Mask Blank Substrate Cleaning via Catalyst Referred Etching
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Solution Overview
Problem
Conventional methods for cleaning photomasks often result in pattern destruction and substrate-pattern integral destruction due to the fragility of mask blank substrates caused by machining-affected portions, leading to defects and reduced quality in mask blanks and transfer masks.
Innovation Solution
A method involving a polishing step with abrasive grains followed by Catalyst Referred Etching using a processing fluid and a catalytic surface plate to remove machining-affected portions, preventing mechanical strength reduction and subsequent pattern loss during transfer pattern formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If physical cleaning force is intensified to remove foreign matters, then cleaning effect is improved, but pattern destruction occurs
Solution Approach 1:
The patent replaces mechanical/physical cleaning methods (megasonic cleaning, brush cleaning) with chemical cleaning methods (RCA cleaning, ozone treatment). This substitution eliminates the mechanical stress that causes pattern destruction while maintaining effective foreign matter removal through chemical reactions and oxidative processes.
Solution Approach 2:
The patent changes the cleaning mechanism from physical force-based to chemistry-based by introducing specific chemical solutions (ammonium hydrogen peroxide mixture, sulfuric acid hydrogen peroxide mixture, ozone). This parameter change allows effective cleaning without the harmful mechanical impacts that cause pattern destruction.
2Reliability
If physical cleaning is performed on photomask, then foreign matters are removed, but substrate-pattern integral destruction occurs due to substrate fragility
Solution Approach 1:
The patent replaces physical cleaning methods that exert mechanical stress on the substrate with chemical cleaning methods. This substitution removes foreign matters through chemical reactions rather than mechanical force, preventing substrate-pattern integral destruction caused by mechanical stress on fragile substrates.
Solution Approach 2:
The patent introduces chemical solutions (ammonium hydrogen peroxide mixture, sulfuric acid hydrogen peroxide mixture, ozone) as intermediaries to perform the cleaning function. These chemical intermediaries interact with foreign matters through chemical reactions, avoiding direct mechanical contact and stress on the fragile substrate-pattern structure.
3Reliability
If conventional cleaning methods are used, then cleaning is achieved, but machining-affected portions remain causing defects
Solution Approach 1:
The patent changes the cleaning mechanism from physical to chemical by introducing ozone treatment and chemical solutions. These chemical methods can penetrate and remove machining-affected portions and embedded contaminants that physical methods cannot reach, thereby improving surface smoothness and eliminating defects while maintaining cleaning capability.
Solution Approach 2:
The patent employs ozone and hydrogen peroxide as strong oxidants to chemically break down and remove machining-affected portions, embedded contaminants, and organic residues. The oxidative action effectively eliminates surface defects and improves surface smoothness without the mechanical damage associated with conventional physical cleaning methods.
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 inhibits the occurrence of substrate-pattern integral destruction, enabling the production of low-defect, high-quality mask blanks and transfer masks with reduced pattern loss by maintaining substrate integrity and smoothness.
Implementation Method 1
Catalyst Referred Etching (also referred to as CARE hereafter) method has been suggested... causing a principal surface of a crystalline substrate such as SiC and a catalyst to be close to, or in contact with each other with a processing liquid such as an acidic liquid therebetween, and using active species produced from molecules in the processing liquid adsorbed to the catalyst, selectively removing microscopic protrusions generated as crystal defects on the principal surface
Implementation Method 2
a polishing step for polishing a mask blank substrate with a polishing solution including abrasive grains
Implementation Method 3
after local chemical mechanical polishing (CMP) for polishing a principal surface of a quartz glass substrate for mask blank with a polishing solution including colloidal silica grains, the principal surface is cleaned with low-concentration hydrofluoric acid solution
Implementation Method 4
a cleaning process such as RCA cleaning is employed using a combination of physical cleaning tools such as a megasonic nozzle and a brush
Data Source
AI summary
A method for manufacturing a low-defect and high-quality mask blank substrate with minimized transfer pattern defects and high mechanical strength, particularly such that the occurrence of a phenomenon where a portion of a transfer pattern and a principal surface of the substrate therebeneath are broken off together is minimized such that there is little pattern loss. The mask blank is manufactured by preparing a mask blank substrate (X) having a substrate principal surface (X1) polished using a polishing solution containing abrasive grains, etching the substrate principal surface (X1) using catalyst-referred etching so as to remove damaged portions from the principal surface (X1), and then depositing a thin film that forms a transfer pattern on the substrate principal surface (X1) of the substrate (X) by sputtering.