Mask Surface Height Measurement in EUV Exposure Devices
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Solution Overview
Problem
In EUV exposure devices, the slit substrate obstructs light measurement, making it difficult to accurately measure the height-direction position of the mask surface, leading to image-forming performance issues and errors in magnification or transfer position.
Innovation Solution
The method involves moving the exposure area defining member, such as a slit substrate, to a position that does not obstruct the light measurement, allowing for precise height-direction position measurement of the mask surface by using optical measurement devices and correcting for any deviations in the mask stage position during exposure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the slit substrate is present between the mask and projection optical system to define exposure area, then exposure area definition is improved, but light measurement is obstructed and mask surface height measurement precision deteriorates
Solution Approach 1:
The slit substrate is made movable between a first position (for exposure) and a second position (for measurement). This dynamic repositioning allows the same component to serve dual functions: defining exposure area during exposure and allowing light measurement during measurement, thereby resolving the contradiction between exposure area definition and measurement precision
Solution Approach 2:
The mask surface height is measured in advance at multiple positions before exposure by repositioning the slit substrate to the second position. These pre-measured height values are stored and used for correction during exposure, allowing measurement to occur when the measurement path is clear of obstructions
2Device complexity
If the mask stage position is not corrected, then device complexity is reduced, but image-forming performance deteriorates due to height position deviations
Solution Approach 1:
The system measures mask surface height at multiple positions, calculates deviation from a reference plane, and uses this feedback information to correct the mask stage position. This closed-loop feedback mechanism improves image-forming performance by compensating for height deviations without requiring complex mechanical precision
Solution Approach 2:
Instead of relying solely on mechanical precision of the mask stage, the system substitutes mechanical adjustment with optical measurement and computational correction. The mask stage position is adjusted based on calculated deviation values from optical measurements, replacing the need for highly precise mechanical positioning
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 measurement and correction of the mask surface height-direction position, reducing image blurring and magnification errors, even when the exposure area defining member is present between the mask and the projection optical system.
Implementation Method 1
Measurement of the height-direction position of each part of the mask is performed by emitting light from an oblique direction onto a measured surface of the mask and observing the position where light reflected by the mask surface enters a receiving surface
Data Source
AI summary
A method to measure the height-direction position of a mask M in an exposure device having a function to irradiate the mask M with light emitted from a light source and transfer a pattern formed on the mask M onto a photosensitive substrate such as a wafer by a projection optical system, a mask surface height-direction position measurement method characterized by moving, before measuring the height-direction position of the mask M, an exposure area defining member 1 which is arranged between the mask M and the projection optical system and defines an exposure area at the time of exposure.