Takayuki Fukasawa

High rate and highly selective SiO2 etching employing inductively coupled plasma and discussion on reaction kinetics

High rate and highly selective SiO2/Si etching employing a C4F8+H2 mixture was achieved in the diffusive region of an inductively coupled plasma where electrons in its diffusive region were not so energetic. It was considered that hydrogen fluoride formed by hydrogen introduced to scavenge fluorine (F) radicals was not dissociated in the region and was exhausted outside. The carbon‐rich film was deposited selectively on the Si surface, thereby providing high selectivity. The thick film, in particular, deposited selectively onto the bottom of holes below 1 μm and exposure of C4F8+30% H2 for as‐etched holes at floating potential showed that polymer films conformed to the inner surfaces of holes. Hence, this selective deposition was ascribed to the accumulation of the resputtered polymer on the bottom films. Appearance mass spectroscopy measurements of fluorocarbon radicals for some discharge conditions showed that the CF1 radical played a major role in the polymer film deposition, while the CF2 radical migh...

High Rate and Highly Selective SiO2 Etching Employing Inductively Coupled Plasma

Plasma and SiO2 etching characteristics employing inductively coupled plasma (ICP) were studied with respect to distance from an antenna. Measurement of the ratio of electron to ion saturation currents in CHF3 plasma shows an increase in negative fluorine ions in the downstream regions. The intensity ratio of C2 (516.5 nm)/F(685.6 nm) also indicates high carbon-concentration in the downstream region. Further more, addition of H2 to C4F8, which has more carbon species, yielded higher C2/F ratio. Accordingly, it was found that selectivity of SiO2/Si was remarkably enhanced by adding a higher concentration of H2 to C4F8 in the downstream region. The favorable results are due to the sheetlike characteristics of ICP. Since the plasma is confined near a quartz plate, HF molecules generated from the reaction of H atoms with F atoms do not undergo dissociation in the diffusive region. Thus high-speed pumping of HF is considered to suppress Si etching and in turn, to allow highiy selective SiO2 etching.

Magnetic interactions among unpaired electrons in charge-transfer complexes of organic donors having a neutral radical

Abstract A new π-electron donor in which TTF is linked with tetramethylpiperidinoxyl radical is synthesized. Three donors consisted of dialkylaminophenyl and nitronyl nitroxide are also prepared. Magnetic properties of the donors and their charge-transfer complexes with the acceptors TCNQ and TCNQF4 are investigated by means of magnetization measurements below 5 K and magnetic susceptibility measurements between 2 and 300 K. Magnetic interactions among the unpaired electrons located on the radical and electron donating moieties of the donor molecule and on the acceptor molecule are discussed.

Helicon wave plasma reactor employing single‐loop antenna

Helicon wave plasma excited by a single‐loop antenna and etching characteristic of Si and SiO2 is studied on a basis of plasma parameters and wave patterns measurements. A wide variety of wavelength with space is observed in the single‐loop antenna, and because of no external boundary for the wavelength, the best match of the rf source with plasma is possible. This fact is ascribable to the density enhancement rather than in the conventional double‐loop antenna. A condition that the magnetic field is lowered in the antenna portion is also effective on the density enhancement. This is explained by a longer time in resonance of the electron. The etching uniformity is also improved by using a larger diameter one‐loop antenna, with a great usefulness.

Healthcare chip for checking health condition from analysis of trace blood collected by painless needle

A healthcare chip for checking the health condition at home has been studied based on the analysis of a trace amount of blood collected by a painless needle. A microcapillary as the main component for the blood flow was fabricated by molding its reverse pattern made of a quartz plate on a cheap and disposable poly(ethylene terephthalate) (PET) plate with an area of 2 cm×2 cm. The painless needle was fabricated by polishing the tip of a stainless steel tube (SUS) with a 100 µm diameter at an angle of 10 degrees using chemical mechanical polishing (CMP) and subsequently finishing it by electropolishing. Coating the 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer on the inner surface of the capillary effectively suppressed the adsorption of corpuscles. A quartz electroosmosis flow pump embedded in the PET plate introduced the blood into a U-shaped capillary through the needle and the blood was centrifugally separated into the corpuscles and plasma on the chip. The plasma was then conveyed to ion-sensitive field-effect transistors (ISFETs) set on the capillary and the Na+ and K+ ion concentrations were measured with high selectivity. Finally, a series of chip operations from blood collection to measurements of the pH, Na+ and K+ ion concentrations was demonstrated.

