Lithographic Inspection Target Edge Diffraction Reduction
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Solution Overview
Problem
Conventional scatterometers have difficulty measuring smaller inspection targets due to significant edge diffraction effects, which complicate accurate metrology and overlay measurements, especially when targets are smaller than the illumination spot and surrounded by product structures.
Innovation Solution
The formation of inspection target structures with a progressive optical contrast transition at their periphery, reducing the edge diffraction effect by smoothing the optical transition between the target and its environment, allowing for smaller target sizes and improved measurement accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the inspection target structure size is reduced to fit within scribe lanes, then the productivity and substrate utilization are improved, but edge diffraction effects increase significantly complicating measurement accuracy
Solution Approach 1:
The periphery region of the inspection target structure is given a different optical property (progressive optical contrast transition) compared to the central region. This local modification at the edges reduces diffraction effects while preserving the target's overall function for metrology measurements.
Solution Approach 2:
Instead of sharp rectangular edges, the periphery is designed with a progressive optical contrast transition that creates a curved or graded profile. This curvature eliminates the abrupt edges that cause diffraction, allowing smaller targets to be measured accurately.
2Ease of manufacture
If conventional sharp-edged targets are used, then the manufacturing process is simple, but edge diffraction effects complicate accurate metrology measurements
Solution Approach 1:
The optical contrast parameter is changed progressively across the periphery region rather than being abrupt. This parameter modification (creating a gradient in optical properties) reduces diffraction effects while the target can still be fabricated using standard lithographic processes.
3Productivity
If the target structure is made smaller than the illumination spot, then multiple targets can be measured in one image improving productivity, but the edge diffraction effects become more significant
Solution Approach 1:
The periphery region is given special optical properties (progressive contrast transition) to reduce diffraction, while the central region maintains the standard target structure for measurement. This local differentiation allows small targets to be measured accurately even when multiple targets are imaged simultaneously.
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 quality of metrology targets by minimizing edge diffraction oscillations, enabling more precise measurements and allowing targets to be positioned within smaller scribe lanes, improving the accuracy of critical dimension and overlay metrology.
Implementation Method 1
Conventional scatterometers have difficulty measuring smaller inspection targets due to significant edge diffraction effects
Data Source
AI summary
A method uses a lithographic apparatus to form an inspection target structure upon a substrate. The method comprises forming the periphery of the inspection target structure so as to provide a progressive optical contrast transition between the inspection target structure and its surrounding environment. This may be achieved by providing a progressive change in the optical index at the periphery of the target structure.