Oxygen Out-diffusion Research Articles

Formation of nanodomain structures during polarization reversal in congruent lithium niobate implanted with ar ions

We present the experimental study of the formation of self-similar nanodomain structures during polarization reversal in single-crystalline congruent lithium niobate (CLN) implanted by Ar ions. The formed dense surface nanodomain structure with charged domain walls differs drastically from the growth of the hexagonal domains in unimplanted CLN. The lack of wall shape stability during sideways domain wall motion was revealed. The analysis of the domain structure images in the bulk, obtained by Raman confocal microscopy, revealed the main stages of the domain structure evolution starting at unimplanted polar surface and consisting of nanodomain chain elongation, merging of isolated domains, and domain widening. The switching current data has been fitted by modification of Kolmogorov-Avrami formula for switching in a linearly increasing field. The observed experimental facts have been attributed to formation of an amorphous thin surface layer and increase of the bulk conductivity resulting from oxygen out-diffusion under radiation heating in vacuum during ion implantation. The formation of the experimentally obtained abnormal domain shapes has been explained while taking into account the step generation at the domain wall in the bulk during switching in a low electric field.

Studies of YBa2Cu3O6+x degradation and surface conductivity properties by Scanning Spreading Resistance Microscopy

Local surface conductivity properties and surface degradation of c-axis oriented YBa2Cu3O6+x (YBCO) thin films were studied by Scanning Spreading Resistance Microscopy (SSRM). For the surface degradation studies, the YBCO surface was cleaned by ion beam etching and the SSRM surface conductivity map has been subsequently repeatedly measured over several hours in air and pure nitrogen. Average surface conductivity of the scanned area was gradually decreasing over time in both cases, faster in air. This was explained by oxygen out-diffusion in both cases and chemical reactions with water vapor in air. The obtained surface conductivity images also revealed its high inhomogenity on micrometer and nanometer scale with numerous regions of highly enhanced conductivity compared to the surroundings. Furthermore, it has been shown that the size of these conductive regions considerably depends on the applied voltage. We propose that such inhomogeneous surface conductivity is most likely caused by varying thickness of degraded YBCO surface layer as well as varying oxygen concentration (x parameter) within this layer, what was confirmed by scanning Auger electron microscopy (SAM). In our opinion the presented findings might be important for analysis of current–voltage and differential characteristics measured on classical planar junctions on YBCO as well as other perovskites.

Nitrogen Doped 300 mm Czochralski Silicon Wafers Optimized with Respect to Voids with Laterally Homogeneous Internal Getter Capabilities

An internally gettering bulk defect zone and a defect denuded zone of at least 5 µm below the wafer surface were generated by out-diffusion of interstitial oxygen during annealing at temperatures in the range 1075-1100 °C in argon atmosphere. The CZ silicon material used was optimized with respect to voids and contained a central OSF region and an outer Pv region. Due to co-doping of at least 3×1013cm-3nitrogen, a laterally homogeneous bulk microdefect density was obtained which is independent of the temperature of the out-diffusion anneal. The internal getter created in this way efficiently getters nickel impurities as demonstrated in a getter test with 6.6×1011cm-3of intentional Ni contamination. In the central OSF region of the as-grown nitrogen co-doped wafers, the nuclei capable of generating OSFs also degrade the gate oxide integrity. Out-diffusion annealing at 1075-1100°C dissolves most of the defects capable of generating OSFs and it strongly improves the integrity of 5 nm gate oxides.

Effects of Substrate Temperature on the Electrical and the Optical Properties of N-Type ZnO/P-Type 4H-SiC

We investigated the effect of the substrate temperature on the electrical and the optical properties of ZnO/4H-SiC structures. The n-type ZnO layer was grown on p-type 4H-SiC substrate by pulsed laser deposition to form p-n hetero-junction diode structure. The n-type ZnO thin films were deposited by pulsed laser deposition at different temperatures of 200, 400, and 600 °C, respectively. It was shown from transmission line method (TLM) and auger electron spectroscopy (AES) data that the sheet resistance of ZnO on SiC was increases from ~760 Ω/square to ~4000 Ω/square as the deposition temperature increases and the oxygen outdiffusion decreases. The I-V characteristics with and without illumination has also been studied.

