Lithographic Apparatus Focus Control via Substrate Topography Decomposition
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Solution Overview
Problem
Lithographic manufacturing processes face challenges in focus control due to substrate topography variations, which can lead to poor patterning performance and yield issues, especially in substrates with device-specific topography and local anomalies like bumps, holes, and edge effects.
Innovation Solution
A method that involves obtaining a parameter map of substrate variations, decomposing it into device-specific and non-device-specific components, deriving a scale factor to correct measurement errors, and using a corrected parameter map to control the lithographic apparatus for improved focus and patterning across the substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If height sensors are used to measure substrate surface variations, then focus control can be improved, but measurement errors occur due to device-specific topography and local anomalies
Solution Approach 1:
The height map is segmented into multiple components: device-specific topography, local anomalies (bumps, holes, edge effects), and global substrate variations. This segmentation allows each component to be processed and corrected independently, improving overall measurement accuracy by addressing specific error sources separately.
Solution Approach 2:
Different correction methods are applied to different regions of the substrate based on local characteristics. Device-specific topography receives one type of correction while local anomalies receive different corrections, allowing optimized handling of each region's specific measurement challenges.
2Device complexity
If the projection system focuses on a flat plane, then imaging is simplified, but poor patterning performance results due to substrate topography variations
Solution Approach 1:
The focal plane is made dynamic by continuously adjusting it according to the measured height map during substrate exposure. This allows the focal plane to adapt to substrate topography variations in real-time, maintaining optimal focus across the entire substrate surface without requiring a physically complex adjustable projection system.
Solution Approach 2:
A digital copy of the substrate topography (height map) is created and used to generate correction data that guides the focal plane adjustment. This virtual model allows the system to compensate for physical substrate variations without adding mechanical complexity to the projection system itself.
3Manufacturing precision
If height maps are used to control focus across the substrate, then patterning uniformity improves, but measurement errors from device topography and local anomalies degrade accuracy
Solution Approach 1:
Error components (device-specific topography and local anomalies) are extracted and separated from the main height map. This extraction allows these problematic elements to be identified and corrected separately, preventing them from degrading the overall height map accuracy used for focus control.
Solution Approach 2:
The system uses feedback from multiple measurements including air gauge data and focus measurements to iteratively refine the height map and correct errors. This feedback loop continuously improves measurement accuracy by comparing expected versus actual measurements and applying corrections.
Data Source
AI summary
A method of controlling a lithographic apparatus to manufacture a plurality of devices, the method including: obtaining a parameter map representing a parameter variation across a substrate by measuring the parameter at a plurality of points on the substrate; decomposing the parameter map into a plurality of components, including a first parameter map component representing parameter variations associated with the device pattern and one or more further parameter map components representing other parameter variations; deriving a scale factor, configured to correct for errors in measurement of the parameter variation, from measurements of a second parameter of a substrate; and controlling the lithographic apparatus using the parameter map and scale factor to apply a device pattern at multiple locations across the substrate.