Large-area microwave and radiofrequency plasma etching of polymers

We have investigated O₂/CF₄ plasma etching of five commercial polymers: polyimide, polyamide, polyethylene terephthalate, polycarbonate and cured epoxy resin. A new large-area microwave plasma apparatus has been used in this work, but the same apparatus can also be used as a capacitively coupled radiofrequency (13.56 MHz) discharge reactor. The effect of operating parameters such as pressure, etchant gas composition, excitation frequency and sample temperature upon etch kinetics has been examined. We have observed distinct maxima in the etch rate as functions of pressure and CF₄ concentration. Activation, energies evaluated from the Arrhenius plots fall in the range 0.04-0.2 eV, in agreement with data in the literature. Dry etch susceptibility of a given polymer correlates strongly with the degree of unsaturation in the polymer's structure     

The use of “actinometer” gases in optical diagnostics of plasma etching mixtures: SF6-O2

The spectroscopic emission intensities from excited F atoms in SF₆-O₂ discharges at 1 torr have been correlated to the densities of atoms in their ground electronic state by measuring the excitation efficiencies of the electrons in the energy range 11 to 17 eV with a method which essentially consists in the analysis of the emission of Ar or N₂, added as actinometer gases to the discharge mixtures. The general applicability of the method has been tested by a direct titration of F atoms with chlorine. The spectroscopic analysis has allowed the determination of useful information on the trends of both the electron densities and their energies as a function of the oxygen percent in the feed.     

Mass spectrometric study of NF3 plasma etching of silicon

NF₃ plasma etching is used for dry cleaning of reactors after plasma-enhanced chemical vapor deposition of hydrogenated amorphous silicon from SiH₄. The NF₃ plasma chemistry, in a closed isothermal plasma box with silicon coated walls, is analyzed by mass spectrometry of gases. Silicon is etched as SiF₄ by F atoms produced in the NF₃ dissociation into F+NF₂, or 2F+NF. The NF radicals recombine as N₂ +2F whereas the long-lived NF₂ radicals do not react with Si, but recombine as N₂F₄ This is the main limitation (or fluorine conversion into SiF₄. The pressure increase at the end point of etching is attributed to the sudden increase of F atom concentration in the gas phase and the consequent recombination q( F atoms as F₂.     

Plasma-assisted etching of aluminum in CCl4−Cl2 mixtures

The etching of aluminum has been studied in a diode reactor fed with CCl₄–Cl₂ mixtures. The overall reaction has been found to be influenced by the contemporaneous deposition of low-volatile etch products and/or a chlorocarbon polymer film originating from the polymerization of CCl_x species. A simple approach is described which allows the chemical contribution to the etch process to be distinguished from the physical one of through-film diffusion. The etching of a clean Al surface is shown to be controlled by chlorine chemisorption at low temperature.Work partially supported by Progetto Finalinalizzato Materiali per l'Elettronica a Stato Solido del CNR and by the Italian Ministry of Education (MPI).     

A model for the etching of silicon in SF6/O2 plasmas

A model has been developed to describe the chemistry which occurs in SF₆/O₂ plasmas and the etching of silicon in these plasmas. Emphasis is placed nn the gas-phase free radical reactions, and the predictions n( the model are compared with experimental results. Forty-seven reactions are included, although a subset of 18 reactions describes the chemistry equally well. Agreement between the calculated and measured concentrations of stable products downstream of the plasma is better than a factor of 2. The need for additional kinetic data and fàr well-characterized diagnostic studies of SF₆/O₂ plasmas is discussed.     

Gas-phase reactions of CF3 and CF2 with atomic and molecular fluorine: Their significance in plasma etching

