Heiji Watanabe

Layer-by-layer oxidation of Si(001) surfaces has been studied by scanning reflection electron microscopy (SREM). The oxidation kinetics of the top and second layers were independently investigated from the change in oxygen Auger peak intensity calibrated from the SREM observation. A barrierless oxidation of the first subsurface layer, as well as oxygen chemisorption onto the top layer, occurs at room temperature. The energy barrier of the second-layer oxidation was found to be 0.3 eV. The initia

The correlation between atomic structure and the electrical properties of thermally grown SiO2/4H-SiC(0001) interfaces was investigated by synchrotron x-ray photoelectron spectroscopy together with electrical measurements of SiC-MOS capacitors. We found that the oxide interface was dominated by Si-O bonds and that there existed no distinct C-rich layer beneath the SiC substrate despite literature. In contrast, intermediate oxide states in Si core-level spectra attributable to atomic scale roughn

Thermal decomposition of ultrathin oxide layers (less than 1 nm thick) on Si(111) surfaces was studied by using scanning reflection electron microscopy and scanning tunneling microscopy. Void formation, where the diameter and density of the voids depend on the oxide film thickness, occurred on terraces randomly and independently of the buried steps at SiO2/Si(111) interfaces. Decomposition of the oxide layers caused by the void growth produced atomic-height holes on exposed Si surfaces. The surf

We used scanning tunneling microscopy (STM) to investigate the local leakage current through ultrathin silicon dioxide (SiO2) films grown on Si substrates. Individual leakage sites, which were created by hot-electron injection from the STM tip under a high sample bias of +10 V, were identified from the local change in surface conductivity due to defect creation in the oxide films. When we reversed the stressing polarity (using a negative sample bias) no leakage sites were created in the oxide fi

Reactions at ZrO2/SiO2/Si interfaces during fabrication and postannealing have been studied in detail. The layered structures were fabricated by deposition of a thin Zr layer on a chemical oxide, followed by oxidation in an UHV chamber without air exposure (i.e., in situ reoxidation). On-line x-ray photoelectron spectroscopy was used to show that in situ reoxidation can be used for precisely designing interfacial structures. It was found that the thermal stability of ZrO2/SiO2/Si interfaces cruc

We have developed a multifunctional surface analysis system based on a scanning electron beam for nanofabrication and characterization of surface reactions for fabrication processes. The system performs scanning electron microscopy (SEM), scanning reflection electron microscopy (SREM), Auger electron spectroscopy (AES), and x-ray photoelectron spectroscopy. Nanometer scale resolution is obtained for ultrahigh vacuum (UHV)-SEM while the mechanical pumping instruments are operated. Single atomic s

Abstract The superior physical and electrical properties of aluminum oxynitride (AlON) gate dielectrics on AlGaN/GaN substrates in terms of thermal stability, reliability, and interface quality were demonstrated by direct AlON deposition and subsequent annealing. Nitrogen incorporation into alumina was proven to be beneficial both for suppressing intermixing at the insulator/AlGaN interface and reducing the number of electrical defects in Al 2 O 3 films. Consequently, we achieved high-quality Al

The stability of a ZrO2/SiO2 bilayer on a Si(001) substrate was investigated in terms of thermal decomposition during ultrahigh-vacuum annealing. In spite of the intrinsic thermal stability of the ZrO2/SiO2 system, void nucleation initiated by local defects and the following lateral growth of the voids proceed at temperatures over 900 °C. The remaining Zr atoms accumulate and react with the Si substrate to form silicide (ZrSi2) islands within the voids. It was found that the decomposition temper

Local dielectric breakdown of ultrathin SiO2 films grown on silicon substrates has been investigated by using scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). We found that STM observation can reveal individual quasibreakdown spots created by hot-electron injection into the oxide, as well as features of the topography such as atomic steps on the oxide surface. STS was used to study the local electrical properties of the oxide films before and after electrical stress

La-based high-k gate dielectrics were fabricated by reoxidation of thin La layers deposited on SiO2 underlayers. Interface reaction that causes metal diffusion through the oxide underlayer increases permittivity of the oxide and forms high-quality La–silicate films. We successfully fabricated ultrathin La–silicates of equivalent oxide thickness ranging from 0.75 to 1.6 nm with low-leakage current by controlling the interface solid phase reaction. We characterized degradation in the silicate film

We fabricated high-quality Hf–silicate (HfSixOy) gate dielectrics by utilizing the solid phase interface reaction between physical-vapor-deposited metal–Hf (typically 0.5nm thick) and SiO2 underlayers. Metal diffusion to the SiO2 layer increases the permittivity of the underlayer, while preservation of the initial SiO2∕Si bottom interface ensures good electrical properties of the gate dielectrics. The Hf–silicate layer remains amorphous and the poly-Si∕HfSixOy gate stack endures activation annea

A reliable low pressure vapor etch process was developed for the selective removal of phosphorus‐doped silicon oxides. With this process, a high etch rate ratio of phosphosilicate glass (PSG) and borophosphosilicate glass (BPSG) over undoped oxide is obtained. The high etch selectivity is accomplished by controlling the total vapor pressure and/or the partial pressure. Under the low vapor pressure conditions, adsorption on the oxide surface is suppressed, resulting in a low etch rate of the undo

The energy band structure of SiO2/4H-SiC fabricated on (0001) Si- and (000-1) C-face substrates was investigated by means of synchrotron radiation x-ray photoelectron spectroscopy (SR-XPS). The band structure was found to be dependent on substrate orientation and oxide thickness due to both intrinsic and extrinsic effects that cause charge transfer at the SiO2/SiC interface. Our SR-XPS analysis revealed that the intrinsic conduction band offset of the SiO2/SiC for the C-face substrate is smaller