Actinometric Optical Emission Spectroscopy Research Articles

Density control of carbon nanowalls grown by CH4/H2 plasma and their electrical properties

We report on successful control of the density of carbon nanowalls (CNWs) synthesized using radical-injection plasma-enhanced chemical vapor deposition (RI-PECVD) employing CH4/H2 plasma, by varying the total pressure and discharge power during growth. As the total pressure was decreased or the power was increased, the density of CNWs decreased in conjunction with an increase in the H atom density measured using actinometric optical emission spectroscopy. The electrical conductivity of the films was found to be determined by the number of CNWs per unit length, i.e., the linear density. We demonstrated that the electrical properties could be controlled while maintaining the crystal quality and chemical bonding state of the synthesized CNWs in the RI-PECVD.

Control of the discharge chemistry of CHF3 in dual-frequency capacitively coupled plasmas

The discharge chemistry of CHF3 in 27/2, 60/2, and 60/13.56 MHz dual-frequency capacitively coupled plasmas (DF-CCPs) is studied with actinometric optical emission spectroscopy and mass spectrometry. The frequency effect on the generation of reactive species was investigated. The reactive radicals and the density ratio of F/CF2 could be controlled by the 2 MHz rf power in 27/2 and 60/2 MHz DF-CCPs. The density ratios of F/CF2 in 27/2 and 60/2 MHz DF-CCPs are observed to increase with an increase in low-frequency power. However, this control could not be obtained in 60/13.56 MHz DF-CCP.

Plasma enhanced chemical vapor deposition of titanium (IV) ethoxide–oxygen–helium mixtures

Thin films were deposited by plasma enhanced chemical vapor deposition from titanium (IV) ethoxide (TEOT)–oxygen–helium mixtures. Actinometric optical emission spectroscopy was used to obtain the relative plasma concentrations of the species H, CH, O and CO as a function of the percentage of oxygen in the feed, R ox. The concentrations of these species rise with increasing R ox and tend to fall for R ox greater than about 45%. As revealed by a strong decline in the emission intensity of the actinometer Ar as R ox was increased, the electron mean energy or density (or both) decreased as greater proportions of oxygen were fed to the chamber. This must tend to reduce gas-phase fragmentation of the monomer by plasma electrons. As the TEOT flow rate was fixed, however, and since the species H and CH do not contain oxygen, the rise in their plasma concentrations with increasing R ox is explained only by intermediate reactions involving oxygen or oxygen-containing species. Transmission infrared (IRS) and X-ray photoelectron (XPS) spectroscopies were employed to investigate film structure and composition. The presence of CH 2, CH 3, C C, C–O and C O groups was revealed by IRS. In addition, the presence of C–O and C O groups was confirmed by XPS, which also revealed titanium in the + 4 valence state. The Ti content of the films, however, was found to be much less than that of the monomer material itself.

Study of effect of H 2 addition on the production of fluorocarbon radicals in H 2 /C 4 F 8 inductively coupled plasma via optical emission spectroscopy actinometry

C4F8 plasma with the addition of H2 is generated by the inductively coupled plasma (ICP) method. The relative densities of CF, CF2, H and F radicals are determined by actinometric optical emission spectroscopy (AOES) as a function of the gas flow rate ratioR=H2/(H2+C4F8) at a pressure of 0.8 Pa and an input r.f. power of 400W, while that of HF is measured by quadrupole mass spectrometry (QMS). The results show that plasma activity increases firstly and then decreases with increasing R. As the gas flow rate ratio R changes from 0 to 0.625, relative densities of both CF and CF2 decrease and the relative [CF] has a similar tendency as the calculated [CF], indicating that CF radicals are generated mainly by the electron impact dissociation of CF2 radicals. Production of HF is also discussed.

