EUV Optical Element Laser Treatment for Uniform Reflectivity
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Solution Overview
Problem
Existing methods for treating optical elements in the EUV wavelength range face challenges such as reflectivity suppression and compaction, with conventional mirrors being ineffective and current processing techniques leading to unwanted structural displacements and non-homogeneous reflectivity.
Innovation Solution
A method involving pulsed laser irradiation with pulse sequences, where each pulse is separated by 100 ns or less, is used to modify optical elements, allowing for controlled reflectivity adjustments and minimizing structural displacements by exploiting the different timescales of electron and lattice heating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If backside illumination is used to treat multilayer systems, then immunity to pattern load is achieved, but high intensities cause multilayer compaction and registration impact
Solution Approach 1:
The patent applies periodic pulsed laser illumination to treat the multilayer system. By using periodic pulses instead of continuous high-intensity illumination, the method achieves the desired modification while allowing thermal diffusion between pulses, thereby reducing compaction and registration errors associated with sustained high-intensity exposure.
Solution Approach 2:
The patent changes the temporal parameters of laser illumination by introducing pulse sequences with specific duty cycles and repetition rates. This parameter modification enables the treatment to proceed at lower average intensities, reducing harmful thermal effects while maintaining effectiveness through cumulative exposure.
2Length of stationary object
If high intensity laser irradiation is applied to modify optical elements, then modification depth is increased, but structural compaction and unwanted side effects increase
Solution Approach 1:
The patent employs periodic pulsed illumination where the laser is turned on and off in cycles. During the off periods, thermal diffusion allows heat to penetrate deeper into the multilayer structure without causing surface compaction. This periodic action enables deep modification while avoiding the harmful side effects of continuous high-intensity irradiation.
Solution Approach 2:
The patent maintains continuous useful action through high repetition rate pulsing, where pulses are delivered so frequently that the cumulative effect achieves deep modification. The short intervals between pulses ensure continuous energy deposition while allowing brief thermal relaxation periods, maintaining treatment effectiveness without excessive compaction.
3Device complexity
If conventional mirrors are used for EUV wavelengths, then simplicity of structure is maintained, but reflectance becomes negligible
Solution Approach 1:
The patent employs composite multilayer structures consisting of alternating layers of materials with different refractive indices for EUV wavelengths. This composite approach replaces simple conventional mirrors, achieving high EUV reflectance through constructive interference while maintaining a manageable structural complexity through systematic layering.
Solution Approach 2:
The patent changes the optical parameters by using materials specifically selected for their refractive index properties at EUV wavelengths. The layer thicknesses are precisely controlled to satisfy Bragg's law for constructive interference, transforming the optical response from negligible reflectance to high reflectance through parameter optimization.
4Reliability
If frontside illumination is used to treat multilayer systems, then pattern load influence is avoided, but reflectivity suppression increases
Solution Approach 1:
The patent applies periodic pulsed illumination from the frontside, using the off-periods between pulses to allow thermal diffusion and reduce cumulative heating effects. This periodic approach maintains process reproducibility by avoiding pattern load influence while mitigating reflectivity suppression through reduced thermal accumulation.
Solution Approach 2:
The patent modifies the illumination parameters by using lower average intensity achieved through pulsing, which reduces thermal effects and reflectivity suppression. The duty cycle and repetition rate are optimized to maintain treatment effectiveness while minimizing energy loss through reduced continuous exposure.
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 achieves homogeneous reflectivity variations of 1% or less and reduces unwanted structural shifts, improving critical dimension control and accuracy in photolithography masks.
Implementation Method 1
exploiting the different timescales of electron and lattice heating
Implementation Method 2
exploiting the different timescales of electron and lattice heating
Implementation Method 3
providing a pulsed laser irradiation, wherein the pulsed laser irradiation comprises a plurality of pulse sequences, each pulse sequence comprising a plurality of pulses, wherein a first pulse and a second pulse of the plurality of pulses are separated by a time of 100 ns or less
Data Source
AI summary
A method for treating an optical element for the extreme ultraviolet (EUV) wavelength range, the method comprises providing a pulsed laser irradiation, wherein the pulsed laser irradiation comprises a plurality of pulse sequences, each pulse sequence comprising a plurality of pulses, wherein a first pulse and a second pulse of the plurality of pulses are separated by a time of 100 ns or less, and directing the laser irradiation onto the optical element for the EUV wavelength range.