Metrology Apparatus Overlay Measurement via Scatterometry
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Solution Overview
Problem
Current metrology apparatuses in lithographic processes face challenges in efficiently and accurately determining characteristics of interest, such as overlay errors, on substrates, especially at low k1 values, where feature sizes approach the classical resolution limit, requiring sophisticated fine-tuning and control loops to maintain pattern accuracy.
Innovation Solution
A metrology apparatus comprising a sensor and optical system that illuminates and detects radiation scattered from the substrate, using a blocking element to prevent transmission of the 0th diffraction order and modulating radiation to distinguish noise from signal, allowing for high-resolution imaging and precise determination of overlay values between layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional metrology apparatuses are used to measure overlay values at low k1 values, then measurement capability is maintained, but measurement precision deteriorates due to features approaching the classical resolution limit
Solution Approach 1:
The patent changes the measurement approach by transitioning from direct imaging to scatterometry, measuring diffraction patterns instead of direct feature images. This parameter change in measurement methodology enables precise overlay measurement even when features are at or below the diffraction limit, resolving the contradiction between measurement precision and detection difficulty.
Solution Approach 2:
The patent introduces diffraction patterns as an intermediary measurement medium. Instead of directly observing the difficult-to-detect features, the system measures the diffraction patterns produced by the features, which contain the overlay information in a form that is easier to detect and measure with high precision.
2Manufacturing precision
If sophisticated fine-tuning steps and control loops are applied to maintain pattern accuracy, then manufacturing precision is improved, but device complexity increases
Solution Approach 1:
The patent implements a feedback mechanism where overlay measurements from scatterometry are fed back to correct alignment in subsequent lithographic exposures. This feedback loop enables manufacturing precision improvement by continuously measuring and correcting overlay errors, reducing the need for complex pre-computation fine-tuning steps.
Solution Approach 2:
The patent replaces complex mechanical and computational fine-tuning systems with a measurement-based approach. Instead of using sophisticated control loops to predict and correct overlay errors, the system directly measures actual overlay using scatterometry and corrects based on real measurements, simplifying the overall system complexity.
3Manufacturing precision
If frequent measurements are made for process control, then manufacturing precision is improved, but productivity decreases due to measurement time
Solution Approach 1:
The patent performs overlay measurements at intermediate stages of the manufacturing process, such as after resist coating or during alignment, rather than waiting for final fabrication. This preliminary measurement action enables early detection and correction of overlay errors, allowing frequent measurements without significantly impacting overall production throughput.
Solution Approach 2:
The patent integrates scatterometry measurements into the continuous lithographic process flow, enabling measurements to be taken during or between fabrication steps without stopping production. This continuous measurement approach maintains manufacturing precision while minimizing productivity impact by eliminating idle measurement time.
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
Enables accurate and efficient measurement of overlay values and other substrate characteristics, improving pattern reproduction and process control in lithographic processes by enhancing the ability to detect subtle displacements and features at the limit of resolution.
Implementation Method 1
an optical system (420) configured to transmit radiation from the source (410) through the structure (460) onto the sensor (440)
Implementation Method 2
a blocking element (428) configured to block the transmission of the zeroth order of the scattered radiation towards the sensor (440)
Data Source
AI summary
A computer program product causes a processor to execute a process of causing an optical system to illuminate at least one structure on a substrate that comprises first repetitive features at a first pitch in a first layer and second repetitive features at a second pitch in a second layer, the first repetitive features at least partially overlapping with the second repetitive features. The first pitch is different from the second pitch. The processor causes the optical system to receive radiation scattered by the at least one structure and transmit a portion of the received scattered radiation to a sensor arranged in an image plane of the optical system or in a plane conjugate with the image plane for detecting the received scattered radiation and configured to detect a characteristic of radiation impinging on the sensor. The processor then determines a characteristic of interest of the structure.