Formation Of Positive Charge Research Articles

Effect of Al Doping on the Reliability of ALD HfO2

CMOS device scaling below the 22 nm technology node requires gate dielectric materials with superior properties to those of conventional high-k materials. It was found that, Al incorporation into HfO2 results in an increase in the transition temperature from amorphous to polycrystalline state (1-2). Improved thermal stability (2) and enhanced permittivity (3) by Al doping into ALD HfO2 was also reported. As a result of the improvement in film properties, improved equivalent oxide thickness (EOT) values, reduced gate leakage current, lower hysteresis and improved interface quality were also observed for Al doped HfO2 (4-6). However, intermixing of HfO2 and Al2O3 depends significantly on the stack structure, which results in variations in the stoichiometry in the film (7). The relative position of HfO2 and Al2O3 in HfO2/Al2O3bi-layer has a significant influence on positive charge formation in the dielectrics and also on the quality of the interfacial layer (IL) (8-10).In this work, we deposited and studied the reliability of 40 cycles ALD HfO2 doped with Al in the deposition process. The ALD thin film composition was measured by X-ray photoelectron spectroscopy (XPS). Thin films with Al/(Al+Hf)% composition ranging 0% to 8% were deposited and annealed at 800oC in N2 ambient. MOS capacitors were then fabricated with ALD TiN as the metal gate. The electrical measurements show that, devices with ~2% Al/(Hf+Al)% have an optimized performance with 17% lower EOT than undoped HfO2. The amount of positive charge and gate leakage current density were also evaluated for all devices.The reliability of these devices was monitored by subjecting them to a constant field stress at E= 27.5 MV/cm in the gate injection mode, where the applied voltage to the gate was modified according to the EOT to have equal field across all the dielectrics. Stress-induced trap generation in the dielectrics was observed due to bulk and interface defects. Trap formation followed a power law function with stress time. Observed stress induced flat-band voltage shift (Fig. 1) shows that devices with Al/(Hf+Al)% =2% have 36% reduction in the rate of trap generation as compared to HfO2, whereas degraded flat-band voltage shift was observed for devices with Al/(Hf+Al)% =7%. It can be inferred that an optimized Al concentration in HfO2can lead to an improvement of the device performance. In order to further understand the reliability characteristics we plan to evaluate the change in interface state density with stress and their time dependent dielectric breakdown (TDDB) characteristics. References M.-Y. Ho et al., Appl. Phys. Lett., 81, 4218 (2002). H. Y. Yu et al., Appl. Phys. Lett., 81, 3618(2002). P. K. Park et al., Appl. Phys. Lett., 89, 192905(2006). W. J. Zhu et al., IEEE Electron. Dev. Lett., 23(11), 649(2002). V. Mikhelasvili et al., Appl. Phys. Lett., 85, 5950(2004).Y.-K. Chiou et al., J. Electrochem. Soc., 154 (4) G99(2007).M. H. Cho et al., Appl. Phys. Lett., 81, 1071(2002).B. H. Lee et al., Appl. Phys. Lett., 76, 1926 (2000).L. G. Gosset et al., J. Non-Cryst. Solids, 303, 17(2002).W. Wang et al., J. Appl. Phys., 105, 064108 (2009).

