Cathodic Arc Synthesis of Ti-Si-C-N Thin Films : Plasma Analysis and Microstructure Formation

Abstract: This Thesis explores the arc deposition process and films of Ti-Si-C-N, inspired by the two ternary systems Ti-Si-N and Ti-C-N, both successfully applied as corrosion and wear resistant films. The correlation between cathode, plasma, and film properties are studied for a comprehensive view on film formation. Novel approaches to adapt arc deposition to form multi-element films are investigated, concluding that the source of C is not a determining factor for film growth. Thus, cubic-phase films of similar properties can be synthesized from processes with either 1) ternary Ti-Si-C cathodes, including the Ti3SiC2 MAX phase, in N2 atmosphere or 2) Ti-Si cathodes in a mixture of N2 and CH4. With the Ti3SiC2 cathodes, superhard (45-50 GPa) cubic-phase (Ti,Si)(C,N) films can be deposited. The structure is nanocrystalline and feather-like, with high Si and C content of 12 and 16 at%, respectively. To isolate the effects of Si on film structure, magnetron sputtered Ti-Si-N films of comparatively low defect density was studied. These films show a strong preference for {200}  growth orientation, and can be grown as a single phase solid solution on MgO(001) substrates up to ~9 at% Si, i.e. considerably higher than the ~5 at% Si above which a feather-like nanocrystalline structure forms in arc deposited films. On (011) and (111) growth surfaces, the films self-organize into TiN columns separated by segregated crystalline-to-amorphous SiNx. The conditions for film growth by arc were investigated through plasma studies, showing that plasma properties are dependent on cathode composition as well as phase structure. Plasma generation from Ti-Si cathodes, with up to 25 at% Si, show higher average ion charge states of Ti and Si compared to plasma from elemental cathodes, which may be related to TiSix phases of higher cohesive energies. The ion energy distributions range up to 200 eV. Furthermore, compositional discrepancies between plasma ions and film infer significant contributions to film growth from Si rich neutral species. This is further supported by depositions with a macroparticle filter, intended for growth of films with low surface roughness, where Si and C contents lower than the stoichiometry of Ti3SiC2 cathodes was measured in both plasma and films. Also the substrate geometry is critical for the film composition in plasma based film deposition, as evidenced by the formation of artificial layering from rotating substrate fixtures common in high capacity arc deposition systems. The layers are characterized by modulations in composition and crystallinity, primarily attributed to preferential resputtering in high ion incidence angle segments repeated through rotation.