Polychromatic Interferometry for EUV Surface Shape Measurement
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Solution Overview
Problem
Existing interferometric measurement methods for surface shapes, particularly in EUV microlithography, face challenges with complex coded diffractive optical elements that lead to increased complexity, measurement time, and inaccuracies due to undesirable diffraction orders and rigorous effects from 3D structures, requiring additional calibration and stability measures.
Innovation Solution
A polychromatic measurement method using two different wavelengths to produce test and reference waves, which are superimposed and evaluated jointly, allowing for simpler setups and simultaneous measurement of surface shapes without separate calibration, reducing the need for complex diffractive optical elements and minimizing drift effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If complex coded diffractive optical elements with multiple encodings are used, then measurement functionality is enhanced, but device complexity and measurement time increase
Solution Approach 1:
The patent segments the measurement process into two distinct wavelength measurements instead of using a single complex multi-encoded CGH. By dividing the functionality into separate wavelength-based measurement paths, the system achieves versatile measurement capability without requiring a single complex diffractive element with multiple encodings.
Solution Approach 2:
The patent uses a simple unencoded or less-encoded CGH that serves multiple functions across different wavelengths. The same diffractive optical element handles both first and second wavelength measurements, providing universal functionality without requiring separate specialized elements for each measurement type.
2Adaptability or versatility
If complex coded diffractive optical elements are used, then measurement functionality is enhanced, but measurement time increases
Solution Approach 1:
The patent employs periodic alternation between two wavelengths in a cyclic measurement process. The measurement switches between first wavelength and second wavelength in periodic cycles, enabling comprehensive surface measurement functionality while maintaining efficient measurement timing through structured alternation rather than sequential complex processing.
Solution Approach 2:
The patent performs preliminary wavelength selection and alternation planning before the actual measurement process. By pre-establishing the measurement cycle structure and wavelength switching sequence, the system optimizes measurement time from the outset, avoiding time-consuming adaptive adjustments during measurement execution.
3Adaptability or versatility
If multiple encodings are used on the CGH, then measurement capabilities are expanded, but undesirable diffraction orders increase
Solution Approach 1:
The patent extracts and removes the problematic multiple encodings from the CGH design. By using a simple unencoded or minimally encoded CGH, the system eliminates the source of undesirable diffraction orders while maintaining measurement capabilities through the alternative approach of using multiple wavelengths with a single encoding scheme.
4Measurement precision
If separate calibration measurements are performed, then measurement accuracy is improved, but measurement time and device complexity increase
Solution Approach 1:
The patent merges the calibration process with the actual measurement process by using the same optical path and components for both purposes. The dual-wavelength measurement system inherently provides calibration information through the wavelength difference, eliminating the need for separate calibration measurements and integrating accuracy assurance into the main measurement workflow.
Solution Approach 2:
The measurement system is designed with universal components that serve both measurement and calibration functions. The same CGH, optical path, and detection system are used for both calibration and production measurements, reducing device complexity and time requirements while maintaining measurement accuracy through the multi-functional design.
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 enables precise and efficient interferometric measurements with reduced measurement time and complexity, eliminating the need for separate calibration and minimizing errors, while maintaining high accuracy and simplicity in the optical setup.
Implementation Method 1
A diffractive optical element, which is arranged in the beam path of the input wave and is configured to produce by way of diffraction from the input wave a test wave
Implementation Method 2
a reflective optical element, which is arranged in the beam path of the reference wave and is designed for the back-reflection of the reference wave
Implementation Method 3
a capture device for capturing an interferogram, which is produced by superposition of the test wave after interaction with the test object and the back-reflected reference wave
Data Source
AI summary
A measurement method for interferometrically measuring the shape of a surface (112) of a test object (114). A test wave (125-1, 125-2) directed at the test object has a wavefront that is at least partially adapted to the desired shape of the surface, and a reference wave (128-1, 128-2) directed at a reflective optical element (130-1, 130 2) has a propagation direction that deviates from the propagation direction of the test wave (125-1, 125-2) for each of two input waves by diffraction at a diffractive element (124). For each wavelength, the test wave is superimposed after interaction with the test object with the associated reference wave after the back-reflection at the first reflective optical element. The test and reference waves are diffracted again at the diffractive element for superposition. An interferogram produced by the superposition is captured in a capture plane (148-1, 148-2). The interferograms are jointly evaluated.