Protective Film for EUV Reflective Mask Etching Resistance
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Solution Overview
Problem
Conventional Ru-based protective films used in reflective masks have insufficient resistance to fluorine-based etching gases during the absorber pattern repair step, which can damage the multilayer reflective film and reduce its reflectance.
Innovation Solution
A substrate with a multilayer reflective film is developed, featuring a protective film composed of a first metal, such as iridium or rhodium, and a second metal, like zirconium or ruthenium, with a standard free energy of fluoride formation higher than RuF5, and an extinction coefficient of 0.03 or less at 13.5 nm, enhancing resistance to fluorine-based etching gases without compromising reflectance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional Ru-based protective film is used, then the protective film provides basic protection to the multilayer reflective film, but the protective film has insufficient resistance to fluorine-based etching gases during the absorber pattern repair step
Solution Approach 1:
The protective film is constructed as a composite material consisting of two distinct layers: a lower layer containing ruthenium (Ru) and an upper layer containing iridium (Ir) or rhodium (Rh). This composite structure combines the benefits of Ru (good adhesion to the multilayer reflective film) with Ir or Rh (high resistance to fluorine-based etching gases), thereby resolving the contradiction between providing basic protection and resisting etching gas damage.
Solution Approach 2:
Different regions of the protective film are assigned different materials with locally optimized properties. The lower layer near the multilayer reflective film uses Ru for strong adhesion, while the upper layer exposed to etching gases uses Ir or Rh for high etching resistance. This local differentiation of material quality allows the protective film to simultaneously satisfy adhesion requirements and etching resistance requirements.
2Reliability
If the protective film is made more resistant to etching gases, then damage to the multilayer reflective film is prevented, but the reflectance of the multilayer reflective film may be compromised
Solution Approach 1:
The thickness parameters of the protective film layers are precisely controlled to balance protection and reflectance. The lower Ru layer is kept thin (1-5 nm) to maintain adhesion while minimizing reflectance impact, and the upper Ir or Rh layer is controlled at 2-10 nm to provide sufficient etching resistance without significantly attenuating EUV light. By optimizing these thickness parameters, both protection and reflectance requirements are satisfied.
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 protective film effectively resists fluorine-based etching gases, preventing damage to the multilayer reflective film and maintaining its reflectance, thus ensuring high accuracy and density in semiconductor device manufacturing.
Implementation Method 1
standard free energy of formation of a fluoride of the first metal is higher than standard free energy of formation of RuF5
Implementation Method 2
Light incident on the reflective mask mounted on an exposure machine for performing pattern transfer on a semiconductor substrate is absorbed in a portion having an absorber pattern, and is reflected by the multilayer reflective film in a portion having no absorber pattern
Implementation Method 3
an absorber pattern which is a patterned absorber film formed on the multilayer reflective film for absorbing exposure light
Data Source
AI summary
Provided are a substrate with a multilayer reflective film comprising a protective film having high resistance to a fluorine-based etching gas used in an absorber pattern repair step without reducing a reflectance of the multilayer reflective film, a reflective mask blank, and a reflective mask.A substrate with a multilayer reflective film 100 comprises a substrate 10, a multilayer reflective film 12 disposed on the substrate 10, and a protective film 14 disposed on the multilayer reflective film 12. The protective film 14 comprises a first metal and a second metal. Standard free energy of formation of a fluoride of the first metal is higher than standard free energy of formation of RuF5. The second metal has an extinction coefficient of 0.03 or less at a wavelength of 13.5 nm.