Ji-soo Kim

Isolated vestibular syndrome in posterior circulation stroke: Frequency and involved structures

SummaryDizziness/vertigo is a common symptom of posterior circulation stroke and usually accompanies other neurologic symptoms and signs. Although strokes involving the brainstem or cerebellum may produce isolated vestibular syndrome (isolated vertigo or imbalance), the overall frequency and involved structures of isolated vestibular syndrome in the posterior circulation stroke remain uncertain. Isolated vestibular syndrome occurs in approximately 25% of the patients with posterior circulation stroke, and mostly involves the cerebellum, inferior or superior cerebellar peduncles, and caudal lateral or rostral dorsolateral medulla. The occasional negative neuroimaging in patients with acute isolated vascular vertigo highlights the importance of appropriate bedside evaluation in acute vestibular syndrome.

Effects of fluorocarbon polymer deposition on the selective etching of SiO2/photoresist in high density plasma

A new periodic two-step process composing SiO2 etching with high bias radio frequency (rf) power and fluorocarbon deposition with low bias rf power was studied for the highly selective etching of SiO2 to photoresist (PR). In this experiment, the time scale of each step is longer than the conventional time-modulation technique in order to maximize the protection layer on PR and prevent the etch stop. Many works have focused on the gaseous chemical species especially CF2 radicals for selective surface reaction. However, normally utilizing only the difference of stoichiometric surface reaction, they inherently limit the etching conditions such as dependence on the chemical composition of PR, densities, and impurities of SiO2 layers. And these conventional processes severely suffer reactive ion etching lag or etch stop in high selective etching. The new process utilizes fluorocarbon deposition with low bias rf power to increase the mask selectivity by enhancing the difference between the polymer thickness on ...

Suppression of topography dependent charging using a phase-controlled pulsed inductively coupled plasma

The topography dependent charging (TDC) potential on the bottom of an oxide contact is measured with an in-situ charge-up monitoring wafer during plasma processing. The effects of the contact aspect ratio and the bias power on the TDC are investigated from the potentials measured on that wafer. By analyzing the potentials, we correlate the TDC to the difference of the charging potentials between a shading and a blank probe. We can suppress TDC considerably using a phase-controlled pulsed inductively coupled plasma, especially when the phase delay of the bias power relative to the source power is near 180/spl deg/ (out-of-phase condition).

Charge-up damage of dual gate transistor during RF pre-cleaning of metal contact before barrier metal deposition

The damage of dual gate (p-gate PMOS and n-gate NMOS) transistors during RF pre-cleaning of their metal contacts before barrier metal deposition has been investigated in logic devices by varying the aspect ratio of metal contacts and RF source power. With higher aspect ratios and a higher source power for RF pre-cleaning, the gate leakage current of PMOS increases, while that of NMOS stays constant. We present a possible explanation for this difference in damage behaviour.

Evaluation of plasma-induced charging damage on metal contact process

The evaluation of plasma-induced charging damage in a metal contact process has been studied with a two dimensional Monte-Carlo simulation and related experiments. From the simulation, it is concluded that the linear shrinkage of the design rule possibly evokes exponential plasma-induced charging damage on the gate oxide during the plasma process. We also confirmed the simulation results with the two different experiments, in-situ charge-up monitoring wafers and fully fabricated test wafers. A phase-controlled pulsed inductively coupled plasma is proposed to suppress the plasma-induced charging damage. Preliminary results show that charging damage is strongly suppressed when the phase delay of the bias power to the source power is near to 180 degrees.

Implementation of the ArF resists based on VEMA for sub-100-nm device

It is expected that ArF lithography will be introduced for device manufacturing for sub-100 nm nodes, as high NA ArF step and scan systems (NA=0.75) become available. We previously reported on a platform, based on a vinyl ether- maleic anhydride (VEMA) alternating polymer system. This platform demonstrated both good resolution and high dry etch resistance in comparison to other platforms based on acrylate and cyclic-olefin-maleic anhydride (COMA) polymer systems. The VEMA platform has been continuously improved to meet the increasing requirements, such as resolution, depth of focus (DOF) iso-dense bias, and post-etch roughness for real device manufacturing. This VEMA system is being implemented for sub-100 nm device with high NA (NA=0.75) ArF exposure systems. In this paper, recent experimental results are reviewed.