PECVD Si nitride and Si oxide layers — Hydrogen analysis and etching after ion implantation

lon-implantation-induced selective etching of dielectric materials is considerably diminished with increasing hydrogen content. Making use of the ¹H(¹⁵N,γ)¹²C resonance reaction, low-temperature PECVD Si oxide and Si nitride layers were observed to contain 12 and 23 at.% H, respectively. For different reagents etch rates were measured regarding the virgin and ion—implanted-He⁺ Ne⁺ at 60, 100 keV — PECVD films.     

Plasma density measurement and downstream etching of silicon and silicon oxide in Ar/NF3 mixture remote plasma source

In this study, plasma density measurements were performed near the plume region of the remote plasma source (RPS) in Ar/ NF₃ gas mixtures using a microwave cutoff probe. The measured plasma density is in the range of 10 ¹⁰ –10 ¹¹ cm ⁻³ in the discharge conditions with RPS powers of 2–4 kW and gas pressures of 0.87–4 Torr. The plasma density decreased with increasing gas pressures and RPS powers under various Ar/ NF₃ mixing ratios. This decrease in the plasma density measured at the fixed measurement position (plume region) can be understood by the reduction of the electron energy relaxation length with increases in the gas pressures and mixing ratio of NF₃/(Ar / NF₃). We also performed downstream etching of silicon and silicon oxide films in this system. The etch rate of the silicon films significantly increases while the silicon oxide is slightly etched with the gas pressures and powers. It was also found that the etch rate strongly depends on the wafer position on the processing chamber electrode, and that the etch selectivity reached 96–131 in the discharge conditions of RF powers (3730–4180 W) and gas pressures (3.6–4 Torr).     

Thermodynamic stability of Na2ZrO3 using the solid electrolyte galvanic cell technique

The sodium potential in the test electrode (a) Pt,O₂,Na₂ZrO₃,ZrO₂ was measured by using the emf technique employing Na-β^″-alumina as the solid electrolyte in conjunction with (b) Pt,O₂,Al₂O₃,NaAl₁₁O₁₇, (c) Pt,O₂,Na₂MoO₄,Na₂Mo₂O₇ and (d) Pt,Na₂CO₃,CO₂,O₂ as the reference electrodes over the ranges 880–1045, 700–800 and 850–940 K, respectively. The emf results between electrodes (b) and (c) were utilized for internal consistency checks. From the results on cells formed between (a) and (b) and those on (a) and (c), the standard Gibbs energy of formation, Δ_fG^o (kJ/mol) of Na₂ZrO₃ was determined to be −1699.4+0.3652T (K) valid over the temperature range 700–1045 K. The break in the emf data at 1045 K was corroborated by independent TG/DTA measurements carried out on Na₂ZrO₃ which exhibited an endotherm at 1055 K indicative of a phase transition in Na₂ZrO₃.     

Optical emission measurement of high-uniformity and high-density O2 supermagnetron plasma

The density and spatial distribution of O₂ supermagnetron plasma generated in between two parallel cathodes were measured by optical emission spectroscopy. Uniform plasma could be generated for the cathode spacing of 20–30 mm and a gas pressure of 2–10 mTorr on a magnetic field application of 130 G. The highest optical emission intensity (OEI) was observed at the cathode spacing of about 20 mm. OEIs of O-ions (464.9 nm) and O-radicals (777.1 nm) showed a strong RF-voltage-phase-difference dependencies of two supplied RF powers, and the OEIs at about 150°, i.e. around 180°, were about 2 times stronger than those of a conventional magnetron plasma generated at a gas pressure of 3–80 mTorr. In the spatial distribution measurements of OEIs, high-uniform plasmas were observed at a wide range of the RF phase difference, e.g. 0 and 120°.     

