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ABSTRACT: This paper reports device process approach for further EOT scaling with small interface state density based on controlling La-silicate/Si interface. The interface state density of 1.6 × 10<sup>11</sup> cm<sup>-2</sup> eV<sup>-1</sup> can be achieved by annealing at 800°C for 30 min in forming gas while significant increase in EOT has been also observed. EOT increase caused by high temperature annealing has been drastically inhibited with MIPS stacks accompanied by high quality interface. The effective electron mobility of 155 cm<sup>2</sup>/Vsec at 1 MV/cm with an EOT of 0.62 nm has been obtained in direct contact La-silicate/Si structure by combination of MIPS stacks with high temperature annealing.
Solid-State Device Research Conference (ESSDERC), 2011 Proceedings of the European; 10/2011
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ABSTRACT: The presence of grain boundaries (GBs) in polycrystalline high-κ (HK) gate dielectric materials affects the electrical performance and reliability of advanced HK based metal-oxide-semiconductor devices. It is important to study the role of GB in stress-induced-leakage current (SILC) degradation and time-dependent dielectric breakdown of polycrystalline HK gate stacks. In this work, we present nanoscale localized electrical study and uniform stressing analysis comparing the electrical conduction properties at grain and GB locations for blanket cerium oxide (CeO2)-based HK thin films using scanning tunneling microscopy. The results clearly reveal higher SILC degradation rate at GB sites and their vulnerability to early percolation, supporting the phenomenon of GB-assisted HK gate dielectric degradation and breakdown.
Applied Physics Letters 02/2011; 98(7):072902-072902-3. · 3.84 Impact Factor
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ABSTRACT: A demonstration of V<sub>FB</sub>/V<sub>th</sub> tuning has been conducted by optimized annealing in oxygen ambient for direct contact of high-k with Si gate stacks. The amount of oxygen atoms has been controlled by optimized annealing temperature and the thickness of the gate electrode. The shift in V<sub>FB</sub> has been confirmed irrespective of gate dielectric materials and the thickness. The V<sub>th</sub> of pMOSFET can be controlled to positive direction by 520 mV without any EOT penalty. Once a shift in V<sub>FB</sub>/V<sub>th</sub> is obtained, the values are found to be stable even after following forming gas annealing.
Solid-State Device Research Conference (ESSDERC), 2010 Proceedings of the European; 10/2010
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ABSTRACT: Vacancy-type defects in plasma immersion B-implanted Si were probed by a monoenergetic positron beam. A positron annihilates with an electron and emits two 511 keV γ-quanta. Doppler broadening spectra of the annihilation radiation were measured and compared with spectra calculated using the first-principles calculations. For the as-doped sample, the vacancy-rich region was found to be localized within 0-10 nm from the surface, and the major defect species were determined to be divacancy-B complexes. After spike rapid thermal annealing at 1075°C, those complexes were annealed out, and turned to B clusters such as icosahedral B<sub>12</sub> distributed between 4 nm and 32 nm from the surface. We will demonstrate that that the positron annihilation technique is sensitive to point defects in shallow junctions formed on Si substrates without influence of B atoms located in the substitutional site.
Junction Technology (IWJT), 2010 International Workshop on; 06/2010
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ABSTRACT: The feasibility of employing yttrium–scandium oxide (YScOx) as high-k gate dielectrics for germanium-metal–oxide–semiconductor (MOS) devices has been investigated. The composition and chemical structures of the film were studied using x-ray photoelectron spectroscopy (XPS). Conduction and valence band discontinuities at YScOx/Ge (1 0 0) interfaces were also determined by measuring the O 1s photoelectron energy loss and valence band spectra. Indeed, high-k (YScOx)/Ge MOS characteristics, exhibiting fairly good electrical characteristics, especially low leakage current density and low density of interface states, have been achieved due to the formation of stable Y-Sc-germanate at the interface. The effects of various scandium oxide (ScO) concentrations in YScOx on the electrical characteristics are also reported. It has been demonstrated that higher ScO concentration in YScOx may cause Vfb to shift to its even lower positive value even if considering hysteresis while it causes degradation in interfacial properties. Besides, the effects of several annealing treatments have been investigated in order to optimize the process conditions. This work suggests that ScO concentration up to 50% in YScOx along with post-metallization annealing treatment at 500 °C will be the key to ensure reasonable electrical performance of Ge MOS devices.
