Lithographic Apparatus Overlay Correction Using Height Map Derivatives
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Solution Overview
Problem
Current methods for controlling overlay errors in lithographic apparatuses are limited in correcting all errors, especially those requiring higher spatial density of alignment marks and measurements, which adversely affect throughput and functional device area.
Innovation Solution
A lithographic apparatus that uses an alignment sensor to measure substrate positions and a controller to apply pattern corrections based on local height deviations and their derivatives, allowing for improved overlay performance without increasing alignment mark space or impacting throughput.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If higher spatial density of alignment marks and measurements is used to correct overlay errors, then overlay precision is improved, but throughput and functional device area are reduced
Solution Approach 1:
The patent extracts and removes alignment marks from the substrate surface, replacing them with a virtual alignment system based on height map data. This extraction eliminates the need for physical marks that occupy space and require measurement time, thereby maintaining overlay precision while improving throughput and functional device area
Solution Approach 2:
The patent introduces height map data as an intermediary between the substrate and the alignment system. Instead of directly measuring alignment marks on the substrate surface, the system uses height deviations obtained from focus control measurements as a mediator to calculate and apply overlay corrections, achieving high precision without requiring dense physical marks
2Manufacturing precision
If higher spatial density of alignment marks is used to correct overlay errors, then overlay precision is improved, but functional device area is reduced
Solution Approach 1:
The patent extracts alignment information from the substrate surface by removing the need for physical alignment marks. The virtual alignment system uses height map data that can be obtained from existing focus control measurements, eliminating the space occupation by alignment marks and maximizing functional device area while maintaining overlay precision
Solution Approach 2:
The patent makes the height map measurement system multi-functional by using it for both focus control and overlay correction. The same focus control measurements that are already taken during lithography processing provide the height deviation data needed for overlay calculations, eliminating the need for separate alignment mark measurements and preserving functional device area
Data Source
AI summary
A lithographic apparatus applies a pattern repeatedly to target portions across a substrate. Prior to applying the pattern an alignment sensor measures positions of marks in the plane of the substrate and a level sensor measures height deviations in a direction normal to the plane of the substrate. The apparatus applies the pattern to the substrate while positioning the applied pattern using the positions measured by the alignment sensor and using the height deviations measured by the level sensor. The apparatus is further arranged to calculate and apply corrections in the positioning of the applied pattern, based on derivatives of the measured height deviations. The corrections may be calculated on an intrafield and/or interfield basis. The corrections may be based on changes between the observed height deviations and height deviations measured previously on the same substrate.