Pore Formation in a p-Type Silicon Wafer Using a Platinum Needle Electrode with Application of Square-Wave Potential Pulses in HF Solution

By bringing an anodically biased needle electrode into contact with n-type Si at its tip in a solution containing hydrofluoric acid, Si is etched at the interface with the needle electrode and a pore is formed. However, in the case of p-type Si, although pores can be formed, Si is likely to be corroded and covered with a microporous Si layer. This is due to injection of holes from the needle electrode into the bulk of p-type Si, which shifts its potential to a level more positive than the potential needed for corrosion and formation of a microporous Si layer. However, by applying square-wave potential pulses to a Pt needle electrode, these undesirable changes are prevented because holes injected into the bulk of Si during the period of anodic potential are annihilated with electrons injected into Si during the period of cathodic potential. Even under such conditions, holes supplied to the place near the Si/metal interface are used for etching p-type Si, leading to formation of a pore at the place where the Pt needle electrode was in contact.