Capacitance Ratio Overlay Measurement for Buried Chip Structures
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Solution Overview
Problem
Current overlay measurement techniques in the semiconductor industry face challenges in accurately measuring relative displacements of structures on a chip, particularly when these structures are buried beneath insulator films, as they often rely on optical methods that are limited by feature size and require separate targets that do not resemble high-resolution features, leading to inefficiencies and inaccuracies.
Innovation Solution
The use of charged particle beams to perform overlay measurements by determining capacitance ratios between symmetrically arranged conductive elements on a substrate, which changes due to relative displacements, enabling precise detection of overlay errors through voltage contrast imaging and capacitance imbalance analysis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If optical methods are used for overlay measurement, then measurement can be performed on visible structures, but measurement precision deteriorates for buried structures and high-resolution features
Solution Approach 1:
The patent replaces optical measurement methods with charged particle beam methods. The charged particle beam (electrons or ions) interacts with the substrate to generate signals that reveal overlay information, enabling precise measurement of both surface and buried structures that are inaccessible to optical methods.
Solution Approach 2:
The patent changes the measurement parameter from optical properties to electrical properties (capacitance). By measuring capacitance ratios between symmetrically arranged conductive elements, the system achieves high-precision overlay measurement that is sensitive to sub-nanometer displacements, overcoming the resolution limits of optical methods.
2Measurement precision
If separate dedicated targets are used for overlay measurement, then overlay can be measured, but the targets do not resemble high-resolution features and require additional fabrication steps
Solution Approach 1:
The patent makes the conductive elements serve dual functions: they are both functional circuit elements and overlay measurement targets. The symmetrically arranged conductive elements that are already part of the device architecture can be used for capacitance-based overlay measurement, eliminating the need for separate dedicated targets.
Solution Approach 2:
The patent merges the overlay measurement function with the functional circuit elements. By using the device's own conductive elements as measurement targets, the system combines manufacturing and measurement purposes into a single integrated approach, reducing fabrication complexity.
3Measurement precision
If charge injection elements are added to the substrate, then overlay measurement can be performed, but measurement time increases and sensitivity is reduced
Solution Approach 1:
The patent uses the substrate's existing conductive elements to perform the measurement function. The symmetrically arranged conductive elements inherently provide the measurement capability through their capacitance characteristics, eliminating the need for separate charge injection elements and reducing measurement time.
Solution Approach 2:
The patent changes from time-intensive charge injection methods to rapid capacitance ratio measurement. By measuring the electrical properties (capacitance) of existing conductive elements, the system achieves high sensitivity without the time penalty of charge injection and relaxation processes.
4Measurement precision
If capacitance ratio measurement is used, then overlay measurement sensitivity is improved, but the system requires precise control of electrical properties
Solution Approach 1:
The patent uses symmetrically arranged conductive elements where the symmetry itself provides the measurement reference. Any overlay displacement breaks the symmetry and creates a measurable capacitance ratio change. This geometric symmetry simplifies the electrical control requirements while maintaining high measurement sensitivity.
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 method allows for accurate, high-resolution overlay measurements without the need for dedicated charge injection elements, reducing measurement time and improving sensitivity while eliminating tradeoffs between sensitivity and observation interface requirements, thereby enhancing the yield of semiconductor manufacturing processes.
Implementation Method 1
determining a first capacitance of a first pair of elements and a second capacitance of a second pair of elements
Implementation Method 2
voltage contrast based on charged particle beams
Implementation Method 3
when the first through third elements become asymmetric, a capacitance imbalance is formed
Data Source
AI summary
A method of determining an overlay measurement of a substrate includes: injecting charge into a charge injection element of the substrate; determining a first capacitance of a first pair of elements and a second capacitance of a second pair of elements; and determining a capacitance ratio based on the first capacitance and the second capacitance. The overlay measurement may be determined based on the capacitance ratio, which may indicate an imbalance.