Layered Substrate Targets for Double-Diffraction Metrology
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Solution Overview
Problem
Existing metrology techniques for lithographic processes are limited by the effective limit on target pitches and wavelengths due to the need to capture propagating diffraction orders within a collection NA, restricting the flexibility in measuring smaller targets and various wavelengths.
Innovation Solution
A method and apparatus that utilize double diffracted radiation from a target arrangement comprising a mediator periodic structure and at least a first target periodic structure, each in a different layer, with pitches below the single diffraction limit, allowing for the measurement of double diffracted radiation from sequential same-order diffractions of opposite sign.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional scatterometry is used with large targets (40 μm by 40 μm), then mathematical reconstruction is simplified by treating the grating as infinite, but the targets cannot be positioned amongst product features and require more space
Solution Approach 1:
The patent changes the fundamental parameter of target size from large (40 μm) to small (10 μm or less), and simultaneously changes the diffraction regime from single diffraction to double diffraction. This allows small targets to be measured while maintaining measurement capability through the use of wavelengths below the single diffraction limit, enabling targets to be positioned amongst product features rather than in scribe lanes.
2Area of stationary object
If dark field scatterometry is used to measure smaller targets (10 μm by 10 μm or less), then targets can be positioned amongst product features, but the zeroth order of diffraction must be blocked and only higher orders can be processed
Solution Approach 1:
The patent introduces an intermediary measurement approach using double diffraction where the first diffraction grating creates diffraction orders that are then diffracted again by a second grating. This intermediary double diffraction process allows measurement of small targets without requiring dark field configuration, as the double diffracted radiation can be collected in a conventional bright field arrangement, simplifying the detection system.
3Length of moving object
If the pitch of the grating is reduced below the single diffraction limit, then smaller target pitches can be measured, but the effective limit on measurement wavelength to pitch ratio restricts the available wavelengths
Solution Approach 1:
The patent transitions from single diffraction to double diffraction, effectively adding another dimensional layer to the diffraction process. By using two sequential diffraction events instead of one, the system can measure smaller pitches while maintaining flexibility in wavelength selection, as the double diffraction geometry provides additional degrees of freedom in satisfying the diffraction conditions.
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 increases flexibility in measuring smaller target pitches and various wavelengths, enabling more accurate and flexible metrology for lithographic processes.
Implementation Method 1
Due to the need to capture propagating diffraction orders within a collection NA, there is an effective limit on the measurement wavelength to pitch ratio
Implementation Method 2
a pitch of at least the mediator periodic structure is below a single diffraction limit defined by the collection numerical aperture and a wavelength of said measurement radiation, such that said scattered radiation comprises double diffracted radiation, said double diffracted radiation comprising radiation having undergone two sequential same-order diffractions of opposite sign
Data Source
AI summary
Disclosed is a method of measuring a target on a substrate comprising: illuminating a target with measurement radiation comprising at least a first wavelength, collecting the resultant scattered radiation within a collection numerical aperture; and determining a parameter of interest from said scattered radiation. The target comprises a mediator periodic structure and at least a first target periodic structure each in a respective different layer on the substrate, wherein a pitch of at least the mediator periodic structure is below a single diffraction limit defined by the collection numerical aperture and a wavelength of said measurement radiation, such that said scattered radiation comprises double diffracted radiation, said double diffracted radiation comprising radiation having undergone two sequential same-order diffractions of opposite sign.