Binary Photomask Blank with Compositionally Graded Light-Shielding Film
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Solution Overview
Problem
Current photomask technologies face challenges in achieving high accuracy and minimizing ghost patterns due to excessive reflectance at the substrate surfaces, particularly when using thin light-shielding films, which can lead to pattern distortion and reduced resolution in microfabrication processes.
Innovation Solution
A binary photomask blank with a light-shielding film composed of silicon-based materials containing transition metals and nitrogen/oxygen, featuring compositionally graded layers to control reflectance on both surfaces, ensuring a thinner film thickness while maintaining effective light shielding and preventing ghost patterns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the thickness of the light-shielding film is reduced to enable miniaturization, then the pattern width is reduced, but the reflectance at the substrate surfaces increases causing ghost patterns
Solution Approach 1:
The patent applies local quality by creating compositionally graded layers within the light-shielding film where the composition varies through the thickness. The first compositionally graded layer (near substrate) has higher nitrogen content to reduce reflectance, while the second layer (远离 substrate) has lower nitrogen content to maintain light-shielding functionality. This gradient structure allows different regions of the film to have optimized properties for their specific functions.
Solution Approach 2:
The patent uses composite materials by combining silicon, transition metals (Mo, W), and nitrogen/oxygen in specific ratios within the light-shielding film. The compositionally graded layers contain varying concentrations of these elements, creating a composite structure that balances optical density requirements with reflectance control. Specifically, the film contains Si, Mo, and N with atomic ratios that optimize both light shielding and reflectance properties.
2Manufacturing precision
If the thickness of the resist film is reduced to transfer finer patterns, then the pattern resolution is improved, but the aspect ratio increases causing resist pattern collapse
Solution Approach 1:
The patent converts the harmful effect of high reflectance (which causes ghost patterns) into a beneficial gradient structure. By intentionally creating compositionally graded layers with varying nitrogen content, the reflectance is controlled to decrease from the substrate interface toward the surface, transforming the potential harm of thin-film reflectance into a controlled optical profile that supports finer patterning.
3Ease of manufacture
If chromium compound films are used as light-shielding material, then the etching process is well-established, but the resist film must be thick enough to prevent damage during etching
Solution Approach 1:
The patent changes the material parameters of the light-shielding film by using silicon-based materials with transition metals and nitrogen/oxygen instead of traditional chromium compounds. This parameter change allows for a thinner light-shielding film (30-70 nm) with controlled reflectance through compositional grading, enabling the use of thinner resist films (50-150 nm) while maintaining adequate protection during etching and achieving better pattern transfer accuracy.
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 solution enables high-accuracy patterning with fully perpendicular sidewalls and reduced ghost patterns, achieving high-resolution microfabrication by optimizing the light-shielding film's thickness and composition to balance reflectance and light-shielding functionality.
Implementation Method 1
a light-shielding film having an optical density of 2.5 to 3.5... featuring compositionally graded layers to control reflectance on both surfaces
Implementation Method 2
a light-shielding film having an optical density of 2.5 to 3.5... ensuring effective light shielding
Data Source
Figure 1A~1B
Figure 2~3
AI summary
A binary photomask blank has on a transparent substrate a light-shielding film including substrate-side and surface-side compositionally graded layers, having a thickness of 35-60 nm, and composed of a silicon base material containing a transition metal and N and/or O. The substrate-side compositionally graded layer has a thickness of 10-58.5 nm, and a N+O content of 25-40 at% at its lower surface and 10-23 at% at its upper surface. The surface-side compositionally graded layer has a thickness of 1.5-8 nm, and a N+O content of 10-45 at% at its lower surface and 45-55 at% at its upper surface.