Scatterometry Overlay Target with Disambiguation Features
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Solution Overview
Problem
Existing methods for determining overlay alignment in semiconductor manufacturing using scatterometry have limitations, including sub-optimal multi-cell targets and ambiguities in periodic signals, which affect the accuracy and repeatability of measurements.
Innovation Solution
The development of improved scatterometry overlay targets with periodic features in multiple layers and disambiguation features to resolve signal ambiguities, allowing for more accurate and repeatable overlay alignment measurements by analyzing spectra from these targets.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If sub-optimal multi-cell targets are used for scatterometry overlay measurement, then the measurement can be performed, but the accuracy and repeatability of the measurements deteriorate
Solution Approach 1:
The target is divided into multiple cells, each containing a specific arrangement of periodic features. By segmenting the target into distinct cells with different feature configurations, the patent enables differentiation between various overlay conditions while maintaining measurement accuracy. Each cell acts as an independent measurement unit that contributes to the overall overlay determination.
Solution Approach 2:
The patent employs asymmetric target designs where cells contain periodic features with intentional asymmetries in their arrangements. This asymmetry creates distinctive scatterometry signals that can be differentiated more effectively, improving measurement accuracy. The asymmetric configurations allow the measurement system to distinguish between small overlay variations that would be indistinguishable in symmetric designs.
2Measurement precision
If periodic features with different pitches are used in top and bottom layers, then overlay measurement capability is improved, but signal ambiguities occur
Solution Approach 1:
The patent introduces an intermediary reference signal or feature that mediates between the periodic features of different pitches. This intermediary element provides a common reference frame that allows the measurement system to interpret signals from features with different pitches unambiguously. The intermediary acts as a bridge that connects the different pitch domains and enables accurate overlay determination without signal confusion.
Solution Approach 2:
The patent resolves signal ambiguities by introducing additional measurement dimensions or parameters. Instead of relying solely on the periodicity signals from single-pitch features, the system uses multi-pitch features combined with additional measurement angles, wavelengths, or spatial positions. This dimensional expansion provides enough independent information to disambiguate the overlay measurement and eliminate periodic signal uncertainties.
3Reliability
If existing scatterometry methods are used, then overlay measurement is possible, but repeatability of measurements deteriorates
Solution Approach 1:
The patent incorporates preliminary calibration and reference measurements into the target design itself. The target includes built-in reference features and calibration structures that are prepared in advance during target fabrication. These preliminary elements enable the measurement system to automatically correct for variations and drift, improving repeatability without requiring extensive external calibration procedures for each measurement.
Solution Approach 2:
The patent employs multiple measurement parameters simultaneously, such as different wavelengths, angles of incidence, or polarization states. By changing and comparing multiple parameters, the system achieves more robust and repeatable measurements. The use of multi-parameter measurement allows the system to identify and correct for variations, ensuring consistent results across different measurement conditions and improving overall measurement reliability.
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
The improved target design enhances the accuracy and repeatability of overlay measurements, effectively addressing the limitations of existing methods by providing clearer and more precise data for overlay alignment.
Implementation Method 1
utilizing radiation scatterometry as a basis for overlay metrology
Data Source
AI summary
Embodiments of the invention include a scatterometry target for use in determining the alignment between substrate layers. A target arrangement is formed on a substrate and comprises a plurality of target cells. Each cell has two layers of periodic features constructed such that an upper layer is arranged above a lower layer and configured so that the periodic features of the upper layer have an offset and/or different pitch than periodic features of the lower layer. The pitches are arranged to generate a periodic signal when the target is exposed to an illumination source. The target also includes disambiguation features arranged between the cells and configured to resolve ambiguities caused by the periodic signals generated by the cells when exposed to the illumination source.