Simulations of Si and SiO2 etching in SF6 + O2 plasma

Chemical etching of Si and SiO₂ in SF₆ + O₂ plasma is considered. The concentrations of plasma components are calculated using values extrapolated from experimental data. Resulting calculations of plasma components are used for the calculation of Si and SiO₂ etching rates. It is found that the reaction constants for reactions of F atoms with Si atoms and SiO₂ molecules are equal to (3.5 ± 0.1) × 10⁻² and (3.0 ± 0.1) × 10⁻⁴, respectively. The influence of O₂ addition to SF₆ plasma on the etching rate of Si is quantified.     

Influence of annealing treatments for ZnO-doped Zr0.8Sn0.2TiO4 thin films by RF magnetron sputtering

Zirconium tin titanium oxide doped 1 wt.% ZnO thin films on n-type Si substrate were deposited by rf magnetron sputtering at a fixed rf power of 300 W, a substrate temperature of 450 °C, a deposition pressure of 5 mTorr and an Ar/O₂ ratio of 100/0 with various annealing temperatures and annealing times. Electrical properties and microstructures of 1 wt.% ZnO-doped (Zr_0.8Sn_0.2)TiO₄ thin films prepared by rf magnetron sputtering on n-type Si(100) substrates at different annealing temperatures (500 °C-700 °C) and annealing times (2 h-6 h) have been investigated. The structural and morphological characteristics analyzed by X-ray diffraction (XRD) and atomic force microscope (AFM) were sensitive to the treatment conditions such as annealing temperature and annealing time. At an annealing temperature of 600 °C and an annealing time of 6 h, the ZnO-doped (Zr_0.8Sn_0.2)TiO₄ thin films possess a dielectric constant of 46 (at f = 10 MHz), a dissipation factor of 0.059 (at f = 10 MHz), and a low leakage current density of 3.8 × 10^− 9 A/cm² at an electrical field of 1 kV/cm.     

Effect of SF6 incorporation in the cyclic process on the low temperature deposition of carbon nanofilaments

To enhance the carbon nanofilaments (CNFs) formation density, SF₆ was incorporated in the source gases (C₂H₂/H₂) during the initial deposition stage. The source gases and SF₆ were manipulated as the cyclic on/off modulation of C₂H₂/H₂/SF₆ flow in a thermal chemical vapor deposition system. The characteristics of the CNFs formation on the substrate were investigated according to the different cyclic modulation processes and the substrate temperatures. By the incorporation of SF₆ in the cyclic process CNFs could be formed at the substrate temperature as low as 350 °C. Among the different processes, mutual alternating cyclic modulation process of C₂H₂ and SF₆ could most highly enhance the CNFs formation density. The cause for the enhancement in the characteristics of as-grown CNFs by the incorporation of SF₆ was discussed in association with the slightly enhanced etching ability by the incorporation of SF₆.     

Anisotropic etching of silicon in SF6 plasma

The reactive ion etching of silicon in SF₆ plasma is considered. During the experiment, silicon substrates are etched in SF₆ plasma at different pressures and energies of incident ions. High etching anisotropy is achieved decreasing the pressure in the reactor and increasing the energy of the bombarding ions. The obtained experimental measurements are compared with theoretical calculations. It is determined that the temperature of the sidewalls decreases with the decrease of concentration of F atoms due to suppressed plasmochemical etching of silicon. The etching anisotropy increases with the decrease of concentration of F atoms due to decreased desorption of SiF₄ molecules.     

Plasma etching of high-k and metal gate materials

Etching characteristics of high-k dielectric materials (HfO₂) and metal electrode materials (Pt, TaN) have been studied in high-density chlorine-containing plasmas at pressures around 10 mTorr. The etching of HfO₂ was performed in BCl₃ without rf biasing, giving an etch rate of about 5 nm/min with a high selectivity of >10 over Si and SiO₂. The etching of Pt and TaN was performed in Ar/O₂ with high rf biasing and in Ar/Cl₂ with low rf biasing, respectively, giving a Pt etch rate of about several tens nm/min and a TaN etch rate of about 200 nm/min with a high selectivity of >8 over HfO₂ and SiO₂. The etched profiles were outwardly tapered for Pt, owing to the redeposition of etch or sputter products on feature sidewalls, while the TaN profiles were almost anisotropic, probably owing to the ion-enhanced etching that occurred.     

