Optical emission spectroscopy as a real time diagnostic tool for plasma-assisted deposition of TiN

Real-time optical emission spectroscopy (OES) was used to monitor the deposition of TiN both from mixtures of tetrakis(dimethylamino)titanium (TDMATi)-N₂ and TiCl₄-H₂-N₂ in an electron cyclotron resonance chemical vapor deposition system. The accurate control of the ratio of the emission intensities of ionized nitrogen at 391.4 nm and molecular nitrogen at 357.7 nm (N ₂ ⁺ /N₂) led to low temperature deposition of stoichiometric TiN (Ti/N ≈ 1) and very low resistivity in both cases. It was found that high ion density plasmas are crucial for a considerable reduction of the deposition temperature while maintaining good film quality. OES shows that the abundance of certain excited plasma species is not only dependent on the gas mixture and the deposition parameters, such as total pressure and microwave power, but also is strongly affected by the magnetic field configuration. The deposition rate and the film resistivity can be related to the emission intensity ratio, I(N ₂ ⁺ )/I(N₂). Finally, the two processes are compared in terms of the quality of as-deposited and heat-treated films. The comparison shows that the films obtained with TDMATi exhibit lower resistivity and are thermally more stable than with TiCl₄.     

RFA as control method of the reactive sputtering process of TiN films

In-situ X-ray fluorescence (XRF) analysis has been used to control the deposition process of Ti-N films on steel substrates during reactive sputtering. The analysis system consisted of a tungsten X-ray tube, secondary targets of Cu, Fe and Cr and a Si (Li) detector. The sputtering off the Ti target has been determined indirectly by plasma monitoring using optical emissions spetroscopy (OES) of the Ti atoms, and the film growth has been measured directly by XRF analysis of the surface mass of Ti atoms deposited on the substrate. For zero bias voltage and varying N₂ flow the increment of surface mass per deposition time has been found to incrase linearly with the intensity of the OES signal of Ti. A negative bias voltage U_B100 V changes strongly the growth rate by resputtering effects, especially in the range where stoichiometric TiN is formed.     

Plasma polymerization of fluoromethanes

Methane and fluoromethanes (CH_nF_4−n, 1 ≤ n ≤ 3) were subjected to an rf glow discharge plasma. All the fluoromethanes (including methane) polymerized in the plasma and formed thin films. The deposition rate of the fluoromethanes depended on their monomer structure: CH₂F₂, of which the F/H ratio is unity, showed the greatest deposition rate. The elimination of H and F atoms as H—F was found to be a key factor for the polymerization of fluoromethanes. The chemical composition of the polymerized film, measured with X-ray photoelectron spectroscopy and glow discharge emission spectroscopy, was also found to be strongly dependent on monomer structure. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2043–2050, 1998     

Mechanism of silicon film deposition in the RF plasma reduction of silicon tetrachloride

Plasma-chemical reduction of SiCl₄ in mixtures with H₂ and Ar has been studied by optical emission spectroscopy (OES) and laser interferometry techniques. It has been found that the Ar:H₂ ratio strongly affects the plasma composition as well as the deposition (r _D) and etch (r _E) rates of Si: H, Cl films and that the electron impact dissociation is the most important channel for the production of SiCl_x species, which are the precursors of the film growth. Chemisorption of SiCl_x and the reactive surface reaction SiCl_x+H–SiCl_(x–1)0+HCl are important steps in the deposition process. The suggested deposition model givesr _D [SiCl_x][H], in agreement with the experimental data. Etching of Si: H, Cl films occurs at high Ar: H₂ ratio when Cl atoms in the gas phase become appreciable and increases with increasing Cl concentration. The etch rate is controlled by the Cl atom chemisorption step.     

