system for evaluating placement errors on lithographic masks by providing a reference result for distance measurements between pairs of points, calculating differences to determine relative placement errors, and using these to detect and compensate for overlay errors, particularly through a global and localized alignment process, enabling the creation of error maps for mask manufacturing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If feature sizes are reduced to sub-45 nm nodes, then lithography precision and resolution are improved, but placement error measurement accuracy deteriorates due to the impact of overlay errors on the CD budget
Solution Approach 1:
The patent introduces a reference element as an intermediary object that contains a reference pair of points with a known distance. This reference element serves as a mediator to enable accurate measurement of placement errors between mask features and wafer features, even at sub-45 nm nodes where direct measurement would be insufficient due to overlay error impacts on the CD budget.
2Measurement precision
If distance measurements are taken between multiple pairs of points on masks, then placement error detection capability is improved, but measurement complexity and time increase
Solution Approach 1:
The patent performs preliminary action by pre-defining multiple pairs of points on the mask and wafer before the actual measurement process. These point pairs are established in advance based on the repetitive pattern structure, allowing the measurement system to efficiently calculate placement errors by comparing distances between corresponding points without requiring complex real-time analysis.
3Manufacturing precision
If overlay errors are compensated for in sub 45 nm nodes, then overall CD budget control is improved, but process complexity increases due to the integration of overlay measurement into the CD control process
Solution Approach 1:
The patent applies universality by using the same reference element and measurement approach for both CD measurement and overlay error measurement. The reference pair of points serves multiple functions: it provides a reference for CD measurements and simultaneously enables overlay error detection by comparing distances between mask features and wafer features, thereby integrating overlay control into the existing CD measurement process without requiring separate complex systems.
Data Source
AI summary
A method for evaluating placement errors within a lithographic mask, the method includes: providing or receiving a reference result that represents a distance between a reference pair of points of a reference element; measuring, for each pair of points out of multiple pairs of points that are associated with multiple spaced apart elements of the lithographic mask, the distance between the pair of points to provide multiple measurement results; wherein differences between a measurement result and the reference result are indicative of relative placement errors; and determining relative placement errors in response to relationships between the reference result and each of the measurement results.