Spectral Interferometry for Thick Transparent Layer OCD Metrology
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Solution Overview
Problem
Scatterometry methods struggle to accurately measure thick, transparent structures due to fast spectral oscillations, requiring high spectral resolution that increases complexity, cost, and is not scalable, leading to sensitivity loss and computational challenges.
Innovation Solution
A spectral interferometry system with an interferometer and processing circuit that extracts coherent reflectivity by OPD matching, using a novel measurement sequence and algorithm to separate coherent and incoherent signals, enabling accurate measurement of thick transparent layers without additional hardware.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high spectral resolution is used to measure fast spectral oscillations in thick transparent structures, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The measurement process is segmented into two distinct phases: first measuring the incoherent reflection spectrum without the sample, then measuring the interferometric signal with the sample. This segmentation allows the use of a standard spectrometer for the first measurement and a simpler interferometric setup for the second, avoiding the need for a complex high-resolution spectrometer throughout.
Solution Approach 2:
An interferometer is introduced as an intermediary device between the light source and the spectrometer. The interferometer modulates the optical path difference to encode depth information, allowing a standard spectrometer to effectively resolve features that would otherwise require high spectral resolution.
2Measurement precision
If high spectral resolution is used to resolve fast spectral oscillations, then measurement precision is improved, but manufacturing cost increases
Solution Approach 1:
The system is segmented into two functional components with different resolution requirements: a standard spectrometer for capturing the overall spectral envelope and an interferometric measurement system for extracting depth-resolved reflectivity information. This segmentation allows the use of lower-cost, commercially available spectrometers rather than expensive high-resolution instruments.
Solution Approach 2:
The system changes the measurement parameter from direct spectral resolution to optical path difference modulation. By varying the OPD in the interferometer, the system extracts depth information that would otherwise require high spectral resolution, thereby reducing the cost of the spectrometer.
3Device complexity
If standard spectral resolution is used for thick transparent layers, then device complexity is reduced, but measurement precision is lost due to spectral feature smearing
Solution Approach 1:
The interferometer acts as an intermediary that compensates for the limited spectral resolution of the spectrometer. By introducing optical path difference modulation, the interferometer encodes depth information in the temporal domain, allowing a standard spectrometer to effectively resolve spectral features that would otherwise be smeared.
Solution Approach 2:
The system transitions from a one-dimensional spectral measurement to a two-dimensional measurement by adding the optical path difference dimension. This additional dimension allows the system to resolve depth information that would otherwise be lost due to limited spectral resolution, effectively trading spectral resolution for temporal modulation.
4Measurement precision
If OPD matching is used to extract coherent reflectivity, then measurement precision for thick layers is improved, but measurement time increases
Solution Approach 1:
The interferometer performs periodic modulation of the optical path difference, scanning through a range of OPD values. This periodic action allows the system to accumulate interferometric data that can be processed to extract coherent reflectivity information, balancing measurement time with precision through efficient scanning protocols.
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
Enables precise measurement of thick transparent layers across the entire spectral range, improving vertical resolution and revealing structural information, while maintaining measurement efficiency and reducing computational complexity.
Implementation Method 1
spectral interferometry system with an interferometer and processing circuit that extracts coherent reflectivity
Implementation Method 2
extracts coherent reflectivity by OPD matching, using a novel measurement sequence and algorithm to separate coherent and incoherent signals
Data Source
AI summary
A method for evaluating a thick transparent layer, the method includes (i) generating information about relationships between measurements of a spectrometer of an interferometer and optical path difference (OPD) values of the interferometer; wherein the generating of the information comprises illuminating the thick transparent layer by the interferometer: (ii) determining one or more thick transparent layer reflection parameters, based on the information about the relationship; and (iii) determining one or more structural properties of the thick transparent layer based on the one or more thick transparent layer reflection parameters.