Chang-Il Kim

Etching properties of Pt thin films by inductively coupled plasma

The inductively coupled plasma etching of platinum with Ar/Cl2 gas chemistries is described. X-ray photoelectron spectroscopy (XPS) is used to investigate the chemical binding states of the etched surface with various Ar/(Ar+Cl2) mixing ratios. Atomic percentage of Cl element increases with increasing Ar/(Ar+Cl2) mixing ratio with the exception of Ar/(Ar+Cl2) mixing ratio of 1. At the same time, the peaks that seem to be subchlorinated Pt at XPS narrow scan spectra are found and Cl–Pt bonds rapidly increase at Ar/(Ar+Cl2) mixing ratio of 0.62. Quadrupole mass spectrometry (QMS) is used to examine the variations of plasma characteristics with various Ar/Cl2 gas chemistries. QMS results show that Cl2 molecules are converted to Cl radicals with adding Ar gas to Cl2 plasma. QMS results support the increased atomic percentages of Cl elements on the etched Pt surface. Single Langmuir probe measures ion current density with various Ar/Cl2 gas plasma. Ion current densities are used to investigate the ion bombardm...

Etching mechanism of (Ba, Sr)TiO3 films in high density Cl2/BCl3/Ar plasma

(Ba, Sr)TiO3 (BST) thin films have attracted great interest as new dielectric materials of capacitors for ultralarge-scale integrated dynamic random access memories such as 1 or 4 Gbit. In this study, inductively coupled BCl3/ Cl2/Ar plasmas was used to etch BST. The Cl2/(Cl2+Ar) was fixed at 0.2, and the BST thin films were etched by adding BCl3. The characteristics of the plasmas were estimated using optical emission spectroscopy (OES). The change of Cl, B radical density was measured by OES as a function of BCl3 percentage in Cl2/Ar. The cross section of BST thin films and residue remaining after the etch was investigated by scanning electron microscopy. The chemical reactions between BST and Cl2 and the surface of BST films etched with different BCl3/Cl2/Ar gas mixing ratios were investigated using x-ray photoelectron spectroscopy.

Etching mechanism of MgO thin films in inductively coupled Cl2∕Ar plasma

The etching mechanism of MgO thin films in Cl2∕Ar plasma was investigated. It was found that the increasing Ar in the mixing ratio of Cl2∕Ar plasma causes nonmonotonic MgO etch rate, which reaches a maximum value at 70%Ar+30%Cl2. Langmuir probe measurement showed the noticeable influence of Cl2∕Ar mixing ratio on electron temperature and electron density. The zero-dimensional plasma model indicated monotonic changes of both densities and fluxes of active species. At the same time, analyses of surface kinetics showed the possibility of nonmonotonic etch rate behavior due to the concurrence of physical and chemical pathways in ion-assisted chemical reaction.

Recovery of plasma-induced damage in PZT thin film with O2 gas annealing

In this study, recovery of plasma induced damage in PZT [Pb(Zr,Ti)O 3 ] thin film with O 2 annealing has been investigated. The PZT thin films were etched as a function of Cl 2 /Ar and additive CF 4 into Cl 2 (80%)/Ar(20%). The etch rates of PZT thin films were 160 nm/min at Cl 2 (80%)/Ar(20%) gas mixing ratio and 197 nm/min at 30% additive CF 4 into Cl 2 (80%)/Ar(20%). The etched profile of PZT films was obtained above 70° by the scanning electron microscopy (SEM). In order to recover properties of PZT thin films after etching, the etched PZT thin films were re-annealed at various temperatures in O 2 atmosphere. From the hysteresis curves, ferroelectrical properties are improved by O 2 re-annealing process. The improvement of ferroelectric behavior at annealed sample is consistent with the increase of the (100) and (200) PZT phase revealed by X-ray diffraction (XRD). From X-ray photoelectron spectroscopy (XPS) analysis, the intensity of the Pb-O, Zr-O and Ti-O peaks are increased and the chemical residue peak is reduced by O 2 re-annealing. The ferroelectric behavior is consistent with the dielectric nature of Ti x O y and is recovered by O 2 recombination during a rapid thermal annealing process. From the atomic force microscopy (AFM) images, it shows that the surface roughness of re-annealed sample after etching is improved.

Plasma-induced damage in PZT thin films etched by inductively coupled plasma

Abstract We investigated the etching damage induced by Ar/(Cl2+CF4) plasma and improvement in etching damage by O2 annealing. PZT thin films were etched for 1 min in an ICP using a gas mixture of Cl2 80%/CF4 20% with 20% Ar addition. The etching conditions were fixed at a substrate temperature of 30 °C, RF power of 700 W, DC bias voltage of −200 V and a chamber pressure of 15 mTorr. To improve the ferroelectric properties of PZT thin films after etching, the samples were annealed for 10 min at 600 °C in O2 atmosphere. After O2 annealing, the remanent polarization-on-fatigue property was recovered to the characteristics of the as-deposited film. According to X-ray diffraction (XRD) analysis, an increase in (100) and (200) phases showed the improvement in structure of the PZT thin films after the O2 annealing process. In addition, transmission electron microscope (TEM) images showed that the etched PZT surface is damaged by the bombardment of energetic particles, but that the damaged surface can be recovered by O2 annealing. The results of electron probe microanalysis (EPMA) and Auger electron spectroscopy (AES) showed that O2 annealing supports the substitution of oxygen vacancies on the PZT surface by O atoms. This decrease in oxygen vacancies improves the fatigue characteristics of PZT thin films.

