H2 plasma development of X-ray imaged patterns on plasma-polymerized resists

An X-ray imaged pattern on a plasma-polymerized film was successfully developed by H₂ plasma etching. Plasma-polymerized MMA and 6FBMA were formed by using an inductively coupled argon flow type reactor. An X-ray imaged pattern on the film was attained through a knife-cut window of a gold plate. The X-ray was generated from a Cu target at 20 kV and main wavelength 1.54 Å. The pattern development was performed using a tubular type reactor with parallel plate electrodes. The quality of plasma-polymerized resists in an X-ray lithography was evaluated by comparing it with the conventional polymer in the dry and wet process, and the minimum dose rate for a visible pattern fabrication was measured to be 4.1 J/cm² for both resists in H₂ plasma etching development.     

Vacuum lithography—A completely dry lithography using plasma processing

The purpose of this paper is to describe a thoroughly dry lithography using plasma polymerization and plasma etching. The new lithography is named vacuum lithography because all processes are performed at reduced pressures. Resist films were formed in bell-jar-type and argon-flow-type reactors. The controllability of plasma polymerization is discussed with respect to the type of reactor and gas mixture. A pattern was delineated in the resist using an electron beam, and it was developed by plasma etching with a mixture of argon and oxygen. It was found that the quality of the plasma-polymerized resist depends strongly on the polymer structure and on the plasma etching conditions. In this experiment, the recorded values of sensitivity and value of plasma-polymerized methyl methacrylate were 700 µC/cm² and 1, respectively.     

Mechanism of plasma polymerization ofN-silyl-substituted cyclodisilazane: Structure and properties of polymer film

NN-Bis(dimethylsilyl)tetramethylcyclodisilazane (NSCDSN) was selected for plasma polymerization as a model monomer representing N-silyl-substituted cyclodisilazanes. Owing to the aromatic character resulting from the strong (d-p) coupling between silicon and nitrogen atoms, these compounds manifest the highest thermal stability among the organosilicones. GC/MS examination of a low-molecular-weight fraction evaporated from the plasma polymer revealed the presence of various monomer derivatives having mostly the general structure of N-silyl-substituted cyclodisilazane (Si₄N₂) units. GC/MS and ATR/IR studies have shown that the Si₄N₂ skeleton displays a high resistance to plasma fragmentation and that it was incorporated as such into the polymer film. A radical mechanism for plasma polymerization was postulated assuming the formation of and propagation precursors. The low value found for the polar component of the surface free energy confirmed the contribution of Si₄N₂ units to the polymer film. TGA investigation showed the rate and degree of thermal decomposition of plasma-polymerized (PP) NSCDSN to be lower than those of plasma polymers from N-hydrogen-substituted silazanes. Vacuum pyrolysis, at 800°C, converted the polymer film into a glassy, dense, and almost inorganic material with a strong adhesion to the metal substrates.     

In situ and Real-Time Monitoring of Plasma-Induced Etching of PET and Acrylic Films

Residual gas analysis (RGA) and optical emission spectroscopy have been evaluated as potential in situ techniques for the detection of plasma-induced polymer surface etching. The detection is based on the measurement of CO and CO₂ species formed in the gas phase following oxidation of the etching fragments released from the polymer surface. Experiments were performed on poly(ethylene terephthalate) and UV-cured acrylic (tripropylene glycol diacrylate) films exposed to O₂ RF (13.56 MHz) plasmas. A linear correlation is obtained between the formation of CO and the polymer etching rate over the entire experimental range, but discrepancies appear for the formation of CO₂ at high treatment powers (etching rate > 1.0 g/min.cm²). This behavior is attributed to a deficit of oxidizing agents relative to the generation of etching fragments. The results suggest that both RGA and optical emission spectroscopy can be used to monitor in situ and in real-time the etching of polymer surfaces during plasma treatment.     