Molecular adsorption and the chemistry of plasma-deposited thin organic films: Deposition of oligomers of ethylene glycol

Weakly ionized, radio-frequency, glow-discharge plasmas formed from methyl ether or the vapors of a series of dimethyl oligo(ethylene glycol) precursors (general formula: H-(CH₂OCH₂)_n-H;n=1 to 4) were used to deposit organic thin films on polytetrafluoroethylene. X-ray photoelecton spectroscopy (XPS) and static secondary ion mass spectrometry (SIMS) of the thin films were used to infer the importance of adsorption of molecular species from the plasma onto the surface of the growing, organic film during deposition. Films were prepared by plasma deposition of each precursor at similar deposition conditions (i.e., equal plasma power (W), precursor flow rate (F), and deposition duration), and at conditions such that the specific energy (energy/mass) of the discharge (assumed to be constrained byW/FM, whereM=molecular weight of the precursor) was constant. At constantW/FM conditions, two levels of plasma power (and, hence, twoFM levels) and three substrate temperatures were examined. By controlling the energy of the discharge (W/FM) and the substrate temperature, these experiments enabled the study of effects of the size and the vapor pressure of the precursor on the film chemistry. The atomic % of oxygen in the film surface, estimated by XPS, and the intensity of theC-O peak in the XPS C_ls spectra of the films, were used as indicators of the degree of incorporation of precursor moieties into the plasma-deposited films. Analysis of films by SIMS suggested that these two measures obtained from XPS were good indicators of the degree of retention in the deposited films of functional groups from the precursors. The XPS and SIMS data suggest that adsorption of intact precursor molecules or fragments of precursor molecules during deposition can have a significant effect on film chemistry. Plasma deposition of low vapor pressure precursors provides a convenient way of producing thin films with predictable chemistry and a high level of retention of functional groups from the precursor.     

Deposition of Gallium Nitride Thin Films by MOCVD in Microwave Plasma

The deposition of GaN thin films in a nitrogen–hydrogen microwave plasma using Ga(CH ₃ ) ₃ as a gallium precursor was investigated. The deposit was identified as stoichiometric GaN by XPS and XRD. The substrate was dielectrically heated in the microwave discharge and the substrate temperature was lower than that in usual thermal MOCVD. The NH radicals, which were the primary N-atoms precursors, and fragments of Ga(CH ₃ ) ₃ were identified in the plasma by OES. The NH radical formation and the decomposition of Ga(CH ₃ ) ₃ in the plasma may be one of the reasons for the lower deposition temperature of GaN. The position dependence of the substrate temperature showed similar tendency as the position dependence of the electron temperature. The plasma state contributes to the deposition of GaN thin films. The deposited GaN exhibited a wide optical band gap of 3.4eV. Material highly oriented along the c axis was detected in the deposit, and a PL spectrum which has the band head at about 450 mm was obtained.     

Hydrocarbon plasma emission as a means to monitor plasma polymerization,revisited

The degree of aromaticity of toluene plasma polymer is shown to decrease with decreasing toluene flow rate into the plasma (constant rf power). Optical emission spectroscopy (OES) of the plasma is predictive; a plasma emitting a higher relative benzyl radical signal results in the deposition of a more aromatic plasma polymer. Such results have been earlier reported in the literature. However, in this work the geometry of OES observation assured that only plasma emissions from the vicinity of the deposition site were observed. Under these conditions it is found that plasma pressure must be kept constant for the predictive nature of OES results to hold.     

Atomic and molecular emission spectroscopy on an expanding argon/methane plasma

A supersonically expanding cascaded arc plasma in argon is analyzed axperimentally by emission spectroscopy. The thermal cascaded arc plasma is allowed to expand through a conically shaped nozzle in the arc anode into the vacuum vessel. In the nozzle monomers (C _n H _v ) are injected. The monomers are dissociated and ionized by the argon carrier plasma, and transported toward a substrate by means of the expansion. Emission spectroscopy is used to obtain temperatures and particle densities. By varying external parameters (e.g., arc power, gas flow rates) plasma parameters can be linked with (e.g. parameters (e.g., refractive index).     

