EUVL Substrate Polishing to Reduce Concave Defects
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Solution Overview
Problem
Current methods for producing glass substrates for EUVL mask blanks are insufficient in suppressing concave defects with depths less than 5 nm, which can disrupt pattern formation during exposure.
Innovation Solution
A method involving final polishing with an upper polishing plate where the substrate is polished with the main surface facing the plate, and the plate is rotated and then separated without stopping, using a polishing slurry with specific viscosity, abrasive grain concentration, and colloidal silica particles to reduce concave defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the upper polishing plate is stopped before separation, then the polishing process is complete, but concave defects with depth less than 5 nm are generated on the substrate surface
Solution Approach 1:
The polishing slurry is supplied to the polishing surface before the polishing process begins, and the upper polishing plate is kept rotating during separation. This preliminary preparation of the slurry film and continuous rotation prevents direct contact between foreign matter and the substrate surface, thereby preventing concave defects while maintaining high surface quality
Solution Approach 2:
The polishing slurry acts as an intermediary substance between the polishing pad and the substrate. By maintaining the slurry film during the separation process through continuous rotation, the slurry prevents direct contact between the polishing pad foreign matter and the substrate surface, thus avoiding concave defects
2Productivity
If foreign matter is present on the polishing pad during finish polishing, then the polishing process can proceed, but concave defects with depth less than 5 nm are generated on the substrate
Solution Approach 1:
The upper polishing plate continues to rotate during the separation process rather than stopping. This continuous rotation maintains the polishing slurry film on the polishing surface, preventing foreign matter from contacting the substrate even when present on the polishing pad, thus maintaining both productivity and surface quality
Solution Approach 2:
The polishing slurry is supplied and distributed on the polishing surface before the separation occurs. This preliminary establishment of the slurry barrier ensures that even if foreign matter is present on the polishing pad, it cannot directly contact the substrate during separation, preventing concave defects while maintaining polishing efficiency
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 effectively reduces concave defects less than 5 nm, resulting in a substrate with high surface quality suitable for EUVL mask blanks.
Implementation Method 1
rotating the upper polishing plate and polishing the substrate stock concomitantly with a polishing slurry on the main surface of the substrate stock
Data Source
Figure 1
AI summary
Proposed herein is a method for producing a substrate suitable for mask blanks for EUVL and the method being capable of suppressing a concave defect having a depth of less than 5 nm. The present invention provides a method for producing a substrate in which final polishing is performed by a polishing apparatus having an upper polishing plate equipped with a polishing pad, the method comprising the steps of placing a substrate stock in the polishing apparatus so that the main surface of the substrate stock face toward the upper polishing plate; rotating the upper polishing plate and polishing the substrate stock concomitantly with a polishing slurry on the main surface of the substrate stock; and raising the upper polishing plate which is kept being rotated to separate it from the main surface of the polished substrate stock.