Photomask Blank Ta-O/N Layer for Fine Assist Pattern Etching
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Solution Overview
Problem
Existing photomask manufacturing methods face challenges in forming fine assist patterns with high resolution and uniformity due to issues such as resist film collapse, pinhole defects, and uneven etching rates, particularly when using materials like silicon and tantalum, which affect adhesion and etching stability.
Innovation Solution
A photomask blank structure comprising a transparent substrate, a chromium film, a tantalum film, and optionally a silicon film, where the tantalum film is nitrogen-containing and has specific composition and thickness, allowing for improved adhesion, uniform etching, and reduced etching rates, enabling finer assist patterns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a silicon film is used as a hard mask layer, then the etching selectivity is improved, but the resist film adhesion deteriorates due to hydroxyl groups on the silicon surface
Solution Approach 1:
A tantalum film is introduced as an intermediary layer between the chromium light-shielding film and the silicon hard mask layer. This tantalum film serves as a bridge that provides both good adhesion to the resist film and appropriate etching selectivity, resolving the conflict between adhesion and selectivity requirements
Solution Approach 2:
The patent uses a composite structure consisting of multiple layers (chromium film, tantalum film, and silicon film) where each layer contributes different properties. The chromium layer provides light shielding, the tantalum layer provides adhesion and etching resistance, and the silicon layer provides hard mask functionality, achieving overall performance that none of the single materials could provide alone
2Manufacturing precision
If the assist pattern line width is reduced to 40 nm or 36 nm, then the pattern resolution is improved, but the resist film collapse and pinhole defects increase
Solution Approach 1:
The tantalum film is formed in advance before the resist film is applied. This preliminary formation of the tantalum layer with its specific composition (40-80 at% tantalum, 5-50 at% oxygen, and optionally nitrogen) creates a stable foundation that prevents resist film collapse and pinhole defects during subsequent processing, enabling the formation of ultra-fine 40 nm or 36 nm line width patterns
3Productivity
If the etching rate of the chromium film is increased to improve productivity, then the manufacturing efficiency is improved, but the etching uniformity and pattern accuracy deteriorate
Solution Approach 1:
The patent optimizes the composition parameters of the tantalum film (tantalum content: 40-80 at%, oxygen content: 5-50 at%, and optionally nitrogen content) to achieve the desired etching rate ratio with chromium. By adjusting these compositional parameters, the etching uniformity and pattern accuracy are maintained while achieving appropriate etching speeds for productivity
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 proposed structure enables the formation of assist patterns with narrow line widths, such as 40 nm or 36 nm, with high CD uniformity and reduced defects, enhancing photomask manufacturing efficiency and quality.
Implementation Method 1
a film composed of a material containing tantalum that is formed on the film composed of a material containing chromium
Implementation Method 2
the material containing tantalum contains tantalum, and oxygen or oxygen and nitrogen, and is free of silicon
Data Source
AI summary
A photomask blank including a transparent substrate, a film composed of a material containing chromium, and a film composed of a material containing tantalum is provided. The film composed of a material containing tantalum is constituted of a single layer or multiple layers, and has a thickness of 0.5 to 15 nm; the material containing tantalum contains tantalum, and oxygen or oxygen and nitrogen, and is free of silicon; the single layer and at least the layer remotest from the transparent substrate among the layers constituting the multiple layers are composed of a material containing tantalum that has a tantalum content of 40 to 80 at %, an oxygen content of 5 to 50 at %, and a nitrogen content of not more than 50 at %; and the layer remotest from the transparent substrate has a thickness of not less than 0.5 nm.