Subhalf-micron gate GaAs MESFET process using phase-shifting-mask technology

For the purpose of an ultra-high-speed GaAs LSI, the phase-shifting-mask technology has been applied to the fabrication process of subhalf-micron gate GaAs MESFETs. The lithography of gate pattern was performed by the PEL (phase-shifter edge-line) mask technique with the double exposure process using the i-line stepper, where the resist spacing was precisely controlled by the exposure dose. The gate metal of W-Al was then etched by ECR plasma with no under-cut, which resulted in fine gate patterning. GaAs MESFETs fabricated in a 3-inch wafer have shown a good uniformity of Vth as small as 40 mV, and a high gm property of 424 mS/mm with a good uniformity of gm (3.5%) at the gate length of 0.22 mu m.<>