Single Cell Scatterometry Overlay Targets for In-Die Metrology
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Solution Overview
Problem
Existing scatterometry overlay metrology targets are limited by their size, leading to increased measurement noise and reduced accuracy due to shrinking node sizes in advanced photolithography processes, and require multiple measurements per target, which increases throughput and usage time.
Innovation Solution
The development of single-cell scatterometry overlay targets with a lattice of elements at two or more layers, periodic along multiple measurement directions, allowing for in-die measurements with reduced cell size and enhanced optical performance, enabling simultaneous measurement in multiple directions and reducing measurement time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional multi-cell scatterometry overlay targets are used, then measurement coverage is sufficient, but target size increases leading to pad-to-pad variations and reduced throughput
Solution Approach 1:
The target is divided into multiple periodic lattices (first lattice and second lattice) with different orientations within a single cell structure. Each lattice provides measurement capability in specific directions, enabling multi-directional overlay measurement within a compact footprint, thus reducing overall target size while maintaining measurement precision
Solution Approach 2:
The invention utilizes vertical layering with a cap layer containing the first periodic lattice and a bottom layer containing the second periodic lattice. This three-dimensional arrangement allows multiple measurement directions to be achieved within a small planar footprint, resolving the contradiction between measurement coverage and target size
2Manufacturing precision
If node sizes are shrunk for advanced photolithography processes, then device density increases, but measurement noise increases and accuracy decreases
Solution Approach 1:
The invention changes the measurement approach by using periodic lattices with carefully designed pitch parameters that are optimized for scatterometry measurements. The lattices are configured with pitch values suitable for the measurement wavelength, enabling accurate overlay measurement even when device features are shrunk to advanced nodes, thus decoupling device node size from measurement precision
3Measurement precision
If multiple measurements per target are performed, then measurement accuracy is improved, but throughput and usage time decrease
Solution Approach 1:
The invention merges multiple measurement capabilities into a single target cell by incorporating both the first periodic lattice and second periodic lattice within one cell. This allows simultaneous or single-measurement acquisition of overlay data in multiple directions, eliminating the need for multiple separate measurements and thereby improving throughput while maintaining accuracy
4Area of stationary object
If targets are placed far from devices in scribe lines, then real estate is sufficient, but measurement relevance to actual devices decreases
Solution Approach 1:
The single-cell target design with multi-directional lattices serves multiple measurement functions within a compact structure, making it suitable for placement in various locations including closer to devices. The target maintains its measurement capabilities across different positions, enabling both scribe line placement and in-die placement without sacrificing measurement relevance or requiring excessive wafer real estate
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 solution provides more accurate metrology results with reduced sensitivity to process variations, shorter measurement times, and higher throughput, while maintaining comparable performance to larger targets, allowing for placement closer to devices and reducing errors from pad-to-pad variations.
Implementation Method 1
scatterometry overlay metrology targets
Implementation Method 2
lattice of elements at least at two layers wherein: the lattice is periodic along at least two measurement directions
Data Source
AI summary
Scatterometry overlay (SCOL) single cell targets are provided, along with target design methods and measurement methods which employ the single cell SCOL targets for in-die metrology measurements, utilizing the small size of the target along with maintained optical performance due to the design of the target. Disclosed single cell targets comprise a lattice of elements at two or more layers which is periodic two or more measurement directions. Elements in different layers are offset with respect to each other and may have the same pitch along the measurement directions. Measurement algorithms are also provided to derive metrology measurements such as overlays from the single cell targets, possibly simultaneously in both (or more) measurement directions, reducing measurement time and enhancing the metrology throughput. Positioning the small targets in-die provides more accurate metrology results which are less sensitive to process variation.