EUV Lithography Mask Absorber Thickness and Refractive Index
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Solution Overview
Problem
Extreme ultraviolet lithography faces challenges due to mask 3D effects, which result in contrast fading, feature-dependent best focus shifts, and telecentricity errors, leading to reduced pattern accuracy and increased defectivity during chip manufacturing.
Innovation Solution
The use of an extreme ultraviolet lithography mask with a patterned absorber layer of specific thickness (15 nm to 35 nm) and refractive index (at most 0.93), combined with a multipolar extreme ultraviolet radiation source and a setup adapted for compensating image shifts, to mitigate mask 3D effects and improve lithography processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional absorber layer thickness is used in the mask, then the mask structure is simpler, but mask 3D effects cause contrast fading and reduced pattern accuracy
Solution Approach 1:
The patent applies parameter changes by precisely controlling the absorber layer thickness to be within 15-35 nm and selecting materials with specific refractive indices (n < 0.93). These parameter optimizations reduce mask 3D effects and improve pattern accuracy without fundamentally changing the mask structure.
Solution Approach 2:
The patent employs composite material strategies by combining the absorber layer with a multi-layer reflector structure. The specific material selection (absorber layer material with n < 0.93 combined with reflector materials) creates a composite optical system that minimizes 3D effects while maintaining functionality.
2Manufacturing precision
If the absorber layer thickness is reduced to minimize 3D effects, then pattern accuracy improves, but the reflectivity decreases and more radiation dose is required
Solution Approach 1:
The patent optimizes the absorber layer thickness parameter to the specific range of 15-35 nm, which balances the competing requirements: thin enough to minimize 3D effects and improve pattern accuracy, but thick enough to maintain adequate reflectivity and reduce required radiation dose.
Solution Approach 2:
The patent applies local quality by selecting absorber materials with specific optical properties (refractive index n < 0.93) at the absorber layer interface. This localized material optimization enhances the optical performance at the critical interface between absorber and reflector, improving reflectivity without increasing thickness.
3Measurement precision
If a multipolar extreme ultraviolet source is used, then pattern placement errors are reduced, but mask 3D effects cause pole-to-pole phase offsets and image shifts
Solution Approach 1:
The patent optimizes the absorber layer optical parameters (thickness and refractive index) to minimize the differential interaction with multipolar radiation sources. By tuning these parameters, the mask reduces pole-to-pole phase offsets and image shifts while maintaining the benefits of multipolar illumination for pattern placement accuracy.
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 enhances the contrast and reduces defectivity in extreme ultraviolet lithography, allowing for a larger process window and reduced stochastic failures, thereby enabling the push of lithography steps to lower k1 imaging processes.
Implementation Method 1
a multi-layer reflector, and a patterned absorber layer positioned over the multi-layer reflector
Implementation Method 2
a patterned absorber layer positioned over the multi-layer reflector
Data Source
AI summary
An extreme ultraviolet lithography mask includes a multi-layer reflector and a patterned absorber layer positioned over the multi-layer reflector. The patterned absorber layer has a thickness between 15 nm and 35 nm and a refractive index of at most 0.93. In some examples, the patterned absorber layer has a thickness between 15 nm and 30 nm.