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Auf dem Weg zu Industrie 4.0: Bestimmung von Messunsicherheitsbudgets in der Oberflächentechnik
(2019)
Vorgestellt wurde die Bestimmung von Messunsicherheitsbudgets für sehr unterschiedliche physikalische Größen, die in der Oberflächentechnik von hoher Relevanz sind: Stufenhöhe h, Schichtdicke d, Eindringhärte HIT und Haftfestigkeit. Die Unterschiede betreffen die Art der Prüfmethodik (optisch zerstörungsfrei vs. mechanisch invasiv/zerstörend), die laterale Größe des Integrationsgebietes der Messung (lokal: nano bis sub-mikro vs. global: mikro bis makro) und die Art der Bestimmung von Messunsicherheitsbudgets (physikalische Größen: direkt rückführbar; Werkstoffkenngröße: genormt; Systemkenngröße: genormt).
Im Rahmen von Industrie 4.0 werden ausgehend der geforderten Spezifikation des beschichteten Produkts (Mittelwert mit Vertrauensbereich oder Mindestwert) durchgehende Toleranzbänder zur Oberflächenmodifizierung/Beschichtung des Substrats, einhergehend mit Prozessfenstern, die diese Toleranzbänder garantieren, erforderlich, die zuverlässig erfasst werden müssen. Die Frage der anzuwendenden Mess- und Prüftechnik und die damit notwendige Betrachtung von Messunsicherheitsbudgets ist für die Digitalisierung von Konditionierungs-, Zustands-, Regel- und Steuergrößen unverzichtbar. Mit Blick auf die Einhaltung von Prozessfenstern und die dafür notwendige Prozessführung wird technologisches Kern-Know-how digitalisiert, das es unbedingt zu schützen gilt. Nur lokale Netze können diese Sicherheit garantieren, in globalen Netzen ist die Datensicherheit bestenfalls maximierbar
In this study, thickness related changes of the optical properties of doped tin oxide were studied. Two different sets of samples were prepared. The first set was doped with iron or nickel on silicon substrate with thicknesses of 29–56 nm, the second was iron doped on gold/glass substrate with 1.6–6.3 nm. The optical constants were determined by using spectral ellipsometry (SE) followed by modelling of the dielectric function with an oscillator model using Gaussian peaks. The analysis of the optical constants shows a dependence of the refraction and the absorption on the thickness of the doped tin oxide coating. In addition to the tin oxide absorption in the UV, one additional absorption peak was found in the near-IR/red which is related to plasmonic effects due to the doping. This peak shifts from the near-IR to the red part of the visible spectrum and becomes stronger by reducing the thickness, probably due to the formation of metal nanoparticles in this layer. These results were found for two different sets of samples by using the same optical model. Afterwards the second sample set was tested in the Surface Plasmon Resonance Enhanced Ellipsometric (SPREE) gas measurement with CO gas. It was found that the thickness has significant influence on the sensitivity and thus the adsorption of the CO gas. By increasing the thickness from 1.6 nm to 5.1 nm, the sensing ability is enhanced due to a higher coverage of the surface with the over coating. This is explained by the high affinity of CO molecules to the incorporated Fe-nanoparticles in the tin oxide coating. By increasing the thickness further to 6.3 nm, the sensing ability drops because the layer disturbs the SPR sensing effect too much.
Coatings deposited by magnetron co-sputtering from a single RF magnetron with a ceramic SnO2 target with iron inset in argon plasma were studied. The mass spectra of the process identified Sn+ and SnO+ species as the dominant species sputtered from the target, but no SnO2+ species were detected. The dominant positive ions in argon plasma are Ar+ species. The only detected negative ions were O-. Sputtered neutral tin related species were not detected. Iron related species were also not detected because their concentration is below the detection limit.
The concentration of iron dopant in the tin oxide coatings was controlled by the RF bias applied on the substrate holder while the discharge pressure also has some influence. The iron concentration was in the range from 0.9 at.% up to 19 at.% increasing with the substrate bias while the sheet resistivity decreases. The stoichiometry ratio of O/(Sn + Fe) in the coatings increased from 1.7 up to 2 in dependence on the substrate bias from floating bias (- 5 V) up to - 120 V of RF self-bias, respectively. The tin in the coatings was mainly bonded in Sn4 + state and iron was mainly in Fe2 + state when other tin bonding states were detected only in a small amounts. Iron bonding states in contrary to elemental compositions of the coatings were not influenced by the RF bias applied on the substrate.
The coatings showed high transparency in the visible spectral range. However, an increased metallic behavior could be detected by using a higher RF bias for the deposition. The X-ray diffraction patterns and electron microscopy pictures made on the coatings confirmed the presence of an amorphous phase.
The 7th International Conference on Spectroscopic Ellipsometry (ICSE-7) was held in Berlin in June 2016, jointly organised by ICSE and BAM. The publication of the proceedings special issue in Applied Surface Science follows this event. In the special issue, about 100 articles on current topics of optics and surface science related to ellipsometry, polarimetry, and similar techniques are presented, underpinning the high significance of these techniques for many fields of materials science.
