EUV Metrology Optics Cleaning With Reactive Gas Photochemistry
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Solution Overview
Problem
Current metrology techniques struggle to accurately measure small features on substrates due to the use of wavelengths that are not available or usable for modern product structures, leading to inaccurate measurements and the need for indirect methods that do not account for distortions in the lithographic process.
Innovation Solution
A method and apparatus that generate high-frequency radiation using a pump radiation to excite a generating medium, producing a second radiation that propagates coaxially with the first radiation to clean optical elements and remove contamination, enabling accurate measurement of small features.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If visible or near-infrared radiation is used for metrology measurements, then the measurement can be performed with available light sources, but the pitch of the grating must be much coarser than the actual product structures, leading to inaccurate measurements
Solution Approach 1:
The patent changes the wavelength parameter of the radiation from visible/near-infrared to extreme ultraviolet (EUV) range (10-20 nm). This parameter change allows the use of available EUV sources (such as synchrotrons or laser-produced plasma sources) while enabling accurate measurement of fine product structures with pitch down to 10 nm or smaller, resolving the contradiction between source availability and measurement precision.
2Measurement precision
If EUV radiation is used for metrology measurements, then accurate measurement of small features is enabled, but optical elements become contaminated and require frequent cleaning
Solution Approach 1:
The patent introduces a cleaning gas (such as oxygen or nitrogen) into the beam path and uses the EUV radiation itself to photodissociate the cleaning gas molecules, generating reactive oxygen or nitrogen species that automatically clean the optical elements. This converts the harmful contamination effect into a beneficial self-cleaning mechanism, where the measurement radiation simultaneously performs the cleaning function.
Solution Approach 2:
The cleaning gas acts as an intermediary substance between the EUV radiation and the optical elements. The gas molecules absorb the EUV radiation and convert it into reactive species that deposit on or react with contaminants on the optical surfaces, removing them without direct contact between the radiation and the optical elements, thus protecting them while maintaining measurement accuracy.
3Ease of manufacture
If indirect measurement methods are used for small features, then measurements can be performed with current technology, but distortions in the lithographic process are not accounted for
Solution Approach 1:
The patent changes the measurement approach from indirect methods (such as scatterometry on larger structures) to direct imaging using EUV radiation. The short wavelength enables direct visualization and measurement of the actual product structures at their true scale, eliminating the need for indirect inference and accounting for lithographic distortions, while EUV sources are becoming increasingly available.
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 approach allows for precise measurement of small features by generating high-frequency radiation that penetrates deeper into the product structures, providing direct and accurate measurements without the distortions encountered by traditional methods.
Implementation Method 1
generate high-frequency radiation using a pump radiation to excite a generating medium, producing a second radiation that propagates coaxially with the first radiation
Implementation Method 2
a reactive medium is generated from at least a part of the cleaning gas by the second radiation for removing a contamination from the surface area
Data Source
AI summary
An assembly comprises a space configured for placing a medium to receive a first radiation for generating a second radiation. In operation, the second radiation propagates coaxially with the first radiation after the medium. The assembly further comprises an optical element after the medium for transmitting or reflecting the first radiation with a surface area. The assembly is configured such that, in operation, a cleaning gas is in contact with the surface area. A reactive medium is generated from at least a part of the cleaning gas by the second radiation for removing a contamination from the surface area.