Etch characteristics of FePt magnetic thin films using inductively coupled plasma reactive ion etching

Etch characteristics of L10 FePt thin films masked with TiN films were investigated using an inductively coupled plasma (ICP) reactive ion etching in a CH₃OH/Ar plasma. As the CH₃OH gas was added to Ar, the etch rates of FePt thin films and TiN hard mask gradually decreased, and the etch profile of FePt films improved with high degree of anisotropy. With increasing ICP rf power and dc-bias voltage to substrate and decreasing gas pressure, the etch rate increased and the etch profile becomes vertical without any redepositions or etch residues. Based on the etch characteristics and surface analysis of the films by X-ray photoelectron spectroscopy, it can be concluded that the etch mechanism of FePt thin films in a CH₃OH/Ar gas does not follow the reactive ion etch mechanism but the chemically assisted sputter etching mechanism, due to the chemical reaction of FePt film with CH₃OH gas.     

Etch characteristics of IrMn thin films using an inductively coupled plasma of CH3OH/Ar

An inductively coupled plasma reactive ion etching of IrMn magnetic thin films patterned with Ti hard mask was studied in a CH₃OH/Ar gas mix. As the CH₃OH concentration increased, the etch rates of IrMn thin films and Ti hard mask decreased, while the etch profiles improved with high degree of anisotropy. The effects of coil rf power, dc-bias voltage to substrate and gas pressure on the etch characteristics were investigated. The etch rate increased and the etch profile improved with increasing coil rf power, dc-bias voltage and decreasing gas pressure. X-ray photoelectron spectroscopy revealed that the chemical reaction between IrMn films and CH₃OH gas occurred, leading to the clean and good etch profile with high degree of anisotropy of 90°.     

Inductively coupled plasma reactive ion etching of titanium thin films using a Cl2/Ar gas

Inductively coupled plasma reactive ion etching of titanium thin films patterned with a photoresist using Cl₂/Ar gas was examined. The etch rates of the titanium thin films increased with increasing the Cl₂ concentration but the etch profiles varied. In addition, the effects of the coil rf power, dc-bias voltage and gas pressure on the etch rate and etch profile were investigated. The etch rate increased with increasing coil rf power, dc-bias voltage and gas pressure. The degree of anisotropy in the etched titanium films improved with increasing coil rf power and dc-bias voltage and decreasing gas pressure. X-ray photoelectron spectroscopy revealed the formation of titanium compounds during etching, indicating that Ti films etching proceeds by a reactive ion etching mechanism.     

Etch characteristics of indium zinc oxide thin films using inductively coupled plasma of a Cl2/Ar gas

Inductively coupled plasma reactive ion etching of indium zinc oxide (IZO) thin films masked with a photoresist was performed using a Cl₂/Ar gas. The etch rate of the IZO thin films increased as Cl₂ gas was added to Ar gas, reaching a maximum at 60% Cl₂ and decreasing thereafter. The degree of anisotropy in the etch profile improved with increasing coil rf power and dc-bias voltage. Changes in pressure had little effect on the etch profile. X-ray photoelectron spectroscopy confirmed the formation of InCl₃ and ZnCl₂ on the etched surface. The surface morphology of the films etched at high Cl₂ concentrations was smoother than that of the films etched at low Cl₂ concentrations. These results suggest that the dry etching of IZO thin films in a Cl₂/Ar gas occurs according to a reactive ion etching mechanism involving ion sputtering and a surface reaction.     

Etch characteristics of CoFeB magnetic thin films using high density plasma of a H2O/CH4/Ar gas mixture

Etch characteristics of CoFeB magnetic thin films patterned with TiN hard masks were investigated using inductively coupled plasma reactive ion etching in H₂O/Ar and H₂O/CH₄ gas mixes. As the H₂O concentration in the H₂O/Ar gas increased, the etch rates of CoFeB and TiN films decreased simultaneously, while the etch selectivity increased and etch profiles improved slightly without any redeposition. The addition of CH₄ to the H₂O gas resulted in an increase in etch selectivity and a higher degree of anisotropy in the etch profile. X-ray photoelectron spectroscopy was performed to understand the etch mechanism in H₂O/CH₄ plasma. A good pattern transfer of CoFeB films masked with TiN films was successfully achieved using the H₂O/CH₄ gas mix.     

