Influence of annealing environment and diffusion barrier on surface topography of copper films

Cu/ZrSiN and Cu/ZrN films were grown on Si (111) substrates by reactive magnetron sputtering and ion beam auxiliary deposition. respectively. After annealing at 800°C in low vacuum(2 ×10^-3 Pa) or in a mixture of hydrogen (10%) and nitrogen (90%) for 1 h, the surface topography of the Cu films was studied with scanning electron microscopy. The results show that surface cracks of the ZrSiN diffusion barrier layers propagate through the Cu layers and a large number of irregularly shaped voids emerge on Cu layers grown both on ZrSiN and ZrN diffusion barrier layers because of the coalescence of Cu atoms. After annealing in a H₂/N₂ mixture. the number and size of the void decrease but the fairly high stresses in Cu/ZrSiN multilayers generate many small cracks on the Cu surface. As for the Cu layers grown on ZrN diffusion barrier layers, no crack was observed due to the lower stress in Cu/ZrN system. It was found that reduction of hydrogen would adversely affect the void formation.