EUV Mask Absorber Bilayers for Phase Shift Control
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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 and a capping layer, where the absorber is composed of bilayers with a first layer of silicon and a second layer selected from materials like TaSb, CSb, TaNi, TaCu, SbN, CrN, Cr, Ir, Pd, Re, Os, Cd, Co, Ag, and Pt, their oxides, or nitrides, to mitigate 3D mask effects and improve reflectivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a single-layer absorber is used in EUV mask blanks, then the manufacturing process is simple, but phase shift effects cause image placement errors and overlay errors
Solution Approach 1:
The absorber layer is segmented into multiple sub-layers with different materials and thicknesses. Each sub-layer contributes differently to the phase shift and absorption characteristics, allowing independent optimization of phase control and absorption properties to reduce image placement errors and overlay errors
Solution Approach 2:
The patent changes the optical parameters of the absorber by using materials with different refractive indices and absorption coefficients. By selecting materials with specific n and k values and controlling layer thicknesses, the phase shift and absorption are independently tuned to achieve precise image placement while maintaining manufacturing feasibility
2Reliability
If the absorber layer thickness is increased to improve light absorption, then absorption performance improves, but 3D mask effects increase due to phase shift
Solution Approach 1:
The patent changes the material parameters of the absorber layers, selecting materials with high absorption coefficients (k values) to achieve effective light absorption with reduced thickness. This allows maintaining absorption performance while minimizing phase shift-induced 3D mask effects
Solution Approach 2:
The absorber is constructed as a composite structure with multiple materials having different optical properties. The combination of materials with complementary characteristics enables simultaneous optimization of absorption efficiency and phase shift control, reducing 3D mask effects while maintaining reliable light absorption
3Device complexity
If conventional absorber materials are used, then the mask blank structure is simple, but reflectivity and depth of focus performance are insufficient
Solution Approach 1:
The patent employs composite absorber structures with multiple material layers, each contributing different optical properties. This composite approach enables simultaneous optimization of reflectivity, depth of focus, and phase shift characteristics, achieving superior performance compared to conventional single-material absorbers
4Manufacturing precision
If the absorber layer is made thicker to reduce overlay errors, then absorption improves, but manufacturing precision requirements increase
Solution Approach 1:
The absorber is divided into multiple controllable sub-layers, each with specific thickness and material composition. This segmentation allows precise control of the cumulative phase shift and absorption effects, achieving overlay precision requirements through systematic layer design rather than relying on a single thick layer
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 reliability of EUV mask blanks, improving depth of focus, normalized image log slope, and telecentricity error, leading to better performance in lithography processes by attenuating EUV light and providing tunable phase shift and reflectance values.
Implementation Method 1
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
Implementation Method 3
there is also a phase shift effect due to the difference between the absorber layer's index of refraction and vacuum's index of refraction (n=1)
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 comprising a plurality of bilayers comprising a first layer of silicon and a second layer selected from the group consisting of TaSb, CSb, TaNi, TaCu, SbN, CrN, Cr, Ir, Pd, Re, Os, Cd, Co, Ag, Pt, oxides of TaSb, CSb, TaNi, TaCu, SbN, CrN, Cr, Ir, Pd, Re, Os, Cd, Co, Ag, Pt, and nitrides of TaSb, CSb, TaNi, TaCu, Cr, Ir, Pd, Re, Os, Cd, Co, Ag, and Pt.