Papers by Author: Seiichi Miyazaki

Abstract: Nickel- and Platinum-silicide nanodots with an areal density of the order of ~1011cm-2 were successfully formed on thermally-grown SiO2 through a process of ultrathin metal film formation on self-assembled Si quantum dots (QDs) on SiO2 and subsequent remote H2 plasma exposure. Chemical shifts in photoemission spectra of core lines and changes in valence band spectrum and work function value with the remote H2-plasma treatment show that silicidation of pre-grown Si-QDs is promoted by the remote H2-plasma treatment. Electrical separation among so-prepared nanodots was verified from the surface potential change after applying a dc bias between the AFM tip and the sample surface. From temporal decay in the surface potential after electron injection to the nanodots, we confirmed that silicide nanodots have superior charge retention to that of Si nanodots with almost the same size as expected in a deeper potential well for electrons in silicide dots than pure Si-QDs. In the application of silicide nanodots to a floating gate in MOS capacitors, distinct hysteresis characteristics caused by charging and discharging of several electrons per dot were verified by capacitance-voltage measurements.

Abstract: We demonstrated a new fabrication method of Pt- and Ni-silicide nanodots with an areal density of the order of ~1011 cm-2 on SiO2 through the process steps of ultrathin metal film deposition on pre-grown Si-QDs and subsequent remote H2 plasma treatments at room temperature. Verification of electrical separation among silicide nanodots was made by measuring surface potential changes due to electron injection and extraction using an AFM/Kelvin probe technique. Photoemission measurements confirm a deeper potential well of silicide nanodots than Si-QDs and a resultant superior charge retention was also verified by surface potential measurements after charging to and discharging. Also, the advantage in many electron storage per silicide nanodot was demonstrated in C-V characteristics of MIS capacitors with silicide nanodots FGs.

Abstract: Electrical properties of thin high-k dielectric films are influenced (or even governed) by the presence of macroscopic, microscopic and atomic-size defects. For most applications, a structurally perfect dielectric material with moderate parameters would have sufficiently low leakage and sufficiently long lifetime. But defects open new paths for carrier transport, increasing the currents by orders of magnitude, causing instabilities due to charge trapping, and promoting the formation of defects responsible for electrical breakdown events and for the failure of the film. We discuss how currents flow across the gate stack and how damage is created in the material. We also illustrate the contemporary basic knowledge on hazardous defects (including certain impurities) in high-k dielectrics using the example of a family of materials based on Pr oxides. As an example of the influence of stoichiometry on the electrical pa-rameters of the dielectric, we analyze the effect of nitrogen incorporation into ultrathin Hf silicate films.

Abstract: We have formed high density nanodots of nickel silicide (NiSi) on ultrathin SiO2 and characterized their electronic charged states by using an AFM/Kelvin probe technique. Si quantum dots (Si-QDs) with an areal dot density of ~2.5x1011cm-2 were self-assembled on ~3.6nm-thick thermally-grown SiO2 by controlling the early stages of LPCVD using pure SiH4 gas. Subsequently, electron beam evaporation of Ni was carried out as thin as ~1.7nm in equivalent thickness at room temperature and followed by 300°C anneal for 5min in vacuum. XPS and AFM measurements confirm the formation of NiSi dots with an average dot height of ~8nm. After removal of Ni residue on SiO2 by a dilute HCl solution, bias conditions required for electron charging to NiSi dots were compared with those to pure Si-QDs dots and Ni dots. The surface potential changes stepwise with respect to the tip bias due to multistep electron injection and extraction of NiSi nanodots. In addition, it is confirmed that charge retention characteristics of NiSi dots are superior to those of Si-QDs with the almost same size.

Abstract: We have studied uniform growth of crystalline Ge films on quartz plate from VHF (60MHz)-ICP of 10% GeH4 diluted with H2 in the temperature range from 150 to 350°C. By optimizing total gas flow rate, gas pressure, VHF power and antenna-substrate distance, the growth rate as high as 7.4nm/s was obtained at 150°C and increased gradually up to ~7.9nm/s at 350°C. The crystallinity, which was evaluated by Raman scattering measurements as an integrated intensity ratio of TO phonons in crystalline phase to those in disordered phase, reached a value as high as ~93 % at 350°C, but degraded down to 64% at 150°C as a result of the formation of a 60~70nm-thick amorphous incubation (A. I.) layer on quartz. By applying a two-step deposition method at 150°C, in which the GeH4 concentration was selected to be 0.6% for the crystalline nucleation in the first 10s deposition, being as thin as 10nm in thickness, and then changed to 10% GeH4 for the high rate growth, the crystallinity was improved to 78% with keeping an effective growth rate as high as 7.5nm/s, because of a significant increase in the growth rate after the crystalline nucleation.

Abstract: Light emitting diode with MOS structures containing multiple-stacked Si quantum dots (QDs)/SiO2 was fabricated and the visible-infrared light emission was observed a room temperature when the negative gate bias exceeded the threshold voltage. The luminescence intensity was increased linearly with increasing the injected current density. The possible luminescence mechanism was briefly discussed and the delta P doping was performed to obtain the doped Si QDs and the improvement of EL intensity was demonstrated.