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The change of the ion transport is investigated with the variation of the focus ring property at the wafer edge of a capacitively coupled plasma under an intermediate pressure of a few Torr. The particle fluxes and the ion trajectories at different locations are investigated with the variations of the gap size between the wafer edge and the focus ring, the focus ring height, and the permittivity of the focus ring. The incident angle and the particle fluxes to the wafer edge increase with the gap size. Conversely, the particle fluxes to the wafer edge decrease with the increase in the focus ring height. The incident angle of ions still keeps normal to the surface at the wafer edge, but on the left side of the focus ring, it increases dramatically with the increase in the focus ring height. With the change of the permittivity of the focus ring, it is possible to control the ratio of the ion flux to the neutral flux on the focus ring surface by enhancing only the ion flux independently.

In this paper, the negative ion behavior in a C4F8 inductively coupled plasma (ICP) is investigated using a hybrid model. The model predicts a non-monotonic variation of the total negative ion density with power at low pressure (1030 mTorr), and this trend agrees well with experiments that were carried out in many fluorocarbon (fc) ICP sources, like C2F6, CHF3, and C4F8. This behavior is explained by the availability of feedstock C4F8 gas as a source of the negative ions, as well as by the presence of low energy electrons due to vibrational excitation at low power. The maximum of the negative ion density shifts to low power values upon decreasing pressure, because of the more pronounced depletion of C4F8 molecules, and at high pressure (∼50 mTorr), the anion density continuously increases with power, which is similar to fc CCP sources. Furthermore, the negative ion composition is identified in this paper. Our work demonstrates that for a clear understanding of the negative ion behavior in radio frequency C4F8 plasma sources, one needs to take into account many factors, like the attachment characteristics, the anion composition, the spatial profiles, and the reactor configuration. Finally, a detailed comparison of our simulation results with experiments is conducted.

It is shown that remarkable improvements essential to a quantitative spectrochemical analysis of hydrogen emissions from the zircaloy samples were achieved when the low-pressure surrounding air used in the previous experiment of Nd-YAG laser-induced shockwave plasma was replaced by an inert gas. Using the high-purity (99.999%) nitrogen gas at 1.5 Torr, a linear calibration curve of the HI 656.2 nm emission line was obtained with a zero intercept from the zircaloy samples prepared with various hydrogen concentrations. Further, when the surrounding nitrogen gas was replaced by a helium gas, more than an order of magnitude enhancement was obtained on the signal-to-noise ratio, yielding a detection limit of less than 5 ppm.

Chemical oxygen-iodine lasers (COIL) are attractive for diverse industrial applications because they are capable of high efficiency, high power operation, and because the 1.315μm wavelength can be transmitted through fiber optics and couples efficiently with most metals. Conventional COILs are pumped with O2(Δ1) that is generated by reaction of Cl2 in a basic H2O2 solution. Current trends in pumping COILs involve producing the O2(Δ1) in electric discharges, thereby circumventing the hazards, complexity, and weight associated with pumping and storing caustic liquids. In this work, we have investigated the scaling of O2(Δ1) yields with specific energy deposition in He∕O2 mixtures in flowing radio frequency (rf) discharges at pressures of a few to tens of Torr using a global plasma kinetics model. We found that O2(Δ1) yield increases nearly linearly with specific energy deposition in O2 molecules up to a few eV per molecule, with yields peaking around 30% by 5–8eV. Further increases in specific energy deposi...

This article presents a front panel structure for an alternating current plasma display panel (AC-PDP) based on a ridged transparent dielectric layer and long hollow gap between the sustain electrodes. The suggested structure can reduce a firing voltage and sustain voltage than a conventional AC-PDP due to a strong electric field between the sustain electrodes. Experiments were conducted with various Xe contents from 10% to 50% at a gas pressure of 450 Torr, and the results confirmed that the ridged dielectric structure reduce the firing and sustain voltages by about 74 and 79 V at 10% Xe content than a conventional structure with 10% Xe content, respectively. Also, the proposed structure improve the luminous efficiency and luminance by about 50.9% and 33%, respectively, with a 50% Xe content when compared to a conventional structure with a 10% Xe content at a similar driving voltage.

We report on the optimization and analysis of a dilute NF3 in situ plasma-enhanced chemical vapor deposition chamber cleaning plasma for an Applied Materials P-5000 DxL chamber. Using design of experiments methodology, we identified and optimized operating conditions within the following process space: 10–15 mol % NF3 diluted with helium, 200–400 sccm NF3 flow rate, 2.5–3.5 Torr chamber pressure, and 950 W rf power. Optical emission spectroscopy and Fourier transform infrared spectroscopy were used to endpoint the cleaning processes and to quantify plasma effluent emissions, respectively. The results demonstrate that dilute NF3-based in situ chamber cleaning can be a viable alternative to perfluorocarbon-based in situ cleans with added benefits. The relationship between chamber clean time and fluorine atom density in the plasma is also investigated.

Single walled carbon nanotubes (SWNT) produced by the anodic arc discharge over a range of constant background pressures of helium (100–1000 Torr) were examined under a high-resolution transmission electron microscope, and a Raman spectrometer. It was found that the average SWNT diameter is about 2 nm and fairly independent of the background pressure. Analysis of the relative purity of SWNTs samples suggests that highest SWNT relative concentration can be obtained at background pressure of about 200–300 Torr. Measured anode ablation rate increases linearly with background pressure. The model of the anodic arc discharge was developed. It was found that the predicted anode ablation rate agrees well with experiment suggesting that electron temperature in the anodic arc is about 0.5 eV.

