Thermal diffusion and epitaxial growth of Ag in Ag/SiO2/Si probed by XRD, depth-resolved XPS, and slow positron beam

Ag/SiO2/Si multilayer samples with different SiO2 layer thicknesses were prepared through deposition of Ag layer onto SiO2/Si substrates at different substrate temperatures (Tsub) by RF magnetron sputtering method. Microstructure of the multilayer was characterized by XRD θ/2θ scan and φ-scan analysis, depth-resolved XPS analysis, and Doppler broadening of annihilation radiation (DBAR) spectra of positron measurements. The experimental results indicate that, at Tsub = 25 °C, the Ag deposition forms Ag/SiO2/Si multilayer structure. With Tsub increasing to 200 °C, Ag atoms are found to diffuse into the SiO2 layer. This thermal diffusion process plays a critical role in removing SiO2 layer on the Si substrate. At Tsub of 600 °C, the 31-nm-thick SiO2 layer is partially desorbed from the Si surface as a result of Ag diffusion, and eventually results in a deposition of Ag layer directly on the Si substrate. This is also confirmed by the XRD φ-scan measurements, which indicates epitaxial growth of Ag atoms directly on the surface of Si substrate at Tsub of 600 °C.