RF Self-Bias Characteristics in Inductively Coupled Plasma

The plasma characteristics and RF self-bias behavior in inductively coupled plasma were studied. In the absence of magnetic field, a newly developed 1-turn antenna provided more uniform radial distribution of electron density than the spiral antenna with the present relatively small diameter, and uniformity of ±5% with 4.5×1011 cm-3 was achieved for 12 cm at 600 W. The electron density increased linearly with increasing power and did not saturate even at 1 kW input power. The ne of 7×1011 cm-3 was obtained in Ar at 1 kW power. For such high-density and large-diameter uniform plasma, the RF self-bias voltage was difficult to generate, because the sheath capacitance is too large. An equivalent circuit analysis clarified that the self-bias voltage behaved as Vpp4ne-2, where Vpp is RF voltage.

Microloading Effect in Highly Selective SiO2 Contact Hole Etching Employing Inductively Coupled Plasma

The highly selective SiO2 etching achieved in the downstream region of the inductively coupled plasma (ICP) employing C4F8+H2 was studied regarding polymer film deposition characteristics. Polymer deposition into as-etched 0.5 µ m holes at floating potential showed an overhang feature with C4F8 alone and a conformal one with C4F8+30%H2. When as-etched 0.5 µ m holes were subjected to C4F8+30%H2 plasma, the film thickness on bottom surfaces increased rapidly with increasing self-bias voltages. This result demonstrated that high selectivity in holes less than 0.8 µ m was achieved by deposition of resputtered film on the side wall onto the bottom. To analyze the bottom Si surface in deep holes, a simulated experiment was also performed using a capillary plate with 10 µ m (aspect ratio 40); the Si surface masked by the plate was exposed to plasma, then the Si surface was measured by X-ray photoemission spectroscopy (XPS). Etching occurred on the Si surface covered by the fluorine-rich polymer in C4F8 alone, and carbon-rich film was deposited on the Si surface with addition of 30%H2. The latter explains the origin of high selectivity.

Generation of Integrated Atmospheric-Pressure Microplasmas

This work is based on the motivation that by integrating microplasmas confined in a small volume, a large area high-density plasma source could be developed. Firstly, He gas microplasmas were generated by capacitively coupled plasma (CCP) and inductively coupled type plasma (ICP-type) in single small diameter ceramic tubes supplied with 13.56 MHz power via electrodes. Then, based upon the obtained characteristics, sustaining voltage and RF power variations were discussed for integrating tubes two and three dimensionally. However, the presence of the CCP component was noticed from the weak discharge around the center of the highly integrated ICP-type. Therefore, the generation of planar-type plasma was also studied using narrow comb electrodes, which enabled us to produce the discharge at a lower voltage in accordance with Paschens law. As a result, uniform plasma was successfully generated in an area of 12 mm×12 mm. Atmospheric-pressure microplasma generation of pure N2 gas as well as He gas was realized by planar type plasma at low sustaining voltages.

Deep Dry Etching of Quartz Plate Over 100 µm in Depth Employing Ultra-Thick Photoresist (SU-8)

The newly developed backside exposure method enabled us to easily fabricate a vertical/high aspect ratio ultra-thick photoresist (SU-8) pattern on a quartz plate. Deep quartz plate etching masked with SU-8 resist was studied employing an ICP etcher with a C4F8/H2/Ar gas mixture. Two issues took place in the long time etching. One was a corn-like defect generated on the quartz surface and the other was the variation of SU-8 etch rates during the etching process. The former was eliminated by a high bias cleaning process and an Ar plasma preheating process of the chamber wall improved the latter. Accordingly, a vertically etched profile of 100 µm in depth was achieved.

Long Line-Shaped Microwave Plasma Generation Employing a Narrow Rectangular Waveguide

Long line-shaped microwave plasma is generated employing a narrow rectangular waveguide. The wavelength of a microwave in a waveguide increases in accordance with the narrowing of the width of the waveguide. A narrow and flat rectangular waveguide is produced with internal dimensions of 500 mm length, 62 mm width and 5 mm height. The waveguide is connected to a TE10 mode rectangular waveguide (WST-AD standard). Two types of line-shaped plasmas are generated; one being a cavity type and the other a slit type. The cavity type line-shaped plasma has a quartz tube in the waveguide as a discharge tube and helium gas is supplied into the quartz tube through orifices of the waveguide. The slit type line-shaped plasma has a slit on its side. A quartz tube as a discharge tube is set beside the slit and helium gas is supplied into it. Electric field intensity and optical emission intensity are then measured. Uniform line-shaped plasmas are generated by varying the width of the waveguide and the microwave power in both types of line-shaped plasmas.