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The optics and semiconductor industries make increasing use of innovative materials and complex nanostructures, whose optical properties are difficult to measure and often not accurately known. This project addresses the development of traceable metrology and advanced mathematical methods to characterize these materials for wavelength ranges from soft-X ray to IR. A database including optical constants with associated uncertainties for bulk materials and ultrathin-film systems and industrially relevant datasets will be set up. This tool is crucial for simulations and design of materials with tailored properties, enabling innovations by development of novel materials and devices in semiconductor industries and nanotechnologies.

WP1: Reference samples and advanced materials

The aim of this work package is to identify, select, design, produce and pre-characterize test samples including ultra-thin layer systems, complex nanostructures (e.g. nanosheets, PillarHalls) and other novel materials (e.g. high-k materials). Within the framework of this work package, 3 case studies will be implemented to produce reference samples for the development of the experimental uncertainty budgets and for the comparative studies of the various measurement instruments of the project partners in WP2. In order to exclude or identify and characterize uncertainties in the sample preparation which could influence the evaluation of the optical constants later, extensive preliminary investigations are carried out by the project partners involved in the preparation. In this pre-characterization, dimensional parameters such as layer thickness, grating linewidths, surface roughness, and other possible impurities and contaminations are addressed. Most of the tools for pre-characterization belong to the usual equipment of the partners specialized in the production of nanostructured surfaces. If very specific questions arise which a partner cannot solve with existing equipment alone, an intensive exchange between the partners is envisaged.

In addition to the reference samples (the case studies), which are essential for the development of a new standard for the determination of optical material parameters, novel nanostructured samples will be produced in the framework of this WP. Examples are more complex layer systems like state-of-the-art 2D or 3D nanostructured surfaces, which will be supplied directly by the project partners from the industrial community. Layered samples with novel high-k materials can be used to apply the methods developed in WP2 and WP3,and extend the data sets for the database developed in WP4. In order to meet the rapidly changing interests in the field of nanotechnology, the needs and preferences of the project partners and stakeholders will be determined through a survey. This survey is also necessary since not all additional samples can be investigated by the whole project consortium. Furthermore, the requirements for sample design and the possibilities of reflectometry, ellipsometry or scatterometry are often conflicting, as well as there are different metrological challenges connected to these samples.

WP2: Traceability of advanced photon-based metrology

This work package represents the instrumental backbone of the JRP. All the measurement techniques, which are needed to obtain a reliable determination of optical constants in thin films materials, including samples endowed with complex geometries, will be developed and characterized in this WP. The goal is to provide the European industrial and metrology communities with a set of instruments that can serve as a metrological reference for further developments and to provide guidelines for the realization of reliable instruments from the X-ray to the IR spectral range. Different techniques have been developed in the last years that are suitable to unveil key information on the physical properties of materials and in this WP those methods are fully promoted to metrology grade. Task 2.1 is about the development of methods, and comprehensive characterization of the instruments available in the consortium, to make those instruments qualify as traceable. In this way, they can provide the reliable measurement data used to feed the database. Since no single technique is able to offer solutions which are valid for all materials and geometries, this task aims to perform a thorough characterization of reflectometers, Mueller ellipsometers, and scatterometers operating in soft X-ray, EUV, optical (from UV to NIR) and IR range of the electromagnetic spectrum. Partners will evaluate the impact on the instruments and samples of the environment, define alignment strategies and draft existing uncertainty budgets. The primary goal is the exchange of knowledge among partners and the generation of a standardized measurement procedure under similar sample environments. This goal cannot be fully achieved by various physical constraints, but the differences must be recognized and identified in order to process them in the analysis performed in WP3 and WP4. In addition to this, some of the advanced mathematical methods, measurement equations and approaches to compute the uncertainty budgets of the measurements are improved in WP3, in order to enhance the traceability of the measurements.

WP3: Advanced inverse modelling and uncertainty evaluation

The aim of the work package is the efficient, reliable inverse modelling of scatterometry, Mueller ellipsometry, reflectometry and the determination of reliable uncertainties for different materials, geometries selected as test samples and for wavelengths from soft-x ray to IR. For this purpose, the work package will develop advanced models and software tools for the measurement data analysis. The work package comprises four tasks. In the first task, different approaches for modelling are summarized and adapted to allow a uniform collection of forward models describing different materials and wavelengths. While models considered in the first task are based on the assumption that the measurement can be performed perfectly and without any perturbations, the second task deals with extended modelling including perturbations caused by imperfections (depolarization/decoherence), roughness and statistical measurement errors present in real measurements. In the third task, the results from the first two tasks are used to solve the statistical inverse problem for the different measurement methods. In particular, the uncertainties (type A and B) and error models determined in WP2 are included in the inverse modelling. This results not only in an estimation of the required parameters, but also in a reliable estimation of their uncertainties. In the fourth and last task, advanced techniques like DNN, PC-approximations and tensor decomposition are used to make inverse modelling more efficient and to speed up data analysis. The uncertainties from the approximations are estimated by additional error models to be developed. By using the forward models, error models and the full uncertainty budget, we will perform virtual experiments considering different measurement setups and test samples that will be used in this project. The software developed for data analysis will be made available to all participants and the general public as open source collection of software tools.

WP4: Determination of optical constants and assembling of a database

The aim of the work package is the determination of optical properties for thin film systems and the reconstruction of nanostructures using the novel measurement techniques developed in WP2 and WP3 for reflectometry, Mueller ellipsometry and scatterometry. In this WP4 optical constants or dielectric tensors of the layer systems and nanostructures are measured for the test samples and indicated including the uncertainties. The results and additional metadata will be used to compile a database which will be made available to the public. The metadata contain information on the measurement process such as instruments or environment parameter and details of the model used. WP4 consists of three tasks. In task one optical constants and associated uncertainties are determined for ultra-thin layer systems and substrates. The results are collected for the database for optical constants. The second task explores nanostructures and a known problem in their reconstruction. It is state-of-the art to use optical constants by using the relevant tables for reconstructions, without knowing the quality of the information or uncertainties. In task 2 a comprehensive study explores this issue and provide resulting the data sets and a scientific report. The core of the 3 tasks is to build a database and to provide the measurement data including uncertainties, metadata and data sets from the case studies.

WP5: Creating impact

The goal of this work package is to ensure the immediate and wider impact and uptake of this project in the European metrology, science, and end user communities related to the methods of spectroscopic ellipsometry and scatterometry. This will include all users and interested parties within the Euramet countries, whether taking part in the EMPIR activity or not. The work of the project will be transferred via different activities, ensuring immediate uptake as well as wider long-term dissemination. This will be achieved via a combined strategy comprising scientific communication (articles, conferences), engaging with standards bodies, stakeholder relations (stakeholder committee, workshops), as well as training and education. Various digital activities will support the presence of the dissemination work of the project.