Lithographic Focus Control via Height Map Decomposition
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Solution Overview
Problem
Lithographic apparatuses face challenges in achieving optimal focus control due to local topographical variations on substrates, such as bumps, holes, and edge effects, especially in devices with device-specific topography, leading to poor patterning performance and manufacturing inefficiencies.
Innovation Solution
The method involves decomposing height maps into components representing device-specific and other topographical variations, using specific control algorithms for each component to calculate set-points, and combining these set-points to control the positioning system for improved focus control, allowing for differential weighting of extreme values and ignoring device-specific topography when necessary.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a single focus control algorithm is used for all topographical variations, then the control system remains simple, but focus performance deteriorates on substrates with device-specific topography
Solution Approach 1:
The height map is decomposed into multiple components: a first component representing device-specific topography and one or more further components representing other topographical variations. Different control algorithms are applied to each component separately, allowing optimized focus control for each type of variation while maintaining overall system manageability.
Solution Approach 2:
Different control algorithms with different characteristics are applied to different components of the height map. The first control algorithm processes device-specific topography while one or more second control algorithms process other topographical variations, enabling locally optimized control strategies for different spatial frequencies and types of variations.
2Manufacturing precision
If focus control follows all local topographical variations, then local focus accuracy improves, but manufacturing productivity decreases due to increased processing time
Solution Approach 1:
By separating the height map into device-specific and non-device-specific components, the system can apply detailed focus control only where necessary (device-specific variations) while using simpler control for other variations, reducing overall processing complexity and time.
Solution Approach 2:
The control system adjusts parameters such as the spatial frequency response and weighting factors differently for each height map component, allowing optimized balance between local accuracy and overall processing efficiency for each type of topographical variation.
Data Source
AI summary
A lithographic apparatus applies a device pattern at multiple fields across a substrate. A height map is decomposed into a plurality of components. A first height map component represents topographical variations associated with the device pattern. One or more further height map components represent other topographical variations. Using each height map component, control set-points are calculated according to a control algorithm specific to each component. The control set-points calculated for the different height map components are then combined and used to control imaging of the device pattern to the substrate. The specific control algorithms can be different from one another, and may have differing degrees of nonlinearity. The combining of the different set-points can be linear. Focus control in the presence of device-specific topography and other local variations can be improved.