Role of dose optimization in Ru atomic layer deposition for low resistivity films

Ruthenium (Ru) is an alternative to copper (Cu) and cobalt (Co) interconnect layers in sub 20 nm features due to its low resistivity in scaled wires and low diffusion into porous low-K dielectrics (SiCOH). Two goals for a successful Ru atomic layer deposition (ALD) process are to enable films with resistivity values as close as possible to that of bulk Ru and to enable selective deposition to achieve bottom-up fill of vias. In this work, the effects of dose variation on resistivity and selectivity of the Ru ALD process using a dicarbonyl-bis(5-methyl-2, 4-hexanediketonato) Ru(II) precursor, Ru(IHD)2(CO)2 (“Carish”), and O2/He coreactant were investigated. Instead of varying the Carish precursor dose to optimize the growth rate per cycle, the precursor dose was optimized to reduce the film resistivity from 18.5 to 10.2 μΩ cm. By varying the O2/He coreactant dose, the substrate selectivity of the ALD process was successfully enhanced as evidenced by the increased nucleation delay on bis(N,N-dimethylamino)dimethylsilane passivated SiO2 over hydrofluoric acid-cleaned SiO2. These findings highlight the importance of dose optimization beyond the ALD saturation point in developing a selective and low resistivity Ru ALD process. Density functional theory calculations were performed to provide a mechanistic understanding of the underlying surface reactions of the Carish precursor and the roles of CH3 passivation and O2 coreactants.