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realistic modelling capability of the whole measurement process and system, the question of the traceability of the measurements is of highest importance for dimensional metrology. A straightforward method to achieve and prove traceability is the development, calibration and successful application of traceable reference standards to the SRMbased metrology method used [ 28 ]. The nanodiamond NV-centre material is a very promising option to realise suitable test structures for STED-like SRM. Low density NV-centre samples, where individual centres can be identified are excellent samples to characterise the PSF and with it the resolution of the method. And they can be arranged stochastically or deterministically as two-dot samples with calibrated distances to be useful for direct resolution measurements of the SRM.
For a planned alternative, high quality calibration grating structures may be utilized. These elements are fabricated by first deposition a chromium hard mask onto a silicon wafer by means of ion beam sputter deposition( Ionfab 300LC by OIPT) [ 80 ]. In a next step, HMDS adhesion promoter and 100 nm of electron beam sensitive OEBR-CAN038 AE 2.0CP( Tokyo Ohka Kogyo Co. LTD) is applied. This is subsequently patterned by a Vistec 350OS electron beam writer with character projection apertures [ 68 ]. Then, the pattern is transferred into the silicon substrate using the chromium as a hardmask by means of inductive coupled plasma etching( SI500C by Sentech Instruments GmbH). The remaining hardmask is removed and the samples are diced. The grating parameters such as period, linewidth and height etc. will then be calibrated by a traceable AFM [ 81 ]. Finally, a polymer layer is formed on top of the structures by means of spincoating. Into this polymer low concentration of nanodiamond powder containing NV centres is embedded, enabling STED measurements.
Potential reference structures for the calibration of the respective metrology systems are shown in Figure 17. Those target structures have been already manufactured, but are not yet treated with the nanodiamond layer. It contains line pairs with different distances, single dots with different diameters and pairs of dots with different distances. The later allow to directly assess the resolution limits.
Funding
This project( 20FUN02“ POLight”) has received funding from the EMPIR program co-financed by the Participating States and from the European Union’ s Horizon 2020 research and innovation program.
Conflicts of interest
The authors declare that they have no competing interests to report.
Data availability statement
This work has been fully performed within the EURAMET project 20FUN02 POLight and EURAMET projects all are in full agreement with the FAIR data principle. All research data associated with this article are available on request from the authors.
Author contribution statement
The work is a result of contributions from all authors. The work followed initial conceptualisation by Stefanie Kroker, Deb Roy and Bernd Bodermann. Mohammad Nouri and Bernd Bodermann collected the different partner input and drafted the basic manuscript. The samples have been designed, manufactured and provided by Paolo Olivero, Pietro Apra and Thomas Siefke, who also significantly contributed to the discussion of future reference standard samples in the conclusions. Ivano Ruo-Berchera significantly supported the design of different structured illumination creation and provided the work on super-resolution SIM by photon statistics evaluation( Sect. 3.1.3). Himanshu Tyagi and Deb Roy developed and performed the wide-field Raman SRM with hyperspectral extension, while Astrid Tranum Rømer and Poul Erik Hansen developed, performed and analysed measurements with through focus microscopy. Deshabrato Mukherjee and Peter Petrik provided the pre-investigations and measurements for plasmonic resonances required for the SUSY SRM technique( Sect. 3.2.3). Miroslav Valtr provided traceable measurements and dimensional characterisations of the different test samples used and strongly supported the measurement uncertainty evaluation processes and discussions. Tim Käseberg and Mohammad Nouri performed and analysed the STED investigations on the NV centre samples and together with Stefanie Kroker and Bernd Bodermann concepts for universal and versatile label-free-SRM and future follow-up work have been discussed.
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