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We used millisecond flash lamp annealing (FLA) to form thin ferroelectric Hf0.5Zr0.5O2 (HZO) films with thicknesses of less than 10 nm and with remanent polarization up to 30 μC cm−2. A clear dependency of the polarization on the annealing temperature and time was observed, indicating that the precise management of the thermal budget is a key factor in forming ferroelectric HZO. We also show and compare the process windows within which ferroelectricity in 10 and 5 nm samples is obtained. The results show that a high thermal budget is necessary for thinner samples. We examined the endurance characteristics and a greater endurance compared to rapid thermal annealing treatment was observed with more than 1010 cycles without breakdown confirmed in 5 nm thick samples. The data indicates that there is the possibility of further thickness scaling whilst retaining highly durable characteristics for films annealed by FLA.

Stroke-prone spontaneously hypertensive rats (SHRSP/Izm; SHRSP) develop severe hypertension and die of cerebral stroke. However, the genetic mechanisms underlying their stroke susceptibility have not been clarified yet. In this study, we used astrocytes from the newborn brain cortex of spontaneously hypertensive rats (SHR/Izm; SHR) and SHRSP to find the difference of genetic characteristics. Astrocytes are known to have functions of vasodilation and nutrient uptake for neurons in the brain. The continuous generation of hydrogen peroxide (H2O2) dose-dependently causes cell death in astrocytes, and SHRSP was more vulnerable than SHR. We found that the total thiols decreased in SHRSP astrocytes but the total glutathione (GSH) did not change. Hydrogen sulfide (H2S), which is known to protect cells through anti-oxidant and vasodilatory effects, is produced by cystathionine β-synthase (CBS) in astrocytes. We found that H2S production was significantly decreased in SHRSP as compared to SHR. This was caused by the decreasing expression of mRNA, protein and enzyme activity of CBS in astrocytes. We also found that astrocyte cell death from oxidative stress could be prevented by GYY4137 H2S donor. H2S is also known to cause protein S-sulfhydration to modify enzyme activity. Sulfane sulfur in astrocytes was significantly lower in SHRSP and decreased by CBS inhibitor. We showed that astrocytes in SHRSP vulnerable to oxidative stress may be caused by reduction of H2S through lower expression and activity of CBS.

Objective: Increased oxidative stress plays an important role in cardiovascular diseases including hypertension and stroke. Evidence has indicated that ketone bodies could exert antioxidative effects. We explored the role of renal mitochondrial 3-hydroxy-3-methylglutaryl-coenzyme A synthase (HMGCS2) expression, a key control site of ketogenesis, in stroke-prone spontaneously hypertensive rats (SHRSPs) and their ancestral hypertensive but stroke-resistant spontaneously hypertensive rats (SHRs). Methods: Two groups of SHRSPs were fed a standard chow or standard chow supplemented with clofibrate (an agonist of HMGCS2 promoter), respectively, and SHRs fed with a standard chow were used as controls. The renal levels of HMGCS2, Akt, and phosphorylated protein kinase B (Akt) were measured by western blotting. Malondialdehyde, catalase, superoxide dismutase, and glutathione peroxidase were detected by assay kits. Results: Compared with SHRs, lower HMGCS2 protein expression, enhanced phosphorylated Akt signal, higher malondialdehyde levels, and higher catalase activity were observed in kidney tissues in SHRSPs (P < 0.05). No differences in superoxide dismutase and glutathione peroxidase activities were observed between SHRSPs and SHRs. Clofibrate treatment significantly upregulated renal HMGCS2 expressions, inhibited phosphorylation of Akt, and decreased malondialdehyde levels and catalase activities in SHRSP kidney tissues (P < 0.05). Conclusion: These results demonstrated the difference in HMGCS2 expression and oxidative stress in kidney tissues between SHRSPs and their SHR controls. The enhanced oxidative stress was partly due to the lower HMGCS2 expression regulated possibly by the Akt signaling pathway.

It was found that critical dimensions of high-k/metal gates obey the multivariate linear approximation with the precision of 3σ=±0.86nm, whose explanatory variables are amounts of metal compounds remaining on the plasma reactor walls. To measure their amounts, the authors assumed they are proportional to amounts of atoms sputtered out by Ar plasma and falling onto a Si wafers placed on a wafer stage. In this study, effects of metal compounds of W, Ti, Ta, and Hf, which are used to construct full-metal/high-k gates, were measured. It was found that Ti and Ta compounds dominate the fluctuation of critical dimensions and the dependency of their amount on wafer numbers being etched obeys a simple difference equation. From these results, they can estimate and minimize the fluctuations of critical dimensions in mass fabrications.

