Phase Masking for Constructive Interference in Optical Inspection
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Solution Overview
Problem
Conventional optical inspection systems suffer from low signal-to-noise ratio (SNR) in detecting defects and imperfections in semiconductor manufacturing due to destructive interference of resonant radiation, which hinders accurate quality control.
Innovation Solution
Deployment of phase masks that impart spatially inhomogeneous phase changes to incident and collected light, using regions that shift the phase by π, aligning electric fields for constructive interference and enhancing SNR in optical signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional optical inspection systems are used, then the inspection process is simple, but the signal-to-noise ratio is low due to destructive interference
Solution Approach 1:
The patent converts the harmful destructive interference into beneficial constructive interference by introducing a phase mask that shifts the phase of resonant radiation by π. This transforms the originally harmful signal cancellation into signal enhancement, improving the signal-to-noise ratio without requiring fundamentally new optical principles
Solution Approach 2:
The phase mask serves as an intermediary optical element that mediates between the resonant radiation from the sample and the detection system. By introducing this intermediate component with specific phase-shifting properties, the system transforms the interference pattern from destructive to constructive, enhancing the detectable signal
2Measurement precision
If phase masks are deployed to improve signal-to-noise ratio, then defect detection accuracy improves, but the optical system becomes more complex
Solution Approach 1:
The phase mask implements local quality by applying different phase shifts to different spatial regions of the optical field. The mask contains regions with different optical path lengths that correspond to different local phase adjustments, enabling selective enhancement of specific interference patterns while maintaining system simplicity
Solution Approach 2:
The phase mask changes the optical path length parameter of the resonant radiation, which directly alters the phase parameter of the light wave. By controlling the optical path difference between reference and sample arms, the system transforms the interference condition from destructive to constructive, thereby improving detection 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
Improves the efficiency and accuracy of defect and imperfection detection by transforming destructive interference into constructive interference, thereby enhancing the signal-to-noise ratio in optical inspections.
Implementation Method 1
phase masks that impart spatially inhomogeneous phase changes to incident and collected light, using regions that shift the phase by π
Implementation Method 2
aligning electric fields for constructive interference and enhancing SNR in optical signals
Data Source
AI summary
Implementations disclosed describe, among other things, a sample inspection system that includes an illumination subsystem to generate a light incident on a sample. The sample inspection system includes a collection subsystem having optical elements to collect a light generated upon interaction of the incident light with the sample. The sample inspection system further includes a light detection subsystem configured to detect the collected light and generate one or more signals representative of characteristics of the sample. The sample inspection system deploys a phase mask that interacts with the incident light and/or the collected light and includes a first region and a second region imparting different phases to the light incident on the phase mask.