Multichromatic Optical Inspection for Accurate Surface Fault Height Mapping
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Solution Overview
Problem
Existing inspection systems for analyzing defects in printed circuit boards and semiconductor wafers face limitations in image quality and accuracy due to the limited length of optical sensor rows, requiring multiple scans and complex setups to compensate for chromatic aberrations and surface reflectance variations, leading to inaccurate height measurements and blurred images.
Innovation Solution
An inspection system utilizing a spectrometer to split white light into monochromatic beams, an area scan camera with a dispersive element, and a correction device to correct longitudinal chromatic aberration, allowing simultaneous capture of high-quality line images with accurate height information by projecting multichromatic light at an angle and correcting wavelength-dependent shifts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a line scan camera with limited sensor row length is used, then the device complexity is reduced, but the measurement precision and image quality deteriorate due to inability to capture entire product surface in single scan
Solution Approach 1:
The patent transitions from a line scan camera (1D detection) to an area scan camera (2D detection), adding a spatial dimension to the detection plane. This enables simultaneous capture of entire product surface or large sections in a single scan, eliminating the need for multiple scans and improving image quality without significantly increasing device complexity
Solution Approach 2:
The area scan camera serves multiple functions: it captures complete product surfaces, provides high-resolution imaging, and enables spectral analysis across the entire detection plane simultaneously. This multi-functionality replaces the need for multiple specialized components required by line scan systems
2Measurement precision
If multiple scans are performed to capture entire product surface, then the measurement precision improves, but the productivity decreases due to increased scanning time
Solution Approach 1:
The area scan camera enables continuous capture of the entire product surface or large sections in a single scanning operation, eliminating the interruptions and time delays associated with multiple sequential scans. This continuous action maintains high image quality while significantly improving scanning speed and productivity
3Device complexity
If chromatic aberration is not corrected, then the device complexity is reduced, but the measurement precision deteriorates due to wavelength-dependent shifts in image plane
Solution Approach 1:
The patent introduces a correction device as an intermediary optical element between the detection unit and image sensor. This device specifically addresses longitudinal chromatic aberration by compensating for wavelength-dependent focal shifts, ensuring that all spectral components are focused at the same image plane position, thereby improving height measurement accuracy without excessive complexity
Solution Approach 2:
The correction device modifies the optical parameters of the system by introducing elements that counteract the dispersion-induced focal shifts. By changing the effective focal length or image plane position as a function of wavelength, the system achieves chromatic aberration correction and improved measurement precision
4Ease of operation
If the detection plane is not perpendicular to product surface, then the ease of operation is improved, but the measurement precision deteriorates due to varying angle of incidence affecting spectral distribution
Solution Approach 1:
The patent establishes an equipotential detection geometry by positioning the detection plane perpendicular to the product surface. This orthogonal arrangement ensures that the angle of incidence is uniform across the detection plane, creating consistent optical conditions for all measured points and eliminating variations in spectral distribution that would otherwise compromise 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
Enables reliable, high-resolution, and accurate defect analysis with a single scan, improving image clarity and height measurement precision by correcting chromatic aberrations and optimizing image capture across varying surface heights and reflectances.
Implementation Method 1
a spectrometer member configured to split white light into its spectral components and project a multichromatic light beam thus formed from monochromatic light beams
Implementation Method 2
the detection unit having a dispersive or diffractive element configured to project the reflected multi-chromatic light beam onto an image plane of the area scan camera
Implementation Method 3
the detection unit having a dispersive or diffractive element configured to project the reflected multi-chromatic light beam onto an image plane
Data Source
AI summary
The invention relates to an inspection system (26) for analyzing defects in a product, the inspection system (26) comprising a projection device (32), an optical detection device (28) and a processing device, the projection device having a spectrometer member configured to split white light into its spectral components and project a multichromatic light beam (37) formed from monochromatic light beams onto a product, a detection unit (29) comprising an area scan camera (27) and an objective (28) being configured to detect the light beam (37) reflected on the product in a detection plane (46) perpendicular, preferably orthogonal, to a product surface (38) of the product. The detection unit has a dispersive or diffractive element (31) configured to project the reflected light beam onto an image plane (49) of the area scan camera, the processing device being configured to derive a height information of the product surface from a spatial distribution of saturation values of the reflected light beam in the image plane, a correction device being configured to correct a longitudinal chromatic aberration of the reflected light beam in the image plane.