Etching of Compound Semiconductors and High-k Materials

The gas overview in the Dry etch processes chapter covers the standard materials of silicon manufacturing: silicon, silicon dioxide, silicon nitride, polysilicon and aluminum. Some material systems, however, cannot be etched well – or at all – with the same chemistries, either because they are too chemically inert, or because the resulting reaction products are not volatile enough at process temperature.

III-V semiconductors such as gallium arsenide, indium phosphide or gallium nitride cannot be etched with fluorine chemistry – the resulting fluorides are not volatile enough at process temperature. Chlorine chemistry (BCl₃, Cl₂) is used instead, forming volatile chlorides with the group III elements.

One challenge is that the different elements of a compound react at different rates – for GaAs, for example, the chemistry must be tuned so that gallium and arsenic are removed at comparable rates. Otherwise the surface becomes depleted of one element, and etching stalls or the surface roughens.