Cyclic Plasma Treatment during ALD Hf1-XZrxO2 Deposition

Use of Hf based high-k dielectric materials enabled CMOS device scaling beyond the 22 nm technology node. In order to scale the equivalent oxide thickness (EOT) to 0.7 nm and beyond, while achieving good reliability performance, improvement of the film properties and the deposition methods are highly desirable. It was observed that, the dielectric constant of ALD HfO2 can be improved by the addition of ZrO2 as it offers higher-k tetragonal stabilization when Zr/(Hf+Zr) percentage is more than 50% (1-2). It has recently been reported that the poor dielectric characteristics of ALD grown oxide films, such as the leakage current, can be improved by exposing the dielectric films to a slot-plane-antenna (SPA) plasma (3). Because of low electron temperature the SPA process causes very little damage as compared to conventional inductively coupled plasma (ICP) or electron cyclotron resonance (ECR) plasma (4). Also cyclic treatment during the ALD deposition process by using room temperature ultraviolet ozone, D2O radical, remote microwave N2O plasma, and/or thermal annealing have shown promising results toward improving film properties (5-7). In this study, for the first time, we examined the performance benefits due to the use of intermediate SPA Ar plasma treatment (DSDS) in the ALD deposition process of Hf1-xZrxO2 with 0%, 31% and 80% Zr/(Hf+Zr) percentages and compared them with the standard deposition process (As_Dep). Zr percentage was varied by precisely controlling the Hf-precursor to Zr-precursor pulse ratio in the ALD cycle. MOSCAPs were formed with TiN as gate material, where ALD Hf1-xZrxO2 was deposited on a SiON interface formed by remote plasma radical flow nitridation of chemically grown oxide on a p-Si substrate. It is observed that, DSDS Hf1-xZrxO2with 80% Zr has the lowest dielectric thickness and interfacial layer thickness as compared to others (Fig. 1(a)). Equivalent oxide thickness (EOT) for different Zr percentages for DSDS and As-Dep processing conditions were also compared. Effect of SPA Ar plasma and Zr addition on the reliability of ALD Hf1-xZrxO2 were monitored from the flat-band voltage shift due to a constant field stress at E= 27.5 MV/cm in the gate injection mode (Fig. 1(b)). Also, the gate leakage current density, before and after stress for different devices were monitored. When subjected to a constant field stress traps are generated in the gate dielectric and at the Si-IL interface. DSDS Hf1-xZrxO2with 80% Zr showed the lowest initial flat-band voltage shift after the first 20-second stress and the subsequent increase of positive charge formation was observed as the stress continued. Devices with intermediate Ar plasma have reduced gate leakage current density before stress and after 1000s stress, which implies suppression of oxide trap formation due to plasma exposure. Intermediate Ar plasma exposure to ALD Hf1-xZrxO2with 80% Zr seems to deposit superior dielectric with better EOT downscaling ability and good reliability performance. While Zr addition helps to produce a fine grain microstructure with less oxygen vacancies (2), SPA plasma further helps by reducing contaminants, increasing mass density, and superior bond structure of the film (3).

Dynamics of laser-induced damage of spherical nanoparticles by high-intensity ultrashort laser pulses

Damage of a metal spherical nanoparticle by femtosecond laser pulses is analyzed by splitting the overall process into two steps. The fast step includes electron photoemission from a nanoparticle. It takes place during direct action of a laser pulse and its rate is evaluated as a function of laser and particle parameters by two approaches. Obtained results sug- gest the formation of significant positive charge of the nanoparticles due to the photoemission. The next step includes ion emission that removes the excessive positive charge and modifies particle structure. It is delayed with respect to the photo-emission and is analyzed by a simple analytical model and modified molecular dynamics. Obtained energy distribution suggests generation of fast ions capable of penetrating into surrounding material and generating defects next to the nanoparticle. The modeling is extended to the case of a nanoparticle on a solid surface to understand the basic mechanism of surface laser damage initiated by nano-contamina- tion. Simulations predict embedding the emitted ions into substrate within a spot with size significantly exceeding the original particle size. We discuss the relation of those effects to the problem of bulk and surface laser-induced damage of optical materials by single and multiple ultrashort laser pulses. © 2012 Society of Photo-Optical Instrumentation Engineers (SPIE). (DOI: 10 .1117/1.OE.51.12.121816)

Charge assisted tailoring of chemical functionality at electrospun nanofiber surfaces

Electrospinning using positive and negative polarity applied voltages is used to produce polyamide nanofibers with tailored surface functionality. The surface free energy of the resultant nanofibers is characterized from individual nanofiber wetting experiments. The polar contribution to the total nanofiber surface energy is seen to vary with the polarity of the applied voltage used. A mechanism to describe the change in the nanofiber surface free energy with electrospinning polarity is proposed, based on the formation of either positive or negative charges at the liquid jet–air interface during the electrospinning process. These charges at the liquid jet–air interface cause molecular orientation of chemical functional groups of the polymer chains during electrospinning and the mechanism is supported by subsequent grazing angle X-ray photoelectron spectroscopy (XPS) of the nanofiber surfaces. A one-step electrospinning process is therefore demonstrated to tailor specific chemical functionalities at polymer nanofiber surfaces.

