Heung-Sik Tae

Low‐temperature silicon homoepitaxy by ultrahigh vacuum electron cyclotron resonance chemical vapor deposition

High quality silicon homoepitaxial layers are successfully grown at 560 °C by ultrahigh vacuum electron cyclotron resonance chemical vapor deposition (UHV‐ECRCVD) using a SiH4/H2 plasma. The effects of substrate dc bias on the in situ hydrogen plasma clean and the subsequent silicon epitaxial growth are examined by the reflection high‐energy electron diffraction (RHEED), secondary ion mass spectroscopy (SIMS), and cross‐section transmission electron microscopy (XTEM). It is observed that the substrate dc bias plays a significant role in obtaining a damage‐free, clean Si substrate prior to epitaxial growth. Severe damage in the Si surface is observed by XTEM, though RHEED shows a streaky pattern, when the substrate is electrically floating, but the damage can be suppressed with +10 V dc bias to the substrate. Substrate dc bias during plasma deposition drastically changes the crystal structure from polycrystalline at −50 V to high quality epitaxial silicon at substrate biases greater than +50 V. Precise con...

Low-temperature in situ cleaning of silicon (100) surface by electron cyclotron resonance hydrogen plasma

Low‐temperature, defect‐free, in situ cleaning of silicon prior to homoepitaxy is successfully developed by an electron cyclotron resonance hydrogen plasma treatment in an ultrahigh vacuum chamber. The plasma potential distribution was measured by a Langmuir probe method to understand the effect of the substrate dc bias during hydrogen plasma cleaning. It changes from downhill to uphill distribution as the dc bias changes from a negative to a positive value, which leads to a decrease in the ion number density arriving at the substrate and results in the complete suppression of the defect formation in the Si substrate. In situ hydrogen plasma cleaned Si wafer always resulted in higher quality epilayers than ones cleaned only by so‐called hydrogen passivation after the HF dip. We found that there is a critical dose of the hydrogen ions during in situ plasma cleaning beyond which crystalline defects are observed in the Si substrate, subsequently leading to the poor crystallinity of the epilayers. The dose of...

Effects of process parameters on low‐temperature silicon homoepitaxy by ultrahigh‐vacuum electron‐cyclotron‐resonance chemical‐vapor deposition

The effects of the process parameters on the low‐temperature Si homoepitaxial growth in an ultrahigh‐vacuum electron‐cyclotron‐resonance chemical‐vapor‐deposition (UHV‐ECRCVD) system are examined by reflection high‐energy electron diffraction and transmission electron microscopy (TEM). The substrate dc bias during plasma deposition drastically changes the crystal structure from polycrystalline silicon at negative bias to single crystalline at positive bias. The defect production during plasma deposition is mainly caused by the energetic ions impinging on the Si substrate, and it can be effectively suppressed by the proper control of the process parameters in the direction of minimizing the ion energy. The positive substrate dc bias is a prerequisite for better crystallinity of low‐temperature Si, but additionally the other process parameters such as microwave power, distance of the ECR layer from the substrate, SiH4 partial pressure, and total pressure should be definitely optimized to obtain dislocation‐...

Synthesis and Characterization of Nanofibrous Polyaniline Thin Film Prepared by Novel Atmospheric Pressure Plasma Polymerization Technique

This work presents a study on the preparation of plasma-polymerized aniline (pPANI) nanofibers and nanoparticles by an intense plasma cloud type atmospheric pressure plasma jets (iPC-APPJ) device with a single bundle of three glass tubes. The nano size polymer was obtained at a sinusoidal wave with a peak value of 8 kV and a frequency of 26 kHz under ambient air. Discharge currents, photo-sensor amplifier, and optical emission spectrometer (OES) techniques were used to analyze the plasma produced from the iPC-APPJ device. Field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), gas chromatography-mass spectrometry (GC-MS), and gel permeation chromatography (GPC) techniques were used to analyze the pPANI. FE-SEM and TEM results show that pPANI has nanofibers, nanoparticles morphology, and polycrystalline characteristics. The FT-IR and GC-MS analysis show the characteristic polyaniline peaks with evidence that some quinone and benzene rings are broken by the discharge energy. GPC results show that pPANI has high molecular weight (Mw), about 533 kDa with 1.9 polydispersity index (PDI). This study contributes to a better understanding on the novel growth process and synthesis of uniform polyaniline nanofibers and nanoparticles with high molecular weights using the simple atmospheric pressure plasma polymerization technique.

