Hyung-Ho Park

Compositional and structural analysis of aluminum oxide films prepared by plasma-enhanced chemical vapor deposition

Aluminum oxide films were deposited on silicon wafers by plasma-enhanced chemical vapor deposition, using trimethylaluminum, N2O and He gases. The chemical composition, states of functional groups and microstructure of the aluminum oxide films were investigated using FTIR, XPS, AES and TEM. Etch rates were measured and related to the microstructure of the films. It was found that carbon and hydrogen atoms are incorporated less at higher deposition temperatures and are almost completely removed as gas phases, such as CO2 and H2O, by post-deposition heat treatment at 800 °C in an oxygen environment. Carbon atoms incorporated into the films are in the chemical form of AlCH3 or AlCOOH, and the atomic concentration varies from 2% at 300 °C to 5% at 120 °C. Hydrogen atoms are in the chemical form of AlOH, and the atomic concentration estimated from the absorbance FTIR band of the OH stretching mode varies from about 7% at 300 °C to about 28% at 120 °C. The aluminum oxide films deposited at 300 °C have a microcrystalline structure of hydrogen-stabilized γ-Al2O3 with an O/Al ratio of 1.6, whereas those deposited at 120 °C have an amorphous structure. Etching properties of the films were related to the change in the microstructure.

A study of the activation behaviour of ZrCrNiLa metal hydride electrodes in alkaline solution

Abstract The hydrogen absorption behaviour of ZrCrNi C14 Laves phase alloys pre-treated in various ways is studied during galvanostatic charging in KOH solution. It is found that the surface oxide layers prohibit hydrogen absorption. In order to investigate the effects of surface properties on the activation behaviours of ZrCrNi and ZrCrNiLa0.05 electrodes, their surfaces are analysed by means of X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). The surface property of ZrCrNiLa0.05 is identical to that of ZrCrNi except for La oxide at the surface. To investigate the effect of adding the element, Ti instead of La is added to ZrCrNi in excess. The Ti-containing alloy shows a poor activation behaviour in alkaline solution. From the results of the surface analysis on ZrCrNi, ZrCrNiLa0.05 and ZrCrNiTi0.05, alloys that show different activation behaviours in alkaline solution, it is suggested that the nature of the oxide layer formed on the surface plays a key role on the activation process of the metal hydrides in alkaline solution.

Characterization and removal of silicon surface residue resulting from CHF3/C2F6 reactive ion etching

The surface properties of an underlying Si substrate after reactive ion etching of SiO2 in CHF3/C2F6 gas plasmas have been studied using x‐ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry, Rutherford backscattering spectroscopy, and high resolution transmission electron microscopy (HRTEM). A 50‐nm‐thick silicon layer that contains carbon and fluorine and a 4‐nm‐thick uniform residue layer composed entirely of carbon, fluorine, oxygen, and hydrogen on the silicon surface have been observed. The residue film has nine different kinds of chemical bonds. At the surface, O—F bond is found on C—F polymer that contains C—CFx (x≤3), C—F1, C—F2, and C—F3 bonds. Between the C—F polymer layer and the silicon substrate, C—C/H, Si—C, Si—O, and Si—F bonds exist. Neither point defect clusters nor distinct planar defects are found in cross‐sectional HRTEM images of the silicon substrate. The changes of peak shapes for C, Si, O, and F in the residual film have been analyzed through an in situ resistive...

In situ solid phase epitaxial growth of C49‐TiSi2 on Si (111)‐7×7 substrate

C49‐TiSi2 film was grown epitaxially on Si(111) substrate by depositing Ti film on Si(111)‐ 7×7 surface followed by in situ annealing in ultrahigh vacuum. The deposition was monitored by means of reflection high energy electron diffraction as a function of the thickness of Ti film. The best result for the growth of epitaxial C49‐TiSi2 was obtained from the Ti(30 ML)/Si(111)‐7×7 sample which was annealed at 650 °C for 20 min. Images of cross‐sectional high resolution transmission electron microscopy shows that the silicide/silicon interface is shown to be clear and flat. The orientation relationships are TiSi2[211]∥Si[011], TiSi2 (120)∥Si(111) without misorientation angle. Almost the whole area of the TiSi2 layer is revealed as an epitaxial C49 structure.

INTERFACIAL REACTION IN THE SPUTTER-DEPOSITED SIO2/TI0.1W0.9 ANTIFUSE SYSTEM

The effects of annealing temperature on the interfacial reactions and the antifuse I‐V characteristics of ultra thin SiO2 layer deposited on Ti0.1W0.9 substrate were investigated. The interfacial reactions were analyzed using x‐ray photoelectron spectroscopy and Auger electron spectroscopy with the sample which is in situ annealed under ultra high vacuum or ex situ annealed in a nitrogen atmosphere. The surface of the Ti0.1W0.9 substrate was oxidized during sputter deposition of SiO2 layer. Ti, W oxides consist of Ti2O3 (Ti3O5), TiO2, WO2, and WO3. The WO3 and Ti2O3 decomposed into metallic W and Ti at 400 and 500 °C, respectively. The breakdown voltage of the antifuse decreased as the annealing temperature increased, due to the thinning of dielectric layer resulted from the decomposition of Ti, W oxides and the formation of metallic W and Ti. Annealing at 600 °C caused the reaction between metallic (Ti,W) and SiO2 layer and formed elemental silicon in the dielectric layer, where SiO2 layer completely los...

