Mask Blank Defect Inspection Using EUV Focus Positioning
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Solution Overview
Problem
Conventional mask blank defect inspection technologies face challenges with low defect detection sensitivity, long inspection times, and high costs, particularly in Extreme Ultraviolet Lithography (EUVL) where fine pattern resolution and phase defect detection are critical, and existing methods struggle to accurately determine defect types and achieve practical throughput.
Innovation Solution
The method involves setting focus positions for maximum signal intensity in darkfield detection images to differentiate between dot-shaped, hole-shaped, and line-shaped defects using EUV light, improving sensitivity and throughput by determining defect types and optimizing inspection processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional mask blank defect inspection methods are used, then inspection can be performed, but defect detection sensitivity is low and inspection time is long
Solution Approach 1:
The inspection method segments the defect detection process by setting multiple focus positions (first focus position and second focus position) at different depths. By dividing the inspection into multiple focal planes, the system can detect defects at different heights within the mask blank structure, thereby improving detection sensitivity without requiring a single lengthy inspection process.
Solution Approach 2:
The inspection system performs periodic scanning at different focus positions. The autofocus mechanism periodically adjusts the focal plane between the first focus position (for convex defects) and the second focus position (for concave defects), enabling continuous inspection while maintaining high detection sensitivity across the entire mask blank surface.
2Measurement precision
If multiple focus positions are used for defect detection, then defect type identification accuracy improves, but inspection process complexity increases
Solution Approach 1:
The system employs an autofocus mechanism that provides feedback between the first focus position and the second focus position. By automatically adjusting the focal plane based on signal intensity comparisons, the system identifies defect types (convex or concave) without requiring complex manual intervention or multiple separate inspection processes.
Solution Approach 2:
The inspection system dynamically adjusts the focal position between two predetermined focus positions during the inspection process. This dynamic focusing capability allows the system to adapt to different defect types and depths, improving identification accuracy while maintaining a relatively simple operational framework through automated control.
3Productivity
If conventional inspection methods are used, then basic defect detection is possible, but throughput and manufacturing efficiency are low
Solution Approach 1:
The system performs preliminary autofocus adjustment to determine the optimal focus position before conducting the actual defect inspection. By pre-positioning the focal plane at the most effective depth for detecting the specific defect type, the system maximizes detection reliability while minimizing the time required for the inspection process, thereby improving throughput without compromising quality.
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 enhances defect inspection sensitivity, enables accurate defect type identification, and improves semiconductor device yields by detecting smaller defects and optimizing mask blank quality, leading to increased manufacturing efficiency and quality.
Implementation Method 1
setting focus positions for maximum signal intensity in darkfield detection images
Implementation Method 2
a multilayered-film (i.e., multilayer) reflective mask using reflection (Bragg reflection) by a multilayer made of, for example, molybdenum (Mo) and silicon (Si)
Implementation Method 3
setting focus positions for maximum signal intensity in darkfield detection images
Data Source
AI summary
Defect detection is performed with two settings, that is, setting of a focus position where a signal intensity obtained from a dot pattern is maximum and setting of a focus position where a signal intensity obtained from a hole pattern is maximum. In addition, defect detection is performed at a predetermined focus position previously set and for the detected defect, the focus position is changed at that position to find a focus position where the signal intensity is maximum. If the focus position is away from a signal light-receiving system, the defect is determined as dot-shaped. If the focus position is close to the signal light-receiving system, the defect is determined as hole-shaped. If the focus position is intermediate of them, the defect is determined as an elongated-shaped.