Radio Frequency Power Density Research Articles

Polycrystalline silicon thin films prepared by plasma enhanced chemical vapour deposition at C using fluorinated source gas

Polycrystalline silicon thin films have been developed using plasma enhanced chemical vapour deposition at a low substrate temperature C on glass substrates. An innovative approach has been introduced to deposit polycrystalline silicon film at such a low temperature. Usually a high deposition temperature is used to develop crystalline thin films. For the formation of crystallites a considerable amount of energy transfer is required at the surface of the growing film, which can be done by high-temperature processing. In the present work a high energy supply to the growing surface has been achieved by the increasing plasma power. Plasma power has been enhanced by the proper choice of deposition parameters, namely the nature of the source gas, the flow rate of diluent gas, the chamber pressure and the radiofrequency power density. Dark and photoconductivities achieved for the polycrystalline silicon thin films are and respectively. The average grain size of such film is as seen by scanning electron microscopy, while the estimated size of crystallites from the x-ray diffraction spectra is 323 Å.

Analysis of the N2O dissociation in a RF discharge reactor

In situ diagnostic measurements and reactor modelling are used to study the N2O dissociation by radio frequency (RF) discharges. Measurements are undertaken at 0.5 and 1 Torr gas pressure with a RF power density varying from 4.2 to 35.7 mW cm-2. The reactor modelling involves an electrical discharge model coupled to hydrodynamic and mass transfer models. Only an electrical discharge model accounting for the negative ion conversion from O- to NO- and the subsequent electron detachment allow a good coherence between the measured and predicted power densities. The electron-N2O dissociation cross sections are first fitted in the present work and then the corresponding dissociation rates, obtained from the electrical model, are used in the mass transfer model which includes eight species (N2O, N2, O2, NO, NO2, N, O(3P) and O(1D)). The corresponding results are in good agreement with the experimental ones related to the production of N2 and O2 and the consumption of N2O. Furthermore, the reactor model results show that N2 and O2 are the most abundant products (>1014 molecules/cm3) at 1 Torr.

Photoresist Damage in Reactive Ion Etching Processes

Photoresist damage and patterned feature distortions generated in reactive ion etch (RIE) processing of , thin films were studied as a function of the applied radio frequency power density in two RIE reactors. The photoresist damage was found to originate from plasma‐ and thermal‐induced phenomena that characterize the etching plasma. The onset of photoresist damage was correlated to the glass transition temperature ( of the thermal‐cured photoresist. was found to be 116 ± 8°C for the AZ P4330 positive photoresist and correlated with an onset radio frequency power density of 2.7 ± 0.2 W/cm2. Below , the plasma‐induced phenomena manifested as photoresist etching, hazing, and creep. Above the of the photoresist, thermal‐induced phenomena, manifested as severe photoresist degradation and creep, was found to be the dominant mechanism for the photoresist damage. A model is also presented that predicts and explains the photoresist behavior in an RIE environment with respect to the of the photoresist and as a function of the applied radio frequency power density.

RF radiation-induced changes in the prenatal development of mice.

The possible effects of radiofrequency (RF) radiation on prenatal development has been investigated in mice. This study consisted of RF level measurements and in vivo experiments at several places around an "antenna park." At these locations RF power densities between 168 nW/cm2 and 1053 nW/cm2 were measured. Twelve pairs of mice, divided in two groups, were placed in locations of different power densities and were repeatedly mated five times. One hundred eighteen newborns were collected. They were measured, weighed, and examined macro- and microscopically. A progressive decrease in the number of newborns per dam was observed, which ended in irreversible infertility. The prenatal development of the newborns, however, evaluated by the crown-rump length, the body weight, and the number of the lumbar, sacral, and coccygeal vertebrae, was improved.

Detoxification of Trichloroethylene in a Low-Pressure Surface Wave Plasma Reactor

Application of surface wave plasmas as an alternative technology for the destruction and removal of chlorinated hydrocarbon pollutants is demonstrated. The destruction of parts per thousand concentrations of trichloroethylene in air/water or oxygen mixtures has been investigated in a low-pressure reactor at 5 Torr. Effluent analysis included the determination of destruction and removal efficiencies by electron capture gas chromatography and product distribution by Fourier transform infrared spectroscopy, mass spectrometry, and titrimetric analysis. TCE conversions of up to 99.998% were achieved using radio frequency power densities ranging from 1.6 to 7.5 kJ/L and millisecond range residence times within the plasma. Product analysis indicated that trichloroethylene conversion was limited to light gases, primarily CO2, CO, HCl, and Cl2.

