Reflective Mask Blank with Segmented Absorber Film
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Solution Overview
Problem
Current reflective masks face challenges in achieving sufficient contrast for inspection light with wavelengths of 200 nm or less and in forming high-resolution fine patterns due to issues with reflectance and phase shift effects, particularly when using ruthenium as a protective film, which affects pattern inspection and transfer accuracy in EUV lithography.
Innovation Solution
A reflective mask blank is designed with a multilayer reflective film and an absorber film having a laminated structure where the uppermost layer is composed of nitrides, oxides, or carbides of silicon and chromium, and a ruthenium-based protective film is used between the multilayer reflective film and the absorber film, optimizing the absorber film's uppermost layer to minimize reflectance for inspection light and enhance transmittance for EUV exposure light.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a ruthenium-based protective film is used between the multilayer reflective film and the absorber film, then the protective film provides effective protection and enables phase shift effect, but the contrast for inspection light with wavelengths of 200 nm or less is insufficient
Solution Approach 1:
The absorber film is divided into multiple layers with different materials and functions. The uppermost layer uses a material that provides low reflectance for inspection light (wavelength ≤200 nm), while the lower layer uses a material that provides high absorptance for EUV light. This segmentation allows each layer to optimize its specific function without compromising the other.
Solution Approach 2:
Different portions of the absorber film structure are assigned different material properties. The uppermost layer is specifically designed with low reflectance for inspection light to improve measurement precision, while the lower layer is designed with high absorptance for EUV light to maintain reliability. This local differentiation of material quality resolves the contradiction between inspection contrast and protective film effectiveness.
2Manufacturing precision
If the absorber film is designed to absorb EUV light effectively, then the mask contrast for EUV exposure is improved, but the reflectance for inspection light with wavelengths of 200 nm or less increases
Solution Approach 1:
The absorber film is segmented into an uppermost layer and a lower layer, where the uppermost layer specifically targets inspection light wavelengths (≤200 nm) to minimize reflectance, while the lower layer targets EUV light absorption. This segmentation enables simultaneous optimization of both mask contrast for EUV and inspection contrast.
Solution Approach 2:
The invention changes the material composition and thickness parameters of the absorber film layers. The uppermost layer uses a material with low reflectance for inspection light wavelengths, while the lower layer uses a material with high absorptance for EUV wavelengths. By adjusting these parameters, the patent achieves both low inspection light reflectance and high mask contrast.
3Device complexity
If a conventional single-layer absorber film is used, then the structure is simple, but the phase shift effect is insufficient for forming high-resolution fine patterns
Solution Approach 1:
The absorber film is segmented into multiple layers, each with specific material composition and thickness designed to produce phase shift effects. The uppermost layer and lower layer work together to create the necessary phase differences for high-resolution pattern formation, overcoming the limitations of conventional single-layer structures.
Solution Approach 2:
The absorber film uses composite materials with different optical properties in each layer. The uppermost layer uses a material optimized for inspection light interaction, while the lower layer uses a material optimized for EUV light absorption and phase shift. This composite structure enables both high pattern resolution and controlled 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 improves contrast for inspection light with wavelengths of 200 nm or less, enables accurate pattern inspection, and enhances the phase shift effect, allowing for the formation of high-resolution fine patterns with improved mask contrast and transfer accuracy for EUV exposure light.
Implementation Method 1
a multilayer reflective film formed on a substrate and adapted to reflect exposure light
Implementation Method 2
an absorber film formed on the multilayer reflective film and adapted to absorb the exposure light
Implementation Method 3
the uppermost layer is formed of a material composed mainly of a nitride, an oxide, an oxynitride, a carbide, a carbonitride, or an oxycarbonitride of at least one or more elements selected from silicon (Si) and chromium (Cr)... optimizing the absorber film's uppermost layer to minimize reflectance for inspection light
Implementation Method 4
enhances the phase shift effect, allowing for the formation of high-resolution fine patterns with improved mask contrast and transfer accuracy
Data Source
AI summary
Provided are a reflective mask blank and a reflective mask which are capable of improving the contrast for inspection light having a wavelength of 200 nm or less in an inspection, capable of improving the contrast for exposure light in use of the mask, and capable of forming a high-resolution fine pattern. A reflective mask blank 10 includes a substrate 1, and a multilayer reflective film 2 adapted to reflect exposure light, a protective film 6 composed mainly of ruthenium (Ru) or its compound on the multilayer reflective film 2, and an absorber film 4 adapted to absorb the exposure light, which are formed in this order on the substrate. The absorber film 4 has a laminated structure including an uppermost layer 4b and a lower layer 4a. The uppermost layer 4b is formed of a material composed mainly of a nitride, an oxide, an oxynitride, a carbide, a carbonitride, or an oxycarbonitride of at least one or more elements selected from Si and Cr. A reflective mask 20 is obtained by forming a transfer pattern in the absorber film of the reflective mask blank.