Wavefront Analysis via Coherence-Shaping Mask and Diffraction Grating
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Solution Overview
Problem
Current methods for analyzing wavefront effects in optical systems, such as microlithography, are complex and prone to equipment complexity and speckle patterns, which hinder accurate wavefront analysis.
Innovation Solution
A method involving a mirror arrangement with independently settable mirror elements to produce varying angular distributions of illumination light, capturing interferograms, and decomposing wavefront deviations into portions to ascertain system wavefront errors, while avoiding scattering centers and tilting mechanisms, thus reducing equipment complexity and speckle patterns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a diffraction grating is used to produce interferograms for wavefront analysis, then measurement precision is improved, but device complexity increases due to additional optical elements and tilting mechanisms
Solution Approach 1:
The patent extracts and eliminates the tilting mechanism from the measurement system. Instead of using a movable tilting element to scan the diffraction pattern across the pupil, the invention uses a stationary diffraction grating combined with a coherence-shaping mask that directly generates the required interferogram patterns, thereby removing the complex mechanical tilting subsystem while preserving wavefront measurement capability
Solution Approach 2:
The patent merges the functions of the diffraction grating and coherence-shaping mask into a integrated measurement approach. The coherence-shaping mask is positioned in conjunction with the diffraction grating to simultaneously control spatial coherence and generate interference patterns, eliminating the need for separate tilting mechanisms and reducing overall system complexity
2Area of stationary object
If scattering centers or diffuse light are used for pupil filling, then measurement coverage is improved, but speckle patterns are generated that degrade measurement quality
Solution Approach 1:
The patent changes the illumination parameter from incoherent diffuse light or scattered light to coherent or partially coherent light. By using a coherence-shaping mask with the diffraction grating, the system achieves full pupil filling while maintaining coherent illumination, thereby eliminating speckle pattern formation while preserving complete measurement coverage of the pupil region
3Adaptability or versatility
If tilting mechanisms are introduced to scan diffraction patterns dynamically, then measurement flexibility is improved, but device complexity and risk of speckle patterns increase
Solution Approach 1:
The patent achieves dynamic measurement capability without mechanical movement by using a coherence-shaping mask that can be programmed or configured to generate different interferogram patterns. This allows the system to adapt to different measurement requirements (different pupil regions, different wavefront components) through optical configuration rather than mechanical tilting, maintaining flexibility while eliminating moving parts
Solution Approach 2:
The patent replaces the mechanical tilting system with an optical field control approach using coherence-shaping masks. Instead of physically tilting optical elements to scan patterns across the pupil, the invention uses mask patterns to directly generate the required interferogram distributions, substituting mechanical action with optical field manipulation
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 precise wavefront analysis with reduced equipment complexity and avoidance of speckle patterns, allowing for accurate measurement of wavefront deviations in optical systems, particularly in microlithographic projection exposure apparatuses, and accounting for thermal effects and aberrations.
Implementation Method 1
producing an interferogram in a specified plane using a diffraction grating from a wavefront that is coming from the measurement mask
Implementation Method 2
produces, in a capturing plane that follows in the light propagation direction, an interference pattern
Implementation Method 3
different angular distributions of the illumination light that is incident on the measurement mask are produced by a mirror arrangement of independently settable mirror elements
Data Source
AI summary
A method for analyzing the wavefront effect of an optical system includes: illuminating a measurement mask (110, 310) with illumination light, producing an interferogram in a specified plane using a diffraction grating (150) from a wavefront from the illuminated measurement mask and traveling through the optical system; and capturing the interferogram with a detector (170). Different angular distributions of the illumination light incident on the measurement mask are produced via a mirror arrangement of independently settable mirror elements. A plurality of interferograms are captured in a plurality of measurement steps, wherein these measurement steps differ respectively in angular distribution of the illumination light that is incident on the measurement mask. A matching wavefront deviation portion in the measurement results obtained respectively in the measurement steps is ascertained to determine the respective system wavefront deviations of the optical system for the pupil regions illuminated respectively in the individual measurement steps.