Two-Layer Phase Shift Photomask Blank for 193nm Transfer Stability
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Solution Overview
Problem
Existing photomasks face challenges in achieving high light transmittance, minimizing pattern dimension variation, and ensuring irradiation and pattern collapse resistance, particularly in advanced semiconductor manufacturing processes.
Innovation Solution
A photomask blank and manufacturing method utilizing a two-layer phase shift film structure, comprising a first phase shift film made of silicon nitride and a second phase shift film made of silicon oxynitride, to achieve a high light transmittance of 20% or more while maintaining a phase difference of around 177 degrees, thereby enhancing wafer transfer characteristics and reducing film thickness for improved durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the phase shift film thickness is increased to achieve high light transmittance (20% or more), then the wafer transfer characteristics are improved, but the film becomes more susceptible to pattern collapse during cleaning
Solution Approach 1:
The phase shift film is divided into two distinct layers: a first phase shift film (silicon nitride) and a second phase shift film (silicon oxynitride). This segmentation allows each layer to have optimized thickness and material properties, achieving high light transmittance while maintaining pattern collapse resistance through the combined structure.
Solution Approach 2:
The invention uses a composite structure of two different materials (silicon nitride and silicon oxynitride) with distinct optical and mechanical properties. The first phase shift film provides structural stability, while the second phase shift film enhances light transmittance, creating a composite system that resolves the contradiction between transmittance and durability.
2Illumination intensity
If the phase shift film thickness is increased to maintain phase difference of 177 degrees while achieving higher light transmittance, then wafer transfer characteristics improve, but irradiation resistance decreases due to oxidation
Solution Approach 1:
The phase shift film is segmented into two layers with different oxidation resistances. The first phase shift film (silicon nitride) provides oxidation resistance, while the second phase shift film (silicon oxynitride) provides high light transmittance. This segmentation allows the system to achieve high transmittance without sacrificing irradiation resistance.
Solution Approach 2:
Different regions of the phase shift film structure have different material compositions optimized for specific functions. The first phase shift film has properties optimized for oxidation resistance, while the second phase shift film has properties optimized for light transmittance, creating local quality variations that resolve the contradiction.
3Device complexity
If a single-layer phase shift film is used, then the structure is simple, but it cannot simultaneously achieve high light transmittance, appropriate phase difference, and pattern collapse resistance
Solution Approach 1:
The single-layer structure is segmented into two layers, each with specific thickness and material properties. This segmentation enables the system to simultaneously achieve high light transmittance, appropriate phase difference (170-190 degrees), and pattern collapse resistance, which cannot be achieved with a single layer.
Solution Approach 2:
The invention changes the parameters of the phase shift film by dividing it into two layers with different material compositions and thicknesses. The first phase shift film has a first thickness and the second phase shift film has a second thickness, allowing independent optimization of optical and mechanical properties to achieve the desired performance.
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 solution achieves high light transmittance, reduces pattern dimension variation, and enhances irradiation resistance and pattern collapse resistance, resulting in improved wafer transfer characteristics such as NILS, DOF, and EMF bias.
Implementation Method 1
a phase difference between an ArF excimer laser beam transmitted through a light-transmissive substrate and an ArF excimer laser beam transmitted through both the light-transmissive substrate and the phase shift film
Implementation Method 2
oxidation of the mask pattern has caused the dimension of the line-based pattern to be enlarged
Data Source
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AI summary
The purpose of the present invention is to provide a photomask blank and a photomask having favorable wafer transfer characteristics and irradiation resistance. A photomask blank (200) is for fabricating a photomask for an exposure wavelength of 193nm, the photomask blank (200) comprising: a light-transmissive substrate (103); a phase shift film (102) formed on the light-transmissive substrate (103) and providing phase shift effects of a light transmittance of at least 30% with respect to exposure light; and a light-shielding film (101) formed on the phase shift film (102). The phase shift film (102) is constituted by lamination of: a first phase shift film (102b) that uses a silicon nitride-based material, has a refractive index n1 of 2.5 to 2.7, and an extinction coefficient k1 of 0.2 to 0.4; and a second phase shift film (102a) that uses a silicon oxynitride-based material, has a refractive index n2 of 1.55 to 2.20, and an extinction coefficient k2 greater than 0 but no greater than 0.1.