Surface Inspection With Differential Interference and Adaptive Shear
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Solution Overview
Problem
Existing methods to improve sensitivity in differential interference contrast measurement, such as increasing shear amount or shortening wavelength, narrow the measurable height range, limiting the detection of gently changing surface shapes.
Innovation Solution
A surface inspection apparatus and software that uses two polarized illumination spots with different phases and a shear amount, combined with a differential interference contrast system, to measure and correct phase shifts exceeding the unique measurement range, allowing for expanded height measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the shear amount is increased to improve sensitivity in differential interference contrast measurement, then the detection sensitivity for smooth surface shapes is improved, but the height measurable range is narrowed
Solution Approach 1:
The invention dynamically adjusts the shear amount based on the local slope characteristics of the sample surface. By making the shear amount variable rather than fixed, the system can adapt to different surface regions - using larger shear amounts for gentle slopes (improving sensitivity) and smaller shear amounts for steep slopes (expanding measurable range), thus resolving the contradiction between detection sensitivity and height measurable range
Solution Approach 2:
The invention changes the parameter of shear amount from a constant value to a variable value that depends on the local surface conditions. This parameter change allows the system to optimize detection sensitivity for smooth surfaces while simultaneously expanding the measurable height range by reducing shear amount when necessary, effectively resolving the technical contradiction
2Measurement precision
If the wavelength is shortened to improve differential interference contrast and detection sensitivity, then the measurement accuracy is improved, but the height measurable range is still narrowed
Solution Approach 1:
The invention introduces dynamic adjustment of the shear amount parameter that compensates for the limited height range caused by short wavelength. By varying the shear amount based on local surface slope, the system maintains high measurement accuracy from the short wavelength while expanding the overall measurable height range through adaptive parameter control
3Measurement precision
If the shear amount is increased to detect gentle surface shape changes, then the sensitivity for smooth surfaces is improved, but the phase shift exceeds the unique measurement range
Solution Approach 1:
The invention dynamically adjusts the shear amount based on local surface characteristics to prevent phase shift from exceeding the unique measurement range. By reducing shear amount in regions where it would cause range exceedance while maintaining larger shear amounts where appropriate, the system preserves both sensitivity and measurement reliability
Solution Approach 2:
The invention changes the shear amount parameter adaptively based on local slope conditions, ensuring that phase shifts remain within the unique measurement range while still achieving high sensitivity for smooth surface detection where conditions permit
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
The solution expands the height measurement range while maintaining high sensitivity and accuracy, overcoming the limitations of increased shear amount and shortened wavelength.
Implementation Method 1
a light amount is changed by generating a phase shift in reflected light based on height displacement between two points on the sample surface
Implementation Method 2
condenses reflected light beams of the two polarized illumination spots reflected from the sample surface to generate interference light beams
Implementation Method 3
a sensor unit that photoelectrically converts the interference light beams generated by the differential interference contrast detection system to generate interference signals
Data Source
AI summary
A defect inspection apparatus that includes a differential interference contrast illumination system that irradiates a sample surface with an illumination spot set composed of two polarized illumination spots that have different phases at a predetermined wavelength and that are offset by a predetermined shear amount, a differential interference contrast detection system that condenses reflected light beams of the two polarized illumination spots reflected from the sample surface to generate interference light beams, a scanning unit that scans the sample surface using the two polarized illumination spots, a sensor unit that photoelectrically converts the interference light beams generated by the differential interference contrast detection system to generate interference signals, a height displacement measurement unit that processes the interference signals to measure height displacement between the illumination spots, and a height shape reconstruction unit that accumulates height displacement data of the illumination spots and reconstructs a height shape of the sample surface.