The excimer emission from direct current glow discharges between a planar cathode and a ring-shaped anode of 0.75 and 1.5 mm diameter, respectively, separated by a gap of 250 μm, was studied in xenon and argon in a pressure range from 75 to 760 Torr. The thickness of the “cathode boundary layer” plasma, in the 100 μm range, and a discharge sustaining voltage of approximately 200 V, indicates that the discharge is restricted to the cathode fall and the negative glow. The radiant excimer emittance at 172 nm increases with pressure and reaches a value of 4 W/cm2 for atmospheric pressure operation in xenon. The maximum internal efficiency, however, decreases with pressure having highest values of 5% for 75 Torr operation. When the discharge current is reduced below a critical value, the discharge in xenon changes from an abnormal glow into a mode showing self-organization of the plasma. Also, the excimer spectrum changes from one with about equal contributions from the first and second continuum to one that i...

Microdischarge (MD) devices are plasma sources typically operating at 100s Torr to atmospheric pressure with dimensions of 10s–100s μm. Their design in based on pd (pressure×characteristic dimension) scaling; smaller dimensions are enabled by higher operating pressures with typical devices operating with pd=1–10 Torr cm. MD devices have exhibited behavior that resemble both Townsend and hollow-cathode discharges, with bulk and beam electrons providing the dominant excitation, respectively. In this article, results from a two-dimensional computational study of MD devices operating in neon using a pyramidal cathode structure are discussed. Pressures of 400–1000 Torr and device dimensions of 15–40 μm are investigated. The onset of behavior resembling negative glow discharges with decreasing pressure correlates with an extension of cathode fall accelerated beam electrons into the bulk plasma. For constant applied voltage, peak electron densities increase with increasing pressure as the beam electrons are slowed in more confined regions. The MD devices typically require higher applied voltages to operate at lower pressures, and so resemble discharges obeying Paschen’s curve for breakdown. MD devices having similar magnitudes and spatial distributions of plasma and excited state densities can be obtained to dimensions of

This article explores electric current and field distributions in dc microplasmas, which have distinctive characteristics that are not evident at larger dimensions. These microplasmas, which are powered by coplanar thin-film metal electrodes with 400-μm minimum separations on a glass substrate, are potentially useful for microsystems in both sensing and microfabrication contexts. Experiments in N2 ambient show that electron current favors electrode separations of 4 mm at 1.2 Torr, reducing to 0.4 mm at 10 Torr. The glow region is confined directly above the cathode, and within 200–500 μm of its lateral edge. Voltage gradients of 100 kV/m exist in this glow region at 1.2 Torr, increasing to 500 kV/m at 6 Torr, far in excess of those observed in larger plasmas. Numerical simulations indicate that the microplasmas are highly nonquasineutral, with a large ion density proximate to the cathode, responsible for a dense space-charge region, and the strong electric fields in the glow region. It is responsible for ...

The experimental values for electron temperature and plasma density are measured in a microfabricated, inductively coupled plasma on a chip (ICP). The miniature ICP system consists of a planar plasma source that is microfabricated on a glass wafer and a miniature aluminum vacuum chamber (φ=6 mm). A reliable Langmuir probe diagnostic for microplasma reactors was developed because classic probe measurements would be hindered by the small plasma volume, the small surface area of grounded reactor walls, collisional ion sheathes, and the radio-frequency (rf) interference from the high-frequency power supply. Once the ion density and electron temperature are determined, the neutral gas temperature was estimated to be nearly equal to room temperature. At low pressures, one finds that the plasma sheath width limits the dimensional scaling of the reactor, since the sheath is, typically, ∼0.6 mm. The plasma operates from 0.1 to 10 Torr, and requires less than 3 W of transmitted power at a frequency of 493 MHz. Dire...

An analysis is carried out to determine radial temperature distributions in the cylindrical positive column of a glow discharge formed in air in free space without confining walls. The analysis considers discharge with current densities lower than 100 mA/cm2 and at gas pressures of several tens of Torr. The plasma is represented by a set of hydrodynamic equations that include the balances for electron number density, translational energy, and the vibrational energy. The equations are solved using an iterative method to obtain gas temperatures for a range of plasma conditions. The results show that increasing discharge current densities lead to higher gas temperatures on plasma axis, however, unlike in the case with glow discharge restricted by dielectric walls, increased current densities also lead to wider radial profiles of temperature. Increased gas pressure, while leading to higher on-axis gas temperatures, results in narrower temperature profiles, mainly due to the reduced diffusion rates and vibrati...

A one-dimensional particle-in-cell/Monte Carlo code with three velocity components is developed to simulate a capacitively coupled radio-frequency Ar/H2 discharge at low pressure, and to investigate the effect of adding hydrogen to an argon discharge. This self-consistent kinetic simulation technique allows one to study fundamental processes in the discharge at the molecular level. It is shown that the addition of small amounts of H2 to an Ar discharge has profound effects on the discharge behavior, i.e., a change in the electron energy probability function, an increase in the electron density at low H2 content and a decrease at higher H2 content, as well as a dip in the Ar+ ion density in the center of the discharge at higher pressure. These effects can be explained by the collision processes taking place in the discharge. The simulations were carried out in the pressure range 50–250 mTorr, at voltages of 300 and 800 V, while the H2 content was varied between 0% and 10%, at a constant driving frequency of 13.56 MHz.

