Etch‐induced damage characteristics of n‐GaN surfaces by capacitively coupled radio frequency He and Ar plasmas

Abstract

The surface morphology of n‐GaN etched by the He plasma is independent of gas pressure and etch time: it is observed to be as smooth as that of the as‐grown. This result is significantly different from that by the Ar plasma etch which causes surface defects at a high gas pressure (50∼100 mTorr) and long etch time (> 60 min) due to synergy effect of plasma ions and UV lights emitted. This difference would result from a difference between UV light spectra emitted: for the He plasma there is no UV light less than 380 nm in wavelength, whereas for the Ar plasma there is the UV light emission. The simulation shows that the N/Ga ratio at the surface etched by the He plasma at each gas pressure (Ga‐rich) is much lower than that by the Ar plasma. The results simulated for the He plasma are in disagreement with those measured by XPS, which would probably indicate additional removal of Ga from the Ga‐rich surface by volatilisation/evaporation due to thermal effect. For the Ar plasma, the experimental N/Ga ratio at a low gas pressure (10 mTorr) is reproduced by physical effect, whereas at the high gas pressure it is not reproduced, which would be closely related to occurrence of the surface defects. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Damage characteristics of n-GaN thin film surfaces etched by ultraviolet light-assisted helium plasmas

“…The previous study shows that the morphological change in the surface etched by the He plasma does not occur regardless of gas pressure. The He plasma emits UV light whose peak wavelength, 388 nm, is longer than that of the GaN band-gap energy regardless of gas pressure [17,19]. A series of our studies indicate that the morphological change in the etched surface probably results from the synergistic effect of the ion bombardment and the irradiation with UV light corresponding to the GaN band-gap energy, i.e., the UV light irradiation effect.…”

“…Samples were placed on the surface of the cathode powered by means of the RF generator. The maximum value of the applied RF voltage V RF was set to 200 V, which was the same as that used in the previous study of the He plasma etching [17][18][19]. The temperature of the cathode was kept at 18°C by recirculating through a water chiller, which suggests a possibility that the temperature of the sample surface facing the plasma increases from 18°C owing to long time exposure.…”

“…A spectrum of the UV light emitted from the Ar plasma has some peaks at a wavelength range shorter than and comparable to that of the GaN band-gap energy, 3.4 eV (365 nm). Our group has also studied damage characteristics of n-GaN thin film surfaces etched by capacitively coupled RF He plasmas [17,18]. The previous study shows that the morphological change in the surface etched by the He plasma does not occur regardless of gas pressure.…”

Damage Characteristics of <i>n</i>-GaN Crystal Etched with N₂Plasma by Soft X-Ray Absorption Spectroscopy

“…The Ar plasma generated at a high gas pressure of 50-100 mTorr caused a morphological change (surface roughening and defect formation) in the surfaces as the etching time increased more than sixty minutes [7]. However, in the samples etched by N 2 plasma with a lower self-bias voltage of −200 V, the surface morphologies changed little, and their surfaces were equivalent to that of the asgrown sample [8].…”

“…We have investigated the damage of n-GaN crystals etched by various plasmas (Ar, He, and N 2 ) using a capacitively coupled radio frequency (RF) plasma reactor [7][8][9]. The Ar plasma generated at a high gas pressure of 50-100 mTorr caused a morphological change (surface roughening and defect formation) in the surfaces as the etching time increased more than sixty minutes [7].…”