Reaction rate coefficients have been measured at 295 K for both CF₃ and CF₂ with atomic and molecular fluorine. The reaction between CF₃ and F was studied over a gas number density range of (2.4–23)×10¹⁶ cm^–3 with helium as the bath gas. The measured rate coefficient increased from (1.1–1.7)×10^–11 cm³ s^–1 as the gas number density increased over this range. In contrast to this relatively small change in rate coefficient with gas number density, the rate coefficient for CF₂+F increased from (0.4–2.3)×10^–12 cm³ s^–1 as the helium gas number density increased from (3.4–28.4)×10¹⁶ cm^–3. Even for the highest bath gas number density employed, the rate coefficient was still more than an order of magnitude lower than earlier measurements of this coefficient performed at comparable gas number densities.Both these association reactions are examined from the standpoint of the Gorin model for association of radicals and use is made of unimolecular dissociation theory to examine the expected dependence on gas number density. The calculations reveal that CF₃+F can be explained satisfactorily in these terms but CF₂+F is not well described by the simple Gorin model for association.CF₃ was found to react with molecular fluorine with a rate coefficient of (7±2)×10^–14 cm³ s^–1 whereas only an upper limit of 2×10^–15 cm³ s^–1 could be placed on the rate coefficient for the reaction between CF₂ and F₂. The values obtained for this set of reactions mean that the reaction between CF₃ and F will play an important role in plasmas containing CF₄. The high rate coefficient will mean that, under certain conditions, this particular reaction will control the amount of CF₄ consumed. On the other hand, the much lower rate coefficient for reactions between CF₂ and F means that CF₂ will attain much higher concentrations than CF₃ in plasmas where these combination reactions are dominant.     

Diagnostics and decomposition mechanism in radio-frequency discharges of fluorocarbons utilized for plasma etching or polymerization

Optical emission (180–800 nm) and mass spectroscopy have been used to study the CF₄, CF₄+O₂, C₂F₆, C₂F₆+H₂, CF₃Cl, and C₂F₄ decomposition in radio-frequency discharges. The analysis of the stable and unstable discharge products has allowed the suggestion of decomposition channels for the various gases and to classify the fluorinated gases according to their predominant etching or polymerizing characteristics on the basis of the active species present in the plasma. A new broad emission continuum centered at =290 nm (FWHM=66 nm) has also been identified and it has been tentatively assigned to CF⁺ ₂.     

Synthesis of nanosized TiO2/SiO2 particles using microwave processes and their photocatalytic activity on the decomposition of orange II

The nanosized titania and TiO₂/SiO₂ particles were prepared by the microwave-hydrothermal method. The effect of physical properties TTIP/TEOS ratio and calcination temperature has been investigated. The major phase of the pure TiO₂ particle is of the anatase structure, and a rutile peak was observed above 800°C. In TiO₂/SiO₂ particles, however, no significant rutile phase was observed, although the calcination temperature was 900°C. No peaks for the silica crystal phase were observed at either silica/titania ratio. The crystallite size of TiO₂/SiO₂ particles decreases as compared to pure TiO₂ at high calcination temperatures. The TiO₂/SiO₂ particles show higher activity on the photocatalytic decomposition of orange II as compared to pure TiO₂ particles.     

氢气对正丁烷/空气混合物催化着火的热作用和化学作用

通过对正丁烷/氢气/空气混合物在Pt 催化表面的详细反应机理分析, 研究了氢气添加对正丁烷/空气混合物催化着火过程的影响. 研究发现, 在正丁烷/空气混合中添加氢气有助于正丁烷在更低的温度下实现催化着火, 而且不同的氢气添加量对混合物的着火温度和着火过程呈现不同的影响: 当氢气添加量较小时, 氢气的作用主要呈现为热影响; 而当氢气添加量较大时, 氢气的作用主要呈现为化学影响. 这些结果与实验结果是一致的. 本文进一步确定了发挥不同作用的氢气添加量的范围, 并分别对热作用和化学作用情况下的着火启动反应进行了动力学分析.     

Experimental and Theoretical Studies of a Pulsed Microwave Excited Ar/CF4 Plasma

The present work deals with a pulsed microwave discharge in an Ar/CF ₄ gas mixture under a low pressure (1–10 mbar). The discharge chamber developed has a cylindrical geometry with a coupling window alternatively made of quartz or alumina. The setup allows one to investigate the plasma–wall interactions (here etching of the quartz window) and the ignition process of the pulsed microwave plasma. Microwave pulses with a duration of 50–200 s and repetition rate between 1 and 10 kHz are typical for the experiments. The space-time behavior of the fluorine number density in the discharge has been investigated experimentally by optical actinometry. The discharge kinetics is modeled using electron-transport parameters and rate coefficients derived from solutions of the Boltzmann equation. Together with the solution of the continuity and electron balance equations and the rate equations describing the production of CF _x (x=2, 3, 4) radicals and F atoms, a good agreement between experimental and theoretical data can be achieved.     

