Comparative analysis of barium titanate thin films dry etching using inductively coupled plasmas by different fluorine-based mixture gas

In this work, the inductively coupled plasma etching technique was applied to etch the barium titanate thin film. A comparative study of etch characteristics of the barium titanate thin film has been investigated in fluorine-based (CF₄/O₂, C₄F₈/O₂ and SF₆/O₂) plasmas. The etch rates were measured using focused ion beam in order to ensure the accuracy of measurement. The surface morphology of etched barium titanate thin film was characterized by atomic force microscope. The chemical state of the etched surfaces was investigated by X-ray photoelectron spectroscopy. According to the experimental result, we monitored that a higher barium titanate thin film etch rate was achieved with SF₆/O₂ due to minimum amount of necessary ion energy and its higher volatility of etching byproducts as compared with CF₄/O₂ and C₄F₈/O₂. Low-volatile C-F compound etching byproducts from C₄F₈/O₂ were observed on the etched surface and resulted in the reduction of etch rate. As a result, the barium titanate films can be effectively etched by the plasma with the composition of SF₆/O₂, which has an etch rate of over than 46.7 nm/min at RF power/inductively coupled plasma (ICP) power of 150/1,000 W under gas pressure of 7.5 mTorr with a better surface morphology.     

Fabrication of diamond nanowires for quantum information processing applications

We present a design and a top-down fabrication method for realizing diamond nanowires in both bulk single crystal and polycrystalline diamond. Numerical modeling was used to study coupling between a Nitrogen Vacancy (NV) color center and optical modes of a nanowire, and to find an optimal range of nanowire diameters that allows for large collection efficiency of emitted photons. Inductively coupled plasma (ICP) reactive ion etching (RIE) with oxygen is used to fabricate the nanowires. Drop-casted nanoparticles (including Au, SiO₂ and Al₂O₃) as well as electron beam lithography defined spin-on glass and evaporated Au have been used as an etch mask. We found Al₂O₃ nanoparticles to be the most etch resistant. At the same time FOx e-beam resist (spin-on glass) proved to be a suitable etch mask for fabrication of ordered arrays of diamond nanowires. We were able to obtain nanowires with near-vertical sidewalls in both polycrystalline and single crystal diamond. The heights and diameters of the polycrystalline nanowires presented in this paper are ≈ 1 μm and 120–340 nm, respectively, having a 200 nm/min etch rate. In the case of single crystal diamond (types Ib and IIa) nanowires the height and diameter for different diamonds and masks shown in this paper were 1–2.4 μm and 120–490 nm with etch rates between 190 and 240 nm/min.     

Reactive ion etching of nanocrystalline diamond for the fabrication of one-dimensional nanopillars

One-dimensional diamond nanostructures (diamond nanopillars) have been fabricated using nanocrystalline diamond films (NCD) as a starting material, and electron beam lithography (EBL) and reactive ion etching in an inductively coupled O₂ plasma (ICP-RIE) as processing techniques. In a first step, the etch rates have been determined as a function of four major plasma parameters, namely the ICP power, the rf power applied to the substrate holder, the pressure, and the oxygen flow rate. These parameters have been varied in wide ranges. In order to get insight into the mechanisms of the etching process, etching experiments have been performed with unpatterned NCD films by varying the process times using rather short intervals. Finally, EBL has been applied prior to the etching to obtain one-dimensional pillars with diameters from 200 nm to 1 μm. Scanning electron microscopy has been employed to characterize the pillars. First results showed the process developed to be successful, and first examples will be presented.     