Etching characteristics of thin SiON films using a liquefied perfluorocarbon precursor of C6F12O with a low global warming potential

Perfluorocarbon gas is widely used in the semiconductor industry. However, perfluorocarbon has a negative effect on the global environment owing to its high global warming potential (GWP) value. An alternative solution is essential. Therefore, we evaluated the possibility of replacing conventional perfluorocarbon etching gases such as CHF₃ with C₆F₁₂O, which has a low GWP and is in a liquid state at room temperature. In this study, silicon oxynitride (SiON) films were plasma-etched using inductively coupled CF₄ +C₆F₁₂O+O₂ mixed plasmas. Subsequently, the etching characteristics of the film, such as etching rate, etching profile, selectivity over Si, and photoresist, were investigated. A double Langmuir probe was used and optical emission spectroscopy was performed for plasma diagnostics. In addition, a contact angle goniometer and x-ray photoelectron spectroscope were used to confirm the change in the surface properties of the etched SiON film surface. Consequently, the etching characteristics of the C₆F₁₂O mixed plasma exhibited a lower etching rate, higher SiON/Si selectivity, lower plasma damage, and more vertical etched profiles than the conventional CHF₃ mixed plasma. In addition, the C₆F₁₂O gas can be recovered in the liquid state, thereby decreasing global warming. These results confirmed that the C₆F₁₂O precursor can sufficiently replace the conventional etching gas.     

Fabrication and basic characterization of silicon nitride ceramics as an inert matrix

Silicon nitride ceramics containing cerium as a simulating element of americium were fabricated to clarify proper sintering conditions. Basic properties of sintered specimens were evaluated for utilization to an inert matrix. Commercial powders of silicon nitride and cerium dioxide (16 or 24.6 wt%), and a powder of aluminum oxide or zirconium oxide as a sintering additive (5 wt%) for some specimens were mixed by ball milling in ethanol. Small amounts of stearic acid as a lubricant were also added. The mixed powder was uniaxially pressed into cylindrical pellets. Then, the pellets were embedded in a packing powder composed of 50 wt%-Si₃N₄ and 50 wt%-BN, and sintered at 2023 or 2073 K for 2 h in a 0.1 MPa N₂ atmosphere. Most of the sintered specimens had high densities (>95% TD). Sintered bodies consisted of columnar silicon nitride grains and grain-boundary phase. XRD analysis clarified that the grain-boundary phase contained crystalline compounds of cerium. The thermal conductivities of sintered specimens except for specimens containing aluminum oxide were about 40 W/m K at room temperature.     

Irradiation effects of swift heavy ions in actinide oxides and actinide nitrides: Structure and optical properties

Actinide oxides have been used as nuclear fuels in the majority of power reactors working in the world and actinide nitrides are under investigation for the fuels of the future fast neutron fission reactors developed in Forum Generation IV. Radiation damage in actinide oxides UO₂, (U_0.92Ce_0.08)O₂, and actinide nitride UN has been characterized after irradiation with swift heavy ions. Fluences up to 3 × 10¹³ ions/cm² of heavy ions (Kr 740 Mev, Cd 1 GeV) available at the CIRIL/GANIL facility were used to simulate irradiation in reactors by fission products and by neutrons. The macroscopic effects of irradiation remains very weak compared with those seen in other ceramic oxides irradiated in the same conditions: practically no swelling can be measured and no change in colour can be observed on the irradiated part of a polished face of sintered disks. The point defects in irradiated actinide compounds have been characterized by optical absorption spectroscopy in the UV–Vis–NIR wavelength range. The absorption spectra before and after irradiation are compared, and unexpected stability of optical properties during irradiation is shown. This result confirms the low rate of formation of point defects in actinide oxides and actinide nitrides under irradiation. Actinide oxides and nitrides studied are >40% ionic, and oxidation state of the actinides seems to be stable during irradiation. The small amount of point defects produced by radiation (<10¹⁶ cm⁻²) has been identified from differences between the absorption spectrum before irradiation and the one after irradiation: point defects in oxygen or nitrogen lattices can be observed respectively in oxides and nitrides (F centres), and small amounts of U⁵⁺ would be present in all compounds.     

