Angled Gas Knife for Immersion Lithography Liquid Removal
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Solution Overview
Problem
In immersion lithographic apparatuses, residual liquid droplets or films on substrates can cause localized cooling, deformation, and contamination, leading to defectivity, and existing liquid removal methods may exacerbate these issues with high-speed gas flows that increase evaporation and bubble formation.
Innovation Solution
A device with angled conduits connected to vacuum and gas sources is positioned to remove liquid from the substrate simultaneously with pattern projection, utilizing a gas flow directed at an acute angle to efficiently extract liquid and minimize evaporation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high-speed gas flow is used to remove liquid from the substrate, then liquid removal efficiency is improved, but evaporation and bubble formation increase causing substrate deformation and contamination
Solution Approach 1:
The patent changes the flow parameters by directing gas at a specific acute angle (10-45 degrees) relative to the substrate surface, and controls the flow velocity to be below a critical threshold. This parameter optimization allows effective liquid removal through the angled flow component while keeping the normal flow component low enough to minimize evaporation and bubble formation.
Solution Approach 2:
The invention applies gas flow with different characteristics at different locations: the angled gas flow is directed specifically at regions with liquid accumulation, while avoiding excessive flow over areas where liquid has already been removed. This localized application of gas flow achieves efficient liquid removal while minimizing harmful effects in different zones of the substrate.
2Reliability
If liquid is removed from the substrate after exposure, then residual liquid causing defectivity is reduced, but the substrate undergoes deformation due to localized cooling when liquid evaporates
Solution Approach 1:
The patent performs liquid removal during the exposure process itself rather than after exposure. By removing liquid while the substrate is still in the exposure station and under controlled conditions, the system prevents the subsequent evaporation-induced cooling and deformation that would occur if liquid remained on the substrate until after exposure and subsequent processing steps.
Solution Approach 2:
The invention converts the potentially harmful effect of gas flow (which could cause evaporation) into a beneficial controlled process. By using the angled gas flow during exposure when the substrate is still supported and controlled, any minor evaporation occurs under controlled conditions rather than causing uncontrolled deformation later. The process transforms a potential harm into an acceptable controlled operation.
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 removes residual liquid, reducing substrate deformation and contamination while minimizing evaporation and bubble formation, thereby improving the reliability and quality of the lithographic process.
Implementation Method 1
a flow of gas directed at an acute angle to the substrate and/or substrate table
Implementation Method 2
vacuum source, a gas source, or both a vacuum source and a gas source
Data Source
AI summary
An immersion lithographic apparatus is described in which a droplet removal device removes droplets from the substrate, e.g. during exposures, using an angled flow of gas from a gas knife.