Kwang-Ho Kwon

Characterizing metal-masked silica etch process in a CHF3/CF4 inductively coupled plasma

A silica etch process conducted using a CHF3/CF4 inductively coupled plasma is characterized. This was accomplished by employing a statistical experimental design in conjunction with neural network process models. As a mask layer, patterned AlSi (1%) metal was used. Parameters varied in the design includes source power, bias power, and gas ratio. Besides those conventional etch responses including etch rate, selectivity, and profile, sidewall roughness of the etched pattern is first modeled. Etch rate and sidewall roughness were found to be predominantly influenced by source power with a trade-off between them. Bias power significantly affected selectivity while controlling a trade-off against etch rate. A decrease in profile angle with increasing bias power was attributed to AlSi (1%) film expansion induced by ion bombardment effects. As gas ratio was varied, profile angle remained almost constant due to nearly same chemical reaction of its plasma on the silica surface. The roughness was little affected ...

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...

A Model-Based Analysis of Plasma Parameters and Composition in HBr/X ( X = Ar , He , N2 ) Inductively Coupled Plasmas

D A Model-Based Analysis of Plasma Parameters and Composition in HBr/X „X = Ar, He, N2... Inductively Coupled Plasmas Kwang-Ho Kwon,* Alexander Efremov, Moonkeun Kim, Nam Ki Min, Jaehwa Jeong, and Kwangsoo Kim Department of Control and Instrumentation Engineering, Korea University, Chungnam 339-700, Korea Department of Electronic Devices and Materials Technology, State University of Chemistry and Technology, 153000 Ivanovo, Russia Sogang Institute of Advanced Technology, Sogang University, Seoul 121-742, Korea

Modeling oxide etching in a magnetically enhanced reactive ion plasma using neural networks

Oxide films etched in a CHF3/CF4 plasma were qualitatively modeled using neural networks. The etching was conducted using a magnetically enhanced reactive ion etcher. A statistical 24-1 experimental design plus one center point was used to characterize relationships between process factors and etch responses. The factors that were varied include a radio frequency power, pressure, CHF3 and CF4 flow rates. The resultant nine experiments were used to train neural networks and trained networks were subsequently tested on eight experiments not belonging to the training data. A total of 17 experiments were thus conducted for modeling. Etch responses modeled are etch rate and etch profile. Root-mean-squared prediction errors of optimized models are 111 A/min and 3.50° for the etch rate and etch profile, respectively. Interaction effects between the factors were examined from the prediction models. Besides the dc bias, the F and CF2 intensities measured with an optical emission spectroscopy were related to the et...

Etching Characteristics and Mechanism of InP in Inductively Coupled HBr/Ar Plasma

Investigations of InP etch characteristics and mechanisms in HBr/Ar inductively coupled plasma were carried out. The etch rates of InP and the photoresist were measured as functions of HBr/Ar mixing ratio at fixed gas pressure (5 mTorr), input power (800 W), and bias power (200 W). Langmuir probe diagnostics and zero-dimensional (global) plasma modeling provided the information on plasma parameters, plasma composition, and fluxes of active species. It was found that, with variations in gas mixing ratio, the InP etch rate follows the changes in Br atom density and flux, but shows opposite behavior of the changes in H atoms and positive ions. These findings allow one to conclude that, under a given set of input process parameters, the InP etch process is not limited by the ion-surface interaction kinetics and that Br atoms are the main chemically active species.

Percolated pore networks of oxygen plasma-activated multi-walled carbon nanotubes for fast response, high sensitivity capacitive humidity sensors

We report on the preparation of capacitive-type relative humidity sensors incorporating plasma-activated multi-wall carbon nanotube (p-MWCNT) electrodes and on their performance compared with existing commercial technology. Highly open porous conductive electrodes, which are almost impossible to obtain with conventional metal electrodes, are fabricated by spray-depositing MWCNT networks on a polyimide layer. Oxygen plasma activation of the MWCNTs is also explored to improve the water adsorption of the MWCNT films, by introducing oxygen-containing functional groups on the CNT surface. Polyimide humidity sensors with optimized p-MWCNT network electrodes exhibit exceptionally fast response times (1.5 for adsorption and 2 s for desorption) and high sensitivity (0.75 pF/% RH). These results may be partially due to their percolated pore structure being more accessible for water molecules, expending the diffusion of moisture to the polyimide sensing film, and partially due to the oxygenated surface of p-MWCNT films, allocating more locations for adsorption or attraction of water molecules to contribute to the sensitivity.

