Semiconductor Inspection Tool Image Normalization
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Solution Overview
Problem
Semiconductor inspection systems face challenges in achieving consistent image quality due to variations in camera settings, light sources, and optics across different systems, leading to unacceptable tool-to-tool correlation and difficulty in sharing product setups.
Innovation Solution
The implementation of a semiconductor inspection tool with a camera and controller that performs light source flat field correction, optical image warping correction, and optical image scale correction, enabling product setup sharing between systems through mathematical techniques and algorithms to normalize pixel gain and offset values, correct for optical distortions, and ensure consistent image output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If vendor default settings are used for camera gain and offset, then system setup time is reduced, but image consistency across systems deteriorates
Solution Approach 1:
The system performs preliminary characterization of each inspection system's optical path, light source, and camera sensor to pre-determine correction factors. This preliminary action creates a baseline understanding of system-specific variations that enables automatic correction during operation, resolving the contradiction between quick setup and consistent images.
Solution Approach 2:
The system dynamically adjusts camera gain, offset, and illumination parameters based on measured system characteristics and reference images. By changing these parameters automatically through algorithmic correction rather than manual setup, the system achieves both rapid deployment and high image consistency across different inspection systems.
2Use of energy by moving object
If standard illumination voltage is applied to light sources, then power consumption is reduced, but light output consistency deteriorates
Solution Approach 1:
The system incorporates feedback mechanisms that measure the actual light output from each illumination source and automatically adjust voltage or current input to compensate for variations. This closed-loop control ensures consistent light output across systems while optimizing power consumption by applying only the necessary energy to achieve target illumination levels.
Solution Approach 2:
The system dynamically adjusts illumination parameters including voltage, current, and pulse width based on measured light output characteristics. By changing these electrical parameters automatically, the system achieves consistent photon output across different light sources without wasting energy on excessive power consumption.
3Measurement precision
If field of view dependent optical corrections are applied, then image accuracy across the field of view is improved, but processing complexity increases
Solution Approach 1:
The system divides the field of view into multiple zones or regions, each with its own correction parameters for distortion, scale, and illumination. By segmenting the image processing into manageable regions with localized correction models, the system achieves high image accuracy across the entire field of view while keeping individual processing tasks computationally efficient.
Solution Approach 2:
The system performs preliminary characterization of optical distortions across the field of view to pre-calculate correction maps and parameters. This preliminary action creates lookup tables and correction profiles that can be applied rapidly during inspection without real-time computational complexity, achieving high image accuracy through pre-computed corrections.
4Reliability
If product setup sharing is implemented across multiple systems, then defect correlation is improved, but system variability must be reduced
Solution Approach 1:
The system introduces an intermediary correction layer that translates images from different inspection systems into a standardized reference frame. This intermediary processing stage applies system-specific correction factors for distortion, scale, and illumination, enabling defect correlation across systems despite their inherent variability, thereby achieving high reliability in shared defect data.
Data Source
AI summary
An inspection tool includes a camera for obtaining images of a wafer and a controller configured for performing light source flat field correction, optical image warping correction, and optical image scale correction of the images. In operation, separate inspection tools are calibrated separately to obtain a characteristic response with respect to imaging and/or illumination for each such inspection tool. A standard target is then imaged by each inspection tool and the response of each of the inspection tools is normalized to ensure uniformity of the output of each inspection tool with respect to the other inspection tools.