Sun Wook Kim

Improved thermal stability of Al2O3/HfO2/Al2O3 high-k gate dielectric stack on GaAs

Thermal stability of HfO2 high-k gate dielectric on GaAs is investigated. Compared to HfO2 gate dielectric, significant improvements in interfacial properties as well as electrical characteristics were found by constructing a Al2O3/HfO2/Al2O3 dielectric stack. At elevated temperatures, the amorphous Al2O3 layers were effective in inhibiting crystallization of HfO2. Since the passivating Al2O3 layers prevent interfacial oxide and trap charge formation, it aids in reducing the increasing rate of equivalent oxide thickness as well as capacitance-voltage hysteresis. Transmission electron microscopy and x-ray photoelectron spectroscopy data supported the improved electrical characteristic of GaAs metal-oxide-semiconductor capacitors with Al2O3/HfO2/Al2O3 gate dielectric stack.

Characterization of channel strain evolution upon the silicidation of recessed source/drain Si1−xGex structures

This letter reports on Ni germanosilicide formation on recessed Si0.82Ge0.18 source/drain structures and its effects on channel strain. A combination of transmission electron microscopy techniques, including nanobeam diffraction, shed some light on a previously unrecognized factor in the channel strain evolution during silicidation: a Ge accumulation layer produced at the bottom of the germanosilicide layer. The formation of such a Ge rich layer added an additional compressive strain to the channel strain upon moderate silicidation, while the contribution of thermal strain arising from the cooling cycle became dominant in an excessively silicided sample, which turned the channel strain into a tensile value.

Achievement of a high channel strain via dry oxidation of recessed source/drain Si1−xGex structures

This study proposes a method of acquiring a high channel strain by locally oxidizing recessed Si1−xGex source/drain structures and forming a Ge condensation layer as an effective stressor. Combination of several transmission electron microscopy characterization techniques including nanobeam diffraction allowed us to analyze the thickness and composition of the Ge condensation layer formed upon oxidation, and the evolution of the channel strain. Nanobeam diffraction results demonstrate that this method can be critically used to effectively increase the channel strain.This study proposes a method of acquiring a high channel strain by locally oxidizing recessed Si1−xGex source/drain structures and forming a Ge condensation layer as an effective stressor. Combination of several transmission electron microscopy characterization techniques including nanobeam diffraction allowed us to analyze the thickness and composition of the Ge condensation layer formed upon oxidation, and the evolution of the channel strain. Nanobeam diffraction results demonstrate that this method can be critically used to effectively increase the channel strain.

Strain characterization of fin-shaped field effect transistors with SiGe stressors using nanobeam electron diffraction

This study undertook strain analysis on fin-shaped field effect transistor structures with epitaxial Si1−xGex stressors, using nano-beam electron diffraction and finite elements method. Combining the two methods disclosed dynamic strain distribution in the source/drain and channel region of the fin structure, and the effects of dimensional factors such as the stressor thickness and fin width, offering valuable information for device design.

Relaxation of misfit strain in silicon-germanium (Si1−xGex) films during dry oxidation

The effects of oxidation on strain relaxation in Si1−xGex layers on silicon substrates were investigated. Si1−xGex layers, with different Ge fractions (x=0.15 and 0.3), were grown on chemically cleaned silicon substrates by an ultrahigh vacuum chemical vapor deposition process. Oxidation at 800 and 900u2009°C under O2 ambient in a tube furnace resulted in the production of silicon oxide layers on top and a Ge-rich region in the Si1−xGex films. It was observed that the oxidation of Si0.85Ge0.15 films at 900u2009°C produced the relaxation of the misfit strain in the remnant Si1−xGex layer and the increase in strain in the Ge pile-up layer with increasing oxidation time, while the oxidation at 800u2009°C produced no changes in the misfit strain in the Si1−xGex layers. The oxidation of Si0.70Ge0.30 films at 800u2009°C showed the relaxation of the misfit strain in the remnant Si1−xGex layer with the accumulation of stain in the Ge pile-up layer. However, the oxidation of Si0.70Ge0.30 layers at 900u2009°C exhibited the strain rela...

Enhancement of a cyclic endurance of phase change memory by application of a high-density C15(Ge21Sb36Te43) film

The lower cyclic endurance of Phase Change Memory (PCM) devices limits the spread of its applications for reliable memory. The findings reported here show that micro-voids and excess vacancies that are produced during the deposition process and the subsequent growth in sputtered carbon-doped GeSbTe films is one of the major causes of device failure in PCM with cycling. We found that the size of voids in C15(Ge21Sb36Te43) films increased with increasing annealing temperature and the activation energy for the growth rate of voids was determined to be 2.22 eV. The film density, which is closely related to voids, varies with the deposition temperature and sputtering power used. The lower heat of vaporization of elemental Sb and Te compared to that for elemental Ge and C is a major cause of the low density of the film. It was possible to suppress void formation to a considerable extent by optimizing the deposition conditions, which leads to a dramatic enhancement in cyclic endurance by 2 orders of magnitude in PCM devices prepared at 300oC-300W compared to one prepared at 240oC-500W without change of compositions.

Growth and electrical properties of in situ phosphorus-doped polycrystalline silicon films using Si3H8 and PH3

In situ phosphorus-doped polycrystalline silicon (polysilicon) films grown on silicon oxide layers using trisilane (Si3H8) and phosphine (PH3) as precursors are investigated as a function of the Si3H8/PH3 gas flow ratio and the growth temperature. At a high flow rate for Si3H8 in the temperature range of 600–700u2009°C, the deposition process is controlled by the rate of desorption of hydrogen molecules on the surface, which has an activation energy of 1.13u2009eV. For a low Si3H8 flow rate at growth temperatures >650u2009°C, however, the deposition is limited by the diffusion of Si3H8 gas to the surface. The presence of phosphorus decreases the crystallization temperature of the polysilicon layers during growth. In addition, the ratio of phosphorus incorporated into the polysilicon decreases with increasing growth temperature because of the increase in the growth rate. The resistivity of the phosphorus-doped polysilicon films decreases with increasing deposition temperature at the same phosphorus concentration, indicating that the use of a high growth temperature results in an enhancement in the activation of phosphorus in the polysilicon films during growth.