We have proposed a single metal/dual high-k gate stack for aggressively scaled complementary metal-insulator-semiconductor field-effect transistors (MISFETs). The threshold voltage is controlled by the dual high-k dielectrics, such as MgO- and Al2O3-containing HfSiON for n- and p-type MISFETs, respectively. The gate profile is precisely controlled by taking advantage of a common gate electrode, which will suppress the variation in device performance. Based on this device concept, we have actually fabricated W/TiN/HfMgSiON n-type MISFETs and W/TiN/HfAlSiO p-type MISFETs and have successfully demonstrated a low threshold voltage operation for both of n- and p-type MISFETs.

We investigated the controversial effective workfunction and electron mobility of TiN/HfSiON devices by intentionally adding MgO or La2O3 into HfSiON and by changing the material on TiN or the TiN thickness. As a result, we found a close relationship between the electron mobility at low effective field and the flatband voltage. This relationship is explained on the basis of the fixed charge in HfSiON and its neutralization. The intrinsic workfunction of TiN/HfSiON without charge is determined to be 4.3 eV from the flatband voltage when the electron mobility at low effective field is the highest.

The conduction mechanism of HfSiON stacked-gate dielectric films after a spike annealing is investigated. FETs fabricated using the Damascene process is used to evaluate the electronic characteristics of a stacked-gate dielectric film. The effect of an additional spike annealing after the TiN gate electrode fabrication on the conductivity is analyzed. The electron current over the entire range of gate voltage is increased, while the hole current remains unchanged. The TAT and Schottky analyses derive a consistent energy level of the intermediate trap centers contributing to the electron conduction. The average lifetime is improved by annealing. However, the spike annealing does not change the slope of the TDDB Weibull plots. The average lifetime is improved by annealing. From NBTI analyses, the threshold voltages displayed linearly shifts with increasing injection charge concentration, both with and without the spike annealing. The slope of the threshold voltage shift is defined as a degradation rate.

We have proposed single metal/dual high-k (SMDH) CMISFETs for aggressively scaled devices. The low threshold voltage (Vth) for n- and pMISFETs are obtained by the dual high-k gate dielectrics. The common gate stack for n- and pMISFETs (single metal) is expected to suppress the variation of gate profile. We have successfully demonstrated low-Vth operation of TiN/HfMgO nMISFETs and TiN/HfAlO pMISFETs that were fabricated in a gate first process flow. We also investigated the high-k-induced Vth variation that can be another origin of the Vth variation. As a result, we found that TiN/HfMgO nMISFETs and TiN/HfAlO pMISFETs do not suffer from high-k-induced Vth variation, but that TiN/HfLaO nMISFETs fabricated by our current process suffer from it. Therefore, we need to optimize the La incorporation process, such as, post-deposition anneal, in order to suppress local high-k-induced Vth variation for TiN/HfLaO nMISFETs.

Film thicknesses of W, TiN, and TaSiN in a full-metal gate stack with photoresist masks were measured in real time during plasma etching with an in situ thickness monitor. The accuracy of such measurement was approximately ±1 nm. The monitor functions on the basis of the interference of plasma optical emission, reflected from the surface and base of the film. Although W and TiN have large absorption indexes, their thicknesses were more accurately measured when they became thinner. In particular, W thickness was estimated more accurately when it was smaller than approximately 10 nm.

We have investigated the time dependent dielectric breakdown (TDDB) for a high-k/metal gate p-type metal–oxide–semiconductor field effect transistors (pMOSFETs) under inversion stress. We have found that electrons, injected from the cathode, are minority carriers in the gate leakage current and play an important role in determining TDDB lifetime and that the existence of oxygen vacancies in HfSiON, decide the electron current mechanism in HfSiON. Since electrons from the cathode flow as a tunneling current with the effective barrier height determined by the energy level of the oxygen vacancies in the HfSiON, electron current is strongly dependent on the effective work function of the metal gate. That implies that a higher work function should be effective to suppress of electron current, due to the elevated barrier height for electrons. Therefore, the formation of a high work function metal gate is essential, not only for low threshold voltage of pMOSFETs but also to achieve long TDDB lifetimes.

We propose a novel approach to control the effective work function by taking advantage of crystal structures in metal gate electrodes. The crystal structures determine the predominant material elements at the metal/high-k interface. We have found that, in a Ru-Mo alloy system, a randomly-oriented Ru (fcc) structure promotes the segregation of Mo at the interface, enabling us to achieve a wide controllability of flatband voltage by the amount of 0.6-0.8 eV. In addition, the segregation of Mo within a Ru-rich electrode is a key to reducing Fermi level pinning at the metal/HfSiON interfaces.

