Reference Interferometer Cyclic Error Correction via Variable Optical Path
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Solution Overview
Problem
Interferometers used in semiconductor lithography face challenges in correcting cyclic errors due to non-perfect optical components and ambient condition changes, which cannot be addressed by changing the optical path length in reference interferometers with fixed geometric lengths.
Innovation Solution
A device and method that utilize a reference interferometer with a means to change the optical path length by altering the refractive index through changes in purge gas composition, pressure, and temperature, or by moving a mirror, allowing for continuous detection and correction of cyclic errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the optical path length of the reference interferometer is kept fixed, then the device structure is simple, but cyclic errors cannot be corrected
Solution Approach 1:
The reference interferometer is transformed from a static fixed-path device to a dynamic one where the optical path length can be varied. A movable reflector is introduced to change the geometric length of the measurement section, enabling the system to actively correct cyclic errors while maintaining structural simplicity through controlled movement rather than complex reconfiguration
Solution Approach 2:
The optical path length parameter of the reference interferometer is made variable through the movable reflector mechanism. By changing this parameter in a controlled manner, the system can detect and correct cyclic errors without requiring fundamentally different or more complex interferometer architecture
2Measurement precision
If the optical path length is changed to correct cyclic errors, then measurement precision improves, but the reference interferometer requires additional components
Solution Approach 1:
The reference interferometer is segmented into a fixed portion and a movable measurement section. Only the measurement section with the movable reflector is modified to enable path length changes, while the rest of the interferometer remains simple and fixed, minimizing the increase in overall device complexity
Solution Approach 2:
A movable reflector is introduced as an intermediary component that enables optical path length changes without requiring fundamental redesign of the interferometer. This single intermediate element provides the necessary functionality for cyclic error correction while adding minimal complexity to the system
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 accurate correction of cyclic errors in interferometers, improving the precision of substrate measurement by adjusting the optical path length, thereby reducing measurement inaccuracies caused by ambient conditions and enhancing the accuracy of position detection and optical imaging.
Implementation Method 1
the means is configured to bring about a change in the refractive index
Implementation Method 2
by a change in the pressure and/or the moisture and/or the temperature of a purge gas
Implementation Method 3
by a change in the pressure and/or the moisture and/or the temperature of a purge gas
Implementation Method 4
Interferometers are highly accurate measuring instruments which can be used for measuring distances
Implementation Method 5
An s-polarized and a p-polarized beam portion are superimposed with the aid of polarizing beam splitters (PBS)
Data Source
AI summary
A device for measuring a substrate for semiconductor lithography with a reference interferometer for ascertaining the change in the ambient conditions, wherein the reference interferometer comprises a means for changing the optical path length of a measurement section of the reference interferometer, and a method for correcting cyclic error components in the reference interferometer using same.