Plasma etched silicon carbide

A method of plasma etching a compound semiconductor substrate to form a feature, the method comprising the steps of:

• providing a substrate with a mask formed thereon, the mask having a mask opening, wherein the substrate is formed from a compound semiconductor material, and wherein the mask includes silicon dioxide;
• performing a first plasma etch step to anisotropically etch the substrate through the mask opening to produce a majority of a partially formed feature having an opening and a bottom surface comprising a peripheral region;
• performing a second plasma etch step to remove a region of the mask adjacent to the opening of the partially formed feature and thereby cause rounding of the edges of the substrate at the opening of the partially formed feature;
• and
• performing a third plasma etch step to anisotropically etch the bottom surface of the partially formed feature through the mask opening of the mask while depositing a passivation material onto the mask and the opening of the partially formed feature so as to reduce a dimension of the opening of the partially formed feature, wherein the reduction of the dimension of the opening of the partially formed feature causes an attenuation in etching of the peripheral region and the opening of the partially formed feature thereby producing a fully formed feature having an opening with rounded edges, a bottom surface comprising a central region and an edge region, wherein the central region is deeper than the edge region of the bottom surface of the fully formed feature.