Ferroelectricity of ultrathin ferroelectric Langmuir-Blodgett polymer films on conductive LaNiO3 electrodes

LaNiO₃ (LNO) films with a surface roughness rms of 0.384 nm and a sheet resistance of about 200 Ω were prepared on SrTiO₃ and Si/SiO₂ substrates respectively by rf magnetron sputtering technique. The surface of LNO on Si/SiO₂ substrate is smoother than that on SrTiO₃ substrate. A nominal 2-monolayer (ML) poly(vinylidenefluoride-trifluoroethylene) film with a thickness of about 3 nm was deposited on LNO coated Si/SiO₂ substrate by Langmuir-Blodgett (LB) technology. Piezoresponse force microscopy (PFM) measurements show that the LB films demonstrate an obvious feature of polarization switching and good voltage durability. The results suggest that the ultrathin polymer films may be utilized to explore ferroelectric tunnel junctions.     

Structure and dielectric properties of sputtered bismuth magnesium niobate thin films

The Bi_1.5MgNb_1.5O₇ (BMN) thin films were prepared on platinum coated sapphire by rf magnetron sputter deposition. Effects of substrate temperature, sputter pressure and O₂/(O₂ + Ar) mixing ratio on phase structures and dielectric properties of thin films were investigated. The results indicated that sufficiently high substrate temperature and low sputter pressure would facilitate the formation of cubic pyrochlore in BMN thin films. Meanwhile, the appropriate O₂/(O₂ + Ar) mixing ratio of sputter atmosphere was required. The deposited Bi_1.5MgNb_1.5O₇ cubic pyrochlore thin films with (222) oriented texture exhibited large tunability of ~ 50% at a maximum applied bias field of 1.5 MV/cm, with low dielectric loss of ~ 0.007. The temperature and frequency dependent dielectric measurements indicated that no noticeable dielectric dispersion was detected in BMN cubic pyrochlore thin films.     

Transport properties of CuGaSe2-based thin-film solar cells as a function of absorber composition

The transport properties of thin-film solar cells based on wide-gap CuGaSe₂ absorbers have been investigated as a function of the bulk [Ga]/[Cu] ratio ranging from 1.01 to 1.33. We find that (i) the recombination processes in devices prepared from absorbers with a composition close to stoichiometry ([Ga]/[Cu] = 1.01) are strongly tunnelling assisted resulting in low recombination activation energies (E_a) of approx. 0.95 eV in the dark and 1.36 eV under illumination. (ii) With an increasing [Ga]/[Cu] ratio, the transport mechanism changes to be dominated by thermally activated Shockley-Read-Hall recombination with similar E_a values of approx. 1.52-1.57 eV for bulk [Ga]/[Cu] ratios of 1.12-1.33. The dominant recombination processes take place at the interface between CdS buffer and CuGaSe₂ absorber independently from the absorber composition. The increase of E_a with the [Ga]/[Cu] ratio correlates with the open circuit voltage and explains the better performance of corresponding solar cells.     

Effect of copper-deficiency on multi-stage co-evaporated Cu(In,Ga)S2 absorber layers and solar cells

