Characterization of grain boundaries in multicrystalline silicon with high lateral resolution using conductive atomic force microscopy

In this work, the electrical characteristics of grain boundaries (GBs) in multicrystalline silicon with and without iron contamination are analyzed by fixed voltage current maps and local I/V curves using conductive AFM (cAFM). I/V characteristics reveal the formation of a Schottky contact between the AFM tip and the sample surface. The impact of both, the polarity of the applied voltage and the illumination by the AFM laser on the behavior of GBs was analyzed systematically. Depending on the polarity of the applied voltage and the iron content of the sample, grain boundaries alter significantly the recorded current flow compared to the surrounding material. The results also show a clear influence of the AFM laser light on the electrical behavior of the grain boundaries. Conductive AFM measurements are furthermore compared to data obtained by electron beam induced current (EBIC), indicating that cAFM provides complimentary information

Großflächige Herstellung plasmonischer Filterstrukturen mittels substratkonformer Imprintlithografie

Plasmonische Farbfilter werden im Bereich der Bildsensorik als möglicher Ersatz für aktuell verwendete Polymerfilter diskutiert. Um einen großtechnischen Einsatz dieser neuartigen optischen Filter zu ermöglichen, muss eine wirtschaftliche Lösung zur Herstellung der benötigten Nanostrukturen gefunden werden. Die Nanoimprintlithografie (NIL) bietet die Möglichkeit einer potentiell kostengünstigen Übertragung von Nanostrukturen durch einen Prägeprozess. Hierbei sind besonders Verfahren wie die substratkonforme Imprintlithografie (SCIL) von Interesse, die es erlauben, Substrate bis zu einem Durchmesser von 200 mm in einem einzigen Prozessschritt zu strukturieren. Aus diesem Grund wurde in der vorliegenden Arbeit die Eignung der SCIL für die großflächige Herstellung plasmonischer Filterstrukturen untersucht. Im Verlauf der Arbeit wurde zunächst nummerisch der Einfluss der Geometrie und der dielektrischen Umgebung der Filter auf das Transmissionsverhalten untersucht. Somit konnten verschiedene Prozessrouten identifiziert werden, um die Transmission in bestimmten Bereichen des Spektrums zu erhöhen bzw. zu unterdrücken, wobei erstmals die Einbettung der Filter in sogenannte Hybridpolymere in Betracht gezogen wurde. Im experimentellen Teil der Arbeit wurden zwei neuartige Verfahren zur Herstellung von Prägeformen entwickelt, die für die schrittweise Replikation mittels UV-NIL geeignet sind und damit für die Fertigung eines großflächig strukturierten Originalsubstrats für die spätere Abformung mittels SCIL in Frage kommen. Von besonderem Interesse ist dabei ein Ansatz, der das direkte Laserschreiben mit der hohen Auflösung der NIL verknüpft und eine innovative Lösung für die Fertigung hierarchischer Strukturen darstellt. Für die großflächige Herstellung der plasmonischen Filter wurden zunächst die einzelnen Schritte des SCIL-Prozesses optimiert. Dabei konnte nachgewiesen werden, dass sowohl das Aufbringen des Imprintlacks als auch die Belichtung während des Prägeprozesses einen großen Einfluss auf die Strukturübertragung besitzen. Durch die Optimierung des Imprintvorgangs konnten schließlich großflächige Filter auf Substraten von 100 mm und 150 mm Durchmesser hergestellt werden, deren aktive Fläche bisher veröffentlichte Werte um ein Vielfaches übertrifft. Darüber hinaus wurden erstmals die durch den SCIL-Prozess hervorgerufenen I II Defekte charakterisiert sowie die Defektdichte der hergestellten Filter abgeschätzt. Dabei konnte die mechanische Abnutzung der Prägeform als eine der Hauptursachen für die detektierten Fehlstellen identifiziert werden. Auf Basis der abgeschätzten Defektdichte konnte zudem die theoretische Ausbeute eines Halbleiterprozesses unter Verwendung der SCIL-Technologie hochgerechnet werden. Die Funktionalität der prozessierten Filter konnte abschließend durch Messungen an einem Spektrometer verifiziert werden. Vor allem die in dieser Arbeit erstmals untersuchte Kombination einer vergrabenen Wellenleiterschicht aus Siliciumnitrid mit einer Deckschicht aus Siliciumdioxid bzw. einem Hybridpolymer lieferte vielversprechende Ergebnisse. Zusammengefasst konnte im Rahmen der Arbeit nachgewiesen werden, dass die SCIL-Technologie grundsätzlich für die großflächige Herstellung plasmonischer Filter geeignet ist. Bevor die SCIL jedoch in einen Halbleiterprozess integriert werden kann, muss die Defektdichte der geprägten Strukturen verringert werden. Dazu sollten vor allem die mechanische Degradation der Prägeformen vermieden bzw. entsprechende Regeln bzgl. des Designs der abzuformenden Strukturen erarbeitet werden.Plasmonic colour filters are considered to be a major alternative to currently used polymer based filter solutions for image sensors. However, in order to enable the large-scale usage of these new optical filters, the required nanostructures have to be fabricated using a cost efficient lithography technique. Nanoimprint lithography (NIL) might be a solution for this challenge, offiering the cheap transfer of nanofeatures by embossing. Especially techniques like substrate conformal imprint lithography (SCIL), that enable wafer-scale pattern transfer on substrates up to 200 mm in diameter, can be of interest for the task at hand. Therefore, this thesis aims at assessing the potential of SCIL for the large area fabrication of plasmonic colour filters. Throughout the experimental part of the thesis, extensive numerical analyses were carried out in order to determine the influence of geometry and dielectric environment on the transmission behavior of the filters. Several process routes for enhancing or suppressing the transmission in different parts of the spectrum could be identified. In this context, the use of hybrid polymers as cladding layer for plasmonic color filters was investigated for the first time. By step & repeat UV-NIL a nanopatterned area of a few square centimeters can be scaled up, thus resulting in a possible large-scale master substrate for the following replication by SCIL. Therefore, two new approaches for the fabrication of UV-NIL molds were developed and verified. One of the approaches combines the high freedom of design offered by direct laser writing with the nanometer resolution of NIL, resulting in an innovative and promising way for the fabrication of hierarchical structures. For large area manufacturing of plasmonic colour filters the individual steps of the SCIL process were optimized. The results showed a great impact of the resist coating and the UV exposure on the structure transfer. By optimizing the imprint process, plasmonic colour filters could be successfully fabricated on substrates with diameters of 100 mm and 150 mm, resulting in an active filter area exceeding previously published values by a maximum factor of 23. In addition, defects caused by the SCIL process were systematically characterized for the first time and the defect density of fabricated filters was estimated based on local measurements. The results indicate, that mechanical degradation of the PDMS molds is one of the key sources for the defects observed on the imprinted substrates. Furthermore, the theoretic yield of a semiconductor process involving the fabrication of plasmonic colour filters using SCIL was calculated based on the estimated defect density. Finally, the functionality of the fabricated filters could be verified by spectroscopic measurements. Especially the combination of a buried silicon nitride waveguide with a cladding layer of silicon oxide or hybrid polymer yielded promising results. In conclusion, it could be successfully proven that the large area fabrication of plasmonic colour filters can be realized using the SCIL technology. However, before SCIL may be integrated into a semiconductor process the defect density of the printed structures must be reduced. As one key element, the mechanical degradation of the PDMS molds has to be avoided, whereby the definition of design rules for master structures might play an important rol