The effect of gas additives on reactive species and bacterial inactivation by a helium plasma jet

In this paper,the influences of gas doping(O_2,N_2,Air)on the concentrations of reactive species and bactericidal effects induced by a He plasma jet are studied.Firstly,results show that gas doping causes an increase in voltage and a decrease in current compared with the pure He discharge under the same discharge power,which might be attributed to the different chemical characteristics of O_2 and N_2 and verified by the changes in the gaseous reactive species shown in the optical emission spectroscopy(OES) and Fourier transform infrared(FTIR)spectroscopy.Secondly,the concentrations of aqueous reactive oxygen species(ROS) and reactive nitrogen species(RNS) are tightly related to the addition of O_2 and N_2 into the working gas.The concentrations of aqueous NO_2~- and NO_3~- significantly increase while the concentrations of aqueous ROS decrease with the admixture of N_2.The addition of O_2 has little effect on the concentrations of NO_2~- and NO_3~- and pH values; however,the addition of O_2 increases the concentration of O_2~- and deceases the concentrations of H_2O_2 and OH.Finally,the results of bactericidal experiments demonstrate that the inactivation efficiency of the four types of plasma jets is He?+?O_2??He+AirHeHe+N_2,which is in accordance with the changing trend of the concentration of aqueous O_2~-.Simultaneously to the better understanding of the formation and removal mechanisms of reactive species in the plasma–liquid interaction,these results also prove the effectiveness of regulating the concentrations of aqueous reactive species and the bacteria inactivation effects by gas doping.     

Effect of N_2 and O_2 on OH radical production in an atmospheric helium microwave plasma jet

UV-pulsed laser cavity ringdown spectroscopy of the hydroxyl radical OH(A–X)(0–0)band in the wavelength range of 306–310 nm was employed to determine absolute number densities of OH in the atmospheric helium plasma jets generated by a 2.45 GHz microwave plasma source.The effect of the addition of molecular gases N_2 and O_2 to He plasma jets on OH generation was studied.Optical emission spectroscopy was simultaneously employed to monitor reactive plasma species.Stark broadening of the hydrogen Balmer emission line(H_β)was used to estimate the electron density nein the jets.For both He/N_2 and He/O_2 jets, newas estimated to be on the order of 10~(15)cm~(-3).The effects of plasma power and gas flow rate were also studied.With increase in N_2 and O_2 flow rates, netended to decrease.Gas temperature in the He/O_2 plasma jets was elevated compared to the temperatures in the pure He and He/N_2 plasma jets.The highest OH densities in the He/N_2 and He/O_2 plasma jets were determined to be 1.0?×10~(16)molecules/cm~3 at x?=?4 mm(from the jet orifice)and 1.8?×?10~(16)molecules/cm~3 at x=3 mm, respectively.Electron impact dissociation of water and water ion dissociative recombination were the dominant reaction pathways, respectively, for OH formation within the jet column and in the downstream and far downstream regions.The presence of strong emissions of the N_2~+ bands in both He/N_2 and He/O_2 plasma jets, as against the absence of the N_2~+ emissions in the Ar plasma jets, suggests that the Penning ionization process is a key reaction channel leading to the formation of N_2~+ in these He plasma jets.     

Optical properties of γ-irradiated synthetic sapphire and yttria-stabilized zirconia spectroscopic windows

Synthetic sapphire and yttria-stabilized zirconia single-crystals were irradiated by increasing doses of γ-radiation to study the changes of their optical properties. The optical transparency of -Al₂O₃ was nearly constant up to the γ-radiation dose of 150 kGy for the spectral range of 400–1000 nm, while yellowish-brown coloration of (Zr_0.89Y_0.11)O_1.94 appeared for irradiation above 1 kGy. However, after a short-term heating in the temperature of 210^oC stable discoloration of zirconia can be achieved.     

Mass spectrometric investigation of the vaporization of li2tio3(s)

The vaporization of Li₂TiO₃(s) has been investigated by the mass spectrometric Knudsen effusion method. Partial pressures of Li(g), LiO(g), Li₂O(g), Li₃O(g) and O₂(g) over Li₂TiO₃(s) have been obtained in the temperature range 1180–1628 K. When the vaporization of Li₂TiO₃(s) proceeds, the content of Li₂O in the Li₂TiO₃(s) sample decreases. The phase of the sample is a disordered Li₂TiO₃ solid solution above 1486 K. The enthalpies of formation and the atomization energies for LiO(g) and Li₃O(g) have been evaluated from the partial pressures to be ΔH^o_f0(LiO, g) = 65.4 ± 17.4 kJ/mol, ΔH^o_f0(Li₃O, g) = − 207.5 ± 56.6 kJ/mol, D^o₀(LiO) = 340.5 ± 17.4 kJ/mol and D^o₀(Li₃O) = 931.6 ± 56.6 kJ/mol, respectively.     

