Tomohisa Kitano

Infrared studies of transition layers at SiO2/Si interface

We investigated transition layers at the interface of the thin SiO2 film successively etched back by diluted HF, using infrared reflection-absorption spectroscopy. The etching rate of the oxide film reveals that there is a Si-rich transition layer within 0.6 nm of the interface. However, frequency shift in the longitudinal optical phonon due to Si-O-Si asymmetric stretching toward lower wave numbers takes place less than 1.5 nm from the interface. We propose a model in which the transition layer is assumed to be Si-rich suboxide layers caused by the compositional roughness of the SiO2/Si interface. Through estimating the phonon frequencies which depend on the composition of the suboxide structure in this model, we found that the phonon frequency apparently starts to shift at around 1.5 nm from the interface, even if there are suboxide-rich layers within 0.6 nm, which can be caused by 1–2 monolayers of roughness.

BONDING CONFIGURATIONS OF NITROGEN ABSORPTION PEAK AT 960 CM-1 IN SILICON OXYNITRIDE FILMS

We investigated bonding configurations of nitrogen atoms in silicon oxynitride films, resulting in a 960 cm−1 absorption peak, which is a higher frequency than that for Si3N4 (840 cm−1). The 960 cm−1 peak was observed in the films for which an N 1s x-ray photoemission peak was observed with a binding energy of about 398.6 eV, which has been reported as a binding energy associated with the ≡Si–N–Si≡ structure. However, the 960 cm−1 peak was absent in the films for which the N 1s peak was observed at about 397.8 eV, being close to the binding energy associated with the Si3≡N structure. We conclude that the absorption peak at 960 cm−1 arises from the ≡Si–N–Si≡ structure of doubly bonded N atoms with two Si atoms, not affected by any oxygen atoms.

Bias-temperature degradation of pMOSFETs: mechanism and suppression

We investigated pMOSFET Bias-Temperature (BT) degradation by using carrier separation analysis. Electrons tunneling from gate electrode to substrate were found to cause impact ionization at the SiO/sub 2//Si interface and result in the creation of trapped charges and interface states. A higher-concentration boron incorporation into the SiO/sub 2/ film was found to suppress BT degradation. This is considered to be a result of tunneling electron current suppression. Degradation due to BT can also be suppressed by reducing the electric field in the oxide between the gate electrode and drain. In other words, BT degradation is lower for the ON-state than the OFF-state. The electric field between the gate electrode and drain can also be reduced by changing the side wall formation process.

Annealing Properties of Defects in B^+- and F^+-Implanted Si Studied Using Monoenergetic Positron Beams

Annealing properties of defects in F+- and B+-implanted Si were studied using monoenergetic positron beams. For F+-implanted specimen with a dose of 2×1013 F/cm2, before annealing treatment, the mean size of the open volume of defects was estimated to be close to the size of divacancies. After rapid thermal annealing (RTA) at 700° C, vacancy-fluorine complexes and vacancy clusters were formed. The mean size of the open volume for the vacancy-fluorine complexes was estimated to be close to the size of monovacancies, and their annealing temperature was determined to be 800° C. For F+-implanted specimen with a dose of 4×1015 F/cm2, complexes between vacancy clusters and fluorine atoms were introduced during solid-phase epitaxial growth of the amorphous region, and they were observed even after RTA at 1100° C. Effects of additional B+ implantation on annealing properties of defects are also discussed.

Small lattice relaxation at the DX center as studied by extended x‐ray absorption fine structure on Se‐doped AlGaAs

Lattice relaxation at the Se DX center in Al0.38Ga0.62As was determined by the extended x‐ray absorption fine structure (EXAFS). During the EXAFS measurements the deep and shallow (metastable) states of the DX center were prepared and the resultant difference of the nearest‐neighbor distance around Se between the two electronic states was found to be quite small (less than 0.04 A). The result is indicative of small lattice relaxation at the DX center.

Effects of Recoil-Implanted Oxygen on Depth Profiles of Defects and Annealing Processes in P+-Implanted Si Studied Using Monoenergetic Positron Beams

Effects of oxygen atoms recoiled from SiO2 films on depth profiles of defects and annealing processes in P+-implanted Si were studied using monoenergetic positron beams. For an epitaxial Si specimen, the depth profile of defects was found to be shifted toward the surface by recoil implantation of oxygen atoms. This was attributed to the formation of vacancy-oxygen complexes and a resultant decrease in the diffusion length of vacancy-type defects. The recoiled oxygen atoms stabilized amorphous regions introduced by P+-implantation, and the annealing of these regions was observed after rapid thermal annealing (RTA) at 700° C. For a Czochralski-grown Si specimen fabricated by through-oxide implantation, the recoiled oxygen atoms introduced interstitial-type defects upon RTA below the SiO2/Si interface, and such defects were dissociated by annealing at 1000° C.

Synchrotron Plane Wave X-Ray Topography of GaAs with a Separate (+,+) Monochro-Collimator

A plane wave X-ray topographic camera was constructed with a separate (+, +) monochro-collimator system at Photon Factory. Undoped and indium-doped GaAs crystals are topographically investigated. For the undoped GaAs, a two-fold symmetric strain field has been observed in a (001) wafer. In the indium-doped sample, a highly stressed region probably produced by the In segregation has been observed.

Synchrotron plane wave X-ray topography of 6 inch diameter Si crystal

A precision three horizontal axis diffractometer system with large crystal stage was developed. It was used for a synchrotron plane wave X-ray topographic camera for a 6 inch Si wafer. A surface sensitive topograph was taken under the condition of specular reflection by (+, +) double crystal arrangement. Change in lattice distortions as small as 0.2 arc second was detected under the condition of plane wave X-ray topography by (+, +, -) triple crystal arrangement.

High precision goniometer system for topography and diffractometry using multiple crystal arrangement

Abstract A microcomputer controlled precision goniometer system for multiple crystal arrangement topography and diffractometry was constructed. The system consists of three goniometers: (a) ω -2 θ goniometer as a premonochromator and (b) two dual-axis precision goniometers as a collimator system, sample and analyzer system. Each component goniometer is designed so as to be used for both the vertical and horizontal axis.

Generation Rule of the Slip Dislocation in LEC GaAs Crystal

In a (001) low dislocation density wafer, an eight-fold circular strain field was observed near the periphery between and radii. The observed result was explained from the viewpoint of ease of slip dislocation generation by calculation of Schmid factor magnitude distribution under the condition that major thermal stress was applied to tangential direction at the round ingot surface. While, in a (001) high dislocation density wafer, a four-fold strain field was observed around the radii. The result was explained by intersection of slip dislocation generated from eight positions at the periphery between and radii as well.