Mitsutoshi Takahashi

Suppression of parasitic bipolar action in ultra-thin-film fully-depleted CMOS/SIMOX devices by Ar-ion implantation into source/drain regions

This paper proposes a new technique that can effectively suppress the parasitic bipolar action (PBA) in ultrathin-film fully-depleted (FD)nMOSFETs/SIMOX with a floating body. In this technique, recombination centers are created in the source and drain (S/D) regions by deep Ar-ion implantation. They act to reduce the number of holes that accumulate in the body region by increasing the hole current flowing from the body region into the source region. Consequently, the rise of the body potential is lowered, and the parasitic bipolar action can be suppressed. A 0.25-/spl mu/m gate nMOSFET/SIMOX fabricated with an Ar dose of 2/spl times/10/sup 14/ cm/sup -2/ exhibited excellent improvements in electrical characteristics: a reduction in the off-leakage current of over two orders of magnitude and an increase in the drain-to-source breakdown voltage beyond 0.6 V.

In Situ Self Ion Beam Annealing of Damage in Si during High Energy (0.53 MeV–2.56 MeV) As + Ion Implantation

High energy As+ ions have been implanted by a 2.5 MeV Van-de-Graaff accelerator. Implantation induced damage in silicon crystal is anomalously smaller than that estimated from the calculation for nuclear deposited energy density. The logarithm for observed damage degree depends linearly on the inverse absolute temperature of the wafer during implantation. The 0.18 eV activation energy coincides with the 0.18 eV migration energy for the doubly negative vacancy. The anomalously small damage is attributed to in situ recrystallization of damage assisted by migration of the doubly negative vacancy (V-) which is formed by high energy heavy ion implantation. As the wafer temperature is below 300°C, and activation energy is small, ordinary solid phase epitaxial regrowth does not occur.

Optical properties of TiN films deposited by direct current reactive sputtering

Optical properties of TiN films have been studied using spectroscopic ellipsometry in the photon-energy range between 1.2 and 5.4 eV at room temperature. The TiN films are deposited on Si(100) substrates by reactive dc magnetron sputtering. The nearly stoichiometric golden-colored (g∼5.3 g/cm3) and brownish TiN films (g∼4.7 g/cm3) are investigated. The measured e(E) spectra reveal distinct structures near the screened plasma edge and at interband critical points. These spectra are analyzed on the basis of a simplified model of the interband transitions including the Drude–Lorentz term contribution. Results are in satisfactory agreement with the experimental data over the entire range of photon energies. Dielectric-related optical constants, such as the complex refractive index, absorption coefficient, and normal-incidence reflectivity, of the sputter-deposited TiN films are also presented.

Characteristics of a new isolated p-well structure using thin epitaxy over the buried layer and trench isolation

An isolated p-well structure for deep-submicrometer BiCMOS LSIs is proposed. The structure consists of a retrograde p-well in an n-type thin epitaxial layer over an n/sup +/ buried layer, and trench isolation. Latchup characteristics in this CMOS structure and breakdown characteristics of the shallow p-well are studied on test devices. Excellent latchup immunity and sufficient voltage tolerance are obtained with a thin 1- mu m epitaxial layer. A CMOS 1/8 dynamic-type frequency divider using this well structure functions properly up to 3.2 GHz at a 2-V supply voltage. >

Spectroscopic ellipsometry study of ion-implanted Si(100) wafers

Optical properties of P+ ion-implanted Si(100) wafers have been studied using spectroscopic ellipsometry (SE). The P+ ions are implanted at 150 keV with fluences ranging from 1×1014 to 2×1015 cm−2 at room temperature. An effective-medium-approximation analysis suggests that the ion-implanted layer can be explained by a physical mixture of microcrystalline and amorphous silicon. The e(E) spectrum of the microcrystalline component is found to differ appreciably from that of single-crystalline silicon, especially in the vicinity of the sharp critical-point features. This difference in e(E) can be successfully interpreted by increasing the broadening parameter at each critical point. Considering these and previous data, we obtain an expression, A=(5.13×1011/EacM)1.872, which enables us to estimate the amorphization-threshold fluence A for silicon implanted with optional ion species of mass number M at energy Eac in keV. No clear change in the original structure of silicon surface after P+ ion implantation has been observed by atomic force microscopy. SE has been proven to be an easy, fast, and nondestructive technique which can be used to assess important ion-implantation parameters.Optical properties of P+ ion-implanted Si(100) wafers have been studied using spectroscopic ellipsometry (SE). The P+ ions are implanted at 150 keV with fluences ranging from 1×1014 to 2×1015 cm−2 at room temperature. An effective-medium-approximation analysis suggests that the ion-implanted layer can be explained by a physical mixture of microcrystalline and amorphous silicon. The e(E) spectrum of the microcrystalline component is found to differ appreciably from that of single-crystalline silicon, especially in the vicinity of the sharp critical-point features. This difference in e(E) can be successfully interpreted by increasing the broadening parameter at each critical point. Considering these and previous data, we obtain an expression, A=(5.13×1011/EacM)1.872, which enables us to estimate the amorphization-threshold fluence A for silicon implanted with optional ion species of mass number M at energy Eac in keV. No clear change in the original structure of silicon surface after P+ ion implantation has...