One-step nanoimprinted Bragg grating sensor based on hybrid polymers

Bragg grating sensors are used for real-time analysis of gases or liquids. Complex processing methods are typically required for the sensor fabrication. A reduction of process steps and costs during their fabrication is essential in order to broaden the field of application. Within this work, we demonstrate an innovative process for a one-step fabrication of integrated Bragg grating sensors and their successful application for temperature and refractive index sensing. UV-enhanced substrate conformal imprint lithography (UV-SCIL) is used to replicate surface relief Bragg grating (SBG) sensors on a full wafer scale. Multiple chips of a planar waveguide system including couplers and junctions were etched into a silicon wafer. Nanostructured SBGs were locally added on the waveguides by focused ion beam processing. The sensor structures were replicated by UV-SCIL into a commercially available hybrid polymer (OrmoComp®). Reflection measurements with different Bragg gratings were performed and compared to simulations. The results reveal narrow-band Bragg reflections, coinciding with the simulations. Further, the temperature dependence of the SBGs was investigated. The imprinted grating structures featured a very high temperature sensitivity of −202 pm/°C. The sensor response to a varying refractive index of the surrounding medium was determined for index matching liquids and aqueous solutions

Large area manufacturing of plasmonic colour filters using substrate conformal imprint lithography

This work presents the large area fabrication of plasmonic colour filters consisting of subwavelength apertures in aluminium films of different thicknesses. Wafer-scale pattern transfer was realized by a soft lithography technique (substrate conformal imprint lithography). The fabricated colour filters have an active area of up to 145 cm2 which presents a considerable increase compared to previously published results. In addition to experimental investigations, simulations of the transmission behaviour were performed using a rigorous electromagnetic field solver based on an extendedRCWA approach. Furthermore, the use of a spin-coated cover layer consisting of the UV-curable hybrid polymer OrmoComp® instead of often applied PECVD-SiO2 was investigated

Characterization of grain boundaries in multicrystalline silicon with high lateral resolution using conductive atomic force microscopy

In this work, the electrical characteristics of grain boundaries (GBs) in multicrystalline silicon with and without iron contamination are analyzed by fixed voltage current maps and local I/V curves using conductive AFM (cAFM). I/V characteristics reveal the formation of a Schottky contact between the AFM tip and the sample surface. The impact of both, the polarity of the applied voltage and the illumination by the AFM laser on the behavior of GBs was analyzed systematically. Depending on the polarity of the applied voltage and the iron content of the sample, grain boundaries alter significantly the recorded current flow compared to the surrounding material. The results also show a clear influence of the AFM laser light on the electrical behavior of the grain boundaries. Conductive AFM measurements are furthermore compared to data obtained by electron beam induced current (EBIC), indicating that cAFM provides complimentary information