High temperature annealing of mnos devices and its effect on si-nitride stress,interface charge density and memory properties

The effects of high temperature annealing in N₂ and H₂ ambients upon the following properties of MNOS devices have been investigated: Si-nitride stress, etch rate, index of refraction, fixed interface charge and fast surface state density, memory window and charge retention at elevated temperatures. The CVD Si-nitride and Si-oxynitride films were deposited at temperatures as low as 610°C with a NH₃/SiH₄ ratio of 1000:1, the heat treatments were performed in the temperature range from 640°C to 1130°C. A similar N₂-annealing behavior was found for film stress and flatband voltage. The film stress increased with increasing annealing time and temperature while the interface charge density changed from high positive values (Q_N/q = 4 × 10¹²cm⁻2) after nitride deposition at 610°C to high negative values (Q_N/q = -4 × 10¹²cm⁻2) after annealing at 930°C, The fast interface state density increased while the charge retention time was drastically reduced. The changes of the properties by N₂ annealing are mainly attributed to decomposition of SiH and NH bonds. Minor effects were obtained by annealing in H₂ and the drastic changes caused by N₂ annealing could be reversed to a great extent by subsequent H₂ annealing. Finally the different effects of deposition and annealing temperature on the propertiesare discussed .     

Preparation and characterization of ZnS thin films prepared by chemical bath deposition

Zinc sulfide thin films were prepared by chemical bath deposition technique using zinc sulfate (ZnSO₄·7H₂O) and thiourea [SC(NH₂)₂] as sources of Zn²⁺ and S^2– ions, and ammonia (NH₃) and hydrazine hydrate (N₂H₄) as complexing agents. The structural, stoichiometric proportion, morphology and optical properties of the ZnS thin films were investigated as a function of thiourea and ammonia concentrations using X-ray diffraction (XRD), energy-dispersive spectroscopy (EDS), scanning electron microscopy (SEM) and UV-visible spectrophotometry measurements. The deposition mechanism is discussed. The results reveal that the ZnS films exhibit poor crystallinity. The ammonia concentration had an obvious effect on the surface morphology, optical properties and deposition mechanism. The S/Zn atomic ratio and optical bandgap of the ZnS thin films first increased and then decreased with increasing ammonia or thiourea concentration.     

Reduction of charge injection into PECVD SiNxHy by control of deposition chemistry

The high rate of charge trapping in thin-film silicon nitride causes its electrical properties to change with stressing level and time. The rate of shift of the high-frequency CV curves of Al/SiN_xH_y/cSi capacitors was used here to measure nitride charging rate and to compare PECVD nitrides deposited under various conditions of plasma power and gas mixture in the same parallel-plate reactor. By operating the plasma under high power to activate the NH₃ or N₂ and under low SiH₄ flow to ensure that all of the SiH4 reacts with N, it is possible to deposit N-rich nitride that has no detectable Si—H bonding, which bonding others have correlated with charge trapping. Nitride deposited under these conditions using NH₃ and 13 MHz rf power had charging rates for both gate polarities that were 20 times lower than those of nitride that had a “stoichiometric” N/Si ratio of 4/3 and that had its H distributed among Si—H and N—H bonds. MIS capacitors made with the latter nitride also had a high negative initial flat-bond voltage, indicating the presence of grown-in positive charge. This charge was large enough to invert the surface ofp-Si substrates. N-rich nitride free of Si—H that was deposited either using N₂ or using low-frequency rf power (≤400 kHz) had higher charging rates than did that deposited from NH₃ at 13 MHz. Also, the low-frequency material contained grown-in positive charge that is attributed to H⁺ implanted by the high ion bombardment energy of the low-frequency plasma.     

