Argon Plasma EUV Mirror Contamination Control
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Solution Overview
Problem
EUV optical systems face contamination issues due to organic residual gases from mechanical components and electric wiring materials, leading to reduced reflectance of mirrors, and existing cleaning methods with hydrogen or helium plasma do not effectively enhance the etching rate for contaminant removal.
Innovation Solution
An optical apparatus and method utilizing argon plasma generation within an EUV or VUV optical path, where argon gas is introduced and converted into plasma using EUV or VUV light, with controlled flow rates and bias voltages to enhance etching efficiency and prevent contamination on optical elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If hydrogen plasma or helium plasma is used to clean optical elements, then contamination is removed, but the etching rate is insufficient
Solution Approach 1:
The patent changes the gas species parameter from hydrogen or helium to argon, which has different plasma characteristics and higher etching capability. This parameter change resolves the contradiction by maintaining contamination removal effectiveness while significantly increasing the etching rate through argon's superior physical sputtering properties
Solution Approach 2:
The patent replaces the chemical cleaning mechanism of hydrogen/helium plasma with a physical sputtering mechanism using argon plasma. This substitution from chemical to physical cleaning method achieves both effective contamination removal and higher etching rates through ion bombardment
2Productivity
If argon is introduced into the chamber, then etching rate increases, but ion current control becomes necessary
Solution Approach 1:
The patent implements a feedback control system where an ammeter measures the ion current flowing to the optical element, and this measurement is used to control the argon introduction amount. This feedback mechanism manages the increased complexity by providing precise control over the plasma density and etching rate, ensuring optimal cleaning performance while preventing excessive ion damage
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 method effectively increases the etching rate of contaminants on optical elements, improving reflectance and reducing debris scattering, while also neutralizing potential damage to EUV masks with pellicles by maintaining floating potential and preventing electrostatic discharges.
Implementation Method 1
the EUV light guided in the chamber may convert the argon gas into argon plasma
Implementation Method 2
a power supply configured to apply a negative voltage to the optical element in the chamber
Implementation Method 3
a method of removing a contamination layer from an optical surface... a voltage generator disclosed in Japanese Unexamined Patent Application Publication No. 2012-256944 generates a potential difference between an EUV reflection optical element and the cleaning heads and accelerates helium ions in a cleaning gas jet flow with the generated potential difference
Implementation Method 4
an ammeter configured to measure an ion current flowing to the optical element
Data Source
AI summary
To provide an optical apparatus and a method of preventing contamination of the optical apparatus that can more effectively prevent contamination. An optical apparatus according to an embodiment includes a light source configured to generate irradiation light including EUV light, an optical system chamber in which a target object to be irradiated with the irradiation light is disposed, a drop-in mirror provided in the optical system chamber in order to guide the irradiation light, an introducing unit configured to introduce argon into the optical system chamber, a power supply configured to apply a negative voltage to the drop-in mirror in the optical system chamber, an ammeter configured to measure an ion current flowing to the drop-in mirror, and a control unit configured to control an introduction amount of the argon according to a measurement result of the ammeter.