Chemical etching of silicon assisted by graphene oxide under negative electric bias.

Chemical etching of silicon assisted by graphene oxide (GO) has been attracting attention as a new method to fabricate micro- or nano-structures. GO promotes the reduction of an oxidant, and holes are injected into silicon, resulting in the preferential dissolution of the silicon under GO. In the conventional etching method with GO, the selectivity of the etching was low due to the stain etching caused by nitric acid. We developed an etching method that applies a negative bias to the p-type silicon substrate. The silicon under GO was more selectively etched in an etchant consisting of hydrofluoric acid and nitric acid than the silicon uncovered by GO. We assume that this is attributed to the difference in hole concentration in the silicon under GO and in the bare silicon. In addition, the in-plane diffusion of holes in silicon is suppressed by this method, resulting in the formation of highly anisotropic pores. From this study, we found that GO-assisted silicon etching occurs with a similar principle to metal-assisted chemical etching. The negative-bias etching with GO has the potential to be a simple and highly anisotropic microfabrication method.