Thickness engineering of atomic layer deposited Al₂O₃ films to suppress interfacial reaction and diffusion of Ni/Au gate metal in AlGaN/GaN HEMTs up to 600°C in air

Abstract

In this paper, we describe the use of 50nm atomic layer deposited (ALD) Al₂O₃ to suppress the interfacial reaction and inter-diffusion between the gate metal and semiconductor interface, to extend the operation limit up to 600°C in air. Suppression of diffusion is verified through Auger electron spectroscopy (AES) depth profiling and X-ray diffraction (XRD) and is further supported with electrical characterization. An ALD Al₂O₃ thin film (10nm and 50 nm), which functions as a dielectric layer, was inserted between the gate metal (Ni/Au) and heterostructure-based semiconductor material (AlGaN/GaN) to form a metal-insulator-semiconductor high electron mobility transistor (MIS-HEMT). This extended the 50nm ALD Al₂O₃ MIS-HEMT (50-MIS) current-voltage (I-ds-V-ds) and gate leakage (I-g,I-leakage) characteristics up to 600°C. Both, the 10nm ALD Al₂O₃ MIS-HEMT (10-MIS) and HEMT, failed above 350°C, as evidenced by a sudden increase of approximately 50 times and 5.3 x 10⁶ times in I-g,I-leakage, respectively. AES on the HEMT revealed the formation of a Ni-Au alloy and Ni present in the active region. Additionally, XRD showed existence of metal gallides in the HEMT. The 50-MIS enables the operation of AlGaN/GaN based electronics in oxidizing high-temperature environments, by suppressing interfacial reaction and inter-diffusion of the gate metal with the semiconductor.