EUV Mask Spectral Purity Layer Design
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Solution Overview
Problem
Current spectral purity filters in EUV lithography systems are difficult to produce due to high surface roughness requirements and cause light path folding, leading to losses when removed, and they fail to effectively separate EUV radiation from undesired deep ultra-violet (DUV) radiation, which affects photo-resist sensitivity and contrast.
Innovation Solution
A multi-layer EUV mask with a spectral filter top layer comprising alternating layers of specific materials like Si3N4, SiO2, and patterned absorber layers to enhance spectral purity, allowing for the separation of EUV and DUV radiation without folding the light path, thus enabling flexible use and minimizing losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a spectral purity filter based on blazed gratings is used, then the separation of EUV and DUV radiation is improved, but the manufacturing precision requirement becomes extremely high (surface roughness lower than 1 nm RMS)
Solution Approach 1:
The spectral purity filter is segmented into multiple functional layers: a multi-layer stack (Mo/Si or W/Si) for EUV reflection, a spectral filter top layer with alternating high and low refractive index materials for DUV filtering, and a patterned absorber layer for selective absorption. This segmentation allows each layer to be optimized independently, reducing the overall manufacturing precision requirement compared to a single blazed grating structure.
Solution Approach 2:
The filter uses composite material structures combining metals (Mo, W) for EUV reflection, dielectric materials (SiO2, Si3N4, TiO2, MgF2) for DUV filtering, and absorber materials (Ta, TaN, Cr, Ru) for selective absorption. This composite approach enables simultaneous achievement of EUV transmission and DUV rejection without requiring ultra-precise single-component fabrication.
2Object-affected harmful factors
If a spectral purity filter is used to remove DUV radiation, then the contrast is improved, but the light path is folded causing system losses
Solution Approach 1:
The spectral filtering function is merged with the mask structure itself. The spectral filter top layer is deposited directly on the multi-layer stack, and the patterned absorber layer is formed on top of that. This integration eliminates the need for separate filtering components that would fold the light path, thereby reducing system losses while maintaining DUV rejection capability.
3Object-affected harmful factors
If a spectral purity filter is used to filter DUV radiation, then the spectral purity is improved, but the device complexity increases
Solution Approach 1:
The multi-layer stack serves multiple functions: it acts as the primary EUV reflector and simultaneously provides the substrate for the spectral filter. The spectral filter top layer with alternating refractive index materials provides both DUV filtering and structural support. The patterned absorber layer provides both selective absorption and pattern definition. This multi-functionality reduces overall device complexity compared to separate dedicated components for each function.
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 enhances the ratio of EUV to DUV radiation, improving contrast and reducing losses, allowing for more efficient and flexible operation of EUV lithography systems by effectively filtering out DUV radiation while maintaining EUV transmission.
Implementation Method 1
a multi-layer stack comprising a plurality of alternating layers with a multi-layer stack top layer
Implementation Method 2
a patterned absorber layer arranged on the spectral filter top layer
Implementation Method 3
a first spectral purity enhancement layer including a material m1 and having a layer thickness d1; an intermediate layer including a material m2 and having a layer thickness d2; a second spectral purity enhancement layer comprising a material m3 and having a layer thickness d3
Implementation Method 4
a spectral filter top layer arranged on the multi-layer stack, the spectral filter top layer comprising a first spectral purity enhancement layer including a material m1 and having a layer thickness d1; an intermediate layer including a material m2 and having a layer thickness d2; a second spectral purity enhancement layer comprising a material m3 and having a layer thickness d3
Data Source
AI summary
An EUV mask includes, on top of a multi-layer mirror, a spectral purity enhancement layer, for application in an EUV lithographic apparatus. On top of the spectral purity enhancement layer, a patterned absorber layer is provided. The spectral purity enhancement layer includes a first spectral purity enhancement layer, but between the multi-layer mirror and first spectral purity enhancement layer there may be an intermediate layer or a second spectral purity enhancement layer and intermediate layer. The patterned absorber layer may also itself function as an anti-reflection (AR) coating. The AR effect of this absorber layer is a function of the aperture sizes in the pattern. The spectral purity of a mask may be enhanced, such that DUV radiation is diminished relatively stronger than EUV radiation.