Study of reactive ion etching of Si and SiO2 for CFxCl4−x gases

A parametric study of the etching of Si and SiO₂ by reactive ion etching (RIE) was carried out to gain a better understanding of the etching mechanisms. The following fluorocarbons (FCs) were used in order to study the effect of the F-to-Cl atom ratio in the parent molecule to the plasma and the etching properties: CF₄, CF₃Cl, CF₂Cl₂, and CFCl₃ (FC-14, FC-13, FC-12, and FC-11 respectively). The Si etch rate uniformity across the wafer as a function of the temperature of the wafer and the Si load, the optical emission as a function of the temperature of the load, the etch rate of SiO₂ as a function of the sheath voltage, and the mass spectra for each of the FCs were measured. The temperature of the wafer and that of the surrounding Si load strongly influence the etch rate of Si, the uniformity of etching, and the optical emission of F, Cl, and CF₂. The activation energy for the etching reaction of Si during CF₄ RIE was measured. The etch rate of Si depends more strongly on the gas composition than on the sheath voltage; it seems to be dominated by ion-assisted chemical etching. The etching of photoresist shifted from chemical etching to ion-assisted chemical etching as a function of the F-to-Cl ratio and the sheath voltage. The etch rate of SiO₂ depended more strongly on the sheath voltage than on the F-to-Cl ratio.     

氧化层结构对铀在CO/H2气氛中表面反应的影响

用Ｘ射线光电子能谱分析研究了不同氧化层结构的铀金属试样在ＣＯ和Ｈ２氢气保的表面反应。ＣＯ和Ｈ２与铀金属表层反应后，氧化物中氧含量均减少，Ｏ／Ｕ比值随气体乾气量的增加而减少。     

Oxidative addition of dihydrogen to Ni(II) complexes.ab initio MO/MP4 calculations of the electronic structure of NiH2Cl2(PH3)2 complex

Electronic state d⁶ Ni(IV) in the complex [NiH₂Cl₂(PH₃)₂] was studied by means ofab initio MO/MP4 calculations.     

Mass spectrometer-wall probe diagnostic of Ar discharges containing SF6 and/or O2: Reactive ions in etching plasmas

Positive and negative ions of Ar/SF₆ and Ar/SF₆/O₂ plasmas (etching plasmas) and of Ar/O₂ plasmas (cleaning plasmas) in Pyrex tubes have been investigated using a mass spectrometer-wall probe diagnostic technique. The measurement of negative ions proved to be a very sensitive method for the detection of wall material. In etching plasmas with small admixtures of SF₆, oxygen was found as the only representative of wall material. At larger amounts of SF₆, silicon could be detected. In cleaning plasmas with small admixtures of O₂ applied to a previously etched Pyrex surface, fluorine was found, indicating the reversal of fluoridation by oxygenation.     

Investigation of radical reactions in C2Cl4 and C2Cl4/O2 discharges by EPR,mass, and emission spectroscopy

The reaction of tetrachloroethylene, C₂Cl₄, with O(³P) atoms as well as the plasma decomposition of C₂Cl₄ and C₂Cl₄/O₂ mixtures have been investigated by combined application of electron paramagnetic resonance (EPR) and emission and mass spectroscopies. C₂Cl₄ plasma decomposition is shown to proceed primarily to the formation of CCl₃ radicals and chlorine-deficient products, which are ultimately involved in the formation of carbonaceous layers. A simple reaction model accounts for all the detected stable and radical species, encountered during the plasma decomposition. The model also enables order-of-magnitude estimates of decomposition rate constants to be made. The suppression of the formation of both carbonaceous layers and products C_mCl_n (m3) in C₂Cl₄/O₂ discharges is explained using results of an investigation of elementary reactions in the system C₂Cl₄/O(³P)/O₂. The stable products of C₂Cl₄/O₂ discharges, i.e., COCl₂, CCl₄, and C₂Cl₆, respectively, are shown to originate from recombination of the peroxy radicals CCl₃OO and C₂Cl₅OO.     