Evolution of etch profile in etching of CoFeB thin films using high density plasma reactive ion etching

Inductively coupled plasma reactive ion etching of CoFeB magnetic thin films patterned with Ti hard mask was studied in a CH₃OH/Ar gas mix. As the CH₃OH concentration increased, the etch rates of CoFeB thin films and Ti hard mask decreased but the etch profiles improved with high degree of anisotropy. The effects of coil rf power, dc-bias voltage and gas pressure on the etch characteristics were investigated. The etch rate increased with increasing coil rf power, dc-bias voltage and decreasing gas pressure. The degree of anisotropy in the etch profile of CoFeB films improved with increasing coil rf power and dc-bias voltage. X-ray photoelectron spectroscopy revealed that the chemical compounds containing Co and Fe components were formed during the etching. However, it was expected that the formation of these compounds could not increase the etch rates of the films due to low volatile compounds despite the improvement in etch profile.     

Investigation on etch characteristics of MgO thin films using a HBr/Ar plasma

Etch characteristics of MgO thin films were investigated using an inductively coupled plasma reactive ion etcher in a HBr/Ar plasma. As the concentration of HBr gas increased, the etch rate of MgO thin films gradually decreased, but the etch rate of Ti hard mask showed initial decrease and then increased with increasing HBr concentration. The etch profile of MgO films was improved with increasing HBr concentration and a high degree of anisotropy in etch profile was achieved at 30% HBr/Ar gas. Based on the etch characteristics and surface analysis by X-ray photoelectron spectroscopy, it can be concluded that the etch mechanism of MgO thin films in a HBr/Ar gas does not follow the reactive ion etch mechanism but the sputter etching mechanism with the assistance of chemical reactions on the film surfaces.     

Dry etching process of GaAs in capacitively coupled BCl3-based plasmas

Dry etching of GaAs was investigated in BCl₃, BCl₃/N₂ and BCl₃/Ar discharges with a mechanical pump-based capacitively coupled plasma system. Etched GaAs samples were characterized using scanning electron microscopy and surface profilometry. Optical emission spectroscopy was used to monitor the BCl₃-based plasma during etching. Pure BCl₃ plasma was found to be suitable for GaAs etching at > 100 mTorr while producing a clean and smooth surface and vertical sidewall. Adding N₂ or Ar to the BCl₃ helped increase the etch rates of GaAs. For example, the GaAs etch rate was doubled with 20% N₂ composition in the BCl₃/N₂ plasma compared to the pure BCl₃ discharge at 150 W CCP power and 150 mTorr chamber pressure. The GaAs etch rate was ∼ 0.21 µm/min in the 20 sccm BCl₃ plasma. The BCl₃/Ar plasma also increased etch rates of GaAs with 20% of Ar in the discharge. However, the surface morphology of GaAs was strongly roughened with high percentage (> 30%) of N₂ and Ar in the BCl₃/N₂ and BCl₃/Ar plasma, respectively. Optical emission spectra showed that there was a broad BCl₃-related molecular peak at 450-700 nm wavelength in the pure BCl₃ plasma. When more than 50% N₂ was added to the BCl₃ plasma, an atomic N peak (367.05 nm) and molecular N₂ peaks (550-800 nm) were detected. Etch selectivity of GaAs to photoresist decreased with the increase of % N₂ and Ar in the BCl₃-based plasma.     

Etch damage characteristics of TiO2 thin films by capacitively coupled RF Ar plasmas

Etch damage of TiO₂ thin films with the anatase phase by capacitively coupled RF Ar plasmas has been investigated. The plasma etching causes a mixed phase of anatase and rutile or the rutile phase. The effect of Ar plasma etching damage on degenerating TiO₂ thin films is dependent on gas pressure and etching time. The physical etching effect at a low gas pressure (1.3 Pa) contributes to the degradation: the atomic O concentration at the thin film surface is strongly increased. At a high gas pressure (13-27 Pa) and long etching time (60 min), there are a variety of surface defects or pits, which seem to be similar to those for GaN resulting from synergy effect between particle and UV radiation from the plasmas. For the hydrophilicity, the thin film etched at the high gas pressure and a short etching time (5 min) seems to have no etch damage: its contact angle property is almost similar to that for the as-grown thin film, and is independent of the black light irradiation. This result would probably result from formation of donor-like surface defects such as oxygen vacancy.     

Dry etching of TiN in N2/Cl2/Ar adaptively coupled plasma

We investigated the N₂ additive effect on the etch rates of TiN and SiO₂ and etch profile of TiN in N₂/Cl₂/Ar adaptively coupled plasma (ACP). The mixing ratio of Cl₂ and Ar was fixed at 75 and 25 sccm, respectively. The N₂ flow rate was increased from 0 to 9 sccm under the constant pressure of 10 mTorr. As N₂ flow rate was increased in N₂/Cl₂/Ar plasma, the etch rate of TiN was linearly increased, but that of SiO₂ was increased non-monotonically. The etch profile and the compositional changes of TiN was investigated with field emission-scanning electron microscope (FE-SEM), FE-Auger electron spectroscopy (FE-AES) and x-ray photoelectron spectroscopy (XPS). When 9 sccm N₂ was added into Cl₂/Ar, a steep etch profile and clean surface of TiN was obtained. In addition, the signals of TiN and Ti were disappeared in FE-AES and XPS when N₂ additive flow into Cl₂/Ar was above 6 sccm. From the experimental data, the increase in TiN etch rate was mainly caused by the increase of desorption and evacuation rate of etch by products because of the increased effective pumping speed. The etch mechanism of TiN in N₂/Cl₂/Ar ACP plasma can be concluded as the ion enhanced chemical etch.     

