Photomask Blank Layer Structure for SPM-Resistant Light Shielding
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Solution Overview
Problem
Existing photomask blanks with light-shielding films containing transition metals like molybdenum suffer from deterioration and reduced light-shielding properties due to repeated sulfuric acid-hydrogen peroxide mixture (SPM) cleaning, leading to inaccurate pattern transfer during miniaturization.
Innovation Solution
A photomask blank design with a light-shielding film composed of multiple layers, including a protection layer free of transition metals and a light-shielding layer containing transition metals and silicon, which provides high resistance to SPM cleaning and maintains light-shielding properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a light-shielding film containing transition metals like molybdenum is used, then good light-shielding properties are achieved, but the film deteriorates and loses light-shielding properties due to repeated SPM cleaning
Solution Approach 1:
The light-shielding film is segmented into multiple layers: a lower light-shielding layer containing transition metals (Mo, W, etc.) that provides excellent light-shielding properties, and an upper protection layer containing silicon and oxygen/nitrogen that provides high resistance to SPM cleaning. This segmentation allows each layer to specialize in one function, resolving the contradiction between light-shielding performance and cleaning resistance.
Solution Approach 2:
The invention uses composite material structure combining different materials with complementary properties: transition metal compounds (MoSiN, MoSiON, WSiN, etc.) for light-shielding and silicon-based compounds (SiO, SiN, SiON) for cleaning resistance. The composite structure synergistically combines the advantages of both material types, achieving both high light-shielding performance and high SPM cleaning resistance.
2Manufacturing precision
If the light-shielding film is miniaturized for finer patterns, then higher integration is achieved, but the aspect ratio increases causing pattern transfer failure
Solution Approach 1:
The segmented structure with a thin protection layer (1-5 nm) on top of the light-shielding layer enables better pattern transfer. The protection layer is thin enough to maintain low aspect ratio while providing sufficient SPM cleaning resistance, allowing finer pattern miniaturization without shape deterioration or collapse.
Solution Approach 2:
The invention optimizes the thickness parameters of each layer: the protection layer thickness is controlled at 1-5 nm (very thin) while the light-shielding layer thickness is optimized for light-shielding performance. This parameter optimization maintains low aspect ratio enabling accurate pattern transfer for miniaturized features.
3Manufacturing precision
If a thicker resist film is used to maintain aspect ratio during miniaturization, then pattern transfer success is achieved, but the resist film becomes too thick for fine pattern definition
Solution Approach 1:
The protection layer is formed in advance before resist coating and pattern transfer. This preliminary protective barrier prevents SPM cleaning damage to the resist pattern, allowing the use of thinner resist films (reducing aspect ratio) while still achieving successful pattern transfer. The protection layer pre-empts the harmful cleaning effect that would otherwise require thicker resist.
Data Source
AI summary
A photomask blank including a light-shielding film that has high light-shielding property and high resistance to SPM cleaning is provided by a light-shielding film including a protection layer that is provided at the side remotest from the transparent substrate and composed of a material containing silicon and being free of a transition metal, and a light-shielding layer that is provided at the transparent substrate-side of the protection layer and composed of a material containing a transition metal and silicon.