Scatterometry Objective Lens Central Obscuration Non-Overlapping Diffraction
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Solution Overview
Problem
The existing quadruple illumination method in scatterometry is limited by the maximal diffraction angle due to zero-order diffracted light spots, which restricts the measurement capabilities and requires shorter wavelengths or longer pitch gratings, limiting its usefulness.
Innovation Solution
A scatterometry measurement system using an objective lens with central obscuration and multiple illumination beams at different angles to generate non-overlapping diffracted orders within the imaging pupil plane, allowing for larger diffraction angles and increased measurement flexibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the quadruple illumination method is used to measure both first and minus first diffraction orders simultaneously, then measurement time is reduced and machine complexity is decreased, but the maximal diffraction angle is limited by the presence of zero order diffracted light spots
Solution Approach 1:
The illumination pupil is divided into four separate apertures positioned at specific locations. Each aperture illuminates the target at a different angle, and the diffracted orders from each aperture are spatially separated in the imaging pupil plane. This segmentation allows simultaneous measurement of multiple diffraction orders without overlap, resolving the contradiction between measurement efficiency and diffraction angle limitation.
Solution Approach 2:
The patent utilizes the spatial dimension in the imaging pupil plane to separate diffracted orders from different illumination apertures. By positioning apertures at different locations in the illumination pupil and exploiting the angular-dependent diffraction geometry, the system maps different diffraction orders to distinct regions in the imaging pupil, enabling simultaneous measurement without angular limitation.
2Manufacturing precision
If shorter wavelengths or longer pitch gratings are used to limit the diffraction angle in the quadruple arrangement, then order overlap is avoided, but the usefulness and measurement flexibility of the method is reduced
Solution Approach 1:
The patent changes the spatial parameters of the illumination apertures in the pupil plane rather than changing wavelength or grating pitch. By adjusting the positions and sizes of the four apertures, the system optimizes the separation of diffracted orders for various measurement conditions, maintaining measurement flexibility without being constrained to specific wavelength or pitch ranges.
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 scatterometry measurements with larger wavelength/pitch combinations, avoiding order overlaps and enhancing measurement accuracy and flexibility, particularly for semiconductor layers and smaller pitch gratings, while maintaining operational compatibility with existing systems.
Implementation Method 1
the objective lens collects at least one diffracted order from the first illumination beam and at least one diffracted order from the second illumination beam
Data Source
AI summary
A scatterometry measurement system includes an objective lens with a central obscuration and an illumination source configured to illuminate a scatterometry target through the objective lens with a first illumination beam at a first illumination angle and a second illumination beam at a second illumination angle in which the scatterometry target includes periodic structures located in at least two layers. The objective lens collects at least one diffracted order from the first illumination beam and at least one diffracted order from the second illumination beam such that the at least one diffracted order from the first illumination beam and the at least one diffracted order from the second illumination beam have a non-overlapping distribution in a portion of an imaging pupil plane not blocked by the central obscuration.