Metrology Apparatus Pupil Plane Polarization Segmentation
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Solution Overview
Problem
Existing metrology systems for determining the topography of substrates in lithographic apparatuses face challenges in accurately measuring the height of substrates with multiple layers due to Height Process Dependency (HPD) errors, which are caused by the interference effects of underlying layers.
Innovation Solution
A metrology apparatus comprising an illumination module, an interferometer module with a non-polarizing beam splitter, first optics for projecting and collecting measurement radiation, and a detector for measuring interference patterns, which allows for the determination of the Mueller matrix of an object for multiple angles of incidence and polarization states simultaneously.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional interferometry is used to measure substrate topography, then height information can be obtained, but Height Process Dependency (HPD) errors occur due to interference effects from underlying layers
Solution Approach 1:
The patent changes the polarization state parameter of the illumination radiation to resolve HPD errors. By illuminating different portions of the pupil plane with radiation having different polarization states (e.g., s-polarized, p-polarized, circularly polarized), the system obtains multiple measurements that can be combined to eliminate the harmful interference effects from underlying layers, thereby improving both measurement precision and reliability
Solution Approach 2:
The patent segments the pupil plane illumination into multiple distinct portions, each with different polarization characteristics. This segmentation allows the system to separately probe the substrate at different polarization states and combine the information to cancel out HPD errors, resolving the contradiction between measurement accuracy and reliability
2Loss of information
If multiple measurements are taken to characterize Mueller matrix at different angles of incidence, then comprehensive optical properties can be obtained, but measurement time increases
Solution Approach 1:
The patent merges multiple measurements into a single simultaneous measurement by illuminating multiple distinct portions of the pupil plane at once. Each portion corresponds to a different angle of incidence and polarization state, and all are measured simultaneously by the detector array, eliminating the need for sequential measurements and thus reducing measurement time while maintaining complete optical characterization
Solution Approach 2:
The patent transitions from sequential single-point measurements to simultaneous multi-point measurements by utilizing the spatial dimension of the pupil plane. Different regions of the pupil plane are illuminated concurrently, each representing different angular and polarization parameters, allowing comprehensive Mueller matrix characterization to be obtained in a single measurement step
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
The apparatus enables more accurate and rapid measurements of substrate height with multiple layers, reducing HPD errors and improving lithographic throughput by allowing simultaneous characterization of the Mueller matrix at various angles of incidence.
Implementation Method 1
a non-polarizing beam splitter arranged to receive radiation and to form measurement radiation and reference radiation therefrom
Implementation Method 2
a detector comprising an array of sensing elements, the detector being arranged to receive: (a) the reference radiation and; (b) the portion of measurement radiation collected by the first optics and to measure an interference pattern between the reference radiation and the measurement radiation collected by the first optics
Data Source
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AI summary
Metrology apparatus comprises: an illumination module; and an interferometer module. The interferometer module comprises: a beam splitter for forming measurement and reference radiation; first optics for: projecting the measurement radiation onto the object; and collecting measurement radiation reflected from the object; and a detector arranged to receive: the reference radiation and; the reflected measurement radiation and to measure an interference pattern therebetween. The illumination module is configured to illuminate a plurality of distinct portions of the first optics pupil plane, each comprising a plurality of regions having different polarization states in the beam spot region. The detector is disposed such that: portions of the reference radiation and the measurement radiation that originate from the same distinct portion of radiation in the pupil plane spatially overlap; and portions of the reference radiation and the measurement radiation that originate from different distinct portions of radiation in the pupil plane are spatially distinct.