Sukhoon Jeong

THE FORMATION MECHANISM OF BARIUM TITANATE THIN FILM UNDER HYDROTHERMAL CONDITIONS

Barium titanate thin films were produced under the hydrothermal conditions, and their formation mechanism was investigated. The phase structure and surface morphology of the resultant films were directly dependent on the reaction conditions. The films that have a reaction time shorter than 8 h below the processing temperature of 150 °C in the 0.8 N Ba(OH)2 solution were composed of compounds with the component ratio m(Ba)/ m(Ti) < 1, and a flower-like surface morphology. With extended reaction time under the higher temperature, the films showed a multiphase structure and a mosaic or island-like surface morphology. In the case of 1.0 N, 1.5 N Ba(OH)2 solution, well-crystallized, monoperovskite BaTiO3 thin films having uniform, mirror-like, and visible-defectless surfaces were produced at a processing temperature of 180 °C after 24 h. The experimental results were explained by hypothesizing that the formation mechanism consists of a “dissolutions-crystallization process”.

Ferroelectric properties of hydrothermally prepared BaTiO3 thin films on Si(100) substrates by low-temperature processing

Polycrystalline BaTiO3 thin films were prepared hydrothermally on Ti-deposited Si(100) substrates at 220 °C for 24 h using a 2.0 N Ba(OH)2 solution. The surface morphology of the films observed by scanning electron microscopy indicated that the films were crack-free and uniform, and the thickness of the cross section was about 350 nm. From the AES analysis of the films, it was found that stoichiometrically uniform films exist and serious interdiffusion in the interface region did not appear. The dielectric constant and dielectric loss at 10 kHz at room temperature were about 150–200 and below 0.08, respectively. The capacitance dependence on applied dc voltage exhibited maximum value at −0.9 V and breakdown did not occur in the measurement range. The hydrothermally prepared films showed ferroelectric behavior and that was found by us for the first time. The measured value of remanent polarization (Pr) and coercive field (Ec) amounted to 21.6 μC/cm2 and 26 kV/cm, respectively.

Experimental Investigation of Material Removal Characteristics in Silicon Chemical Mechanical Polishing

The material removal characteristics of a silicon wafer were experimentally investigated with respect to the chemical dissolution and mechanical abrasion of the wafer during silicon chemical mechanical polishing (CMP) using an alkali-based slurry. The silicon surface without native oxide is rapidly dissolved by the slurry containing an amine agent, which effectively leads to the reduced hardness of the loaded silicon wafer due to Si–Si bond breaking during polishing. The abrasive particles in the slurry easily remove the reacted silicon surface, and the removal rate and wafer non-uniformity for abrasive concentrations of 1.5 – 3 wt % are better than those for other concentrations because of the low and steady coefficient of friction (COF) owing to the evenness of abrasive particles between the wafer and pad. Also, it was found that a high slurry flow rate of 700 –1000 cm 3 /min improves wafer non-uniformity owing to the reduced temporal variation of temperature, because the slurry acts as a good cooling source during polishing. However, the removal rate remains almost constant upon varying the slurry flow rate because of the effective dissolution characteristic of the slurry with abundant amine as an accelerator, regardless of the reduction of average temperature with increasing slurry flow rate. In the break-in process used to stabilize the material removal, the viscoelastic behaviors of the pad and the ground wafer surface with native oxide and wheel marks cause a temporal change of the friction force during polishing, which is related to the removal rate and wafer non-uniformity. As a result, the stabilization of removal rate and wafer non-uniformity is achieved through a steady-state process with elevated temperature and reduced COF after a total polishing time of 60 min, based on the removal process of the wafer surface and the permanent deformation in the viscoelastic behavior of the pad. # 2009 The Japan Society of Applied Physics

Effects of OH Radicals on Formation of Cu Oxide and Polishing Performance in Cu Chemical Mechanical Polishing

The amount of OH radicals generated varied according to the complexing agent or Cu ion, and the accelerating effect of OH radicals on the rate of Cu oxide formation was found in acidic pH. When Cu(I) ions and oxalic acid were added to H 2 O 2 -based slurry, the decreases in etch and removal rates of Cu were observed because more generation of OH radicals resulted in the formation of thicker Cu oxide compared to additive-free slurry. Therefore, proper control of the formation and dissolution of Cu oxide led to an increase in etch and removal rates.