The Treatment of Textile Materials in Air Plasma

The effect of treatment in an air glow-discharge plasma on a poly(ethylene terephthalate) film and fabric with different specific surface areas was examined. The rates of mass loss, oxygen uptake, and evolution of gaseous products (CO₂ , H₂O, H₂) were measured over the pressure range 50–200 Pa at a sample temperature of 357 K. It was found that textiles with different textures had different specific etching rates. Possible reasons for this phenomenon are discussed.     

Zone-resolved mass spectroscopic study on RF plasma polymerization of styrene

The radiofrequency (rf) glow discharge plasma of styrene was investigated by direct sampling mass spectroscopy. Measurements were taken in three regions of the discharge: the plasma column and two dark zones before the electrodes. The plasma-polymerized styrene (PPS) thin films were analyzed by infrared spectroscopy (IR). The effects of monomer pressure and rf power on the ratios of mass peak heights C₄H/C₄H, C₆H/C₆H₅()CH in the three discharge regions, the polymer deposition rate, and the polymeric structure of the PPS films were studied. It was found that in the different discharge regions and under various discharge conditions, a variety of reactive species were formed by electron impact on monomer molecules. The polymer deposition rate was mainly dependent on the total number of the reactive species produced in the discharge. The concentration of phenyl groups in PPS films was proportional to the relative concentration of phenyl ring-containing reactive species in the gas phase plasma. © 1996 John Wiley & Sons, Inc.     

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).     

The Chemistry of Methane Remediation by a Non‐thermal Atmospheric Pressure Plasma

The destruction of methane by a nonthermal plasma in atmospheric pressure gas streams of nitrogen with variable amounts of added oxygen has been investigated. The identities and concentrations of the endproducts are determined by online FTIR spectroscopy and the plasma chemistry is interpreted using kinetic modelling. For a deposited energy of 118 kJ m^–3, the destruction is 12% in nitrogen decreasing monotonically to 5% in air. The major endproducts are HCN and NH₃ in nitrogen and CO, CO₂, N₂O, NO and NO₂ for gas streams containing oxygen. The chemistry in pure nitrogen is predominantly due to reactions of electronicallyexcited nitrogen atoms, N(²D). The addition of oxygen converts the excited state nitrogen into nitrogen oxides reducing the methane destruction which then arises by O and OH reactions yielding CO and, to a lesser extent, CO₂. The modelling correctly predicts the magnitude of the methane destruction as a function of added oxygen and the concentrations of the endproducts for processing in both nitrogen and air.     

Deposition of Diamond-Like Carbon Film in a Closed-Space CH4 RF Plasma

Deposition of diamond-like carbon (DLC) film and mass spectrometry measurements were carried out in a closed-space CH₄ rf (13.56 MHz) plasma (without both gas injection and vacuum pumping during the process). At pressures less than 0.6 Torr, the thickness of the DLC film deposited increased with increasing elapsed deposition time, and reached a maximum value, but after this the film thickness started to decrease, which was considered to be caused predominantly by ion-induced sputter etching. The maximum film thickness appeared at larger elapsed time for higher deposition pressure. The mass concentrations of hydrocarbon ions indicated anomalous behavior at early deposition times, but those of higher hydrocarbon ions are clearly increased at the point where the film thickness started to decrease. These results suggested that the ratio of precursor CH₃al density to the total hydrocarbon ion density (_CH3/_ion in the CH₄a was an important factor for the carbon film formation, and when this ratio reduced to a certain critical value with increasing elapsed deposition time, the deposited film was then re-etched predominately by the secondary higher hydrocarbon ions. At 1.0 Torr where a polymer-like soft carbon film was deposited, such re-etching of the deposited film was not observed.     

