Dynamic Gas Extraction for Substrate Loading in Lithography
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Solution Overview
Problem
Lithographic apparatuses face challenges in efficiently loading substrates onto support tables without deformation, leading to increased overlay and throughput time due to the need for precise pressure control and gas extraction during the loading process.
Innovation Solution
A support table with a gas extraction system that adjusts flow rates based on the distance between the substrate and the support table, using burls and protrusions to manage gas extraction rates, ensuring efficient clamping and minimizing deformation by reducing pressure differences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If gas extraction is performed at high flow rate during substrate loading, then substrate deformation is reduced, but substrate clamping accuracy deteriorates due to excessive pressure difference
Solution Approach 1:
The gas extraction system dynamically adjusts the flow rate based on the loading stage: high flow rate during initial loading to prevent deformation, then automatically switches to low flow rate near the end to ensure accurate clamping. This dynamic adjustment resolves the contradiction between preventing deformation and ensuring clamping accuracy.
Solution Approach 2:
The gas extraction process is divided into two distinct periods: first period with high extraction flow rate for deformation prevention, second period with low extraction flow rate for accurate clamping. This periodic action allows the system to optimize for different objectives at different times, resolving the precision contradiction.
2Measurement precision
If gas extraction flow rate is reduced during loading, then substrate clamping accuracy is improved, but substrate deformation increases leading to increased overlay
Solution Approach 1:
The system uses dynamic flow rate adjustment where the extraction rate is high during the majority of the loading process to maintain substrate flatness and low overlay, then automatically reduces to a low rate during the final approach to ensure accurate clamping. This resolves the contradiction between overlay and clamping accuracy.
Solution Approach 2:
The high flow rate gas extraction is performed in advance during the loading process to prevent substrate deformation before clamping occurs. This preliminary action ensures the substrate is already flat and free of deformation when clamping takes place, thereby achieving both low overlay and high clamping accuracy.
3Productivity
If substrate is clamped immediately upon contact with support table, then throughput time is reduced, but substrate deformation occurs due to pressure difference
Solution Approach 1:
The gas extraction system operates at high flow rate during the entire loading process, even as the substrate approaches contact with the support table. This dynamic high-rate extraction prevents deformation while maintaining fast loading speed, resolving the contradiction between throughput and flatness.
Solution Approach 2:
The high flow rate gas extraction action continues continuously throughout the loading process without interruption or reduction, ensuring substrate flatness is maintained at all times. This continuous useful action allows immediate clamping upon contact without deformation, achieving both high throughput and good flatness.
4Manufacturing precision
If gas extraction is delayed until substrate contact with support table, then substrate flatness is maintained, but loading throughput time increases
Solution Approach 1:
Gas extraction begins in advance during the loading process rather than waiting for contact. This preliminary high-rate extraction maintains substrate flatness throughout the approach, allowing immediate clamping upon contact and thereby maintaining high throughput while ensuring flatness.
Solution Approach 2:
The gas extraction action is performed continuously at high rate from the beginning of loading through contact and clamping. This continuous action maintains flatness throughout the entire process, eliminating the need to delay clamping and thereby maintaining high loading throughput while ensuring substrate flatness.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach reduces substrate deformation and overlay while maintaining high throughput by optimizing gas extraction rates during the loading process, allowing for more accurate and efficient substrate clamping.
Implementation Method 1
Gas is extracted through the holes from the region enclosed by the substrate and the support table, thereby reducing the pressure in this region for clamping of the substrate
Implementation Method 2
gas is extracted from the gap at a first loading flow rate when the distance between the substrate and the support plane is greater than a threshold distance and gas is extracted from the gap at a second loading flow rate when the distance between the substrate and the support plane is less than the threshold distance
Data Source
AI summary
A lithographic apparatus includes a support table and a gas extraction system. The gas extraction system is configured to extract gas from a gap between the base surface of the support table and a substrate through at least one gas extraction opening when the substrate is being lowered onto the support table. The lithographic apparatus is configured such that gas is extracted from the gap at a first loading flow rate when the distance between the substrate and the support plane is greater than a threshold distance and gas is extracted from the gap at a second loading flow rate when the distance between the substrate and the support plane is less than the threshold distance, wherein the second loading flow rate is lower than the first loading flow rate.