Etch characteristics of indium zinc oxide thin films in a C2F6/Ar plasma

Dry etching of indium zinc oxide (IZO) thin films was performed using inductively coupled plasma reactive ion etching in a C₂F₆/Ar gas. The etch characteristics of IZO films were investigated as a function of gas concentration, coil rf power, dc-bias voltage to substrate, and gas pressure. As the C₂F₆ concentration was increased, the etch rate of the IZO films decreased and the degree of anisotropy in the etch profile also decreased. The etch profile was improved with increasing coil rf power and dc-bias voltage, and decreasing gas pressure. An X-ray photoelectron spectroscopy analysis confirmed the formation of InF₃ and ZnF₂ compounds on the etched surface due to the chemical reaction of IZO films with fluorine radicals. In addition, the film surfaces etched at different conditions were examined by atomic force microscopy. These results demonstrated that the etch mechanism of IZO thin films followed sputter etching with the assistance of chemical reaction.     

Resistive switching characteristics of ytterbium oxide thin film for nonvolatile memory application

This paper studies the effects of both the positive and negative forming processes on the resistive switching characteristics of a Pt/Yb₂O₃/TiN RRAM device. The polarity of the forming process can determine the transition mechanism, either bipolar or unipolar. Bipolar behavior exists after the positive forming process, while unipolar behavior exists after the negative forming process. Furthermore, the bipolar switching characteristics of the Pt/Yb₂O₃/TiN device can be affected by using a reverse polarity forming treatment, which not only reduces the set and reset voltage, but also improves the on/off ratio.     

Effects of tunnel oxide process on SONOS flash memory characteristics

In this paper, various process conditions of tunnel oxides are applied in SONOS flash memory to investigate their effects on charge transport during the program/erase operations. We focus the key point of analysis on Fermi-level (E_F) variation at the interface of silicon substrate and tunnel oxide. The Si-O chemical bonding information which describes the interface oxidation states at the Si/SiO₂ is obtained by the core-level X-ray photoelectron spectroscopy (XPS). Moreover, relative E_F position is determined by measuring the Si 2p energy shift from XPS spectrums. Experimental results from memory characteristic measurement show that MTO tunnel oxide structure exhibits faster erase speed, and larger memory window during P/E cycle compared to FTO and RTO tunnel oxide structures. Finally, we examine long-term charge retention characteristic and find that the memory windows of all the capacitors remain wider than 2 V after 10⁵ s.     

Electrical characteristics of a ZrO2/SiO2 modified tunnel barrier for low-temperature non-volatile memory

The electrical characteristics of nonvolatile memory, which consists of an asymmetrical ZrO₂/SiO₂ (ZO) modified tunnel barrier, a high-k HfO₂ trapping layer and an Al₂O₃ blocking layer, were investigated for the application of a tunnel barrier engineered nonvolatile memory at low process temperatures. The efficiency of the ZO modified tunnel barrier on the charge trap flash (CTF) memory cell was compared to a conventional single SiO₂ tunnel barrier. The ZO tunnel barrier revealed field sensitivity larger than the single SiO₂ tunnel barrier. The programming and erasing speeds as well as the retention and endurance characteristics of CTF memory were largely enhanced. Moreover, the forming gas annealing process in 2% diluted H₂/N₂ ambient improved the charging trapping property and tunneling sensitivity of the ZO modified tunnel barrier.     

Development of random access memory in Nd0.7Ca0.3MnO3/YBa2Cu3O7 heterostructure

The effects of electrode on the resistive switching in Nd_0.7Ca_0.3MnO₃(NCMO)/YBa₂Cu₃O₇(YBCO) heterostructure are investigated at room temperature. For Cu/NCMO/YBCO, resistance can be switched on-and-off from a high- to low-resistance state at a steady ratio of 25% with a pulsed-voltage of ± 3 V. On the other hand, a giant resistance-change as large as 1350% is observed with ± 5 V for Ag/NCMO/YBCO with a fast decay down to 550%. Our experimental results show clear evidences that the nature of interfaces can be modified by the electric field and it dictates the resistive switching behavior of these heterostructure devices, which are the potential candidates for the random access memory.     