Study on surface reaction of (Ba, Sr)TiO3 thin films by high density plasma etching

Ferroelectric devices are extremely useful for dynamic random access memories applications because of their high dielectric constant. Using ferroelectric device structure, manufacturing cell capacitance of highly integrated memory device is possible. The small feature size requires anisotropic etching. Since the research of (Ba, Sr)TiO3 thin film etching is seriously lacking, we studied the surface reaction of (Ba, Sr)TiO3 thin films by using high density plasma etching. In this study, (Ba, Sr)TiO3 thin films were etched with Cl2/Ar gas combination in an inductively coupled plasma. This was done by varying the etching parameters such as radio frequency power, direct current bias, and chamber pressure. The maximum etch rate of the BST films was 560 A/min under Cl2/(Cl2+Ar) of 0.2, 600 W/250 V, and 5 mTorr. The selectivity of BST to Pt and SiO2 was 0.52, 0.43, respectively. The surface reaction of the etched (Ba, Sr)TiO3 thin films was investigated with x-ray photoelectron spectroscopy (XPS) using narrow sc...

Volume and heterogeneous chemistry of active species in chlorine plasma

Abstract Chlorine plasma parameters and the mechanisms of both volume and heterogeneous reactions were investigated using a combination of experimental methods and plasma modeling. It was found that increasing gas pressure within the range 20–200 Pa leads to sufficient deformation of the electron energy distribution function and to corresponding changes in kinetic and transport coefficients. Direct electron impact dissociation and ionization were found to be the main mechanisms for radical and ion generation, while contributions from dissociative attachment and dissociative ionization were negligible. Heterogeneous recombination of chlorine atoms is the dominant decay channel, which is described by a first-order kinetic mechanism.

Ferroelectric properties of Pb(Zr,Ti)O 3 heterolayered thin films for FRAM applications

Ferroelectric PZT (20/80)/PZT (80/20) heterolayered thin films were fabricated by spin-coating method on a Pt/Ti/SiO2/Si substrate alternately using PZT (20/80) and PZT (80/20) alkoxide solutions. All PZT heterolayered films show dense and homogeneous structure without the presence of the rosette microstructure. The relative dielectric constant and dielectric loss at 100 kHz of the PZT-6 film were about 355 and 0.016, respectively. As the number of coats increased, remanent polarization increased, the coercive field decreased and the values of the PZT-6 film were 16.14 µC/cm2 and 97.1 kV/cm, respectively. Leakage current density of the PZT-6 heterolayered film was 2.5 × 10-7 A/cm2 at 5 V.

On mechanisms of argon addition influence on etching rate in chlorine plasma

Abstract Parameters of Cl 2 /Ar plasma were investigated aimed to understand the mechanism of Ar addition influence on etching rate acceleration. Analysis was carried out on the base of combination of experimental methods and plasma modelling. It was found that the addition of Ar to chlorine under a constant total pressure condition cause changes in plasma electro-physical properties (EEDF, mean electron energy) due to the ‘transparency’ effect. Direct electron impact dissociation of Cl 2 molecules was found as the main source of chlorine atoms while the contributions of dissociative attachment and stepwise dissociation involving Ar metastable atoms are negligible. It was supposed that the main reason of etching rate increasing in Cl 2 /Ar mixture plasma is connected with simultaneous action of Ar on volume chemistry and the heterogeneous stage of etching process.

Etching mechanism of Bi4−xLaxTi3O12 films in Ar/Cl2 inductively coupled plasma

The etching behavior of Bi4−xLaxTi3O12 (BLT) films in inductively coupled Ar/Cl2 plasma was investigated in terms of etch parameters. The etching rate as a function of Ar/Cl2 mixing ratio showed a maximum of 50.3 nm/min for the mixture of Ar(80%)/Cl2(20%). The increase of r.f. power and d.c.-bias voltage caused an increase in BLT etch rate under any fixed gas composition. To understand etch mechanism, the plasma diagnostics were performed using Langmuir probe (LP) and optical emission spectroscopy (OES). The LP measurement indicated that the increase of Ar mixing ratio in Ar/Cl2 plasma leads to monotonic changes of both electron density and total density of positive ions. The same tendencies were found for chlorine atoms and molecules using OES. The chemical states of BLT were studied using X-ray photoelectron spectroscopy (XPS). XPS narrow scan analysis shows that the La-chlorides remained on the etched surface. The analysis of surface reactions and plasma diagnostics in the frameworks of an ion-assisted etching mechanism confirms the possibility of non-monotonic etch rate behavior due to the concurrence of physical sputtering and chemical etching activated by ion bombardment.