Design, fabrication, and experimental demonstration of a piezoelectric cantilever for a low resonant frequency microelectromechanical system vibration energy harvester

Abstract. We compare the performances of vibration-powered microelectromechanical system (MEMS) electrical generators using a Pb(Zr,Ti)O3 (PZT) material. With the aid of a finite element method simulation, we have designed a PZT cantilever-based energy-harvesting system that uses mechanical vibration. We fabricate cantilevers on the MEMS scale with an integrated variable Si proof mass to obtain a low resonant frequency and high current. Based on simulation results, we fabricate cantilever devices with integrated Si proof masses with volumes of about 0.32 and 0.53  mm3. These devices compare favorably to the data obtained through simulation. Further, by comparing variable mass volumes, we obtain a high current and low resonant frequency. Similar results are obtained by simulation and experiment. Therefore, we offer a new and predictable means of obtaining a low resonant frequency for application to a micropower source area. Furthermore, from the size effect of the proof mass volume, we obtain the current and resonant frequency of these energy harvester systems. The possibility of a MEMS-scale power source for energy conversion experiments is also tested.

Etch characteristics of CeO2 thin films as a buffer layer for the application of ferroelectric random access memory

Cerium oxide (CeO2) thin film has been proposed as a buffer layer between the ferroelectric film and the Si substrate in metal–ferroelectric–insulator–silicon structures for ferroelectric random access memory applications. In this study, CeO2 thin films were etched with a Cl2/Ar gas combination in an inductively coupled plasma. The etch properties were measured for different gas mixing ratios of Cl2/(Cl2+Ar) while the other process conditions were fixed at rf power (600 W), dc bias voltage (−200 V), and chamber pressure (15 mTorr). The highest etch rate of the CeO2 thin film was 230 A/min and the selectivity of CeO2 to YMnO3 was 1.83 at a Cl2/(Cl2+Ar) gas mixing ratio of 0.2. The surface reaction of the etched CeO2 thin films was investigated using x-ray photoelectron spectroscopy (XPS) analysis. There is a Ce–Cl bonding by chemical reaction between Ce and Cl. The results of secondary ion mass spectrometer analysis were compared with the results of XPS analysis and the Ce–Cl bonding was discovered at 176....

Effects of dopant ion and Mn valence state in the La1−xAxMnO3(A=Sr,Ba) colossal magnetoresistance films

The structural and electrical properties of Mn-based colossal magnetoresistance (CMR) thin films with controlled tolerance factor and Mn ion valance ratio were studied using crystal structure and chemical bonding character analyses. La0.7Sr0.3MnO3, La0.7Ba0.3MnO3, and La0.82Ba0.18MnO3 thin films with different contents of divalent cations and Mn3+/Mn4+ ratios were deposited on amorphous SiO2/Si substrate by rf magnetron sputtering at a substrate temperature of 350 °C. The films showed the same crystalline structure as the pseudocubic structure. The change in the sheet resistance of films was analyzed according to strain state of the unit cell, chemical bonding character of Mn–O, and Mn3+/Mn4+ ratio controlling the Mn3+–O2−–Mn4+ conducting path. Mn L-edge x-ray absorption spectra revealed that the Mn3+/Mn4+ ratio changed according to different compositions of Sr or Ba and the Mn 2p core level x-ray photoelectron spectra showed that the Mn 2p binding energy was affected by the covalence of the Mn–O bond and...

Effect of gas mixing ratio on etch behavior of ZrO2 thin films in Cl2-based inductively coupled plasmas

This article reports a study carried out on a model-based analysis of the etch mechanism for ZrO2 thin films in a BCl3∕He inductively coupled plasma. It was found that an increase in the He mixing ratio at a fixed gas pressure and input power results in an increase in the ZrO2 etch rate, which changes from 36to57nm∕min for 0–83% He. Langmuir probe diagnostics and zero-dimensional plasma modeling indicated that both plasma parameters and active species kinetics were noticeably influenced by the initial composition of the BCl3∕He mixture, resulting in the nonmonotonic or nonlinear behaviors of species densities. Using the model-based analysis of etch kinetics, it was demonstrated that the behavior of the ZrO2 etch rate corresponds to the ion-flux-limited etch regime of the ion-assisted chemical reaction.