Oxidation of Styrene in a Silent Discharge Plasma

A silent discharge plasma reactor has been developed to study the oxidation of styrene vapor in argon/oxygen mixtures. A number of analytical techniques were employed to determine the destruction efficiency and to characterize the intermediate products. The destruction efficiency was measured as a function of initial styrene concentration, temperature, and energy density of the plasma. The formation of solid products was observed in most experiments. At low temperature (100°C), the solid deposit was polymeric in nature, while at high temperature (300°C) the solid appeared to be amorphous carbon. A combination of high temperature and high energy density resulted in high destruction efficiency and minimal production of solid films. The destruction efficiency vs. energy density is shown to be more complex than a simple model predicting exponential behavior. Several reasons for the discrepancy are suggested. The e-folding energy density for the destruction of styrene is compared to literature values for other organic compounds, measured using similar types of plasma reactors.     

Electron beam generated plasma decomposition of 1,1,1-trichloroethane

Dilute concentrations of 1,1,1-trichloroethane (TCA) in air were decomposed in an electron beam generated plasma reactor. The energy required for high levels of TCA decomposition (greater than 90%) was determined as a function of inlet concentration. For 99%, decomposition of TCA, ez300 eV/molecule at 250 ppm inlet concentration, and ¨~100 eV/molecule at 3000 ppm. A radical reaction mechanism is proposed which accounts for the formation of the major reaction products: 1,1-dichloroethylene, HCl, chloroacetylchloride, CO₂, and COCl₂. A model is derived based on first-order inhibited kinetics; a fit of the data to the model shows that at high decomposition fractions, radical scavenging by reaction products is a significant inhibitor of TCA decomposition.This work was supported by the Contaminant Plume Containment and Remediation Focus Area, Office of Environmental Management, U.S. Department of Energy.Also affiliated with the Department of Nuclear Engineering.     

Decomposition of CO2 Using Pulsed Corona Discharges Combined with Catalyst

The combination of pulsed corona discharges and catalyst was examined for decomposition of pure carbon dioxide in a corona reactor packed with porous -Al₂O₃ pellets. The decomposition of CO₂ was greatly enhanced by packing -Al₂O₃. In the presence of -Al₂O₃, the conversion of CO₂, yield of CO reach 23 and 15%, respectively. The CO₂ conversion increases with increasing applied voltage and decreasing gas flow rate. The maximum energy efficiency for decomposition of CO₂ reaches 318.7 g/kW hr. It was found that high surface area of -Al₂O₃ and strong adsorption capacity of CO₂ on -Al₂O₃ play an important role in CO₂ decomposition under corona discharges. At the same time, the presence of -Al₂O₃ suppresses the reaction of CO and O.     

Methyl Concentration Measurements During Microwave Plasma-Assisted Diamond Deposition

Absolute line-of-sight averaged measurements of methyl radical concentrationsin a microwave plasma-assisted diamond deposition reactor arepresented. The measurements are based on the use of broadband ultravioletabsorption spectroscopy to characterize the distinguishing absorptionfeature of methyl at 216 nm associated with the X(²A₂)(²A₁) electronictransition. The dependence of the line-of-sight methyl concentration andmole fractions with the percentage of methane in the feed-gas, plasma powerdensity, and position of substrate relative to the optical probe volume isstudied. The measurements suggest that the near-substrate methyl molefraction is only weakly sensitive to changes in substrate temperature andare largely influenced by the gas-phase temperature. A comparison is madebetween the measured mole fractions and recent predictions based on aone-dimensional model of this process. The measured mole fractions areconsistently greater than those predicted by about a factor of ten. Thisdiscrepancy is explained in part by the line-of-sight limitations in theexperimental facility.     

Dry etching of InGaP and AlInP in CH4/H2/Ar

Electron cyclotron resonance (ECR) plasma etching with additional rf-biasing produces etch rates 2,500 A/min for InGaP and AlInP in CH₄/H₂/Ar. These rates are an order of magnitude or much higher than for reactive ion etching conditions (RIE) carried out in the same reactor. N₂ addition to CH₄/H₂/Ar can enhance the InGaP etch rates at low flow rates, while at higher concentrations it provides an etch-stop reaction. The InGaP and AlInP etched under ECR conditions have somewhat rougher morphologies and different stoichiometries up to 200 Å from the sur face relative to the RIE samples.     

