Wafer Thickness Variation Measurement Using Intensity Signal Segmentation
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Solution Overview
Problem
Existing bright field inspection systems face challenges in accurately detecting thin film thickness variations across semiconductor wafers due to reflectivity changes, which can lead to detection errors during die-to-die or die-to-database comparisons.
Innovation Solution
A method and system for measuring thin film thickness variations by scanning wafers, obtaining intensity measurements from corresponding regions, calculating signal variations, and using these variations to estimate thickness changes, thereby improving the accuracy of defect detection by filtering out thickness-related noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If bright field inspection is performed on wafers with non-uniform dielectric layers, then inspection coverage is achieved, but detection accuracy deteriorates due to reflectivity variations from thickness variations
Solution Approach 1:
The patent introduces an intermediary computational layer that processes raw inspection signals by separating thickness variation components from defect components. The system uses reference signals from regions known to be free of defects as mediators to establish baseline reflectivity patterns, then compares these against signals from regions of interest to isolate true defects from thickness-induced variations.
Solution Approach 2:
The system dynamically adjusts inspection parameters including wavelength selection, polarization angles, and illumination angles based on measured thickness variations. By changing these parameters adaptively, the system optimizes the contrast between defects and the varying background reflectivity caused by thickness non-uniformity.
2Measurement precision
If signal processing is performed to compensate for thickness variations, then detection accuracy improves, but system complexity increases
Solution Approach 1:
The patent segments the inspection signal into distinct components: a background component representing thickness variations and a foreground component representing defects. This segmentation is achieved through statistical analysis of signal distributions across multiple measurement points, allowing independent processing of each component to reduce overall system complexity.
Solution Approach 2:
The system performs preliminary characterization of thickness variations across the wafer surface before conducting defect inspection. By pre-mapping the thickness landscape using reference measurements, the system establishes correction factors that are applied during subsequent defect detection, avoiding the need for complex real-time compensation during the actual inspection.
3Measurement precision
If multiple measurements are taken to account for thickness variations, then measurement precision improves, but inspection time increases
Solution Approach 1:
The patent implements periodic measurement sampling at strategically selected locations across the wafer to characterize thickness variations. Rather than continuous measurement, the system uses a periodic sampling pattern that captures the essential thickness profile with minimal measurements, then interpolates between samples to generate correction maps for the entire surface.
Solution Approach 2:
The system performs measurements on a subset of locations that are statistically representative of the overall thickness distribution, rather than measuring every point. By selecting critical measurement points based on process knowledge and statistical sampling theory, the system achieves adequate thickness characterization with fewer measurements than a complete surface scan would require.
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
This approach enhances the accuracy of defect detection by isolating thickness variations from other signal changes, leading to improved inspection outcomes and reduced false defect rates.
Implementation Method 1
The interference results from multiple reflections of light between two substrates of a thin layer (or film) of transparent material. The multiple reflected beams of radiations undergo distinct optical paths and generate interference patterns.
Implementation Method 2
a single beam of radiation that is directed towards a thin layer of transparent material that is followed by an object that has a refractive index different from the film causes multiple beams of radiations to be reflected from the thin layer
Data Source
AI summary
A method for measuring thin film thickness variations of inspected wafer that includes an upper non-opaque thin film. The method including (i) scanning the wafer and obtain wafer image that includes die images each of which composed of pixels, (ii) identifying regions in a first die image and obtain first intensity measurements of the respective regions, (iii) identifying corresponding regions in a second die image and obtain second intensity measurements of the respective regions, (iv) processing the first intensity measurements and the second intensity measurements to obtain signal variations between the second intensity measurements and the first intensity measurements, whereby each calculated signal variation is indicative of thickness variation between a region in the second die and a corresponding region in the first die.