Using both analytical and experimental methods, we show that micron scale patterned growth of small molecular weight organic semiconductor thin films can be achieved by the recently demonstrated process of organic vapor phase deposition (OVPD). In contrast to the conventional process of vacuum thermal evaporation, the background gas pressure during OVPD is typically 0.1–10 Torr, resulting in a molecular mean free path (mfp) of from 100 to 1 μm, respectively. Monte Carlo simulations of film growth through apertures at these gas densities indicate that when the mfp is on the order of the mask-to-substrate separation, deposit edges can become diffuse. The simulations and deposition experiments discussed here indicate that the deposited feature shape is controlled by the mfp, the aperture geometry, and the mask-to-substrate separation. Carefully selected process conditions and mask geometries can result in features as small as 1 μm. Furthermore, based on continuum and stochastic models of molecular transport in confined geometries, we propose the in situ direct patterning growth technique of organic vapor jet printing. The high pattern definition obtained by OVPD makes this process attractive for the growth of a wide range of structures employed in modern organic electronic devices.

The kinetics of nitrogen incorporation in SiO2/4H–SiC using NO are presented. Samples were annealed in NO at pressures of 100 Torr and 1 atm, at temperatures from 1050 to 1175 °C, and for times from 0.5 to 6 h. Annealing in NO incorporates ∼1014 cm−2 of nitrogen at the SiO2/SiC interface. The nitrogen content initially increases with time and temperature, but nitrogen is removed at later times at temperatures above 1050 °C. This nitrogen removal, and the associated oxide growth in the SiC substrate, is caused by O2 formed by the thermal decomposition of NO. Eventually, the nitridation and oxidation reactions reach equilibrium, and the nitrogen content saturates as the oxide thickness increases.

Bottom-gate-type thin film transistors using ZnO as an active channel layer (ZnO–TFT) have been constructed. The ZnO layers were deposited using pulsed laser deposition at 450 °C at an oxygen pressure of 3 m Torr, and the material that was formed had a background carrier concentration of less than 5×1016 cm−3. A double layer gate insulator consisting of SiO2 and SiNx was effective in suppressing leakage current and enabling the ZnO–TFT to operate successfully. The Ion/Ioff ratio of ZnO–TFTs fabricated on Si wafers was more than 105 and the optical transmittance of ZnO–TFTs fabricated on glass was more than 80%. These results show that it is possible to fabricate a transparent TFT that can even be operated in the presence of visible light.

An analytic kinetic model is elaborated to determine the spatial evolution of the concentration of ground and excited Li atoms (up to the 3 2D level) present in the plasma generated by pulsed laser ablation of a LiNbO3 crystal in gas atmospheres (at 1 Torr) of different nature, both reactive (O2) and inert (Ar). Whereas the Li atom population densities in the plasma produced in gas are, in general, higher than those found in vacuum, the concentration of ground Li atoms close to the substrate is similar in vacuum and Ar, though lower than in O2. It is suggested that the reabsorption of radiation by the plasma is more important within O2 than in Ar since the absorber (ground Li) concentration is higher in O2 environments. A very reasonable qualitative agreement is found when comparing the Li I-670.8 nm spectral line emission intensity predicted by the model with that obtained experimentally in Ar and O2 atmospheres.

Cavity ring-down spectroscopy has been used to measure the absorbances, concentrations and temperatures of C2(a3Πu v=0) and CH(X2Π v=0) radicals in a ⩽10 kW dc arc jet used for chemical vapor deposition (CVD) of polycrystalline diamond films and operated with CH4/H2/Ar gas mixtures. Gas temperatures derived from the intensities and widths of rotationally resolved C2 d3Πg−a3Πu spectral lines are 3300±200 K in the free plume, rising to ∼4800 K close to the substrate on which the diamond film is grown. For an input power of ∼6 kW, a 3.3% CH4/H2 ratio with excess Ar and a pressure of 50 Torr, the conditions typically employed for diamond film CVD, concentrations of C2(a) are between 6.0±0.2×1012 and 1.5±0.2×1013 cm−3 in the free plume at distances >5 mm from the substrate. These values are derived assuming a 1 cm column length as implied by spatially resolved studies of C2(d−a) optical emission; the spread reflects the decline in performance of the arc jet torch heads over time. The concentration of CH(X) in ...

The electrochromic properties of Ni oxide films grown at different working pressures (2.7, 5, 15, and 20 mTorr) by rf sputtering were investigated by means of in situ transmittance measurement and the resulting data were related to the crystallographic structure, surface morphology, and film density. At working pressures of over 5 mTorr, the sputter-deposited Ni oxide films crystallized gradually due to the plasma heating effect at a low growth rate. Although the Ni oxide film grown at 2.7 mTorr had the same amorphous crystallographic structure as the film grown at 5 mTorr, the former had a considerably more inhomogeneous surface and a much lower film density due to the rapid growth rate, and resulted in a defect-rich Ni oxide film. The electrochromic properties, such as the transient cycling period, coloration efficiency, and coloring/bleaching response times, were best for the sample grown at 5 mTorr and they are discussed in terms of defect-rich and crystalline Ni oxide films.

