Surface Inspection Optics for Stable Wavelength Scanning
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Solution Overview
Problem
Surface inspection apparatuses face detection failures due to chromatic aberration in the optical system caused by fluctuations in the wavelength range of light from the light source, leading to measurement inaccuracies or impossibility, especially when intense scattered light from the substrate edge saturates the detector.
Innovation Solution
A surface inspection apparatus with a scanning optical system that corrects chromatic aberration within a predetermined wavelength range by adjusting the total lighting time of the light source across scanning periods, using a lighting control map to optimize light source ON/OFF duty variation, ensuring the wavelength range remains within design specifications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the light source is turned on and off during scanning to avoid detector saturation from edge scattered light, then detector saturation is prevented, but the total lighting time varies among scanning periods causing wavelength range fluctuations and chromatic aberration
Solution Approach 1:
The light source is controlled to be turned on and off periodically during scanning, with the lighting pattern repeating across multiple scanning periods. This periodic control prevents detector saturation while maintaining consistent wavelength range through standardized lighting durations in each period
Solution Approach 2:
The total lighting time of the light source is adjusted and standardized across scanning periods to maintain the wavelength range within the predetermined corrected range. By controlling the lighting duration parameter, the system prevents chromatic aberration while avoiding detector saturation
2Measurement precision
If an optical system is designed to suppress chromatic aberration across a wide wavelength range, then measurement accuracy is maintained, but design difficulty and manufacturing cost increase
Solution Approach 1:
The chromatic aberration correction is performed in advance during the optical system design phase for a predetermined wavelength range. The lighting control system then ensures the light source operates within this pre-corrected wavelength range, avoiding the need for complex wide-range correction while maintaining measurement accuracy
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 prevents detector saturation and maintains measurement accuracy by stabilizing the wavelength range of the light source, reducing the occurrence of chromatic aberration and ensuring reliable detection of foreign substances on the substrate.
Implementation Method 1
a scanning optical system configured to scan light from the light source along a first direction for a plurality of times
Implementation Method 2
a detector configured to detect scattered light from a surface of the substrate
Data Source
AI summary
Surface inspection apparatus includes stage for holding substrate, light source, scanning optical system for scanning light from the light source along first direction for plural times, stage scanning mechanism for scanning the stage in second direction intersecting with the first direction, and detector for detect scattered light from the substrate Inspection target region of the substrate is scanned by the light from the light source by an operation of the scanning optical system and the stage scanning mechanism. Chromatic aberration of the scanning optical system is corrected to fall within predetermined wavelength range. Fluctuation range of wavelength of the light from the light source is determined based on variation in total lighting time of the light source in scanning period of each light scanning operation along the first direction. The fluctuation range falls within the predetermined wavelength range.