Damage Characteristics of TiO₂ Thin Film Surfaces Etched by Capacitively Coupled Radio Frequency Helium Plasmas

Abstract

Damage characteristics of TiO2 thin film surfaces etched by capacitively coupled RF He plasmas are found to be dependent on gas pressure and etch time. At a low gas pressure (10 mTorr), the morphology of TiO2 surface etched for 5 min is smooth like the as-grown surface. When the etch time lengthens to 60 min, the surface morphology is smoother. However, the atomic O concentration at the surface is lower than that of the as-grown surface. On the other hand, at a high gas pressure (50–100 mTorr), the He plasma etch causes a rough surface morphology (surface defects) when the etch time lengthens to 60 min.

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

“…As described above, a spectrum of UV light emitted only from the He plasma showed a peak at a wavelength of 388 nm at each gas pressure [19]. The peak in the spectrum was due to a HeI transition line [19]. The intensity of the peak in the spectrum increased from 3 to 10 μW/cm 2 as the gas pressure increased from 1.3 to 13 Pa [19].…”

“…The penetration depth of the UV light in GaN is known to be a few hundred nm [20]. As described above, a spectrum of UV light emitted only from the He plasma showed a peak at a wavelength of 388 nm at each gas pressure [19]. The peak in the spectrum was due to a HeI transition line [19].…”

“…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.…”

“…The peak in the spectrum was due to a HeI transition line [19]. The intensity of the peak in the spectrum increased from 3 to 10 μW/cm 2 as the gas pressure increased from 1.3 to 13 Pa [19]. The photon flux of the emitted UV light increased from 6 × 10 16 to 2 × 10 17 m −2 s −1 as the gas pressure increased from 1.3 to 13 Pa.…”

“…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.…”