Fluoride-based Plasma Treatment Research Articles

1.48-kV enhancement-mode AlGaN/GaN high-electron-mobility transistors fabricated on 6-in. silicon by fluoride-based plasma treatment

Enhancement-mode AlGaN/GaN high-electron-mobility transistors (HEMTs) were fabricated on a Si substrate by fluorine plasma treatment without pre-etching. The threshold voltage shifted from −8 to 2.3 V, effectively converting the depletion-mode HEMT to the enhancement-mode HEMT. The leakage current was reduced by two orders of magnitude by CF4 plasma treatment. The device exhibited a superior performance with a maximum drain saturation current of 210 mA/mm at VGS = 10 V and a peak gain of 44.1 mS/mm. A low off-state gate leakage current of 10−6 mA/mm, ION/IOFF ratio of approximately 108, and high breakdown voltage of 1480 V were obtained.

Effect of Fluoride-based Plasma Treatment on the Performance of AlGaN/GaN MISFET

Effect of Fluoride-based Plasma Treatment on the Performance of AlGaN/GaN MISFET

DC Characteristics of AlGaN/GaN HEMTs Using a Dual-Gate Structure.

Multiple techniques such as fluoride-based plasma treatment, a p-GaN or p-AlGaN gate contact, and a recessed gate structure have been employed to modulate the threshold voltage of AlGaN/GaN-based high-electron-mobility transistors (HEMTs). In this study, we present dual-gate AlGaN/GaN HEMTs grown on a Si substrate, which effectively shift the threshold voltage in the positive direction. Experimental data show that the threshold voltage is shifted from -4.2 V in a conventional single-gate HEMT to -2.8 V in dual-gate HEMTs. It is evident that a second gate helps improve the threshold voltage by reducing the two-dimensional electron gas density in the channel. Furthermore, the maximum drain current, maximum transconductance, and breakdown voltage values of a single-gate device are not significantly different from those of a dual-gate device. For the fabricated single- and dual-gate devices, the values of the maximum drain current are 430 mA/mm and 428 mA/mm, respectively, whereas the values of the maximum transconductance are 83 mS/mm and 75 mS/mm, respectively.

Normally-off metamorphic AlInAs/AlInAs HEMTs on Si substrates grown by MOCVD**Project supported by the Young Scientists Fund of the National Natural Science Foundation, China (Grant No. 61401373), the Fundamental Research Funds for Central University, China (Grant No. XDJK2013B004 and 2362014XK13), and the Research Fund for the Doctoral Program of Southwest University, China (Grant No. SWU111030).

A combination of self-aligned fluoride-based plasma treatment and post-gate rapid thermal annealing was developed to fabricate a novel 120-nm T-shaped gate normally-off metamorphic Al0.49In0.51As/Ga0.47In0.53As HEMT device on a Si substrate grown by metal-organic chemical vapor deposition (MOCVD). A shift of the threshold voltage, from −0.42 V to 0.11 V was obtained and the shift can be effectively adjusted by the process parameter of CF4 plasma treatment. Furthermore, a side benefit of reducing the leakage current of the device up to two orders of magnitude was also observed. E-mode transistors with 120 nm gate length own fT up to 160 GHz and fmax of 140 GHz. These characteristics imply the potential of the fluoride-based plasma treatment technology for the fabrication of monolithic enhancement/depletion-mode mHEMTs, which also encourage the massive production with this low-cost technology.

Impacts of recessed gate and fluoride-based plasma treatment approaches toward normally-off AlGaN/GaN HEMT.

We report two approaches to fabricating high performance normally-off AIGaN/GaN high-electron mobility transistors (HEMTs). The fabrication techniques employed were based on recessed-metal-insulator-semiconductor (MIS) gate and recessed fluoride-based plasma treatment. They were selectively applied to the area under the gate electrode to deplete the two-dimensional electron gas (2-DEG) density. We found that the recessed gate structure was effective in shifting the threshold voltage by controlling the etching depth of gate region to reduce the AIGaN layer thickness to less than 8 nm. Likewise, the CF4 plasma treatment effectively incorporated negatively charged fluorine ions into the thin AIGaN barrier so that the threshold voltage shifted to higher positive values. In addition to the increased threshold voltage, experimental results showed a maximum drain current and a maximum transconductance of 315 mA/mm and 100 mS/mm, respectively, for the recessed-MIS gate HEMT, and 340 mA/mm and 330 mS/mm, respectively, for the fluoride-based plasma treated HEMT.