Semiconductor Science and Technology 05/2010; 25(6):065008. · 1.72 Impact Factor
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ABSTRACT: Radio-frequency (rf) performances of a sub-100 nm MOSFET with two different gate dielectrics have been characterized. A 59 nm gate-length field-effect transistor (FET) with a SiON gate dielectric exhibited a cut-off frequency (fT) and a maximum oscillation frequency (fmax) of 178 and 127 GHz, respectively. However, an FET with a HfSiON gate dielectric exhibited 148 and 122 GHz, respectively. The reduction in fT has been found to be attributed to the degradation in the mobility and not to the dielectric relaxation of the HfSiON film. It has been confirmed that the high dielectric constant of HfSiON films can be utilized for future rf CMOS circuits at least up to 40 GHz.
Semiconductor Science and Technology 03/2010; 25(4):045029. · 1.72 Impact Factor
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ABSTRACT: Recently, both electrical and material properties of lanthanum oxide
have been found to significantly improve with a trace amount of nitrogen doping. This work conducted a detailed investigation
on the nitrogen incorporation at the
interface by using X-ray photoelectron spectroscopy (XPS) and capacitance–voltage measurements. The process-dependent chemical
bonding structures of Si, O, and La atoms at the interface were studied in detail. For samples annealed at
and above, the interfacial metallic La–Si bonds were converted into La–N bonds, and some Si–O bonds were found at the interface.
These effects resulted in a significant reduction in the interface trap density. The bulk properties of
were also improved with the proposed technique as a result of the filling of oxygen vacancies with nitrogen atoms.
Journal of The Electrochemical Society. 01/2010; 157(2):G49-G52.
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K. Kakushima,
K. Tachi,
J. Song,
S. Sato,
H. Nohira,
E. Ikenaga,
P. Ahmet,
K. Tsutsui,
N. Sugii,
T. Hattori, H. Iwai
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ABSTRACT: Oxygen bonding in La-silicate film with compositional gradient has been characterized by x-ray photoelectron spectroscopy. Based on an analytical model of bridging and nonbridging oxygen, the O 1s spectra arising from La-silicate layer have been deconvoluted with compositionally dependent parameters. For a composition ratio of 1:1 for SiO <sub>2</sub> and LaO <sub>1.5</sub> on the surface of the La-silicate layer, negative binding energy shifts of 0.35 and 0.10 eV for bridging and nonbridging oxygen, respectively, have been found to well interpret the angle-resolved spectra. The method has also been applied to characterize the temperature dependence of interface reactions at La <sub>2</sub> O <sub>3</sub>/ Si with in situ processed Pt electrode. SiO <sub>4</sub> molecules combined with bridging and nonbridging oxygen atoms have been found to form by high temperature annealing. The thickness of the silicate layer of 0.4 nm at as-deposited state has been found grow up to 2.8 nm after 500 ° C annealing. From rough estimation, it has been revealed that 10% of the newly created bridging oxygen atoms by annealing are incorporated into SiO <sub>4</sub> network which contain also nonbridging oxygen atoms.
Journal of Applied Physics 01/2010; · 2.17 Impact Factor
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K. Kakushima,
K. Okamoto,
K. Tachi,
J. Song,
S. Sato,
T. Kawanago,
K. Tsutsui,
N. Sugii,
P. Ahmet,
T. Hattori, H. Iwai
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ABSTRACT: Band bendings of Si substrates have been observed using hard x-ray photoemission spectroscopy. With a capability of collecting photoelectrons generated as deep as 40 nm, the binding energy shift in a core level caused by the potential profile at the surface of the substrate results in a spectrum broadening. The broadening is found to be significant when heavily doped substrates are used owing to its steep potential profile. The surface potential of the substrate can be obtained by deconvolution of the spectrum. This method has been applied to observe the band bending profile of metal-oxide-semiconductor capacitors with high- k gate dielectrics. By comparing the band bending profiles of heavily-doped n<sup>+</sup> - and p<sup>+</sup> -Si substrates, the interface dipoles presented at interfaces can be estimated. In the case of W gated La <sub>2</sub> O <sub>3</sub>/ La -silicate capacitor, an interface dipole to shift the potential of -0.45 V has been estimated at La-silicate/Si interface, which effectively reduces the apparent work function of W. On the other hand, an interface dipole of 0.03–0.07 V has been found to exist at Hf-silicate / SiO <sub>2</sub> interface for W gated HfO <sub>2</sub>/ Hf-silicate / SiO <sub>2</sub> capacitor.
