EUV Lithography Mirror Contamination Control via Cyclic Gas
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Solution Overview
Problem
In semiconductor lithography, EUV radiation causes carbonaceous deposits on optical components, leading to reduced illumination and productivity due to the formation of carbonaceous films on lenses and mirrors, which is difficult to mitigate without expensive or complex ultra-clean environments or careful oxygen monitoring.
Innovation Solution
Cyclically supplying a first gas with an oxidizing species to react with carbonaceous deposits, followed by a second gas with a reducing species, with the duration of the oxidizing gas supply being at least five times longer than the reducing gas, to inhibit carbonaceous deposit growth and prevent oxide buildup.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If oxygen is added to combust carbonaceous films, then carbonaceous deposit growth is controlled, but mirror surfaces may be damaged due to oxidation
Solution Approach 1:
The patent applies periodic action by cyclically switching between oxidizing and reducing gas environments. The method involves alternating periods of oxygen exposure (to combust carbonaceous deposits) and reducing gas exposure (to prevent oxide buildup on mirror surfaces). This periodic switching allows the system to achieve deposit removal while protecting the mirror surfaces from permanent oxidation damage.
Solution Approach 2:
The patent utilizes parameter changes by controlling the partial pressures and concentrations of oxidizing and reducing species in the gas phase. By dynamically adjusting these chemical parameters and the duration of exposure to each gas type, the method optimizes the combustion of carbonaceous films while limiting oxidation of the mirror surfaces to acceptable levels.
2Object-affected harmful factors
If ultra clean environment is used to reduce hydrocarbon partial pressure, then carbonaceous film growth rate is reduced, but system cost and complexity increase significantly
Solution Approach 1:
The patent replaces the mechanical approach of maintaining ultra-high vacuum environments with a chemical approach. Instead of relying solely on sophisticated vacuum pumping systems to reduce hydrocarbon partial pressures, the method uses controlled chemical reactions (oxidation followed by reduction) to remove carbonaceous deposits. This substitution simplifies the vacuum system requirements while achieving the same protective effect.
Solution Approach 2:
The patent changes the approach from controlling physical parameters (vacuum pressure) to controlling chemical parameters (gas composition and reaction conditions). By introducing controlled amounts of oxidizing and reducing gases and managing their partial pressures, the system achieves carbonaceous film control without requiring extremely low base vacuum pressures, thereby reducing system complexity.
3Manufacturing precision
If EUV radiation is used to improve optical resolution, then small features are accurately reproduced, but carbonaceous deposits form on optical components
Solution Approach 1:
The patent converts the harmful effect of EUV radiation (which causes carbonaceous deposit formation) into a beneficial process. The high-energy EUV radiation that initially creates the problem of carbonaceous film deposition is also used to activate the combustion reaction of these deposits when oxygen is introduced. The same radiation that causes the harm provides the energy needed to eliminate the harm through controlled oxidation.
Solution Approach 2:
The patent applies periodic action by alternating between periods of EUV radiation exposure (which produces carbonaceous deposits during normal operation) and periods of oxidizing gas introduction (which combusts these deposits). This cyclic process allows the system to tolerate temporary deposit formation while systematically removing accumulations, maintaining optical component performance over time.
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 removes carbonaceous deposits while preventing surface oxidation, simplifying the control process and avoiding costly monitoring systems, thus maintaining tool productivity and extending the life of optical components.
Implementation Method 1
a first gas containing an oxidising species for reacting with carbonaceous deposits formed on the surface from the carbonaceous material
Implementation Method 2
a second gas containing a reducing species for reacting with oxidising species on said surface
Implementation Method 3
This radiation stimulates the emission of secondary electrons from these surfaces
Data Source
AI summary
A method is described of controlling contamination of a surface exposed to a carbonaceous material and ionising radiation, such as EUV radiation, DUV radiation or electrons. The method comprises cyclically supplying to the surface a first gas comprising an oxidising species, for example NO, for reacting with carbonaceous deposits formed on the surface from the carbonaceous material, followed by a second gas comprising a reducing species, for example CO, for reacting with oxidising species on the surface.