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.