Compositionally Graded Phase Shift Film for KrF Lithography
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Solution Overview
Problem
Existing phase shift films for KrF excimer laser in photolithography suffer from poor in-plane uniformity of optical characteristics and pattern deterioration due to thickness and composition differences in multilayer films, which affects pattern miniaturization and three-dimensional effects.
Innovation Solution
A phase shift film composed of silicon and nitrogen with a compositionally graded layer, where refractive index and extinction coefficient vary continuously in the thickness direction, providing a phase shift of 170 to 190° and transmittance of 4 to 8%, without thickening the film, ensuring high in-plane uniformity and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a phase shift film is formed as a single layer with uniform composition to achieve high light resistance and washing resistance, then the film requires a thickness of approximately 100 nm, but this results in poor in-plane uniformity of optical characteristics due to formation in the transition mode region
Solution Approach 1:
The phase shift film is divided into multiple layers with different compositions and optical characteristics. The first phase shift film layer has a refractive index of 2.0-2.5 and the second phase shift film layer has a refractive index of 2.5-3.0, allowing each layer to be formed under stable sputtering conditions while collectively achieving the required optical performance and uniformity
Solution Approach 2:
The invention uses a composite structure of two different phase shift film materials with distinct optical properties. This composite approach enables both layers to be formed in stable regions, avoiding the transition mode region issues, while the combination provides the necessary phase shift and transmittance characteristics with improved in-plane uniformity
2Manufacturing precision
If a multilayer structure is used to improve in-plane uniformity of optical characteristics, then the film can be formed under stable sputtering conditions, but the film thickness increases which is disadvantageous for pattern miniaturization and three-dimensional effects
Solution Approach 1:
The invention optimizes the refractive index range of each layer to achieve the required phase shift and transmittance with minimal total thickness. The first layer has refractive index 2.0-2.5 and the second layer has refractive index 2.5-3.0, with controlled thicknesses that together provide the necessary optical function while maintaining thin overall profile for pattern miniaturization
3Manufacturing precision
If a multilayer structure with significantly different compositions is used to achieve high uniformity, then the film can be formed under stable sputtering conditions, but the cross-sectional shape of patterns deteriorates due to different etching rates
Solution Approach 1:
The invention assigns specific compositional characteristics to each layer where the first phase shift film layer has lower refractive index (2.0-2.5) and the second phase shift film layer has higher refractive index (2.5-3.0). This local differentiation allows each layer to be optimized for its specific function while maintaining overall pattern integrity and uniform etching characteristics
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 results in a thinner phase shift film with improved patterning capabilities and reduced three-dimensional effects, maintaining necessary phase shift and transmittance for KrF excimer laser exposure, while enhancing washing resistance and light resistance.
Implementation Method 1
utilizing interference of lights. The phase shift film pattern has a phase shift of approximately 180° that is a difference between a phase through the phase shift film and a phase through a portion that is not formed the phase shift film
Implementation Method 2
the phase shift film includes at least one compositionally graded layer having a composition continuously varying in a thickness direction, and having optical constants, with respect to exposure light, varying in the thickness direction
Data Source
AI summary
Provided is a phase shift mask blank including a substrate, and a phase shift film thereon, the phase shift film composed of a material containing silicon and nitrogen and free of a transition metal, the phase shift film including at least one compositionally graded layer having a composition continuously varying in a thickness direction, and a refractive index n and an extinction coefficient k, with respect to exposure light, varying in the thickness direction, the exposure light being KrF excimer laser, the compositionally graded layer having a difference between a maximum refractive index n(H) and a minimum refractive index n(L) of up to 0.40, and a difference between a maximum extinction coefficient k(H) and a minimum extinction coefficient k(L) of up to 1.5.