Magnetron ion etching of through-wafer via holes for GaAs monolithic microwave integrated circuits using SiCl₄

A dry etching process is described for the fabrication of through-wafer via holes in GaAs-based monolithic microwave integrated circuits by magnetron ion etching using SiCl₄. The process has been used to etch via holes through 80 μm GaAs substrates with good anisotropy and etch rates exceeding 1 μm/min for via holes as small as 18×20 μm². Etch anisotropy appears to be due to an etch-inhibiting layer, which forms on the sidewalls but can be removed readily using a brief SF₆/O₂ etch. The process also exhibits good selectivity to Au and Ni frontside metal.