Polarization Reversal in MgO:LiNbO3 Single Crystals Modified by Plasma-Source Ion Irradiation

The polarization reversal has been studied by domain structure visualization and switching current recording in LiNbO3 single crystals doped by 5% MgO irradiated by Ar+ ions. The abnormal domain structure evolution representing formation of charged domain walls has been revealed. It has been shown that low energy ion irradiation leads to increase of the bulk conductivity due to oxygen out-diffusion induced by radiative heating in vacuum. The inhomogeneous distribution of the electric field terminated the polarization reversal in high conductive layer. The analysis of the switching current data allowed revealing the input of the conductive current through charged domain walls.

Correlation between luminescent properties and growth conditions for ZnO films grown on Si(100) by sputtering technique

We report the effects of the growth condition on emission properties of ZnO films grown on Si (100) by rf magnetron sputtering. With increasing the O2/Ar+O2 ratio in the growing ambient, the visible emission in the roomtemperature photoluminescence spectra (PL) was drastically suppressed without sacrificing the intensity of excitonrelated emission at ultraviolet region. This tendency was estimated to be due to the reduction in intrinsic defects such as the oxygen vacancies and zinc interstitials in the film with an improvement of the film stoichiometry in oxygen rich condition, indicating that the visible emission of ZnO may originate from oxygen vacancy or zinc interstitial related defects. An additional violet emission peaked at about 401 nm (3.09 eV) was also observed in the low temperature PL (LTPL) spectra of the ZnO films grown under oxygen-rich conditions and this violet emission peak was gradually weakened as the growth temperature increases from 400 o C to 700 o C, and ultimately, disappeared at 800 o C. From the above observation, it is deduced that this emission band has a close relation with the intrinsic defects related to an oxygen-rich condition, and the dependence of this emission on growth temperature can be due to an improvement of the film stoichiometry by an oxygen out-diffusion at high growth temperature.

Role of environmental and annealing conditions on the passivation-free in-Ga–Zn–O TFT

We examined the characteristics of passivation-free amorphous In–Ga–Zn–O thin film transistor (a-IGZO TFT) devices under different thermal annealing atmospheres. With annealing at higher temperature, the device performed better at the above-threshold operation region, which indicated the film quality was improved with the decrease of defects in the a-IGZO active region. The mobility, threshold voltage and subthreshold swing of a-IGZO TFT annealed at 450 °C was 7.53 cm 2/V s, 0.71 V and 0.18 V/decade, respectively. It was also observed that the a-IGZO was conductive after thermal annealing in the vacuum, due to the ease of oxygen out-diffusion from the a-IGZO back channel. The oxygen deficiency resultantly appeared, and provided leaky paths causing electrical unreliability when TFT was turned off. In contrast, the annealing atmosphere full of O 2 or N 2 would suppress the oxygen diffusion out of the a-IGZO back channel. The worst V th degradation of a-IGZO TFT after positive gate bias stress and negative gate bias stress (NGBS) was about 2 V and − 2 V, respectively. However, the V th shift in the NGBS testing could be suppressed to − 0.5 V in vacuum chamber. Material analysis methods including X-ray photoelectron spectroscopy and scanning electron microscopy were used to investigate the change of a-IGZO film after different thermal annealing treatments. The variation of O 1s spectra with different annealing atmospheres showed the consistence with our proposed models.

