Guangrui Xia

Strained silicon MOSFET technology

Mobility and current drive improvements associated with biaxial tensile stress in Si n- and p-MOSFETs are briefly reviewed. Electron mobility enhancements at high channel doping (up to 6 /spl times/ 10/sup 18/ cm/sup -3/) are characterized in strained Si n-MOSFETs. For low inversion layer carrier concentrations, channel-dopant ionized impurity scattering does reduce the strain-induced mobility enhancement, but the enhancement is recovered at higher inversion charge concentrations, where screening is efficient. Mobility enhancement in strained Si p-MOSFETs is also discussed. There are process integration challenges and opportunities associated with this technology. Dopant diffusion, and its impact on profile engineering in strained Si CMOS structures, is one example. While the slower diffusion of B in Si/sub 1-x/Ge/sub x/ enables improved doping profile control, the diffusivity of the n-type dopants is dramatically enhanced in Si/sub 0.8/Ge/sub 0.2/.

Orientation of pentacene films using surface alignment layers and its influence on thin-film transistor characteristics

We have investigated the effect of surface order on the orientation and mobility of pentacene. The surface order was created using monolayers and polymers that are normally used to align liquid crystals. Rubbed polyvinylalcohol layers were found to align approximately 27% of the pentacene grains within a 30° range. When introduced in a thin-film transistor, they were found to enhance the saturation current by a factor of 2.5. A mechanism for this enhancement is proposed.

Si–Ge interdiffusion in strained Si/strained SiGe heterostructures and implications for enhanced mobility metal-oxide-semiconductor field-effect transistors

Si–Ge interdiffusivity in epitaxial strained Si∕Si1−yGey/strained Si/relaxed Si1−x0Gex0 heterostructures is extracted for Ge fractions between 0 and 0.56 over the temperature range of 770–920°C. Boltzmann-Matano analysis is applied to determine interdiffusivity from diffused Ge profiles in strained Si/relaxed Si1−x0Gex0 heterostructures [L. Boltzmann, Wiedemanns Ann. Phys. 53, 959 (1894) and C. Matano, Jpn. J. Phys. 8, 109 (1933)]. A model for the interdiffusivity suitable for use in the process simulator TSUPREM-4 is constructed. Si–Ge interdiffusivity increases by 2.2 times for every 10% increase in Ge fraction for interdiffusion in strained Si/relaxed Si1−x0Gex0 samples. Significantly enhanced Si–Ge interdiffusion is observed for Si1−yGey layers under biaxial compressive strain. Si–Ge interdiffusivity is found to increase by 4.4 times for every 0.42% increase in the magnitude of biaxial compressive strain in the Si1−yGey, which is equivalent to a decrease in the Ge percentage in the substrate by 10at.%...

High-performance nMOSFET with in-situ phosphorus-doped embedded Si:C (ISPD eSi:C) source-drain stressor

For the first time, embedded Si:C (eSi:C) was demonstrated to be a superior nMOSFET stressor compared to SMT or tensile liner (TL) stressors. eSi:C nMOSFET showed higher channel mobility and drive current over our best poly-gate 45 nm-node nMOSFET with SMT and tensile liner stressors. In addition, eSi:C showed better scalability than SMT plus tensile liner stressors from 380 nm to 190 nm poly-pitches.

Strain dependence of Si–Ge interdiffusion in epitaxial Si∕Si1−yGey∕Si heterostructures on relaxed Si1−xGex substrates

The strain dependence of Si–Ge interdiffusion in epitaxial Si∕Si1−yGey∕Si heterostructures on relaxed Si1−xGex substrates has been studied using secondary ion mass spectrometry, Raman spectroscopy, and simulations. At 800 and 880 °C, significantly enhanced Si–Ge interdiffusion is observed in Si∕Si1−yGey∕Si heterostructures (y=0.56, 0.45, and 0.3) with Si1−yGey layers under compressive strain of −1%, compared to those under no strain. In contrast, tensile strain of 1% in Si0.70Ge0.30 layer has no observable effect on interdiffusion in Si∕Si0.70Ge0.30∕Si heterostructures. These results are relevant to the device and process design of high mobility dual channel and heterostructure-on-insulator metal oxide semiconductor field effect transistors.

