EUV Mask Etch Stop Trench for Defect Isolation
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Solution Overview
Problem
Conventional masks for extreme ultraviolet lithography face challenges in forming fine patterns due to insufficient process capability and high sensitivity to defects, leading to reduced yield and imaging performance.
Innovation Solution
A mask design featuring a reflective structure with multiple unit layers laminated on a substrate, including an etch stop layer and an absorption pattern in a trench, where the unit layers consist of a first and second material layer, and the etch stop layer is made of silicon oxide, allowing for improved imaging performance by isolating defects from the absorption pattern.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a thick absorber structure (70 nm Ta-based absorber) is used to maximize contrast ratio, then reflection area and absorption area contrast is improved, but process capability for fine patterns (10 nm level) becomes insufficient and imaging performance deteriorates
Solution Approach 1:
The mask structure is segmented into multiple functional layers: a reflective multilayer structure (alternating Mo and Si layers) for light reflection, a separate absorber layer (Ru, Rh, or Ir) for pattern absorption, and an etch stop layer (SiO2) for process control. This segmentation allows each layer to be optimized independently for its specific function, enabling fine pattern formation while maintaining contrast ratio.
Solution Approach 2:
The mask employs composite material structure combining different materials with complementary properties: Mo/Si multilayers for high reflectivity, Ru/Rh/Ir for absorption with appropriate etch selectivity, and SiO2 for etch stop functionality. This composite approach enables simultaneous optimization of contrast ratio and fine pattern capability by selecting materials with specific optical and etching properties.
2Ease of manufacture
If a conventional mask structure is used, then manufacturing is simpler, but sensitivity to defects increases and yield of exposure process is lowered
Solution Approach 1:
The etch stop layer (SiO2) acts as an intermediary between the reflective multilayer structure and the absorber layer. It provides a controlled interface that enables precise positioning of the absorber pattern while protecting the underlying reflective structure from damage during etching. This intermediary layer reduces defect sensitivity by providing a buffer zone and controlled etching process.
Solution Approach 2:
The etch stop layer is placed beforehand to prevent direct contact between the etching process and the reflective multilayer structure. This prior cushioning protects the delicate Mo/Si layers from etching damage, reducing the likelihood of defects propagating to critical areas and improving overall process yield.
3Device complexity
If the absorber pattern is placed directly on the reflective structure, then manufacturing steps are reduced, but defects cannot be focused out and imaging performance is compromised
Solution Approach 1:
The absorber pattern is positioned in a different dimensional space - specifically, in a trench etched into the reflective multilayer structure at a lower elevation. This vertical separation creates a three-dimensional configuration where defects on the mask surface are focused out of the imaging plane, while the absorber pattern remains in focus. This dimensional change enables improved imaging performance without significantly increasing manufacturing 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
The design enhances imaging performance by focusing defects out of the image, increasing the difference in light intensity between defect and non-defect areas, thus improving yield and throughput of the exposure process.
Implementation Method 1
Since the extreme ultraviolet exposure (EUV) process uses light with a wavelength of 13.5 nm, a reflective mask is used instead of a transmissive mask
Implementation Method 2
a tantalum (Ta)-based absorber having a thickness of 70 nm is used in order to maximize a contrast ratio between a reflection area and an absorption area
Data Source
AI summary
A mask for extreme ultraviolet lithography is provided. The mask for extreme ultraviolet lithography comprises: a reflective structure comprising a plurality of unit layers laminated on a substrate and an etch stop layer placed between one pair of adjoining unit layers among the plurality of unit layers and having a trench through which the etch stop layer is exposed; and an absorption pattern placed on the bottom surface of the trench, wherein each of the unit layers comprises a first material layer and a second material layer on the first material layer.