The enhancement of neural growth by amino-functionalization on carbon nanotubes as a neural electrode

This paper reports the success of amino-functionalization on multi-walled carbon nanotubes (MWCNTs) to promote neuronal cells growth on MWCNT electrode for extracellular recording, attributed to the formation of positive charge of NH 2 molecules on their surfaces. Besides, the surface of MWCNT electrode becomes hydrophilic after amino-functionalization (AF-MWCNTs) which can enhance electrical conductivity because of lower MWCNT/electrolyte interfacial impedance and higher interfacial capacitance. Durability tests show that electrical characteristics of the MWCNTs treated by 2 wt% 1,4-diaminobutane solution (2 wt%-AF-MWCNTs) can last for at least six months in air ambient. The neural recording of crayfish shows that 2 wt%-AF-MWCNTs can provide better capability on detecting action potentials of caudal photoreceptor (CPR) interneuron compared to suction glass pipette from the evidence of a higher S/N ratio (126 versus 23). The amino-functionalized MWCNT electrode is feasible for long-term recording application according to the results of biocompatibility tests. As the MWCNTs were directly synthesized on Si-based substrates by catalyst-assisted thermal chemical vapor deposition (CVD) at a low temperature (400 °C), these self-aligned MWCNT electrodes could be friendly implemented in integrated circuits fabrications.

Synthesis and characterisation of novel organopalygorskites for removal of p-nitrophenol from aqueous solution: Isothermal studies

Organopalygorskites were synthesised by using dimethyldioctadecylammonium bromide (DMDOA) and cetylpyridinium chloride (CP) with surfactant loadings equivalent to 100% and 200% CEC of the palygorskite. The four organopalygorskites, thus produced, were characterised by Fourier Transform Infrared Spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and zeta potential measurement. FTIR and TGA data demonstrated that higher surfactant loadings as well as long branched chain DMDOA produced highly ordered surfactant conformation. SEM morphological results showed that the organopalygorskites had less entangled fibres than the unmodified palygorskite. The zeta potential values showed positive charge formation on the organopalygorskites surface when they were synthesised with surfactant loadings equivalent to 200% CEC of the palygorskite. The organopalygorskites were tested for adsorption of p-nitrophenol (PNP) with a special focus on the adsorption isotherms. The adsorption data could be fitted with multiple isothermal models indicating that the adsorption was controlled by multiple mechanisms. Sorbent loading rate, initial pH, temperature and ionic strength might all affect the adsorption process. Also, DMDOA modified organopalygorskites reduced desorption/redispersal of adsorbed PNP back into the environment to a great extent. This study will be helpful in designing palygorskite-based organoclay adsorbents for remediating organic environmental contaminants which are ionic in nature.

Electric field distributions in CdZnTe due to reduced temperature and x-ray irradiation

Real-time Pockels imaging is performed on semi-insulating CdZnTe to measure the electric field profile in the material bulk. In steady-state room temperature conditions the measured electric field profile is uniform, consistent with a low space charge concentration. At temperatures <270 K a significant nonuniform electric field profile is observed, which we explain in terms of temperature-induced band bending at the metal-semiconductor interface, causing the formation of positive space charge in the bulk. Similar electric field distortion effects are observed when room temperature CdZnTe is irradiated by x-rays, causing a high rate of photoinduced charge injection.

