Overlay Error Measurement Using Spectral Segmentation
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Solution Overview
Problem
Current methods for measuring overlay error between successive layers in lithographic processes are not accurate enough, as they rely on linear relationships between intensity variations and offset, which can be affected by second harmonic components, leading to measurement errors.
Innovation Solution
Forming periodic structures with the same pitch on each layer, offset relative to each other, and measuring specific portions of the spectrum where the relationship between the offset and intensity variation is more linear, allowing for precise calculation of overlay error using angularly resolved scatterometers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the relationship between intensity variation and offset is assumed to be linear for overlay error measurement, then the measurement process is simple, but the measurement precision deteriorates due to second harmonic components
Solution Approach 1:
The spectrum is divided into multiple portions, and specific portions are selected for overlay error measurement. By segmenting the spectrum and choosing portions with more linear characteristics, the method maintains measurement simplicity while improving precision by avoiding portions affected by second harmonic components.
Solution Approach 2:
Different portions of the spectrum are evaluated for their linearity characteristics, and portions with more linear relationships between intensity variation and offset are selected for measurement. This local quality approach ensures that measurement is performed on the most suitable spectral regions, balancing simplicity and precision.
2Ease of operation
If the entire spectrum is used for overlay error measurement, then the measurement process is straightforward, but the reliability deteriorates due to second harmonic effects
Solution Approach 1:
The spectrum is segmented into multiple portions, and specific portions are selected for measurement. This segmentation allows the method to maintain straightforward measurement processes while improving reliability by excluding portions contaminated by second harmonic effects.
Solution Approach 2:
The method extracts and selects specific portions of the spectrum that have more linear characteristics and are less affected by second harmonic components. By taking out only the useful portions for measurement, the method maintains process straightforwardness while enhancing reliability.
3Measurement precision
If periodic structures with the same pitch are formed on each layer, then the overlay error can be measured, but the manufacturing precision requirement increases
Solution Approach 1:
The method uses periodic structures with the same pitch as a controlled parameter, and by measuring the spectral characteristics of these structures, overlay error is determined. The parameter change approach allows overlay measurement while maintaining manufacturable precision requirements for structure formation.
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 the accuracy of overlay error measurement by reducing the impact of second harmonic effects, resulting in a more reliable determination of layer alignment in lithographic processes.
Implementation Method 1
One form of specialized inspection tool is a scatterometer, in which a beam of radiation is directed onto a target on the surface of the substrate and properties of the scattered or reflected beam are measured
Implementation Method 2
properties of the scattered or reflected beam are measured. By comparing the properties of the beam before and after it has been reflected or scattered by the substrate
Implementation Method 3
Any overlay errors are measured by measuring asymmetry in the reflected spectrum from the two overlaid gratings
Data Source
AI summary
An overlay error between two successive layers produced by a lithographic process on a substrate is determined by using the lithographic process to form at least one periodic structure of a same pitch on each of the layers. One or more overlaid pairs of the periodic structures are formed in parallel, but offset relative to each other. A spectrum, produced by directing a beam of radiation onto the one or more pairs of periodic structures is measured. One or more portions of the spectrum are determined in which the relationship between the offset between the one or more pairs of periodic structures and the resultant variation in measured intensity of the spectrum at the one or more portions is more linear than the relationship outside the one or more portions. The offset between the one or more pairs of periodic structures on the basis of intensity measurements of the spectrum in the one or more portions of the spectrum is determined and used to determine the overlay error.