Microstructures of silver films plated on different substrates and annealed at different conditions

We performed systematic experiments to study the morphologies and microstructures of silver (Ag) films grown on different substrates and annealed at different conditions. It was found out that Ag microstructure varies widely versus the surface onto which Ag is plated and versus annealing conditions. The substrates used in this study include alumina/TiW(40nm)/Au(2.5μm), Bi₂Te₃/Pd(100nm)/ Au(100nm), Cu, Si/Cr(30nm)/Au(100nm), Si/Pd(100nm)/ Au(100nm), and 304 stainless steel(304SS)/Ni(2um). The annealing conditions are from 250°C to 550°C for 5 to 30 hours. The microstructures and grain size are evaluated using scanning electron microscope (SEM) and X-ray diffraction pattern (XRD). The grain size ranges from 13nm to 15μm. Ag surface morphology looks pretty similar on all these substrates expect Si. Ag films plated on alumina, Bi₂Te₃, Cu and stainless steel show smooth and flat morphology. However, Ag plated on the Si has dome-shaped morphology. This is true even when Ag is grown on the same adhesion material. These Cr, Pd, and Au adhesion layers are all coated on the substrates by thermal evaporation in high vacuum. All Au layers demonstrate same morphology. But the Ag films grown on these Au layers show different morphologies. XRD results indicate that Ag has preferred orientation on (111) plane; the preference is especially manifest on Si. Ag grain sizes on Si/Cr(30nm)/Au(100nm) and alumina/TiW(40nm)/Au(2.5μm) were studied before and after various annealing processes by either XRD analysis or SEM observation. The grain size growth seems to follow the grain growth law. The activation energy is calculated to be 134~140kJ/mol and 118~128kJ/mol, respectively at 523K to 723K.