Toru Tatsumi

Ge growth on Si using atomic hydrogen as a surfactant

We have examined the effect of adsorbed atomic hydrogen (H) on the evolution of Ge films on Si(001) and (111) substrates in solid‐source molecular‐beam epitaxy. The H flux was supplied separately from the Ge flux. By cross‐sectional high‐resolution transmission electron microscopy it was observed that H acted as a surfactant during growth, suppressing island formation of Ge on both substrates. The effect of the H surfactant on variation of the growth mode is also discussed.

Fluorinated amorphous carbon thin films grown by plasma enhanced chemical vapor deposition for low dielectric constant interlayer dielectrics

Fluorinated amorphous carbon films were proposed as low dielectric constant interlayer dielectrics for ultralarge scale integration circuits. The films were deposited by plasma enhanced chemical vapor deposition with CH4 and CF4 in a parallel plate rf (13.56 MHz) reactor. The dielectric constant of the amorphous carbon films deposited with CH4 was increased with increases in rf power. The addition of CF4 to CH4 raised the deposition rate and reduced the dielectric constant. At an rf power of 200 W, and at a flow rate of 47 sccm for CF4 and 3 sccm for CH4, the dielectric constant of the fluorinated amorphous carbon films was 2.1.

Channel engineering for the reduction of random-dopant-placement-induced threshold voltage fluctuation

A simple model is proposed, which is able to calculate V/sub TH/ standard deviation due to random dopant placement in the channel, for arbitrary vertical impurity distributions. Substantial decrease in V/sub TH/ fluctuation, while keeping V/sub TH/ the same, is confirmed for low surface impurity channel MOSFETs, in agreement with the model prediction.

A 0.1-/spl mu/m delta-doped MOSFET fabricated with post-low-energy implanting selective epitaxy

A simple fabrication technology for delta-doped MOSFETs, named post-low-energy implanting selective epitaxy (PLISE) is presented. The PLISE technology needs no additional photo-lithography mask, deposition step or etching step even for CMOS devices. The only additional step is growing undoped epitaxial channel layers by UHV-CVD after the channel implantation. With this technology, delta-doped NMOSFETs with 0.1-/spl mu/m gate length were successfully fabricated. By optimizing the epi-layer thickness and the channel doping level, short-channel effects are suppressed enough to achieve 0.1-/spl mu/m gate length. Moreover, the junction capacitance at zero bias is reduced by 50%.

Plasma deposition of low-dielectric-constant fluorinated amorphous carbon

Fluorinated amorphous carbon thin films (a-C:F) for use as low-dielectric-constant interlayer dielectrics are deposited by helicon-wave plasma enhanced chemical vapor deposition. To improve their thermal stability, the feasibility of adjusting the fluorine-to-carbon (F/C) ratio by changing the deposition pressure was investigated. Decreasing the pressure increased the dissociation of a source fluorocarbon material in the plasma and decreased the F/C ratio of the deposited film. Both the thermal stability and the dielectric constant of the a-C:F films were increased as the F/C ratio was decreased. Thus, there is a tradeoff relationship between a low dielectric constant and high thermal stability and the tradeoff could be optimized by the pressure during deposition. The mechanism of the pressure dependency of the dielectric constant of a-C:F films was investigated by quantifying the contribution of each polarization and found that a decrease in the dielectric constant of a-C:F films can be attributed to dec...

Near‐band‐gap photoluminescence of Si1−xGex alloys grown on Si(100) by molecular beam epitaxy

Photoluminescence spectra in the near‐band‐gap region of Si1−xGex alloys (x=0.04 and 0.15) grown on Si(100) substrates by molecular beam epitaxy have been measured at 4.2 and 12 K. Radiative recombinations of free and bound excitons in thin layers of Si1−xGex alloys have been clearly observed for the first time. No‐phonon transitions and transverse‐optical (TO) phonon‐assisted transitions have been identified.The luminescence lines become broader with an increase in excitation intensity; the broadening is interpreted to be due to the generation of the bound multiexciton complexes (BMECs). The position of the band‐edge luminescence lines is determined by the strain in the epitaxial layer as well as the alloy composition. The defect‐related L band appears in the case of x=0.15.

Fluorinated amorphous carbon thin films grown by helicon plasma enhanced chemical vapor deposition for low dielectric constant interlayer dielectrics

Fluorinated amorphous carbon thin films (a‐C:F) for interlayer dielectrics are grown by helicon plasma enhanced chemical vapor deposition. The source gases are CH4, CF4, C2F 6 and their H2mixtures. a‐C:F films can be fabricated without adding hydrogen using the helicon reactor, while in the previously reported parallel‐plate reactor, no film grows unless a hydrogen source is added. The films grown in the helicon reactor have no hydrogen content. The growth rate of the films reaches 0.3 μm/min (C2F 6) and 0.15 μm/min (CF4). The thickness of the films deposited with C2F6 does not decrease on heating to 300 °C, while the films with CF4 shrink. The dielectric constants of the films deposited from C2F6 and CF4 are 2.4 and 2.3 respectively at 1 MHz. The dielectric loss tangent of these films is 0.01 at 1 MHz.

Selective growth condition in disilane gas source silicon molecular beam epitaxy

Selective epitaxial growth condition in the disilane gas source silicon molecular beam epitaxy was studied as functions of the substrate temperature and the growth rate. At lower substrate temperature or at lower silicon growth rate, perfect selectivity was attained. The selectivity dependence on the temperature and that on the growth rate indicate that the control of the disilane molecule’s dissociation on the SiO2 surface is important for selective growth.

Gas source silicon molecular beam epitaxy using disilane

The apparatus and its preliminary results of gas source silicon molecular beam epitaxy are reported for the first time. In this study, silane (SiH4) was used as a source gas. A subchamber was designed to control the gas flow precisely. SiH4 exposure during the initial cleaning was effective in lowering the cleaning temperature and saving the cleaning time. Epitaxial silicon films grew uniformly on 4‐in. wafers. There was no spitting defect on the epitaxial films. Moreover, selective epitaxial growth was realized using a patterned SiO2 mask.

Dual workfunction Ni-Silicide/HfSiON gate stacks by phase-controlled full-silicidation (PC-FUSI) technique for 45nm-node LSTP and LOP devices

We present a new threshold-voltage (Vth) control technique for fully-silicided (FUSI) metal/high-k gate stacks which are suitable for 45nm-node LOP and LSTP CMOS. The key is the phase control of FUSI Ni-silicide by changing Ni film thickness prior to silicidation anneal. As a result, Ni/sub 3/Si and NiSi/sub 2/ are formed whose effective workfunctions (WFs) on HfSiON are found to be 4.8eV and 4.4eV, respectively, being largely displaced from Si-midgap by /spl plusmn/0.2eV. Meanwhile, the dopant segregation method, known to be successful in Vth-control of NiSi on SiO/sub 2/, did not work on HfSiON. With Ni/sub 3/Si-PMOS and NiSi/sub 2/-NMOS transistors, a wide range of Vth-tuning is achieved coping with both LSTP and LOP requirements. At the same time, leakage suppression merit is better than the 45nm-node targets at electrical thickness (Tinv) around 2.0 nm. Also, our phase-controlled fully silicided (PC-FUSI) devices show excellent mobility characteristics.