Studies on metal/benzocyclobutene (BCB) interface and adhesion

Interfacial characteristics such as chemical reaction, metal diffusion, and morphology were investigated for Cu/BCB, Cr/BCB and Ti/BCB structures. Using Auger and XPS depth profiling, the formation of titanium carbide and chromium oxide was confirmed at the metal/BCB interface. Annealing at 250°C for extended periods resulted in the diffusion of Cu, Cr and Ti into the BCB and subsequent formation of Cu-Si, CrSi₂ and Ti-Si compound precipitates. The reaction is a thermal diffusion controlled process which is dependent on time and temperature. Ar sputtering treatment of BCB film before metallization was found to roughen the surface, resulting in metal spikes which penetrate into the roughened BCB film. However, the peel strength of metals on BCB was only about 177 g cm^_1presumably due to the brittleness of the BCB film. The etch rates of the BCB film in a reactive ion etcher (RIE) and a plasma etcher were measured using Ar, O₂, O₂ + CF₄, and O₂ + SF₆ gas mixtures. Faster etch rates were obtained when CF₄ and SF₆ were added to oxygen, since the presence of atomic fluorine enhances the etch rate of organics, while also etching Si and SiO₂ formed by exposure of Si-containing BCB film to oxygen gas. Surface compositional changes on the BCB film were observed by XPS after plasma modification. Pure O₂ and O₂ + CF₄ plasmas oxidized the carbo-siloxane linkage (C_—Si_—O) of the BCB, resulting in the formation of SiO₂ on the surface. The O₂ + SF₆ plasma, however, did not produce the surface SiO₂, because of its faster Si and SiO₂ etch rates.     

Surface energy of the plasma treated Si incorporated diamond-like carbon films

Surface energy and surface chemical bonds of the plasma treated Si incorporated diamond-like carbon films (Si-DLC) were investigated. The Si-DLC films were prepared by r.f. plasma assisted chemical vapor deposition using benzene and diluted silane (SiH₄/H₂ = 10:90) as the precursor gases. The Si-DLC films were subjected to plasma treatment using various gases like N₂, O₂, H₂ and CF₄. The plasma treated Si-DLC films showed a wide range of water contact angles from 13.4° to 92.1°. The surface energies of the plasma treated Si-DLC films revealed a high polar component for O₂ plasma treated Si-DLC films and a low polar component for CF₄ plasma treated Si-DLC films. The CF₄ plasma treated Si-DLC films indicated the minimum surface energy. X-ray photoelectron spectroscopy (XPS) revealed that the polarizability of the bonds present on the surface explains the hydrophilicity and hydrophobicity of the plasma treated Si-DLC films. We also suggest that the O₂ plasma treated surface can provide an excellent hemocompatible surface from the estimated interfacial energy between the plasma treated Si-DLC surface and human blood.     

Differential dissolution and electron-beam lithographic sensitivity of poly(methyl methacrylate)

Photolithographic and electron-beam integrated circuit fabrication techniques rely heavily upon differences in polymer resist dissolution (development) rates to produce circuit patterns. We have applied the wide-line NMR, technique, augmented by dynamic nuclear polarization, to the measurement of polymer dissolution rates of poly(methyl methacrylate), (PMMA). At high gamma-ray exposures, we find PMMA to have dissolution rates from 2X to 1000X those of unirradiated material. The highest radiation-enhanced dissolution rates are obtained with carbon tetrachloride-based developer solutions, whereas generally lower enhanced rates are observed with 1:3 acetone or methylethylketone/isopropanol standard developer. E-beam line exposures are developed in PMMA and poly(ethyl methacrylate), PEMA, resists using similar developers for comparison. Using straight CCl₄ as a developer, e-beam lines 1-2 μ wide were developed in 3800 Å thick PEMA resist at 1 × 10^?5 C/cm² with ≤200 Å loss in unexposed resist thickness. The higher differential dissolution with CCl₄, a poorer solvent for unirradiated PMMA than acetone or MEK, is explained by decline in polarity of PMMA by radiationinduced decarboxylation.     