Low-temperature metalorganic chemical vapour deposition of AlN for surface passivation of GaAs

Aluminium nitride (AlN) thin films have been grown by low-temperature metalorganic chemical vapour deposition (MOCVD) to passivate GaAs. By utilizing hydrazine (N₂H₄), highly resistive amorphous-like AlN films were obtained at growth temperatures around 400°C. At the AlN-GaAs interface, three deep trap levels were found: 0.6 eV (DL1) and 0.9 eV (DL2) below the conduction band minimum and 0.5 eV (DL3) above the valence band maximum. The number of DL1 levels was reduced by preparing As-dimer-stabilised surfaces of GaAs. The capture cross-sections and time constants of DL1–DL3 suggest that these levels originated from point defects, not from precipitates or disorder. Neither precipitation nor reaction was detectable by Auger electron spectroscopy after annealing at 900°C for 20 min, indicating that the AlN-GaAs interfaces are thermally stable. These results demonstrate that these AlN films are applicable as capping films for processing GaAs as well as passivation films.     

Improvement in dielectric properties of low temperature PECVD silicon dioxide by reaction with hydrazine

The dielectric properties of plasma-enhanced chemical vapor deposition (PECVD) SiO₂ deposited at 150°C were improved by reaction with anhydrous hydrazine vapor at 150–350°C. The permittivity and loss decreased ~32% and ~86%, respectively, after reaction with hydrazine at 150°C. The decrease in permittivity and loss correlated with a decrease in the dipole concentration (silanol + water). During exposure to humid conditions, water uptake in the SiO₂ films degraded the dielectric properties. A nitrogen anneal at 350°C did not improve the dielectric properties of the PECVD SiO₂. Although water was removed from the films, silanol remained. When the PECVD SiO₂ deposited at 150° was reacted with hydrazine vapor at 150°C, both silanol and water were removed from the films. The dielectric properties and resistance to water absorption improved.     

Atomic-layer-deposited silicon-nitride/SiO2 stack––a highly potential gate dielectrics for advanced CMOS technology

An extremely thin (2 monolayers) silicon nitride layer has been deposited on thermally grown SiO₂ by an atomic-layer-deposition (ALD) technique and used as gate dielectrics in metal–oxide–semiconductor (MOS) devices. The stack dielectrics having equivalent oxide thickness (T_eq=2.2 nm) efficiently reduce the boron diffusion from p⁺ poly-Si gate without the pile up of nitrogen atoms at the SiO₂/Si interface. The ALD silicon nitride is thermally stable and has very flat surface on SiO₂ especially in the thin (<0.5 nm) thickness region.An improvement has been obtained in the reliability of the ALD silicon-nitride/SiO₂ stack gate dielectrics compared with those of conventional SiO₂ dielectrics of identical thickness. An interesting feature of soft breakdown free phenomena has been observed only in the proposed stack gate dielectrics. Possible breakdown mechanisms are discussed and a model has been proposed based on the concept of localized physical damages which induce the formation of conductive filaments near both the poly-Si/SiO₂ and SiO₂/Si-substrate interfaces for the SiO₂ gate dielectrics and only near the SiO₂/Si-substrate interface for the stack gate dielectrics.Employing annealing in NH₃ at a moderate temperature of 550 °C after the ALD of silicon nitride on SiO₂, further reliability improvement has been achieved, which exhibits low bulk trap density and low trap generation rate in comparison with the stack dielectrics without NH₃ annealing.Because of the excellent thickness controllability and good electronic properties, the ALD silicon nitride on a thin gate oxide will fulfill the severe requirements for the ultrathin stack gate dielectrics for sub-0.1 μm complementary MOS (CMOS) transistors.     

Effect of thermal annealing on the sensitivity of Si-based MOS diodes to reducing gases

We study the effect of thermal annealing in the range of 200–610°C on the sensitivity and time dependences of the response of the Pd-SiO₂-n-Si diodes to hydrogen and ammonia. The postannealing surface of a Pd electrode was examined using atomic force microscopy. The high-frequency C-V characteristics were measured in air and gas mixtures H₂-air and NH₃-air. It is shown that, after annealing at 200°C for 10 min, the response of diode capacitance to hydrogen is higher than that to ammonia. After annealing at 300°C and higher, the sensitivity of MOS diodes to hydrogen nearly vanishes. The response to ammonia still remains high, although it gradually weakens as the annealing temperature is increased. A decrease in sensitivity of the Pd-SiO₂-n-Si diodes to ammonia with increasing temperature is attributed to worsening of the electrical characteristics of the Pd electrode.     

