EUV Mask Blank Ru Protective Layer Oxidation Interlayer
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Solution Overview
Problem
The use of ruthenium (Ru) as a protective layer in EUV lithography leads to a decrease in EUV light reflectance due to oxidation during production steps or EUV exposure, requiring frequent adjustments in exposure conditions and reducing the lifespan of EUV masks.
Innovation Solution
A double-layer interlayer structure composed of a nitrogen and silicon-containing first layer and a ruthenium and nitrogen-containing second layer is introduced between the Mo/Si multilayer reflective layer and the Ru protective layer to suppress oxidation and maintain reflectance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Ru protective layer is used, then etching selectivity for absorber layer is improved and high reflectance is obtained, but reflectance decreases over time due to oxidation during production steps or EUV exposure
Solution Approach 1:
A TiN interlayer is introduced between the Ru protective layer and the Mo/Si multilayer reflective film. This intermediary layer prevents direct contact and oxidation of the Ru layer with oxygen during storage and EUV exposure, thereby maintaining the reflectance stability and extending the mask lifespan while preserving the high etching selectivity and initial reflectance properties of the Ru layer.
2Ease of manufacture
If Ru protective layer is used, then high etching selectivity is obtained, but oxidation occurs during cleaning, heating, dry etching or defect-correcting steps
Solution Approach 1:
The TiN interlayer serves as a protective intermediary that prevents oxidation of the Ru layer during various processing steps including cleaning, heating, and dry etching. This allows the Ru layer to maintain its high etching selectivity for the absorber layer without suffering from oxidation damage that would otherwise occur during these manufacturing processes.
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 interlayer structure effectively prevents the decrease in EUV light reflectance due to Ru protective layer oxidation, ensuring stable reflectance over time and extending the operational life of EUV masks.
Implementation Method 1
The reflective layer is usually a Mo/Si multilayer reflective film, which comprises silicon (Si) layers as high refractive layers and molybdenum (Mo) layers as low refractive layers alternately stacked to increase a light reflectance when the layer surface is irradiated with EUV light.
Implementation Method 2
a Mo/Si multilayer reflective film, which comprises silicon (Si) layers as high refractive layers and molybdenum (Mo) layers as low refractive layers alternately stacked to increase a light reflectance
Implementation Method 3
the Ru protective layer and further the outermost layer of the multilayer reflective film (i.e. the Si layer in the case of the Mo/Si multilayer reflective film) are likely to be oxidized in a step to be carried out for production of a mask blank or in a step to be carried out for production of a photomask from the mask blank
Implementation Method 4
The absorber layer is made of a material having a high absorption coefficient to EUV light
Data Source
AI summary
To provide an EUV mask blank whereby deterioration in reflectance due to oxidation of a Ru protective layer is suppressed, a functional film-attached substrate to be used for the production of the EUV mask blank, and a process for producing the functional film-attached substrate. A substrate with a reflective layer for EUV lithography, comprising a substrate, and a reflective layer for reflecting EUV light and a protective layer for protecting the reflective layer formed in this order on the substrate, wherein the reflective layer is a Mo/Si multilayer reflective film, the protective layer is a Ru layer or a Ru compound layer, between the reflective layer and the protective layer, an interlayer is formed which is composed of a first layer containing from 0.5 to 25 at % of nitrogen and from 75 to 99.5 at % of Si, and a second layer containing from 60 to 99.8 at % of Ru, from 0.1 to 10 at % of nitrogen and from 0.1 to 30 at % of Si and which has a total thickness of the first and second layers being from 0.2 to 2.5 nm, the first layer constituting the interlayer is formed on the reflective layer side, and the second layer is formed on the first layer, and the protective layer contains substantially no Si.