Fabrication of 150‐nm AlGaN/GaN field‐plated High Electron Mobility Transistors using i ‐line stepper

Abstract

This article reports a high throughput 150-nm-gate AlGaN/GaN high electron mobility transistor (HEMT) process using i-line stepper lithography and a thermal reflow technique. Optimizing thermal reflow conditions, fabrication of a 150-nm gate structure was successfully realized with the initial resist opening of 0.7 μm. AlGaN/GaN fieldplated HEMTs were fabricated on a semi-insulating SiC substrate by using this process. In spite of unoptimized structures, fabricated 150nm gate devices exhibited the maximum drain current of 0.65 A/mm and the gate-drain breakdown voltage exceeding 200 V. Based on cold HEMT extraction measurements, the average gate length of 187 nm and the standard deviation of 30 nm were obtained on a quarter 4-in. wafer.

RF characteristics of 150‐nm AlGaN/GaN high electron mobility transistors fabricated using i‐line stepper lithography

“…This carrier modulation effect of the field plate may be related to the smaller R s and R d values in this structure. In Table 1, also listed are parameters of the previously reported device in [10]. The gate structure is field‐plated but with a longer field plate and a larger ohmic metal separation ( L g = 0.15 μm, L top = 1.8 μm, and L sg = L gd = 3 μm).…”

“…It was then thermally reflowed to have the trench shrunk down. A minimum opening was obtained for the reflow temperature ( T reflow ) of 150°C and the reflow duration ( t reflow ) of 4 min [10]. The slit pattern was transferred to the SiN film by fluorine‐based inductively coupled plasma reactive‐ion etching (ICP‐RIE).…”

“…Several authors reported GaN-HEMTs fabricated using EB lithography and the thermal reflow process [7][8][9]. Recently, the authors reported a 150-nm GaN-HEMT process using the thermal reflow technique combined with the i-line stepper lithography [10]. Fabricated devices, however, showed relatively inferior gain characteristics due to unoptimized device dimensions.…”

“…Equivalent circuit parameters of fabricated GaN-HEMTs (W g = 25 μm×2) and those in[10] (W g = 50 μm×2)…”

A novel field plate with arcuate end for improving GaN HEMTs

“…One typical technique is the field plate (FP), which gains the widest applications due to its effectiveness and simplicity. Although various FP structures such as the gate FP, source FP, drain FP, floating FP and stepped FP have been developed [4–11], they have a consistent principle that the improved distribution of E channel relies on inducing charges at the FP end. Since these induced charges can expand the depleted channel and introduce new peaks of E channel , the E channel_gate is reduced.…”