Ayumi Ando

Control of atomic layer degradation on Si substrate

To develop 32nm node devices, the degradation of atomic layers on the surface of Si substrates must be controlled. During the etching of a SiO2 or Si3N4 hard mask or sidewall, the surface of Si is attended due to exposure to fluorocarbon plasma. The authors have quantitatively evaluated the relationship between the energy of incident ions and the thickness of the fluorocarbon polymer for a CH2F2∕CF4∕Ar∕O2 plasma in a dual frequency CCP system. At a fixed ion energy the thickness of the damage layer (Td) basically depended on the thickness of the fluorocarbon polymer (TC–F). When the TC–F was changed by controlling the O∕CFx gas ratio, Td had a minimum thickness under the conditions at balance point: Pb, under which the TC–F was nearly equal to ion penetration depth: Dp. Using molecular dynamics simulation, reaction around the transition from SiO2 to Si was clarified. The damage was done to the Si before the SiO2 was completely removed, and the largest Td was observed when the SiO2 was etched off. After th...

Extracellular Matrix Patterning for Cell Alignment by Atmospheric Pressure Plasma Jets

Low-temperature atmospheric-pressure plasma (APP) jets and a metal stencil mask have been used for the patterning of fibronectins deposited on a silicon (Si) wafer. Fibronectins typically constitute the extracellular matrix (ECM) and a micro-patterned ECM may be used for arranging living cells in a desired pattern on the substrate surface. Such a technique can be used for the fabrication of cell chips. In this study, patterning of 100-µm-wide lines of fibronectin layers has been demonstrated. Desorption of fibronectins from the surface by plasma application has been confirmed by atomic force microscopy (AFM) and Fourier transform infrared spectroscopy (FT-IR).

Proliferation assay of mouse embryonic stem (ES) cells exposed to atmospheric-pressure plasmas at room temperature

Proliferation assays of mouse embryonic stem (ES) cells have been performed with cell culture media exposed to atmospheric-pressure plasmas (APPs), which generate reactive species in the media at room temperature. It is found that serum in cell culture media functions as a scavenger of highly reactive species and tends to protect cells in the media against cellular damage. On the other hand, if serum is not present in a cell culture medium when it is exposed to APP, the medium becomes cytotoxic and cannot be detoxified by serum added afterwards. Plasma-induced cytotoxic media hinder proliferation of mouse ES cells and may even cause cell death. It is also shown by nuclear magnetic resonance spectroscopy that organic compounds in cell culture media are in general not significantly modified by plasma exposure. These results indicate that if there is no serum in media when they are exposed to APPs, highly reactive species (such as OH radicals) generated in the media by the APP exposure are immediately converted to less reactive species (such as H2O2), which can no longer readily react with serum that is added to the medium after plasma exposure. This study has clearly shown that it is these less reactive species, rather than highly reactive species, that make the medium cytotoxic to mouse ES cells.

Protein patterning by atmospheric-pressure plasmas

Low-frequency (LF) atmospheric-pressure plasma (APP) jets have been used for patterning of thin fibronectin films deposited on a silicon (Si) wafer with the use of a metal stencil mask. Since fibronectin is an adhesion protein that can be found in the extracellular matrix (ECM), a micro-patterned fibronectin film may be used for arranging living cells in a desired pattern on a surface. Removal of fibronectin from the surface by plasma application was observed by Fourier transform infrared spectroscopy (FT-IR) and atomic force microscopy (AFM). It has been found that removal of fibronectin takes place even in the location away from the direct plasma jet application spot, which indicates that desorption of fibronectin is likely to be caused by chemically reactive charge-neutral species that can diffuse away from the plasma without emitting visible light.

Electron density measurement of inductively coupled plasmas by terahertz time-domain spectroscopy (THz-TDS)

The electron densities of argon inductively coupled plasmas were measured by terahertz time-domain spectroscopy (THz-TDS). At a low pressure, the electron densities were also measured with a Langmuir-type double probe and the validity of THz-TDS electron-density measurement in a plasma has been corroborated. As the input radio-frequency (RF) power increases, the plasma density and gas temperature increase, which makes the probe measurement less reliable or even impossible, due to the large heat load to the probe surface. On the contrary, the THz-TDS measurement is unaffected by the gas temperature and becomes more reliable due to the higher electron density at higher input power for plasma generation.

Diagnosis of atmospheric pressure plasmas by using terahertz time-domain spectroscopy

A parallel-plate atmospheric plasma generator has been built with discharge electrodes that also serve as a non-dispersive terahertz (THz) waveguide for plasma diagnostics based on THz time-domain spectroscopy. It has been confirmed that, in the system, a uniform glow-like atmospheric pressure plasma is generated and THz waves propagate as designed.

Electron density measurement for plasmas by Terahertz time- domain spectroscopy

A new plasma diagnostic tool of terahertz time-domain spectroscopy (THz-TDS) has been developed. The THz-TDS system allows one to obtain the electron density and collision frequency of a plasma simultaneously from the phase shift and absorption rate of THz waves that are transmitted through the plasma. The line-averaged electron densities of Ar inductively coupled plasmas (ICPs) and CH4/Ar capacitively coupled plasmas (CCPs) were evaluated by the system and found to be 10

Estimation of electron densities of plasmas by terahertz time-domain spectroscopy

A new plasma diagnosis tool is developed based on terahertz time-domain spectroscopy (THz-TDS). Electromagnetic wave transmission characteristics of inductively-coupled Ar plasmas are examined by THz-TDS. The electron densities inferred from THz-TDS are found to be in good agreement with those obtained from Langmuir probe measurements.