Calibration Mask Diffractive Structures Interferometric Error Separation
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Solution Overview
Problem
Conventional calibration methods for position measurement apparatuses in lithography masks are limited in detecting and separating specific types of errors, such as mirror unevenness and image field rotation, leading to increased measurement complexity and failure to identify systematic errors inherent to the method and machine type.
Innovation Solution
A calibration method using a calibration mask with diffractive structures that enables interferometric position measurement, allowing for high-accuracy determination of diffractive structure positions and subsequent calibration of the position measuring apparatus, which includes using a calibration mask with diffractive structures configured for wavefront detection and Littrow reflection to achieve precise error separation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional self-consistency calibration methods are used, then calibration can be performed using only the position measuring apparatus itself, but specific types of errors such as mirror unevenness and image field rotation cannot be detected and separated
Solution Approach 1:
The patent introduces a calibration mask with known diffractive structures as an intermediary reference object. This calibration mask serves as a mediator between the position measuring apparatus and the calibration process, enabling the detection and separation of systematic errors that would otherwise be undetectable using self-consistency methods alone.
Solution Approach 2:
The patent changes the measurement parameters by using diffractive structures with specific spatial frequencies that are reflected by the interferometer mirrors. By analyzing the spatial frequency content of the reflected waves, the system can separate and identify specific error types such as mirror unevenness, transforming the calibration approach from purely positional to including spatial frequency domain analysis.
2Measurement precision
If calibration is performed by measuring alignment marks individually with a positioning table, then position determination can be achieved, but the measurement complexity increases and systematic errors inherent to the method and machine type are not identified
Solution Approach 1:
The patent merges multiple measurement functions into a single calibration mask. The calibration mask contains diffractive structures that simultaneously serve as reference markers for position measurement and as test objects for detecting systematic errors, eliminating the need for separate calibration procedures and reducing overall measurement complexity.
Solution Approach 2:
The patent replaces the mechanical positioning table-based individual measurement approach with an optical interferometric method using diffractive structures. This substitution eliminates the need for mechanical movement and individual alignment mark measurement, reducing mechanical complexity while maintaining or improving measurement precision.
3Measurement precision
If interferometric length measurement is used for distance determination, then position measurement can be performed, but mirror unevenness and other interferometer errors affect measurement accuracy
Solution Approach 1:
The patent implements a feedback mechanism where the calibration mask with known diffractive structures provides reference information about interferometer errors. By comparing the measured positions against the known positions of the diffractive structures, the system generates feedback that identifies and enables correction of mirror unevenness and other interferometer errors.
Solution Approach 2:
The calibration mask acts as an intermediary reference that mediates between the interferometer and the measurement process. The known spatial frequencies of the diffractive structures serve as a reference standard, allowing the system to identify and compensate for interferometer errors without requiring perfect interferometer performance.
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 enhances the absolute accuracy of position measurement calibration, achieving accuracy better than 2 nm, and allows for the identification and exclusion of systematic errors, thereby improving the overall calibration quality and accuracy of the position measuring apparatus.
Implementation Method 1
the measurement wave is radiated onto the calibration mask in such a way that it is reflected in Littrow reflection at the diffractive structures
Implementation Method 2
qualifying a calibration mask comprising diffractive structures arranged thereon by determining positions of the diffractive structures with respect to one another by means of interferometric measurement
Data Source
AI summary
A method for calibrating an apparatus for the position measurement of measurement structures on a lithography mask comprises the following steps: qualifying a calibration mask comprising diffractive structures arranged thereon by determining positions of the diffractive structures with respect to one another by means of interferometric measurement, determining positions of measurement structures arranged on the calibration mask with respect to one another by means of the apparatus, and calibrating the apparatus by means of the positions determined for the measurement structures and also the positions determined for the diffractive structures.