Debris Protection Gas Flow for EUV Optical Elements
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Solution Overview
Problem
Plasma-based illumination source systems, such as LPP EUV sources, suffer from debris generated during plasma formation, which damages optical elements like entrance windows, collectors, and mirrors, leading to reduced performance and shorter lifetimes.
Innovation Solution
A debris protection system using a directional gas flow from nozzles positioned around optical elements, with a Peclet number greater than or equal to 2, to prevent debris from reaching these elements, and employing computational fluid dynamics to optimize nozzle count, size, and gas selection for effective debris mitigation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If optical elements are placed inside the EUV source vacuum chamber to collect and direct illumination radiation, then the illumination delivery path is established and radiation can be directed towards the sample, but debris generated during plasma formation damages these optical elements, shortening their lifetime and reducing system reliability
Solution Approach 1:
A gas buffer (e.g., nitrogen or argon) is introduced as an intermediary substance between the plasma source and optical elements. This buffer gas absorbs and neutralizes debris particles generated during plasma formation, preventing them from reaching and damaging the optical elements. The buffer gas acts as a protective mediator that allows the illumination delivery system to function while protecting vulnerable components.
Solution Approach 2:
The patent employs replaceable protective foils or membranes positioned between the plasma source and optical elements. These thin, inexpensive protective layers are designed to be consumed or damaged in place, absorbing debris impact while allowing illumination radiation to pass through. When degraded, they can be quickly replaced without replacing expensive optical elements.
2Object-affected harmful factors
If magnetic fields are used to deflect debris away from optical elements, then some protection is provided against charged particles, but the method is ineffective against neutral particles and requires complex magnetic field generation systems
Solution Approach 1:
The patent uses gas flow systems (pneumatics) to protect optical elements instead of magnetic fields. A controlled flow of buffer gas is directed across the optical elements to physically sweep away debris particles. This pneumatic approach is effective against both charged and neutral particles and avoids the complexity of generating and controlling magnetic fields.
Solution Approach 2:
The patent changes the physical state and parameters of the protective medium from magnetic field parameters (strength, direction) to gas flow parameters (velocity, pressure, composition). By using gas flow with adjustable parameters, the system can effectively deflect various types of debris particles without requiring complex magnetic field configurations.
3Reliability
If gas buffers are used to protect optical elements from debris, then protection against both neutral and charged particles is achieved, but the gas may condense on optical elements at low temperatures and the flow rate must be carefully controlled
Solution Approach 1:
The patent carefully controls gas flow parameters including temperature, pressure, and composition to prevent condensation on optical elements. By maintaining the buffer gas above its dew point temperature and optimizing flow rates, the system achieves effective debris protection without the harmful side effect of gas condensation that would degrade optical performance.
Solution Approach 2:
The patent uses composite protective systems combining multiple gases or combining gas buffer with other protective layers (such as hydrophobic coatings on optical elements). This composite approach allows the system to benefit from the debris-deflecting properties of the gas buffer while preventing condensation through the complementary properties of the coating or additional gas components.
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 directional gas flow effectively suppresses debris, extending the lifetime of optical elements and maintaining EUV light transmission, outperforming traditional methods like magnetic fields and gas buffers in protecting against both neutral and charged particles.
Implementation Method 1
flowing gas out of a plurality of nozzles and away from the optical element at a velocity towards the plasma so as to prevent debris from reaching such optical element resulting in a Peclet number averaged over a protected area of the optical element that is greater than or equal to 2
Data Source
AI summary
Disclosed are methods and apparatus for generating an illumination beam. In one embodiment, the apparatus includes a vacuum chamber configured to hold a target material, an optical element positioned within the vacuum chamber or within a wall of such vacuum chamber, and an illumination source system for generating at least one excitation source that is focused on the target in the vacuum chamber for generating a plasma in the vacuum chamber so as to produce illumination radiation. The apparatus further includes a debris protection system for flowing gas out of a plurality of nozzles and away from the optical element at a velocity towards the plasma so as to prevent debris from reaching such optical element.