Solar cell absorber films of Cu(In,Ga)S₂ have been fabricated by multi-stage co-evaporation resulting in compositional ratios [Cu]/([In] + [Ga]) = 0.93-0.99 and [Ga]/([In] + [Ga]) = 0.15. Intentional doping is provided by sodium supplied from NaF precursor layers of different thicknesses. Phases, structure and morphology of the resulting films are investigated by X-ray diffraction (XRD) and scanning electron microscopy. The XRD patterns show CuIn₅S₈ thiospinel formation predominantly at the surface in order to accommodate decreasing Cu content. Correlated with the CuIn₅S₈ formation, a Ga-enrichment of the chalcopyrite phase is seen at the surface. Since no CuS layer is present on the as-deposited films, functioning solar cells with CdS buffer and ZnO window layers were fabricated without KCN etch. The open-circuit voltage of solar cells correlates with the copper content and with the amount of sodium supplied. The highest efficiency cell (open-circuit voltage 738 mV, short-circuit current 19.3 mA/cm², fill factor 65%, efficiency 9.3%) is based on the absorber with the least Cu deficiency, [Cu]/([In] + [Ga]) = 0.99. The activation energy of the diode saturation current density of such a cell is extracted from temperature- and illumination-dependent current-voltage measurements. A value of 1.04 eV, less than the band gap, suggests the heterojunction interface as the dominant recombination zone, just as in cells based on Cu-rich grown Cu(In,Ga)S₂.     

Sputter-assisted plasma CVD of polymer-like amorphous CNx:H films using supermagnetron plasma

By using a sputter-assisted chemical vapor deposition (CVD) of supermagnetron plasma, amorphous CN_x:H films were deposited on the lower part of two parallel electrodes. By applying rf power to the upper electrode (UPRF) at 5 W to 800 W, polymer-like a-CN_x:H films were deposited on substrates placed on the lower electrode with an rf power (LORF) of 10 W. The deposition rate increased as UPRF increased. The hardness was as low as about 6.5 GPa, which is less than that of glass (13.1 GPa). The refractive index changed only slightly as UPRF changed from 1.6 to 1.75. The FT-IR spectrum showed strong absorption bands of NH and CH bonds at high and low UPRFs, respectively. The optical band gap was as large as 2.1 to 2.5, and it decreased as UPRF increased. These a-CN_x:H films showed white photoluminescence (PL) with broadband. With the increase of UPRF from 5 W to 800 W, the PL peak energy shifted down from 2.3 eV to 1.9 eV.     

The effect of In ion on the optical characteristics of Er in Er/Yb:LiNbO3 crystal

The effect of In³⁺ ion on the optical characteristics of Er³⁺ ion in Er/Yb:LiNbO₃ crystal under 980 nm excitation has been investigated. The Er and Yb contents in the crystals were measured by an inductively coupled plasma atomic emission spectrometer (ICP-AES). A significant enhancement of 1.54 μm emission was observed for Er/Yb:LiNbO₃ crystal doped with 1 mol% In₂O₃. The studies on the UV-vis absorption and the OH⁻ absorption spectra indicate that the threshold concentration of In³⁺ ion decreases with the Er/Yb doping in Er/Yb/In:LiNbO₃ crystal. The 1 mol% In₂O₃ doping results in the reduction of absorption cross section in the UV-vis region, meaning the formation of Er³⁺ cluster sites. The enhancement of 1.54 μm emission is attributed to the larger probabilities of the cross relaxation processes ⁴S_3/2 + ⁴I_15/2 → ⁴I_9/2 + ⁴I_13/2 (Er), ⁴S_3/2 + ⁴I_15/2 → ⁴I_13/2 + ⁴I_9/2 (Er) and ⁴I_9/2 + ⁴I_15/2 → ⁴I_13/2 + ⁴I_13/2 (Er) induced by Er³⁺ cluster sites.     

The properties of ion-implanted LiNbO3 waveguides measured by the RBS and ion beam etching stripping methods

Z-cut LiNbO₃ crystals were implanted at room temperature with 3.0 MeV O ions with a fluence of 6 × 10¹⁴ ions/cm². The effective refractive index of the guided mode was obtained by the prism coupling technique combined with mechanical stripping (ion beam etching) at room temperature. Surface layers, with thicknesses of 300, 630, 880, 1100, and 1500 nm, were removed. The channel spectra of LiNbO₃ waveguides with different etching depths were measured by the RBS technique. The damage profile of the LiNbO₃ waveguide was studied by dechannelling analysis with a multiple scattering function based on the channel spectrum. The refractive index profile was calculated based on the lattice damage ratio. The effective refractive index of the guided mode simulated by BPM showed good agreement with the experiment value.     

