Metal-assisted etching of p-type silicon under anodic polarization in HF solution with and without H2O2

Pore formation under anodic polarization of a lightly doped p-type Si wafer previously loaded with Pt, Pd and Ag nanoparticles was investigated in HF solution with and without H₂O₂. In HF solution without H₂O₂, a microporous layer was formed in p-Si loaded with Pt or Pd. However, Ag metal nanoparticles yielded pores due to their intrusion in the Si wafer. The addition of H₂O₂ to the etching solution leads to different pore morphologies depending on the metals. Particles of Ag were found at the bottom of most pores. In the presence of Pt nanoparticles, cone-shaped macropores were produced, and the pore depth and diameter increased with increasing H₂O₂ content. Current density influenced the pore morphology. For a sample loaded with Pt or Ag, an increase in applied current density widened the pore diameter. The mechanism of the metal-assisted pore formation was discussed by considering a competitive process between the formation of a microporous layer under polarization and metal-assisted chemical oxidation of the microporous layer by a dissolved oxidizing agent.