The dissociative recombination (DR) coefficient in decaying low temperature Cs plasma is calculated based on the experimentally measured relaxation time of decaying Cs plasma by L. P. Harris [J. Appl. Phys. 36, 1543 (1965)]. Results showed that DR is the dominant recombination process over three-body recombination at T

Silicon–germanium alloy nanoparticles with spherical shape have been prepared by the thermal evaporation method. The shape and structure of these dots have been studied. Transmission electron microscopy images show that the SiGe nanoparticles grown at 100 Torr may be composed of two half-moon shaped sections. Furthermore from the transmission electron diffraction patterns and Raman spectra, a change of structure from amorphous to crystalline at the 0.4 Torr growth pressure was observed. It is also found that if the growth pressure increases, the Ge composition of SiGe dots will decrease. A model is proposed to explain this phenomenon.

We have studied, both experimentally and numerically, the radiometric efficiency of low-pressure barium–argon positive column discharges. Using a 14 mm inner diameter alumina discharge tube to reduce chemical reactivity, we have operated discharges with Ba vapor pressures corresponding to a range of oven temperatures from 600 to 800 °C, Ar buffer gas pressures of 0.5 and 5 Torr, and currents of 100–800 mA. The spectral power distribution has been determined by examining the visible radiation emitted perpendicular to the discharge axis from a small aperture in the side of the alumina discharge tube. Absolute emitted powers were determined by comparison to a calibrated tungsten–quartz–halogen lamp. The measured efficiencies for production of visible radiation from the positive column ranged from 2.5% to 52%. These efficiencies correspond to luminous efficacies ranging from 6 to 97 lm/W. Strong emission on Ba ion lines at 455.4, 493.4, 614.2, and 649.7 nm contributed significantly to the best efficiency, 52%, and yielded a white light. A numerical model, incorporating a substantial number of excited levels and atomic processes, has been used to examine the same conditions. The model reproduces most of the major experimental trends.

Germanium nanoparticles with spherical shape have been prepared by the thermal evaporation method. The shape and structure of these particles have been studied. Transmission electron microscopy images show that a change of Ge structure from amorphous to crystalline occurs at a growth pressure of 0.4 Torr and is attributed to the change of lattice constant. When the growth pressure becomes larger than 0.4 Torr, a fractallike tree structure made of Ge nanoparticles is observed. As the pressure increases further, the dot shape becomes clearer and many dots overlap. From the Raman spectra, it is found that the diamond structure is dominant for Ge dots.

Particle dynamics during Si nanoparticle synthesis in a laser-ablation plume in different background gases were investigated by laser-spectroscopic imaging techniques. Two-dimensional laser induced fluorescence and ultraviolet Rayleigh scattering techniques were used to visualize the spatial distribution of the Si atoms and nanoparticles grown, respectively. We have developed a visualization technique called re-decomposition laser-induced fluorescence to observe small nanoparticles (hereafter called clusters) which are difficult to observe by the conventional imaging techniques. In this article, the whole process of nanoparticle synthesis in different background gases of He, Ne, Ar, N2 and O2 was investigated by these techniques. In He, Ne, Ar and N2 background gases at 10 Torr, the clustering of the Si atoms started 200, 250, 300 and 800 μs after ablation, respectively. The growth rate of the clusters in He background gas was much larger than that in the other gases. The spatial distributions of the Si n...

This paper reports on a series of identical experiments and on a respective particle-in-cell and Monte Carlo simulation to investigate the stability of runaway electron beam currents produced in nitrogen at a highly inhomogeneous electric field. The experiments demonstrate a strong effect of cathode emissivity on the beam current. The numerical simulation shows that the cathode emissivity influences not only the current of the beam but also the mechanisms of its formation.

A one-dimensional radial slice of an Ar positive column discharge is simulated with a radiation transport coupled particle-in-cell model. The discharge is maintained by an axial current in the positive column which induces a self-consistent axial electric field. Power balance and radiation efficiency are investigated for variations of axial driving current Iz, gas pressure p, and radius R. The parameter regimes are from 0.1 to 1 cm for radius, 1 mTorr to 20 Torr for gas pressure, from 4 to 14 eV for electron temperature, from 1015 to 1017 m−3 for peak plasma density, and from 0.15 to 50 mA for axial current. The radiation efficiency is related to the product of the pressure and the radius, pR; it is restricted by the large wall loss for small pR and by the collisional quenching of the radiative state for large pR. The optimal value is about pR=1 Torr cm for this parameter regime.

An experimental investigation of a single-gap pseudospark was conducted using a flexible discharge chamber. The voltage breakdown characteristics were studied against a wide range of parameters such as gas pressure, gap separation, cathode cavity depth, cathode aperture size, external capacitance and applied voltage. An empirical formula, VB=(0.20±0.05) p−4.02±0.18 d−1.77±0.01, was obtained for the breakdown voltage VB in kV, given the gas pressure p in Torr and the gap separation d in mm. The electron beam extracted from this single gap was also studied and a current of up to 100 A was measured at 10 kV.

