Halftone Phase Shift Photomask Blank with Selective Etch Films
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Solution Overview
Problem
Current halftone phase shift photomasks face challenges in forming fine patterns due to the thickness of light shielding films, which leads to defects and reduced accuracy, especially when exposed to shorter wavelength excimer laser light, causing chromium migration and foreign particle generation.
Innovation Solution
A halftone phase shift photomask blank with a specific film structure comprising a transparent substrate, a halftone phase shift film, a light shielding film, a hard mask film, and an additional thin chromium-containing film, where the first and third films are resistant to chlorine base dry etching and removable by fluorine base dry etching, and the second and fourth films are resistant to fluorine base dry etching and removable by chlorine base dry etching, allowing for a thinner resist film and minimized defect generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the light shielding film is made thick to ensure sufficient light shielding in the outer frame region, then the light shielding performance is improved, but the difficulty of forming fine patterns increases and manufacturing precision deteriorates
Solution Approach 1:
The light shielding function is segmented into two separate films: a chromium-containing light shielding film (second film) for providing light shielding in the outer frame region, and a silicon-containing hard mask film (third film) for enabling fine pattern formation. This segmentation allows each film to be optimized for its specific function without compromise.
Solution Approach 2:
Different regions of the photomask blank are assigned different film compositions tailored to local requirements: the outer frame region uses chromium-containing film for light shielding, while the photomask pattern region uses silicon-containing hard mask film for fine pattern formation. This local differentiation resolves the contradiction between light shielding and fine pattern formation.
2Reliability
If the light shielding film is made thick to ensure sufficient light shielding, then the light shielding performance is improved, but the defect generation increases and manufacturing precision deteriorates
Solution Approach 1:
The thick chromium-containing light shielding film is segmented into a thinner chromium-containing film (second film) combined with a silicon-containing hard mask film (third film). This segmentation reduces the thickness of the chromium film, minimizing defect generation while maintaining light shielding performance through the combined structure.
3Reliability
If the light shielding film is made thick to ensure sufficient light shielding, then the light shielding performance is improved, but chromium migration occurs and reliability deteriorates
Solution Approach 1:
The silicon-containing hard mask film (third film) serves as an intermediary layer between the chromium-containing light shielding film (second film) and the outer environment. This intermediary film prevents chromium migration while allowing the chromium film to maintain its light shielding function, thus resolving the contradiction between light shielding performance and prevention of harmful chromium migration.
4Manufacturing precision
If a three-layer structure including hard mask film is used to enhance resolution, then the resolution is improved, but the device complexity increases
Solution Approach 1:
The chromium-containing light shielding film (second film) and silicon-containing hard mask film (third film) are merged into a single integrated structure where the chromium film provides light shielding and the silicon film provides mechanical support and etching protection. This merging achieves the resolution enhancement benefits while minimizing the complexity increase compared to separate three-layer structures.
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 configuration enables the production of halftone phase shift photomasks with high accuracy and reduced defect likelihood, maintaining chromium-containing films for light shielding without surface exposure, thus preventing chromium migration and enhancing pattern fidelity.
Implementation Method 1
the phase shift method is by forming a pattern of film capable of phase reversal of approximately 180 degrees on a photomask, such that contrast may be improved by utilizing optical interference
Implementation Method 2
an outer frame pattern for shielding exposure light must be formed outside the photomask pattern-bearing region
Implementation Method 3
the first and third films are formed of silicon-containing materials which are resistant to chlorine base dry etching and removable by fluorine base dry etching
Implementation Method 4
the second and fourth films are formed of silicon-free, chromium-containing materials which are resistant to fluorine base dry etching and removable by chlorine base dry etching
Data Source
Figure 1A~1B
Figure 2A~2F
Figure 3A~3C
AI summary
A halftone phase shift photomask blank has on a transparent substrate (10) a first film (1) serving as a halftone phase shift film, a second film (2) serving as a light shielding film, a third film (3) serving as a hard mask film, and a fourth film (4). The first and third films are formed of silicon-containing materials which are resistant to chlorine base dry etching and removable by fluorine base dry etching. The second and fourth films are formed of silicon-free, chromium-containing materials which are resistant to fluorine base dry etching and removable by chlorine base dry etching.