Epitaxial growth of Fe3Si/CaF2/Fe3Si magnetic tunnel junction structures on CaF2/Si(111) by molecular beam epitaxy

The Fe₃Si(24 nm)/CaF₂(2 nm)/Fe₃Si(12 nm) magnetic tunnel junction (MTJ) structures were grown epitaxially on CaF₂/Si(111) by molecular beam epitaxy (MBE). The 12-nm-thick Fe₃Si underlayer was grown epitaxially on CaF_2/Si(111) at approximately 400 °C; however, the surface of the Fe₃Si film was very rough, and thus a lot of pinholes are considered to exist in the 2-nm-thick CaF₂ barrier layer. The average roughness (Ra) of the CaF₂ barrier layer was 7.8 nm. This problem was overcome by low-temperature deposition of Fe and Si at 80 °C on CaF₂/Si(111), followed by annealing at 250 °C for 30 min to form the Fe₃Si layer. The Ra roughness was significantly reduced down to approximately 0.26 nm. A hysteresis loop with coercive field H_c of approximately 25 Oe was obtained in the magnetic field dependence of Kerr rotation at room temperature (RT).     

Effect of structural transformation on the electrical properties for Ge1Sb2Te4 thin film

Dependence of electrical properties of phase change Ge₁Sb₂Te₄ thin film on structural transformation was investigated. The electrical resistivity of the film decreases with increasing annealing temperature with a steep drop at ∼ 230 °C (the second crystallization temperature), at which the structure of Ge₁Sb₂Te₄ changes from face-centered cubic to trigonal state. The steep drop of resistivity at the second crystallization temperature is mainly due to the increase of hole density within the p-type film, according to Hall measurement. The crystallization process has been followed by in situ resistance measurement at various annealing temperatures. Transmission electron microscope and atomic force microscope were also employed to study the film.     

Optical and magnetic properties of elliptical hematite (α-Fe2O3) nanoparticles coated with uniform continuous layers of silica of different thickness

Elliptical-type α-Fe₂O₃ nanoparticles with/without silica shell have been prepared. The core particles were coated with uniform continuous layers of silica of two different thicknesses by hydrolysis of TEOS. The obtained HCP structure elliptical α-Fe₂O₃ nanoparticles with ∼ 240 nm length and 100 nm width is polycrystalline in nature. The thicknesses of SiO₂ shell coated on α-Fe₂O₃ are about 55 and 30 nm, respectively. The optical and magnetic properties of these nanoparticles have been investigated.     

The effects of gas flow rates on the etch characteristics of silicon nitride with an extreme ultra-violet resist pattern in CH2F2/N2/Ar capacitively coupled plasmas

The effects of CH₂F₂ and N₂ gas flow rates on the etch selectivity of silicon nitride (Si₃N₄) layers to extreme ultra-violet (EUV) resist and the variation of the line edge roughness (LER) of the EUV resist and Si₃N₄ pattern were investigated during etching of a Si₃N₄/EUV resist structure in dual-frequency superimposed CH₂F₂/N₂/Ar capacitive coupled plasmas (DFS-CCP). The flow rates of CH₂F₂ and N₂ gases played a critical role in determining the process window for ultra-high etch selectivity of Si₃N₄/EUV resist due to disproportionate changes in the degree of polymerization on the Si₃N₄ and EUV resist surfaces. Increasing the CH₂F₂ flow rate resulted in a smaller steady state CH_xF_y thickness on the Si₃N₄ and, in turn, enhanced the Si₃N₄ etch rate due to enhanced SiF₄ formation, while a CH_xF_y layer was deposited on the EUV resist surface protecting the resist under certain N₂ flow conditions. The LER values of the etched resist tended to increase at higher CH₂F₂ flow rates compared to the lower CH₂F₂ flow rates that resulted from the increased degree of polymerization.     

Advantages of inductively coupled plasma-assisted sputtering for preparation of stoichiometric VO2 films with metal-insulator transition

Inductively coupled plasma (ICP)-assisted sputtering with an internal coil enabled deposition of stoichiometric crystalline vanadium dioxide (VO₂) films on a sapphire (Al₂O₃) (001) substrate under widely various deposition conditions. The films showed a metal-insulator (M-I) transition around temperatures of 68 °C with several orders of change in resistivity. Particularly, low-temperature (250 °C) growth of VO₂ film with two orders transition decade was achieved in ICP-assisted sputtering, in contrast with conventional sputtering, which required 400 °C for VO₂ growth. Rutherford back scattering (RBS) measurements revealed that the VO₂ film prepared by ICP-assisted sputtering was exactly stoichiometric, containing no impurity atoms from the inserted coil material. The ICP-assisted sputtering was examined in comparison to conventional sputtering in view of plasma characteristics.