EUV Wavefront Sensor with Dispersive Array for HHG Source Stabilization
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Solution Overview
Problem
Current wavefront measurement techniques in extreme ultraviolet (EUV) and soft x-ray (SXR) spectral regions face challenges due to high absorption by materials and difficulty in fabricating focusing optics, limiting the ability to achieve fast, spectrally resolved 2-D wavefront measurements, which are essential for stabilizing HHG sources used in lithographic metrology.
Innovation Solution
A wavefront sensor with integrated dispersive elements at each location across the array, enabling simultaneous spectral and spatial resolution of wavefront tilts, allowing for real-time monitoring and control of radiation source conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional wavefront measurement techniques are used in EUV/SXR regions, then material absorption and difficulty in fabricating focusing optics occur, but fast spectrally resolved 2-D wavefront measurements cannot be achieved
Solution Approach 1:
The wavefront sensor divides the beam profile into multiple discrete locations across an array, with each location having a dispersive element that independently measures spectral components. This segmentation allows simultaneous spectrally resolved measurements at multiple spatial points, achieving fast 2-D wavefront measurements without requiring complex focusing optics for each spectral component
Solution Approach 2:
A dispersive element is introduced as an intermediary component at each location in the array to separate spectral components. This mediator enables spectral resolution without requiring complex focusing optics, as the dispersive element naturally disperses radiation into its spectral components which can then be detected at each spatial location
2Loss of information
If spectrally resolved wavefront measurements are implemented, then complete beam information is obtained, but measurement time increases
Solution Approach 1:
By segmenting the measurement into discrete locations across an array with dispersive elements at each location, the system captures complete spectral information at multiple spatial points simultaneously in a single measurement snapshot, eliminating the need for sequential scanning that would increase measurement time
Solution Approach 2:
The dispersive elements are pre-positioned at each location in the array to immediately separate spectral components as radiation passes through. This preliminary spectral separation at the point of measurement allows complete beam information to be captured without requiring subsequent spectral analysis steps that would extend measurement 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
Enables accurate, fast measurement of wavefront tilts with spectral resolution, improving the stability and performance of HHG sources by providing complete EUV beam information on timescales relevant to high-volume manufacturing, without the need for additional EUV spectrometers.
Implementation Method 1
said wavefront sensor is provided with a dispersive element at each location in said array and is arranged to measure wavefront tilts with spectral resolution at each location in said array
Data Source
AI summary
A metrology apparatus (302) includes a higher harmonic generation (HHG) radiation source for generating (310) EUV radiation. Operation of the HHG source is monitored using a wavefront sensor (420) which comprises an aperture array (424, 702) and an image sensor (426). A grating (706) disperses the radiation passing through each aperture so that the image detector captures positions and intensities of higher diffraction orders for different spectral components and different locations across the beam. In this way, the wavefront sensor can be arranged to measure a wavefront tilt for multiple harmonics at each location in said array. In one embodiment, the apertures are divided into two subsets (A) and (B), the gratings (706) of each subset having a different direction of dispersion. The spectrally resolved wavefront information (430) is used in feedback control (432) to stabilize operation of the HGG source, and/or to improve accuracy of metrology results.