RuCr Phase Shift Blankmask for EUV Lithography
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Solution Overview
Problem
Current phase shift blankmasks for EUV lithography face challenges in achieving high reflectance and appropriate phase shift amounts, leading to issues with pattern fidelity, surface roughness, and line edge roughness during wafer printing, particularly for semiconductor devices below 10 nm in size.
Innovation Solution
A phase shift blankmask is developed with a substrate, a reflective layer, and a phase shift layer made of a material containing ruthenium (Ru) and chromium (Cr), along with additional elements like molybdenum (Mo), silicon (Si), titanium (Ti), and boron (B), optimized for high relative reflectance and controlled surface roughness to enhance printing quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If tantalum (Ta)-based material is used as phase shift layer material to achieve phase shift amount, then phase shift amount of about 180° is realized, but relative reflectance of the reflective layer becomes less than 5% making it difficult to have high wafer printing effect
Solution Approach 1:
The patent changes the material parameters of the phase shift layer by using ruthenium (Ru) and chromium (Cr) materials with specific refractive index and extinction coefficient values. By controlling the thickness parameter of the phase shift layer to 30-70 nm, the patent achieves both high relative reflectance (5-20%) and appropriate phase shift amount (170-230°), resolving the contradiction between phase shift amount and relative reflectance that existed with tantalum-based materials.
Solution Approach 2:
The patent employs composite material strategy by combining ruthenium (Ru) and chromium (Cr) in specific ratios (Ru:Cr = 1:4 to 4:1) to create a phase shift layer with optimized optical properties. This composite material approach allows simultaneous achievement of high relative reflectance and appropriate phase shift amount, overcoming the limitations of single-material tantalum-based phase shift layers.
2Illumination intensity
If phase shift layer is formed to have high reflectance, then wafer printing effect is improved, but line edge roughness (LER) and line width roughness (LWR) of wafer pattern may deteriorate due to increased surface roughness
Solution Approach 1:
The patent controls the thickness parameter of the phase shift layer within 30-70 nm and manages surface roughness to be 0.5 nmRMS or less. By optimizing these parameters, the patent achieves high relative reflectance (5-20%) while maintaining smooth surface quality, thereby improving wafer printing effect without deteriorating line edge roughness or line width roughness.
3Reliability
If binary photomask is used for semiconductor device manufacturing at 5 nm or less, then existing process can be maintained, but double patterning lithography (DPL) technology needs to be applied reducing productivity
Solution Approach 1:
The patent changes the optical parameters of the photomask by implementing a phase shift layer with specific thickness (30-70 nm) and material composition (Ru:Cr ratio of 1:4 to 4:1). This enables the photomask to achieve phase shift amounts of 170-230° and relative reflectance of 5-20%, providing enhanced resolution capability that allows direct patterning at 5 nm and below without requiring double patterning lithography, thus maintaining process compatibility while significantly improving manufacturing efficiency.
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 solution provides a phase shift blankmask with improved contrast, line edge roughness, and line width roughness, enabling excellent resolution for semiconductor devices down to 7 nm or less by achieving high relative reflectance and precise phase shift control.
Implementation Method 1
a multi-layer reflective layer reflecting EUV light
Implementation Method 2
a phase shift layer formed on the reflective layer, in which the phase shift layer is made of a material containing ruthenium (Ru) and chromium (Cr)
Implementation Method 3
an absorbing layer absorbing EUV light
Data Source
AI summary
A blankmask for EUV lithography includes a substrate, a reflective layer, a capping layer, and a phase shift layer. The phase shift layer is made of a material containing ruthenium (Ru) and chromium (Cr), and a total content of ruthenium (Ru) and chromium (Cr) is 50 to 100 at %. The phase shift layer may further contain boron (B) or nitrogen (N). The phase shift layer of the present invention has a high relative reflectance (relative reflectance with respect to a reflectance of the reflective layer under the phase shift layer) with respect to a tantalum (Ta)-based phase shift layer and has a phase shift amount of 170 to 230°. It is possible to obtain excellent resolution when finally manufacturing a pattern of 7 nm or less by using a photomask manufactured using such a blankmask.