EUV Reflective Mask Phase Shift Absorber Blind Area Removal
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Solution Overview
Problem
In EUV lithography, the use of halftone masks leads to unintended sensitization of resist films due to overlapping between transfer patterns and leakage light areas, as reflected light from the absorber film in the leakage light area can expose regions that should not be sensitized.
Innovation Solution
A reflective mask with a phase shift absorbing film and a multilayer reflective film structure where the multilayer reflective film is removed from the upper layer in the blind area, including the leakage light area, to reduce reflectance and prevent sensitization of the resist film, and a conductive film is interposed between the substrate and the multilayer reflective film for grounding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a halftone mask with absorber film is used in EUV lithography, then the mask contrast is improved, but unintended sensitization of resist films occurs due to reflected light from the absorber film in the leakage light area
Solution Approach 1:
The patent removes the multilayer reflective film from the blind area including the leakage light area, extracting only the necessary reflective structure from the mask. This eliminates the source of harmful reflected light in the leakage area while preserving the phase shift effect in the transfer area, thereby preventing unintended resist sensitization without sacrificing mask contrast
Solution Approach 2:
The patent applies different structures to different areas of the mask: the transfer area retains both the absorber film and multilayer reflective film to achieve phase shift and high contrast, while the blind area (including leakage light area) has only the absorber film without the multilayer reflective film to eliminate harmful reflections. This local differentiation resolves the contradiction between maintaining mask contrast and preventing unintended sensitization
2Object-affected harmful factors
If the multilayer reflective film is removed from the blind area, then the harmful reflected light is reduced, but the grounding of the multilayer reflective film becomes difficult
Solution Approach 1:
The patent segments the multilayer reflective film structure by removing it only from the blind area while retaining it in the transfer area. This segmentation allows the mask to have different functional requirements met in different regions: the transfer area maintains full functionality including grounding capability, while the blind area eliminates harmful reflections
Solution Approach 2:
The absorber film serves multiple functions: it acts as a phase shift element in the transfer area when combined with the multilayer reflective film, and it serves as the sole reflective control layer in the blind area where the multilayer structure is removed. This multi-functionality allows the absorber film to maintain electrical connectivity for grounding purposes even when the multilayer reflective film is removed from certain areas
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 suppresses the sensitization of resist films at overlapping portions between the low-reflection portion and the leakage light area, ensuring accurate pattern transfer without unwanted exposure, and facilitates easy grounding of the multilayer reflective film to prevent electrostatic charging.
Implementation Method 1
a multilayer reflective film (13) formed on the conductive film (12) in the transfer area (1)
Implementation Method 2
having a structure in which high refractive index layers and low refractive index layers are alternately laminated
Implementation Method 3
an absorbing film (15) formed on the multilayer reflective film (13) and adapted to absorb EUV exposure light
Implementation Method 4
a conductive film is interposed between the substrate and the multilayer reflective film for grounding
Data Source
AI summary
A reflective mask of this invention includes a multilayer reflective film (13), on a substrate (11), having a structure in which high refractive index layers and low refractive index layers are alternately laminated, and an absorbing film (15) stacked on the multilayer reflective film (13) and adapted to absorb EUV exposure light. The absorbing film (15) is a phase shift film that allows the EUV exposure light having passed therethrough and reflected by the multilayer reflective film to have a predetermined phase difference with respect to the EUV exposure light directly incident on and reflected by the multilayer reflective film. A plurality of the layers or all the layers of the multilayer reflective film (13) in a blind area are removed from its upper layer.