Chemical bonding features in metal (TiN or Ru)/HfSiON gate stacks and electrical potential changes due to dipoles at the metal/dielectric interfaces have been studied by back-side x-ray photoemission measurements of the samples after wet-chemical removal of Si substrate. The photoemission threshold of the metal gate measured through the ultrathin dielectric layer confirms that the potential change of the gate metals, which is nearly equivalent to the difference in the flat-band voltage shift between capacitors with SiO2 and HfSiON, is caused by electron transfer from the HfSiON layer to the metal gate near the interface. From the recovery in the gate potential induced by oxygen incorporation into HfSiON, oxygen vacancies in the HfSiON layer are likely to be possible origin of the gate potential change. Also, from the experimental fact that the gate potential change becomes significant with decreasing thickness of the interfacial SiO2 layer below 3.5nm in Ru/HfSiON/SiO2 gate stacks, it is suggested that the generation of oxygen vacancies in HfSiON caused by oxidation reaction of Si substrate through ultrathin SiO2 layer plays an important role on the electron transfer near the Ru/HfSiON interface.

Three SiN offset spacers were compared regarding the suppression of the gate-edge metamorphoses (GEMs) of scaled TaSiN/HfSiON n-type metal–oxide–semicondutor field-effect-transistors. The offset-spacer-induced GEM appears only in short-channel devices as a high threshold voltage (Vth) and a parasitic resistance. On the basis of the device characteristics, the origin of GEMs was hypothesized to be the negative fixed charge in HfSiON on the gate edges. The low-temperature, Cl-free SiN offset spacer is promising for use in scaled metal/high-k devices because it provides the lowest Vth and the highest drivability, particularly in short-channel devices, by suppressing GEMs.

We have investigated the impacts of the nitrogen content in a TaSiNx metal gate on the performance of metal/HfSiON n-type field-effect transistors (FETs). To obtain a low threshold voltage and low electrode resistance, low nitrogen concentration in TaSiNx is preferable. However, the use of a TaSi gate ([N] = 0%) causes the degradation of HfSiON dielectric characteristics such as an increase in leakage current under gate negative bias, positive-bias temperature instability lifetime degradation, time-dependent dielectric breakdown lifetime degradation, and reduction of the electron mobility. Then, a low-nitrogen-concentration TaSiN ([N] = 20%) gate shows the highest electron mobility, excellent reliability characteristics, and low threshold voltage.

RuO2 films were investigated as a work-function-determining metal in metal/high-k gate stacks required for scaled complementary metal–oxide–semiconductor (CMOS) devices. After a low-thermal-budget processing below 400 °C, RuO2 on HfSiON exhibits a high effective work function of about 5.5 eV, which is applicable in p-channel field-effect transistors. However, RuO2 is easily reduced to Ru metal in metal/high-k gate stacks by annealing above 400 °C. Consequently, the high effective work function is unintentionally lowered. This is because RuO2 is thermodynamically unstable when in contact with W and polycrystalline silicon, which are both common components of a metal gate electrode structure. The insertion of TiN and TaN between RuO2 and W does not suppress the reduction. It is concluded that RuO2 is difficult to employ as a metal gate in metal/high-k gate stacks.

This paper describes a fabrication process that uses flash-lamp annealing (FLA) and the characteristics of the CMOS transistors that are constructed with an ultralow-thermal- budget process tuned for 45-nm metal/high-k FETs. FLA enhances the drivability of pFETs with the solid-phase epitaxial (SPE) extension junction, but reducing the thermal budget deteriorates the poly-gate depletion and the electron mobility. Metal gate, however, prevents the depletion problem and leads to higher drain currents and better threshold-voltage (VTH) roll-offs when processed with tilted extension implantation combined with SPE + FLA than when processed with untilted extension implantation combined with spike rapid thermal annealing. Reducing the thermal budget is also effective in obtaining low VTH values in p-metal/HfSiON gate because of the reduced vacancy formation. Moreover, cluster-boron implantation for pFETs has superiority over monomer-boron implantation with Ge postamorphous implantation in terms of VTH roll-offs and Ion-Ioff's if FLA is used as activation. The superior electrical characteristics of full-metal- gate HfSiON transistors whose gate length is less than 50 nm, which are fabricated by using the FLA process, are demonstrated.

Stroke-prone spontaneously hypertensive rats (SHRSP/Izm) are salt sensitive: they develop severe hypertension and die of stroke within a short time after salt loading. We studied the role of cytochrome P-450 (CYP) isoforms in the brain and the effect of clofibrate to investigate the mechanism of salt sensitive stroke-proneness in SHRSP/Izm. Male SHRSP/Izm at 9 weeks of age were fed a regular diet with or without 0.25% clofibrate and given a 1% NaCl solution for drinking water for 10 d. The expression levels of CYP4A1, 2C11, and 2C23 were measured by Western blotting. Cerebral blood flow was measured with a laser Doppler method and blood vessel diameters were measured under microscopic observation. SHRSP/Izm died within 60 d after salt loading; however, clofibrate prolonged the survival (mean life span, 33+/-7 vs. 215+/-23 d, p0.0001) without significant attenuation of the severe hypertension. CYP4A1 and CYP2C11 expression levels were lower in SHRSP/Izm than those in age-matched male spontaneously hypertensive rats (SHR/Izm) in the cerebral cortex (p0.05). Salt loading down-regulated CYP2C11 expression in the cerebral cortex of SHRSP/Izm (p0.05). No obvious change in cerebral CYP4A1 was observed in either salt-loaded SHRSP/Izm or SHR/Izm. Clofibrate significantly up-regulated the expression of cerebral CYP2C11 and significantly attenuated its salt-induced suppression (p0.05). Additionally, clofibrate significantly increased blood vessel diameters (p0.01) and cerebral blood flow (p0.0001). CYP2C11 plays an important role in regulating cerebral blood flow and, as a result, in preventing stroke in the salt-sensitive stroke-prone SHRSP/Izm.

