Optimization of passivation in AlGaN/GaN heterostructure microwave transistor fabrication by ICP CVD

In present study is considered the influence of the regimes of passivating dielectric silicon nitride SiN x films deposition by the chemical vapor deposition in an inductively coupled plasma (ICP CVD) on the parameters of the high electron mobility transistors (HEMT) based on AlGaN/GaN heterostructures. By the investigation of dielectric material layers’ parameters was revealed the influence of RF and ICP generators power, working gases flows ratio on the films growth rate and perfection, also their effect on the CVC of passivated HEMT. With RF power increasing the deposition rate did not change, while its growth was observed with ICP power increasing. The transistor slope strongly decreases with RF power increasing, its maximum was achieved with a minimum RF power of 1 W. At the initial moment of deposition even at low values of RF power (at 3 W already) the transistor structure becomes completely inoperative. Shown, that the deposition process of dielectrics for the HEMT passivation must begin at the lowest possible RF power. An AlGaN/GaN UHF HEMT structure passivation process has been developed, allowing the deposition of conformal films and obtaining low drain-source currents in turn-off transistors without deterioration in the open state — at no more than 15 and 100 μA for 1,25 and 5 mm Т-gate width respectively ( U G = –8 V and U SD = 50 V).