Large area ashing process using an atmospheric pressure plasma

We present an atmospheric pressure plasma processing for ashing photo-resist (PR) layer in the flat panel display and semiconductor manufacturing. Removal of KrF PR, i-line PR, and negative color filter PR layers on a 6th-generation large area (1640 × 30 mm²) substrate was investigated by making use of a dielectric barrier discharge (DBD) plasma device, which is with a large number of gas-flowing holes. The nitrogen DBD plasma was generated with a mixture of compressed dry air (CDA) and SF₆. To prevent thermal shrinkage of the PR layer, samples were maintained at a temperature less than 100 °C. Uniformity and reproducibility experiments have been carried out in terms of treatment time. Eventually, we obtained an ashing rate of about 600 nm/min for negative color filter PR, and 450 nm/min for KrF and i-line PR at a CDA concentration of 1%, a SF₆ concentration of 0.5%, a carrier N₂ gas flow rate of 1500 liters per minute (lpm) and at an applied power of 8 kW. Amorphous-Si layer loss which strongly depends on the fluorine radicals was at an acceptable level of 5 nm/min in the given conditions.     

Development of random access memory in Nd0.7Ca0.3MnO3/YBa2Cu3O7 heterostructure

The effects of electrode on the resistive switching in Nd_0.7Ca_0.3MnO₃(NCMO)/YBa₂Cu₃O₇(YBCO) heterostructure are investigated at room temperature. For Cu/NCMO/YBCO, resistance can be switched on-and-off from a high- to low-resistance state at a steady ratio of 25% with a pulsed-voltage of ± 3 V. On the other hand, a giant resistance-change as large as 1350% is observed with ± 5 V for Ag/NCMO/YBCO with a fast decay down to 550%. Our experimental results show clear evidences that the nature of interfaces can be modified by the electric field and it dictates the resistive switching behavior of these heterostructure devices, which are the potential candidates for the random access memory.     

Influence of contaminations on the performance of thin-film silicon solar cells prepared after in situ reactor plasma cleaning

This paper addresses the influence of the chemical memory effect (CME) of in situ plasma cleaning by using the fluorinated gases on the properties of subsequently deposited thin-film silicon solar cells and discusses methods to avoid or reduce this effect. Secondary ion mass spectrometry (SIMS) and time-of-flight secondary ion mass spectrometry (TOF-SIMS) profiles analysis showed a high impurity concentration in the intrinsic (i)-layer of p-i-n solar cells prepared directly after in situ cleaning. With increasing number of cell depositions these contaminations decrease and the solar cell performance recovers to the standard value. Restoring solar cell performance is accompanied by a decrease of contaminants concentration in the i-layer. The intentional variation of the F-content in the i-layer obtained by adding SiF₄ to the process gas mixture during a-Si:H i-layer preparation reveals that for solar cells a fluorine content above 1.5 × 10¹⁹ cm^− 3 is critical. We applied NF₃ or SF₆ + O₂ as cleaning gases and optimized the cleaning procedure. In case of using NF₃ as the cleaning gas, the CME was less pronounced as compared to the SF₆ + O₂ case and by additional procedures, like increasing the total gas flow rate during deposition, hydrogen plasma treatment of reaction chamber, the high solar cell quality could be achieved directly after in situ reactor cleaning. Low concentration of impurities in such cells was observed. Also the long-term illumination test (light-soaking for 1000 h, AM1.5 radiation) shows the same stabilized efficiency as compared to reference cells.     

Room-temperature synthesis of nanometric α-Bi2O3

Nanometric Bi₂O₃ powder was successfully synthesized by applying the method based on self-propagating room temperature reaction (SPRT) between bismuth nitrates and sodium hydroxide. X-ray powder diffraction (XRPD) and Rietveld's structure refinement method were applied to characterize prepared powder. It revealed that synthesized material is a single phase monoclinic α-Bi₂O₃ (space group P2₁/c with cell parameters a = 5.84605(4)Å, b = 8.16339(6) Å, c = 7.50788(6) Å and β = 112.9883(8)). Powder particles were of nanometric size (about 50 nm). Raman spectral studies conformed that the obtained powder is single phase α-Bi₂O₃. Specific surface area of obtained powder was measured by Brunauer-Emmet-Teller (BET) method.     

