Laminated Phase Shift Mask Blank for ArF Lithography
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Solution Overview
Problem
In photomask production, existing technologies face challenges in forming fine mask patterns with reduced resist film thickness to prevent pattern collapsing and ensure high transfer accuracy, particularly in hyper-NA lithography, where the resist film thickness and aspect ratio affect pattern miniaturization and resolution.
Innovation Solution
A phase shift mask blank with a laminated light-shielding film structure comprising a lower layer, interlayer, and upper layer, where the interlayer is a metallic nitride film with a lower etching rate than the other layers, optimized for ArF excimer laser exposure, allowing for reduced resist film thickness and improved etching efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the light-shielding film thickness is increased to improve light shielding performance, then the optical density is improved, but the etching time is increased and the resist film thickness must be increased causing pattern collapsing
Solution Approach 1:
The light-shielding film is segmented into multiple layers with different materials and etching rates. The first light-shielding layer has a higher etching rate than the second light-shielding layer, allowing selective removal during etching processes. This segmentation enables optimization of both optical density and etching time by controlling which layers remain and their respective thicknesses.
Solution Approach 2:
Different regions of the light-shielding film structure are assigned different properties. The first light-shielding layer near the resist film has high etchability for rapid removal, while the second light-shielding layer closer to the substrate provides stable optical shielding. This local differentiation of material properties allows simultaneous optimization of etching speed and optical performance.
2Manufacturing precision
If the resist film thickness is decreased to enable fine pattern formation, then the pattern collapsing is prevented, but the etching time is increased and the light-shielding film must be thinner reducing optical density
Solution Approach 1:
The light-shielding film is divided into layers with different etching characteristics. The first layer with higher etching rate can be quickly removed when using thin resist films, reducing the required etching time and allowing thinner resist films to be used without collapsing, while the second layer maintains adequate optical density.
Solution Approach 2:
The etching rate parameter is varied across different layers of the light-shielding film. By making the first layer more etchable than the second layer, the process allows for reduced etching times that are compatible with thin resist films, thereby enabling fine pattern formation while maintaining sufficient optical shielding from the second layer.
3Productivity
If the light-shielding film thickness is reduced to shorten etching time, then the etching time is decreased, but the optical density is reduced affecting light shielding performance
Solution Approach 1:
The light-shielding function is segmented between two layers with different thicknesses and etching rates. The first layer is thinner and more etchable, contributing to faster etching, while the second layer is optimized for optical shielding performance. This segmentation allows the total thickness to be reduced for faster etching while maintaining adequate optical density through the second layer.
Solution Approach 2:
The light-shielding film uses composite material structure with two different materials having different etching rates. This composite structure enables the film to exhibit both high etching efficiency (from the first layer) and sufficient optical density (from the second layer), resolving the contradiction between productivity and optical performance.
Data Source
AI summary
The present invention provides a photomask blank used for producing a photomask to which an ArF excimer laser light is applied, wherein: a light-shielding film is provided on a light transmissive substrate; the light-shielding film has a laminated structure in which a lower layer, an interlayer and an upper layer are laminated in this order from the side close to the light transmissive substrate; the thickness of the entire light-shielding film is 60 nm or less; the lower layer is made of a film containing a metal and has a first etching rate; the upper layer is made of a film containing a metal and has a third etching rate; the interlayer is made of a film containing the same metal as that contained in the lower layer or the upper layer and has a second etching rate that is lower than the first etching rate and the third etching rate; and the thickness of the interlayer is 30% or less of the thickness of the entire light-shielding film.