Enhancement-mode Al2O3/InAlN/AlN/GaN metal–insulator–semiconductor high-electron-mobility transistor with enhanced breakdown voltage using fluoride-based plasma treatment

We demonstrate an enhancement-mode (E-mode) Al2O3/InAlN/AlN/GaN metal–insulator–semiconductor high-electron-mobility transistor (MISHEMT) with enhanced breakdown voltage. The threshold voltage Vth shifts from −7.6 to 1.8 V using fluoride-based plasma treatment. The gate leakage current and the buffer leakage current were reduced by the conduction band modulation of negative fluorine charges. The reduction in the buffer leakage current enhanced the breakdown voltage from 80 to 183 V with LGD = 3 µm. The fabricated E-mode MISHEMT with a gate length of 1 µm exhibits a respectable drain current of 416 mA/mm and a peak transconductance of 150 mS/mm.

Simulation and Experimentation for Low Density Drain AlGaN/GaN HEMT

In order to improve the breakdown voltage of AlGaN/GaN high electron mobility transistors (HEMTs), we report a feasible method of low density drain (LDD) HEMT. The fluoride-based plasma treatment using CF4 gas is performed on the drain-side of the gate edge. The channel two-dimensional electron gas (2DEG) concentrations are modulated by fluoride plasma treatment, and the peak electric field at the gate edge is effectively reduced, so the breakdown voltage is improved. The electric field distributions of the LDD-HEMTs are simulated using the Silvaco software, and the peak of the electric field on the gate edge is effectively reduced. Experimental results show that, compared with the conventional HEMT, LDD-HEMTs have a lower reverse leakage current of the gate, and the breakdown voltage is increased by 36%. The current collapse characteristics of the LDD-HEMTs are confirmed by dual-pulse measurement, and an obvious pulse current reduction is due to the surface states by implanting F ions between the gate and the drain.

Fluorine plasma ion implantation in AlGaN∕GaN heterostructures: A molecular dynamics simulation study

Fluoride-based plasma treatment is a robust technique that enables shallow implantation of fluorine ions into group III-nitride epitaxial structures. This technique has been used to achieve robust threshold voltage control of the AlGaN∕GaN high electron mobility transistors and led to the realization of self-aligned enhancement-mode devices. To reveal the atomic scale interactions and provide a modeling tool for process design and optimization, a molecular dynamics (MD) simulation is conducted for fluorine plasma ion implantation. Specific potential functions are applied to calculate the interactions among atoms and simulate the dynamic process of fluorine ions’ penetration and stopping in III-nitride materials. The MD simulation provides accurate information on dopant profiles that are verified by secondary-ion-mass-spectrum measurements. Defect formation and distributions, that are critical in process development, are also investigated.

AlGaN/GaN Schottky-ohmic combined anode field effect diode with fluoride-based plasma treatment

Proposed is a novel AlGaN/GaN field effect diode with relatively thick AlGaN barrier layer, named the Schottky-ohmic combined anode field effect diode (SOCFED) because of its distinguishing anode structure. To obtain a low turn-on voltage, a method of fluoride-based plasma exposure was used. The fabricated SOCFED has a turn-on voltage of 0 V and a breakdown voltage of over 200 V.

Surface acoustic wave device on AlGaN∕GaN heterostructure using two-dimensional electron gas interdigital transducers

Surface acoustic wave (SAW) devices using two-dimensional electron gas (2DEG) as interdigital transducers (IDTs) on AlGaN∕GaN heterostructure has been demonstrated using a planar isolation technique based on the fluoride-based (CF4) plasma treatment technique. The rf characteristics of the SAW filters with planar 2DEG IDTs are compared with SAW devices that are made of metal IDTs or hybrid metal/2DEG IDTs.

Control of Threshold Voltage of AlGaN/GaN HEMTs by Fluoride-Based Plasma Treatment: From Depletion Mode to Enhancement Mode

