EUV Reflection Photomask Stack for High-Fidelity Pattern Transfer
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Solution Overview
Problem
As semiconductor device feature sizes decrease below the wavelength of radiation used in lithography processes, the ability to manufacture minimum feature sizes becomes sensitive to optical fringing, requiring higher resolution lithography processes, and existing methods struggle to maintain pattern transfer fidelity and reduce contamination and costs in mask fabrication.
Innovation Solution
The development of a reflection mode mask with a specific configuration including a substrate, reflective multilayer, capping layer, etch stop layer, absorber layer, and anti-reflective coating layer, optimized for EUV lithography, which reduces the number of pattern transfer steps, minimizes contaminants, and enhances manufacturing efficiency by using a thinner ARC layer and etch stop layer to improve reflectivity and prevent radiation absorption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional lithography methods are used for manufacturing minimum feature sizes below the wavelength of radiation, then the manufacturing process becomes sensitive to optical fringing, but the existing methods struggle to maintain pattern transfer fidelity and require multiple pattern transfer steps
Solution Approach 1:
The patent combines multiple functions into a single photomask structure: the absorber layer provides pattern definition, the etch stop layer prevents over-etching, and the reflective multilayer enables radiation reflection. This integrated design eliminates the need for multiple separate pattern transfer steps while maintaining manufacturing precision for sub-wavelength features.
Solution Approach 2:
The etch stop layer is deposited beforehand to a greater thickness than the absorber layer, creating a preliminary protective barrier that prevents radiation from reaching the reflective multilayer during processing. This preliminary action ensures pattern transfer fidelity by stopping the etching process before it compromises the underlying reflective structure.
2Reliability
If a thicker anti-reflective coating layer is used to prevent radiation absorption, then contamination is reduced, but manufacturing time and cost increase
Solution Approach 1:
The patent optimizes the thickness parameter of the anti-reflective coating layer to a specific range (1 nm to 5 nm) that provides sufficient contamination protection while minimizing manufacturing time. This parameter optimization balances reliability and production efficiency, avoiding both excessive thickness that would increase manufacturing time and insufficient thickness that would allow contamination.
3Productivity
If the photomask is used for extended periods to reduce manufacturing costs, then cost efficiency improves, but surface deformation and energy loss increase
Solution Approach 1:
The etch stop layer serves as a beforehand cushion that protects the reflective multilayer from damage during extended mask usage. By preventing radiation from reaching the reflective multilayer, this layer cushions against energy loss and surface deformation, thereby extending mask lifetime while maintaining reflectivity and reducing energy loss over time.
4Manufacturing precision
If higher resolution lithography processes are developed to improve depth of focus, then pattern transfer precision improves, but manufacturing complexity and cost increase
Solution Approach 1:
The reflective photomask structure serves itself by using the reflective multilayer to enhance depth of focus and pattern transfer precision inherently. The multilayer reflection provides optical path differences that improve depth of focus without requiring external complexity, allowing the mask to achieve high precision while keeping the lithography process relatively simple.
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 configuration enhances the resolution and fidelity of pattern transfer, reduces manufacturing costs and time, and extends the lifetime of the mask by minimizing energy loss and surface deformation, while maintaining high reflectivity and chemical resistance.
Implementation Method 1
a reflective multilayer configured to reflect a selected range of wavelengths
Implementation Method 2
one or more opaque materials deposited on one side to block penetration of a lithographic radiation
Implementation Method 3
an anti-reflective coating layer directly over the absorber layer
Data Source
AI summary
A reflection mode photomask includes a multilayer over a substrate. The reflection mode photomask further includes a plurality of absorber stacks over the multilayer. Each absorber stack of the plurality of absorber stacks includes an absorber layer, wherein a material of the absorber layer is selected from the group consisting of tantalum oxynitride and tantalum silicon oxynitride. Each absorber stack of the plurality of absorber stacks further includes an anti-reflective coating (ARC) layer on the absorber layer, wherein a material of the ARC layer is selected from the group consisting of tantalum nitride and tantalum silicon.