Fabrication of AlGaN/GaN HEMT with the improved ohmic contact by encapsulation of silicon dioxide thin film

Abstract

We compared to the characteristics of fabricated AlGaN/GaN HEMTs on a Si substrate with conventional ohmic contact and improved ohmic contact. In conventional ohmic contact with metal scheme of Ti/Al/Ni/Au or Ti/Al/Ti/Au, generally ohmic contact resistance is good but, surface topography has bad morphology due to ball-up by low Al melting point at high temperature RTA over 800°C. In order to improve that, we applied the encapsulation of silicon dioxide thin film in ohmic contact process and fabricated AlGaN/GaN HEMT with improved ohmic contact better than surface morphology and resistance of the conventional. As the results, ohmic metal morphology was improved more over 50% than the conventional and contact resistance was also low. Besides, at the T-gate formation, the alignment mark detection of e-beam lithography system was improved. The fabricated AlGaN/GaN HEMT with conventional ohmic contact has obtained I dss of 260mA/mm, V p of −1.7V, G m,max of 230mS/mm, BV gd of over 90V, f T of 31GHz and f max of 51GHz, while it has obtained I dss of 350mA/mm, V p of −1.6V, G m,max of 280mS/mm, BV gd of over 100V, f T of 34GHz and f max of 50GHz for improved ohmic contact, relatively.