Impact of Plasma‐Damaged‐Layer Removal on GaN HEMT Devices

Abstract

Plasma‐damage during the dry‐etch process often induces degradation of the electric performance in GaN high electron mobility transistor (HEMT) devices. In this paper, the effects of wet‐etch processing on plasma‐damaged AlGaN films using various chemical solutions and propose the best chemical formulation are reported. Three chemical solutions are selected by a combinatorial method. A MIS‐capacitor TEG is fabricated on an AlGaN/GaN structure, and each surface is evaluated by XPS, SIMS, TEM, and AFM. From the results of C–V measurements of wet‐etched samples, the study reveals that the wet chemicals successfully remove charge traps at ≈−2.3 eV induced by the dry‐etch process. Moreover, these C–V results show excellent agreement with simulated trap models. The XPS results show that O/Ga ratios increase from 0.32 to 1.00 after the dry‐etch process, whereas after the wet‐etch process, the ratios return to less than 0.31. Moreover, the TEM observations reveal that an amorphous layer is only detected in the dry‐etched sample. Therefore, this amorphous layer should be an oxidized AlGaN layer. Thus, the selected chemical formulation can successfully remove the damaged‐layer induced by the dry‐etch process. The increase of surface roughness by the wet‐etch process is suppressed less than 0.1 nm.

Characterization technique for detection of atom-size crystalline defects and strains using two-dimensional fast-Fourier-transform sampling Moiré method

“…With the after RIE sample, a 2-3-nm-thick amorphous layer was observed at the surface of the AlGaN film. Since we have already confirmed a high concentration of oxygen at the surface of this sample 30,31) from prior X-ray photoelectron spectroscopy (XPS) measurements, this amorphous layer is thought to be an oxidized layer. Applying the 2D FFT sampling Moiré method, we confirmed that more than 200 defects were clearly observed along the amorphous= AlGaN boundary.…”

“…This chemical formulation was carefully selected among numerous chemical candidates using a combinatorial method and also confirmed to be effective for removal of the plasmadamaged layer. 30,31) All processes including epitaxy growth, plasma etching, and oxygen ashing were performed with commercially available equipment. As for the patterned samples assuming a GaN MOSFET structure, the AlGaN=GaN heterostructure grown on a Si substrate was prepared, and afterward recessed by ICP-RIE.…”

“…The decrease in the number of defects at the plasma-etched AlGaN film was also confirmed to cause improvement of capacitance-voltage (C-V ) results in a basic test elemental group (TEG). 30,31) A metal-insulating-semiconductor (MIS) capacitor TEG was fabricated on both after RIE and after wet treatment AlGaN=GaN samples for C-V measurements. As a result, the after RIE sample showed a positive threshold voltage shift and a deformation of the C-V curve caused by charge or electron traps generated during RIE, while the after wet treatment sample showed a much better C-V result.…”

A Comprehensive Review of Recent Progress on GaN High Electron Mobility Transistors: Devices, Fabrication and Reliability

“…The dry etching rate can reach to the level of micron per minute handily [55,56]. However, many factors need to be considered to evaluate the dry etching quality of GaN and AlGaN, such as the surface morphology, sidewall profile, etching anisotropy, material selectivity, material damage, etching uniformity and so forth.…”