Encapsulation of silver by nitridation of Ag-Ti alloy/bilayer structures

Thin encapsulated silver films have been prepared on oxidized silicon. As a preparatory step, silver was deposited either as ∼ 200 nm thick Ag-χ%Ti alloys (where χ= 6-26 at.%) or Ag(120 nm)/Ti(22 nm) bilayers. Subsequent encapsulation was formed by Ti reactions during anneals between 300 and 700°C in an ammonia ambient. This process has been studied in detail by Rutherford backscattering, scanning Auger, secondary ion mass spectrometry and X-ray diffraction, which showed that Ti nitride and Ti oxide-silicide formation take place at the surface and interface, respectively. Kinetic studies showed that the Ti reactions take place within the first 10 min. This self-limiting behavior occurs for all annealing temperatures, but the extent to which the encapsulation reaction takes place increases with temperature. Four-point probe analysis of the alloy films suggests that the resistivity is controlled by the residual Ti concentration. Resistivity values of ∼ 3 μΩ cm were measured in encapsulated Ag alloy films with low initial Ti concentrations. The annealed bilayer structure had minimal Ti accumulations in Ag and the resistivity values were comparable to that of the as-deposited Ag (∼ 2.5 μΩ cm).