Wavefront Sensor Indent Array for EUV Metrology
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Solution Overview
Problem
Current inspection techniques using visible or ultraviolet radiation are limited in measuring smallest features in modern lithographic processes, and measuring wavefronts in extreme ultraviolet (EUV) and soft x-ray (SXR) spectral regions is challenging due to high absorption by materials and difficulty in fabricating focusing optics.
Innovation Solution
A wavefront sensor with an indent array is developed to measure the tilt of a wavefront at multiple locations across a radiation beam, integrated with a processor to determine operating conditions of the radiation source, enabling improved compatibility with EUV and SXR wavelengths and enhancing spatial resolution without interference between spectral components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If visible or ultraviolet radiation is used for inspection, then the inspection system can operate with simpler technology, but it cannot measure the smallest features in modern lithographic processes
Solution Approach 1:
The patent changes the wavelength parameter of the radiation from visible/ultraviolet to extreme ultraviolet (EUV) range (1-100 nm). This parameter change enables measurement of smaller features while the use of zone plates with specific geometric designs maintains ease of manufacture by providing a fabrication approach suitable for EUV wavelengths
Solution Approach 2:
The patent introduces zone plates as intermediary focusing elements that enable EUV radiation to be focused effectively. These zone plates serve as a mediator between the EUV radiation source and the sample, solving the focusing problem at EUV wavelengths without requiring complex conventional optics
2Measurement precision
If EUV or SXR radiation is used to measure smaller features, then measurement precision improves, but material absorption increases and focusing optics become difficult to fabricate
Solution Approach 1:
The patent optimizes the zone plate parameters (zone width, depth, and material composition) to minimize absorption losses at EUV wavelengths. By carefully controlling these parameters, the system achieves effective focusing while reducing the harmful absorption effect
Solution Approach 2:
The patent employs composite zone plate structures combining different materials with complementary properties. The zone plates use materials with appropriate atomic numbers and densities to achieve both focusing capability and reduced absorption at EUV wavelengths
3Measurement precision
If EUV or SXR radiation is used to measure smaller features, then measurement precision improves, but device complexity increases due to difficulty in fabricating focusing optics
Solution Approach 1:
The patent introduces zone plates as a specialized intermediary component that simplifies the overall device architecture. Instead of requiring complex conventional optics, the zone plates provide a relatively simple diffractive focusing element that can be fabricated using standard microfabrication techniques adapted for EUV wavelengths
Solution Approach 2:
The patent replaces complex mechanical focusing optics with a diffractive optical system based on zone plates. This substitution eliminates the need for complex mechanical adjustment mechanisms and precision alignment systems, reducing overall device complexity while maintaining focusing capability
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 solution allows for accurate monitoring and control of radiation source conditions, improving the measurement of wavefronts and focusing capabilities, thereby enabling more precise inspection and control in lithographic processes, especially for smaller features and higher resolution requirements.
Implementation Method 1
each indent of the indent array is operable to perform focusing of the radiation
Data Source
AI summary
Disclosed is a wavefront sensor for measuring a tilt of a wavefront at an array of locations across a beam of radiation, wherein said wavefront sensor comprises a film, for example of Zirconium, having an indent array comprising an indent at each of said array of locations, such that each indent of the indent array is operable to perform focusing of said radiation. Also disclosed is a radiation source and inspection apparatus comprising such a wavefront sensor.