Etude par spectroscopie d'emission optique de decharges radiofrequence et micro-onde lors du depot chimique en phase vapeur (PACVD) dans le systeme Si-C-H-Ar

This work highlights optical emission spectroscopy (OES) results used for a better understanding of processes occuring in radiofrequency and microwave plasma enhanced chemical vapor deposition in the Si-C-H-Ar gas system. Optical lines such as Si⁺ and H_α (λ = 634.71; 656.29 nm), C₂ (λ = 516.52 nm), CH and SiH (λ = 431.42; 412.80 nm) can be considered as tracers of chemical species in the plasmas. Process parameters (growth rate, composition, residual stresses in the films and gas temperature) have their optical signatures (respectively: Si⁺, H_α lines and rotational G¹Σ⁺g → B¹Σ⁺u structure of H₂).     

Deposition behavior in a low‐temperature cascade arc torch (CAT) polymerization process

Two kinds of hydrocarbon type monomers and three kinds of organosilicons were polymerized by a low‐temperature cascade arc argon plasma torch. Their deposition behaviors were studied as a function of experimental parameters and monomer elemental compositions. It was found that the normalized deposition rate (DR), expressed as deposition yield of DR/(FM)_m, was determined by a composite operational parameter, W*(FM)_c/(FM)_m, where W is the power input, and (FM)_c and (FM)_m are the mass flow rates of carrier gases and monomers, respectively. Experimental results indicated that the deposition yield is highly dependent on the elementary compositions of monomers. Optical emission spectroscopy study on the argon plasma torch showed that the emission intensity of excited argon neutrals was proportional to the value of the parameter W*(FM)_c. These results further certified that excited argon neutrals are the main energy carriers from the cascade arc column to activate monomers in the argon plasma torch. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 967–982, 1999     

The importance of electron-molecule interactions in free-free continuum emission for microwave discharge CVD

Optical emission spectroscopic (OES) measurements are acquired by collecting absolute line and continuum emission from a hydrogen/methane plasma (300 sccm H₂, 3 sccm CH₄, 40–70 torr, 1600–3200 W) used for diamond deposition. The experimental results are used in tandem with numerical modeling to infer plasma parameters of interest. Numerical solutions for a microwave chemical vapor deposition (CVD) reactor are generated by coupling solutions of the Boltzmann equation and the electron energy equation to a collisional-radiative model (CRM). Results indicate that the electron-neutral free-free emission, which depends strongly on neutral density, electron density, and electron temperature, is the dominant source of continuum emission. All numerical solutions are found to be inconsistent with the experimentally measured continuum emission. A meaningful interpretation, however, is possible if the electron-H₂ cross-section, used for calculating electron-neutral free-free continuum emission, is increased by between 4 and 20 above the momentum cross-section value. We believe that such an increase is justified because of enhanced energy exchange in electron-molecule interactions.     

The Effect of N-alkyl Substitution on Binding of Polycarboxylic Anions by Linear Polyammonium Cations

The interaction between three N-alkyl-substituted polyamines[1,1,4,4-tetramethylethylenediamine, 1,1,4,7,7,-pentamethyldiethylenetriamine,and 1,1,4,7,10,10-hexamethyltriethylenetetramine; general formula C_3nN_nH_(7n+2)] with fourpolycarboxylic ligands (malonate, citrate, 1,2,3-propanetricarboxylate, and1,2,3,4-butanetetracarboxylate) has been studied potentiometrically in aqueous solution at25°C. For all the systems, the species ALH_r (r = 1, 2 ... n + m – 1;n and m are the maximum degrees of protonation for the amine A and the carboxylicligand L, respectively) are formed. The stability of these species is quite high(in particular, that of species with r = n and r = n + 1) and is a linear functionof the charges involved in the formation reaction. The effect of N-alkyl substitutionis quite small: comparison with the analogous unsubstituted polyamines C_(2n–2)N_nH_(5n–2) shows only a small decrease in stability. On average we have–G ^o/n = 5.9 kJ-mol^–1 for N-alkyl-substitutedamines and 6.6 kJ-mol^–1 for unsubstituted ones (ndenoting the number of possible salt bridges). Other linear charge—stabilityrelationships are considered.     

