Ta-Nb EUV Mask Absorption Layer for Smoothness and Etching
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Solution Overview
Problem
Conventional EUV masks face challenges in achieving high resolution and smoothness due to surface roughness and line edge roughness issues, particularly with tantalum-niobium compounds, and existing nitride materials have low reflectance, making them unsuitable for halftone EUV masks.
Innovation Solution
A reflective EUV mask blank with a substrate, a reflective layer, and an absorption layer containing tantalum and niobium, with a composition ratio of Ta:Nb from 4:1 to 1:4, and a half-width FWHM of 1.0° or more, ensuring flexibility in reflectance selection and ease of etching while maintaining high smoothness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If tantalum-niobium compounds are used in the absorption layer, then etching accuracy and flexibility in reflectance selection are improved, but surface roughness and line edge roughness increase
Solution Approach 1:
The patent applies parameter changes by precisely controlling the composition ratio of Ta and Nb within 4:1 to 1:4, and controlling the half-width FWHM to be 1.0° or more. This optimization of material parameters achieves a balance between etching accuracy and surface smoothness, resolving the contradiction between manufacturing precision and surface quality.
Solution Approach 2:
The patent uses composite materials by combining tantalum and niobium in specific ratios to create an absorption layer that exhibits both good etchability and acceptable surface smoothness. The composite Ta-Nb material with controlled composition ratio and crystalline structure provides the desired properties that neither pure Ta nor pure Nb can achieve alone.
2Measurement precision
If halftone mask is used to enhance resolution, then mask contrast and transfer accuracy are improved, but surface smoothness deteriorates due to absorption layer material limitations
Solution Approach 1:
The patent optimizes the absorption layer parameters by controlling the Ta:Nb composition ratio and half-width FWHM, achieving a state where the absorption layer provides sufficient phase shift for halftone mask functionality while maintaining surface smoothness within acceptable ranges for high-resolution patterning.
3Shape
If nitride materials are used in absorption layer, then surface smoothness is improved, but reflectance becomes too low for halftone EUV mask application
Solution Approach 1:
The patent employs composite Ta-Nb materials that combine the advantages of different materials. The Ta-Nb composite provides sufficient reflectance for halftone mask application while maintaining acceptable surface smoothness, overcoming the limitations of pure nitride materials which have too low reflectance.
Solution Approach 2:
The patent changes the material parameters by selecting Ta-Nb composition ratios and controlling the half-width FWHM to achieve the optimal balance between reflectance and surface smoothness, ensuring the absorption layer meets the requirements for halftone EUV mask functionality.
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 EUV mask blank provides a halftone EUV mask with improved resolution, smoothness, and etching accuracy, suitable for fine line widths and resistant to cleaning liquids, enhancing the overall performance in EUV lithography.
Implementation Method 1
EUV light is readily absorbed by various kinds of substances, and the refractive index of the substance at such a wavelength is close to 1.
Implementation Method 2
a catoptric system, i.e., a system using a reflective photomask and a mirror, is employed
Implementation Method 3
transmitted and diffracted light beams having a 180° phase difference cancel each other in a region between two transmission areas
Data Source
AI summary
A reflective mask blank for EUV lithography includes a substrate, a reflective layer for reflecting EUV light, and an absorption layer for absorbing EUV light. The reflective layer and the absorption layer are formed on or above the substrate in this order. The absorption layer contains tantalum (Ta) and niobium (Nb), and the absorption layer has a composition ratio Ta:Nb of Ta (at %) to Nb (at %) of from 4:1 to 1:4. Among diffraction peaks derived from the absorption layer observed at 2θ: from 20° to 50° by out-of-plane XRD method, a peak having the highest intensity has a half width FWHM of 1.0° or more.