Hybrid dry-wet chemical etching process for via holes for galliumarsenide MMIC manufacturing |
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Authors: | Chang EY Nagarajan RM Kryzak CJ Pande KP |
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Affiliation: | Comput. Syst. Div., Unisys Corp., St. Paul, MN ; |
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Abstract: | 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-μm-thick gallium arsenide wafers. The dry process is based on the use of SiCl4-BCl3-Cl2 and BCl3-Cl2 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 H3PO4-H2O2-H2O at 45°C is used. The combined dry-wet etching approach is used to fabricate <120-μm diameter via-holes in 100-μm-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 mΩ per via for 5-μ-thick selective gold plating |
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