SUB-QUARTER-MICRON GATE FABRICATION PROCESS USING PHASE-SHIFTING MASK FOR MICROWAVE GAAS DEVICES

A phase-shifting mask technique using an i-line stepper was applied to the gate formation process of AlGaAs/GaAs high electron mobility transistors (HEMTs). To obtain a fine gate pattern of less than a quarter micron, the phase-shifter edge-line mask, which has the highest resolution and wide focus margin for an isolated pattern, was used and the double exposure process was developed to form a real gate pattern. The controllable gate length was in the range of 0.50-0.15-mu-m. By using this technique, 0.18-mu-m-gate HEMTs with good and uniform microwave performances in a 3-inch wafer were obtained. This technique has great advantages for applications to microwave GaAs devices and ultrahigh-speed GaAs LSIs.