Doping Density, not Valency, Influences Metal Assisted Plasma Etching of Silicon

In metal assisted plasma etching (MAPE), the direct interfacial contact of metals such as Au and Ag can greatly increase the etch rate of Si and SiO2 in fluorine-based gases. In contrast to metal assisted chemical etching (MACE), it has been discovered that MAPE has a fundamentally different mechanism, which is interesting because both methods utilize metal-silicon contact in the presence of fluorine based oxidizing etchants to increase etch rates. In MAPE, the increase in doping causes a decrease in etch rate for both n- and p-type doping, in contrast to MACE, where increased n-type doping increases etch rate while increased p-type doping decreases etch rate. For further details on this see

This finding was reported by Julia SunNamphung PeimyooJames Douglas, and Ben Almquist at the Imperial College London. The work was performed in part using an STS-Elionix ELS-G100 electron beam lithography system at the London Centre for Nanotechnology.

metal assisted plasma etching on silicon SEM image.

Image: Scanning electron micrograph images showing MAPE enhanced etching using Cr/Au nanoparticles on n- (top row) and p-type (bottom row) silicon with doping concentrations decreasing from left to right. The Cr is used as a protective layer on top of Au, with the Au being the bottom layer in direct contact with the silicon surface. As the doping concentration decreases in the silicon the etching rate increases. All scale bars represent 500 nm. (Reproduced from with permission from the Royal Society of Chemistry.)