Growth and Characterization of Amorphous Multicomponent Nitride Thin Films

• Main Author: Fager, Hanna
• Format: Doctoral Thesis
• Language: English
• Published: Linköpings universitet, Tunnfilmsfysik 2014
• Online Access: http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-106576; http://nbn-resolving.de/urn:isbn:978-91-7519-337-3 (print)

This thesis explores deposition of amorphous thin films based on the two transition metal nitride systems, TiN and HfN. Additions of Si, Al and B have been investigated using three different deposition techniques: dc magnetron sputtering, cathodic arc evaporation, and high power impulse magnetron sputtering (HIPIMS). The effect of elemental composition, bonding structure, growth temperature, and low-energy ion bombardment during growth has been investigated and correlated to the resulting microstructure and mechanical properties of the films. The thermal stability has been investigated by annealing experiments. Deposition by cathodic arc evaporation yields dense and homogeneous coatings with essentially fully electron-diffraction amorphous structures with additions of either Al+Si, B+Si or B+Al+Si to TiN. The B-containing coatings have unusually few macroparticles. Annealing experiments show that Ti-Al-Si-N coatings have an age hardening behavior, which is not as clear for B-containing coatings. Compositional layering, due to rotation of the sample fixture during deposition, is present but not always visible in the as-deposited state. The layering acts as a template for renucleation during annealing. The coatings recrystallize by growth of TiN-rich  domains. Amorphous growth by conventional dc magnetron sputtering is possible over a wide range of compositions for Ti-B-Si-N thin films. The Ti content in the films is reduced compared to the content in the sputtering target. Without Si, the films consist of a BN onion-like structure surrounding TiN nanograins. With additions of Si the films eventually grows fully amorphous. The growth temperature has only minor effect on the microstructure, due to the limited surface diffusion at the investigated temperature range (100-600 °C). Ion assisted growth leads to nanoscale densification of the films and improved mechanical properties. Ti-B-Si-N thin films are also deposited by a hybrid technique where dc magnetron sputtering is combined with HIPIMS. Here, the Ti:B ratio remains equal to the target composition. Films with low Si content are porous with TiN nanograins separated by BN-rich amorphous channels and have low hardness. Increasing Si contents yield fully electron-amorphous films with higher hardness. Finally, Hf-Al-Si-N single-layer and multilayer films are grown by dc magnetron sputtering from a single Hf-Al-Si target. Amorphous growth is achieved when the growth temperature was kept at its minimum. Low-energy substrate bias modulation is used to grow nanocomposite/nanocolumnar multilayers from the single Hf-Al-Si target, where the layers has essentially the same composition but different Si bonding structure, and different degree of crystallinity.