Combined analysis methods for investigating titanium and nickel surface contamination after plasma deep etching

Plasma etching techniques can result in damage and contamination of materials, which, if not removed, can interfere with further processing. Therefore, characterisation of the etched surface is necessary to understand the basic mechanisms involved in the etching process and enable process control and cleaning procedures to be developed. A detailed investigation by means of the combined use of scanning electron microscopy coupled with energy-dispersive X-ray spectrometry (SEM/EDS), X-ray photoelectron spectroscopy (XPS) and optical microscopy (OM) has been carried out on deep titanium trenches etched by plasma. This innovative approach has provided a further insight into the microchemical structure of the surface contamination layer on both the titanium and the nickel hard mask surfaces. The described experiments were conducted on 25 to 100-μm wide trenches, first etched in bulk titanium by an optimised Cl₂/SF₆/O₂-based inductively coupled plasma process, through an electroplated nickel hard mask. The results allow to identify chlorine, fluorine and carbon as the main contaminating agents of the nickel mask and to associate three oxidation states around the etched trenches highlighting certain specific aspects related to the passivation mechanism. These observations reinforce the scientific relevance of the combined use of complementary optical and imaging analytical techniques.     

Molecular Beam Mass Spectrometry System for Characterization of Thermal Plasma Chemical Vapor Deposition

A molecular beam mass spectrometry system for in situ measurement of the concentration of gas phase species including radicals impinging on a substrate during thermal plasma chemical vapor deposition (TPCVD) has been designed and constructed. Dynamically controlled substrate temperature was achieved using a variable thermal contact resistance method via a backside flow of an argon/helium mixture. A high quality molecular beam with beamtobackground signal greater than 20 was obtained under film growth conditions by sampling through a small nozzle (75 m) in the center of the substrate. Mass discrimination effects were accounted for in order to quantify the species measurements. We demonstrate that this system has a minimum detection limit of under 100 ppb. Quantitative measurements of hydrocarbon species (H, H₂, C, CH₃, CH₄, C₂H₂, C₂H₄) using Ar/H₂/CH₄ mixtures and silicon species (Si, SiH, SiH₂, SiCl, SiCl₂, Cl, HCl) using Ar/H₂/SiCl₄ mixtures were obtained under thermal plasma chemical vapor deposition conditions.     

Destruction of Styrene in an Air Stream by Packed Dielectric Barrier Discharge Reactors

This study presents the decomposition rates of styrene vapors with non-packed and packed bed dielectric barrier discharge reactors. The concentrations of intermediate byproducts at various plasma operation conditions were evaluated. The results showed that although styrene vapors could be almost completely removed at low styrene inlet concentration of 132 ppm, the selectivity of CO₂ as the major product was rather low in a non-packed bed reactor. It was found that solid carbon containing compound was the major byproduct. An increase in the styrene inlet concentration tended to reduce the styrene removal efficiency, it also led to increase in the solid byproduct. The reactors that packed with glass, Al₂O₃ or Pt–Pd /Al₂O₃ pellets could improve the styrene decomposition efficiency and reduce the formation of intermediate products, of which the best oxidation of styrene to CO₂ could be achieved with a Pt–Pd /Al₂O₃ packed bed reactor. The carbon byproducts could also be reduced if the rector length was increased. The concentrations of ozone formed during the plasma process were also evaluated for the non-packed and packed bed reactors. The plasma reactor that packed with Pt–Pd /Al₂O₃ pellets was proved to have the lowest O₃ concentration.     

