Seok Joo Doh

Structural evolution of ZnO/sapphire(001) heteroepitaxy studied by real time synchrotron x-ray scattering

The structural evolution during heteroepitaxial growth of ZnO/sapphire(001) by radio-frequency magnetron sputtering has been studied using real-time synchrotron x-ray scattering. The two-dimensional (2D) ZnO(002) layers grown in the initial stage are highly strained and well aligned to the substrate having a mosaic distribution of 0.01° full width at half maximum (FWHM), in sharp contrast to the reported transition 2D layers grown by molecular-beam epitaxy. With increasing film thickness, the lattice strain is relieved and the poorly aligned (1.25° FWHM) three-dimensional (3D) islands are nucleated on the 2D layers. We attribute the 2D–3D transition to the release of the strain energy stored in the film due to the film/substrate lattice mismatch.

A highly manufacturable MIPS (metal inserted poly-Si stack) technology with novel threshold voltage control

The novel technique to control the V/sub th/ of n/pMOS for HfSiO(N) in both poly-Si and MIPS (metal inserted poly-Si stack) gates is demonstrated. By adding AlO/sub x/ on HfSiO prior to poly-Si deposition, we successfully achieve symmetrical V/sub th/, values of 0.52V (nMOS), /-0.51V (pMOS) and high performance as I/sub on/, of 423uA/um for nMOS and 207uA/um for pMOS at I/sub off/=20pA/um. In addition, we find out that the ultra-thin and conformal TaN layer in MIPS gate does not contribute to the gate work function. By optimizing the TaN thickness, similar V/sub th/ values, compared to poly-Si gate, are achieved. Consequently, the measured saturation currents at I/sub off/=20pA/um are 430uA/um for nMOS and 250uA/um for pMOS. Both issues of PBTI for HfSiO/AlO/sub x//poly-Si structure and NBTI for HfSiO/AlO/sub x//MIPS structure are resolved by optimizing the post deposition annealing condition and using ozone interfacial oxide, respectively.

Thickness dependence of the crystallization of Ba-ferrite films

The crystallization of Ba-ferrite/sapphire(001) films of various thicknesses has been studied using synchrotron x-ray scattering, field emission scanning electron microscope, and atomic force microscope. In films thinner than 1000 A, Ba-ferrite amorphous precursor was crystallized into perpendicular grains keeping the magnetically easy c-axis normal to the film plane during annealing to 750 °C. In films thicker than 1000 A, however, acicular grains keeping the c-axis parallel to the film plane were grown on top of the perpendicular grains. The behavior of the saturation magnetization and the intrinsic coercivity was consistent with the thickness dependence of the crystallization. We attribute the thickness dependence of the crystallization to the substrate effect, which prefers the growth of the epitaxial, c-axis oriented perpendicular grains near the film/substrate interfacial area.

Improvement of NBTI and electrical characteristics by ozone pre-treatment and PBTI issues in HfAlO(N) high-k gate dielectrics

For the first time, we have investigated the effect of ozone (O/sub 3/) pre-treatment on the bias temperature instability (BTI) characteristics of high-k gate dielectrics. We found that O/sub 3/ pre-treatment improved NBTI and the electrical characteristics of HfAlON gate dielectric. We suggest that O/sub 3/ pre-treatment effectively suppresses the incorporation of the impurities (such as nitrogen (N), hydrogen (H) and water related species), resulting in the improvement of NBTI characteristics (-2.32 V operating voltage for 10 years lifetime). For the PBTI characteristics, the high-k gate dielectric with poly-Si gate electrode was severely degraded. We suggest that dopants (such as arsenic (As) and phosphorus (P)) in the gate electrode of nMOSFETs diffuse into the gate dielectrics, causing the severe degradation of PBTI characteristics (/spl sim/1.1 V operating voltage for 10 years lifetime). We believe that the optimization in the high-k gate stack can improve the PBTI characteristics by suppressing the dopants incorporation.

Influence of Cr and Mo on the passivation of stainless steel 430 (18Cr) and 444 (18Cr–2Mo): In situ XANES study

Abstract We have studied the influence of metal elements on the passivation of stainless steel (SS) 430 (18Cr) and 444 (18Cr–2Mo) by real time X-ray absorption near edge spectroscopy. We developed an electro-chemical cell that is suitable for in situ electro-chemistry experiments. The behavior of Fe, Cr and Mo elements of SS 430 and 444 was studied in passive region reaction in a borate buffer solution (pH 7.0). We found that the Cr 2 O 3 /Fe 2 O 3 ratio gradually decreased with passivation time due to the oxidation of Cr 2 O 3 to CrO 4 2− , indicating weakening of passivity. In the meanwhile, the amount of Mo at passive films increased with passivation time. The improvement of passivity in the SS 444 is mainly attributed to the substitution of Cr oxide by Mo oxide in the passive film.