Plasma polymerization of perfluoro-2-butyltetrahydrofuran/methane and perfluorobezene/tetrafluoromethane mixtures and gas permeation properties of the plasma polymers

Plasma polymer films prepared from perfluoro-2-butyltetrahydrofuran (PFBTHF) and perfluorobenzene (PFB) were investigated by elemental analysis, infrared spectroscopy, and ESCA. The gas separation properties were also investigated to seek plasma polymer films with good permselectivity. Plasma polymer films from PFBTHF and PFB were composed of polymer chains with fluorinated moieties such as C –CF_n, C F, C F–CF_n, C F₂, and C F₃ groups. Changes in the afcurrent as an operating condition for plasma polymerization showed less influence on the distribution of the fluorinated moieties but more influence on the permselectivity of the plasma polymer films formed. The permselectivity was improved by plasma polymerization in the PFBTHF/CH₄ or PFB/CF₄ mixture systems. The P_O2/P_N2 ratio for the plasma polymer films prepared from PFBTHF/CH₄ and PFB/CF₄ mixtures increased from 3.1 at 0 mol % CH₄ to 4.0 at 50 mol % CH₄ addition, and from 4.1 at 0 mol % CF₄ to 5.0 at 25 mol % CF₄ addition, respectively. The permselectivity of the plasma polymer films may be related to the crosslinkage and aggregation of polymer chains rather than the elemental composition.     

Reactive ion etching of selected polymers in O2 and in CF4/O2

A series of 17 polymers was etched in the reactive ion-etching (RIE) mode. The etch rates were monitored using a laser interferometer. The gases used were oxygen alone and a mixture of carbon tetrafluoride with oxygen (8% O₂). The polymers fell into three groups: the aromatics (polystyrene and derivatives), the aliphatics (methacrylates and vinyl acetate), and the cellulosics (methyl ether and nitrate). In oxygen with a power density of 0.25 W/cm², the etch rates for the three groups fell in the range of 200–300 nm/min, 350–450 nm/min, and 500–850 nm/min, respectively. The etch rates were also measured at a power density of 0.50 W/cm². The etch rates at the higher-power density were about 75–80% higher than those at the lower-power density. The etch rate in the fluoride mixture was about half that in the oxygen, all other parameters being the same. Plasticizers that lower the glass transition temperature of polymers based on vinyl chloride, methyl methacrylate, or styrene do not change the etch rate of the polymers very much. There is a slight increase in the rate for polystyrene and a slight decrease in the rate for poly(methyl methacrylate). All the effects of composition on etching rate can be correlated to a first approximation with the molar fractions of carbon and oxygen in the resist. © 1993 John Wiley & Sons, Inc.     

A polymer complex as a new type of electron beam resist for dry development

Polymer complex of poly (4-vinylpyrldine) and malonic acid was investigated as a new type of electron beam (EB) resist for dry development, as malonic acid was decomposed by EB irradiation. It was found that the polymer complex could be developed with O₂ plasma etching and that the positive resist patterns with high resolution could be obtained. The mechanism for this lithography process was studied by means of IR and ESCA spectra.     

Surface characterization of nickel alloy plasma-treated by O2/CF4 mixture

The micro- or nano-structured mold used for polymer embossing typically must be coated with an anti-adhesion material to reduce its interaction with the embossing. The mold is typically made by nickel sulphamate electroforming. For the anti-adhesion coating to adhere to the mold, the nickel mold surface must be clean and preferably unoxidized or possess reactive groups suitable for covalent bonding with the anti-adhesion coating. The effectiveness of plasma cleaning using mixtures of oxygen (O₂) and tetrafluoromethane (CF₄) with varying ratios versus liquid-only cleaning was investigated. To simulate the nickel mold, Ni200 alloy was used. Plasma treatment using mixtures of O₂ and CF₄ was found to be more effective in cleaning the Ni200 surface than liquid-only cleaning or pure O₂ or pure CF₄ plasma treatment. Using a 1 : 1 O₂ /CF₄ mixture plasma, the contact angles of water, glycerol and diiodomethane on Ni200 were the lowest and the calculated surface energy was the highest among the investigated treatments. From X-ray photoelectron spectroscopy (XPS), the amount of organic contamination on Ni200 was significantly reduced with plasma treatment. For liquid-only cleaned samples, metallic nickel, NiO and Ni(OH)₂ are present on the surface. With pure O₂ or pure CF₄ or 1 : 1 O₂ /CF₄ mixture plasma, both oxidation and fluorination occur and the surface contains combinations of NiF₂, Ni(OH)₂, Ni(OH)F, Ni₂O₃ and NiO₁₅F instead (without metallic nickel and NiO). The proportions of these different compounds vary according to the O₂/CF₄ ratio; O/Ni ratio is highest for pure O₂ plasma treatment, whilst F/Ni is highest for pure CF₄ plasma treatment.     

