Ta-Based Photomask Blank for High Resolution Etching
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Solution Overview
Problem
Current photomask manufacturing methods face challenges in achieving high resolution and optical density while simplifying processes and reducing the number of layers, as well as ensuring resist film thickness and chemical cleaning resistance.
Innovation Solution
A photomask blank with a light-shielding film mainly containing Ta and an antireflection layer made of Ta oxide, where the Ta-based film is etched with a fluorine-based gas and the Cr-based film is etched with a chlorine-based gas, allowing for reduced resist film thickness and improved processing accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a light-shielding film made of Cr is used, then it can be etched with chlorine-based gas, but the resist film thickness must be large to ensure sufficient etching selectivity and pattern accuracy
Solution Approach 1:
The patent changes the material composition of the light-shielding film from pure Cr to a Ta-based film (tantalum nitride or tantalum oxide), which fundamentally alters the etching characteristics. This material parameter change enables the use of fluorine-based etching gas instead of chlorine-based gas, thereby achieving better etching selectivity with thinner resist films and improving overall manufacturing precision.
Solution Approach 2:
The patent substitutes the etching chemistry system by replacing chlorine-based etching gas with fluorine-based etching gas. This substitution is enabled by the Ta-based light-shielding film material, which has high etching selectivity with fluorine-based gas, allowing for thinner resist films and simplified manufacturing processes while maintaining or improving pattern accuracy.
2Ease of manufacture
If the number of film layers is reduced to simplify the manufacturing process, then process complexity decreases, but it becomes difficult to simultaneously achieve high resolution and optical density
Solution Approach 1:
The patent employs composite material structures where the Ta-based light-shielding film is combined with specific etching mask films (Cr-based or Mo-based) and antireflection films. These composite structures achieve both high resolution and optical density while maintaining process simplicity, as the Ta-based film provides excellent etching selectivity that reduces the need for additional process steps.
Solution Approach 2:
By changing the light-shielding film material to Ta-based compounds, the patent achieves superior etching selectivity parameters that allow for thinner resist films and reduced layer counts. This material parameter change enables the simultaneous achievement of high resolution (65 nm or less) and simplified manufacturing processes.
3Manufacturing precision
If the light-shielding film thickness is reduced to improve resolution, then pattern resolution increases, but the optical density may be insufficient
Solution Approach 1:
The patent changes the material composition from Cr to Ta-based films, which have superior optical properties. The Ta-based light-shielding film maintains high optical density (OD>3) even at reduced thicknesses, thereby achieving both high resolution and sufficient optical density simultaneously.
Solution Approach 2:
The patent uses composite film structures where the Ta-based light-shielding film is combined with antireflection films (Ta oxide layers). This composite structure optimizes both the optical density and resolution by controlling light reflection and absorption characteristics, allowing thin film thickness while maintaining OD>3.
4Quantity of substance
If conventional Cr-based films are used, then etching can be performed with chlorine-based gas, but the resist film must be thick to ensure adequate etching protection and pattern fidelity
Solution Approach 1:
The patent changes the etching chemistry parameter by switching from chlorine-based gas to fluorine-based gas, which is enabled by the Ta-based light-shielding film material. This parameter change dramatically improves etching selectivity, allowing for much thinner resist films (reducing the quantity of substance) while maintaining pattern fidelity, thereby improving processing efficiency.
Solution Approach 2:
The patent substitutes the etching system by replacing chlorine-based gas with fluorine-based gas. This substitution, enabled by the Ta-based film material, achieves superior etching selectivity that allows for thinner resist films and simplified processes, thereby improving productivity without sacrificing pattern accuracy.
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 enables the achievement of high resolution (65 nm or less) and optical density (OD>3) with a simplified manufacturing process, reduced number of layers, and enhanced resistance to chemical cleaning and hot water.
Implementation Method 1
a light-shielding film, on a surface of the etching mask film, that is made of a material mainly containing tantalum and has a thickness so as to be removable during the dry etching for forming the dug-down part of the light-transmitting substrate
Implementation Method 2
an etching mask film, on a digging-side surface of the light-transmitting substrate, that is made of a material being dry-etchable with a chlorine-based gas, but not dry-etchable with a fluorine-based gas
Implementation Method 3
a phase shift portion adapted to give a predetermined phase difference to transmitted exposure light, wherein the phase shift portion is a dug-down part that is dug down from a surface of the light-transmitting substrate to a digging depth adapted to produce the predetermined phase difference
Implementation Method 4
an antireflection layer made of Ta oxide
Data Source
AI summary
A photomask blank is for manufacturing a phase shift mask having a light-transmitting substrate provided with a phase shift portion adapted to give a predetermined phase difference to transmitted exposure light. The phase shift portion is a dug-down part that is dug down from a surface of the light-transmitting substrate to a digging depth adapted to produce the predetermined phase difference with respect to exposure light transmitted through the light-transmitting substrate at a portion where the phase shift portion is not provided. The photomask blank includes, on the digging-side surface of the light-transmitting substrate, an etching mask film that is made of a material being dry-etchable with a chlorine-based gas, but not dry-etchable with a fluorine-based gas, and serves as an etching mask at least until, when forming the dug-down part by dry etching, the dry etching reaches the digging depth. The photomask blank further includes, on a surface of the etching mask film, a light-shielding film that is made of a material mainly containing tantalum and has a thickness so as to be removable during the dry etching for forming the dug-down part of the light-transmitting substrate.