Relative Rates for Plasma Homo- and Copolymerizations of a Homologous Series of Fluorinated Ethylenes

The relative rates of plasma homo- and Copolymerizations of ethylene, vinyl fluoride, vinylidene fluoride, trifluoroethylene and tetrafluoroethylene (VF _x , x = 0–4, respectively) were determined in an rf, capacitively coupled, tubular reactor with external electrodes using identical plasma parameters. The deposition rates for VF _x (x = 1–3) and 20 different monomer blends, when plotted versus the F/C ratios of the monomers or monomer blends, followed a concave-downward curve situated above the straight-line joining the rates for VF₀ and VF₄. The deposition rates for VF _m /VF _n blends (m = 3 or 4; n = 0–2) likewise yielded concave-downward curves situated above the straight lines joining the rates for the respective monomers; the rates for VF _m /VF _n blends (m = 0 or 1; n = 1 or 2) yielded concave-upward curves situated below the straight lines joining the rates for the respective monomers; while the rates for VF₃/VF₄ blends fell along the straight line joining the rates for VF₃ and VF₄. The mechanisms for plasma (co) polymerizations of VF _x monomers responsible for the wide range of relative deposition rates remain to be elucidated.     

Monitoring the deposition process of metal-doped polymer films using optical emission spectroscopy

Simultaneous plasma polymerization of halocarbons (CF₄ and C₂F₃Cl) and sputtering of metals (Au and Al) or cosputtering [Au + polytetrafluoroethylene (PTFE, Teflon)] have been performed by means of an RF (20 MHz) glow discharge excited by a planar magnetron. The optical emission spectroscopy (OES) has been used for monitoring the deposition process of metal-doped polymer films. The light emission intensity ratios of the relevant species in the plasma volume are given in connection with the characteristics of the films prepared.     

Deposition of SiO2-Like Films by HMDSN/O2 Plasmas at Low Pressure in a MMP-DECR Reactor

The effects of process parameters such as O₂/HMDSN (hexamethyldisilazane) ratio, microwave discharge power and deposition pressure on the growth rate, chemical bonding nature, and refractive index of thin films deposited by microwave plasma from HMDSN with oxygen, have been investigated. The plasma was created in a Microwave Multipolar reactor excited by Distributed Electron Cyclotron Resonance. The films were deposited at room temperature and characterized by Fourier Transform Infrared spectroscopy and ellipsometry. Growth rate increased with the discharge power P or the deposition pressure but decreased significantly with increasing O₂/HMDSN ratio. A large change in the film composition was observed when the O₂/HMDSN ratio was varied: films deposited with only HMDSN precursor are polymer-like but as the O₂/HMDSN ratio increased, organic groups decreased. For relative pressure values over 70%, deposited films are SiO₂-like with refractive index values close to those found for thermal silicon dioxide.     

Deposition of Diamond-Like Carbon Film and Mass Spectrometry Measurement in CH4/O2 RF Plasma

The deposition of diamond-like carbon (DLC) film and the measurements of ionic species by means of mass spectrometry were carried out in a CH ₄ /O ₂ RF (13.56 MHz) plasma. The film deposition rate greatly decreased with increasing O ₂ content up to 10% O ₂ . The oxygen ion density indicated the remarkable increase with the increase of O ₂ content up to 10%. The hydrocarbon ion density is increased considerably by the addition of 5% O ₂ , and then decreased monotonically for O ₂ contents more than 5%. Many oxygenated hydrocarbon ions were detected in the CH ₄ /O ₂ plasma. They were classified into three kinds of ions: C _n H _m O ⁺ , C _n H _m OH ⁺ , and C _n H _m O ₂ H ⁺. When the O ₂ content was increased, the higher hydrocarbon C _n H _m ⁺ (n2) ion densities (except C ₂ H ₄ ⁺ ) decreased more than the principal (CH ₃ ⁺ and CH ₄ ⁺ ) ion densities, since the generation of higher hydrocarbon ions would be suppressed by the formation of oxygenated hydrocarbons. It was also suggested that the great decrease in the film deposition rate in the CH ₄ /O ₂ plasma was mainly associated with considerable decrease in the higher hydrocarbon ion densities. The properties of DLC film obtained in CH ₄ /O ₂ plasma did not indicate considerable change from those obtained in pure CH ₄ plasma.     

