Gate Shorts: A Process Engineer’s Nightmare

Thorsten Saeger, Travis A Abshere, Fabian Radulescu and Jack Lail

TriQuint Semiconductor, 2300 NE Brookwood Parkway, Hillsboro, OR 97124
tsaeger@tqs.com, (503) 615-9365

Keywords: Front end process, pHEMT, Lithography, Wet chemical cleaning, Ohmic metal deposition

Abstract

Gate shorts are devastating for the basic function of a FET. For one of TriQuint Semiconductor’s SAGpHEMT processes two sources of gate shorts were found and eliminated. The dominant source of gate shorts was the accumulation of ohmic metal on a ledge of unexposed photo resist. That could be fixed by varying the Focus Offset on the stepper during exposure of the ohmic photo layer. The secondary source was residue underneath ohmic metal. This residue could be removed by a wet clean.

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