Lithographic Inspection Apparatus for Overlay Calibration
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Solution Overview
Problem
In lithographic manufacturing processes, achieving accurate measurements across entire substrates or batches is challenging due to process variations, particularly as features become smaller and taller, requiring adjustments in inspection apparatus settings and signal analysis, and there is a need for additional information on process variations to refine measurement results without significant overhead.
Innovation Solution
A method and apparatus that capture and compare images of scattered inspection radiation across nominally identical target structures at different locations or substrates to infer differences in structure, allowing for improved monitoring and adjustment of calibration information to enhance measurement accuracy, particularly using image processing to characterize pupil images and adjust calibration settings based on inferred differences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If detailed measurements are performed using inspection apparatus to account for process variations, then measurement precision is improved, but productivity deteriorates due to time-consuming measurements
Solution Approach 1:
The patent performs preliminary characterization of process variations by comparing images from multiple targets before detailed measurements are taken. This preliminary action identifies which targets require detailed measurement and which can use adjusted settings, thereby improving productivity without sacrificing measurement precision for critical targets.
Solution Approach 2:
The patent applies partial action by performing detailed measurements only on selected targets that show significant process variations, while using adjusted inspection settings on other targets. This selective approach reduces overall measurement time while maintaining precision where needed most.
2Measurement precision
If inspection apparatus settings and signal analysis are carefully adjusted to account for refractive index and layer thickness variations, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The system performs preliminary characterization of process variations by comparing images from multiple targets before detailed measurements are taken. This preliminary action identifies which targets require detailed measurement and which can use adjusted settings, thereby improving productivity without sacrificing measurement precision for critical targets.
Solution Approach 2:
The patent uses feedback from comparing multiple target images to automatically adjust inspection settings and measurement parameters. This feedback mechanism allows the system to adapt to process variations without requiring complex manual configuration, reducing device complexity while maintaining measurement precision.
3Reliability
If multiple targets are measured to infer process variations, then reliability of process monitoring is improved, but loss of time increases due to additional measurements
Solution Approach 1:
The patent performs preliminary characterization of process variations by comparing images from multiple targets before detailed measurements are taken. This preliminary action identifies which targets require detailed measurement and which can use adjusted settings, thereby improving productivity without sacrificing measurement precision for critical targets.
Solution Approach 2:
The patent extracts key process variation information from a small subset of targets and applies this information to adjust measurements for other targets. This extraction approach reduces the total number of detailed measurements needed while maintaining reliable process monitoring.
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 enables efficient monitoring of process variations with minimal additional measurement and computational overhead, improving the accuracy of performance parameters like overlay and critical dimension measurements, and allowing for real-time adjustments in lithographic manufacturing processes.
Implementation Method 1
capturing at least one image representing an angular distribution of the inspection radiation after it has been scattered by the target structure
Data Source
AI summary
Multilayered product structures are formed on substrates by a combination of patterning steps, physical processing steps and chemical processing steps. An inspection apparatus illuminates a plurality of target structures and captures pupil images representing the angular distribution of radiation scattered by each target structure. The target structures have the same design but are formed at different locations on a substrate and/or on different substrates. Based on a comparison of the images the inspection apparatus infers the presence of process-induced stack variations between the different locations. In one application, the inspection apparatus separately measures overlay performance of the manufacturing process based on dark-field images, combined with previously determined calibration information. The calibration is adjusted for each target, depending on the stack variations inferred from the pupil images.