Kinematical Modeling of Pad Profile Variation during Conditioning in Chemical Mechanical Polishing

Conditioning is the process of removing the glazing area from a polishing pad surface and restoring the quality of the surface to maintain a stable polishing performance. However, the conditioning process can induce a non-uniform profile variation of the pad, which can result in nonuniform material removal rates across the wafer. In this paper, a kinematical model based on Prestons equation is proposed to examine the pad profile variation (PPV) induced by swing arm conditioning with a diamond disk. The proposed model was simulated with various swing arm velocity profiles (SAVPs), and the results were compared with experimental results. The results showed the relationship between kinematical parameters and the PPV. The PPV was proportional to sliding distance based on the kinematical model, and then the sliding distance distribution across the pad was dependent on the SAVP. This study has proven the effectiveness of the kinematical model on the PPV during conditioning in chemical mechanical polishing (CMP).

Effect on Two-Step Polishing Process of Electrochemical Mechanical Planarization and Chemical–Mechanical Planarization on Planarization

Chemical–mechanical planarization (CMP) is a technique used for planarizing an overburden film in the fabrication of semiconductor devices by chemical treatment and mechanical abrasion. However, a variety of defects such as dishing of metal interconnects, erosion, delamination, and metal layer peeling are generated by a high down force in CMP. A high down force is required to generate a high material removal rate (MRR), which results in greater defects. To minimize these defects, a new planarization process is used, known as electrochemical mechanical planarization (ECMP), which requires electrochemical and mechanical energies. ECMP first involves using an electrochemical reaction to change the surface on the target material into a passivation film. Then, the passivation film is worn down using a polishing pad or abrasives on the contacted areas of the metal film with the polishing pad under a low down force. The electrochemical energy dissolves the copper solid into copper ions in an aqueous electrolyte on the contacted areas of the metal film and the polishing pad. Therefore, the low-down-force ECMP reduces the defects such as dishing, erosion, delamination and metal layer peeling to a greater degree than a conventional high-down-force CMP. Also, the MRR of the ECMP process is higher than that of the low-down-force CMP process because the MRR of the ECMP process is proportional to current density. However, some residual metal between the dielectric material was generated through the use of a nonconductive polishing pad in the ECMP process. Therefore, the CMP process is required for the final process to remove residual metals. In this research, we investigated a two-step polishing method that consists of ECMP with a nonconductive polishing pad and a conventional CMP process to planarize a micro-patterned wafer for microelectromechanical systems (MEMS). First, the ECMP process using a nonconductive polishing pad removed several tens of micrometers (µm) of bulk copper on the patterned wafer over a shorter process time than the copper CMP process only. Then, the residual copper was completely removed through the low-down-force copper CMP process. The total process time and the amount of dishing defects were reduced by applying the two-step polishing method.

Phase Transition in LiCsSO4 by EPR of Mn2+ Ions

Temperature EPR studies of Mn2 +-doped LiCsSO4 have been reported. The coexistence of resonance lines ascribed to the para- and ferro-phase has been found in the vicinity of the second order phase transition.

Magnetism depending on carrier in (Zn,Co)O

The ferromagnetic properties of (Zn,Co)O were observed by a magnetometer at low temperatures. This is, however, inconsistent with the results from the magneto-optical measurements. They reflect the presence of Co metal precipitates in (Zn,Co)O. On the other hand, the formation of Co metal precipitates was strongly suppressed by the additional Cu doping. It appears that the formation of Co metal precipitates is related to the carrier concentration in the system.

EPR study of intermediate phase in Pb3(PO4)2

Abstract EPR studies of Pb3(PO4)2 in the temperature region 430–455 K are reported. It has been shown that anomalies of the EPR spectra occurring in this intermediate phase can originate from the microdomain ferroelastic structure postulating for this temperature region.

A study on the twin domain of Pb3(PO4)2 ferroelastic crystal

Abstract Ferroelastic Pb3(PO)4)2 crystal exhibits two types of domain walls. We constructed the geometrical lattice structure in the vicinity of the domain walls and observed the tilted angle of the W′-walls geometrically. Using the polarization microscope we investigated the temperature dependence of the domain wall and the change of the conoscope image at the phase transition temperature. Near Tc . the narrow domains between two W′-walls were widened and new needle shape W-walls appeared. Above Tc we observed the separation of the Isogyre in the conoscope image by the rotation of the crystal plate, which was inferred due to the infinitesimal lattice mismatch between the cleavage planes above Tc .