EUV Reflection Mask Phase Shift for Shadowing Effect
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Solution Overview
Problem
Conventional reflection-type exposure masks face challenges in forming optical images with adequate contrast at finer dimensional regions due to the shadowing effect, especially for line patterns extending perpendicular to the incident EUV light, which degrades the quality of patterns transferred to wafers.
Innovation Solution
A reflection-type exposure mask is designed with a multilayer reflective film and an absorber pattern that includes a phase difference of 180°±10° between reflection lights, using a Ru-based absorber layer with a thickness of 30 nm or less, and a reflectance ratio of 4% to 40%, allowing for improved contrast values of 0.6 or more for both parallel and perpendicular patterns, even at target dimensions of 16 nm HP or less.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the thickness of the absorber pattern is reduced to reduce the shadowing effect, then the dimensional error of the transfer pattern is reduced, but the contrast value of the optical image for line patterns extending perpendicular to the incident EUV light direction deteriorates at finer dimensional regions
Solution Approach 1:
The invention changes the optical parameters by introducing a phase shift mechanism. By controlling the phase difference between reflected light from the multilayer film and absorbed light from the absorber pattern to be 180°, the invention transforms the optical interference condition, enabling high contrast images even with reduced absorber thickness that minimizes shadowing effects.
Solution Approach 2:
The invention introduces a phase shift layer as an intermediary element between the multilayer reflective film and the absorber pattern. This phase shift layer mediates the optical path difference, creating the necessary 180° phase difference that enables constructive and destructive interference to produce high-contrast images while allowing thinner absorber patterns.
2Device complexity
If a conventional reflection-type exposure mask is used, then the structure is simple, but it is difficult to form optical images with adequate contrast at target dimensions of 16 nm HP or less due to the shadowing effect
Solution Approach 1:
The invention segments the absorber pattern into functionally distinct layers: a phase shift layer that controls the phase of reflected light and an absorber layer that absorbs EUV light. This segmentation allows each layer to perform its specific function optimally, achieving high image contrast at fine dimensions while maintaining a relatively simple overall mask structure.
Solution Approach 2:
The invention uses composite material structures, specifically combining materials with different optical properties in the phase shift layer and absorber layer. The phase shift layer uses materials with specific refractive indices to achieve the 180° phase difference, while the absorber layer uses materials with high absorption coefficients, creating a composite structure that achieves superior optical performance.
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 effectively suppresses the shadowing effect, maintaining high image contrast and enabling precise pattern transfer at finer dimensions, surpassing the limitations of conventional masks by widening the usable reflectance ratio range for halftone-type phase shift masks.
Implementation Method 1
a multilayer reflective film provided in the main surface and serving as a high reflective region to the exposure light
Implementation Method 2
an absorber pattern provided on the multilayer reflective film and configured to absorb the exposure light
Implementation Method 3
a phase difference between a reflection light of the exposure light from the multilayer reflective film and a reflection light of the exposure light from the absorber pattern is in a range of 180°±10°
Data Source
AI summary
A reflection-type exposure mask includes a multilayer reflective film in a main surface and serving as a high reflective region to an exposure light, and an absorber pattern on the multilayer reflective film and serving as a low reflective region to the exposure light, wherein a phase difference between reflection lights of the exposure light from the multilayer reflective film and the absorber pattern is in a range of 180°±10°, and the absorber pattern includes first and second linear patterns having longitudinal directions intersecting at right angles, contrast values of optical images of the first and second linear patterns formed on a wafer is to be 0.6 or more when one of the longitudinal directions of the first and second patterns agree with an incident direction of the exposure light to the main surface viewed from above the main surface.