Thermal conductivity of AlN thin films deposited by RF magnetron sputtering

Aluminum nitride (AlN) film, which is being investigated as a possible passivation layer in inkjet printheads, was deposited on a Si (1 0 0) substrate at 400 °C by radio frequency (RF) magnetron sputtering using an AlN ceramic target. Dependence on various reactive gas compositions (Ar, Ar:H₂, Ar:N₂) during sputtering was investigated to determine thermal conductivity. The crystallinity, grain size, and Al–N bonding changes by the gas compositions were examined and are discussed in relation to thermal conductivity. Using an Ar and 4% H₂, the deposited AlN films were crystalline with larger grains. Using a higher nitrogen concentration of 10%, a near amorphous phase, finer morphology, and an enhanced Al–N bonding ratio were achieved. A high thermal conductivity of 134 W/mk, which is nine times higher than that of the conventional Si₃N₄ passivation film, was obtained with a 10% N₂ reactive gas mixture. A high Al–N bonding ratio in AlN film is considered the most important factor for higher thermal conductivity.     

Interfacial Engineering Promoting Electrosynthesis of Ammonia over Mo/Phosphotungstic Acid with High Performance

Electrochemical nitrogen reduction reaction (eNRR) is recognized as a promising approach for ammonia synthesis, which is, however, impeded by the inert nitrogen and the unavoidable competing hydrogen evolution reaction (HER). Here, a Mo-PTA@CNT electrocatalyst in which Mo species are anchored on the fourfold hollow sites of phosphotungstic acid (PTA) and closely embedded in multi-walled carbon nanotubes (CNT) for immobilization is designed and synthesized. Interestingly, the catalyst presents a high ammonia yield rate of 51 ± 1 µg h⁻¹ mg_cat.⁻¹ and an excellent Faradaic efficiency of 83 ± 1% at −0.1 V versus RHE under ambient conditions. The concentrations of NH₄⁺ are also quantitatively calculated by ¹H NMR spectra and ion chromatography. Isotopic labeling identifies that the N atom of the formed NH₃ originates from N₂. The controlled experiments confirm a strong interaction between Mo-PTA and N₂ with an adsorption energy of 50.46 kJ mol⁻¹ and activation energy of 21.36 kJ mol⁻¹. More importantly, due to CNT's gas storage and hydrophobicity properties, there is a fourfold increase in N₂ content. The concentration of H₂O is reduced by more than half at the interface of the electrode. Thus, the activity of eNRR can be significantly improved with ultrahigh electron selectivity.     

Semiconductor nanowires surrounded by cylindrical Al2O3 shells

The GaN, GaP, InP, Si₃N₄, SiO₂/Si, SiC, and ZnO semiconductor nanowires were synthesized by a variety of growth methods, and they were wrapped cylindrically with amorphous aluminum oxide (Al₂O₃) shells. The Al₂O₃ was deposited on these seven different semiconductor nanowires by atomic layer deposition (ALD) at a substrate temperature of 200°C using trimethylaluminum (TMA) and distilled water (H₂O). Transmission electron microscopy (TEM) images taken for the nanowires revealed that Al₂O₃ cylindrical shells surround uniformly all these semiconductor nanowires. Our TEM study illustrates that the ALD of Al₂O₃ has an excellent capability to coat any semiconductor nanowires conformally; its coating capability is independent of the chemical component, lattice structure, and growth direction of the nanowires. This study suggests that the ALD of Al₂O₃ on nanowires is one of the promising methods to prepare cylindrical dielectric shells in coaxially gated, nanowire field-effect transistors (FETs).     