Fabrication of zirconia-based targets for transmutation

The fabrication of homogeneous (Am,Y,Zr)O_2−x pellets and heterogeneous pellets, containing (Am,Y,Zr)O_2−x spheres dispersed in an inert matrix, by dust-free processes has been investigated. Due to the high activity of americium, the preparatory fabrication tests and process development are being carried out using cerium analogue element. The sol gel route is used to produce highly porous Y_0.15Zr_0.85O_2−x spheres, which are then infiltrated with a cerium nitrate solution to give (Ce,Y,Zr)O_2−x. The goal (28 wt% Ce) can be achieved. Homogeneous targets with densities up to 94 %TD have been obtained.     

Threshold oxygen levels in sodium necessary for the formation of NaCrO2 in sodium-steel systems

A knowledge of the threshold oxygen level in liquid sodium necessary for the formation of NaCrO₂ in sodium-steel systems is useful in the operation of fast breeder reactors. There is considerable discrepancy in the data reported in the literature. In order to resolve this, the problem was approached from two sides. Direct measurement of oxygen potential in the Na(l)-Cr(s)-NaCrO₂(s) phase field using the galvanic cell In, In₂O₃/YDT/Na, Cr, NaCrO₂ yielded: _o2 = −800847 + 147.85 T J/mol O₂ (657–825 K). Knudsen cell-mass spectrometric measurements were carried out in the phase field NaCrO₂(s)-Cr₂O₃(s)-Cr(s) to obtain the Gibbs energy of formation of NaCrO₂ as: ΔG^o_f,T(NaCrO₂) = −870773 + 193.171 T J/mol (825–1025 K). The threshold oxygen levels deduced from G^o_f,T (NaCrO₂) data were an order of magnitude lower than the directly measured values. The difference between the two sets of data as well as differing experimental observations from operating liquid sodium systems are explained on the basis of the influence of dissolved carbon.     

Study of the permeability of thin films of a-Si:H using MeV ion beams

MeV heavy ion irradiation of hydrogenated plasma-deposited silicon nitride induces formation of the volatile molecules H₂ and N₂ inside the material. This type of nitride appears permeable for these molecules and they effuse at relatively low temperature. These effusing molecules are used to study the low temperature permeation in a 100 nm hydrogenated amorphous silicon layer, deposited onto the nitride. Upon irradiation of the double layer stack with 43.3 MeV Ag ions, appearance of D₂ and N₂ from the bottom deuterated silicon nitride layer in the vacuum does not take place up to an ion fluence of 3×10¹² ions/cm². This shows that the 100 nm plasma-deposited hydrogenated amorphous silicon top layer is initially not permeable for D₂ and N₂ molecules.     

The thermal conductivity of UO2 vapor

The thermal conductivity, λ of a saturated vapor over UO_1.96 is calculated in the temperature range 3000–6000 K. The calculation shows that the contribution to λ from the transport of reaction enthalpy dominates all other contributions. All possible reactions of the gaseous species UO₃, UO₂, UO, U, O, and O₂ are included in the calculation. We fit the total thermal conductivity to the empirical equation λ = exp(a+ b/T+cT+dT² + eT³), with λ in cal/(cm s K), T in kelvins, a = 268.90, B = − 3.1919 × 10⁵, C = −8.9673 × 10⁻², d = 1.2861 × 10⁻⁵, and E = −6.7917 × 10⁻¹⁰.     

Surface properties of Al-doped ZnO thin film before and after CF4/Ar plasma etching

Al-doped ZnO (AZO) is considered as an alternative to transparent conductive oxide materials. Patterning and achieving a stable surface are important challenges in the development and optimization of dry etching processes, which must be overcome for the application of AZO in various devices. Therefore, in this study, the etch rate and surface properties of an AZO thin film after plasma etching using the adaptive coupled plasma system were investigated. The fastest etch rate was achieved with a CF₄/Ar ratio of 50:50 sccm. Regardless of the ratio of CF₄ to Ar, the transmittance of the film in the visible region exceeded 80%. X-ray photoelectron spectroscopy analysis of the AZO thin film confirmed that metal-F bonding persists on the surface after plasma etching. It was also shown that F eliminates O vacancies. Consequently, the work function and bandgap energy increased as the ratio of CF₄ increased. This study not only provides information on the effect of plasma on AZO thin film, but identifies the cause of changes in the device characteristics during device fabrication.     