Metalizable Polymer Thin Films in Supercritical Carbon Dioxide

We report an environmentally “green” method to improve adhesion at a polymer/metal interface by using supercritical carbon dioxide (scCO₂). Spun-cast polystyrene (PS) and poly(methyl methacrylate) (PMMA) thin films on cleaned Si wafers were used for this study. Film thicknesses of both polymer films were prepared in the range of 100 Å to 1600 Å. We exposed the films to scCO₂ in the pressure-temperature (P–T) range corresponding to the density-fluctuation ridge, where the excess swelling of both polymer films occurred, and then froze the swollen structures by quick evaporation of CO₂. A chromium (Cr) layer with film thickness of 300–400 Å was deposited onto the exposed film by using an E-beam evaporator. X-ray reflectivity (XR) measurements showed that the interfacial width between the Cr and exposed polymer layers increased by a factor of about two compared with that without exposure to scCO₂. In addition, the large interfacial broadening was found to occur irrespective of the thickness of both polymer films. After the XR measurements, the dewetting structures of the PS/Cr films induced by additional annealing were characterized by using atomic force microscopy, showing improved surface morphology in the exposed films. Contact angle measurements showed that a decrease in interfacial tension with exposure to scCO₂ accompanied the increase in interfacial width.     

Dry etching of SrBi2Ta2O9: Comparison of inductively coupled plasma chemistries

A systematic study of the etch characteristics of SrBi₂Ta₂O₉ (SBT) thin films in inductively coupled plasmas (ICPs) has been performed with various chemistries of Cl₂/Ar, Cl₂/O₂/Ar, Cl₂/NF₃/Ar, and Cl₂/NF₃/O₂/Ar. Etch rate was dependent on plasma chemistries and parameters. Addition of O₂ stabilized the perovskite structure of SBT film and suppressed the etch rate, but NF₃ enhanced the etch rate substantially mainly due to reactive fluorine radicals. Maximum etch rates obtained were: 740 å/min with Cl₂/Ar, 320 å/min with Cl₂/O₂/Ar, 1,500 å/min with Cl₂/NF₃/Ar, and 1,600 å/min with Cl₂/NF₃/O₂/Ar at 5 mTorr, 700 W. ICP power and 150 W. rf chuck power. Electrical properties of the SBT films were quite dependent on plasma chemistries employed; Cl₂/NF₃/O₂/Ar showed the least damage in the films and resulted in the best P-E hysteresis loop having remnant polarization (2P_r)=12.3 ΜC/cms² and coercive field (E_c)=41.9 V/cm.     

