Ru-Mo Protective Layer for EUV Lithography Reflectivity
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Solution Overview
Problem
The use of ruthenium (Ru) as a protective layer in EUV lithography leads to deterioration in EUV light reflectivity due to oxidation, resulting in a short useful life of photomasks and mirrors, as the Ru protective layer and uppermost Si layer of the Mo/Si multilayer reflective film oxidize during processing and exposure, necessitating frequent adjustments in exposure conditions.
Innovation Solution
A three-layer protective layer structure is implemented, with a thin Mo layer interposed between Ru layers, where the Mo layer acts to suppress oxidation and maintain EUV light reflectivity by controlling film thickness and surface roughness, thereby preventing the deterioration of the Ru protective layer and the underlying Mo/Si multilayer reflective film.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a Ru protective layer is used, then etching selectivity to the absorber layer is improved, but EUV light reflectivity deteriorates due to oxidation during processing and exposure
Solution Approach 1:
The protective layer is divided into multiple functional sub-layers: a Ru-based etch-resistant layer providing etching selectivity, and a Mo-based oxidation-resistant layer preventing oxidation of the reflective film. This segmentation allows each layer to specialize in one function, resolving the contradiction between etching protection and oxidation prevention.
Solution Approach 2:
The protective layer uses a composite structure combining Ru (for etching resistance) and Mo (for oxidation resistance). This composite approach integrates the beneficial properties of both materials, achieving both high etching selectivity and maintained EUV reflectivity without requiring a single material to perform both functions.
2Strength
If the protective layer is made thicker to improve protection, then etching resistance is improved, but EUV light reflectivity deteriorates due to increased absorption
Solution Approach 1:
The protective function is segmented between two thin layers instead of one thick layer. The Ru layer provides etching resistance while the Mo layer provides oxidation resistance, allowing each layer to remain thin and minimize EUV absorption while collectively providing comprehensive protection.
Solution Approach 2:
The invention changes the protective approach from increasing thickness to changing material composition. By selecting materials with appropriate properties (Ru for etching resistance, Mo for oxidation resistance) and optimizing their thin-film thicknesses, the system achieves adequate protection while minimizing EUV light absorption.
3Reliability
If a Mo layer is added to the protective layer structure, then oxidation resistance is improved, but device complexity increases
Solution Approach 1:
The protective function is segmented into specialized sub-layers, with Mo added as a specific oxidation-resistant component. This targeted addition addresses the oxidation vulnerability of Ru without completely redesigning the protective layer, minimizing complexity increase while achieving the desired oxidation resistance.
Solution Approach 2:
The protective layer evolves from a single Ru layer to a Ru-Mo composite structure. This composite approach systematically addresses both etching resistance (Ru) and oxidation resistance (Mo) in a coordinated manner, achieving enhanced reliability with a manageable increase in structural complexity.
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 prevents the deterioration of EUV light reflectivity over time, eliminating the need for mid-exposure condition adjustments and extending the useful life of EUV masks and mirrors by maintaining high reflectivity and etching selectivity.
Implementation Method 1
a reflective layer to reflect EUV light
Implementation Method 2
a Mo/Si multilayer reflective film having a molybdenum (Mo) layer as a low refractive index layer and a silicon (Si) layer as a high refractive index layer alternately laminated to have the light reflectivity improved
Implementation Method 3
an absorber layer to absorb EUV light, are formed in this order on a substrate
Implementation Method 4
the Ru protective layer and further, the uppermost layer of the multilayer reflective film (the Si layer in the case of the Mo/Si multilayer reflective film) are oxidized
Data Source
AI summary
There are provided an EUV optical member, in which deterioration in the reflectivity due to oxidation of the Ru protective layer is prevented, a functional film-equipped substrate to be employed for production of the EUV optical member. A reflective layer-equipped substrate 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 has a three-layer structure wherein a first layer made of a Ru layer or a Ru compound layer, a second layer made of a Mo layer and a third layer made of a Ru layer or a Ru compound layer are laminated in this order on the reflective layer.