Radio-frequency survey at the bore of a 1.5-T MR imager.

A survey at the bore of a 1.5-T magnetic resonance (MR) imager assessed radio-frequency (RF) exposure. With variable pulse sequences and loading conditions, the RF power density at relevant occupational positions was below measurable limits (less than the threshold limit value for occupational workers of 1 mW/cm2). Exposure to RF fields is below safe limits for personnel who routinely work within an MR imaging suite.

LT-GaAs with high breakdown strength at low temperature for power MISFET applications

Low temperature grown GaAs has been fabricated containing a limited amount of excess arsenic. The material has a low conductivity in the order of 100KΩ cm, due to hopping in a deep donor band. This σ-LT-GaAs was grown reproducibly by using the lattice mismatch as the primary parameter for substrate temperature calibration. Breakdown fields, in the order of 100kV/cm, are observed for planar structures and increased at low measurement emperatures. Low hopping conductivity and high breakdown field are also observed in the lossy dielectric metal-insulator-semiconductor field-effect transistor device using σ-LT-GaAs as a surface layer. The record radio frequency power density of 4.0W/mm at 77K is extracted from the dc output characteristics.

Characterization of [formula omitted] plasma passivation process for poly-Si thin film transistors (TFTs)

The effects of nitrogen additives on the plasma hydrogenation of polycrystalline silicon thin film transistors (poly-Si TFTs) have been investigated with various radio-frequency (RF) power densities, substrate heating temperature, gas flow rates, as well as chamber pressures. The nitrogen-containing hydrogen ( H 2 N 2 ) plasma treatments show better passivation effects on the electrical characteristics of the poly-Si TFTs than the pure H 2 hydrogenation. It is attributed to the passivation effect of the nitrogen radicals themselves and the promotion of the hydrogen plasma generation due to the radical collision. The passivation effects have been enhanced by properly chosen RF power density, gas flow rate and chamber pressure. Furthermore, the H 2 N 2 plasma were also utilized to passivate the poly-Si TFTs with different grain structures.

Lower hybrid wave coupling in TORE SUPRA through multijunction launchers

The TORE SUPRA lower hybrid current drive experiments (8 MW/3.7 GHz) use large phased waveguide arrays, four rows of 32 active waveguides and two passive waveguides for each of the two grills, to couple the waves to the plasma. These launchers are based on the 'multijunction' principle which allows them to be quite compact and is therefore attractive for the design of efficient multi-megawatt antennas in NET/ITER. Extensive coupling measurements have been performed in order to study the radiofrequency (RF) characteristics of the plasma loaded antennas. Measurements of the plasma scattering coefficients of the antennas show good agreement with those obtained from the linear coupling theory (SWAN code). Global reflection coefficients of a few per cent have been measured in a large range of edge plasma densities (0.3 × 1018 m-3 ⩽ neg ⩽ 1.4 × 1018 m-3) or antenna positions (0.02-0.05 m from the plasma edge) and up to a maximum injected RF power density of 45 MW/m2. When the plasma is pushed against the inner wall of the chamber, the reflection coefficient is found to remain low up to distances of the order of 0.10 m

Reactive ion etching of ZnSe by gas mixture of ethane and hydrogen

ZnSe epitaxial layers grown by gas source molecular beam epitaxy were etched by reactive ion etching (RIE) with a gas mixture of ethane and hydrogen (C2H6/H2). Smooth etching surfaces were obtained under the following RIE conditions: an ethane concentration (flow fraction) of 3%, total flow (C2H6+H2) of 55 sccm, total pressure of 15 Pa and radio frequency power density of 0.6 W/cm2. This ethane concentration is smaller than that in III–V semiconductors, 5%–7%. The etching rate of ZnSe was 21 nm/min and smaller than that of III–V semiconductors.