Oxygen-Doped Si Epitaxial Film (OXSEF)

We propose a new wide-gap material, an oxygen-doped Si epitaxial film (OXSEF), for applications to Si heterobipolar transistors (HBTs). OXSEF containing several tens of at.% of oxygen can be grown on a Si substrate by depositing Si in about 10-6 Torr O2. OXSEF is literally almost a single crystal with an identical crystalline structure to Si, although it includes {111} twins as defects caused by oxygen. Temperature and O2 pressure dependences of oxygen concentration in OXSEF are dominated by oxygen adsorption on the Si surface. Oxygen atoms in OXSEF segregate to some extent toform incomplete oxides like SiO1.5, but complete phase separation as a mixture of Si and SiO2. regions does not occur, probably bcause of non-equilibrium conditions in MBE growth. Valence band discontinuity at the Si/OXSEF interface is deduced to be 0.26 eV based on photoelectrical measurements.

Multiple SOI Structure Fabricate by High Dose Oxygen Implantation and Epitaxial Growth

A triple SOI (Silicon crystal On Insulator) structure has been fabricated on (100) and (111) Si substrates, utilizing three SIMOX (Separation by IMplanted OXygen) cycles. The SIMOX process consists of high-dose oxygen implantation followed by annealing and epitaxial growth of silicon, and provides good surface morphology. The top Si layer of the present triple SOI is single crystalline, which is confirmed by reflection electron diffraction and Rutherford backscattering measurement.

I-V Characteristics of oxygen-doped Si epitaxial film (OXSEF)/Si heterojunctions

We have fabricated oxygen-doped Si epitaxial film (OX-SEF)/Si heterodiodes to examine device capabilities of the new wide-gap material, OXSEF. Various locations of the p-n junction with respect to the OXSEF/Si interface are achieved by changing the annealing time for arsenic diffusion from the implanted poly-Si layer on top of the OXSEF. When the p-n junction is located at the heterointerface, the diode n-value is 1.4-1.5 after H2annealing. This can be reduced to 1.1-1.2 by pushing the p-n junction into a Si substrate of about 600 Å.

Model-dielectric-function analysis of ion-implanted Si(100) wafers

Optical properties of Si+, P+, and Ar+ ion-implanted Si(100) wafers have been studied using spectroscopic ellipsometry. The Si+, P+, and Ar+ ions are implanted at 150 keV with fluences ranging from 1×1014 to 2×1015 cm−2 at room temperature. A model dielectric function (MDF), which was developed for modeling the optical constants of perfectly crystalline semiconductors, has been applied to investigate the optical response of the ion-implanted Si(100) wafers. The MDF analysis indicates a distinct structural transition from the crystalline to amorphous phase at some ion fluences around 1014–1015cm−2. Since the critical points do not have any validity in amorphous material, the band gaps used in the MDF are not a result of the Bragg gaps at the Brillouin-zone boundaries, but are considered to arise from the short-range order determined by the covalent bonding. Using these results, we obtain an expression, D=(1.6×108/M)2.2 cm−2 which enables us to estimate the crystalline-amorphous phase transition fluence D f...

Determination of Hydrogen Concentration in PCVD Silicon Nitride Films by Elastic Recoil Detection Analysis

The hydrogen concentrations of PCVD silicon nitride films were measured by Elastic Recoil Detection (ERD) analysis using 2.5 MeV He+ ions. For annealed films, H concentrations measured by ERD analysis are smaller than those measured by an infrared absorption analysis. These results indicate that absorption cross sections of Si-hydrogen and N-hydrogen bonds are changed by annealing.