Substrate Inspection Using Evanescent-Wave Defect Scattering
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Solution Overview
Problem
Existing substrate inspection systems face challenges in accurately detecting fine defects on semiconductor wafers due to the difficulty in distinguishing signals from noise caused by surface roughness, especially when using shorter wavelength light beams.
Innovation Solution
A substrate inspection apparatus that employs a combination of first and second laser beams with different wavelengths, matched and adjusted in incidence angle to generate an evanescent wave through four-wave mixing, which enhances defect detection by producing scattered light from defects while minimizing background noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a shorter wavelength light beam is used for defect detection, then the detection capability for fine defects is improved, but the difficulty in distinguishing signals from noise increases
Solution Approach 1:
The patent changes the wavelength parameter of the light beam from conventional visible light to extreme ultraviolet (EUV) light with wavelength of 13.5 nm. This parameter change enables detection of finer defects (10 nm or less) while the specific EUV wavelength provides sufficient signal strength to distinguish from noise, resolving the contradiction between detection precision and signal-to-noise ratio
Solution Approach 2:
The patent employs pulsed laser beams instead of continuous light sources. By using periodic pulsed action with precise timing synchronization, the system enhances the detectability of scattered light signals from defects while reducing background noise, thereby improving signal-to-noise ratio for fine defect detection
2Measurement precision
If multiple laser beams with different wavelengths are combined, then the signal-to-noise ratio is improved, but the device complexity increases
Solution Approach 1:
The patent combines multiple laser beams (first laser beam and second laser beam with different wavelengths) into a single optical path using beam combining technology. This merging approach enables four-wave mixing to generate evanescent waves that enhance defect detection signals while maintaining a compact system structure, balancing improved signal-to-noise ratio with controlled device complexity
Solution Approach 2:
The patent introduces an evanescent wave as an intermediary phenomenon generated by four-wave mixing of multiple laser beams. This evanescent wave acts as a mediator that enhances the interaction with defects on the substrate, providing improved signal-to-noise ratio while the mixing process itself manages the complexity of handling multiple wavelengths
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 improves the signal-to-noise ratio and enables accurate detection of fine defects as small as 10 nm or less, enhancing the reliability and yield of semiconductor devices.
Implementation Method 1
mixing the first laser beam and the second laser beam to generate an evanescent wave on the substrate
Implementation Method 2
The evanescent wave generates scattered light due to a defect of the substrate
Data Source
AI summary
A substrate inspection apparatus includes a light source unit, a pulsed beam matching unit, a substrate support unit, an incidence angle adjusting unit, and a detecting unit. The light source unit emits a first laser beam having a first wavelength and a second laser beam having a second wavelength. The pulsed beam matching unit matches the first laser beam and the second laser beam to superimpose a pulse of the first laser beam on a pulse of the second laser beam in time and space. The substrate support unit supports a substrate to be inspected. The incidence angle adjusting unit adjusts angles of incidence of the matched first laser beam and second laser beams to irradiate the first laser beam and the second laser beam on the substrate, and mixes the first laser beam and the second laser beam to generate an evanescent wave on the substrate. The evanescent wave generates scattered light due to a defect of the substrate. The detecting unit detects the scattered light generated due to the defect of the substrate.