Mapping of ion beam induced current changes in FinFETs

We report on progress in ion placement into silicon devices with scanning probe alignment. The device is imaged with a scanning force microscope (SFM) and an aligned argon beam (20keV, 36keV) is scanned over the transistor surface. Holes in the lever of the SFM tip collimate the argon beam to sizes of 1.6μm and 100nm in diameter. Ion impacts upset the channel current due to formation of positive charges in the oxide areas. The induced changes in the source–drain current are recorded in dependence of the ion beam position with respect to the FinFET. Maps of local areas responding to the ion beam are obtained.

A combined experimental and theoretical investigation on the oxygenation of organic sulfides by oxo(salen)chromium(V) ion

AbstractThe mechanism of oxygenation of organic sulfide by oxo(salen)chromium(V) complexes has been studied experimentally and by the density functional theory (DFT) method. Spectral studies show DMSO ligands bind with the Cr center of oxidant and the adduct formed was responsible for the oxygenation reaction. The reaction was first order with respect to oxidant and substrate. Hammett plot shows the formation of positive charge over sulfur atom and the development of negative charge over the oxidant in the transition state (TS). For the substrate ρ values are in the range from −1.5 to −1.8. The geometry has been correctly predicted by the B3LYP function, and it gives better results for spin states, harmonic frequencies, and thermodynamic energies for the system. DFT results indicate the existence of oxo(salen)chromium(V) and Cr(III)–salen at doublet and quartet as ground state, respectively. Binding of donor ligand weakens the CrO bond. TS structures show an increase in the negative charge and spin density over Cr atom indicating the involvement of spin inversion and radical character. The low activation energy and high free energy change are responsible for the enhancement of the reaction rate and product yield in the presence of DMSO donor ligand, while the rebound mechanism and the direction of substrate approach perpendicular to the salen plane are responsible for their higher selectivity. From this combined study, a mechanism involving consecutive two‐electron transfer from the oxo(salen)chromium(V) ion to the electron‐rich sulfur atom is proposed. Copyright © 2008 John Wiley & Sons, Ltd.

On the Formation of Positive Charges in Ultrathin Silicon-Oxynitride p-MOSFETs Subjected to Negative Bias Temperature Stress

p-MOSFET negative bias temperature instability (NBTI) has become the most important reliability issue for the CMOS industry. This letter investigates the formation of oxide positive charges (PCs) and its effects on the NBTI. Evidence shows that PC dominates NBTI at stress temperature lower than 373 K, whereas interface-state generation has an obvious contribution above 373 K. Two kinds of PC are distinguished as follows: The trapped holes are the main origin of NBTI at lower temperatures, and the generated PC plays a role at higher temperatures. The physical mechanisms of the two kinds of PC are also discussed in this letter.

On positive charge formed under negative bias temperature stress

As nitrogen concentration in silicon oxynitride (SiON) increases, negative bias temperature instability (NBTI) becomes a limiting factor for device lifetime. Despite recent efforts, there are confusions and issues remaining unsolved. One of them being how important positive charge formation in SiON is for NBTI and whether all positive charges are the same type. The objective of this work is to investigate positive charge formed in SiON during negative bias temperature stress (NBTS). In comparison with the positive charge formed during substrate hole injection where interface state generation is negligible, it will be shown that NBTS can induce three different types of positive charges: as-grown hole trapping, antineutralization positive charge (ANPC), and cyclic positive charge. Efforts have been made to search for the feature of NBTI, which cannot be explained without involving positive charge. It is unambiguously identified that the impact of measurement temperature on NBTI originates from only one type of defect: ANPC. By using the “on-the-fly” measurement technique, the positive charge density observed in a 2.7nm SiON can reach to the upper half of 1012cm−2, which is comparable with the positive charge reported for relatively thick SiO2 (>5nm). The relative importance of positive charge formation depends on measurement interruption time. The shorter the interruption, the more important positive charge becomes for NBTI.