Neutronic performance comparation of MOX, nitride and metallic fuel based 25–100 MWe Pb–Bi cooled long life fast reactors without on-site refuelling

In this paper the performance of 25–100 MWe Pb–Bi cooled long life fast reactors based on three type of fuels: MOX, Nitride and Metal are compared and discussed. In general MOX fuel (UO₂–PuO₂) has lower atomic density compared to the nitride or metal fuel, but MOX fuel has some advantages such as higher Doppler coefficient, high melting point and availability. Nitride fuel has advantages such as high density, high thermal conductivity, and high melting point, but need N-15 to avoid C-14 problems.

The results show that nitride fuel as well as MOX fuel can be used to develop 25–100 MWe (75–300 MWth) Pb–Bi cooled long life reactors without on-site fuelling. The results show that nitride fuels have more superior neutronic characteristics compared to that of MOX fuel due to higher density. However, in the large power level both fuels can be easily applied. In lower power level the MOX fuel need higher fuel volume fraction to reach the comparable target of nitride fuelled cores.     

Ion beam induced desorption from thin films: SiO2 single layers and SiO2/Si multilayers

The occurrence of O₂ molecular loss from the bulk of SiO₂ single layers and SiO₂/Si multilayers as a result of 50 MeV Cu⁹⁺ irradiation has been investigated. This process did not take place with a significant rate, if it occurs at all. Instead both Si and O are removed from the SiO₂ surface region, releasing molecular O₂. If an elemental Si layer is on top in a multilayer, removal of Si and O with an appreciable rate is not observed. The irradiation creates bubbles in the SiO₂/Si multilayers, which contain O₂. The distinct SiO₂ sublayers remain chemically intact. The bubbles deteriorate the depth resolution in elastic recoil detection.     

Thermochemical study of vaporization of LiTiO by a mass spectrometric Knudsen effusion method

The vaporization of Li₄TiO₄ has been studied by a mass spectrometric Knudsen effusion method in the temperature range 1082–1582 K. Identified vapors are Li(g), LiO(g), Li₂O(g) and Li₃O(g). When the vaporization proceeds, the content of Li₂O in the Li₄TiO₄ sample decreases and the condensed phase of the sample changes to β-Li₄TiO₄ plus l-Li₂TiO₃ below 1323 K, to β-Li₄TiO₄ plus h-Li₂TiO₃ in the range 1323–1473 K and to h-Li₂TiO₃ plus liquid above 1473 K. On the basis of the partial pressure data, the enthalpies of formation for β-Li₄TiO₄ from elements and from constituent oxides have been determined to be ΔH_f,298^°(β-Li₄TiO₄,s) = −2247.8 ± 14.3 kJ mol⁻¹ and Δ_fox,298^°(β-Li₄TiO₄, s) = −107.3 ± 14.3 kJ mol⁻¹, respectively.     

Influence of the surface conditions on permeation in the deuterium–MANET system

The condition of the surfaces is of crucial importance for the deuterium permeation through materials. In this work a study of the surface constants for the adsorption (σk₁) and release (σk₂) of deuterium under different surface conditions on the martensitic steel DIN 1.4914 (MANET) has been carried out. The growth of an oxide surface layer (Cr₂O₃) of about 25–30 nm in a MANET sample, heat treated in an oxidizing environment, compared to the bare MANET that have a ‘natural' oxide of about 5 nm has provoked a reduction of both the permeation rate and the recombination coefficient (about 3 orders of magnitude). In addition, the permeation governing process has changed from diffusion-limited to surface-limited. The measurements of the permeation rate of deuterium were performed by a gas-phase permeation technique over the temperature range 574–746 K and for deuterium driving pressures in the range from 3 to 10⁵ Pa.