Se-Koo Kang

Etching of CoFeB Using CO ∕ NH3 in an Inductively Coupled Plasma Etching System

A CoFeB thin film composing a magnetic tunneling junction of CoFeB/MgO/CoFeB was etched in an inductively coupled plasma (ICP) etching system using CO/NH 3 gas mixtures, and its etch characteristics were compared with those of the CoFeB thin film etched using Cl 2 /Ar. When Cl 2 /Ar was used to etch the CoFeB thin film, even though its etch rate was faster than that of the CoFeB thin film etched using CO/NH 3 , a rough CoFeB surface could be observed due to the corrosion of the CoFeB surface during exposure to the air in addition to the significant change of surface composition. On the other hand, no corrosion of the CoFeB thin film was observed after the etching using CO/NH 3 . When the ratio of CO/NH 3 was varied, the highest etch rate of 12 nm/min could be observed at the ratio of 1:3 compared to about 4 nm/min for CO or NH 3 at the ICP source power of 700 W, bias power of 300 W, and 5 mTorr of operating pressure. The highest etch rate was related to the formation of volatile metal carbonyls between metal and CO, where NH 3 appeared to assist the easier formation of metal carbonyl by preventing the dissociation of CO into C and CO 2 .

Low angle forward reflected neutral beam source and its applications

As one of the many nano-device fabrication techniques employed in the semiconductor industry, neutral beams are being examined using various methods to solve possible charge-related problems that occur during device processing. This review introduces a neutral beam generated by surface neutralization of an ion beam using a low angle forward reflection technique and explains its application to various areas such as surface treatments and etching. The neutralization efficiency of an ion beam using a low angle forward reflection technique was approximately 99.7%. When a metal-oxide-semiconductor device was etched using a reactive neutral beam, it was confirmed that charge-related problems such as aspect-ratio-dependent etching and gate oxide charging could be removed using reactive neutral beam etching instead of conventional reactive ion etching. Neutral beams can be beneficial to other devices such as the III-V device and field emission device.

X-ray photoelectron spectroscopic study of Ge2Sb2Te5 etched by fluorocarbon inductively coupled plasmas

X-ray photoelectron spectroscopy was used to determine the level of surface fluorination damage of Ge2Sb2Te5 (GST) etched by fluorocarbon gases at different F/C ratios. When blank GST was etched, the gas with a higher F/C ratio produced a thinner C–F polymer on the etched surface but fluorinated Ge, Sb, and Te compounds were observed in the remaining GST. When the sidewall of the etched GST features was investigated, a thicker fluorinated layer was observed on the GST sidewall etched by the higher F/C ratio gas, indicating more fluorination due to the difficulty in preventing F diffusion into the GST through the thinner C–F layer.

Etch Damage of Ge2Sb2Te5 for Different Halogen Gases

Etch damage of Ge2Sb2Te5 (GST) has been investigated after etching in halogen inductively coupled plasmas (ICPs) such as CF4, Cl2, and HBr. X-ray photoelectron spectra of Ge, Sb, and Te on the etched surfaces showed different depths of etch damage depending on the halogen-based plasmas. The blank GST etched by CF4 showed a lower total-halogen-percentage remaining on the etched surface than that etched by Cl2 even though the depth of halogenations was the deepest for the GST etched by CF4 owing to the highest reactivity. However, when a GST feature masked by SiO2/Ti/TiN was etched, owing to the reaction of O from the SiO2 mask and C from CF4, a thinner/or no C–F polymer appeared to be formed on the etched sidewall; therefore, the highest halogenation was observed on the GST etched by CF4. Among the halogen-gases investigated, HBr showed the lowest damage due to the lowest reactivity.

Enhancement-Mode Metal Organic Chemical Vapor Deposition-Grown ZnO Thin-Film Transistors on Glass Substrates Using N2O Plasma Treatment

Thin-film transistors (TFTs) were fabricated on a glass substrate with a metal organic chemical vapor deposition (MOCVD)-grown undoped zinc oxide (ZnO) film as a channel layer and plasma-enhanced chemical vapor deposition (PECVD)-grown silicon nitride as a gate dielectric. The as-fabricated ZnO TFTs exhibited depletion-type device characteristics with a drain current of about 24 µA at zero gate voltage, a turn-on voltage (Von) of -24 V, and a threshold voltage (VT) of -4 V. The field-effect mobility, subthreshold slope, off-current, and on/off current ratio of the as-fabricated TFTs were 5 cm2 V-1 s-1, 4.70 V/decade, 0.6 nA, and 106, respectively. The postfabrication N2O plasma treatment on the as-fabricated ZnO TFTs changed their device operation to enhancement-mode, and these N2O-treated ZnO TFTs exhibited a drain current of only 15 pA at zero gate voltage, a Von of -1.5 V, and a VT of 11 V. Compared with the as-fabricated ZnO TFTs, the off-current was about 3 orders of magnitude lower, the subthreshold slope was nearly 7 times lower, and the on/off current ratio was 2 orders of magnitude higher for the N2O-plasma-treated ZnO TFTs. X-ray phtotoelectron spectroscopy analysis showed that the N2O-plasma-treated ZnO films had fewer oxygen vacancies than the as-grown films. The enhancement-mode device behavior as well as the improved performance of the N2O-treated ZnO TFTs can be attributed to the reduced number of oxygen vacancies in the channel region.