Conversion of green emission into white light in Gd2O3 nanophosphors

Gd₂O₃ nanophosphors were prepared by combustion synthesis with and without doping of Dy³⁺ ions. The X-ray powder diffraction patterns indicate that as-prepared Gd₂O₃ and 0.1 mol% Dy₂O₃ doped Gd₂O₃ nanophosphors have monoclinic structures. The transmission electron microscope (TEM) studies revealed that the as-prepared phosphors had an average crystallite sizes around 37 nm. The excitation and emission properties have been investigated for Dy³⁺ doped and undoped Gd₂O₃ nanophosphors. New emission bands were observed in the visible region for Gd₂O₃ nanophosphors without any rare earth ion doping under different excitations. A tentative mechanism for the origin of luminescence from Gd₂O₃ host was discussed. Emission properties also measured for 0.1 mol% Dy³⁺ doped Gd₂O₃ nanophosphors and found the characteristic Dy³⁺ visible emissions at 489 and 580 nm due to ⁴F_9/2 → ⁶H_15/2 and ⁴F_9/2 → ⁶H_13/2 transitions, respectively. The chromaticity coordinates were calculated based on the emission spectra of Dy³⁺ doped and undoped Gd₂O₃ nanophosphors and analyzed with Commission Internationale de l'Eclairage (CIE) chromaticity diagram. These nanophosphors exhibit green color in undoped Gd₂O₃ and white color after adding 0.1 mol% Dy₂O₃ to Gd₂O₃ nanophosphors under UV excitation. These phosphors could be a promising phosphor for applications in flat panel displays.     

Effect of the composition on the bandgap width of high-κ MexTiyOz (Me = Hf, Ta, Sr) layers

To explore the possibility of bandgap engineering in Ti-oxide based insulators, we investigated the effect of added cations of another kind (Hf, Ta, Sr) on the optical absorption and photoconductivity of thin titanate films. A bandgap of 3.1-3.4 eV, typical for pure polycrystalline TiO₂, was found in crystallized Sr_xTi_yO_z of different composition as well as in amorphous Ta₂Ti₃O_z. By contrast, the gap width of Hf titanates increases starting from 3.5 eV for 30% Hf/(Hf + Ti) to 4.2 eV for 84% Hf/(Hf + Ti). We suggest that this gap widening is associated with reduced interaction between electron states of neighboring Ti cations as influenced by a wide-gap (E_g = 5.6 eV) HfO₂ sub-network.     

Construction of new iodide selective electrodes based on bis(trans-cinnamaldehyde)1,3-propanediimine(L) zinc(II) chloride [ZnLCl2] and bis(trans-cinnamaldehyde) 1,3-propanediimine(L) cadmium(II) chloride [CdLCl2]

New plasticized PVC membranes iodide selective electrodes have been prepared by incorporating bis(trans-cinnamaldehyde)1,3-propanediimine zinc(II) chloride [ZnLCl2] and bis(trans-cinnamaldehyde) 1,3-propandiimine cadmium(II) chloride [CdLCl2] on the surface of graphite disk electrodes. At optimum value of variables the proposed electrodes have selective response to iodide with respect to a number of inorganic and organic anions with near-Nernstian slopes of − 60 ± 1.9 and − 58.5 ± 1.9 mV/decade of iodide concentration over the range 1.0 × 10^− 6-1.0 × 10^− 1 M with detection limits of 4.0 × 10^− 7 and 3.0 × 10^− 7 M for the electrodes based on [ZnLCl₂] and [CdLCl₂], respectively. The electrodes based on both ionophores have response times of about (6 s), with stable reproducible response during 2 months, while their responses is independent of pH over the range 2.5-10.5. The proposed electrodes successfully have been applied for evaluation of iodide ion content in real samples with complicated matrices including water and pharmaceutical samples.