We have succeeded in imaging the leakage sites of hafnium silicate gate dielectrics of metal-oxide-semiconductor field-effect transistors (MOSFETs) by using electron-beam-induced current (EBIC) method. Leakage sites of p-channel MOSFETs were identified as bright spots under appropriate reverse bias condition when the electron beam energy is high enough to generate carriers in the silicon substrate. Most of the leakage sites were observed in the peripheries of shallow trench isolation. These results suggest that some process induced defects are the cause of leakage in these MOSFETs. Our observation demonstrates the advantage of EBIC characterization for failure analysis of high-k MOSFETs.

Objective Caveolin-1 (Cav-1) is considered as a negative regulator of endothelial nitric oxide synthase (eNOS) and influences various cardiovascular functions. The objective of the study is to investigate the effects of high-fat diet on vascular Cav-1 expression and eNOS activities. Methods Male outbred Sprague-Dawley rats were fed with a high-fat diet for 15 weeks to induce obesity. The diet-induced obese (DIO) rats were then divided into two groups. One group (DIO-LF) was fed a normal diet and another group (DIO-HF) along with diet-resistance (DR) rats were fed a high-fat diet for 8 more weeks. Cav-1 expression was determined using reverse transcription (RT)-PCR, Western blotting, and immunohistochemistry techniques. NOS activities were assessed using Griess reagents. Protein kinase B (PKB/Akt) and eNOS expression and phosphorylation were determined by Western blotting. Results A high-fat diet up-regulated Cav-1 and down-regulated eNOS expression in aorta of DIO rats, but not in that of DR rats. These effects were reversed in DIO rats after switching to a low-fat diet for 8 weeks. Decreased NOS activities in aortas were observed in DIO rats, but not in DR rats. Phosphorylation of PKB/Akt and eNOS (Ser1177) were enhanced in aortas of DIO rats of both DIO-HF and DIO-LF groups. Conclusion These findings suggest that the decrease of vascular NOS activities in rats fed a high-fat diet were due, at least in part, to the up-regulation of Cav-1 expression.

Methods of improving Fermi-level pinning of pure metal gate electrodes on Hf-based high-k dielectrics have been investigated. The pinning phenomenon is a crucial problem, resulting in an unintentional threshold voltage increase in p-MOSFETs when applying pure metal gate electrodes such as Ru and TiN in Hf-based high-k CMOS. After systematic investigation of the relation between oxygen vacancies in Hf-based high-k dielectrics and electrical characteristics, we concluded that the Fermi-level pinning is unavoidable in principle with a thin EOT, but is a stable phenomenon that should be intentionally utilized. It is necessary to modulate the stable pinning energy position of Hf-based high-k dielectrics in p-MOSFETs in order to obtain thin EOTs in the gate-first process.

Vacancy-type defects in MOSFET structures fabricated with high-k (HfSiON) gate dielectrics were studied by monogenetic positron beams. An expansion of open volumes in HfSiON fabricated on Si substrates using atomic layer deposition technique was observed with increasing nitrogen concentration. This fact was discussed in terms of a role of nitrogen in Hf-related oxide using results obtained by first-principles calculation and XPS. MOSFETs fabricated by F-channel implantation technique were also characterized. The major defect species which causes the Vth shift of MOSFETs was identified as vacancy-fluorine complexes (such as V3F2) locate in channel regions of Si substrates. The preset work suggests that positron annihilation can be used to detect microscopic defects in MOSFETs, and it is a useful tool for determining process parameters for MOSFET fabrications with high-k gate dielectrics.

Ionicity has been raised as an important factor in discussing defect formation in Hf-based oxides. It has been elucidated from our first-principles calculations, that the stability of defects is dominated by Coulomb interactions between charged defects and surrounding ions. For instance, the formation energy of positively charged oxygen vacancies (VO+2) is markedly decreased when they are coupled with substitutional N atoms at O sites, as the nominal charges of N3- are negatively greater than those of the oxygen ions O2-. Our computational results have further revealed that the ionic character of Hf causes generation of a low-lying Si dangling bond level in Si doped HfSiOx. These results suggest that one must take into account the ionicity of the Hf-based compounds, which possess totally different properties from the conventional gate insulator SiO2 in terms of defect formation.