Positive and negative photoresist applications of thin films surface-photopolymerized from hexachlorobutadiene

Polymeric films deposited from the vapor of C₄Cl₆ by the surface-photopolymerization technique are electrically and mechanically continuous on various substrates when very thin. The thickness of the films depends upon irradiation time with wavelengths in the region 2000-3000Å. Re-irradiation in oxygen (air) of the polymeric films with light of these low wavelengths leads to patterned removal of the films. Since films 500Å thick and less can resist etchants for various substrates, a new and extremely thin positive photoresist system is possible. Resolution of etched substrates to lines a few microns wide has been demonstrated. If the polymeric films from C₄Cl₆ are deposited from the monomeric vapor at lower substrate temperatures they are soluble in various solvents. Re-irradiation with UV light with the films in vacuum produces a patterned fixing of the polymer with respect to acetone. A negative photoresist system is therefore possible. Again, films of thickness 500Å and less can resist various etchants such that substrates can be etched to high resolution.     

Etching of plasma-polymerized tetrafluoroethylene,polytetrafluoroethylene, and sputtered polytetrafluoroethylene induced by atomic oxygen [O(3P)]

A study was carried out of the surface recession (etching) of thin films of plasma-polymerized tetrafluoroethylene (PPTFE), polytetrafluoroethylene (PTFE), and ion-beam sputter-deposited polytetrafluoroethylene (SPTFE), exposed to atomic oxygen [O(³P)] downstream from a nonequilibrium radio-frequency O₂ plasma. At 22°C, the etch rates for PTFE, SPTFE, and PPTFE were in the ratio of 8.7 : 1.0. A thin, conformal coating of PPTFE (etch rate of 0.3 nm/h at 22°C) was found to protect an underlying, cast film of a reactive polymer, cis-1,4-polybutadiene (etch rate of 0.13 mg/cm² h ≡ 1300 nm/h at 22°C), against O(³P) attack for the time required to fully etch away the PPTFE coating. From ESCA analysis, PTFE exhibited only minor surface oxidation (uptake of 0.5 atom % O) upon etching, its F/C ratio decreasing slightly from 2.00 to 1.97; PPTFE exhibited considerable surface oxidation (uptake of 5.9 atom % O) and a decrease in F/C ratio from 1.30 to 1.23; and SPTFE exhibited a surface oxidation (uptake of 2.2 atom % O) intermediate between those of PTFE and PPTFE, with a decrease in F/C ratio from 1.73 to 1.67. The O(³P)-induced etching of PTFE had an activation energy of 3.8 Kcal/mol, but no activation energy value was obtained for PPTFE which gave a nonlinear Arrhenius plot apparently because of thermally induced thinning above 50°C.     

Nanometer-sized patterning of polysilicon thin films by high density plasma etching using Cl2 and hbr gases

High density plasma etching of polysilicon thin films was carried out in an inductively coupled plasma (ICP) for the formation of nanometer-sized patterns. The etch rate and etch selectivity of polysilicon films were investigated as a function of the concentration of Cl₂ and HBr etch gases. The fast etch rate of polysilicon films was obtained in Cl₂/Ar gas, and the high selectivity of polysilicon to photoresist was found in HBr/Ar gas. Finally, the etching of polysilicon films masked with photoresists was attempted in HBr/Ar and Cl₂/Ar gases. The good pattern profile of polysilicon films with 60 nm lines was achieved in an HBr/Ar plasma.     

Effects of CF4/O2 gas plasma power/exposure time on dielectric properties and breakdown voltages of PVDF films

Dielectric properties and electrical breakdown strengths were measured on 12-μm-thick poly(vinylidene fluoride) films before and after exposure to various power levels and exposure times in a 96% CF₄/4% O₂ gas plasma. Significant changes in dielectric constant, dielectric losses, and breakdown voltages were observed. Breakdown voltages for PVDF films as a function of exposure time and plasma power appear to go through a maximum. © 1992 John Wiley & Sons, Inc.     