Hot carrier effect on gate-induced drain leakage current in high-k/metal gate n-channel metal-oxide-semiconductor field-effect transistors

This paper investigates the channel hot carrier stress (CHCS) effects on gate-induced drain leakage (GIDL) current in high-k/metal-gate n-type metal-oxide-semiconductor field effect transistors. It was found that the behavior of GIDL current during CHCS is dependent upon the interfacial layer (IL) oxide thickness of high-k/metal-gate stacks. For a thinner IL, the GIDL current gradually decreases during CHCS, a result contrary to that found in a device with thicker IL. Based on the variation of GIDL current at different stress conditions, the trap-assisted band-to-band hole injection model is proposed to explain the different behavior of GIDL current for different IL thicknesses.

On the Origin of Hole Valence Band Injection on GIFBE in PD SOI n-MOSFETs

This letter systematically investigates the mechanism of gate-induced floating-body effect (GIFBE) in advanced partially depleted silicon-on-insulator metal-oxide-semiconductor field-effect transistors. Based on different operation conditions, we found that the hole current collected by the body terminal is strongly dependent on electrons in the inversion layer under a source/drain ground. This implies that GIFBE can be attributed to anode hole injection (AHI) rather than the widely accepted mechanism of electron valence band tunneling. Moreover, GIFBE was also analyzed as a function of temperature. The results provide further evidence that the accumulation of holes in the body results from the AHI-induced direct tunneling current from the gate.

On the Origin of Gate-Induced Floating-Body Effect in PD SOI p-MOSFETs

This letter systematically investigates the origin of gate-induced floating-body effect (GIFBE) in partially depleted silicon-on-insulator p-type MOSFETs. The experimental results indicate that GIFBE causes a reduction in the electrical oxide field, leading to an underestimate of negative-bias temperature instability degradation. This can be partially attributed to the electrons tunneling from the process-induced partial n+ polygate. However, based on different operation conditions, we found that the dominant origin of electrons was strongly dependent on holes in the inversion layer under source/drain grounding. This suggests that the mechanism of GIFBE at higher voltages is dominated by the proposed anode electron injection model, rather than the electron valence band tunneling widely accepted as the mechanism for n-MOSFETs.

Impact of ion implantation damage and thermal budget on mobility enhancement in strained-Si N-channel MOSFETs

The impact of processing factors such as ion implantation and rapid thermal annealing on mobility enhancement in strained-Si n-channel metal-oxide-semiconductor field-effect transistors (n-MOSFETs) has been investigated. Long-channel strained-Si and bulk n-MOSFETs were fabricated with various channel-region implant doses and thermal budgets. Neutral Si and Ge species were used to study the impact of the implant damage on mobility separately from ionized impurity scattering effects. Electron mobility enhancement is shown to degrade considerably when the implant dose is above a critical dose for a given thermal budget. Transmission electron microscopy, secondary ion mass spectrometry and Raman spectroscopy were used to investigate the mobility degradation mechanisms. Residual implant damage and implant damage enhanced Ge up-diffusion into the Si are shown to be responsible for the mobility degradation. Two-dimensional damage simulations of 30-nm scale MOSFETs are used to examine potential technological implications of these findings.

Atomistic simulation of radiation damage to carbon nanotube

Damaging carbon nanotube upon energetic irradiation has been modeled with molecular-dynamics simulations. The angular dependence of the threshold energy of the primary knock-on atom (PKA) escaping from the tube is investigated in the initial PKA directions spanning half space. The average value of the threshold energy is calculated to be 19.3 eV. The simulations provided a detailed picture of the damaging processes, in which four mechanisms were revealed. The interactions between carbon atoms are described with the Tersoff mode modified to match a screened Coulomb potential at short range.