The first report on general corrosion during metal-assisted etching of silicon.

Metal-assisted etching has attracted increasing attention as a method to produce porous silicon (Si). We previously found that gold (Au)-and platinum (Pt)-particle-assisted etching causes general corrosion of the Si substrate, but not in the case of silver (Ag)-particle-assisted etching [A. Matsumoto, et al., RSC Adv., 10, 253 (2020)]. In this work, we discussed the 2 mechanism of the general corrosion with electrochemical approaches. We demonstrated that potentials of the Au-and Pt-deposited Si during the metal-particle-assisted etching are higher than that of the bare Si in the etchant, but not in the case of the Ag-deposited Si. We also performed electrochemical etching of the bare Si by applying the potential during the Pt-particle-assisted etching, resulting in the formation of a mesoporous layer which was dissolved in the etchant. We concluded that the general corrosion occurs during the metal-particle-assisted etching due to the dissolution of the mesoporous layer formed by anodic polarization of the Si substrate.

Metal-assisted etching (metal-assisted chemical etching) has attracted increasing attention as a low-cost and versatile microfabrication technique of semiconductors. In platinum (Pt)-particle-assisted etching of silicon (Si), a composite structure of straight macropores and a mesoporous layer can be produced, but the mechanism of the structure formation is still open to discussion. We employed an electrochemical approach to investigate the composite structure formation by the Pt-assisted etching. Polarization curves of Pt-deposited Si and bare Si were measured in hydrofluoric acid (HF) solutions containing different concentrations of hydrogen peroxide (H 2 O 2 ). The open circuit potential during the Pt-assisted etching was more positive than that of the bare Si and it shifted in the positive direction with increasing the H 2 O 2 concentration as a consequence of the enhancement of the H 2 O 2 reduction reaction. For the structure observation, both the macropore depth and the mesoporous layer thickness increased with increasing the H 2 O 2 concentration, while the ratio between them changed. We discussed the structure change on the basis of the polarization characteristics. The mesoporous layer formation can be explained by the hole consumption at the Si surface under the positive potential which is determined by mixed potential theory.

Electroless deposition of metal particles on silicon (Si) followed by the metal-assisted etching (metal-assisted chemical etching) is a simple way to fabricate Si nanostructures. A composite porous structure consisting of straight macropores and a mesoporous layer can be created by platinum (Pt)-particle-assisted etching. In this work, we studied the composite structure formation on a highly-doped p-Si (ca. 5×1018 cm−3) in comparison with a moderately-doped p-Si (ca. 1×1015 cm−3). The composite structure drastically changed: the ratio of mesoporous layer thickness to macropore depth increased to 1.1 from 0.16 by using the highly-doped Si instead of the moderately-doped Si. The open-circuit potential of Si in the etching solution shifted to the positive direction by the Pt deposition. The potential shift of highly-doped Si was smaller than that of moderately-doped Si, which can be explained by the polarization characteristics. We calculated the band bending in Si by using a device simulator that reproduced the conditions of Pt-particle-assisted etching. The results indicated that, in the case of highly-doped Si, the consumption rate of positive holes at the Si surface away from the Pt particles increases due to the tunneling effect, which is consistent with the thick mesoporous layer formation.