EUV Lithography Phase Shift Mask with Multi-Layer Absorption
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Solution Overview
Problem
In extreme ultraviolet lithography, existing masks struggle to achieve high resolution and contrast due to the absorption of EUV light by refractive optical materials, necessitating the use of reflective systems, but these systems require improved phase shift patterns to enhance image quality.
Innovation Solution
A phase shift mask with a substrate, reflection layer, capping layer, and phase shift patterns where the upper absorption pattern has a higher refractive index and thinner than the lower absorption pattern, optimized to achieve a phase shift of 180° to 250° and satisfy optical density conditions, improving contrast and resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a reflective optical system is used instead of a refractive optical system, then EUV light absorption is avoided, but mask contrast and image quality are insufficient
Solution Approach 1:
The phase shift pattern is divided into multiple layers with different materials (first phase shift layer with Mo, second phase shift layer with Ru, third phase shift layer with Ta). Each layer contributes differently to the phase shift and absorption, allowing independent optimization of contrast and image quality without requiring higher single-layer thickness that would increase absorption
Solution Approach 2:
The patent uses composite material structure combining multiple metals (Mo, Ru, Ta) with different optical properties. The Mo layer provides base phase shift, Ru layer enhances absorption contrast, and Ta layer provides additional phase shift control. This composite approach achieves superior mask contrast and image quality compared to single-material phaseshift masks
2Manufacturing precision
If the thickness of absorption patterns is increased to achieve phase shift, then EUV light absorption increases, but resolution and contrast improve
Solution Approach 1:
The total phase shift requirement is segmented across three different material layers instead of using a single thick layer. This allows achieving the necessary phase shift (180° to 250°) with optimized distribution of thickness across layers, minimizing total absorption while maintaining resolution
Solution Approach 2:
The patent optimizes specific parameter combinations: first phase shift layer thickness of 10-20 nm, second phase shift layer thickness of 5-15 nm, third phase shift layer thickness of 15-30 nm. These parameter adjustments balance phase shift achievement with minimal EUV absorption
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 mask achieves improved contrast and high-resolution imaging by adjusting the thickness and refractive index of absorption patterns, leading to enhanced EUV lithography performance.
Implementation Method 1
a reflection layer on the substrate
Implementation Method 2
Each of the phase shift patterns may include a lower absorption pattern on the capping layer and an upper absorption pattern on the lower absorption pattern
Data Source
AI summary
Phase shift masks for an extreme ultraviolet lithography process includes a substrate, a reflection layer on the substrate, a capping layer on the reflection layer, and phase shift patterns on the capping layer. Each of the phase shift patterns may include a lower absorption pattern on the capping layer and an upper absorption pattern on the lower absorption pattern. A refractive index of the upper absorption pattern may be higher than a refractive index of the lower absorption pattern, and a thickness of the upper absorption pattern is smaller than a thickness of the lower absorption pattern.