Gate dielectrics composed primarily of lanthana and zirconia were prepared by reactive evaporation. The stability of the layers during high temperature anneals was investigated. By controlling the oxygen partial pressure during heat treatment, lanthana and zirconia films could be protected against reaction with the underlying Si substrate and against the growth of low-e interface layers. The electrical thickness of the dielectrics could be maintained after a 900 °C exposure. The critical oxygen pressure at 900 °C for low-e interface formation beneath ZrO2 and La2O3 dielectrics was ∼2e−4 Torr. The interfaces that formed beneath the ZrO2 and La2O3 layers are distinctly different. The sub-ZrO2 interface, influenced primarily by phase separation, tends towards pure SiO2, while the sub-La2O3 interface, influenced primarily by silicate formation, tends towards a La–Si–O alloy. For both materials, reducing the oxygen pressure to values below 10−7 Torr resulted in rapid degradation of the metal oxide. This dielec...

We report on the effect of ion energy on photoresist etching in an inductively coupled large area plasma source driven by a 13.56 MHz traveling wave with oxygen gas. To control the ion energy at the substrate surface, the electrode on which the substrate is placed is independently driven by a capacitively coupled 1 MHz power source. The etch rate increases with increasing ion energy for gas pressure ranging from 1 to 100 mTorr. Ion-induced desorption rate constants (etch yields) are shown to be proportional to the square root of the ion energy. An increase in the ion energy leads to etch-uniformity improvement over the processing area of 40 cm×50 cm, particularly at a low gas pressure of 5 mTorr. A modified photoresist etch kinetics model combined with a spatially-varying oxygen discharge model is used to explain these experimental results.

The buildup of a plasma produced by short-pulse (0.05–1.2 μs), high-power (60–100 kW) microwaves is studied in a pressure range of 10 mTorr–10 Torr, by measurements of the temporal variation of the current and the optical intensity. The plasma is produced in a cylindrical tube and confined by a minimum-B field. The buildup of the electron current and the optical intensity are found to continue beyond the end of the pulse, for a few to tens of μs depending upon the pressure, and a minimum in their peak values and buildup times occur around 1 Torr. Increase in microwave pulse duration increases the buildup rate and peak current, whereas the pulse repetition frequency (10–500 Hz) has only a weak influence. The results are discussed from the growth of electron temperature during the pulse, and the following plasma evolution after the end of pulse. Collisional wave absorption, electron cyclotron heating, and diffusion are found to play important roles in plasma production and maintenance over the pressure range.

Laser induced fluorescence was used to measure the spatially resolved CF, CF2, and SiF radical density in inductively driven discharges containing fluorocarbon gases. Measurements of the spatially resolved CF density were performed in C2F6, and CHF3 containing discharges as functions of inductive power, pressure and bias condition on a silicon substrate. In addition, CF rotational temperatures were calculated, assuming saturated spectra. Measurements of the spatially resolved CF2 and SiF density were performed in C4F8, C2F6, and CHF3 containing discharges as functions of inductive power, pressure and bias condition. SiF rotational temperatures were also estimated. As the induction coil power was increased, the SiF density in the center (r=0 cm) increased while the CF2 density decreased and the CF density slightly decreased. In all cases, the radical density in the center of the glow increased with pressure changes from 5 to 30 mTorr while changes in the bias power had little influence on any of the measur...

The crystal morphologies and phase composition of diamond crystallites during bias enhanced nucleation and initial growth stages in microwaveplasma chemical vapor deposition were investigated. Diamond nuclei were first formed in the central regions of substrates and then propagated to the sample edges. During the course of bias nucleation, excessive ion bombardment induced secondary nucleation sites on the already formed nuclei. The secondary nucleation deteriorated the overall alignment of the growing crystals. Hence, the elimination of secondary nucleation and homogeneous nucleation over substrates are fundamental requirements for the deposition of large-area uniformly oriented diamondfilms. Decreasing reactant pressure was found to be effective for improving plasma homogeneity and consequently nucleation uniformity. The results of bias enhanced nucleation within a pressure range from 8 to 20 Torr showed that the lower pressure of reactants enlarged the area of oriented diamondfilms. However, the optimum bias and duration of nucleation was found to be specific for each pressure.

Transient trapping/detrapping of electrons at the Si(100)/SiO2 outer surface is studied studied in vacuum or with an O2 ambient (between 10−3 and 30 Torr) following internal electron photoemission from Si. Photoemission-current (produced by a 150 fs, 800 nm laser source) and contact-potential-difference techniques were used to investigate a wide variety of n- and p-doped samples at 300 K with thermally grown, steam grown, and dry oxides with thickness ⩽5 nm as well as samples with the oxide layers removed. Characteristics of the steam grown oxide were also studied at 400 and 200 K. For samples in vacuum charging is attributed to direct filling of at least two families of traps, one related to the oxide and the other the Si/SiO2 interface. For samples in O2, details of oxygen-assisted surface charging as reported previously [Phys. Rev. Lett. 77, 920 (1996)] are given. A fast, Coulomb-repulsion driven spillover of surface charge from the irradiated spot to the rest of the surface was detected. Oxygen aids t...

