SiN Light Semitransmissive Layer for ArF Phase Shift Mask
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Solution Overview
Problem
Conventional halftone phase shift masks face issues with resistance against ArF excimer laser exposure light and cleaning resistance, leading to pattern dimension changes and damage during ultrasonic cleaning, and have limited design flexibility due to thick light semitransmissive layers.
Innovation Solution
A mask blank with a light semitransmissive layer made of Si and N or Si, N, and O, having an extinction coefficient of 0.2 to 0.45, a refractive index of 2.3 to 2.7, and a transmittance of 15% to 38% at 193 nm, which is thinner (57-67 nm) to prevent oxide layer growth and reduce damage during cleaning, and a light-shielding layer with adjusted optical density to enhance pattern clarity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a metal (Mo) is incorporated into the light semitransmissive layer to adjust light transmittance, then the transmittance can be controlled, but the mask becomes susceptible to oxidation during ArF excimer laser exposure and cleaning, causing pattern dimension changes
Solution Approach 1:
The patent removes the problematic metal component (Mo) from the light semitransmissive layer, extracting the harmful element that causes oxidation while retaining the layer's essential light transmission function through alternative material composition
Solution Approach 2:
The patent changes the material composition parameters of the light semitransmissive layer from metal-containing to metal-free materials, specifically using materials with controlled refractive indices and thicknesses to achieve the desired optical properties without the harmful metal component
2Manufacturing precision
If the light semitransmissive layer is made thicker to improve phase shift effect, then the phase shift is enhanced, but the layer becomes more susceptible to damage during ultrasonic cleaning
Solution Approach 1:
The patent optimizes the thickness parameter of the light semitransmissive layer to a specific range (57-67 nm) that provides sufficient phase shift effect while maintaining adequate mechanical strength to resist damage during ultrasonic cleaning processes
Solution Approach 2:
The patent employs composite material structures, specifically combining the light semitransmissive layer with a protective hard mask layer, where the hard mask layer provides mechanical strength and cleaning resistance while the light semitransmissive layer provides the necessary optical phase shift
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 phase shift mask with improved transferring properties, resistance against ArF excimer laser exposure, and enhanced cleaning resistance, while also increasing design flexibility and reducing pattern chipping during ultrasonic cleaning.
Implementation Method 1
a light semitransmissive layer formed on the transparent substrate and made only of Si and N or a light semitransmissive layer formed on the transparent substrate and made only of Si, N and O, characterized in that the light semitransmissive layer has an extinction coefficient of 0.2 to 0.45 at a wavelength of ArF excimer laser exposure light, a refractive index of 2.3 to 2.7 at the wavelength of ArF excimer laser exposure light, and a transmittance of 15% to 38% at the wavelength of ArF excimer laser exposure light
Implementation Method 2
In the case of a halftone phase shift mask, interference of light at its pattern-element boundary regions that is based on phase effect makes the intensity of the light at the interference-caused regions into a value of zero, so that images to be transferred can be improved in contrast
Data Source
AI summary
The present invention provides a mask blank used to produce a halftone phase shift mask to which ArF excimer laser exposure light is to be applied. The present invention attains the object by providing the mask blank comprising a transparent substrate, and a light semitransmissive layer formed on the transparent substrate and made only of Si and N or a light semitransmissive layer formed on the transparent substrate and made only of Si, N and O, wherein the light semitransmissive layer has an extinction coefficient of 0.2 to 0.45 at a wavelength of ArF excimer laser exposure light, a refractive index of 2.3 to 2.7 at the wavelength of ArF excimer laser exposure light, and a transmittance of 15 to 38% at the wavelength of ArF excimer laser exposure light, and further has a layer thickness of 57 to 67 nm.