Ruthenium based metals using atomic vapor deposition for gate electrode applications

The impacts of ruthenium-based metal gate electrodes (Ru,RuOx,RuSiOx) with atomic vapor deposition (AVD) on flatband voltage (VFB) and equivalent oxide thickness (EOT) are demonstrated using a low temperature (<400 °C) process. Increasing thickness of Ru and RuOx exhibits higher VFB, attributed to filling oxygen vacancies [Vo] in high-k gate dielectric with oxygen supplied from AVD metal gate electrodes upon annealing. Ru is efficient to attain a higher work-function and thinner EOT compared to RuOx and RuSiOx. Subsequent physical-vapor-deposition (PVD) TiN capping on AVD metals blocks oxygen out-diffusion, leading to higher VFB than PVD W or AVD TiN capping.

Spreading of an SR beam spot (diameter 0.5 μm, 95 eV) photoelectron image on the surface of WO3 − x films

The 2D-photoemission image of the beam spot was obtained for the first time for the W5+ oxidation state on the preliminary irradiated WO3 − x thin film surface, created by scanning of the SR beam over the film surface. The W5+ beam profile intensity was found to spread up to a distance of 3.2 μm for an amorphous film and 5.5 μm for a polycrystalline film, it exceeds considerably the beam spot size. The image saturation dose was reached faster for a polycrystalline film. Among the possible mechanisms explaining this phenomenon, for the case of an almost unchangeable O2s state under irradiation, a choice was made in favor of a photon-generated charge diffusion due to low-energy secondary electrons from photoemission, which produce the “coloration” effect, e− + W6+ (W5+) W5+ → W5+(W4+). The O512-eV Auger peak was found to degrade at the distance of 1.5–2 mm outside the beam spot under long-time electron beam irradiation, which is attributed to electron-stimulated oxygen desorption and outdiffusion.

Temperature dependence of the resistance switching effect studied on the metal/YBa2Cu3O6+x planar junctions

The resistive switching (RS) effect observed in capacitorlike metal/insulator/metal junctions belongs to the most promising candidates for next generation of memory cell technology. It is based on a sudden change of the junction resistance caused by an electric field applied to the metal electrodes. The aim of this work was to study this effect on the structure metal/YBCO6/YBCO7, where YBCO7 is a metallic phase and YBCO6 is an insulator phase that arises spontaneously by outdiffusion of oxygen from a few nanometers wide YBCO surface layer. Oriented YBa2Cu3O7 thin films were prepared by the method of magnetron sputtering and consequently planar structures with metal-YBCO junction were made by the means of the optical lithography, ion etching, and vacuum evaporation. On these junctions, the authors have studied the temperature dependence of the RS effect with I-V and dI/dV-V transport measurements down to liquid He temperature. They have determined the temperature dependence of the RS effect threshold voltage in the temperature range 100–300 K and showed that this dependency is compatible with common idea of oxygen ion migration under electric field within the YBCO surface layer.

Compensation mechanism in N-doped ZnO nanowires

N-doped ZnO nanowires are synthesized at a relatively low growth temperature of500 °C by directly heatingzinc powder using NH3 as the dopant. The incorporation of N into the ZnO nanowires is experimentally confirmedby x-ray photoelectron spectroscopy, Raman spectra and photoluminescence measurements.By combining post annealing experiments after growth with first-principles calculations,the detailed migration mechanism of N and compensation mechanism in N-dopedZnO nanowires are systematically studied. The larger aspect ratio of nanowiresfavors the formation of oxygen vacancy and out-diffusion of substitutional N (NO), makingNO in ZnO nanowires always compensated by hydrogen interstitials (HI). Our results can help to explain the challenge in getting p-type ZnO and shed new lighton the possible realization of p-type doping of ZnO in the future.

