Glass Substrate Polishing for EUVL Reflective Masks
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Solution Overview
Problem
Current polishing methods for glass substrates used in EUVL fail to achieve sufficient surface smoothness and accuracy, particularly in reducing concave defects, which are critical for high-precision semiconductor device production.
Innovation Solution
A polishing method using a suede-based polishing pad with a reduced polishing load and preliminary dressing processing with an electrodeposited diamond dress plate, combined with a polishing slurry containing colloidal silica or ceria, to effectively minimize concave defects and enhance surface smoothness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional polishing methods are used with high polishing load, then polishing efficiency is improved, but concave defects increase and surface smoothness deteriorates
Solution Approach 1:
The patent changes the polishing load parameter from conventional high values (80 g/cm²) to a reduced range (1-60 g/cm²), and adjusts slurry pH to 2-10 to optimize the balance between polishing efficiency and surface quality, reducing concave defects while maintaining productivity
Solution Approach 2:
The patent applies preliminary dressing processing to the polishing pad surface before actual polishing to create an optimal pad surface structure, which enables reduced polishing load to be effective in preventing concave defects while maintaining polishing efficiency
2Productivity
If high polishing load is applied, then material removal rate increases, but surface roughness increases and concave defects are generated
Solution Approach 1:
The patent optimizes multiple parameters simultaneously: reduces polishing load to 1-60 g/cm², adjusts slurry pH to 2-10, and controls abrasive particle size, achieving both adequate material removal rate and surface roughness of 0.15 nm or less
3Productivity
If conventional polishing slurry is used, then polishing speed is maintained, but concave defects increase
Solution Approach 1:
The patent changes the chemical environment by adjusting slurry pH to 2-10 and controls abrasive concentration, which modifies the interaction between slurry and glass substrate to prevent concave defect formation while preserving acceptable polishing speed
Solution Approach 2:
The patent uses composite polishing slurries containing specific abrasive materials (such as colloidal silica or ceria) combined with pH adjustment, creating a composite chemical-mechanical system that prevents 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
The method significantly reduces concave defects and improves surface smoothness, making the glass substrates suitable for reflective masks in EUVL, achieving surface roughness of 0.15 nm or less and inhibiting phase defects during exposure with EUV light.
Implementation Method 1
a suede-based polishing pad, having undergone preliminary dressing processing with an electrodeposited diamond dress plate
Implementation Method 2
a polishing slurry containing colloidal silica or ceria, to effectively minimize concave defects and enhance surface smoothness
Implementation Method 3
polishing a major surface of the glass substrate while feeding a polishing slurry between the glass substrate and a nap layer of a polishing pad
Data Source
AI summary
An object of the present invention is to provide a polishing method for diminishing concave defects of a glass substrate used in a reflective mask for EUVL and the like. The invention relates to a method of polishing a glass substrate which comprises polishing a major surface of the glass substrate while feeding a polishing slurry between the glass substrate and a pad surface of a polishing pad, wherein the polishing load of the polishing pad is from 1 to 60 g/cm2. The pad surface of the polishing pact is preferably dressing-processed.