Conductive Polymer Synthesis with Single-Crystallinity via a Novel Plasma Polymerization Technique for Gas Sensor Applications

This study proposes a new nanostructured conductive polymer synthesis method that can grow the single-crystalline high-density plasma-polymerized nanoparticle structures by enhancing the sufficient nucleation and fragmentation of the pyrrole monomer using a novel atmospheric pressure plasma jet (APPJ) technique. Transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and field emission scanning electron microscopy (FE-SEM) results show that the plasma-polymerized pyrrole (pPPy) nanoparticles have a fast deposition rate of 0.93 µm·min−1 under a room-temperature process and have single-crystalline characteristics with porous properties. In addition, the single-crystalline high-density pPPy nanoparticle structures were successfully synthesized on the glass, plastic, and interdigitated gas sensor electrode substrates using a novel plasma polymerization technique at room temperature. To check the suitability of the active layer for the fabrication of electrochemical toxic gas sensors, the resistance variations of the pPPy nanoparticles grown on the interdigitated gas sensor electrodes were examined by doping with iodine. As a result, the proposed APPJ device could obtain the high-density and ultra-fast single-crystalline pPPy thin films for various gas sensor applications. This work will contribute to the design of highly sensitive gas sensors adopting the novel plasma-polymerized conductive polymer as new active layer.

Characteristics of an address discharge in ac plasma display panels

In this study, the basic characteristics of an address discharge have been investigated on the dependence of an address pulse voltage and its characteristics were analyzed by the wall voltage measurement method. During the address operation, the discharge between an address electrode and a scan electrode is first generated by an address pulse voltage and then the discharge between a scan electrode and a common electrode is induced. The resultant wall voltage between the address electrode and a scan electrode is strongly dependent on an address pulse voltage while the resultant wall voltage between a scan electrode and a common electrode is roughly independent on an address pulse voltage.

Electric field in magnetized inductively coupled plasma

A wave equation has been solved to visualize two-dimensional axis symmetric electric field profiles in magnetized inductively coupled discharge having flat, concentric current loops operated at 13.56 MHz. The DC magnetic induction level of interest is 0-20 gauss. We assumed that the plasma is uniform throughout the discharge volume. The conductivity tensor derived from cold plasma approximation was used to consider electrical properties of the discharge. For a typical operation regime of high density materials processing plasmas (electron density /spl sim/1/spl times/10/sup 11//cm/sup 3/, collision frequency /spl sim/3 MHz, length of the vessel =25 cm), we observed a standing wave structure of RF electric fields.

A Study on Wall-Charge Behavior of Single-Sustain Waveform Based on

The wall-charge behaviors of the conventional and two types of single-sustain waveforms during address and sustain periods are investigated based on a simulated result and a Vt close-curve analysis. The single-sustain waveform means that the sustain pulse having both positive and negative voltage levels is applied only to the single-side electrode, i.e., the scan (Y) electrode in this paper, where the common (X) electrode remains grounded. In the single-sustain waveform, the address discharge characteristics were observed to be improved by applying a higher voltage level without causing a misfiring discharge during an address period. An asymmetric IR emission was observed for both positive and negative sustain pulses during a sustain period, which was caused by the simultaneous discharge, including the plate gap discharge between the scan (Y) and the address (A) electrodes only when applying the negative sustain pulse to the scan (Y) electrode.

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The improvement of luminous efficiency is one of the most important issues in making a plasma display into a large flat panel device. Accordingly, a new combination of a four-component gas, He–Ne–Xe–Ar, is proposed in order to achieve a high luminous efficiency in color plasma display panels (PDP). The densities of 32 species and electron temperature were calculated using a zero-dimensional simulation. The results were then compared with measurements of brightness and luminous efficiency to identify the optimum mixing condition of He(7): Ne(3)–Xe(4%)–Ar gas for a color PDP. The reaction mechanism was computationally analyzed to comprehend the discharge mechanism in He–Ne–Xe–Ar as well as in He–Ne–Xe. By simulation, the maximum peak point of the Xe*(1S4) state was obtained between a 0.1% and 0.5% Ar mixing ratio and the maximum luminous efficiency was measured with a 0.3% Ar mixing ratio in the PDP. As a result, the luminous efficiency was considerably improved (about 20%) with a 0.3% Ar addition, compared...

Close-Curve Analysis in AC Plasma Display Panel

A 70 MHz inductively coupled rf bridge probe is used to measure the minority carrier lifetime of the Si and SiGe epilayers grown by ultrahigh vacuum electron cyclotron resonance chemical vapor deposition (UHV‐ECRCVD) at temperatures below 560 °C. Proper surface treatments before HF immersion are required for the accurate measurement of the bulk minority carrier lifetime. The effects of the process parameters such as the substrate dc bias, the distance of the ECR layer from the substrate, and the substrate temperature, including in situ surface cleaning, on the minority carrier lifetime of the Si and SiGe epilayers are examined by the rf bridge probe. It is confirmed that the rf bridge probe can monitor the epitaxial quality of low temperature Si and SiGe epilayers, making it an indispensable tool for the high quality device fabrication with Si and SiGe epitaxial layers grown by low temperature UHV‐ECRCVD.