In-Young Bang

This study investigated the effect of temperature on the aspect-ratio etching of SiO₂ in CF₄/H₂/Ar plasma using patterned samples of a 200 nm trench in a low-temperature reactive-ion etching system. Lower temperatures resulted in higher etch rates and aspect ratios for SiO₂. However, the plasma property was constant with the chuck temperature, indicated by the line intensity ratio from optical emission spectroscopy monitoring of the plasma. The variables obtained from the characterization of the etched profile for the 200 nm trench after etching were analyzed as a function of temperature. A reduction in the necking ratio affected the etch rate and aspect ratio of SiO₂. The etching mechanism of the aspect ratio etching of SiO₂ was discussed based on the results of the surface composition at necking via energy-dispersive X-ray spectroscopy with temperature. The results suggested that the neutral species reaching the etch front of SiO₂ had a low sticking coefficient. The bowing ratio decreased with lowering temperature, indicating the presence of directional ions during etching. Therefore, a lower temperature for the aspect ratio etching of SiO₂ could achieve a faster etch rate and a higher aspect ratio of SiO₂ via the reduction of necking than higher temperatures.

Upon reentering the Earth’s atmosphere from space, a reentry vehicle becomes enshrouded in an ionization layer. This layer is known as the reentry plasma sheath and is caused by aerodynamic heating. Owing to the oscillation of charged particles in the reentry plasma sheath, the electromagnetic waves for communication between the vehicle and ground are attenuated. Analysis of the plasma density and attenuation of electromagnetic waves in a reentry plasma environment would require experimentation in an environment in which an actual aircraft reenters the atmosphere. Alternatively, an experiment in a large-scale plasma wind tunnel would be necessary. Unfortunately, these experiments would be extremely costly. Therefore, in this study, the reentry plasma was reproduced at laboratory scale using the hot refractory anode vacuum arc (HRAVA) method. In addition, the pressure in the vacuum chamber was used as a variable to probe the characteristics of the reentry plasma according to the altitude. The plasma density and attenuation of electromagnetic waves propagating through the plasma medium were measured using heterodyne interferometry and reflectometry capable of frequency analysis in the range of 10−35 GHz. The results confirmed that the plasma density and attenuation of the electromagnetic waves increased as the pressure in the vacuum chamber increased.

The use of NF₃ is significantly increasing every year. However, NF₃ is a greenhouse gas with a very high global warming potential. Therefore, the development of a material to replace NF₃ is required. F₃NO is considered a potential replacement to NF₃. In this study, the characteristics and cleaning performance of the F₃NO plasma to replace the greenhouse gas NF₃ were examined. Etching of SiO₂ thin films was performed, the DC offset of the plasma of both gases (i.e., NF₃ and F₃NO) was analyzed, and a residual gas analysis was performed. Based on the analysis results, the characteristics of the F₃NO plasma were studied, and the SiO₂ etch rates of the NF₃ and F₃NO plasmas were compared. The results show that the etch rates of the two gases have a difference of 95% on average, and therefore, the cleaning performance of the F₃NO plasma was demonstrated, and the potential benefit of replacing NF₃ with F₃NO was confirmed.