The flowing afterglow of a microwave discharge can be used to efficiently inactivate bacterial spores. We have conducted a parametric study of the operating conditions of such a system, which shows that the species participating in the killing of spores are oxygen atoms and ultraviolet (UV) photons. The oxygen atoms and the excited atoms and molecules emitting the photons being carried by the flowing afterglow can be made available throughout the sterilization chamber. Typical operating conditions are: gas mixture 2%O2/98%N2, pressure range 1–7 Torr and gas flow 0.5–3 slm. Total inactivation of 106 B. subtilis spores is achieved within 40 min with 100 W absorbed microwave power, at afterglow gas temperatures not exceeding 50 °C, a feature of interest for heat sensitive medical devices. The present scheme depends on the gas flow reaching all parts of the objects to be sterilized and on the short-lived active species being transported there sufficiently rapid. Under our operating conditions, it is the UV emission intensity that sets the sterilization time as there are always more than sufficient oxygen atoms available for the process.

A simple low-pressure condition at 80 mTorr has been employed to study the kinetics and role of C, O, and OH in diamond growth by using inductively coupled CO/CH4/H2 and O2/CH4/H2 plasmas. Vacuum ultraviolet absorption spectroscopy (VUVAS) and actinometric optical emission spectroscopy (OES) were used to examine the densities of ground-state C atoms and emissive species such as OH, C2, and O, respectively. Diamond films consisting of nanocrystallites with sizes as small as 20 nm were obtained on positively biased Si substrates only when CH4 was fed. Both diamond and nondiamond growth were enhanced with increasing CO for a fixed CH4 concentration of 5%, while diamond growth was suppressed with increasing O2. Comprehensive discussion along with the VUVAS and OES results suggested that the C atoms resulting mainly from CO by electron impact dissociation had a close relation with the formation of C2 or still larger species as the precursors to nondiamond phase, while the OH radicals resulting predominantly by...

A cylindrical Langmuir probe has been used to measure the electron energy distribution function (EEDF) in atomic and molecular gases in a shielded inductively coupled plasma. We report the EEDFs in these gases as a function of pressure. While the electron properties in a discharge depend on the product of the neutral number density (N0) and the effective discharge dimension (deff) for a given gas, this dependence is different for different gases. We find that pressure is a convenient parameter for comparison of the EEDFs in these gases. The EEDFs in inert (Ar, Kr, Xe) and molecular gases (H2,N2,O2,H2O,CO2,CF4) in the low pressure limit (below 1 mTorr) show a “three-temperature” structure. Since this wide range of gases display similar EEDF shape, we propose this structure to be common to all gas discharges in this limit. The EEDF in all of the gases shows a two-temperature structure with apparent tail depletion at 3 mTorr. The similarity of the EEDFs in all of the above gases is probably due to nonlocality of the electrons at these low pressures. The molecular gases exhibit a nearly Maxwellian EEDF between about 10 and 30 mTorr, while the EEDF in argon is non-Maxwellian in this range. At pressures above 30 mTorr, the EEDFs in molecular gases show deviations from a Maxwellian distribution, reflecting the electron-neutral collision cross sections of each gas. The EEDFs in molecular gases at 100 mTorr show significant deviations from a Maxwellian distribution. We find that the EEDF in molecular gases can be approximated by a Maxwellian distribution over a fairly large pressure range of 3–50 mTorr for the purposes of modeling these discharges.

Characteristics of chlorine, transformer-coupled pulsed plasmas are reported. Time dependencies of electron (ne), positive ion (ni+), and negative ion (ni−) densities and electron temperatures (Te) were measured with a Langmuir probe and microwave interferometry at 240 and 500 W input powers, and pressures between 3 and 20 mTorr. During the OFF portion of the power modulation, ne decreases rapidly as Cl− is formed by dissociative attachment of Cl2. The formation of Cl− is accelerated at high Cl2 densities (at high pressures and low powers). At 10 mTorr and higher pressures, an ion–ion plasma forms near the end of the OFF portion of the cycle, the sheath collapses, and Cl− reaches the wafer. Te decays rapidly in the OFF period and increases with a similar time constant at the beginning of the ON cycle if electrons are present at a sufficiently high level. If ne is very low at the beginning of the ON cycle, such as at high pressure (10 mTorr), then Te exhibits a spike at the beginning of the ON period. In a comparison study, plasma induced damage is reduced when aluminum is etched under similar source power modulation conditions.

The spatial distributions of the 3p54s metastable state of Ar have been measured in radio frequency argon plasmas in a Gaseous Electronics Conference Reference Cell by means of high resolution absorption spectroscopy. A single-mode, tunable diode laser has been used to obtain absorption profiles at 750 and 801 nm. Spatial profiles across the gap between electrodes have been measured with 1 mm resolution for various pressures (0.15–1.0 Torr) and plasma powers (1–320 W). The densities of 3p54s metastable were obtained from integrated absorption profiles.

