Hybrid dry-wet chemical etching process for via holes for gallium arsenide MMIC manufacturing

Through the wafer via-hole connections for monolithic microwave integrated circuits (MMIC) manufacturing have been developed by combining reactive ion etching (RIE) and wet chemical spray etching processes for 100- mu m-thick gallium arsenide wafers. The dry process is based on the use of SiCl/sub 4/-BCl/sub 3/-Cl/sub 2/ and BCl/sub 3/-Cl/sub 2/ gas mixtures at room temperature is a reactive ion etcher. The etching parameters are optimized for anisotropic etching, initially, followed by slightly isotropic etching. To remove the residual 'lip' and surface roughness, following reactive ion etching, a dynamic wet chemical spray etching based on H/sub 3/PO/sub 4/-H/sub 2/O/sub 2/-H/sub 2/O at 45 degrees C is used. The combined dry-wet etching approach is used to fabricate <120- mu m diameter via-holes in 100- mu m-thick GaAs substrates with a wider process latitude. With this process, the authors have achieved >95 percent yield across 3-in wafers. Metallized via-hole contacts to power FET chips show a contact resistance <20 m Omega per via for 5- mu -thick selective gold plating.<
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