Choonghyun Lee

A 7nm FinFET technology featuring EUV patterning and dual strained high mobility channels

We present a 7nm technology with the tightest contacted poly pitch (CPP) of 44/48nm and metallization pitch of 36nm ever reported in FinFET technology. To overcome optical lithography limits, Extreme Ultraviolet Lithography (EUV) has been introduced for multiple critical levels for the first time. Dual strained channels have been also implemented to enhance mobility for high performance applications.

Preparation and Photocatalytic Activity of Potassium- Incorporated Titanium Oxide Nanostructures Produced by the Wet Corrosion Process Using Various Titanium Alloys

Nanostructured potassium-incorporated Ti-based oxides have attracted much attention because the incorporated potassium can influence their structural and physico-chemical properties. With the aim of tuning the structural and physical properties, we have demonstrated the wet corrosion process (WCP) as a simple method for nanostructure fabrication using various Ti-based materials, namely Ti–6Al–4V alloy (TAV), Ti–Ni (TN) alloy and pure Ti, which have 90%, 50% and 100% initial Ti content, respectively. We have systematically investigated the relationship between the Ti content in the initial metal and the precise condition of WCP to control the structural and physical properties of the resulting nanostructures. The WCP treatment involved various concentrations of KOH solutions. The precise conditions for producing K-incorporated nanostructured titanium oxide films (nTOFs) were strongly dependent on the Ti content of the initial metal. Ti and TAV yielded one-dimensional nanowires of K-incorporated nTOFs after treatment with 10 mol/L-KOH solution, whereas TN required a higher concentration (20 mol/L-KOH solution) to produce comparable nanostructures. The obtained nanostructures revealed a blue-shift in UV absorption spectra due to the quantum confinement effects. A significant enhancement of the photocatalytic activity was observed via the chromomeric change and the intermediate formation of methylene blue molecules under UV irradiation. This study demonstrates the WCP as a simple, versatile and scalable method for the production of nanostructured K-incorporated nTOFs to be used as high-performance photocatalysts for environmental and energy applications.

High performance and record subthreshold swing demonstration in scaled RMG SiGe FinFETs with high-Ge-content channels formed by 3D condensation and a novel gate stack process

We demonstrate scaled high-Ge-content (HGC) strained SiGe pMOS FinFETs with very high short channel (SC) performance using a Replacement High-K/Metal Gate (RMG) flow, for the first time. A novel RMG gate stack process was introduced to create Ge-free interface-layer (IL) with excellent reliability and sub-threshold swing (SS) as low as 62mV/dec, the best reported to date for Si-cap-free SiGe FinFETs. We also present some structural details of the gate stack, for the first time. Short channel characteristics of HGC SiGe FinFETs have also been studied for various fin widths. Compared to our earlier RMG work, improved I/I free process with ultra-thin spacers has led to considerable R<inf>on</inf> and R<inf>ext</inf> reduction. As a result, we have demonstrated very high SiGe performance with I<inf>on</inf>=0.45mA/μm at I<inf>off</inf>=100nA/μm at V<inf>dd</inf>=0.5V for L<inf>G</inf>=25nm, matching our record for gate-first SiGe FinFETs and outperforming the gate-first results at such LG.

Germanium out diffusion in SiGe-based HfO2 gate stacks

The authors report about a detailed study of the chemical composition of advanced HfO2/interfacial layer/SiGe stacks for future p-channel metal-oxide-semiconductor field-effect transistors. Several state-of-the-art characterization techniques are implemented to provide consistent and complementary information about interfacial chemical states and Ge diffusion along the stack. Angle-resolved x-ray photoelectron spectroscopy is performed in both standard and parallel modes. Results highlight the presence of elemental Ge in the HfO2, suggesting some Ge out diffusion from the SiGe substrate. This trend is confirmed by time-of-flight secondary ion mass spectrometry and plasma profiling time-of-flight mass spectrometry, a recently developed technique to monitor thin films compositions during device manufacturing.The authors report about a detailed study of the chemical composition of advanced HfO2/interfacial layer/SiGe stacks for future p-channel metal-oxide-semiconductor field-effect transistors. Several state-of-the-art characterization techniques are implemented to provide consistent and complementary information about interfacial chemical states and Ge diffusion along the stack. Angle-resolved x-ray photoelectron spectroscopy is performed in both standard and parallel modes. Results highlight the presence of elemental Ge in the HfO2, suggesting some Ge out diffusion from the SiGe substrate. This trend is confirmed by time-of-flight secondary ion mass spectrometry and plasma profiling time-of-flight mass spectrometry, a recently developed technique to monitor thin films compositions during device manufacturing.

Understanding the interfacial layer formation on strained Si 1−x Ge x channels and their correlation to inversion layer hole mobility

We investigate the mechanism of interfacial layer formation on Si<inf>1−x</inf>Ge<inf>x</inf> (0 < x < 0.5) channel and its correlation to hole mobility. It is found that the mobility degradation in low-Ge-content Si<inf>1−x</inf>Ge<inf>x</inf> (x < 0.2) pFETs is attributed to a Ge-rich top surface in the channel directly induced by interfacial layer formation. In addition, the depth profile of a Si-rich top surface in high-Ge-content Si<inf>1−x</inf>Ge<inf>x</inf> channel is presented to understand the surface atomic configuration of Si<inf>1−x</inf>Ge<inf>x</inf> channel as well as mobility enhancement mechanism.

Selective GeO x -scavenging from interfacial layer on Si 1−x Ge x channel for high mobility Si/Si 1−x Ge x CMOS application

We demonstrate a technique for selective GeO_x-scavenging which creates a GeO_x-free IL on Si_1-xGe_x substrates. This process reduces N_it by >60% to 2e11 and increases high-field mobility at N_inv=1e13 cm^-2 by ~1.3× in Si_0.6Ge_0.4 pFETs with sub-nm EOT.

Engineering the electronic defect bands at the Si 1−x Ge x /IL interface: Approaching the intrinsic carrier transport in compressively-strained Si 1−x Ge x pFETs

We identify the existence of electronic defect levels close to the Si<inf>1−x</inf>Ge<inf>x</inf> band edges associated with the Ge surface concentration at the Si<inf>1−x</inf>Ge<inf>x</inf>/IL interface (0 < x < 0.5). These electronic defects act as carrier scattering centers severely degrading the channel mobility and modulate the device threshold voltage. By successfully eliminating the electronic defects states at the Si<inf>1−x</inf>Ge<inf>x</inf>/IL interface, through control of the Ge surface concentration, high channel carrier mobility over wide charge densities in compressively-strained Si<inf>1−x</inf>Ge<inf>x</inf> channel pFETs is demonstrated. For the first time, the dominant scattering mechanisms for hole mobility in Si<inf>1−x</inf>Ge<inf>x</inf> channel pFETs are investigated to understand the carrier transport physics.