It is well known that radiolysis, induced by the electron bombardment, leads to different defects in SiO2, but little is known about the trapping behavior of these defects. In this article, the charging behavior and the depth profiles of the irradiation damage introduced by electron bombardment are studied with Auger electron spectroscopy (AES). For charge reduction an environmental AES using O2 (up to 8×10−8 Torr) and specimen heating are applied. In environmental AES, a strong charge reduction is observed, and the importance of the environment for charge compensation reveals a correlation with electron stimulated desorption. By heating the sample, a strong charge reduction takes place above 500 °C; complete charge compensation can be expected by heating the sample above 700 °C in an O2 environment of 5×10−8 Torr. We suggest that E′ centers, nonbridging oxygen hole centers, and peroxy radicals, are responsible for the efficient trapping of electrons. The observed discharging is believed to be related to ...

The distribution of self-bias potential (Vdc) on a powered electrode of a supermagnetron plasma system, where both electrodes are supplied phase-shifted radio frequency (rf) currents, was measured using five electrical probes buried in the electrode. For comparison, the same was measured for a conventional magnetron plasma system. Measurements were carried out with an Ar discharge at the pressure region of 4–50 mTorr. The data obtained with the supermagnetron and the conventional magnetron plasm systems were used to map the Vdc distribution on the powered electrodes of each plasma source. When the phase difference between rf currents applied to the two parallel electrodes of supermagnetron plasma system were changed, a drastic change of the Vdc is observed. The uniformity of the Vdc distribution is greatly improved when the phase difference between rf currents is varied from 0° to about 180°. The further increase of phase difference between two rf currents causes a decrease of the uniformity of the Vdc di...

A systematic study of the effect of growth conditions (temperature, microwave power, and pressure) on the hydrogen incorporation and growth rate of (111) homoepitaxial diamond synthesized by microwave plasma assisted chemical vapor deposition is carried out by secondary ion mass spectrometry. Significant quantities of hydrogen incorporation in the (111) homoepitaxial diamond are detected for the growth conditions employed. Hydrogen concentration and growth rate are found to increase with an increase in the substrate temperatures. The increase of microwave power decreases the hydrogen incorporation and increases the growth rate. The effect of pressure rise is similar to that of microwave power. However, the effect of pressure rise over 50 Torr on hydrogen incorporation and growth rate is small. The decrease of hydrogen incorporation can be explained by the suppression of defects in the growing film by atomic hydrogen in the gas phase.

We designed, constructed, and studied a novel probe-coupled 2.45 GHz microwave arrangement to drive a Xe excimer lamp. Electrical efficiency and output power in the 160–200 nm range (Xe second continuum) both increased with pressure and input power up to 1500 Torr and 600 W (42.5 W/cm3), respectively. The maximum in-range optical power was 60 W, more than 80% of the total. Cooling with liquid nitrogen boil off rather than room air more than doubled output power. Model calculation and experimental measurement of the angular distribution of emission find considerable intensity well away from the surface normal. Correcting experimental measurements of excimer lamp output power accordingly brings good agreement with the 20%–40% electrical efficiency predicted by theory.

A surface investigation by atomic force microscope of InP and slightly lattice-mismatched InGaAs epilayers grown by metalorganic vapor phase epitaxy shows the effect of strain on InGaAs/InP surface morphology. Epilayers were grown at 600 °C with arsine at 760 Torr. We could clearly observe the regular step/terrace-like feature of the vicinal surface morphology for InP and InGaAs lattice-matched epilayers. It is shown that the step flow mode appears with a step edge with regular spacing for lattice-matched epilayers. A crosshatch pattern, i.e., an array of perpendicular lines visible at the surface, were obtained for strain-relaxed InGaAs epilayers (|(Δa/a)⊥|>10−3) with an average separation of 1000–1500 nm. The detailed surface structure of the step edge presents a specific bending of terraces. The influence of step kinetics on the morphological stability of the surface will be illustrated. The relationship between the misfit dislocation network and anisotropic growth rate of the front step will be discussed.

A time-modulated and time-averaged two-dimensional (2D) profile of the net excitation rate of Ar(3p5) and Ar+(4p4D7/2) was observed in capacitively coupled plasma (CCP) in Ar as a function of the driving frequency (1–100 MHz) through the use of 2D-t optical emission spectroscopy (OES). A significant improvement in the detection efficiency was achieved for the time-resolved OES. Results are presented for the basic characteristics of 2D and 2D-t profiles of the net excitation rate in Ar from 1 to 100 MHz at 1.0 Torr. For comparison, 2D profiles in CCP between high frequency (13.56 MHz) and very high frequency (100 MHz) at 0.1 Torr and 25 mTorr under the same power dissipation are discussed. The advantages of VHF operation are described and discussed based on the radial uniformity and high density in CCP at low pressure. The appearance of a local emission peak at the edge of the rf electrode is observed in CCP, which is caused by changes in the sustaining mechanism due to increases in the driving frequency.