FORMATION AND EPITAXIAL-GROWTH OF TITANIUM-DISILICIDE ON SI (111)

Titanium-disilicide was formed by deposition of high purity titanium (99.99%) on a silicon (111) wafer in ultra-high vacuum and in-situ annealing. The deposition was monitered using reflection high energy electron diffraction as a function of deposited titanium thickness. The epitaxial growth of TiSi2 on Si (111) by deposition of 200 monolayer thick titanium on the clean surface of silicon and annealing at 750°C for 1 h was identified using a transmission electron microscope. Almost the whole area of the silicide layer was revealed as epitaxial TiSi2 with C54 structure. Cross-sectional high resolution images of the sample showed that the TiSi2/Si interface is incoherent. Three kinds of orientation relationships were identified as (111)TiSi2|(220)Si, [123]TiSi2|[112]Si, (311)TiSi2|(002)Si, [136] TiSi2|[110]Si and (022)TiSi2|(200)Si, [233]TiSi2|[011]Si with misorientations of 6°, 2° and 14.74°, respectively.

Evolution of high Tc superconductivity of Bi4Sr3−xLaxCa3Cu4Oy upon iodine intercalation

Abstract X-ray photoelectron spectroscopic study has been performed to investigate the chemical bonding nature of the iodine intercalated in the lattice of Bi 4 Sr 3−x La x Ca 3 Cu 4 O y , which is strongly correlated with the evolution of superconductivity. X-ray diffraction analyses indicate the formation of first staged iodine intercalates, I 2 Bi 4 Sr 3−x La x Ca 3 Cu 4 O y , whose superconducting transition temperatures were changed depending upon La substitution rate(x). X-ray photoelectron spectroscopic results exhibit the coexistence of the negative-charged iodine(I δ− ) and the highly oxidized periodate(I +VII ) with a different ratio, depending upon the amount of La substitution. The periodate species seems to increase as the increase of the La substitution rate(x), which has led to a conclusion that the excess oxygen may oxidize the intercalated iodine to a highly oxidized periodate. Remarkable depression of periodate concentration during Ar + -ion sputtering underlines that such a highly oxidized species are surely enriched on the surface and/or the grain boundary. T c evolution upon iodine intercalation will be discussed in view of charge transfer and enhancement of two dimensionality.

Growth Mode of Ti-Thin Films on Si(111) and Double Heteroepitaxial Growth of Epi-Si/Epi-TiSi2/Si(111)

The growth mode of a Ti film on a Si(111)-7×7 surface and the heteroepitaxial growth of Si/C54 TiSi2/Si(111) have been investigated. The initial stage of the growth of the Ti film is a Stransky-Krastanov type when the substrate temperature is room temperature. Polycrystalline Ti layer is grown with an amorphous Ti-Si interlayer at the Ti/Si interface. A 30 ML of Ti deposited on Si(111)-7×7 surface at room temperature transformed to an epitaxial C54 TiSi2 by in situ annealing at 750°C for 20 min in ultra-high vacuum. Furthermore an epi-Si/ epi-C54 TiSi2/Si(111) structure was obtained by depositing Si film on the C54 TiSi2 at 600°C followed by in situ annealing at 800°C for 10 min in UHV. The orientation relationships are TiSi2[ 1 ¯ 41]‖Si[0 1 ¯ 1] and TiSi2(202)‖Si(111), and the matching face relationships for the epi-Si/epi-C54 TiSi2/Si(111) structure are Si(111)‖C54 TiSi2(202)‖Si(111) without a misorientation angle. The microstructure shows that the interface is abrupt and pseudomorphic.

Influence of TiAs precipitate formation on morphology degradation of the TiSi2/As-doped polysilicon system☆

The formation of TiAs precipitates between TiSi2 with C54 structure and arsenic-doped polysilicon and the influence of TiAs and silicon resulting from the reaction TiSi2 + As → TiAs + 2Si on layer morphology degradation have been studied. The formation of TiAs precipitates has been revealed by X-ray diffraction in a sample annealed at 900 °C for 60 min and a sequential increase in sheet resistance with increasing annealing time has been observed. Cross-sectional scanning electron microscopy of the sample annealed for 60 min has shown irregular-shaped protrusions. Point analyses by Auger electron spectroscopy and cross-sectional transmission electron microscopy of the same sample have shown the presence of TiAs precipitates and extra silicon near the TiSi2-polysilicon interface under the protrusion area. From the results it has been found that TiAs precipitates and extra silicon resulting from the reaction TiSi2 + As → TiAs + 2Si lead to morphology degradation of this system.

Synthesis and structural analysis of the new layered compound [FeWO4Cl]

The compound [FeWO4Cl] has been prepared under a temperature gradient of 400–450°C by the chemical vapour transport technique. The crystal symmetry is tetragonal with unit-cell dimensions of a= 6.677(5) and c= 5.270(5)A(space group P4/nmm and Z= 2). The structure was refined by the least-squares method to a conventional reliability factor of R= 0.06.