DIC Prism Shear Calculation for Consistent Interference Inspection
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Solution Overview
Problem
Existing defect inspection and categorization methods for compound semiconductor wafers and glass substrates face challenges in maintaining consistent light signal intensity due to varying shear amounts, leading to inconsistent brightness and difficulty in setting uniform inspection thresholds across different apparatuses.
Innovation Solution
A method and apparatus for calculating the shear amount of a differential interference contrast prism by capturing an interference contrast image, measuring fringe intervals, and adjusting the prism's position to maintain consistent path difference, enabling uniform inspection conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the shear amount of the differential interference contrast prism is not calculated and adjusted, then the inspection process can be performed quickly, but the intensity of the received light signal cannot be maintained constant leading to inconsistent brightness
Solution Approach 1:
The patent applies preliminary action by calculating the shear amount of the differential interference contrast prism before performing defect inspection. The shear amount is calculated using a quadric surface and fringe interval measurement, and this calculated value is then used to adjust the prism position in advance. This preliminary calculation and adjustment ensures that the path difference is optimized before inspection, maintaining constant light signal intensity and consistent brightness throughout the inspection process.
2Measurement precision
If the path difference of the differential interference contrast prism is adjusted, then the light signal intensity can be maintained constant, but the inspection conditions become complex requiring precise control
Solution Approach 1:
The patent replaces complex mechanical adjustment mechanisms with a calculation-based approach. Instead of relying on mechanical adjustments to achieve the correct path difference, the system calculates the required shear amount using optical principles (quadric surface geometry and fringe interval measurements) and uses this calculation to guide the prism position adjustment. This substitution simplifies the control process by providing a direct mathematical relationship between measurable quantities and the desired optical path difference.
3Ease of manufacture
If different apparatuses use the same inspection method without shear amount calculation, then the setup is simple, but machine differences cause inconsistent inspection results
Solution Approach 1:
The patent applies parameter changes by introducing the shear amount as a critical control parameter that varies between apparatuses. Each apparatus calculates its specific shear amount using the quadric surface and fringe interval method, and adjusts the differential interference contrast prism accordingly. This parameter-based approach allows each apparatus to be optimized for its specific optical characteristics while maintaining consistent inspection results across all apparatuses, eliminating machine differences without complicating the overall inspection methodology.
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 precise and consistent defect inspection by maintaining constant light signal intensity, reducing machine differences, and facilitating uniform inspection thresholds across multiple apparatuses.
Implementation Method 1
A differential interference contrast microscope separates illumination light into ordinary light and extraordinary light by a differential interference contrast prism such as a Nomarski prism
Implementation Method 2
A term d1 denotes a difference in height in a case where the ordinary light and the extraordinary light are reflected by the sample 50 when the shear amount is ΔS1
Data Source
AI summary
A calculation method, an image-capturing method, and an image-capturing apparatus are provided which can easily calculate a shear amount produced by an optical element arranged on an optical path of an interference optical system. A calculation method according to the present disclosure is a calculation method of calculating a shear amount produced by a predetermined optical element which is arranged on an optical path of an image-capturing optical system. The calculation method includes a step of capturing an interference contrast image of a quadric surface included in an object surface by the image-capturing optical system, a step of measuring a fringe interval of interference fringes included in the interference contrast image, and a step of calculating the shear amount based on a constant in a formula expressing the quadric surface and the fringe interval.