Studies on C22 radical by optical emission spectroscopy in an induc tively-coupled CF44/CH44 plasma

In this paper, actinometric optical emission spectroscopy (AOES) is used to inve stigate the discharge of CF44 and CH44 mixtures. Relat ive concentratio ns of radicals in an inductively_coupled plasma are determined as functions of rf input power, pressure and the gas flow ratio R (R=［CH44］/{［CH 44］+［CF44］}). It is found that CF，CF22 ，CH，H and F radicals exis t in the CF44/CH44 plasma as well as C22 radical. The relative co ncentration of C22 increases with increasing power, and shows a rev erse “U” shape tendency with increasing pressure. As R increases, the variati on of the relative concentration of C22 is not monotonical. It reac hes a ma ximum value when Ｒ＝75%, then decreases followed by almost no change with the further increase of R. Based on these results, it is concluded that gas_pha se reaction from the reaction of CF and CH （ＣＦ＋ＣＨ→Ｃ２2＋ＨＦ ） contribu tes to the production of C22 radical. At the same time, activation reaction model of radical collision is suggested. Result of simulation agrees well with that of experiment.

Recombination of oxygen atomic excited states produced by non-equilibrium RF plasma on different semiconductor materials: catalytic phenomena and modelling

The purpose of this work is the study of oxygen atoms recombination on type n or p oxide semiconductors with various gap energies. The oxygen atoms are produced by a non-equilibrium low pressure RF plasma tubular reactor. The pressure is between 100 and 200 Pa. The relative oxygen atom concentration and the recombination coefficient ( γ) were measured by actinometric optical emission spectroscopy (AOES). A plot of the γ coefficient versus 1/ T allows the determination of the activation energy recombination. The results for p-type semiconductors show an increase of the activation energy with the gap energy. The recombination coefficient increases as gap energy decreases. In the case of n-type semiconductors, the activation energy depends on the number of active sites. Hence, the recombination of oxygen atoms depends on the electronic properties of the oxide semiconductors. The simulation of recombination of oxygen atoms on the oxide semiconductors was performed with a kinetic model of 18 reaction including three gas–surface reactions, using the Chemkin ® Surface code. The calculated values of the recombination coefficient show a good agreement with the experimental results in the temperature range of 300–900 K and give a good prediction up to 1200 K.

Measurement of Si, SiF, and SiF2 radicals and SiF4 molecule using very high frequency capacitively coupled plasma employing SiF4

The behavior of the densities of Si, SiF, and SiF2 radicals and SiF4 molecule were investigated for variations in electron density at pressure of 40 mTorr in a very high frequency (VHF) 60 MHz capacitively coupled plasma employing SiF4 gas. The SiF4 molecule was measured by infrared diode laser absorption spectroscopy, the SiF2 and SiF radicals were measured by laser-induced fluorescence, the Si atom was measured by ultraviolet absorption spectroscopy, and the F atom was measured by actinometric optical emission spectroscopy. The SiF4 density decreased with an increase in electron density, and the dissociation ratio of SiF4 was saturated to about 63% at electron densities of above 8.7×1010 cm−3. The SiF2 density decreased due to electron impact dissociation, whereas the F, Si, and SiF densities increased with an increase in electron density above 1.2×1011 cm−3. The total Si density was estimated to be of the order of 1010–1011 cm−3. Furthermore, the spatial distributions of SiF, SiF2, and SiF4 densities were investigated. They were almost flat inside the plasma region, but the SiF and SiF2 radicals decreased gradually outside the plasma region, and the SiF4 molecule increased. The behavior of the Si, SiF, and SiF2 radicals was in good agreement with the emission intensity of rare gases injected as trace gases. The kinetics of the species in VHF 60 MHz SiF4 plasma was clarified on the basis of the densities of the species and electrons measured. These experimental results are useful in predicting the radical densities of VHF SiF4 plasma using simulation.