Synthetic Routes and Formation Mechanisms of Spherical Boron Nitride Nanoparticles

A new concept is proposed to explain the formation of spherical boron nitride (BN) nanoparticles synthesized by the chemical vapor deposition (CVD) reaction of trimethoxyborane (B(OMe)₃) with ammonia. The intermediate phases formed during the CVD under different reaction conditions are analyzed by X‐ray diffraction, electron microscopy, thermogravimetry, and spectroscopy techniques. The transition mechanism from an intermediate B(OMe)_3–xH_3–xN (x < 2) phase having single B? N bonds to the BN nanoparticles is elucidated. This particularly emphasizes the CVD temperature effect governing the conversion of the N? H···O? B hydrogen bonds in (OMe)₃B · NH₃ into the N? B bonds in B(OMe)_3–xH_3–xN. The spherical morphology strongly depends on the remnant impurity oxygen formed upon Me₂O group elimination in the intermediate. Two types of spherical BN nanoparticles primarily attractive for immediate commercialization (with C and H impurities at a level less than 1 wt %) are synthesized by the adjustment of experimental parameters: high oxygen‐containing (～6.3 wt %) BN spheres with a diameter of ～90 nm and a specific surface area of 26.8 m² g^?1; and low oxygen‐containing (<1 wt %) BN spheres with a diameter of ～30 nm and a surface area of 52.7 m² g^?1. Finally, the regarded synthetic techniques are fully optimized in the present work.     

Boron Nitride Fibers Prepared from Symmetric and Asymmetric Alkylaminoborazines

The thermolysis of 2,4,6‐[(CH₃)₂N]₃B₃N₃H₃ ( 1 ), 2,4‐[(CH₃)₂N]₂‐6‐(CH₃HN)B₃N₃H₃ ( 2 ), and 2‐[(CH₃)₂N]‐4,6‐(CH₃HN)₂B₃‐N₃H₃ ( 3 ) led to polyborazines 4 , 5 , and 6 respectively. The polymers display direct B–N bonds between borazinic B₃N₃ rings and, in addition, a proportion of –N(CH₃)– bridges for 5 and 6 , as clearly underlined by ¹³C NMR spectroscopy. Melt‐spinning of these three polymeric precursors exemplified that their ease of processing increases in the order 4 < 5 < 6 . Nevertheless, polyborazine filaments could be prepared from each of them and a subsequent thermal treatment up to 1800 °C resulted in the formation of crystalline hexagonal boron nitride fibers, which were characterized by X‐ray diffraction analysis, Fourier transform infrared (FTIR) spectroscopy, and Raman spectroscopy. Scanning electron microscopy (SEM) images showed that the ceramic fibers are circular and dense without major defects. The mechanical properties for 4 ‐derived fibers could not be measured because of their brittleness, whereas measurements on 5 ‐ and 6 ‐derived fibers gave tensile strength σ^R = 0.51 GPa, Young’s modulus E = 67 GPa, and σ^R = 0.69 GPa, E = 170 GPa, respectively. The improvement in mechanical properties for ceramic fibers prepared respectively from 4 , 5 , and 6 could be explained to a large extent by the improvement of the processing properties of the preceramic polymers. This evolution could be related to the increased ratio of bridging –N(CH₃)– groups between the B₃N₃ rings within the polymers 4 , 5 , and 6 and therefore to the functionalities of the starting monomers 1 , 2 , and 3 .     

Unique P?Co?N Surface Bonding States Constructed on g‐C3N4 Nanosheets for Drastically Enhanced Photocatalytic Activity of H2 Evolution

