Reflective Mask Blank Reference Marks for Accurate Defect Positioning
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Solution Overview
Problem
Existing methods for producing reference marks on reflective mask blanks for EUV lithography are costly and have low throughput, and they compromise positioning accuracy due to the need for multiple devices and slow processing speeds, particularly with focused ion beam methods.
Innovation Solution
A reflective mask blank design featuring a reference mark with at least two pairs of parallel line segments in concave or convex shapes, perpendicular to each other, formed on the same side as the multilayer reflective film, allowing for low-cost and high-throughput production using focused ion beam processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional lithography methods with multiple devices (coater, drawing machine, develop device, etching device) are used to form reference marks, then positioning accuracy can be maintained, but the introduction cost becomes extremely high and throughput decreases
Solution Approach 1:
The patent combines multiple reference mark formation operations into a single FIB processing step. Instead of using separate coater, drawing machine, develop device, and etching device, the FIB system performs all reference mark formation operations (etching grooves, forming patterns) in one integrated process, dramatically reducing device complexity while maintaining positioning accuracy through the FIB's inherent precision
Solution Approach 2:
The patent replaces the mechanical lithography system (coater, drawing machine, develop device, etching device) with a focused ion beam system. The FIB uses ion bombardment to directly etch and form reference marks without requiring the complex mechanical lithography equipment, thereby reducing device complexity while maintaining or improving positioning accuracy
2Device complexity
If FIB method is used to form reference marks, then device complexity is reduced, but processing speed becomes slow and throughput decreases
Solution Approach 1:
The patent divides the reference mark into multiple discrete components (first reference mark portion, second reference mark portion, third reference mark portion) that can be formed by separate FIB processing operations. This segmentation allows the FIB to process each portion independently and efficiently, improving overall processing speed while maintaining the simplicity of using a single FIB device
Solution Approach 2:
The patent forms reference mark portions with specific dimensions (e.g., groove widths of 1-10 μm, lengths of 10-100 μm) that are optimized for FIB processing speed. By designing the reference mark structure with appropriate partial dimensions rather than attempting to form the entire mark in one operation, the processing speed is improved while maintaining positioning accuracy
3Productivity
If reference mark width is narrowed to shorten processing time, then throughput improves, but positioning accuracy achieved by detector deteriorates
Solution Approach 1:
The patent enhances positioning accuracy by utilizing the vertical dimension (depth) in addition to the horizontal width. The reference mark grooves have controlled depths (e.g., 1-10 μm) that provide strong detection signals for the detector. This dimensional transition allows the system to maintain high positioning accuracy even when the horizontal width is narrowed to reduce processing time
Solution Approach 2:
The patent designs the reference mark structure in advance with optimized dimensions (groove width of 1-10 μm, length of 10-100 μm, depth of 1-10 μm) that are pre-calculated to balance processing speed and positioning accuracy. This preliminary design allows the FIB to process the reference mark efficiently while ensuring the detector can achieve high positioning accuracy without requiring excessive processing time
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 proposed design enables cost-effective and efficient production of reference marks with improved detection position accuracy, reducing processing time and enhancing the precision of defect detection.
Implementation Method 1
a multilayer reflective film that reflects EUV light
Implementation Method 2
an absorber film that absorbs EUV light
Implementation Method 3
FIB (focused ion beam, hereinafter referred to as FIB) methods
Data Source
AI summary
A reflective mask blank according to the present invention includes at least: a substrate; a multilayer reflective film provided on the substrate and reflecting exposure light; and an absorber film provided on the multilayer reflective film and absorbing the exposure light; wherein the reflective mask blank comprises a reference mark serving as a reference position for detecting a defect position and formed on a surface of the reflective mask blank on a same side as the multilayer reflective film; and the reference mark has at least two pairs of parallel line segments, each pair consisting of two parallel line segments in a concave or convex shape, and the directions of the two pairs of parallel line segments are in a position perpendicular to each other. This makes it possible to produce a reference mark at a relatively low cost and with high throughput, and to improve the accuracy of the position detection achieved by a detector.