Masahiko Yoshiki

Interfacial properties of single-crystalline CeO2 high-k gate dielectrics directly grown on Si (111)

Interfacial properties of single-crystalline CeO2 high-k dielectrics directly grown on Si (111) were investigated by comparing metal–insulator–semiconductor field-effect transistors (MISFETs) without any interfacial layer [(w/o-IL); direct growth of CeO2 on Si] and those with an interfacial layer (w-IL). FET characteristics, such as the drain current and the S factor, for the w/o-IL MISFET were much worse than those for the w-IL MISFET. The in-gap states attributed to the oxygen defects were detected in the CeO2 directly grown on Si by x-ray photoelectron spectroscopy measurements. The large interface state density induced by the oxygen defects at the CeO2/Si interface may deteriorate the w/o-IL MISFET performances.

Hole generation by icosahedral B12 in high‐dose boron as‐implanted silicon

It was found that a high concentration of holes was generated without any post‐annealing by boron ion implantation into silicon in the high‐dose region of more than 1×1016 cm−2. X‐ray photoelectron spectroscopy and Fourier transform infrared absorption spectrum revealed that B12 icosahedra were created just after implantation. The generation of holes can be explained by the model in which B12 icosahedra act as a double acceptor.

Hole Generation without Annealing in High Dose Boron Implanted Silicon: Heavy Doping by B12 Icosahedron as a Double Acceptor

A high hole concentration region of about 1×1021 cm-3 was generated without any post-annealing by the implantation of high doses of boron into silicon substrates. X-ray photoelectron spectroscopy (XPS) measurement and Fourier transform IR spectroscopy (FTIR) absorption spectra revealed that B12 icosahedra were created in as-implanted samples. A new model of the generation of holes is proposed in which B12 icosahedron acts as a double acceptor.

Thermally stable ultra-thin nitrogen incorporated ZrO/sub 2/ gate dielectric prepared by low temperature oxidation of ZrN

Ultra-thin nitrogen incorporated ZrO/sub 2/ (ZrON) film is successfully prepared by low temperature oxidation of ZrN. Capacitance equivalent thickness (CET) of 15 /spl Aring/ with Jg=1 mA/cm/sup 2/@ Vg=-1 V is demonstrated. There is no increase in CET up to 1000/spl deg/C. Silicide formation at poly-Si/ZrO/sub 2//Si stack at high temperature annealing is also inhibited. In addition, the boron penetration from p+ poly-Si to Si substrate is substantially suppressed.

Precipitation of Boron in Highly Boron-Doped Silicon

The clustering of boron in highly boron-doped silicon and its influence on electrical deactivation are reported. Highly boron-doped crystalline silicon was fabricated as a starting material by solid phase epitaxy of boron-doped amorphous silicon films. Boron can be supersaturated in the crystallized samples annealed at a low temperature of about 600°C. A lot of precipitates, containing clustered boron, were observed in the samples annealed at high temperatures of about 1000°C. The chemical states and the atomic configuration of boron in samples annealed at various temperatures corresponded to the electrical deactivation of boron.

Diffusion and Segregation of Carbon in SiO2 Films

Diffusion of carbon in SiO2 films and its segregation at the Si/SiO2 interface were investigated using carbon-incorporated borophosphosilicateglass (BPSG) films and carbon-implanted SiO2 films. It was found that carbon atoms diffuse in SiO2 film at a temperature as low as 500° C. Carbon atoms segregated at the Si/SiO2 interface and induced positive charge. The positive charge density was proportional to the segregated carbon concentration. Field emission transmission electron microscopy (FE-TEM) and electron energy loss spectra (EELS) observations revealed that carbon atoms exist on the SiO2 side of the interface, and another carbon-rich phase is formed in SiO2.

