Optical Height Detection System Using Dual Grating Masks
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Solution Overview
Problem
Existing optical height detection systems in charged particle beam inspection systems face challenges in achieving precise and fast height detection due to sensitivity to zero drifting and complex structures, particularly when using single detection grating masks and incandescent lamps.
Innovation Solution
The system employs a modulated illumination source, a projection grating mask, and two detection grating masks with overlapping grating images to determine sample height based on light intensity, using photodetectors and demodulation units to reduce sensitivity to zero drifting and simplify the structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single detection grating mask is used, then the structure is simpler, but the sensitivity to zero drifting increases and measurement precision deteriorates
Solution Approach 1:
The detection system is divided into multiple independent detection grating masks (at least two) instead of using a single mask. Each mask detects light intensity independently, and the results are combined to determine sample height. This segmentation reduces sensitivity to zero drifting in any single mask while maintaining structural feasibility through modular design.
2Device complexity
If an incandescent lamp is used as illumination source, then the structure is simpler, but the detection speed is slower and productivity is reduced
Solution Approach 1:
The illumination source uses a modulated light source (such as LED or laser) that emits light in periodic pulses rather than continuous illumination. This periodic action enables faster detection cycles and higher productivity while reducing heat generation and energy consumption compared to traditional incandescent lamps, despite requiring more complex modulation control.
3Productivity
If a modulated illumination source is used, then the detection speed and productivity improve, but the device complexity increases
Solution Approach 1:
The system replaces mechanical or thermal illumination methods (incandescent lamps) with optically modulated sources (LEDs or lasers). This substitution enables electronic control of illumination timing and intensity, achieving faster detection speeds through electrical modulation rather than mechanical or thermal processes, despite requiring additional modulation and demodulation electronics.
4Reliability
If multiple detection grating masks are used, then the measurement precision and reliability improve, but the device complexity increases
Solution Approach 1:
Multiple detection grating masks are combined in a unified detection optical path, where light reflected from the sample passes through multiple masks sequentially or in parallel. The detection signals from all masks are merged and processed together to determine sample height. This merging approach improves reliability through redundant measurement while maintaining a compact integrated structure rather than separate independent systems.
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 provides accurate and fast height detection with reduced sensitivity to zero drifting and a simpler structure, enabling precise and efficient operation in charged particle beam inspection systems.
Implementation Method 1
a modulated illumination source
Implementation Method 2
a projection optical unit for projecting the projection grating pattern to a sample
Implementation Method 3
a detection optical system for forming a first grating image from the projection grating pattern onto the first detection grating mask and forming a second grating image from the projection grating pattern onto the second detection grating masks
Implementation Method 4
using photodetectors and demodulation units to reduce sensitivity to zero drifting
Data Source
AI summary
An optical height detection system in a charged particle beam inspection system. The optical height detection system includes a projection unit including a modulated illumination source, a projection grating mask including a projection grating pattern, and a projection optical unit for projecting the projection grating pattern to a sample; and a detection unit including a first detection grating mask including a first detection grating pattern, a second detection grating mask including a second detection grating pattern, and a detection optical system for forming a first grating image from the projection grating pattern onto the first detection grating mask and forming a second grating image from the projection grating pattern onto the second detection grating masks. The first and second detection grating patterns at least partially overlap the first and second grating images, respectively.