Amorphous Metal EUV Mask Absorber for Shadowing Reduction
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Solution Overview
Problem
EUV lithography faces challenges in achieving high-precision, fine-dimension pattern transfer due to the shadowing effect caused by the three-dimensional absorber pattern, which limits the reduction of absorber film thickness and affects transfer accuracy in semiconductor device manufacturing.
Innovation Solution
A reflective mask blank with a multilayer reflective film and an absorber film made of amorphous metals containing cobalt (Co) and nickel (Ni), with additional elements like tungsten (W), niobium (Nb), and tantalum (Ta), is used, along with a protective film and etching mask films to reduce shadowing effects and achieve precise pattern formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the absorber film thickness is reduced to minimize shadowing effects, then transfer accuracy improves, but the absorber pattern becomes too thin to adequately absorb EUV light
Solution Approach 1:
The patent uses composite absorber films combining multiple materials (e.g., Ta and Mo, or Ta and W) in specific thickness ratios. This composite structure provides both sufficient EUV light absorption and minimal shadowing effect, resolving the contradiction between needing thin films for accuracy and thick films for absorption.
Solution Approach 2:
The patent changes the material composition parameters of the absorber film by incorporating specific elements (Ta, Mo, W, Nb) in controlled proportions. This parameter optimization allows the film to achieve the dual function of adequate absorption with minimal thickness, thereby reducing shadowing while maintaining absorption performance.
2Object-affected harmful factors
If a three-dimensional absorber pattern is formed to absorb EUV light, then light absorption improves, but shadowing effects increase and transfer accuracy decreases
Solution Approach 1:
The patent applies local quality by creating absorber patterns with varying thicknesses in different regions. The film thickness is locally optimized to provide sufficient absorption where needed while maintaining minimal profile elsewhere, thus reducing shadowing effects while preserving light absorption capability.
Solution Approach 2:
The patent transitions from purely vertical thickness control to a more sophisticated structure where the absorber film's optical properties are enhanced through material composition rather than just thickness. This dimensional shift in the problem-solving approach allows adequate absorption with reduced three-dimensional shadowing.
3Object-affected harmful factors
If the absorber film thickness is increased to improve light absorption, then absorption performance improves, but shadowing effects increase and sidewall roughness increases
Solution Approach 1:
The patent employs composite materials (Ta-Mo, Ta-W, Ta-Nb) that provide superior absorption performance per unit thickness compared to pure Ta. This allows achieving the required absorption with thinner films, thereby reducing sidewall roughness and shadowing effects while maintaining adequate light absorption.
Solution Approach 2:
The patent substitutes the mechanical approach of increasing film thickness to improve absorption with a material composition approach. By selecting materials with higher absorption coefficients and forming them as amorphous or nanocrystalline structures, the system achieves better absorption with thinner films, reducing mechanical shadowing and sidewall roughness.
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 solution enables the reduction of absorber film thickness to less than 50 nm, minimizing shadowing effects and allowing for the formation of highly accurate, fine phase shift patterns with reduced sidewall roughness, thereby improving the precision of semiconductor device manufacturing.
Implementation Method 1
an absorber film made of an amorphous metal containing at least one or more elements among cobalt (Co) and nickel (Ni)... absorbs EUV light... formation of highly accurate, fine phase shift patterns
Implementation Method 2
a multilayer reflective film that reflects exposure light... phase shift reflective masks composed of a comparatively thin absorber pattern that generates reflected light in which the phase is nearly completely inverted (phase inversion of about 180°)
Data Source
AI summary
Provided are a reflective mask blank and a reflective mask, which are able to reduce the shadowing effects of EUV lithography and form a fine pattern. As a result, a semiconductor device can be stably manufactured with high transfer accuracy. The reflective mask blank comprises a multilayer reflective film and an absorber film in that order on a substrate, and the absorber film comprises a material comprising an amorphous metal comprising at least one or more elements among cobalt (Co) and nickel (Ni).