Leakage current characteristics with significantly reduced dispersion were achieved for HfSiON gate dielectric film by selecting TiN gate electrode with low reactivity, compared to the conventional poly-Si gate. The breakdown lifetime and its characteristic homogeneity were also enormously improved. With intensive study on these electrical characteristics, it was concluded that the concentration of oxygen vacancy was significantly reduced, giving rise to the homogeneity improvement. Moreover, we have shown an explanation for the dielectric breakdown in terms of oxygen transport in the Hf-based dielectric film.

High-dielectric constant (high-k) gate materials, such as HfSiOx and HfAlOx, fabricated by atomic-layer-deposition techniques were characterized using monoenergetic positron beams. Measurements of the Doppler broadening spectra of annihilation radiation and the lifetime spectra of positrons indicated that positrons annihilated from the trapped state by open volumes that exist intrinsically in amorphous structures of the films. The size distributions of the open volumes and the local atomic configurations around such volumes can be discussed using positron annihilation parameters, and they were found to correlate with the electrical properties of the films. We confirmed that the positron annihilation is useful technique to characterize the matrix structure of amorphous high-k materials, and can be used to determine process parameters for the fabrication of high-k gate dielectrics. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We have studied the effect of tantalum–silicon–nitride (TaSiN) metal electrode thickness on the electrical properties of ultrathin HfSiON gate dielectrics formed by atomic layer deposition (ALD) technology using Hf(N(CH3)(C2H5))4 and SiH(N(CH3)2)3 precursors. The TaSiN/HfSiON gate stacks were intended for use in conventional metal gate transistors with a high temperature thermal budget of 950 °C. Leakage current, effective mobility and the drain current in 30 nm thick TaSiN gate electrodes were improved with respect to the values for 10 nm thick TaSiN gate electrodes. From back-side secondary ion mass spectrometry (SIMS) analyses, it was concluded that thick TaSiN gate electrodes suppressed the nitrogen diffusion from the SiN hard mask into HfSiON/SiON gate stacks during activation annealing.

The effect of gate metal film stress on the performance of gate-last metal–oxide–semiconductor field-effect transistors (MOSFETs) with a W/TiN/SiO2 gate stack was investigated. The channel strain induced by the electrode film was controlled by the W film stress. The W film stress was determined by the deposition method and film thickness. The compressive and tensile stresses of the electrode film enhance nFET and pFET performances, respectively. The enhancements of the performances are introduced not only by the stress of the film on the channel but also by the stress of the film on the side in the groove of the gate-last MOSEFTs. Metal electrode stress can be a further controlling factor in the performance of scaled devices.

The impact of TiN deposition on thin high-k (HfO2 and HfSiON) films formed on Si substrates was studied using monoenergetic positron beams. For the predeposition sample, the positrons implanted into Si diffuse toward the high-k/Si interface under the influence of the electric field, suggesting the presence of negative charges in the high-k films. After TiN was deposited on HfO2, positive charges were introduced at the TiN/HfO2 interface, which were associated with the incorporation of nitride into HfO2, resulting in the formation of positively charged oxygen vacancies (VOs). From the isochronal annealing experiments for TiN/HfSiON/Si, it was found that positively charged defects (such as VO) were introduced into HfSiON after annealing at 700–900 °C. These defects were introduced by the interaction between TiN and HfSiON, resulting in the formation of polycrystalline TiO2 at the interface. The positively charged defects were annealed out at 1100 °C, but the dielectric properties of HfSiON degraded.

We have studied the electrical and breakdown characteristics of 5 nm-thick HfSiO x N y (Hf/(Hf + Si) =∼0.43, nitrogen content = 4.5-17.8 at.%) in Al-gate and NiSi-gate capacitors. For Al-gate capacitors, the flat-band shift due to positive fixed charges increases with the nitrogen content in the dielectric layer. In contrast, for NiSi-gate capacitors, the flat band is almost independent of the nitrogen content, which is presumably controlled by the quality of the interface between NiSi and the dielectric layer. The leakage current markedly increases with nitrogen content. Correspondingly, although the time-to-soft breakdown, t SBD , gradually decreases with increasing nitrogen content, the charge-to-soft breakdown, Q SBD , increases with the nitrogen content. For Al-gate capacitors, the Weibull slope of time-dependent dielectric breakdown (TDDB) under constant voltage stress (CVS) remains constant at ∼2 for a nitrogen content of up to 12.5 at.% and then decreases to unity at 17.8 at.%. This must be a condition critical to the formation of the percolation path for breakdown. In contrast, for NiSi gate capacitors, a Weibull slope smaller than unity was obtained, suggesting that structural inhomogeneity, involving defect generation, is introduced during the NiSi gate fabrication, but this negative impact is reduced with nitrogen incorporation.