Silicon Dioxide as a Boundary for Oxygen Outdiffusion from CZ-Si

Oxygen out-diffusion from CZ-Si or in-diffusion into FZ Si was studied with Secondary Ion Mass Spectrometry. For anneals up to 1200oC , the value of 16O concentration Csurf that develops at the semiconductor surface in bare wafers with ~2 nm thick natural oxide was found to be comparable to that in thermally oxidized wafers with 260 nm thick SiO2. Beyond this temperature, at 1280oC, Csurf in non-oxidised sample appears 5 times lower that in the oxidised one. This means that the spontaneous oxide becomes permeable to the oxygen species and no longer constitutes a barrier preventing the oxygen atoms from direct out-diffusion into the ambient. The effect becomes more pronounced when the specimens were heated to 1150oC in a chamber evacuated to ~ 10-7 Torr. The resultant bare Cz-Si and, to even greater extent, FZ Si with previously in-diffused oxygen exhibited deep oxygen depletion, 10x below the respective values for annealing under atmospheric pressure. Undoubtedly, it is the removal of residual oxides by sublimation that enables oxygen atoms to freely out-diffuse into vacuum.

Thermal stability of TiN metal gate prepared by atomic layer deposition or physical vapor deposition on HfO2 high-K dielectric

In this paper, the thermal stability of TiN metal gate with various composition prepared by different preparation technology [(e.g., atomic layer deposition (ALD) or physical vapor deposition (PVD)] on HfO2 high-K dielectric is investigated and compared by physical and electrical analysis. After annealing of the TiN/HfO2 stack at 1000 °C for 30 s, it is observed that: (1) Nitrogen tends to out-diffuse from TiN for all the samples; (2) Oxygen from the interfacial layer (IL) between HfO2 and Si tends to diffuse toward TiN. PVD Ti-rich TiN shows a wider oxygen distribution in the gate stack, and a thinner IL than the N-rich sample. Ti penetration into HfO2 is also observed in the Ti-rich sample, which can potentially lead to the dielectric break-down. Besides, the oxygen out-diffusion can be significantly suppressed for ALD TiN compared to the PVD TiN samples.

Oxygen out-diffusion from buried layers in SOI and SiC–SOI substrates

We have made a comparative study of the oxygen out-diffusion process during heat treatment of SOI wafers and SiC–SOI hybrid substrates. SOI materials with three different thicknesses (2, 20 and 410nm) of buried oxide (BOX) were used in the investigation. High-resolution cross-sectional transmission electron microscopy (HRXTEM) together with laser interferometry was used to determine the remaining thickness of the BOX-layer after heat treatment. After complete removal of the BOX-layer of SOI wafers, the Si/Si interface appears to be sharp and defect-free. Similar results were obtained for SiC–SOI hybrid substrates after removal of the entire buried oxide layer. For all combinations investigated oxide removal was accompanied by a thickness reduction and roughening of the silicon surface layer as verified by atomic force microscopy (AFM).

Trans-R<sub>P</sub> Gettering and Out-Diffusion of Oxygen Implanted into Highly B-Doped Silicon

Implantation of 18O into highly B-doped and undoped silicon provides the possibility to investigate the effect of B-doping and to distinguish the processes of in-diffusion and out-diffusion of oxygen by profiling of 16O and 18O, respectively. The simultaneous in- and outdiffusion of oxygen was observed at 1000°C under oxidizing conditions. For silicon, heavily Bdoped to concentrations of 1019 B cm-3, oxygen tends to diffuse out toward the surface. Moreover, a fraction of the oxygen from both sources, implanted 18O and in-diffused 16O, also migrates deep into the substrate and is trapped far beyond the mean ion range RP in the depth of x 3RP at the so-called trans-RP gettering peak. In undoped silicon oxygen accumulation only takes place at vacancy-type defects introduced by ion implantation at a position shallower than RP. The mobility of oxygen implanted into B-doped Si is higher than for implantation into undoped Si. Highly mobile defects are suggested to be formed in B-doped silicon beside the common mobile interstitial oxygen, Oi, and the immobile SiOX precipitates. These I OXBY defects may involve selfinterstitials, I, and O and B atoms. The trans-RP peak appears due to the decay of these defects and the segregation of their constituents.

