EUV Mask Absorber Asymmetric Sidewall Shadowing
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Solution Overview
Problem
Conventional EUV lithography masks experience a shadowing effect due to the sidewall portions of absorber structures, which skews the critical dimensions of semiconductor devices, and reducing absorber structure thickness to mitigate this effect decreases absorptivity.
Innovation Solution
The formation of EUV masks with absorber structures featuring sidewall portions of varying angular orientations and shapes, achieved through directional etching and the use of absorber materials with different etch selectivity, prevents the shadowing effect by allowing EUV light to pass around the absorber structures without contacting their sidewalls.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the thickness or height of absorber structures is reduced to minimize the shadowing effect, then the shadowing effect is reduced, but the absorptivity of the absorber material decreases
Solution Approach 1:
The patent applies asymmetry by creating absorber structures with non-uniform cross-sectional areas along their height. Specifically, the absorber structures have a larger cross-sectional area at the base than at the top, forming a tapered or stepped configuration. This asymmetric geometry allows the structures to maintain sufficient absorptive material at the base to ensure high absorptivity, while reducing the cross-sectional area toward the top to minimize the shadowing effect on adjacent structures. The asymmetric design thus simultaneously addresses both requirements: maintaining absorptivity while reducing shadowing.
Solution Approach 2:
The patent applies local quality by varying the cross-sectional area of absorber structures at different heights and positions. The absorber structures are designed with different cross-sectional areas at their base versus their top, and potentially different cross-sectional areas at different lateral positions. This local variation in geometry allows specific regions of the absorber structures to optimize for different functions: the base region maintains larger dimensions for high absorptivity, while the top region reduces dimensions to minimize shadowing. This localized geometric optimization resolves the contradiction between absorptivity and shadowing effect.
2Productivity
If the critical dimensions of structures on the wafer are reduced to increase the number of structures, then the number of structures increases, but the shadowing effect becomes more pronounced
Solution Approach 1:
The asymmetric absorber structure design with larger base cross-sections and smaller top cross-sections allows for reduced spacing between adjacent structures without increasing shadowing effects. The tapered geometry concentrates the absorptive function at the base while minimizing the upper portions that would cast shadows, thereby enabling higher structure density on the wafer without compromising pattern fidelity.
Solution Approach 2:
By optimizing the local geometry of absorber structures with position-dependent cross-sectional areas, the patent enables increased structure density. The varied cross-sectional profiles allow adjacent structures to be placed closer together while maintaining adequate shadow-free zones, thus increasing the number of patternable structures per wafer area.
3Ease of manufacture
If conventional lithography is used instead of EUV lithography, then the manufacturing process is simpler, but the critical dimension requirements cannot be satisfied
Solution Approach 1:
The asymmetric absorber structure design is specifically optimized for EUV lithography applications. The non-uniform cross-sectional geometry, with larger bases and smaller tops, is tailored to the unique optical characteristics of EUV illumination at oblique angles. This asymmetric configuration maximizes the effectiveness of EUV light absorption while minimizing shadowing effects, thereby enabling the high critical dimension precision required for advanced semiconductor manufacturing using EUV lithography.
Solution Approach 2:
The patent employs local geometric optimization of absorber structures to achieve the precise critical dimensions required by EUV lithography. By varying the cross-sectional areas at different heights and positions, the design fine-tunes the optical interaction with EUV light, ensuring that the absorber structures provide sufficient contrast and definition for patterning features at the required sub-28nm critical dimensions.
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 effectively minimizes the shadowing effect, maintaining absorptivity while ensuring accurate critical dimension transfer in semiconductor fabrication, even at reduced absorber structure heights.
Implementation Method 1
The absorber layer is designed to absorb EUV at the same chosen EUV wavelength
Implementation Method 2
The ML reflector is designed to reflect EUV light at a chosen EUV wavelength (e.g., 13.5 nanometers)
Data Source
AI summary
An extreme ultraviolet (EUV) mask including an absorber structure is disclosed. The absorber structure may include at least one slanted and/or concave sidewall. The absorber structure may include a sidewall including a step. A method of forming an absorber for an EUV mask is disclosed. The method may include etching an absorber layer using a mask to form an absorber structure having a sidewall wherein an outer edge of the top surface of the sidewall is closer to a central vertical axis of the absorber structure than an outer edge of the bottom surface of the sidewall. The method may include performing additional etching steps to form a step along the sidewall of the absorber structure. The etching may include combinations of anisotropic etching in different directions, and/or isotropic etching. The method may include etching an absorber layer including multiple absorber layers having different material properties on the ML reflector.