Effect of Interface Layers on Phase-Change Recording Material Analyzed by Hard X-ray Photoelectron Spectroscopy Method

The influence of interface layers on the chemical and electronic states of a phase-change recording material, GeBiTe (GBT) alloy, used in high-speed rewritable HD DVD media was investigated for the first time by hard-X-ray photoelectron spectroscopy (HX-PES). The binding state of elements for the amorphous state of the phase-change recording film with interface layers is closer to that of the crystalline state than the amorphous film without interface layers. The density of states (DOS) for the valence band of the amorphous state without an interface layer was smaller than that of the crystalline state. The band-edge energy of the amorphous state without an interface layer was lower than that of the crystalline state by about 0.5 eV. On the other hand, the DOS and the band-edge energy of the amorphous state of GBT with interface layers were almost the same as those of the crystalline state. This result may lead to almost the same carrier density for electrical conduction for the crystalline state as the amorphous state, which is totally unexpected, thus very interesting, because the atomic arrangements should differ from each other. We speculate that these effects are a factor allowing high-speed crystallization.

Effective Work Function Control With Aluminum Postdoping in the Ni Silicide/HfSiON Systems

A simplified method of effective work function (Phi_eff) control to near the Si conduction band edge (<i>Ec</i>) was demonstrated in the Ni fully silicided (Ni-FUSI) gate/HfSiON system. The Phi_eff of NiSi (4.51 eV) decreased and saturated at 4.27 eV, owing to the use of an Al postdoping process, in which the implantation of Al ions into the upper part of the Ni silicide gate electrodes was followed by low-temperature drive-in annealing ( les 500degC) . There is no degradation of the gate leakage characteristics at the Ni-FUSI/HfSiON interface. The metallic state of piled-up Al just at the Ni-FUSI/HfSiON interface seems to be responsible for the Phi_eff near the vacuum work function of Al. The Al postdoping process simplifies a dual metal gate process, owing to single-step Al implantation for nMOS devices without complicated metal etching process for pMOS region. The physical mechanism of bidirectional Phi_eff modulation of Al pileup was also investigated. It was revealed that the opposite Phi_eff modulation, which is the increase in Phi_eff, occurs, owing to the formation of interfacial Al₂O₃ layer at the Ni-FUSI/SiO₂ interface. Although the Al₂O₃ state also formed, it has little influence on the Phi_eff value at the Ni-FUSI/HfSiON interface.

Physical mechanism of effective work function modulation caused by impurity segregation at Ni silicide/SiO2 interfaces

An effective work function (Φeff) modulation caused by impurity doping in Ni-FUSI/SiO2 systems has been systematically investigated. To clarify the physical origin, we reveal the relationship between changes of Φeff modulation factors at gate electrode interfaces and Φeff modulation ranges (ΔΦeff) in two different doping processes (predoping and post-doping). In the predoping process, in which impurities (As or B) are implanted into polycrystalline Si gate before Ni fully silicided gate formation, both the crystal structure of the Ni silicide layer and the impurity concentration at the Ni silicide/SiO2 interface change depending on the impurity species. On the other hand, the impurity post-doping process, in which impurities are implanted and introduced to the Ni silicide/SiO2 interface after Ni silicide formation, makes it possible to introduce the desired amount of impurities into the interface without any structural change of the Ni silicide. In both cases, dependence of ΔΦeff on interface impurity con...

Enhancement of Dielectric Constant due to Expansion of Lattice Spacing in CeO2 Directly Grown on Si(111)

We have investigated the reason behind the enhancement of dielectric constant (e), which occurred in CeO2 directly grown on Si(111). e of directly grown CeO2 is enhanced to 52, which is twice as large as the reported value. From in-plane X-ray diffraction measurements and electron diffraction pattern observations using a transmission electron microscope, it has been found that the lattice spacings in CeO2 were isotopically expanded by 0.6%, as compared with the reported values in bulk CeO2. In addition, from X-ray photoelectron spectroscopy measurements, the existence of oxygen defects in CeO2 was confirmed. The oxygen defects in CeO2 may cause the decrease in coulomb interaction in the ionic crystal, resulting in the expansion of lattice spacings. The enhancement of ion movability, due to the expansion of lattice spacings is considered as the reason behind the enhancement of e.