We consider the cause of different behavior of effective work function of gate metals after high and low temperature treatments. After high temperature treatment, reaction between Hf-based high-k dielectrics and a Si substrate generates oxygen vacancies (Vo) in high-k dielectrics, which leads to the subsequent electron transfer from Vo to gate metals. As a result, effective work function of gate metals becomes small and Fermi level pinning of gate metals occurs. Thus, Fermi level pinning is unavoidable phenomena for gate-first- processes. On the other hand, intrinsic hybridization between metal and high-k wave function at the interface is crucial factor to determine effective work function of gate metals after low temperature treatment. Accordingly, interface structures and band structures of metals govern the intrinsic effective work functions of metals.

This paper describes a new NBTI/PBTI evaluation method which uses high-temperature pulsed IV. The benefit of this method is that because the bulk charge is detrapped during the interval before each measurement sequence, only the interfacial component can be extracted. PBTI lifetime of HfSiON, when measured by pulsed IV, is found to be on the line of log(t) vs 1/Vg, contrary to NBTI lifetime which is defined by log(t) vs Vg. Moreover, it is found that temperature dependence of PBTI is smaller than that of NBTI. These findings lead to the conclusion that electric field, rather than thermodynamic energy, affects the reaction at/near Si interface under PBTI stress. PBTI lifetime of TaSiN/HfSiON becomes larger than NBTI lifetime of TiN/HfSiON because of the different Vg dependence.

Silicon dangling bonds (Si-DBs) in HfSiOx have been studied using first-principles calculations. Interestingly, our computational result revealed that the Si-DB-related gap state in HfSiOx locates in a much lower energy region than that in SiOx. This is because Hf atoms enhance the ionic character of the HfSiOx film, which in turn induces a positive charge at the Si site. We consider that the low-lying Si-DB level, which is now very near the N 2p state, contributes to the formation of strong Si–N bonds in HfSiON. The lower shift of the Si-DB level upon cation metal inclusion can be useful information not only for improving the electric properties of high-k gate stacks but also for developing prominent silicon–oxide–nitride–oxide–silicon (SONOS) nonvolatile memories where controllability of the charge trap level is a crucial issue.

The interfacial reaction of a TiN/HfSiON/SiO2 gate stack in high-temperature annealing was investigated from the viewpoint of the redistribution of the elements of gate stack materials. Oxygen incorporation enhanced the redistribution of the elements not only of the dielectric film of HfSiON/SiO2 but also of the gate electrode film of TiN. Oxygen incorporation in high-temperature annealing enhances the partial release of Hf, N, and Si from HfSiON or the disassembly of the HfSiON film, which leads to an increase in the equivalent-oxide thickness (EOT). The EOT increase can be determined by the combination of the decrease in the HfSiON film caused by the Hf and N release from HfSiON and the increase in the interfacial layer created by the oxidation of the Si substrate surface by the penetrating oxygen. It is also found that Ti diffused from the TiN into the interfacial layer through the HfSiON/SiO2. The suppression of oxygen incorporation is a key technique in the high-temperature annealing of metal/high-k gate stacks.

We systematically investigated intrinsic and extrinsic thermal reactions at TiN/HfSiON gate stacks. The formation of an ultrathin TiO2 interlayer was found to be an intrinsic reaction at the metal/insulator interface, but growth of SiO2 underlayers between HfSiON and Si substrates, which determines the electrical thickness of metal-oxide-semiconductor (MOS) devices, depends on the structure and deposition method of the gate electrodes. Physical vapor deposition (PVD) grown TiN electrodes covered with W overlayers exhibited excellent thermal stability at up to 1000 °C. Formation of ultrathin TiO2 interlayers reduced gate leakage current (Ig), and growth of the oxide underlayer was suppressed by less than a few angstroms even for 1000 °C annealing. In contrast, we found that halogen impurities within CVD-grown metal electrodes enhance interface SiO2 growth, resulting in deterioration of equivalent oxide thickness (EOT) versus Ig characteristics of the gate stacks.

We previously showed that 24-h urinary taurine (Tau) excretion was inversely associated with mortality due to coronary heart diseases (CHD) and stroke. The aim of this study was to examine the association between 24-h urinary Tau/creatinine (Cre) ratio and cardiovascular disease risk factors, including body mass index (BMI), blood pressure (BP), serum total cholesterol (TC) and prevalence of obesity, hypertension and hypercholesterolemia.

Typical p-metals show similar effective work functions close to p+ polycrystalline silicon (poly-Si) pinning position irrespective of materials after high-temperature process. We found that this phenomenon can be explained by the modified Vo model taking into account the effect of Si substrate. Oxygen absorption by Si substrate and subsequent electron transfer to metal electrode clearly explain the p-metal Fermi level pinning as well as p+ poly-Si pinning. In addition, unsuppressed Fermi level pinning by insertion of barrier layer at p+ poly-Si/barrier layer/high-k gate stack, which is one of the open issues concerning p+ poly-Si pinning, has the same overall reaction scheme. The modified model also consistently explains this phenomenon.

