Wavefront Aberration Measurement Apparatus Illumination Homogenization
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Solution Overview
Problem
Existing measurement apparatuses for wavefront aberration in optical imaging systems face limited measurement accuracy due to distortion aberrations characterized by field-point-dependent Zernike coefficients Z2 and Z3, which are influenced by non-homogeneous mask illumination.
Innovation Solution
A measurement apparatus that generates a measurement wave and includes diffusing structures to homogenize the illumination radiation, allowing for the determination of the intensity distribution's influence on the wavefront measurement, thereby improving the accuracy of distortion aberration measurement through optical propagation calculations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If shearing interferometry is used for measuring wavefront aberration, then measurement capability is provided, but measurement accuracy of distortion aberrations is limited due to non-homogeneous mask illumination
Solution Approach 1:
The intensity distribution of the illumination radiation is ascertained beforehand (before the wavefront measurement) and stored for subsequent correction. This preliminary characterization of the illumination system allows the evaluation device to compensate for non-homogeneous mask illumination during the actual measurement, thereby improving measurement accuracy without adding complexity to the measurement procedure itself
Solution Approach 2:
The evaluation device uses the ascertained intensity distribution as feedback to correct the measurement result. By determining the influence of the intensity distribution on the measurement result and applying this correction, the system compensates for illumination non-uniformity effects, improving the accuracy of distortion aberration measurements
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 significantly enhances the measurement accuracy of distortion aberrations by accounting for the intensity distribution of the illumination radiation, reducing distortion aberrations and enabling precise wavefront aberration determination.
Implementation Method 1
comprising an illumination system for illuminating a mask plane with an illumination radiation
Implementation Method 2
comprising diffusing structures arranged in the beam path of the illumination radiation upstream of the mask plane for homogenizing an intensity distribution of the illumination radiation in the region of the mask plane
Implementation Method 3
coherence structures arranged in the mask plane
Implementation Method 4
shearing interferometry is a phase-shifting interferometry technique
Implementation Method 5
a phase-shifting structure, such as e.g. a displaceable diffraction grating, also referred to as analysis grating below
Data Source
AI summary
A measurement apparatus (10) for measuring a wavefront aberration of an imaging optical system (12) includes (i) a measurement wave generating module (24) which generates a measurement wave (26) radiated onto the optical system and which includes an illumination system (30) illuminating a mask plane (14) with an illumination radiation (32), as well as coherence structures (36) arranged in the mask plane, and (ii) a wavefront measurement module (28) which measures the measurement wave after passing through the optical system and determines from the measurement result, with an evaluation device (46), a deviation of the wavefront of the measurement wave from a desired wavefront. The evaluation device (46) determines an influence of an intensity distribution (70) of the illumination radiation in the region of the mask plane on the measurement result and, when determining the deviation of the wavefront, utilizes the influence of the intensity distribution.