The development and optimization of sputtering techniques for the deposition of refractory metal thin films for very large scale integration (VLSI) barrier and encapsulation layers is of significant concern for the microelectronic fabrication industry. A number of directed sputtering techniques such as collimation and low pressure longthrow configurations have been applied to this problem. This paper addresses a number of issues present in the understanding and simulation of the growth of films deposited by directed sputtering techniques over VLSI topography. In particular the role of high energy neutral gas atoms reflected from the target is investigated as a source of resputtering. Also addressed is the creation of a low density porous film on the sidewalls of vias/contacts due to oblique incident fluxes on these areas. Experimentally Ti and W films are deposited at pressures varying from 0.2 to 12.0 mTorr with and without collimators present. A number of re-emission/resputtering mechanisms were investigated using a Monte Carlo growth simulator and it was found that the model most consistent with the experimental films was an assumption of resputtering due to reflected neutrals. A significant result is a dramatic increase in the resputtering rate when a collimator was present due to a relative increase in the reflected neutral flux. Finally, the paper presents an analysis of the effect of pressure on bottom and step coverage in high aspect topography.The development and optimization of sputtering techniques for the deposition of refractory metal thin films for very large scale integration (VLSI) barrier and encapsulation layers is of significant concern for the microelectronic fabrication industry. A number of directed sputtering techniques such as collimation and low pressure longthrow configurations have been applied to this problem. This paper addresses a number of issues present in the understanding and simulation of the growth of films deposited by directed sputtering techniques over VLSI topography. In particular the role of high energy neutral gas atoms reflected from the target is investigated as a source of resputtering. Also addressed is the creation of a low density porous film on the sidewalls of vias/contacts due to oblique incident fluxes on these areas. Experimentally Ti and W films are deposited at pressures varying from 0.2 to 12.0 mTorr with and without collimators present. A number of re-emission/resputtering mechanisms were investi...

An investigation was conducted using absorption and emission spectroscopy of the afterglow from rf inductive discharges in Xe/I2 mixtures. RF power at 11.5 MHz was supplied to coils surrounding a cylindrical discharge cell. Total pressures were between 0.8 and 5.3 Torr. Measurements were made as a function of radius and time following the termination of the discharge. Results presented here indicate that in the afterglow the XeI* excimer is formed by highly excited I2 and ground state Xe. Evidence is also presented that ion–ion neutralization is a major precursor reaction for the formation of other excited species in the afterglow.

The transient response of electronegative radio-frequency glow discharges is important for process control, charge free etching, and highly selective etch applications. The step response of typical electronegative process gases (silane at 1 Torr and chlorine at 100 mTorr) is studied using a drift-diffusion model for silane and a three-moment model for chlorine. The silane simulations include a blocking capacitor whereas the chlorine results do not. For the silane results with a blocking capacitor in series with the plasma, it is found that there are three types of transients. Depending on the final steady-state value of the source rf voltage, the step response can be characterized either by smooth transitions in the number densities of species in the discharge from one steady state to the next, temporary extinction of the discharge or a discharge mode characterized by temporary extinction and reignition of the discharge. In the case of silane definite thresholds separate the phenomena. The step response o...

We report on the influence of the gas velocity on the discharge equilibrium in a low-pressure (1 Torr) microwave driven hydrogen plasma. We show that the gas velocity has a great influence on the dissociation degree, the key parameter being the residence time of the molecules in the plasma with respect to their effective dissociation time. The power balance (plasma length, electric field…) is substantially modified by the variations of the dissociation degree induced by the change in gas velocity. On the contrary, the gas temperature, determined by Doppler broadening of H atom Balmer lines, is not directly dependent on the gas velocity. Simple calculations confirm that the gas temperature is determined by local parameters and that heat is not axially transported. Surprisingly, dissociation of the H2 molecules does not seem to play any significant role for the heating of the gas.

The percent dissociation of Cl2 was determined for two configurations of a commercial transformer-coupled plasma (TCP) reactor (LAM Research Alliance metal etcher), using Cl2 and BCl3/Cl2 feed gases, during slow etching of SiO2 covered Si wafers. Emission from Cl2 at 305 nm was recorded as a function of TCP source power, along with emission from 1% Ar and Xe, added as part of an equal mixture of the five rare gases. Absolute Cl2 number densities were determined from the Cl2-to-rare gas emission intensity ratios. The Cl2 percent dissociation increases with power, reaching 70% between 1 and 2 mTorr at the highest power (900 W, 0.080 W/cm3). The percent dissociation decreases with increasing pressure between 1 and 10 mTorr. Decreasing the gap between the TCP window and the wafer chuck from 11 to 6.5 cm decreases dissociation at pressures between 0.5 and 2 mTorr, and increases dissociation slightly at 10 mTorr. The percent dissociation as a function of power, and for the most part as a function of pressure and gap, is reproduced by a zero-dimensional model that includes electron-impact dissociation and dissociative attachment of Cl2, and diffusion-controlled recombination of Cl at the walls. Addition of BCl3 to Cl2 increases the percent dissociation of Cl2, most likely due to a passivation of the chamber walls by adsorbed BClx, lowering the Cl-atom recombination coefficient.

A spatially resolved experimental investigation of the electron energy distribution function (EEDF) and wave propagation characteristics in a high frequency surface wave (SW) discharge in nitrogen has been performed. The measurements reveal the specific changes of the EEDF and its integrals which occur as a result of a different coupling between the electrons and the inhomogeneous SW electric field as a function of gas pressure. At a pressure of 0.5 Torr it was found that the EEDF and corresponding integrals depend on the spatial position, which means that local plasma response occurs. As a result, a strong radial inhomogeneity of the discharge is observed which relates to the radial variation of the wave field intensity. On the contrary, at 0.05 Torr nonlocal plasma response is observed. In a molecular plasma, electron energy relaxation occurs faster than in inert gases, this being why the transition from the local to the nonlocal regime takes place here at a lower gas pressure. A turning back of the axi...