Thin SiO2 layers were deposited by atomic layer deposition (ALD) using either Bis-dimethylamino-silane (BDMAS: SiH2(N(CH3)2)2) or Tris-dimethylamino-silane (TDMAS: SiH(N(CH3)2)3) precursors. The purpose of this study is to evaluate these precursors for their suitability for ALD of hafnium (Hf)-silicate gate dielectrics. The advantages of these precursors are that the melting points and vapor pressures are moderate. The thickness of SiO2 deposited using ALD process is controlled by the number of growth cycles and the growth rate was different for each precursor, that for BDMAS being 1.5 times that for TDMAS at the same reactor pressure. The carbon impurity in the SiO2 film deposited using BDMAS was about half an order of magnitude less than that using for TDMAS. Furthermore, the carbon impurity was reduced to about the detection limit of secondary ion mass spectrometry after high temperature annealing at 1000 °C during 5 s.

The conventional theory of work functions (Schottky barriers) does not work at pure-metal/high-k-dielectrics interfaces. This occurs due to the selective interface atom bonding reflecting the large ionicity of high-k materials and the characteristic density of p-metal electronic states. Taking into accounts these features, we have constructed a new theory of work functions based on a concept of generalized charge neutrality levels. This theory systematically explains work functions of various gate materials on high-k dielectrics, in particular the unusual behavior of p-metal work functions, and naturally reproduces band offsets at various semiconductor/semiconductor interfaces.

In order to improve the NBTI of pMOSFETs with ultra-thin HfSiON gate dielectrics, a novel plasma nitridation process has been developed. Inclusion of hydrogen in the plasma nitridation ambient brings about an increased NBTI lifetime of about half an order of magnitude. The improvement is due to the suppression of bulk hole traps, presumably originating from the Hf-N bond. Hydrogen in the plasma ambient is thought to prevent the formation of additional Hf-N bonds during post- nitridation annealing.

We have theoretically investigated poly-Si and metal gates on Hf-related high-k gate dielectrics. First, we have investigated the cause of the substantial threshold voltage ( V th ) shifts observed in Hf-related high- k gate stacks with p+poly-Si gates. The oxygen vacancy ( Vo ) level in ionic HfO 2 is located in a relatively higher part of the band gap. If the p+poly-Si-gate is in contact with HfO 2 , Vo formation in the HfO 2 induces a subsequent electron transfer across the interface because of the higher energy level position of Vo , causing a substantial V th shifts in p+poly-Si gate MISFETs. Next, we also investigate the microscopic electronic structures at metal gates/HfO 2 interfaces. We have found that the wave functions of metal induced gap states (MIGS) have large amplitudes both around Hf and O atoms, which may be the cause of unusual work function behaviors of p-like metals. INTRODUCTION The considerable downscaling of Si devises has brought about the requirement for a continuing need for significant reduction in gate dielectric film thickness, and even current commercial based large scale integrated (LSI) circuits have SiO

We have investigated theoretically the cause of the substantial threshold voltage (Vth) shifts observed in Hf-related high-k gate stacks with p+poly-Si gates, by focusing on the ionic nature of HfO2. The oxygen vacancy (Vo) level in ionic HfO2 is located in a relatively higher part of the band gap. This high position of the Vo level results in a significant elevation of the Fermi level for p+poly-Si gates, if the p+poly-Si gate is in contact with the high-k HfO2. Vo formation in the HfO2 induces a subsequent electron transfer across the interface, causing a substantial Vth shifts in p+poly-Si gate MISFETs. Moreover, our theory also systematically reproduces other recent experimental results.

In order to obtain high performance CMOS devices, introduction of new technologies into the front-end fabrication process are required and therefore so-called technology boosters such as strained channel, metal gate, high-k gate dielectrics, thin body SOI, and multi-gate transistor, are proposed so far. Among these technologies, gate stack technology is common key issue for scaled CMOS devices. In this proceeding, we will discuss on high-k gate dielectrics and metal gate technology, and recent achievements of these technologies are reviewed.

We have proposed an area-selective post-deposition annealing (PDA) process that involves a combination of flash lamp annealing and the use of a Si photoenergy absorber (Si-PEA) for metal/high-k gate last metal–insulator–semiconductor field-effect transistors (MISFETs) with NiSi on source/drain (S/D). The process makes it possible to suppress the increase in both the sheet resistance and junction leakage current of NiSi S/D regions. This PDA process also showed optimality for silicide gate electrode formation with silicidation of part of the Si-PEA. It was found that the flash lamp PDA with Si-PEA on nickel–silicide/HfAlOx/SiO2 gate-last MISFETs reduced electron trapping at the gate dielectric and resulted in better PBTI immunity than conventional rapid thermal PDA and flash lamp PDA without Si-PEA.

