Entwicklung eines Prozesses zur Vorbehandlung von Kupfersubstraten für CVD-Graphen
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In der vorliegenden Arbeit wird ein wasserstoffbasierter Annealingprozess zur Vorbehandlung von Kupfersubstraten für die Herstellung von CVD-Graphen entwickelt. Ziel ist die Erzeugung einer Substratoberfläche mit großen Körnern, geringer Rauheit und ein Minimung an Verunreinigungen. Dazu wurden Versuchsreihen bei verschiedenen Temperaturen und Drücken durchgeführt und ihre Vor- und Nachteile hinsichtlich der Zielparameter bewertet. Während der Untersuchungen konnte spontanes Wachstum von Graphen-Flakes ohne Zufuhr externer kohlenstoffhaltiger Precursoren beobachtet werden. Durch Abätzen der Graphen-Flakes und abgeschwächtes Wachstum beim erneuten Glühen konnte nachgewiesen werden, dass das Wachstum primär auf intrinsische Kohlenstoffverunreinigungen im Kupfer-Bulk zurückzuführen ist. Diese migrieren unter der Wasserstoffatmosphäre an die Oberfläche und nukleieren dort größtenteils an Verunreinigungspartikeln. Diese spontan gebildeten Graphen-Flakes sowie zusätzlich nachgewiesene silizium- und sauerstoffhaltige Partikel wirken für anschließende Wachstumsprozesse als unerwünschte Störstellen, die ein kontrolliertes CVD-Wachstum beeinträchtigen. Die Ergebnisse verdeutlichen, dass der Annealingprozess vor dem Wachstumsschritt bereits die Bedingungen für das finale Graphenwachstum maßgeblich determiniert.
In this work, a hydrogen-based annealing process is developed for the pretreatment of copper substrates for the production of CVD-graphene. The aim is to create a substrate surface with large grains, low roughness and impurities. To this end, a series of experiments were carried out at different temperatures and pressures, and their advantages and disadvantages with regard to the target parameters were evaluated. During the investigations, spontaneous growth of graphene flakes was observed without the addition of external carbon-containing precursors. By etching the graphene flakes and observing reduced growth during re-annealing, it was demonstrated that the growth is primarily due to intrinsic carbon impurities in the copper bulk. These migrate to the surface under the hydrogen atmosphere and nucleate there, mostly on impurity particles. These spontaneously formed graphene flakes, as well as additionally detected silicon- and oxygen-containing particles, act as undesirable impurities for subsequent growth processes, impairing controlled CVD growth. The results illustrate that the annealing process prior to the growth step already significantly determines the conditions for the final graphene growth.
In this work, a hydrogen-based annealing process is developed for the pretreatment of copper substrates for the production of CVD-graphene. The aim is to create a substrate surface with large grains, low roughness and impurities. To this end, a series of experiments were carried out at different temperatures and pressures, and their advantages and disadvantages with regard to the target parameters were evaluated. During the investigations, spontaneous growth of graphene flakes was observed without the addition of external carbon-containing precursors. By etching the graphene flakes and observing reduced growth during re-annealing, it was demonstrated that the growth is primarily due to intrinsic carbon impurities in the copper bulk. These migrate to the surface under the hydrogen atmosphere and nucleate there, mostly on impurity particles. These spontaneously formed graphene flakes, as well as additionally detected silicon- and oxygen-containing particles, act as undesirable impurities for subsequent growth processes, impairing controlled CVD growth. The results illustrate that the annealing process prior to the growth step already significantly determines the conditions for the final graphene growth.