EUV Mask Particle Attraction via Ruthenium Exposure
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Solution Overview
Problem
In EUV photolithography, variations in the thickness of the EUV light absorbing layer and surface roughness of the layers can cause shadow effects and affect the proper functioning of the EUV light reflecting and absorbing structures, leading to suboptimal pattern transfer on the target substrate.
Innovation Solution
The introduction of particle attractive patterns on the EUV mask, specifically fine patterns exposing the ruthenium surface in non-circuit areas, which attract particles and prevent them from settling on the absorber and anti-reflection layers, thereby improving the cleanliness and reflectivity of the EUV mask.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If particle attractive patterns are added to the EUV mask, then particle accumulation on the mask is improved, but mask structure complexity increases
Solution Approach 1:
The mask surface is segmented into functional zones: circuit pattern areas, particle attractive areas with fine patterns, and border areas. This segmentation allows particles to be directed to specific regions (particle attractive areas) while keeping circuit areas clean, resolving the contradiction by organizing complexity spatially rather than uniformly across the entire mask.
Solution Approach 2:
Different regions of the mask are given different properties: circuit areas maintain smooth absorber layers for pattern fidelity, while particle attractive areas feature fine line-and-space patterns that actively attract particles. This local differentiation allows the mask to simultaneously protect circuit areas from particles while managing particle accumulation in designated zones.
2Object-affected harmful factors
If fine patterns are created in particle attractive areas, then particle attraction capability is improved, but manufacturing precision requirements increase
Solution Approach 1:
The fine patterns in particle attractive areas are intentionally designed to be smaller than the resolution limit of the EUV exposure apparatus (pitch < λ/2NA). This excessive fineness ensures maximum particle attraction capability while accepting that these specific patterns cannot be printed on the wafer, thereby sacrificing printability in non-critical areas to achieve the particle management goal.
Solution Approach 2:
The particle attractive patterns are generated from circuit pattern data through automated processes that create fine line-and-space patterns in designated areas. This systematic generation approach maintains manufacturing consistency while clearly delineating which patterns are for particle attraction only and should not be printed.
3Object-affected harmful factors
If particle attractive areas are designated in non-circuit regions, then particle management is improved, but mask area utilization decreases
Solution Approach 1:
Particle attractive areas are extracted from the circuit pattern regions and placed in border areas and non-critical regions of the mask. This separation ensures that particles are attracted away from the critical circuit areas where pattern fidelity is essential, effectively removing the harmful particle accumulation problem from the functional circuit regions.
Solution Approach 2:
The mask design incorporates particle management functionality in the spatial dimension by utilizing border areas and regions outside the critical circuit footprint. This dimensional approach allows particle attractive patterns to coexist with circuit patterns without significantly reducing the area available for actual device fabrication.
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 solution enhances the cleanliness of the EUV mask by attracting and removing particles from the absorber and anti-reflection layers, leading to improved reflectivity and reduced shadow effects, resulting in better pattern transfer quality on the target substrate.
Implementation Method 1
particle attractive patterns on the EUV mask, specifically fine patterns exposing the ruthenium surface in non-circuit areas, which attract particles and prevent them from settling on the absorber and anti-reflection layers
Implementation Method 2
the EUV light rays emitted from a plasma are reflected off a collector mirror, directed toward a patterned EUV mask, and reflected off the mask onto the target substrate
Implementation Method 3
an EUV reflective mask includes a substrate, an EUV reflective multilayered structure
Implementation Method 4
the EUV absorbing layers absorb the EUV light rays so as not to pattern the target substrate in the undesired regions
Data Source
AI summary
An extreme ultraviolet (EUV) mask includes a multilayer Mo/Si stack comprising alternating Mo and Si layers disposed over a first major surface of a mask substrate, a capping layer made of ruthenium (Ru) disposed over the multilayer Mo/Si stack, and an absorber layer on the capping layer. The EUV mask includes a circuit pattern area and a particle attractive area, and the capping layer is exposed at bottoms of patterns in the particle attractive area.