Effect of grid and bias on the characteristic of CHF3 electron cyclot ron resonance discharge plasma

The characteristics of CHF3 electron cyclotron resonance(ECR) plasma, which is formed in the case of a floating grid in an ECR-chemical vapor deposition system and +60V or -60V biased at grid, were investigated by an actinometric optical emission spectroscopy. It is found that the effects of grid and biasing on the distribution of radicals occur mainly at a low microwave input power. It is considered that the distribution of radicals at a low power is controlled by ele ctron collision and sheath potential together due to low electron temperature. H owever, the effect of sheath potential at a high power decreases due to increasi ng electron temperature. As a result, the distribution of radicals at a high pow er is dominated by electron collision.

Environmentally benign etching process of amorphous silicon and tungsten using species evaporated from polytetrafluoroethylene and fluorinated ethylene propylene

Environmentally benign etching process of amorphous silicon (a-Si) and tungsten (W) by using a plasma process with an evaporation of solid materials system has been developed for replacing a conventional plasma process using green house gases, such as SF6 gas and perfluorocompound gases causing global warming. The evaporation system was designed to generate fluorocarbon species from solid materials by a CO2 laser irradiation. An electron cyclotron resonance (ECR) plasma using O2 accompanied with injection of species evaporated from solid materials has been applied to a-Si and W etching for cleaning process in chemical vapor deposition chamber. Fluorinated ethylene propylene (FEP) and polytetrafluoroethylene (PTFE) are selected as the solid material and the etching characteristics between FEP and PTFE have been compared. Furthermore, the etching of a-Si and W films has been performed in the divergent magnetic field ECR downstream plasma [electron density (ne); ∼1010 cm−3, electron temperature (Te); 1.5–2.8 eV] and a planar ECR plasma [ne; ∼1010 cm−3, Te; 3.4–4.4 eV] using O2 gas with FEP evaporation. As a result, high etching rates of a-Si and W films of above 100 nm/min were successfully obtained at a substrate temperature of 400 °C in the planar ECR plasma of higher electron temperature. CFx (x=1–3) radical densities and F atom density in plasmas were measured by an infrared diode laser absorption spectroscopy and an actinometric optical emission spectroscopy, respectively. On the basis of these measurements of species, the etching mechanisms of a-Si and W films are discussed.

Silicon oxide contact hole etching employing an environmentally benign process

An environmentally benign etching process using a solid material evaporation technique has been investigated for preventing global warming. In this process, a polytetrafluoroethylene is evaporated by a CO2 laser, resulting in production of fluorocarbon species working as the etching species. Therefore, this system employs no perfluorocompound feed gases, which cause global warming, and enables us to design a new plasma chemistry using the solid material. The system was successfully applied to a SiO2 contact hole etching process employing a planar electron cyclotron resonance plasma. The etched profile was successfully controlled by varying the Ar dilution ratio and the process pressure. In a 0.6 μm contact hole and a 0.08 μm trench fabrication process, this novel process enables us to realize high etching performances, where the etching rate of SiO2, selectivities of SiO2/resist, and SiO2/Si were 340 nm/min, 6.8 and 31, respectively, in optimal condition. To clarify the plasma chemistry using solid material evaporation, CFx (x=1–3) radical densities and F atom density were measured by infrared diode laser absorption spectroscopy and actinometric optical emission spectroscopy, and fluorocarbon films deposited on SiO2 were analyzed by x-ray photoelectron spectroscopy. On the basis of these results, the etching mechanism was discussed.

RF Plasma Deposition of PEO-Like Films: Diagnostics and Process Control

Organic thin films deposited by means of radio-frequency glow discharges fed with Triglyme vapors have been investigated to explore the feasibility for deposition of organic thin films with polyethylene oxide-like features. The film chemical composition has been analyzed by means of X-ray Photoelectron Spectroscopy and FT Infrared Absorption Spectroscopy. Plasma phase diagnostics has been accomplished by means of Optical Emission Spectroscopy. It is shown that the surface density of ether carbon, which is considered the marker of the content of ethylene oxide units in the coating, decreases as the power input is increased. It is also shown that the retention of monomer structure in the film can be easily controlled in situ by actinometric optical emission spectroscopy.