Impact of gate materials on positive charge formation in HfO2∕SiO2 stacks

The use of metal gates removes gate depletion and allows aggressive downscaling of equivalent oxide thickness. The impact of changing gate from poly-Si to metal on device reliability has not been fully addressed. This work focuses on how TaN gate affects the positive charge formation in HfO2∕SiO2 stacks. Under positive gate bias stresses, the results show that positive charge formation in metal-gated samples is significantly higher than in poly-Si gated samples. However, positive charge formation is similar in these two types of samples, when stressed under negative gate bias. The results are explained by assuming that there are more hydrogenous species at the metal/dielectric interface and the hydrogen release from the anode dominates the positive charge formation. The behavior of positive charges in the stack is also compared with that in a single SiO2 layer.

Worst case stress conditions for hot carrier induced degradation of p-channel SOI MOSFETs

In this paper a comprehensive study of the worst case hot carrier stress conditions for p-channel partially depleted SOI MOSFETs is carried out. It is found that while stress at maximum gate current results to the conventional PMOSFET degradation mechanism (i.e., electron trapping in the gate oxide on the drain side), significant damage is also introduced following stress at the high gate/high drain voltage ( V G = V D) condition. A series of experiments unambiguously demonstrate that this damage is not caused by hot hole injection and that device degradation mechanism at V G = V D stress condition (formation of interface states and positive oxide charges) is in fact due to negative bias temperature instability which is activated because of the self-heating effect. In addition, stress at high temperature is found to result in a shift of the worst case stress condition from maximum gate current to V G = V D.

Radiation tolerance of epitaxial silicon detectors at very large proton fluences

Detectors processed on epitaxial silicon are a promising solution for the extreme radiation levels in the innermost tracking layers at future particle physics experiments as in the upgraded (S-LHC). In order to systematically investigate their radiation tolerance, sets of 25 and 50-μm-thick diodes had been irradiated with 24 GeV/ c protons up to fluences of Φ eq=10 16 cm −2. The full depletion voltage was measured during full isothermal annealing cycles at both 60 and 80 °C. A voltage of only 290 V was measured for the 50 μm diodes after Φ eq=10 16 cm −2. In contrast to likewise thin float zone (FZ) diodes, the depletion voltage in epi-devices decreases with annealing during foreseen operational and storage periods. Low-temperature storage during beam-off periods as inevitable for FZ devices could be avoided. The reverse annealing components reveal an overall similar functional time dependence as observed in FZ diodes. However, the most important stable component is drastically different. In contrast to the well-known negative space charge build up observed in FZ diodes, the behavior in epi-diodes can only be explained by an additional formation of positive space charge. The immense improvement of the radiation tolerance of epi-detectors is thus attributed to a compensation effect between acceptor generation and donor creation unique for the epi-material. Charge collection efficiency drops only to about 80% after Φ eq=6×10 15 cm −2 proving that epi-detectors are indeed adequate candidates for the tracking area at extremely large radiation levels.

Effects of hydrogen on positive charges in gate oxides

Positive charge formation in gate oxides is a main source for the instability of the state-of-the-art metal-oxide-semiconductor device. Despite past efforts, the relation between hydrogenous species and positive charges is not fully understood. In this work, the effects of hydrogen on positive charges will be investigated at both elevated temperature (e.g., 400°C) and room temperature. At 400°C, it is found that hydrogen can convert some defects into hole traps. Three different types of positive charges have been reported recently. They are as-grown hole traps, anti-neutralization positive charges (ANPC), and cyclic positive charges (CPC). Although an exposure to hydrogen at 400°C neutralizes all three, impacts of hydrogen on these three types of defects are markedly different. After the hydrogen-induced neutralization, the defect responsible for ANPC is fully recovered and is the same as that in a fresh device. In contrast, the defect for CPC is not fully recovered and can be reactivated easily by stresses. The as-grown hole trap can be converted to ANPC through hydrogenation. At room temperature, it will be shown that there are two parallel processes for forming positive charges. One involves hydrogen and the other is through hole trapping. The relative importance of these two depends on the relative density of hydrogen against that of holes.

