Antireflection Layer Reflectance Control for Photomask Stability
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Solution Overview
Problem
In photomask manufacturing, the challenge lies in controlling the change in front-surface reflectance due to thickness variations of the front-surface antireflection layer, particularly when using molybdenum silicide-based materials, which are prone to film loss during cleaning processes, affecting the optical density and resolution of the light-shielding film.
Innovation Solution
A photomask blank is designed with a light-shielding film comprising a transition metal and silicon, and a front-surface antireflection layer made of materials containing oxygen and nitrogen, with specific refractive index and extinction coefficient values to maintain front-surface reflectance within predetermined limits, even with thickness changes of the antireflection layer, ensuring minimal change in reflectance during cleaning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the thickness of the front-surface antireflection layer is reduced to control reflectance, then the front-surface reflectance decreases, but the film becomes more susceptible to film loss during cleaning processes
Solution Approach 1:
The patent changes the material parameters of the front-surface antireflection layer by incorporating specific ratios of oxygen and nitrogen (e.g., O:N ratio between 0.5:1 and 2:1) to achieve optimal optical properties. This allows the film to maintain appropriate thickness for reflectance control while gaining resistance to cleaning processes through modified chemical composition
Solution Approach 2:
The patent creates a composite antireflection layer by combining multiple elements (transition metal, silicon, oxygen, and nitrogen) in specific proportions. This composite structure provides both the desired optical properties (low reflectance) and improved mechanical/chemical stability during cleaning operations
2Manufacturing precision
If the thickness of the light-shielding film is reduced to improve resolution, then the resolution increases, but the optical density decreases
Solution Approach 1:
The patent changes the material composition parameters of the light-shielding film by incorporating nitrogen into the transition metal silicide matrix. This compositional parameter change increases the absorption coefficient, allowing thinner films to achieve the required optical density while maintaining high resolution
3Illumination intensity
If a molybdenum silicide-based material is used for the front-surface antireflection layer to reduce reflectance, then the front-surface reflectance decreases, but the film loss during cleaning increases significantly
Solution Approach 1:
The patent develops a composite material system where molybdenum silicide is combined with specific ratios of oxygen and nitrogen. This composite structure maintains the low-reflectance property of molybdenum silicide while the oxygen-nitrogen matrix provides enhanced chemical stability and resistance to cleaning processes
Solution Approach 2:
The patent applies different compositional qualities to different functional requirements: the molybdenum silicide component provides optical properties (low reflectance) while the oxygen-nitrogen matrix provides mechanical/chemical properties (cleaning resistance). Each element is optimized for its specific function within the composite structure
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 approach effectively controls the change in front-surface reflectance to within 2-3% when the thickness of the front-surface antireflection layer changes, preventing significant increases in reflectance and maintaining optimal optical density, thus enhancing the stability and performance of the photomask.
Implementation Method 1
the front-surface antireflection layer formed above and in contact with the light-shielding layer and made of a material containing at least one of oxygen and nitrogen, the light-shielding film has a front-surface reflectance of a predetermined value or less for the exposure light
Implementation Method 2
the light-shielding film comprises a light-shielding layer containing a transition metal and silicon... the light-shielding film has a front-surface reflectance of a predetermined value or less for the exposure light
Data Source
AI summary
A photomask blank is for use in manufacturing a photomask to be applied with exposure light having a wavelength of 200 nm or less. The photomask blank has a light-transmitting substrate and a light-shielding film formed thereon. The light-shielding film has a light-shielding layer containing a transition metal and silicon and a front-surface antireflection layer formed contiguously on the light-shielding layer and made of a material containing at least one of oxygen and nitrogen. The light-shielding film has a front-surface reflectance of a predetermined value or less for the exposure light and has a property capable of controlling the change width of the front-surface reflectance at the exposure wavelength to be within 2% when the thickness of the front-surface antireflection layer changes in the range of 2 nm. The material of the front-surface antireflection layer having a refractive index n and an extinction coefficient k capable of achieving such property is selected.