Sangmo Koo

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.

Selective epitaxial growth of stepwise SiGe:B at the recessed sources and drains: A growth kinetics and strain distribution study

The selective epitaxial growth of Si1-xGex and the related strain properties were studied. Epitaxial Si1-xGex films were deposited on (100) and (110) orientation wafers and on patterned Si wafers with recessed source and drain structures via ultrahigh vacuum chemical vapor deposition using different growing steps and Ge concentrations. The stepwise process was split into more than 6 growing steps that ranged in thicknesses from a few to 120 nm in order to cover the wide stages of epitaxial growth. The growth rates of SiGe on the plane and patterned wafers were examined and a dependence on the surface orientation was identified. As the germanium concentration increased, defects were generated with thinner Si1-xGex growth. The defect generation was the result of the strain evolution which was examined for channel regions with a Si1-xGex source/drain (S/D) structure.

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 600–700 °C, the deposition process is controlled by the rate of desorption of hydrogen molecules on the surface, which has an activation energy of 1.13 eV. For a low Si3H8 flow rate at growth temperatures >650 °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.

Enhancement of a Channel Strain via Dry Oxidation of Recessed Source/Drain Si1−xGex Structures

As the conventional method of scaling-down the device size of CMOS faces limitations beyond the 90 nm technology generation, an alternative route has recently gained much attention: device performance improvement via channel strain engineering. The integral part of channel strain engineering is incorporating a stressinducing structure into the transistor structure. For pchannel transistors, a widely adopted approach is growing epitaxial Si1−xGex layers in the source and drain (S/D) regions to introduce compressive strain in the Si channel. This approach, however, has limitations in increasing the channel strain to an extent large enough to significantly influence the hole mobility, since increasing the thickness or Ge composition of the Si1−xGex layer greater than a critical value would prompt the formation of the defects such as misfit dislocations. Thus, developing a process capable of inducing a high channel strain without the generation of defects is pivotal for strain engineering. 90nm-thickness Si1−xGex (x=0.15, 0.3) layer was grown on recessed source/drain structure using SEG process by UHV-CVD at 550°C, Si2H6 and GeH4 were used as a precursor for Si and Ge, respectively. The Si1−xGex / Si structures were then oxidized at 800 °C for different durations (1, 2, and 4 h) in a dry O2 ambient using a vertical furnace, followed by the removal of native oxide by treatment with an HF solution. The composition of Gerich layers and the channel strain were characterized using several techniques of TEM (JEOL, JEM-2100F). For strain measurement, in particular, we use NBD method, in which the electron beam size was approximately 2 nm with 0.1% strain sensitivity. The results of our study helped us to understand the potentials and limits of the Ge condensation method adopted in this study. The selective oxidation of the Si1−xGex S/D regions produced a Ge-enriched layer underneath the oxide layer. Modulating the Ge concentration of the S/D and the oxidation time changed significantly the thickness and composition of the Ge condensation layer. The 2 h oxidation of a Si0.7Ge0.3 sample produced a 12.8 nm thick layer enriched with around 60% Ge and raised drastically the strain level from 0.4% to 1.2%. However, extending the oxidation time further increased the thickness of the Ge condensation layer to 13.5 nm and pushed the stress level beyond the critical value of the defect formation, generating dislocations and thus relieving much of the channel strain. Thus the critical thickness of the Ge condensation layer is probably some number between 12.8 and 13.5 nm for our S/D structures. These results indicate that locally oxidizing recessed S/D structures allowed us to grow a much thicker Ge condensation layer without producing defects and hence strain the channel region to a much greater extent. In summary, we investigated the possibility of effectively increasing the channel strain by locally oxidizing recessed Si1−xGex S/D structures and producing a Ge condensation layer. By combining EDS and NBD techniques, we were able to thoroughly analyze the thickness and composition of the Ge condensation layer formed upon oxidation, and the evolution of the channel strain. The NBD results clearly showed that this method can be critically used to effectively increase the channel strain.

Erratum to: Branch length similarity entropy-based descriptors for shape representation (Journal of the Korean Physical Society, (2017), 71, 10, (727-732), 10.3938/jkps.71.593)

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Observation of in situ B-doped Epitaxial Ge layer growth on Si(111) by ultra-high vacuum chemical vapor deposition

In situ B-doped epitaxial Ge layers were grown on a Si(111) substrate using UHV CVD for the application to S/D regions of pMOS devices. The Ge surface evolution with the deposition time, showing (111) terrace structures, were influenced by the B2H6 flow rate.

The Effect of Gate Length on Channel Strain of Recessed Source/Drain Si1-xCx

In this study, we experimentally evaluated the effects of scaling on the channel strain in terms of gate lengths. We used transistor arrays incorporating Si1-xCx as a stressor with systematically varying gate and source/drain lengths, and employed the NBD method to measure the channel strain. We also carried out simulation to check the validity of the NBD data.

The Effect of Ge Condensation on Channel Strain during the Post Annealing Process of Recessed Source/Drain Si1-xGex

In summary, we investigated the possibility of effectively increasing the channel strain by oxidation and silicidation of recessed Si1-xGex S/D structures and producing a Ge condensation layer. By combining EDS and NBD techniques, we were able to analyze the thickness and composition of the Ge condensation layer formed upon post annealing process, and the evolution of the channel strain. The NBD results clearly showed that this method can be critically used to effectively increase the channel strain.

Investigation of Process Parameters on the Properties of Selective Epitaxial Growth SiGe Structure

As conventional methods for scaling down have reached its limit, strain engineering in MOSFETs using embedded SiGe, SiC in recessed source/drains has recently been investigated as a potential candidate. For PMOS devices, in which compressive strain in channel region of MOSFET improves hole mobility and drive current, selective epitaxial growth SiGe is an efficient method to induce a compressive stress into the Si channel. In this work, the effect of process parameters such as substrate condition, flow rate of precursors and dopant sources on selective epitaxial growth SiGe films was discussed.