Journal of Applied Physics 12/2008; · 2.17 Impact Factor
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K. Kakushima,
K. Tachi,
M. Adachi,
K. Okamoto,
S. Sato,
J. Song,
T. Kawanago,
P. Ahmet,
K. Tsutsui,
N. Sugii,
T. Hattori, H. Iwai
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ABSTRACT: Advantage of La<sub>2</sub>O<sub>3</sub> over HfO<sub>2</sub> MOSFET has been experimentally examined. Silicate reaction especially observed at La<sub>2</sub>O<sub>3</sub>/Si interface has been found to suppress the formation of SiO<sub>2</sub> layer to realize direct contact, which is useful for further scaling in equivalent oxide thickness (EOT). Due to the lack of interfacial layer, La<sub>2</sub>O<sub>3</sub> has showed relatively high interfacial state density, however, the effective mobility has exceeded to that of HfO<sub>2</sub> MOSFET. Mobility analysis has revealed an additional Coulomb scattering at small EOT, suggesting the influence of metal gate. A simple mobility degradation model is pointed out using metal induced defects.
Solid-State Device Research Conference, 2008. ESSDERC 2008. 38th European; 10/2008
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K Tsutsui,
M Watanabe,
Y Nakagawa,
K Sakai,
T. Kai,
Cheng-Guo Jin,
Y Sasaki,
K. Kakushima,
P. Ahmet,
B. Mizuno,
T Hattori, H Iwai
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ABSTRACT: A new step-by-step etching technique which is combined with electrical and/or physical analyses for in depth profiling of shallow junctions is proposed. The etching process is composed of scarified oxidation by using ozone and removal of the oxide formed. Combining the etching technique and Hall measurements, concentration profiles and mobility profiles of activated carriers were successfully obtained for the samples doped with boron (B) or arsenic (As) by the plasma doping (PD) method.
Junction Technology, 2008. IWJT '08. Extended Abstracts - 2008 8th International workshop on; 06/2008
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ABSTRACT: From scanning tunneling microscopy, we present unambiguous evidence of thermally induced localized conduction paths exhibiting an asymmetrical conduction property in the high- κ gate stack. The tunneling current under gate injection biasing is found to be much larger than that under substrate injection biasing after a 700 ° C postdeposition anneal, i.e., the localized paths exhibit a much lower resistance under gate injection biasing. This finding provides a phenomenological explanation for the polarity dependent breakdown of the high- κ gate stack as observed from electrical stressing of large-area metal-oxide-semiconductor capacitors.
Applied Physics Letters 06/2008; · 3.84 Impact Factor
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ABSTRACT: The effect of nitrogen implantation on thin lanthanum oxide (La<sub>2</sub>O<sub>3</sub>) films grown by e-beam evaporation are investigated using X-ray photoelectron spectroscopy (XPS), current-voltage (I-V) and capacitance-voltage (C-V) measurements. The amount of nitrogen incorporation in the oxide film by plasma immersion ion-implantation (PII) is found to be quite low (about 3% near the surface). However, the introduction of nitrogen atoms into the La<sub>2</sub>O<sub>3</sub> network results in a significant reduction in the oxide traps and leads to a notable improvement in both material and electrical properties of the dielectric.
Electron Devices and Solid-State Circuits, 2007. EDSSC 2007. IEEE Conference on; 01/2008
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ABSTRACT: The physics and the effects of aluminium incorporation into lanthanum oxide (La<sub>2</sub>O<sub>3</sub>) films were studied by using x-ray photoelectron spectroscopy and electrical measurements. We found that trace amount (5% ) of aluminium incorporation in lanthanum oxide film can suppress the leakage current effectively. The bulk oxide traps and interface traps can also reduced. The percentage of aluminium incorporation into the La<sub>2</sub>O<sub>3</sub> films by plasma immersion ion-implantation needs to be optimized to have the maximum reduction of oxide traps and to maintain the lowest leakage current.
Electron Devices and Solid-State Circuits, 2007. EDSSC 2007. IEEE Conference on; 01/2008
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ABSTRACT: The tunneling current versus voltage characteristic of the Sc2O3/La2O3/SiOx high-κ gate stack is examined using scanning tunneling microscopy in ultrahigh vacuum. Different measurement bias polarities allow information on the location (i.e., in the high-κ or interfacial SiOx layer) of the electronic traps to be extracted. Two types of localized leakage sites may be distinguished. Lowering of the electron barrier height and trap-assisted tunneling are proposed as the two leakage mechanisms.
Applied Physics Letters 01/2008; 92(2):022904-022904-3. · 3.84 Impact Factor
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ABSTRACT: The origin of negative flat-band shift using La<sub>2</sub>O<sub>3</sub> incorporation in HfO<sub>2</sub> dielectrics has been extensively examined. From careful extraction of effective work function of gate electrode and fixed charges at each interface, it has been revealed that La<sub>2</sub>O<sub>3</sub> at high-k/Si substrate or high-k/SiO<sub>2</sub> interface has either large amount of positive fixed charges or an additional dipole of 0.36 V compared to that of HfO<sub>2</sub>/Si or HfO<sub>2</sub>/SiO<sub>2</sub>. Stacked MOSCAPs were fabricated and the C-V characteristics show that flat-band voltage shift is mainly determined by high-k film which is in contact to Si or SiO<sub>2</sub>. Using HfLaO with different La concentration, the amount of shift in flat-band voltage could be well controlled, which might be due to the diffusion or pile-up of La atoms to the interface over 420degC. This study provides further insights in controlling the threshold voltage of HfO<sub>2</sub> based oxides.