This paper presents a method with an accurate control of threshold voltages (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sub> ) of AlGaN/GaN high-electron mobility transistors (HEMTs) using a fluoride-based plasma treatment. Using this method, the V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sub> of AlGaN/GaN HEMTs can be continuously shifted from -4 V in a conventional depletion-mode (D-mode) AlGaN/GaN HEMT to 0.9 V in an enhancement-mode AlGaN/GaN HEMT. It was found that the plasma-induced damages result in a mobility degradation of two-dimensional electron gas. The damages can be repaired and the mobility can be recovered by a post-gate annealing step at 400 degC. At the same time, the shift in V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sub> shows a good thermal stability and is not affected by the post-gate annealing. The enhancement-mode HEMTs show a performance (transconductance, cutoff frequencies) comparable to the D-mode HEMTs. Experimental results confirm that the threshold-voltage shift originates from the incorporation of F ions in the AlGaN barrier. In addition, the fluoride-based plasma treatment was also found to be effective in lowering the gate-leakage current, in both forward and reverse bias regions. A physical model of the threshold voltage is proposed to explain the effects of the fluoride-based plasma treatment on AlGaN/GaN HEMTs

Planar integration of E/D-mode AlGaN/GaN HEMTs using fluoride-based plasma treatment

A planar-fabrication technology for integrating enhancement/depletion (E/D)-mode AlGaN/GaN high-electron mobility transistors (HEMTs) has been developed. The technology relies heavily on CF/sub 4/ plasma treatment, which is used in two separate steps to achieve two objectives: 1) active device isolation and 2) threshold-voltage control for the enhancement-mode HEMT formation. Using the planar process, depletion- and enhancement-mode AlGaN/GaN HEMTs are integrated on the same chip, and a direct-coupled FET logic inverter is demonstrated. Compared with the devices fabricated by a standard mesa-etching technique, the HEMTs by a planar process have comparable dc and RF characteristics with no obvious difference in the device isolation. The device isolation by a plasma treatment remains the same after 400 /spl deg/C annealing, indicating a good thermal stability. At a supply voltage (V/sub DD/) of 3.3 V, the E/D-mode inverters show an output swing of 2.85 V, with the logic-low and logic-high noise margins at 0.34 and 1.47 V, respectively.

Enhancement-Mode AlGaN/GaN HEMTs with Low On-Resistance and Low Knee-Voltage

Based on fluoride-based plasma treatment of the gate region in AlGaN/GaN HEMTs and post-gate rapid thermal annealing (RTA), enhancement mode (E-mode) AlGaN/GaN HEMTs with low on-resistance and low knee-voltage were fabricated. The fabricated E-mode AlGaN/GaN HEMT with 1 μm-long gate exhibits a threshold voltage of 0.9 V, a knee-voltage of 2.2 V, a maximum drain current density of 310 mA/mm, a peak g m of 148 mS/mm, a current gain cutoff frequency f T of 10.1 GHz and a maximum oscillation frequency f max of 34.3 GHz. In addition, the fluoride-based plasma treatment was also found to be effective in lowering the gate leakage current, in both forward and reverse bias. Two orders of magnitude reducation in gate leakage current was observed in the fabricated E-mode HEMTs compared to the conventional D-mode HEMTs without fluoride-based plasma treatment.

Enhancement-mode AlGaN/GaN HEMTs on silicon substrate

High-performance enhancement-mode AlGaN/GaN HEMTs (E-HEMTs) were demonstrated with samples grown on a low-cost silicon substrate for the first time. The fabrication process is based on a fluoride-based plasma treatment of the gate region and postgate annealing at 450 /spl deg/C. The fabricated E-HEMTs have nearly the same peak transconductance (G/sub m/) and cutoff frequencies as the conventional depletion-mode HEMTs fabricated on the same wafer, suggesting little mobility degradation caused by the plasma treatment.

High-performance enhancement-mode AlGaN/GaN HEMTs using fluoride-based plasma treatment

We report a novel approach in fabricating high-performance enhancement mode (E-mode) AlGaN/GaN HEMTs. The fabrication technique is based on fluoride-based plasma treatment of the gate region in AlGaN/GaN HEMTs and post-gate rapid thermal annealing with an annealing temperature lower than 500/spl deg/C. Starting with a conventional depletion-mode HEMT sample, we found that fluoride-based plasma treatment can effectively shift the threshold voltage from -4.0 to 0.9 V. Most importantly, a zero transconductance (g/sub m/) was obtained at V/sub gs/=0 V, demonstrating for the first time true E-mode operation in an AlGaN/GaN HEMT. At V/sub gs/=0 V, the off-state drain leakage current is 28 /spl mu/A/mm at a drain-source bias of 6 V. The fabricated E-mode AlGaN/GaN HEMTs with 1 /spl mu/m-long gate exhibit a maximum drain current density of 310 mA/mm, a peak g/sub m/ of 148 mS/mm, a current gain cutoff frequency f/sub T/ of 10.1 GHz and a maximum oscillation frequency f/sub max/ of 34.3 GHz.