Microstructure of epitaxial α-Fe2O3 grains in Ba-ferrite thin films grown on sapphire (001)

We revealed the existence of epitaxial α-Fe2O3 grains in Ba-ferrite thin films on sapphire (001) using synchrotron x-ray scattering. The antiferromagnetic α-Fe2O3 grains were formed during the crystallization of amorphous Ba-ferrite films grown on sapphire (001) by radio frequency sputtering deposition. The crystal domain size of the α-Fe2O3 grains was about 250 A in the film plane, similar to that of the Ba-ferrite grains. The in-plane crystalline axis of the α-Fe2O3 was aligned to that of sapphire, while the Ba-ferrite film was rotated by 30° in the film plane. We confirm that the existence of these antiferromagnetic α-Fe2O3 grains greatly degraded magnetic properties of the Ba-ferrite films.

Thermal stability and decomposition of the HfO2–Al2O3 laminate system

The thermal stability of the HfO2–Al2O3 laminate gate stack grown by atomic layer chemical vapor deposition was investigated using medium-energy ion scattering spectroscopy and high-resolution x-ray photoelectron spectroscopy. The laminate structure was maintained up to 800 °C under ultrahigh vacuum conditions, while it was drastically degraded at 850 °C, resulting in silicide formation on the film surface. Dissociated oxygen in the Hf–Al-oxide preferentially diffuses out through the film and desorbing at the surface. Volatile SiO species and Al–O components desorb through the sample surface, while HfO2 contributes to Hf silicide formation on the film surface.

Inhibition of abnormal acicular grain growth of nanostructured Ba–ferrite films by secondary α-Fe2O3 phase

We have studied the inhibition of abnormal acicular grain growth of the Ba–ferrite phase in the crystallization of Ba–ferrite films using real time synchrotron x-ray scattering, field emission scanning electron microscope, and vibrating sample magnetometer. Amorphous Ba–ferrite film on a SiO2 substrate is naturally crystallized into the abnormal acicular Ba–ferrite grains (major axis of ∼1000 nm in the in-plane direction). However, on α-Al2O3 substrate, fine grain sizes of the primary Ba–ferrite phase (∼70 nm) are obtained during crystallization. Nucleation of the α-Fe2O3 phase on the α-Al2O3 surface at an early stage induces the inhibition of the abnormal acicular grain growth of the Ba–ferrite phase. Because of the grain size refinement of the magnetic Ba–ferrite phase, the intrinsic coercivity of Ba–ferrite/α-Al2O3 film enhances 4.4 kOe, much larger than that of Ba–ferrite/SiO2 film (1.9 kOe). We suggest that the secondary α-Fe2O3 phase act as a useful inhibitor to abnormal grain growth in Ba–ferrite f...

HCI and BTI characteristics of ALD HfSiO(N) gate dielectrics as the compositions and the post treatment conditions

For the first time, we evaluate the HCI and BTI degradation of ALD HfSiO(N) gate dielectrics as the compositions and the post annealing conditions. The HCI and PBTI degradation are minimized at Hf to Si cycle ratio of 3 to 1 (Hf/(Hf+Si) = 0.75) and the post reoxidation annealing suppresses both degradations. It is believed that the HCI and PBTI degradation are related to the electron traps in the gate oxide. However, NBTI degradation is negligibly small compared to PBTI degradation. This indicates that the positive fixed charge generation or hole traps are not significant in ALD HfSiO(N) gate dielectrics.

Iron-Oxide Interlayer Existing in Ba-Ferrite/Sapphire(001) Films Grown by Sputtering

We revealed the existence of a very thin (~50 A thick) epitaxial iron-oxide interlayer in amorphous Ba-ferrite thin films on sapphire(001) using synchrotron x-ray scattering. Depending on the sputtering gases used in radio frequency sputtering deposition, two different iron-oxide interlayers were formed; non-magnetic α-Fe2O3 interlayer by pure Ar gas and ferromagnetic Fe3O4 interlayer by Ar-10% O2 gas mixture. The α-Fe2O3 interlayer much more promoted the crystallization of amorphous Ba-ferrite, compared to the Fe3O4 interlayer. We suggest that the interlayer existing between amorphous Ba-ferrite and sapphire substrate greatly contributes to the reduction of the activation energy for the crystallization of amorphous Baferrite film.