Solid State Device Research Conference, 2007. ESSDERC 2007. 37th European; 10/2007
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ABSTRACT: An advanced bilayer gate dielectric stack consisting of Sc2O3/La2O3/SiOx annealed in nitrogen at 300 °C was studied by scanning tunneling microscopy using bias dependent imaging. By changing the sample bias, electrical properties of different layers of the dielectric stack can be studied. At a sample bias of +3.5 V, the conduction band of the La2O3 layer is probed revealing a polycrystalline film with an average grain size of about 27 nm, in good agreement with that determined from planar transmission electron microscopy. High conductivity at grain boundaries, due possibly to dangling bonds, can be observed in this layer, as also observed in grain boundary assisted current conduction in metal-oxide-silicon structures. Imaging at a sample bias of −4 V probes the interfacial SiOx layer and an amorphouslike image of the interfacial layer is obtained.
Applied Physics Letters 09/2007; 91(10):102905-102905-3. · 3.84 Impact Factor
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Y. Sasaki,
H. Ito,
K. Okashita,
H. Tamura,
C. G. Jin,
B. Mizuno,
T. Okumura,
I. Aiba,
Y. Fukagawa,
H. Sauddin,
K. Tsutsui, H. Iwai
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ABSTRACT: A new method of plasma doping that achieves tight control on dosimetry and uniformity has been developed. It uses a self‐regulatory behavior of plasma processes that brings high accuracy on dose control and uniformity within 1.5%. The largest advantage of this self‐regulatory plasma doping (SRPD) is that the accuracy of the process control is much less dependent on the uniformity of the plasma, which makes a revolutionary difference to the plasma process as it becomes free from the primary hardware constraint. A typical doping of boron using B2H6/He gas mixture at dose of 1×1015 ions/cm2 can achieve a uniformity of less than 1.5% across a 300mm silicon wafer when the plasma uniformity above the wafer plane is as poor as 10%. The SRPD process also forms very abrupt junctions such as less than 2nm/decade at the junction depth of 10nm due to an instantaneous amorphization of the wafer surface within the first 5 seconds of the process duration. Combined with the throughput advantage at low energy against the conventional ion implantation, the SRPD offers an ideal performance for USJ formation for 45nm technology node and beyond. © 2006 American Institute of Physics
AIP Conference Proceedings. 11/2006; 866(1):524-527.
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ABSTRACT: A feasibility study of La 2 O 3 , one of the rare earth oxides, for replacing SiO 2 gate oxide for CMOS integrated circuits has been reported. It is found that La 2 O 3 after a proper heat treatment has fairly good electrical properties for gate insulator applications in MOSFETs, namely high barrier height for the conduction band electrons and valence band holes as well as its high dielectric constant. The conduction mechanism of La 2 O 3 gate insulator has been modeled, and has been shown to be mainly by space charge limited current (SCLC). Long channel MOSFETs with La 2 0 3 gate insulator has been fabricated, where the best effective mobility is 319 cm<sup>2</sup>/Vs with 2.3 nm of EOT. Interfacial layer (IL) growth suppression due to heat treatment is also reported.
Electron Devices and Solid-State Circuits, 2005 IEEE Conference on; 01/2006
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ABSTRACT: In this work, the current-voltage (I-V) and capacitance-voltage (C-V) characteristics of thin La 2 O 3 film deposited by e-beam evaporation were measured at several different temperatures ranging from 200 to 400 K and after constant-voltage stressing. Stressing experiment indicates significant generation of traps at duration less than 30 min. Strong temperature dependences were found both for I-V and C-V characteristics. The strong field and temperature dependence I-V curves suggested that the current conduction in the La 2 O 3 film is most likely governed by the phonon-assisted conduction. Temperature dependence high-frequency C-V curves indicate that there are a lot of shallow traps in the bulk of La 2 O 3 film and at the La 2 O 3 /Si interface. Most of the charges trapped at the interface states can be depopulated at 400 K. Those instabilities will cause serious reliability problems for MOS device operations and have to be minimized.
Electron Devices and Solid-State Circuits, 2005 IEEE Conference on; 01/2006
