Pellicle-less EUV Reticle Protection via Electrostatic Deflection
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Solution Overview
Problem
EUV lithography tools face challenges in maintaining the surface of optical components free from foreign particles, leading to printable defects, as traditional pellicles are fragile, reduce light throughput, and have limited lifetime, especially with more powerful EUV sources and increased thermal loads.
Innovation Solution
A pellicle-less approach combining passive and active particle deflection methods, where protection electrodes are arranged across the optical path to limit particle trajectories and particle traps like electrostatic, gas, or plasma curtains are used to remove particles within the optical path.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional pellicles are used to maintain reticle surface free of particles, then particle protection is improved, but light throughput is reduced and device complexity increases
Solution Approach 1:
The patent removes the pellicle component entirely from the system, replacing it with an electrostatic particle control system. Extraction plates are positioned around the reticle to create electrostatic fields that deflect particles away from the reticle surface, eliminating the need for light-absorbing pellicle materials and restoring full light throughput.
Solution Approach 2:
The patent replaces the mechanical pellicle structure with an electrostatic field-based particle control system. Instead of using a physical membrane to block particles, the system uses electric fields generated by extraction plates to actively deflect charged particles away from the reticle, substituting mechanical/passive protection with an active electromagnetic approach.
2Reliability
If traditional pellicles are used to maintain reticle surface free of particles, then particle protection is improved, but device lifetime is reduced due to fragility
Solution Approach 1:
The patent removes the fragile pellicle membrane from the system entirely, eliminating its inherent limitations of fragility and limited lifetime. The replacement electrostatic system uses robust extraction plates that generate electric fields for particle deflection without the mechanical weaknesses of thin membranes.
Solution Approach 2:
The patent replaces the mechanical pellicle structure with an electrostatic field-based system that has no fragile moving parts or thin membranes. The extraction plates and power supplies create sustained electric fields that actively protect the reticle indefinitely, removing the lifetime constraints of traditional pellicles.
3Illumination intensity
If more powerful EUV sources are used to increase light throughput, then illumination intensity is improved, but thermal load increases reducing pellicle lifetime
Solution Approach 1:
The patent removes the pellicle that would be damaged by thermal loads from the optical path, allowing full-power EUV illumination without the thermal constraints that limit pellicle-based systems. The electrostatic extraction system does not absorb EUV light and is not subject to the same thermal damage mechanisms.
4Reliability
If pellicles are used for particle control, then particle protection is improved, but ease of operation is reduced due to cleaning and inspection disruptions
Solution Approach 1:
The patent replaces the mechanical pellicle that requires periodic removal for cleaning and inspection with an electrostatic field system that operates continuously without interruption. The extraction plates remain in place throughout operation, providing constant particle protection without requiring shutdowns for maintenance.
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 method effectively reduces the number of particles reaching the reticle surface, minimizing defects and maintaining light throughput without the limitations of traditional pellicles, even with more powerful EUV sources and increased thermal loads.
Implementation Method 1
The electrostatic particle control system comprises a plurality of extraction plates, each extractable along a respective extraction direction from a reticle position towards a mirror position
Implementation Method 2
particles ionized by a light beam
Implementation Method 3
particle traps like electrostatic, gas, or plasma curtains are used to remove particles within the optical path
Implementation Method 4
particle traps like electrostatic, gas, or plasma curtains are used to remove particles within the optical path
Data Source
AI summary
The present invention is directed to a method and apparatus for maintaining a surface of an optical component free of foreign particles using passive and active approaches to particle control.