Hole Traps in Silicon Dioxides—Part I: Properties

As the downscaling of gate oxides continues, trap density in the oxide bulk will reduce, but positive charges formed near to the SiO/sub 2//Si interface become relatively important. For gate oxides used in industry, hole trapping is the most important process for positive charge formation. Apart from as-grown hole traps, we recently reported that new hole traps were generated by electrical stresses. Information on these hole traps, however, is still limited. In part I of this work, properties of both generated and as-grown hole traps are investigated. For the first time, it will be clearly shown that generated hole traps consist of two components; cyclic positive charges (CPC) and antineutralization positive charges (ANPC). The charging and discharging rates of CPC are similar, while the neutralization of ANPC is much more difficult than its charging. Differences between them are also observed in generation kinetics and dependence on measurement temperature. Efforts will be made to explain their differences in terms of energy levels and to link them with positive charges reported in earlier works. We will also show that as-grown traps, regardless their distance from the interface, are not responsible for either ANPC or CPC. This is to say that generated hole traps are not the same as as-grown traps and their differences will be highlighted. In part II, hole trap generation mechanisms will be investigated.

Molecular weight dependent electroluminescence of silicon polymer near-ultraviolet light-emitting diodes

We investigated the electroluminescence (EL) of single-layer near-ultraviolet (NUV) light-emitting diodes (LEDs) made from poly[bis(p-n-butylphenyl)silane] (PBPS) with three different molecular weights (MWs). Although the NUV EL spectra of the three LEDs exhibited no noticeable differences, we observed a marked MW dependence on such aspects of the operating performance as the EL external quantum efficiency, EL threshold current density and electric field, which were improved as the MW of PBPS decreased. The MW dependence of the hole transport behavior suggested that the MW decrease promoted positive space charge formation in the PBPS layer during LED operation. We attributed the origin of the MW dependence of the LED performance to this positive space charge formation, which played an important role in improving the electron–hole supply balance from the external electrodes of the LED.

Temperature dependence of capacitance/current–voltage characteristics of highly (0001)-oriented YMnO3 thin films on Si

Highly (0001)-oriented YMnO3 thin films on Si(100) substrates were obtained by using a stable precursor solution and rapid thermal annealing at a low temperature of 650 °C in a chemical solution deposition process. Temperature-dependent capacitance–voltage (C–V) and current–voltage (I–V) characteristics were discussed in a metal-ferroelectric-semiconductor structure. At 300 K, the voltage-dependent increase of the memory window (ΔV) in the C–V curve and the asymmetric I–V curve were attributed to the formation of positive interfacial charges by field- and thermal-excited electron transport. On the other hand, at 220 K, the voltage-independent ΔV was attributed to ferroelectric polarization switching.

Electrical stress and plasma-induced traps in SiO 2

High field stress and N 2 reactive ion etching (RIE)-mode plasma-generated positive oxide charge in thin (13 nm) SiO 2–Si structures have been studied. A threshold field of about 8.5–9 MV/cm for positive charge formation is found. It is established that both high field stress and RIE-like plasma treatment create nonuniformly distributed positive charge in the depth of the oxide, in the form of bulk traps and slow states. It is found that the generation of neutral bulk traps is an attribute, only of the high field stressing. The structural nature of the process-induced traps is discussed. It is suggested that the impact ionization of oxygen vacancies accounts for the positive charge and neutral trap creation.

Association of high-temperature kink-effect in SIMOX SOI fully depleted n-MOSFET with bias temperature instability of buried oxide

A high-temperature drain current “jump” in fully depleted SOI n-channel MOSFET is reported for the first time. The phenomenon appears in the SIMOX SOI MOSFETs at temperatures above 200°C after a negative voltage is applied to the substrate. Direct link of the current “jump” with the positive charge formation in the buried oxide (BOX) has been demonstrated. The current “jump” or a front channel high-temperature kink-effect is explained by electron retrapping in the (BOX) in the vicinity of the BOX-silicon body interface.