Kinetics and role of C, O, and OH in low-pressure nanocrystalline diamond growth

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 loss reactions of the byproduct O atoms with H2 and CH4 were highly responsible for the enhanced diamond growth. A large amount of O atoms from O2 was shown to affect the initial nucleation stage seriously. The results support the growth chemistry of diamond from H-hybridized carbon radicals fragmented from CH4 rather than from H-stripped carbon radicals.

Deposition mechanisms and properties of oxygenated carbon nitride films from rf discharges of acetylene, nitrogen, oxygen and argon mixtures

Oxygen-containing carbon nitride films were deposited in rf discharges of C 2H 2, N 2, O 2 and Ar mixtures. Actinometric optical emission spectroscopy was used to determine relative concentrations of the species H, O, CH, CN and CO in the discharge as a function of the proportion of oxygen in the feed, using Ar as an actinometer. The Ar emission intensity decreases as the proportion of O 2 in the feed increases, indicating that O 2 has a `cooling effect' on the discharge. The variations in the concentrations of CH and CN species, two possible precursors of film formation, showed different behaviors. The concentration of CH increases monotonically as the proportion of O 2 in the feed is increased, but the concentration of CN shows a maximum at an oxygen to acetylene ratio of about 0.15, which coincides with the maximum film deposition rate. This strongly suggests that the CN species is the main precursor of film formation. Infrared reflection spectroscopy revealed the presence of CN, CH, NH and CO functionalities in the deposited films. The presence of such species and their relationship to deposition via gas-phase and surface reactions are outlined. The optical properties of the films were investigated using transmission and reflection ultraviolet–visible spectroscopy. At increasing proportions of oxygen in the gas feed, the refractive index decreases while the optical gap increases. Free radicals were investigated using electron paramagnetic resonance. Unpaired spin concentrations of the order of 10 20 cm −3 were measured in the films a short time after deposition. These large spin concentrations are common in films prepared by plasma-enhanced chemical-vapor deposition (PECVD) but decrease at relatively high rates with time. Possible mechanisms accounting for the high spin concentrations and for the disappearance of the free radicals are discussed.

Plasma-deposition of Ag-containing polyethyleneoxide-like coatings

Ag-containing polyethyleneoxide (PEO)-like thin films have been deposited in Radio Frequency Glow Discharges fed with vapors of diethyleneglycol-dimethylether and argon. Proper experimental conditions have been utilized in order to fragment the monomer in the glow and, at the same time, sputter Ag from the silver RF cathode of the reactor, in a way that polyethyleneoxide(PEO)-like coatings with embedded Ag clusters have been deposited at the ground electrode. The compostion of the coatings has been investigated by means of different techniques; the plasma process has been investigated by means of Actinometric Optical Emission Spectroscopy. A correlation has been found between the amount of silver embedded in the coatings and that sputtered in the discharge, monitored by actinometry, that could eventually be utilized to control in situ the deposition process.

Silicon oxide selective etching process keeping harmony with environment by using radical injection technique

A novel radical control method using a radical injection technique was proposed for preventing global warming. This system consists of a new fluorocarbon radical source where the polytetrafluoroethylene was ablated by a CO2 laser resulting in producing fluorocarbon radicals working as etching species and a radical filter set in front of the radical source which controls radicals generated from the radical source. Therefore, this system does not employ any fluorocarbon feed gases causing the global warming. The system was successfully applied to SiO2 over Si selective etching process employing an electron cyclotron resonance plasma. CFx (x=1–3) radical densities, F atom densities and higher species were successfully controlled by using the radical filter, which was confirmed by an infrared diode laser absorption spectroscopy and an actinometric optical emission spectroscopy. From these results, it was found that this technique was applicable to SiO2 over Si selective etching process keeping harmony with the environment, particularly for preventing global warming.

