Kuchuk A. Structure and physical properties of W-Ti-N and Ta-Si-N thin film diffusion barriers on gallium arsenide and gallium nitride substrates

Thesis is devoted to investigation of dependences of WTiN and TaSiN films structure and physical properties, on nitrogen amount in reactive magnetron sputtering processes. The reactive magnetron sputtering process of WTiN, with increase of partial pressure of nitrogen, can be deviated into three regions of sputtering: 1) MM-metallic mode; 2) TM-transition mode; 3) NM-nitride mode. Change in type of film-forming species (МM: Ме (W, Ti) atoms; TM: МеN clusters; NM: Ме and N atoms) result in radical change of structure and properties of WTiN films. Films sputter-deposited in the MM are formed by a interstitial solid solution of Ti(N) in b.c.c. W phase. In TM (N=12 at.%)) amorphous-like structure is observed. In the NM, the films have a single f.c.c. WTiN phase. The complexity of the structure, results in a substantial improvement in the barrier properties of W64Ti16N20 films compared with polycrystalline W-Ti-N films. This film suppresses interdiffusion between Au-overlayer and GaAs substrate under thermal annealing at 750oC. For reactive sputtering of TaSiN films, increasing of N2 flow ratio results in N concentration increase due to incorporation of reactive N2 into the film during the sputtering process. Increase of the "degree of amorphism", which agrees well with change of chemical composition and an increase of TaSiN films resistivity, is result of silicon nitride SiNx fraction rises into the films, and of tantalum nitride TaNx decreases. TaSiN films may be viewed as a mixture of tantalum nitride imbedded in a silicon nitride amorphous matrix. This model explain the high temperature crystallization (1000oC) and excellent thermal stability (800oC) in Au-,Ag-GaAs and Au-GaN systems, of Ta-Si-N diffusion barrier with N content more than 40 at.%.