Single-Cell Overlay Metrology via Parallax Effect
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Solution Overview
Problem
Scatterometry overlay metrology techniques require alignment to multiple cells, leading to reduced measurement throughput and potential inaccuracies due to navigation calibration errors, and are often too large for certain sample areas, resulting in reduced yield.
Innovation Solution
A system and method utilizing a single-cell overlay metrology approach with off-axis illumination, generating effective stack heights and overlay measurements by exploiting the parallax effect, allowing for efficient measurement of a single cell with no intended offset, similar to multiple cells with physical offsets, thereby improving measurement efficiency and reducing target size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple cells are used for overlay measurement, then measurement accuracy is improved, but measurement throughput deteriorates and device size increases
Solution Approach 1:
The patent segments the overlay measurement function into two parts: (1) a calibration step using multiple cells to determine effective stack heights, and (2) a measurement step using a single cell with the pre-determined stack heights. This segmentation allows the system to achieve single-cell measurement speed while maintaining multi-cell accuracy through the calibration cache mechanism.
Solution Approach 2:
The patent performs preliminary calibration measurements on multiple cells to determine effective stack heights before actual overlay measurements are needed. These pre-determined stack heights are stored in a cache and reused for subsequent single-cell measurements, eliminating the need to repeatedly measure multiple cells for each overlay assessment.
2Measurement precision
If multiple cells are used for overlay measurement, then measurement accuracy is improved, but device complexity and size increase
Solution Approach 1:
The patent separates the calibration function (performed once on multiple cells) from the measurement function (performed on single cells). This allows the measurement target to be simplified to a single cell while maintaining accuracy through the pre-acquired stack height information stored in the calibration cache.
Solution Approach 2:
The patent creates a calibration cache that stores effective stack height information obtained from multiple cells. This cached information is then copied and applied to single-cell measurements, allowing the system to use simplified single-cell targets while leveraging the accuracy benefits of multi-cell calibration data.
3Measurement precision
If multiple cells with different offsets are used, then overlay measurement is achieved, but navigation calibration errors and unintended differences between cells introduce inaccuracies
Solution Approach 1:
The patent uses the single cell to self-determine its overlay measurement by utilizing its own diffraction signal in combination with pre-calibrated effective stack heights. This self-service approach eliminates the need for complex inter-cell comparisons and reduces errors from navigation calibration and cell-to-cell variations.
Solution Approach 2:
The patent replaces the mechanical/physical approach of using multiple physically-offset cells with an optical/computational approach. By using off-axis illumination and calculating effective stack heights from diffraction signals, the system achieves overlay measurement without relying on physical cell offsets, thereby eliminating navigation calibration errors.
4Productivity
If single-cell measurement is implemented, then measurement throughput and yield are improved, but measurement accuracy may deteriorate
Solution Approach 1:
The patent performs preliminary calibration to determine effective stack heights from multiple cells before conducting single-cell measurements. This preliminary action ensures that the single-cell measurements are based on accurate, pre-characterized stack height information, maintaining measurement accuracy while achieving high throughput.
Solution Approach 2:
The patent introduces effective stack heights as an intermediary parameter that bridges the gap between multi-cell calibration data and single-cell measurements. The stack heights serve as a mediator that allows single-cell diffraction signals to be accurately interpreted for overlay determination without requiring actual multi-cell measurements.
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 approach enhances measurement efficiency and target size by allowing single-cell measurements, reducing the number of cells needed and improving accuracy by using the parallax effect to determine overlay measurements similar to those from multiple cells with intended offsets.
Implementation Method 1
scatterometry overlay metrology techniques
Implementation Method 2
exploiting the parallax effect, allowing for efficient measurement of a single cell
Data Source
AI summary
An overlay metrology system may illuminate overlay targets sample with a dipole pair of illumination beams, generate a first set of metrology data associated with two or more cells having nonzero offset values from a first set of the overlay targets, determine overlay measurements for the first set of overlay targets, determine effective stack heights representative of an effective distance between layers at the locations of the first set of the overlay targets, generate a second set of metrology data from a second set of the overlay targets, determine the effective stack heights at locations of the second set of the overlay targets based on the first effective stack heights, and determine overlay measurements for the second set of overlay targets based on the effective stack heights at the locations of the second set of the overlay targets and the second set of metrology data.