Optical emission diagnostics of permanent and pulsed microwave discharges in H2–CH4–N2 for diamond deposition

A microwave plasma of H2–CH4–N2 gas mixture used for diamond film deposition has been characterized by optical emission spectroscopy in the continuous and in the pulsed modes. In the continuous mode, a dynamic form of actinometric optical emission spectroscopy was used to determine temporal trends in the concentrations of H, CH and CN species following the cut-off of either the CH4 or N2 flows. These data show that the gas-phase reactions play a major role in the production of the above-mentioned species, but also the plasma–diamond surface reactions contribute significantly to the production of the CN radical. In the pulsed-discharge mode, time-resolved optical emission spectroscopy was used to determine the evolution of the relative concentrations of reactive species H, CH, CN and Ar with time. This evolution during the discharge, post-discharge and transient stages gives information on the processes leading to the population of excited states.

PECVD of amorphous hydrogenated oxygenated nitrogenated carbon films

An actinometric optical emission spectroscopy (AOES) study of the trends in the concentrations of the plasma species H, CH, CO, OH, and CN in film-producing glow discharges of mixtures of isopropanol and nitrogen was undertaken. Conventional AOES was used to obtain the trends in the plasma concentrations of these species as a function of the proportion of nitrogen in the feed, Rn. A dynamic variant of actinometry in which trends in the concentrations of plasma species are measured as a function of time following the cutting of one of the principal gas flows was also employed to investigate the relative importance of gas phase and plasma/polymer–surface interactions in the production of the species of interest. Each of the above-mentioned species is produced, to some degree, by plasma/polymer–surface reactions. As revealed by transmission infrared spectroscopy, the films deposited contain CH, CO, and OH groups. For Rn > 0, the films become nitrogenated, with both NH and CN groups being present. As revealed by transmission ultraviolet-visible spectroscopy, both the optical gap and the refractive index of the deposited films decrease as Rn is increased. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1881–1888, 1998

Thin film deposition from plasmas of tetramethylsilane-helium-argon mixtures with oxygen and with nitrogen

Films were produced by plasma enhanced chemical vapor deposition (PECVD) of tetramethylsilane (TMS)–helium–argon mixtures with either oxygen or nitrogen in a vacuum system fed with radiofrequency power. Actinometric optical emission spectroscopy was used to determine trends in the concentrations of plasma species of interest (H, CH, O, CO, and CN) as a function of the ratio of the inorganic reactive gas (oxygen or nitrogen) to the monomer (TMS) in the system feed. As the ratio of oxygen to TMS in the feed is increased, the degree of oxygenation of the deposited material, as revealed by transmission infrared spectroscopy, is also increased. Similarly, the degree of nitrogenation of the films increases with increasing nitrogen to monomer ratio in the feed. Strong correlations exist between the plasma concentrations of the above-mentioned plasma species and film structure and composition. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1873–1879, 1998

An N2 : CH4 : H2O DC glow discharge plasma probed by optical and electric techniques : significance to the radiation chemistry of Titans upper atmosphere in the presence of meteoritic water

This paper presents optical and electrical measurements on plasma generated by DC excited glow discharges in mixtures composed of 95% N2, 4.8% CH4 and 0.2% H2O at pressures varying from 1.064 mbar to 4.0 mbar. The discharges simulate the chemical reactions that may occur in Titans atmosphere in the presence of meteorites and ice debris coming from Saturns systems, assisted by cosmic rays and high energy charged particles. The results obtained from actinometric optical emission spectroscopy, combined with the results from a pulsed Langmuir probe, show that chemical species CH, CN, NH and OH are important precursors in the synthesis of the final solid products and that the chemical kinetics is essentially driven by electronic collision processes. It is shown that the presence of water is sufficient to produce complex solid products whose components are important in prebiotic compound synthesis.

Process control of organosilicon plasmas for barrier film preparations

Abstract