Multi-Pitch Overlay Target Layout for Fast Scanning Metrology
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Solution Overview
Problem
Current overlay metrology systems face challenges in achieving accurate and efficient measurements due to time-consuming static measurement approaches and errors introduced by various sources, while also requiring valuable wafer footprint space for compact pitch designs.
Innovation Solution
An overlay metrology system that uses a single-cell overlay target with different pitches in each direction to minimize cross-talk, allowing for simultaneous data capture of time-varying signals in both X and Y directions, and a compact design that reduces footprint size, utilizing a controller with processors to execute metrology recipes and determine overlay measurements from detection signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a static move and measure approach is used for overlay metrology, then measurement accuracy is improved, but throughput decreases due to translation stage settling time
Solution Approach 1:
The patent transitions from a static measurement approach to a dynamic scanning approach where the overlay target is scanned across the measurement field of view while collecting time-varying signals. This eliminates the need for translation stage settling time between measurements, thereby improving throughput while maintaining measurement accuracy through continuous signal acquisition during motion.
2Area of moving object
If overlay targets with multiple pitches are used to minimize footprint space, then area is reduced, but cross-talk between signals increases
Solution Approach 1:
The patent segments the overlay target into multiple isolated cells, each containing grating structures with different pitches. By spatially separating the pitch measurements into distinct cells and using a scanning approach that sequentially measures each cell, the system minimizes cross-talk between different pitch signals while maintaining a compact overall footprint on the wafer.
Solution Approach 2:
The patent assigns different local properties to different regions of the overlay target by using different pitches in different cells. Each cell is optimized for measuring a specific pitch in a specific direction, and the scanning system sequentially activates measurement in each local region, thereby minimizing cross-talk while achieving comprehensive overlay measurement in a compact footprint.
3Measurement precision
If a single-cell overlay target with different pitches in each direction is used, then cross-talk is minimized and measurement accuracy is improved, but footprint space increases
Solution Approach 1:
The patent merges multiple measurement functions into a single scanning system that can measure different pitches in different directions by scanning across a multi-cell overlay target. Instead of requiring separate measurement systems or larger single-cell targets, the system combines multiple compact cells into an integrated target structure that achieves the same measurement capabilities with reduced overall footprint.
Data Source
AI summary
An overlay metrology system with pitches in multiple directions in a single cell is disclosed. The overlay target may, according to a metrology recipe, include a multi-layer structure on two or more layers of a cell of the sample. The multi-layer structure may include structures in each layer having one or more pitches in one or more directions of periodicity. The multi-layer structure may include structures with a first pitch in a first direction, a second pitch in a second direction, a third pitch in the first direction, and a fourth pitch in the second direction. At least one of the first pitch or the third pitch may be different than at least one of the second pitch or the fourth pitch.