High-resolution Rutherford backscattering spectrometry study on process dependent elemental depth profile change of hafnium silicate on silicon

Process characterization of HfSiO(N)/SiO(N) films was performed by nondestructive elemental depth profile analysis using high-resolution Rutherford backscattering spectrometry. As-grown atomic layer deposition HfSiO film (2 nm) was found not to be uniform but to have a gradient near the top surface with Si concentration higher than the bulk. Regardless of native oxide removal, HfSiO grown on HF-last Si results in an almost identical interfacial SiOx thickness with that of HfSiO grown on chemical oxide. Dependence of interfacial layer on oxygen transport behavior during high-temperature annealing was also investigated. Whereas only the upward oxygen outdiffusion from the HfSiO layer was observed for the films deposited on HF-last Si and SiON, downward oxygen transport to the bottom interfacial layer was also observed when HfSiO film was deposited on chemical oxide. This result indicates that the bonding properties of chemical oxide are different from those of SiO2 and that chemical oxide can accommodate oxygen ions. Finally, thermal stability of nitrogen in HfSiO introduced by NH3 annealing and plasma nitridation was compared. Nitrogen desorption by spike anneal was only observed for HfSiON film with nitrogen introduced by plasma nitridation process.

Size-dependent resistivity in a micro-processedYBa2Cu3O7−δ superconducting whisker

We report the results of a detailed geometrical and electrical study which has been performed on aYBa2Cu3O7−δ superconducting whisker. This sample has undergone three subsequentsteps of micro-machining by means of a focused ion beam (FIB)instrument, in order to progressively decrease its cross-sectional area from∼77 to∼4 µm2, over a lengthof about 150 µm. A simple analytical model based on the exact shape both of the electrical contacts and ofthe micro-machined material has been proposed for the voltage drop; besides,an accurate geometrical characterization of all of the sample details has beenperformed by means of SEM microscopy. This enabled us to extract accurateelectrical resistivity curves from the resistance versus temperature characteristics foreach of the fabrication steps of the whisker, showing an increase of the sheetresistivity with decreasing cross-sectional area. Among the possible physical reasonsfor such behaviour, inelastic electron scattering at the sample surfaces has beenruled out because of the very short mean free path of carriers in YBCO. Onthe other hand, oxygen out-diffusion and Ga ion implantation due to the FIBprocessing are most likely to be responsible for the observed resistivity trend.

On some Conceptual Considerations for the Finite Element Simulation of the Oxygen Out-Diffusion in Ag-MgO Composites

The presence of atomic oxygen at internal metal-ceramic oxide interfaces signi¯- cantly affects the physical properties of the interfaces which in turn affects the bulk properties of the material. The application of numerical tools such as the ¯nite element method requires some conceptional considerations if results from different finite element meshes of methods should be comparable. This paper summarises some of these thoughts in order to provide the right basis for comparative investigations.

Oxygen out-diffusion in partially melted YBa2Cu3Oy−0.325Ag superconductor at reduced oxygen partial pressure

In this study, we examined the chemical diffusion coefficient of oxygen out-diffusion(\(\tilde D_{out} \)) in partially melted YBa2Cu3Oy (Y123)−Ag superconducting tape produced by the thermomechanical processing of the silverclad precursor (doped with 5 wt.% Ag) containing BaCuO2.5 at reduced oxygen partial pressure (P02). The\(\tilde D_{out} \) value of Y123−Ag (O7.0 to O6.2), obtained by using the thermogravimetric relaxation technique at 950°C and a P02 of 0.28 kPa, was 1.0476×10−7 cm2/s.

Oxygen out-diffusion in partially melted YBa2Cu3Oy−0.325Ag superconductor at reduced oxygen partial pressure

Oxygen out-diffusion in partially melted YBa2Cu3Oy−0.325Ag superconductor at reduced oxygen partial pressure