Investigation of etchant composition on the contact angle and morphology of the black silicon, formed by MACE with Ni

In recent years, there has been much interest in the chemical formation of the silicon nanostructures by methods without electrical bias – metal-assisted chemical etching (MACE). Noble metals or its reaction products are... [ view full abstract ]

In recent years, there has been much interest in the chemical formation of the silicon nanostructures by methods without electrical bias – metal-assisted chemical etching (MACE). Noble metals or its reaction products are used for MACE application remains on the etched Si surface. Recently shown, that Ni-assisted chemical etching leads to black silicon formation without contamination. There is a problem during MACE with Ni - hydrogen evolution. It prevents access reagents to surface. Addition of ethanol into solution leads to wetting of the Si and reduces H₂ on the surface.

The goal of this work is investigation of the effect of C₂H₅OH and oxidizing agent H₂O₂ on the morphology, etchant contact angle and roughness coefficient of the black silicon, formed by MACE. The etching of Si/Ni was carried out in a solution of HF\H₂O₂\C₂H₅OH\H₂O with different volume concentration (VC) of H₂O₂ and C₂H₅OH. Contact angle was investigated in situ during 1 minute. Black silicon surface morphology was investigated after treatment during 40 minutes.

Increasing of ethanol VC promotes increasing of etchant wettability of Si/Ni and black silicon surface. Increasing of ethanol VC (0-12 vol.) leads to decreasing H₂O₂ VC (0.12-0.2). The greatest value of the contact angle is 32-33˚. It is observed in the case without ethanol in the solution, but the H₂O₂ volume concentration is 0.14 and 0.2 (Fig.1). Further, with the addition of alcohol in solution or decreasing of H₂O₂ VC to 0.12 and 0.17 the reduction of the contact angle to 25 and 21˚ is observed. It is due to the spreading solution over the surface.

Reduction of the contact angle to 12 ± 1° and 15 ± 1°, intensive gas evolution and darkening of the Si/Ni after 1 minute of treatment indicate black silicon formation by MACE. In the subsequent decrease the H₂O₂ concentration leads to uniform and continuous black silicon formation (Fig.2).

This study was supported by the Russian Science Foundation, project no. 16-19-10625.