Energy Considerations in the Deposition of High‐Quality Plasma‐Enhanced CVD Silicon Dioxide

Silicon dioxide films deposited from the plasma‐enhanced chemical vapor deposition (PECVD) reaction of silane and nitrous oxide in the presence of helium were studied to determine the effects of temperature and radio frequency (RF) power on the deposition process. Increased RF power density yielded oxides which were structurally more relaxed and homogeneous. Temperature had a more significant effect on the impurity levels in the films. The combination of elevated power density with increased susceptor temperature resulted in the deposition of films of high physical integrity.

Density of States of Amorphous Germanium Thin Films Deposited by the Pecvd of H2-Diluted Germane

ABSTRACTThe disorder in a-Ge:H thin films produced by the plasma-enhanced chemical vapor deposition (PECVD) technique is strongly reduced when the GeH4 gas is diluted at 1% in H2 and the radiofrequency power density is increased to 0.1 W.cm−2. This improvement is attributed to a better surface passivation by the hydrogen atoms during the growth. However, the poor transport properties indicate a still high defect density. The midgap defect absorption and the Urbach energy, obtained from the photothermal deflection spectra calibrated with optical data, both decrease as a function of the film thickness. The optical defect density is calibrated with EPR spin measurements. For a-Ge:H films thicker than 2 μm, obtained at a deposition temperature Ts ranging from 150 to 250°C, the Urbach tail parameter E° is lower than 50 meV and not sensitive to Ts ; the dangling bond density is around 4.107 cm−3, which is higher by a factor of 100 than in a-Si:H. Preliminary transport measurements indicate that the Fermi level density of states is larger than 1018 cm−3.eV−1.

Examination of fluorocarbon-based plasmas used in the selective and uniform etching of silicon dioxide by response-surface methodology: Effects of helium addition

The process parameter space for fluorocarbon plasmas (C2F6/CHF3 and CF4/CHF3, with and without He) which are used to etch SiO2 has been examined with a Lam Research Autoetch 580 parallel plate, single‐wafer etching system by response‐surface methodology. The response or behavior of the plasmas differs very significantly with reactor pressure, etch gas mixture, and He addition. In particular, substantially higher SiO2 etch rates are obtained with C2F6/CHF3 plasmas than with CF4/CHF3 plasmas at an equivalent radio frequency power density for similar gas flow rates at significantly different reactor pressures: ∼2500 Å/min at ∼400 mTorr with C2F6/CHF3 mixtures and ∼750 Å/min at ∼1500 mTorr with CF4/CHF3 mixtures. Upon addition of He to the plasmas, the SiO2 etch rate maximum for the C2F6‐based plasma shifts to ∼800 mTorr and declines to ∼2000 Å/min, while that for the CF4‐based plasma remains near 1400 mTorr and increases to ∼1000 Å/min. Whereas the addition of He sharply degrades the etching uniformity with C2F6/CHF3 mixtures, it has no apparent effect on the etching uniformity with CF4/CHF3 mixtures, which is high with or without the addition of He over the parameter space which was explored. For the C2F6/CHF3 plasma, the etch selectivity to silicon is highest at 700–1100 mTorr, while for the CF4/CHF3 plasma the selectivity is highest at 1100–1500 mTorr. Although addition of He substantially improves the selectivity with the CF4/CHF3 plasmas, it has no effect on selectivity with the C2F6/CHF3 plasma. These detailed characterizations of process parameter space have led to a uniform and selective SiO2 sidewall spacer etching process which may be readily extended to other SiO2 etching processes with this equipment and these gas mixtures.

Power dependence of the reflection coefficient at lower hybrid heating

Due to the ponderomotive action of the radiofrequency (RF) field at the plasma edge, conditions for minimizing the power reflection coefficient R2 can change considerably with increasing RF power. Dependences of R2 on the unperturbed edge plasma density and on the RF power density are computed for a series of illustrative examples.

New Techniques for Microwave Radiation Hazard Monitoring

Extremely high radio frequency power densities exist in the vicinity of modern microwave transmitting equipment and constitute a hazard to personnel and material. This paper discusses the problem and describes a new simple means of measuring and indicating the presence of hazardous microwave radiation. The equipment described utilizes a unique integrating component to accumulate the total radiation received from hazardous RF sources during a fixed sampling period. In this manner it correctly measures the damaging dosage received from RF sources which often produce widely time varying fields due to pulsing and antenna scanning.