SELECTIVE-AREA ION-IMPLANTATION USING POSITIVE PHOTORESIST MASK FOR GAAS DIGITAL INTEGRATED-CIRCUITS

Positive photoresist has been investigated for use as an implantation mask for the fabrication of GaAs digital integrated circuits by select ive ion implantation. Proper photoresist processing and surface cleanl iness of GaAs have been found to play a significant role in obtaining good selectivity and isolation between devices. n-SIGaAs-n structures were fabricated and characterized by their breakdown voltage, leakage current and capacitance measurements. The results also show that the i ntroduction of an intermediate layer of Si3N4 between the photoresist and GaAs further improves the isolation. The results obtained have bee n compared with reported results on the proton bombardment isolation p rocess. Using the developed selective implantation process, a quad two -input NOR gate was fabricated and tested.