次甲基硅SiH与H2X(X=O,S)反应的热力学及动力学性质研究

在量子化学对SiH与H₂O和H₂S反应计算的基础上,运用统计热力学和Wigner校正的Eyring过渡态理论,计算了上述两反应在200～2000 K温度范围内的热力学函数、平衡常数、频率因子A和速率常数随温度的变化。计算结果表明,两反应在低温下具有热力学优势,而在高温下具有动力学优势。比较两反应的计算结果发现,在相同的温度下,SiH与H₂O反应比SiH与H₂S反应放热较多,但速率常数却较小。SiH与H₂O反应和前文报道的SiH与HF反应的比较表明,SiH与H₂O反应放热较少,而且在相同温度下,速率常数也较小。     

冷等离子体强化制备TiO2光催化材料及其机理

等离子体技术在材料制备和改性方面的优势得到众多研究者的认可。Ti O2具有化学稳定性高、氧化活性强、生产成本低等优势,被广泛应用于太阳能电池和光催化领域。本文综述了近年来介质阻挡放电等离子体在强化制备Ti O2光催化材料方面的研究成果,包括等离子体辅助制备Ti O2光催化薄膜和Ti O2的等离子体法掺杂两个方面,并分析了其作用机理。从目前的研究成果来看,等离子体技术制得的Ti O2光催化材料具有更好的均匀性和催化活性,这主要得益于等离子体中的高能电子,一方面,Ti O2粒子吸附电子,彼此之间产生静电场的斥力作用,可以抑制颗粒的团聚,另一方面,电子的强还原能力,能够打断Ti-O键,形成氧空位,从而提高其催化性能。     

An experimental study on the asymmetry and the dip form of the Hβ line profiles in microwave produced plasmas at atmospheric pressure

An experimental study on the asymmetry of the Balmer H_β profile in plasmas produced by microwaves at atmospheric pressure is presented. The study is based on the definition of several functions that quantify the asymmetry aspects of the profile. Apart from the asymmetry aspects of the flanks also form-functions are defined that characterize the central part of the profile, the so-called dip or central valley, the combination of the two peaks and the dip in between them. The study shows the experimental dependence of these characteristics on the electron density and control parameters such as the gas flow and the hydrogen admixture ratio. The possible use of these newly introduced profile characteristics to plasma diagnosis is discussed.     

Mass spectrometric study of SF6-N2 plasma during etching of silicon and tungsten

The reaction products in the SF₆-N₂ mixture rf plasma during reactive ion etching of Si and W have been measured by a mass spectrometric method. Two kinds of cathode materials were used in this work; they were stainless steel for the Si etching, and SiO₂ for the W etching. The main products detected in the etching experiments of Si and W included SF₄, SF₂, SO₂, SOF₂, SOF₄, SO₂F₂, NSF, NF₃, N₂F₄, N_xS_y, NO₂, and SiF₄. In the W etching with the SiO₂ cathode, additional S₂F₂, N₂O, and WF₆ molecules were also obtained. The formation reactions about the novel NSF compound and the sulfur oxyfuorides were discussed.     

微波原位合成Ag NPs/MoS2复合材料及其电化学性能

二硫化钼纳米片（MoS₂）受到带电杂质、结构缺陷和易聚集等因素的影响,导致其电子转移性能下降,使其应用受限。将银纳米颗粒（Ag NPs）与少层MoS₂纳米片复合,可提升MoS₂纳米片的电化学性能。本研究创新性地采用微波还原法,使Ag NPs原位沉积于MoS₂,得到Ag NPs/MoS₂复合材料。结果表明,将Ag NPs/MoS₂复合材料修饰于丝网印刷电极（screen printed elec-trodes,SPE）后,测得的循环伏安（cyclic voltammetry,CV）曲线峰电流值为同浓度单一MoS₂修饰电极的1.8倍,方波伏安（square wave voltammetry,SWV）曲线峰电流值为单一MoS₂修饰电极的3.4倍,电化学阻抗谱（electrochemical impedance spectroscopy,EIS）的电子转移阻抗值（R_et）仅为167 Ω,相比MoS₂/SPE的R_et （320 Ω）显著减小,说明Ag NPs与MoS₂复合可显著增强单一MoS₂的电化学性能。此外,还推测了高导电性Ag NPs/MoS₂复合材料的导电机理。最后,基于Ag NPs/MoS₂复合材料构建了电化学传感器并对前列腺特异性抗原（PSA）进行检测。结果表明,该传感器针对PSA的检测限为0.009 ng·mL^-1,线性检测范围为0.1~1 000 ng·mL^-1,灵敏度为0.011 μA·mL·ng^-1。