Developing high‐efficiency and low‐cost photocatalysts by avoiding expensive noble metals, yet remarkably improving H₂ evolution performance, is a great challenge. Noble‐metal‐free catalysts containing Co(Fe)? N? C moieties have been widely reported in recent years for electrochemical oxygen reduction reaction and have also gained noticeable interest for organic transformation. However, to date, no prior studies are available in the literature about the activity of N‐coordinated metal centers for photocatalytic H₂ evolution. Herein, a new photocatalyst containing g‐C₃N₄ decorated with CoP nanodots constructed from low‐cost precursors is reported. It is for the first time revealed that the unique P(δ^?)? Co(δ⁺)? N(δ^?) surface bonding states lead to much superior H₂ evolution activity (96.2 µmol h^?1) compared to noble metal (Pt)‐decorated g‐C₃N₄ photocatalyst (32.3 µmol h^?1). The quantum efficiency of 12.4% at 420 nm is also much higher than the record values (≈2%) of other transition metal cocatalysts‐loaded g‐C₃N₄. It is believed that this work marks an important step toward developing high‐performance and low‐cost photocatalytic materials for H₂ evolution.     

Efficient Photocatalytic Nitrogen Fixation: Enhanced Polarization,Activation, and Cleavage by Asymmetrical Electron Donation to NN Bond

Photocatalytic nitrogen (N₂) fixation suffers from low efficiency due to the difficult activation of the strongly nonpolar N?N bond. In this study, a Ru–Co bimetal center is constructed at the interface of Ru/CoS_x with S‐vacancy on graphitic carbon nitride nanosheets (Ru‐Vs‐CoS/CN). Upon adsorption, the two N atoms in N₂ are bridged to the Ru–Co center, and the asymmetrical electron donation from Ru and Co atoms to N₂ adsorbate highly polarized N?N bond to double bond order. The plasmonic electric‐field‐enhancement effect enables the Ru/CoS_x interface to boost the generation of energetic electrons. The Schottky barrier between Ru and CoS_x endows the interface with electron transfer from CoS_x to Ru. The Ru‐end bound N at the Ru–Co center is preferentially hydrogenated. As a result, the Ru‐Vs‐CoS/CN photocatalyst shows an NH₃ production rate of up to 0.438 mmol g^?1 h^?1, reaching a high apparent quantum efficiency of 1.28% at 400 nm and solar‐to‐ammonia efficiency of 0.042% in pure water under AM1.5G light irradiation.     

Growth and characterization of GaN thin films on SiC SOI substrates

SiC semiconductor-on-insulator (SOI) structures have been investigated as substrates for the growth of GaN films. The SiC SOI was obtained through the conversion of Si SOI wafers by reaction with propane and H₂. (111) SiC SOI have been produced by this carbonization process at temperatures ranging from 1200 to 1300°C. X-ray diffraction (XRD) and infrared spectroscopy (FTIR) are used to chart the conversion of the Si layer to SiC. Under our conditions, growth time of 3 min at 1250°C is sufficient to completely convert a 1000? layer. XRD of the SiC SOI reveals a single SiC peak at 2θ = 35.7° corresponding to the (111) reflection, with a corrected full width at half-maximum (FWHM) of ~590±90 arc-sec. Infrared spectroscopy of SiC SOI structures obtained under optimum carboniza-tion conditions exhibited a sharp absorption peak produced by the Si-C bond at 795 cm⁻¹, with FWHM of ∼ 20–25 cm⁻¹. Metalorganic CVD growth of GaN on the (111) SiC SOI was carried out with trimethylgallium and NH₃. The growth of a thin (≤200?), low temperature (500°C) GaN buffer layer was followed by the growth of a thick (∼2 μm) layer at 1050°C. Optimum surface morphology was obtained for zero buffer layer. XRD indicates highly oriented hexagonal GaN, with FWHM of the (0002) peak of ~360±90 arc-sec. Under high power excitation, the 300°K photoluminescence (PL) spectrum of GaN films exhibits a strong near band-edge peak (at λ_p~371 nm, with FWHM = 100–150 meV) and very weak yellow emission. Under low power excitation, the 370 nm PL emission from the GaN/SiC SOI structure increases rapidly with SiC carbonization temperature, while the yellow band (∼550–620 nm) correspondingly decreases.     