PE-CVD of Fluorocarbon/SiO Composite Thin Films Using C4F8 and HMDSO

Plasma copolymerization of hexamethyldisiloxane (HMDSO,(CH₃)₃-Si-O-Si-(CH₃)₃) and C₄F₈ was performed using an RF plasma enhanced chemical vapor deposition method for application to low dielectric constant intermetal dielectrics. Structure of the films was investigated by X-ray photoelectron spectroscopy and Fourier transform infrared (FT-IR) spectroscopy. The film composition was controlled gradually from fluorinated carbon to organic siloxane by changing the mixing ratio of HMDSO/Ar. Dielectric constant of the films ranged from 2–3.3. Thermal stability of the films, which was characterized by intensity loss of IR absorbance peak around 1000–1500 cm^–1 corresponding to C-F _n , Si-O-Si and Si-(CH₂)_n-Si bonds, was inferior to that from C₂F₄/HMDSO/Ar. In situ gasphase FT-IR spectroscopy revealed that there was a marked difference between the gas phase of C₄F₈/HMDSO/Ar and that of C₂F₄/HMDSO/Ar discharges. The IR spectrum of the former combination plasma contained a peak at 1250 cm^–1 with full width at half maximum as large as 150 cm^–1, which suggests that fluorocarbon particles and/or dusts are formed in the plasma. This suggests also that deposition precursors are not only CF _n (n = 1, 2, and 3) but also larger precursors such as C _x F _y (x > 1, y < 2x + 2) in C₄F₈/HMDSO/Ar discharges, which is presumably the cause of difference in thermal stability of the films prepared from C₄F₈/HMDSO/Ar and C₂F₄/HMDSO/Ar mixtures.     

Studies on the cracking ofn-hexane over H-ZSM-48

The influence of various reaction parameters such as temperature, WHSV and H₂ ton-C₆ molar ratio onn-hexane cracking at atmospheric pressure over ZSM-48 has been studied. The influence of SiO₂/Al₂O₃ variations and isomorphous substitution by Ga and Fe has also been investigated. A linear relationship between the specific catalytic activity for the cracking ofn-hexane and the concentration of strong acid sites has been found.     

The electronic structure of small lithium clusters

Ab initio molecular orbital calculations using the STO-6G and STO6-21G basis sets have been performed for the cluster series Li _n ⁺ , Li _n , and Li _n ^– (wheren=2–7). Thirty-two optimized structures are discussed and reported, many of which (especially for the anionic structures) have not yet been considered. The calculations suggest that for all three species the optimum geometries are planar. Of the two levels of theories that were investigated, STO-6G//STO-6G and STO6-21G//STO-6G, the latter hybrid theory was found to be less reliable. In particular, for the anionic structures these calculations should provide a platform from which more sophisticated, i.e., configuration interaction, geometry optimization can be performed.     

Dynamics of radiationless transitions in large molecules: 1. Absorption spectra of adjoin reservoir states

The dynamics of radiationless transitions in large molecules interacting with the surroundings is determined by the dense discrete spectrum of final states {R _n }, close in energy to the initial state s, and by the sets of SR-coupling matrix elements and the decay rate constants of S and {R _n }. It has been shown that the shape and the fine structure of the absorption band of the optical transition from the ground to the initial state S ← S ₀ makes it possible to find the characteristic function of these three distributions. The transformation of the regular spectrum into the stochastic one has been considered.