Photomask Blank Layer Stack for Fine Pattern Etching and Resist Adhesion
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Solution Overview
Problem
The challenge in manufacturing photomasks for semiconductor integrated circuits is to achieve high accuracy and fine patterns while ensuring adhesion of the resist film to the silicon-containing film, preventing resist peeling and residue defects during cleaning.
Innovation Solution
A method involving a photomask blank with a transparent substrate, a first inorganic film containing silicon and free of chromium, and a second inorganic film containing chromium and free of silicon, where the second film is etched by fluorine-based dry etching, allowing for high accuracy and fine pattern formation without resist residue issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the resist film thickness is reduced to achieve finer photomask patterns, then the pattern resolution is improved, but the adhesion between resist film and silicon-containing film deteriorates causing resist peeling
Solution Approach 1:
A chromium-containing inorganic film is introduced as an intermediary layer between the silicon-containing film and the resist film. This intermediate film serves as a bridging layer that provides both good adhesion to the silicon-containing film and excellent adhesion properties for the resist film, thereby preventing resist peeling while enabling fine pattern formation
Solution Approach 2:
The patent employs a composite film structure combining silicon-containing film and chromium-containing film with specific compositional ratios. The chromium content is controlled at 1-10 at% to achieve optimal balance between adhesion enhancement and etching selectivity, creating a composite material system that resolves the adhesion-patterning contradiction
2Reliability
If silylation treatment is applied to improve resist adhesion on silicon-containing film, then adhesion is enhanced, but resist residues remain after cleaning
Solution Approach 1:
The patent extracts the silylation treatment step from the manufacturing process and replaces it with a chromium-containing film formation. By removing the problematic silylation treatment while maintaining good adhesion through the chromium film, the source of resist residue generation is eliminated while adhesion performance is preserved
Solution Approach 2:
The chromium-containing film serves as a temporary adhesion promoter that fulfills its function during pattern formation and can be selectively removed afterward. This disposable intermediate layer provides the necessary adhesion enhancement without leaving persistent residues like silylation treatment
3Reliability
If a hard mask is used to reduce load on resist pattern during dry etching, then etching stability is improved, but the process complexity increases
Solution Approach 1:
The chromium-containing inorganic film performs multiple functions simultaneously: it acts as an adhesion promoter between silicon-containing film and resist film, provides etching selectivity control during fluorine-based dry etching, and serves as a pattern definition layer. This multi-functionality eliminates the need for separate hard mask layers and reduces overall process complexity
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 method ensures strong adhesion of the resist film, prevents resist peeling and residue defects, and allows for high accuracy and fine pattern formation in photomasks, addressing the limitations of existing technologies.
Implementation Method 1
a second inorganic film which contains chromium and is free of silicon, when a pattern of the second inorganic film is formed by etching the second inorganic film by fluorine-based dry etching
Data Source
AI summary
A photomask is manufactured from a photomask blank including a transparent substrate, a first inorganic film which comprises silicon and is free of chromium, and a second inorganic film which comprises chromium and is free of silicon, and is in contact with the first inorganic film by a method including steps of forming a pattern of the second inorganic film by fluorine-based dry etching with using a resist pattern, and forming a pattern of the first inorganic film by fluorine-based dry etching with using the pattern of the second inorganic film.