Processing and characterisation of PECVD silicon nitride films

Amorphous Si-N films are synthesised from an NH₃/SiH₄ gas mixture by plasma-enhanced chemical vapour deposition (PECVD) at fixed radio frequency (13.56 MHz) and total gas pressure (34 ± 4 Torr). The variable process parameters and their ranges are: (i) substrate temperature, 200–400°C; (ii) RF power density, 0.08–0.35 W cm⁻²; (iii) NH₃/SiH₄ flow ratio, 40:400–40: 1200 ml min⁻¹. Fundamental properties of the Si-N films are characterised through elemental composition, chemical speciation, optical and electrical properties, all of which are dependent on the process parameters.     

Anisotropical C2−O reflection bands measured in α-helixes of silk fibroin

From analysis of 36 anisotropical reflectrion spectra of the C₂?O bending bands of silk fibroin at ≈700～200 cm^?1 region at static state, presence of the A, B, C and D-band and reflection edge was also confirmed. Furthermore, we confirmed stepnized reflectivity overlapping on the C₂?O bending bands and stenized values of the reflection integral (optical activity). Second, analysing four diffusion diagrams of these bands, we inspected stepnized polar distribution of the band and quantized polar distribution was confirmed as, θ^N = 27.5·N + 2.5 (degrees) with N=1, 2, 3, 4...12 and 13, without N=5,6 and 7 at θ=120°～180° as in case of polar distribution of the C₂?O and Si?O stretching reflection bands and C₂?O bending band measured in case of silicate cellulose present in the surface skin layer of bamboo's stem.     

Preparation and characterization of thin films of MgO,Al2O3 and MgAl2O4 by atomic layer deposition

MgO, Al₂O₃ and MgAl₂O₄ thin films were deposited on silicon substrates at various temperatures by the atomic layer deposition (ALD) method using bis(cyclopentadienyl)magnesium, triethylaluminum, and H₂O and were characterized systematically. High-quality polycrystalline MgO films were deposited for a substrate temperature above 500°C, and amorphous thin films were deposited around 400°C. The deposited Al₂O₃ and MgAl₂O₄ thin films were characterized as amorphous in structure. Applicability of ALD to complex oxides is discussed.     

Characteristics of PECVD grown tungsten nitride films as diffusion barrier layers for ULSI DRAM applications

We have developed tungsten nitride (W-Nitride) films grown by plasma enhanced chemical vapor deposition (PECVD) for barrier material applications in ultra large scale integration DRAM devices. As-deposited W-Nitride films show an amorphous structure, which transforms into crystalline, β-W₂N and α-W phases upon annealing at 800°C. The resistivity of the as-deposited films grown at the NH₃/WF₆ gas flow ratio of 1 is about 160 μω-cm, which decreases to 50 μω-cm after an rapid thermal annealing treatment at 800°C. In the contact holes with the size of 0.35 μm and aspect ratio of 3.5, the bottom step coverage of the tungsten nitride films is about 60%, which is about three times higher than that of collimated-TiN films. We obtained contact resistance and leakage current with the tungsten nitride barrier layer comparable to those with conventional collimated TiN films. The contact resistance and leakage current are stable upon thermal stressing at 450°C up to 48 h.     

Unique phenomena in SnO2-based gas sensing devices exposed to ammonia gas

Gas detection characteristics for NH₃ gas have been studied for SnO₂ mixed with ZrO₂ and hydrophilic silica. Both an increase and a decrease in device conductivity can be obtained when the device is exposed to NH₃ gas independently of the device temperature. This unique feature is exhibited when the device temperature is kept above 260°C. For a device mixed with 1 wt% hydrophilic silica, especially, a remarkable decrease in conductivity has been observed at 370°C device temperature. It is also found that this property can be utilized to make a highly selective NH₃ gas detector, since the conductivity of SnO₂-based devices usually increased for other reducing gases. Oscillation phenomena are also observed in devices mixed with 5 wt% hydrophilic silica at 370°C device temperature and 200 ppm NH₃ concentration. The oscillation period varies from 4 to 20 min and the amplitude varies from 2 × 10^?8 to 11 × 10^?8 mho.