XPS and IR analysis of thin barrier films polymerized from C2H4/CHF3 ECR-plasmas

Thin fluorocarbon polymer films are prepared on PE-foils in low-pressure electron cyclotron resonance plasmas using ethylene (C₂H₄) and trifluoromethane (CHF₃) as monomers. The thin fluorinated hydrocarbon layers strongly reduces the permeability of polyethylene to alkanes. For example, the permeation of toluene was decreased by a factor of about 100 by a single, thin fluorocarbon layer. A further reduction of the permeation down to a factor of 1600 can be obtained by a multilayer coating. X-ray photoelectron spectroscopy and Fourier transform IR spectroscopy are used to characterize the plasma polymerized films. It is shown that the addition of CHF₃ to a C₂H₄ plasma leads to an increase of CF₃—, CF₂—, and CF— groups and to a decrease of CH₃— and CH₂— groups in the film. The chemical composition of the polymer layers and their toluene permeabilities are discussed. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 717–722, 1997     

Enhanced performance of polymer light‐emitting device via optimization of processing conditions and device configuration

The improved performance of polyalkylfluorene light‐emitting device has been achieved through the optimization of processing conditions and device configuration. The current density, brightness, power efficiency, and operation lifetime of polymer light‐emitting device (PLED) were strongly dependent on the surface treatment of anode, the film thickness of light‐emitting polymer (LEP), and the cathode configuration. The anode surface treated with O₂ plasma exhibited a higher current density and brightness than the CF₄ plasma treated device. However, better operation stability was obtained for the CF₄ plasma treated device than for the O₂ plasma treated device. The maximum of brightness and power efficiency has been achieved for the PLED with an LEP thickness of 80 nm. The PLED with LiF/Ca/Al cathode possesses a better power efficiency and operation stability than does the Ca/Al or LiF/Al based PLED. The influences of device fabrication conditions and device configuration on the performance of a polyalkylfluorene‐based PLED are discussed in detail. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 133–141, 2006     

Oxygen plasma removal of thin polymer films

Relative rates of polymer removal in an oxygen plasma have been measured for 40 polymer samples. The rates of removal are correlated, with structural factors which enhance or retard removal. Strong backbone bonds, aromatic and polar functional groups, and metallic atoms decrease the removal rates. Weak bonds not attached to the- polymer backbone have little affect while weak bonds attached directly to the chain or in the chain greatly accelerate removal. Chlorine present in the polymer catalyzes removal. This can be mimicked by mixtures of CF₄, and O₂ for which much enhanced removal rates are observed.     

Free-radical synthesis of narrow polydispersed 2-hydroxyethyl methacrylate-based tetrapolymers for dilute aqueous base developable negative photoresists

Novel (meth)acrylate tetrapolymers based on 2-hydroxyethyl methacrylate (HEMA) were synthesized via free-radical polymerization in refluxing xylene under monomer-starved conditions for use in negative photoresist formulations. 2,2′-Azobis(2-methylbutyronitrile) was used as initiator and 2-mercaptoethanol as chain transfer agent. Optimized resist formulations were obtained with a relatively narrow polydispersed (D=1.86) low molecular weight copolymer (M_n=1677) of 2-hydroxyethyl methacrylate (HEMA), isobornyl methacrylate (IBMA), cyclohexyl methacrylate (CHMA) and acrylic acid (AA), in a 40/30/23/7 weight ratio. A novel high-resolution single layer negative tone photoresist suitable for 193 nm and e-beam lithography that meets basic performance requirements (aqueous-base development, enhanced etch resistance, sub-0.2 μm resolution) was developed from the aforementioned (meth)acrylate tetrapolymer, the poly(2-hydroxyethyl methacrylate-co-cyclohexyl methacrylate-co-isobornyl methacrylate-co-acrylic acid) (PHECIMA) and a sulfonium salt photo acid generator. The key-components for the negative image formation (photoacid induced crosslinking) are the hydroxyl groups of the HEMA moieties. The swelling-free negative resist material was developed in diluted aqueous base [tetramethyl ammonium hydroxide, (TMAH) 0.26×10⁻²N] and presented enhanced etch resistance without the use of etch resistance promoters. 0.20-0.14 μm lines were obtained upon 193 nm and/or e-beam lithography.