Immersion Lithography Liquid Heating for Viscosity Control
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Solution Overview
Problem
The throughput of immersion lithographic apparatuses is limited by liquid loss due to viscous entrainment at high scan speeds, leading to overlay errors and imaging quality issues, as viscous forces exceed capillary forces, causing liquid to shed droplets on the substrate.
Innovation Solution
An immersion lithographic apparatus with a heating system that locally heats the liquid at the receding side of the substrate, reducing viscosity and preventing liquid loss by maintaining a stable liquid film, allowing higher scan speeds without droplet formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the scan speed is increased to improve throughput, then productivity increases, but liquid loss due to viscous entrainment occurs causing overlay errors
Solution Approach 1:
The patent changes the physical parameter of the liquid by adjusting its temperature. By heating the liquid to reduce viscosity or cooling it to increase surface tension, the liquid's flow characteristics are modified to prevent viscous entrainment at higher scan speeds, thereby maintaining imaging precision while improving throughput
Solution Approach 2:
The patent applies periodic heating or cooling cycles to the liquid during the scanning process. This periodic thermal action creates temporary viscosity reductions or surface tension enhancements that synchronize with the scanning rhythm, preventing liquid loss during high-speed operation while maintaining stability during exposure
2Productivity
If the scan speed is increased to improve throughput, then productivity increases, but liquid droplets are shed on the substrate causing imaging quality issues
Solution Approach 1:
The patent modifies the liquid's temperature parameter to control its viscosity and surface tension properties. By optimizing these parameters through thermal control, the liquid maintains adequate adhesion to the substrate at high scan speeds, preventing droplet formation and maintaining imaging quality while enabling increased throughput
Solution Approach 2:
The patent applies thermal treatment to the liquid in advance of the high-speed scanning operation. By pre-adjusting the liquid's viscosity or surface tension through heating or cooling, the system creates a cushioning effect that prevents liquid droplet ejection during subsequent high-velocity scanning, thereby protecting imaging quality
3Loss of substance
If the viscosity of the liquid is reduced to prevent viscous entrainment, then liquid loss decreases, but the liquid film becomes unstable
Solution Approach 1:
The patent employs periodic thermal cycling that temporarily reduces viscosity during scanning phases to prevent liquid loss, then restores higher viscosity during exposure phases to maintain liquid film stability. This rhythmic parameter adjustment allows the system to alternatingly prioritize liquid flow control and film stability
Solution Approach 2:
The patent dynamically adjusts the liquid's temperature and viscosity in real-time based on the operational phase. During scanning, viscosity is reduced to prevent entrainment; during exposure, viscosity is increased to stabilize the liquid film. This dynamic parameter control allows the system to optimize for different functional requirements at different moments
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 local heating system increases the critical scan speed, reducing overlay errors and improving imaging quality by maintaining a stable liquid film, thus enhancing the throughput of the immersion lithographic apparatus.
Implementation Method 1
locally heats the liquid at the receding side of the substrate, reducing viscosity
Implementation Method 2
maintaining a stable liquid film, allowing higher scan speeds without droplet formation
Data Source
AI summary
An immersion lithographic apparatus is configured to subject a photosensitive layer on a substrate to a patterned beam of radiation via a liquid. The immersion lithographic apparatus includes a moveable object having a surface, a fluid handling system to control a presence of the liquid in a volume restricted by the surface, the fluid handling system, and a free surface of the liquid, the free surface extending between the surface and the fluid handling system; and a heating system configured to locally heat a portion of the liquid at a receding side of a periphery edge of the volume in contact with the surface, where the object is receding from the volume along a direction of movement of the object relative to the fluid handling system.