Asymmetric Ring Fluid Purging System for Lithographic Optics
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Solution Overview
Problem
Conventional fluid purging systems in lithographic apparatuses suffer from stagnation points and back-flow, leading to sub-optimal purging performance and contamination of optical elements.
Innovation Solution
A fluid purging system featuring a ring with varying wall heights, where a fluid supply system positions fluid to pass over a second wall portion, reducing stagnation points and enhancing fluid flow over optical elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional fluid purging systems are used, then the system structure is simple, but stagnation points are generated and back-flow occurs leading to sub-optimal purging performance
Solution Approach 1:
The ring structure employs asymmetric wall portions with different heights (first wall portion and second wall portion) to create directional fluid flow patterns. This asymmetry prevents stagnation points and back-flow by ensuring fluid continuously moves across the optical element surface without reversing direction, thereby improving purging performance while maintaining a relatively simple overall structure.
Solution Approach 2:
Different portions of the ring structure are designed with locally optimized characteristics - the first wall portion has a greater average height than the second wall portion. This local differentiation creates specific flow zones that collectively eliminate stagnation points across the entire optical element surface, achieving effective purging without requiring complete structural redesign.
2Reliability
If fluid is supplied to the micro-environment in conventional systems, then the optical element is protected, but stagnation points are generated where fluid is not moving and purging is not effectively carried out
Solution Approach 1:
The asymmetric ring structure with first and second wall portions of different heights creates non-uniform flow distribution that intentionally directs fluid along specific paths. This asymmetric geometry ensures fluid continuously sweeps across the optical element surface without creating stagnant zones, improving purging effectiveness while maintaining operational simplicity through a single ring component.
3Reliability
If conventional purging systems are used, then the system is compact, but back-flow occurs where fluid containing contaminants reverses direction
Solution Approach 1:
The ring structure uses asymmetric wall portions where the first wall portion has a greater average height than the second wall portion. This height difference creates a one-way flow path that allows fluid to move forward across the optical element while preventing backward movement, thereby eliminating back-flow and contamination reversal without requiring complex active flow control mechanisms.
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 system improves purging performance by reducing stagnation points and back-flow, maintaining a higher pressure within the purging volume, and optimizing fluid flow velocity, thereby extending the lifespan of optical elements and maintaining radiation beam uniformity.
Implementation Method 1
a fluid supply system positioned radially outwards of the ring and configured to supply fluid to pass over the at least one second wall portion to the space
Implementation Method 2
an average height of the first wall portion is greater than an average height of the second wall portion
Data Source
AI summary
The present invention provides a fluid purging system (100) for an optical element (30), comprising a ring and a fluid supply system (40). The ring being formed of a body entirely surrounding the optical element, the ring defining a space (5) radially inwards thereof and adjacent to the optical element. The ring is formed by at least one first wall portion (10) and at least one second wall portion (20A; 20B), wherein an average height of the first wall portion is greater than an average height of the second wall portion. The fluid supply system is positioned radially outwards of the ring and configured to supply fluid to pass over the at least one second wall portion to the space.