Localized Cleaning Beam for Lithographic Substrate Table
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Solution Overview
Problem
Contamination on the top surface of a substrate table in lithographic apparatuses leads to overlay errors and reduced accuracy in positioning and alignment due to immersion liquids, particularly from contaminants originating from the substrate surface.
Innovation Solution
A method and apparatus that utilize a cleaning radiation beam, adjusted to limit its cross-sectional area, is projected through a liquid between the optical system and the substrate table to specifically target and clean contaminated areas, such as sensors, without affecting UV-sensitive materials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a large body of liquid is used to fill the space between the projection system and substrate, then imaging of smaller features is enabled, but additional motors are required and turbulence in the liquid leads to unpredictable effects
Solution Approach 1:
The patent applies local quality by confining the immersion liquid to a localized area between the projection system and substrate, rather than filling the entire space. This is achieved through a liquid confinement system that creates a controlled liquid environment only where needed for imaging, reducing the overall volume of liquid while maintaining the refractive index benefits for high-precision imaging of small features.
2Quantity of substance
If a liquid confinement system is used to provide liquid on a localized area, then the liquid volume is reduced, but the system complexity increases
Solution Approach 1:
The patent employs flexible thin films as part of the liquid confinement system to create a localized liquid environment. These thin films act as barriers that contain the immersion liquid in specific regions, reducing the overall liquid volume required while maintaining the optical benefits. The flexible nature of these films allows for adaptation to the imaging geometry without requiring complex rigid structures.
3Reliability
If UV radiation is used to clean contaminants, then chemical bonds are broken and contaminants are removed, but UV-sensitive materials on the substrate may be affected
Solution Approach 1:
The patent applies segmentation by dividing the radiation beam into two distinct modes: a full-area exposure beam for imaging and a localized cleaning beam for contaminant removal. The cleaning beam is spatially segmented to target only specific contaminated areas on the substrate or substrate table, avoiding exposure of UV-sensitive materials to harmful radiation doses while maintaining effective cleaning where needed.
Solution Approach 2:
The patent implements local quality by directing the cleaning radiation beam only to specific localized areas that require cleaning, rather than exposing the entire substrate. This spatial selectivity ensures that UV-sensitive materials in non-contaminated areas are not exposed to damaging radiation, while contaminants in targeted areas are effectively removed through photodissociation of chemical bonds.
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
Effectively removes contaminants by breaking chemical bonds with UV radiation, ensuring accurate positioning and alignment by maintaining the cleanliness of critical surface areas, thereby enhancing the precision and reliability of lithographic processes.
Implementation Method 1
Effectively removes contaminants by breaking chemical bonds with UV radiation
Implementation Method 2
projecting a cleaning radiation beam through the liquid using the optical system
Data Source
AI summary
A system for cleaning a limited area of a top surface of a substrate table or an object positioned on a top surface of a substrate table is disclosed. The optical system used during normal imaging is adjusted to limit the cross-sectional area of a radiation beam to form a cleaning radiation beam which impinges on the limited area.