Synthesis and X-ray structural analysis of a unique Co-crystallization complex of [NaSal]2DB24C8 and [KSal]2DB24C8

Sodium salicylate (NaSal where Sal=2-hydroxybenzoate), when mixed with dibenzo-24-crown-8 (DB24C8) yields a bimetallic complex [NaSal]₂DB24C8 in most polar organic media, while potassium salicylate (KSal) under similar conditions shows a tendency to yield 11 or 21 complexes depending upon medium or synthesis. However, the presence of both NaSal and KSal together results in a unique mixed cation complex of composition NaKSal₂DB24C8. This product melts sharply (190-92°C) without decomposition, displays IR spectral characteristics comparable to those of [Na(Sal)]₂DB24C8, and is stable in aqueous media as shown by the detectable cation effect on the UV absorption bands of Sal and DB24C8. Single crystal X-ray analysis of NaK(Sal)₂DB24C8 reveals that the system represents a co-crystallization complex of individual (KSal)₂DB24C8 and (NaSal)₂DB24C8 molecules. The crystals are monoclinic,P2₁/c,a=19.976(2) Å,b=9.031(1) Å,c=25.541(5) Å,=122.065(9)°, ų,T=298 K,Z=2+2, CuK =1.5418 Å, and 2 (2.5°–100°). FinalR factor for the 3012 observed reflections (F>3) is 0.092. Both the Na₂- and K₂-molecules possess crystallographic centers of symmetry with one metal and its associated anion on each side of the crown ring. However, the conformations of the crowns are very different in the two molecules, with the K₂-crown being nearly planar and the Na₂-crown being quite puckered. Four oxygen atoms from the DB24C8 (KO, 2.680–2.908 Å) and three carboxyl oxygen atoms (KO, 2.472–2.708 Å) from separate salicylate ions coordinate with each potassium. Three oxygens from the crown (NaO, 2.536–2.65 Å) and three carboxyl oxygens (NaO, 2.31–2.563 Å) coordinate with each sodium. The salicylate ions lie on opposite sides and nearly perpendicular (77.2°, Na₂-molecule; 82.7° K₂-molecule) to each crown but coordinate to both of the metal ions within a molecule. The K⁺K⁺ and Na⁺Na⁺ distances in the respective molecules are 3.95 and 3.34 Å. Supplementary Data relating to this article are deposited with the British Library as Supplementary Publication No. SUP 82044 (18 pages).     

Diamond synthesis by DC thermal plasma CVD at 1 atm

Diamond crystals and films have been success full y synthesized by DC thermal plasma jet CVD at a pressure of I atrn. A novel triple torch plasma reactor has been used to generate a convergent plasma volume to entrain the participating gases. Three coalescing plasma jets produces! by this reactor direct the dissociated and ionized gaseous species onto ( 100) silicon wafer substrates where the diamond grows. In a typical 10-min run, depending on the method of .substrate preparation, either microcrystals with sizes up to 8 m or continuous films with thicknesses of 1–2 m have been obtained. X-ray diffraction, scanning electron microscopy, and Raman spectroscopy have been used for the characterization of the crystals and of the films.     

Solid-Phase Synthesis of Calcium Carbide in a Plasma Reactor

A laboratory-scale spout-fluid bed reactor with a dc plasma torch was used to study the solid-phase synthesis of calcium carbide. Calcium oxide powder with a mean particle size of 170 m was reacted with graphite powder (130 m). Argon was used to initiate the plasma and hydrogen gas was then added to increase power and raise the plasma jet enthalpy. Experimental results showed that the reaction took place in the vicinity of the plasma jet and that conversion to calcium carbide increased linearly with reaction time. The rate of conversion increased exponentially with plasma jet temperature, indicating that chemical reaction was the controlling mechanism. Microscopic analysis of the solid product showed that calcium carbide was formed around both reactants, and that the reaction followed a shrinking core model. Although melting and agglomeration of partially reacted particles occurred at high temperature, resulting in instability of the bed and impeding the reaction progress, high conversions are expected in a continuous process with optimized reactor design.