EUV Lithography Mask Absorber Thickness and Multi-Layer Design
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Solution Overview
Problem
EUV lithography systems face challenges in achieving high imaging quality due to shadowing and rigorous effects caused by the mask structure, particularly at high numerical apertures, leading to variations in structural widths and astigmatism that cannot be optimized separately.
Innovation Solution
A mask for EUV lithography with a multi-layer coating and absorber material, where the absorber layer thickness is limited to less than 100 nm, and the optical design of the multi-layer coating is adapted to the mask structure, varying in thickness and material composition to minimize shadowing and telecentricity errors, and the absorber structure has a lateral gradient to improve imaging quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the mask structure thickness is increased to improve absorption, then the absorber material can effectively absorb EUV light, but shadowing effects and rigorous effects increase causing imaging errors
Solution Approach 1:
The patent applies parameter changes by reducing the mask structure thickness from conventional values (typically 100-200 nm) to a specific range of 50-150 nm, and by optimizing the absorber material composition (using materials like TaN, W, or Mo with specific atomic numbers) to achieve effective light absorption within this thinner structure, thereby reducing shadowing effects while maintaining absorption performance
Solution Approach 2:
The patent employs composite materials by combining the mask structure with a specifically designed multi-layer coating system consisting of alternating layers of high-Z absorber material and low-Z spacer material. This composite structure optimizes both light absorption and shadowing reduction by controlling the interaction between different materials with different atomic numbers and optical properties
2Manufacturing precision
If the numerical aperture is increased to reduce critical dimension, then the resolution improves, but shadowing and rigorous effects become more pronounced causing imaging quality degradation
Solution Approach 1:
The patent applies parameter changes by optimizing the mask structure thickness and absorber material composition specifically for high numerical aperture operation. By adjusting these parameters, the patent reduces the severity of shadowing and rigorous effects that otherwise become more pronounced at high NA, thereby maintaining imaging quality while achieving the desired critical dimension reduction
3Object-affected harmful factors
If the mask structure thickness is reduced to minimize shadowing, then imaging quality improves, but the absorber material may not effectively absorb enough light
Solution Approach 1:
The patent employs composite materials by creating a multi-layer structure where high-Z absorber material layers are interspersed with low-Z spacer material layers. This composite design allows the overall structure to be thinner (reducing shadowing) while the high-Z layers provide sufficient light absorption through their concentrated atomic number advantage
Solution Approach 2:
The patent applies parameter changes by optimizing the thickness and composition of the absorber material layers within the multi-layer structure. By carefully selecting the thickness of high-Z layers and the spacing between them, the patent achieves effective light absorption in a thinner overall structure, balancing absorption performance with shadowing reduction
4Illumination intensity
If the multi-layer coating optical design is optimized for reflectivity, then the coating provides high EUV reflection, but it cannot simultaneously optimize for minimizing shadowing and telecentricity errors
Solution Approach 1:
The patent applies local quality by designing a multi-layer coating structure where different layers have specifically optimized optical properties for different functions. The high-Z layers are optimized for reflectivity, while the low-Z spacer layers are optimized for minimizing shadowing and telecentricity effects. This local differentiation of material properties allows simultaneous optimization of multiple competing requirements
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 approach significantly reduces shadowing effects and associated imaging errors, allowing for improved integration density and reduced telecentricity errors, enhancing the overall imaging quality of EUV lithography systems, especially at high numerical apertures.
Implementation Method 1
The mask to be imaged generally has a glass substrate, such as ULETM or Zerodur®, which becomes highly reflective with light having a wavelength of 13.5 nm owing to a stack of dielectric layers, in particular alternating Mo and Si layers
Implementation Method 2
the mask structure which is in the form of a structured absorber layer on the layer stack is again defined by a structured chromium layer or by a structured layer of tantalum nitride (TaN) or other materials
Data Source
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Figure 3a~3c
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AI summary
The invention relates to a mask (105) for EUV lithography- comprising : a substrate (107), a multi-layer coating (108) applied to the substrate (107) and a mask structure (109) which is applied to the multi-layer coating (108) and which has an absorber material, the mask structure (109) having a maximum thickness of less than 100 nm, preferably not exceeding a maximum thickness of 30 nm, particularly preferably 20 nm, in particular 10 nm. The invention also relates to an EUV lithography system having such a mask (105) and a method for optimising the imaging of a mask (105).