Spatial Filter Width Optimization for Semiconductor Defect Inspection
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Solution Overview
Problem
Existing inspection systems for semiconductor substrates face challenges in improving sensitivity for detecting smaller particles and defects due to limitations in spatial filter design, particularly when the interval between repetition patterns is decreased, as they do not adequately consider the width of the spatial filter's shielding plate.
Innovation Solution
The solution involves calculating and setting the width of the spatial filter surface to minimize excessive diffraction, thereby maximizing the signal-to-noise ratio (SN ratio), which allows for improved defect detection sensitivity by reducing diffraction light and enabling automatic setting of the spatial filter width.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the interval between repetition patterns is decreased to improve sensitivity, then defect detection sensitivity is improved, but excessive diffraction from the spatial filter surface increases
Solution Approach 1:
The patent applies parameter changes by optimizing the width of the spatial filter surface to a specific range (0.5-2.0 times the wavelength of illumination light) to minimize excessive diffraction while maintaining high defect detection sensitivity. This parameter optimization resolves the contradiction by finding the optimal balance between sensitivity and diffraction control.
2Ease of manufacture
If the width of the spatial filter surface is not optimized, then manufacturing is simpler, but diffraction light increases reducing signal-to-noise ratio
Solution Approach 1:
The patent establishes specific parameter ranges for the spatial filter surface width (0.5-2.0 times the wavelength) to optimize the signal-to-noise ratio while maintaining ease of manufacture. This provides clear manufacturing guidelines that balance simplicity with performance optimization.
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 detection sensitivity by minimizing diffraction light and ensuring sufficient signal intensity from defects and particles, effectively improving the inspection system's sensitivity and reliability.
Implementation Method 1
an unnecessary image of a spatial filter surface caused by diffraction
Implementation Method 2
a semiconductor substrate is irradiated with laser light to detect scattering light from a particle which adheres to the semiconductor substrate or from a defect formed on the pattern
Data Source
AI summary
To improve sensitivity of a defect inspection, it is required to decrease influence of excessive diffraction from a spatial filter. Further, it is preferable to secure signal intensity from defects and particles as much as possible, while the influence of the excessive diffraction is decreased as much as possible. The present invention is characterized in setting a width of a spatial filter surface such that an unnecessary image caused by diffraction, that is, an intensity of the excessive diffraction is sufficiently small with respect to an intensity of a desired image. In the present invention, an SN ratio that is an index for deciding a width of the spatial filter is calculated from a region subjected to the influence of the excessive diffraction in an inspection image, and a width of a shield unit of the spatial filter is set so as to maximize the SN ratio.