Lithographic Substrate Cooling via Localized Gas Conduits
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Solution Overview
Problem
Lithographic apparatuses face challenges in maintaining accuracy due to localized heating causing substrate expansion and slippage, which affects the precision of pattern projection onto substrates, especially when using EUV radiation.
Innovation Solution
A lithographic apparatus with a cooling apparatus that includes a cooling element positioned above the substrate table to locally cool the substrate, using a gas delivery system to manage heat transfer and prevent substrate expansion, combined with a heating apparatus to maintain thermal stability at the edges of the exposure area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a radiation beam is used to project a pattern onto a substrate, then the desired pattern is formed on the substrate, but localized heating of the substrate occurs which reduces projection accuracy
Solution Approach 1:
The patent applies local quality by implementing a cooling apparatus with cooling elements positioned specifically adjacent to the exposure area on the substrate table. This localized cooling approach targets only the regions experiencing heat buildup from radiation beam exposure, rather than cooling the entire substrate table, thereby maintaining high cooling efficiency while preserving overall substrate temperature stability for accurate pattern projection.
2Manufacturing precision
If the substrate is locally cooled to suppress heating, then substrate expansion is reduced, but the complexity of the lithographic apparatus increases
Solution Approach 1:
The cooling apparatus is segmented into multiple independent cooling elements that can be individually positioned and controlled along the substrate table. Each cooling element corresponds to specific exposure areas, allowing the system to address thermal management needs in discrete zones. This segmentation reduces overall system complexity by breaking down the cooling function into manageable, modular components rather than requiring a single complex cooling system.
3Loss of energy
If the cooling element is positioned close to the exposure area, then heat removal efficiency is improved, but the risk of substrate slippage on burls increases
Solution Approach 1:
The patent introduces gas delivery conduits as intermediaries between the cooling elements and the substrate. These conduits deliver controlled amounts of cooling gas to the substrate surface in the vicinity of the exposure area, enabling effective heat removal without requiring direct physical contact between cooling elements and substrate. This intermediary approach maintains substrate positioning stability by avoiding mechanical interference with substrate-burl contact while still achieving efficient thermal management.
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
The solution effectively reduces substrate expansion and slippage, enhancing the accuracy of pattern projection by maintaining thermal stability and preventing distortion, thereby improving the overlay performance of the lithographic apparatus.
Implementation Method 1
the cooling element being configured to remove heat from a substrate held on the substrate table... The cooling element may be in thermal communication with the substrate held on the substrate table
Implementation Method 2
The gas conduit allows controlling the pressure within the cavity of the cooling element... The combination of the pressure of gas delivered to the cavity and the separation between the cavity roof and the substrate surface may be such that the accommodation coefficient of the substrate does not have a significant effect upon transfer of heat from the substrate to the cooling element body
Data Source
AI summary
A lithographic apparatus comprising a projection system configured to project a patterned radiation beam to form an exposure area on a substrate held on a substrate table, the lithographic apparatus further comprising a cooling apparatus for cooling the substrate, wherein the cooling apparatus comprises a cooling element located above the substrate table and adjacent to the exposure area, the cooling element being configured to remove heat from the substrate.