Low Expansion Glass Substrate Side Surface Flatness Control
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Solution Overview
Problem
The precision measurement of the flatness of the main surface of a reflective mask substrate is affected by the surface properties of its side surfaces and chamfered portions, leading to inaccuracies in EUV lithography, where conventional processing of these areas is insufficient.
Innovation Solution
A low expansion glass substrate with side surfaces and chamfered portions having a flatness of 25 μm or less, and parallelism of 0.01 mm/inch or less, to prevent local deformation during measurement, allowing for precise flatness measurement of the main surface with an error within ±10 nm.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional processing is applied to side surfaces and chamfered portions, then manufacturing complexity is reduced, but measurement precision of the main surface deteriorates due to local deformation
Solution Approach 1:
The patent applies different processing standards to different regions of the substrate. Specifically, side surfaces and chamfered portions are processed to achieve a flatness of 25 μm or less, while the main surface requires ultra-precise flatness of 50 nm or less. This local differentiation of quality requirements resolves the contradiction by focusing complex processing only where absolutely necessary (main surface measurement area) while applying simpler processing to peripheral areas, thereby improving measurement precision without unnecessarily increasing overall manufacturing complexity.
2Measurement precision
If side surfaces and chamfered portions are not precisely processed, then manufacturing cost and complexity are reduced, but the flatness measurement of the main surface becomes inaccurate
Solution Approach 1:
The patent implements a differentiated processing strategy where side surfaces and chamfered portions are processed to a moderate flatness standard of 25 μm or less, which is sufficiently precise to prevent local deformation during measurement but does not require the ultra-precise processing needed for the main surface. This local quality approach maintains manufacturing ease while ensuring measurement accuracy by eliminating the source of deformation without applying excessive processing to areas where it is not needed.
3Measurement precision
If ultra-precise flatness of 50 nm or less is achieved on the main surface, then measurement precision is improved, but the influence of side surface deformation on measurement increases
Solution Approach 1:
The patent applies preliminary processing to side surfaces and chamfered portions, achieving a flatness of 25 μm or less before performing the ultra-precise processing on the main surface. This preliminary anti-action prevents local deformation from occurring during subsequent measurement processes, thereby eliminating the harmful factor that would otherwise compromise the ultra-precise main surface measurements. By addressing the side surface issue in advance, the patent enables achievement of 50 nm flatness on the main surface without measurement interference.
Data Source
AI summary
The present invention relates to a low expansion glass substrate which serves as a substrate of a reflective mask used in a lithography step of semiconductor production steps, wherein two side surfaces positioned to face each other among side surfaces formed along a periphery of the low expansion glass substrate, each have a flatness of 25 μm or less.