Changes in optical thickness and equivalent oxide thickness (EOT) during postdeposition annealing (PDA) and postnitridation annealing (PNA) were investigated to fabricate sub-1-nm-EOT nitrided hafnium silicate (HfSiON) gate dielectrics. In spite of optical thickness reductions by PDA, none of the PDA conditions could reduce the EOT and bring about the merit in leakage current reduction. On the other hand, high-temperature PNA without oxygen was found to be effective for reducing both optical thickness and EOT. Furthermore, leakage current reduction ratio and effective mobility were improved by applying high-temperature PNA. Consequently, the fabrication of 0.81-nm-EOT HfSiON gate dielectrics with a gate leakage current of 0.74 A/cm2 at 0.7 V and an electron mobility of 235 cm2/(V s) at 0.8 MV/cm (76% of SiO2) has been realized.

We present in-depth profiling of chemical bonding features and defect state density in ultrathin HfSiOxNy (Hf/(Hf+Si)=~43%) films with average nitrogen contents up to ~18at.% by using x-ray photoelectron spectroscopy (XPS) and total photoelectron yield spectroscopy (PYS) in combination with oxide thinning in a dilute HF solution. The films were prepared on pre-cleaned Si(100) by an atomic layer chemical vapor deposition (ALCVD) method and followed by plasma nitridation. By annealing at 1050°C in N2 ambience, Si-N bonding units in the films are increased as a result of thermal decomposition of Hf-Nx(x=2 and 3) units and the interfacial oxidation accompanied with nitrogen incorporation is caused. For the annealed samples, Hf ions coordinated with two N atoms are distributed with a profile peaked around 1nm from the top surface. Also, from the depth profiles of chemical compositions, which were determined from the change in the intensity at each thinning step, we found that the oxygen content becomes its minimum around ~1.2nm from the surface while the nitrogen content becomes its maximum within ~1.5nm from the surface. The result suggests that the surface re-oxidation is promoted coincidentally with the diffusion of N atoms generated by thermal decomposition of the Hf-Nx units during the N2- annealing. The photoelectron yield from filled defect states in the dielectric stacks was increased in the early stages of oxide thinning and then decreased with further progressive thinning. The depth profile of the defect states, which was derived from the change in the yield, shows that the defect state density becomes its maximum in the near-surface region where oxygen deficiency becomes significant. It is likely that the imbalance in chemical coordination between anions and cations is responsible for the defect generation.

We have constructed a universal theory of the work functions at metal/high-k HfO2 and La2O3 dielectric interfaces by introducing a new concept of generalized charge neutrality levels. Our theory systematically reproduces the experimentally observed work functions of various gate metals on Hf-based high-k dielectrics, including the hitherto unpredictable behaviors of the work functions of p-metals. Our new concept provides effective guiding principles to achieving near-band-edge work functions of gate metals. Moreover, we discuss the potential of the new high-k dielectrics of La2O3 based on this new concept.

A decaborane implantation system has been developed. The maximum beam current achieved at a wafer is 30 μA at 5 keV with the divergence less than 0.4°, which corresponds to the equivalent 500 eV–300 μA boron monomer implantation without an energy contamination. As-implanted secondary ion mass spectroscopy (SIMS) profile of the decaborane implanted at the equivalent energy 500 eV shows the steeper and shallower profile than that of the boron implanted. The result of R s – X j proves the higher activation with shallower junction depth. These advantages possibly arise from the self-amorphization layer by the decaborane implantation.

Objective : The present study was aimed to examine the relation of dietary patterns and oxidative DNA damage to blood pressure (BP) among five Chinese national ethnic populations. Methods : A random sample of 1901 middle-aged Chinese men and women was collected from five ethnic groups in 11 cooperative study centers in China. Results : (1) Significant differences in mean BP, prevalence of hypertension and various dietary markers were observed among the five populations. (2) Na, Na/K ratio and body mass index (BMI) were positively correlated with BP, and magnesium (Mg), 3-methyhistidine (3MH) and taurine were inversely correlated with BP. (3). Factor analyses using eight variables (BMI, Na, K, Na/K ratio, calcium, Mg, 3MH and taurine) yielded three factors that explained 68% of total variance of BP among the five ethnic samples. Conclusion : Geoethnic sensitive and cross-cultural differences should partly explain the diet–BP association.

A polymetal dual gate dynamic random access memory (DRAM) for application specific memory (ASM) with dual nitrogen concentrated oxynitrides was developed for the first time. This technology uses selective nitrogen implantation performed just after gate oxidation. The nitrogen concentration of p-type metal oxide semiconductor (PMOS) in gate dielectric combined with nitrogen implantation and NO (nitric oxide) annealing is sufficiently high to suppress boron penetration, whereas that of the cell array transistor (cell-Tr) and n-type metal oxide semiconductor (NMOS) is sufficiently low to maintain the threshold voltage (Vth) without increasing the channel dosage by using only NO annealing.