Metal assisted chemical etching
Metal Assisted Chemical Etching (also known as MACE) is the process of wet chemical etching of semiconductors (mainly silicon) with the use of a metal catalyst, usually deposited on the surface of a semiconductor in the form of a thin film or nanoparticles. The semiconductor, covered with the metal, is then immersed in an etching solution containing an oxidizing agent and hydrofluoric acid.
Source: Wikipedia — Metal assisted chemical etching (CC BY-SA 4.0)