An ellipsometric gas sensor based on the surface Plasmon resonance (SPR) effect of ~ 43 nm thick gold layers was investigated. To protect the gold layer from contamination and to improve the detection limits, the gold layers were top-coated with 5–6 nm thick layers of organic a-C:H or with inorganic metal oxides TiO2 or ZrO2. The additional layers increased the long-term stability, whereas the metal oxide layers protect better than a-C:H. Furthermore, the additional layers decreased the detection limits by one order of magnitude in case of a-C:H and two orders of magnitude in case of the oxides. It could be shown that the detection limits also depend on the kind of preparation (sol–gel process or physical vapour deposition) of the additional layers.
Standardisation of ellipsometry is mainly based on three documents: pioneering work at NIST [1] on film standards, a publicly available specification and stan-dard testing procedure [2] for real-world samples by BAM and a standard specification for integrated metrology by SEMI [3]. Other activities refer to inter-laboratory comparisons for selected layer/substrate systems and analytical methods including ellipsometry [4] and the development of combined standards for thickness d and step height h [5].
Generally, precision of ellipsmetry in terms of raw data Ψ and Δ meets the major demands for all ellipsometric principles (RPE, RAE, PME, RCE, NE).
As a result, fingerprint capabilty is al-most perfect for various layer/substrate systems. However, this is not true for accuracy in terms of physical quantities such as thickness d, optical (n, k) and dielectric constans (ε1, ε2,) as modelling is required. Hence, the layer/substrate and material dependent validation of models is nowadays a key issue.
In contrast to the sub-nanometer sensi-tivity in vertical direction, the effective lateral resolution of almost all ellipso-metric principles except for imaging null
ellipsometry is rather poor, usually be-yond 100 µm.
Hence, nanometer-scaled homogeneity testing and the measurement of micro- and nanopatterned structures is not feasible by standard configurations.
Public, hidden, and forensic features either encoded or directly legible are used for authentication. Fabry-Perot layer stacks as information carriers in combination with imaging ellipsometry as optical read-out system provide all-in-one anti-counterfeiting capability that may establish the new security level 'encoded forensic'. Different layer designs are described with regard to all three security levels: public features (e.g. color and tilt effect) perceptible by the human eye, hidden features (e.g. spectroscopic response in the UV or IR), and forensic features (ellipsometric quantities Ψ and Δ as a function of wavelength λ and angle of incidence AOI). Physically uncloneable functions (PUF) could be realized as a result of a multi-material and a multi-parameter deposition approach as well as by means of specific design features of the Fabry-Perot layer stack. Hence, they are not subject to any reverse engineering strategies. Examples of stratified, micro-structured, and laser-modified Fabry-Perot layer systems are considered that may be used at all perception levels (e.g. human eye, bar code reader, and imaging ellipsometry) for authentication against product counterfeiting and related areas. --------------------------------------------------------------------------------------------------------------------
Zur Authentifizierung werden offene, versteckte und forensische Merkmale entweder codiert oder direkt auslesbar verwendet. Mit Fabry-Perot Schichtsystemen als Informationsträger in Kombination mit der abbildenden Ellipsometrie als optischem Auslesesystem steht ein 'all-in-one' Fälschungsschutz-System zur Verfügung, das ein neues Sicherheitsniveau 'kodiert-forensisch' darstellt. Es werden unterschiedliche Schichtdesigns beschrieben, mit denen alle drei Sicherheitsniveaus realisiert werden können: offene Merkmale (z.B. Farbe und Kippeffekt), die mit dem menschlichen Auge wahrnehmbar sind, versteckte Merkmale (z.B. die spektrale Antwort im Sichtbaren oder im IR) sowie forensische Merkmale (ellipsometrische Größen Ψ und Δ als Funktion der Wellenlänge λ und des Einfallswinkels AOI).
Physikalisch nicht klonbare Funktionen (PUF) können im Ergebnis einer Multi-Material- und Multi-Parameter Beschichtungsstrategie sowie durch spezifische Design-Merkmale des Fabry-Perot Schichtsystems realisiert werden. Folglich sind solche Schichtsysteme dem 'reverse engineering' nicht zugänglich. Es werden Beispiele für lateral ausgedehnte, mikrostrukturierte und Laser modifizierte Schichtsysteme auf verschiedenen Ausleseniveaus (menschliches Auge, Barcode-Lesegerät, abbildendes Ellipsometer) vorgestellt, die zur Authentifizierung von Produkten und verwandte Gebiete geeignet sind.
The irradiation of ~0.9-µm-thick hydrogenated amorphous carbon (a-C:H) layers deposited on silicon substrates with single femtosecond (fs) laser pulses (35 fs pulse duration, 790 nm centre wavelength) in air is studied experimentally. Irradiation spots have been generated with different peak fluences and subsequently investigated by optical topometry, micro Raman spectroscopy and microscale mechanical indentation in order to evaluate their microscopic, topographical, structural and mechanical properties (e.g. elastic modulus). By this multi-method approach, a clear separation of different effects (delamination and graphitisation) becomes possible. The joint application of mechanical and spectroscopic techniques provides unique insights into the effects of the fs-laser radiation on the carbon layer.