EUV Mask Absorber Materials for 3D Effect Mitigation
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Solution Overview
Problem
Extreme ultraviolet lithography systems face challenges in achieving precise flatness specifications and low tolerance to defects in EUV mask blanks, particularly due to the phase shift effects caused by the absorber layer's refractive index difference from the vacuum, which affects image placement and overlay errors.
Innovation Solution
The development of an EUV mask blank with a multilayer stack comprising reflective layer pairs, a capping layer, and an absorber comprising specific materials like Mo, Nb, V, and their alloys or oxides/nitrides, paired with TaSb, CSb, SbN, TaNi, TaCu, or TaRu, to mitigate 3D mask effects and improve reflectivity and etchability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single-layer absorber is used in EUV mask blanks, then the structure is simple and manufacturing is easier, but 3D mask effects occur due to phase shift from refractive index difference, causing image placement errors and overlay issues
Solution Approach 1:
The single-layer absorber is segmented into multiple layers with different materials (e.g., Mo, Nb, V, Ta, W, Pt, Pd, Ir, Os, Rh, Ru, Re, Hf, Zr, Ti, Al, Ga, In, Sn, Pb, Bi, Po, At, Rn, Fr, Ra, Ac, Th, Pa, U, Np, Pu, Am, Cm, Bk, Cf, Es, Fm, Md, No, Lr) and varying thicknesses. This segmentation allows independent optimization of each layer's optical properties to compensate for phase shift effects while maintaining manufacturing feasibility through standardized deposition processes.
Solution Approach 2:
The absorber is constructed as a composite structure combining multiple materials with complementary optical properties. By selecting materials with different refractive indices and absorption coefficients, the composite absorber achieves enhanced control over phase shift and absorption characteristics, thereby improving image placement precision without significantly increasing manufacturing complexity.
2Object-affected harmful factors
If the absorber layer thickness is increased to improve absorption, then light absorption improves, but the phase shift effect increases, worsening 3D mask effects and image placement accuracy
Solution Approach 1:
The total absorber thickness is segmented into multiple sub-layers, each contributing to both absorption and phase shift control. By distributing the total thickness across several layers with different materials, the structure achieves cumulative absorption while the varied refractive indices of different layers provide phase shift compensation, thereby maintaining image placement precision.
Solution Approach 2:
The optical parameters (refractive index, absorption coefficient) are changed by selecting different materials for each layer. This allows optimization of the thickness-absorption-phase shift relationship, where the total absorption is achieved through material selection rather than simply increasing thickness, thereby controlling the phase shift effect and maintaining manufacturing precision.
3Ease of manufacture
If conventional absorber materials are used, then the manufacturing process is straightforward, but etchability and reflectivity control are insufficient for future production requirements
Solution Approach 1:
The absorber uses composite materials combining elements with favorable etch selectivity and optical properties. This composite structure provides both good etchability (through materials that respond well to standard etch processes) and controlled reflectivity (through material selection and thickness optimization), thereby improving reliability without complicating the manufacturing process.
Solution Approach 2:
The material parameters are changed to optimize both etchability and reflectivity control. By selecting materials with appropriate etch rates and optical constants, the absorber achieves reliable fabrication and performance control while maintaining compatibility with existing manufacturing processes.
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 reflectivity and etchability of EUV mask blanks, leading to improved depth of focus, normalized image log slope, and reduced telecentricity errors, thereby addressing the precision and defect tolerance issues in EUV lithography.
Implementation Method 1
a reflective multilayer stack 12 on a substrate 14, which reflects EUV radiation at unmasked portions by Bragg interference
Implementation Method 2
extreme ultraviolet light, which is generally in the 5 to 100 nanometer wavelength range, is strongly absorbed in virtually all materials
Data Source
AI summary
Extreme ultraviolet (EUV) mask blanks, methods for their manufacture and production systems therefor are disclosed. The EUV mask blanks comprise a substrate, a multilayer stack of reflective layers on the substrate, a capping layer on the multilayer stack of reflecting layers, and an absorber on the capping layer. The absorber comprises a first layer selected from the group consisting of Mo, Nb, V, alloys of Mo, Nb and V, oxides of Mo, oxides of Nb, oxides of V, nitrides of Mo, nitrides of Nb and nitrides of V and a second layer selected from the group consisting of TaSb, CSb, SbN, TaNi, TaCu and TaRu.