M. Hane

Atomistic 3D process/device simulation considering gate line-edge roughness and poly-Si random crystal orientation effects [MOSFETs]

Using newly developed simulation tools for the precise design of sub-100 nm MOSFETs, intrinsic statistical fluctuations in device characteristics were examined. Ion implantation and subsequent dopant diffusion/activation were simulated based on Monte Carlo procedures. 3D device simulations were performed based on the conventional drift-diffusion model in which electrostatic potential distributions were constructed from the long-range Coulombic components of individual discrete dopant atom potentials. Gate line-edge-roughness (LER) and random discrete dopant effects were incorporated in this simulation. Another possible source of fluctuation, i.e. gate poly-Si crystalline grain random orientation effects in conjunction with oblique halo implantation, was also examined. An atomistic approach to both 3D process and device simulations enabled us to closely examine the coupling effects of the significant sources of fluctuation, i.e. LER and random-discrete-dopant, in the context of practical fabrication processes.

A model for boron short time annealing after ion implantation

A simulation model is proposed for boron diffusion in silicon. It is especially useful for analyzing the short time annealing process subsequent to ion implantation. This model takes into account nonequilibrium diffusion and reactions of point defects and defect-dopant pairs, considering their charge states, and the dopant inactivation by the introduction of a boron clustering reaction. It is assumed that the boron-interstitial-silicon pair (BI) is a dominant diffusion species that contributes to the total boron diffusion. A primary model parameter, the binding energy of BI, is determined and used to reproduce the equilibrium gaseous source diffusion data. Using a single set of reasonable parameter values, the model covers not only the equilibrium diffusion conditions, from intrinsic, but also the nonequilibrium postimplantation diffusion. Experimental boro distribution profiles can be accurately reproduced. It is shown that the time constant for the BI dissociation reaction rules the transient behavior of boron diffusion enhancement during postimplantation annealing. >

Investigation of soft error rate including multi-bit upsets in advanced SRAM using neutron irradiation test and 3D mixed-mode device simulation

We investigated the SRAM soft error rate (SER) by using neutron irradiation testing and computational modeling. Experimentally observed multibit-error patterns can be clarified by our detailed SRAM upset model derived from the 3D device-circuit mixed-mode simulation. This work describes several essential key issues for predicting SER accounting for practical SRAM circuit-layout design issues.

Practical finFET design considering GIDL for LSTP (low standby power) devices

Practical design of double-gate undoped-channel FinFET has been investigated through 3D device simulations considering gate-induced drain leakage (GIDL). Optimization of FinFET structure was carried out for hp45 low standby power (LSTP) device (Lg = 25nm). GIDL is reduced by using gradual and offset source/drain (S/D) profile while degradation of drive current is minimized. Through the optimization of lateral spread and offset of S/D profile, the ITRS specifications for drive current and off-state leakage current are achievable by FinFET with 10nm fin width

SRAM critical yield evaluation based on comprehensive physical / statistical modeling, considering anomalous non-Gaussian intrinsic transistor fluctuations

Critical SRAM yield evaluation/analysis for more robust design optimizations against variation is presented based on comprehensive physical modeling and statistical analysis of transistor intrinsic fluctuations for 65 nm-node and beyond MOSFETs. Predictive atomistic-3D-TCAD simulations reveal the origins of the non-Gaussian Vth-distribution that causes large sigmaVth deviation from the Pelgrom-relationship for specific small gate length devices. By using realistic statistical compact-modeling and fast Monte Carlo circuit simulations, it was demonstrated that the appropriate cell-design recognizing the anomalous sigmaVth enables to rescue significant possible yield loss caused by the particular behaviors of the intrinsic transistor fluctuations.

Ion implantation model considering crystal structure effects

An ion implantation model for crystalline targets, based on the Monte Carlo method, is proposed. Crystal structure effects on ion channeling are directly modeled by taking into account simultaneous collisions with multitarget atoms. The model can reproduce an experimental boron distribution profile in crystalline silicon. Some important effects on distribution profile, such as thermal lattice vibrations, tilted implantation, and surface imperfection, have been investigated. It is found that a subchannelling effect is important in determining the boron distribution profile.<<ETX>>

3D MOSFET simulation considering long-range Coulomb potential effects for analyzing statistical dopant-induced fluctuations associated with atomistic process simulator

We have developed a realistic 3-D process/device simulation method for investigating the fluctuation in device characteristics induced by the statistical nature of the number and position of discrete dopant atoms. We used it to investigate the variations in characteristics of a sub-100 nm CMOS device induced by realistic dopant fluctuations considering practical device fabrication processes. In particular, sensitivity analysis of the threshold voltage fluctuation was performed in terms of the independent dopant contribution, such as that of the dopant in the source/drain region or channel region.

Simulation of reverse short channel effects with a consistent point-defect diffusion model

A consistent point-defect diffusion model including the impurity clustering was implemented, and the reverse short channel effect (RSCE) strength of the nMOSFETs was compared with the pMOSFETs using a common model parameter set. As the result of simulations for typical single-drain MOSFETs, the RSCE was calculated in the nMOSFETs but not in the pMOSFETs. The reason of this RSCE difference is that in the nMOSFETs the interstitials are generated during the arsenic (As) clustering process in the source/drain (S/D) region, but in the pMOSFETs the interstitials are absorbed during the boron (B) clustering process. It is clarified that this interstitial generation or absorption plays a significant role in the difference of the RSCE between nMOSFETs and pMOSFETs.

Self-Consistent Quantum Mechanical Monte Carlo MOSFET Device Simulation

We have developed a self-consistent quantum mechanical Monte Carlo device simulator that takes electron transport in quantized states into consideration. Two-dimensional quantized states in MOSFET channels are constructed from one-dimensional solutions of the Schrödinger equation at different positions along the channel, and the Schrödinger and Poisson equations are solved self-consistently in terms of electron concentration and electrostatic potential distribution. The channel electron concentration, velocity and drain currents are calculated with the one particle Monte Carlo approach incorporating the intra-valley acoustic phonon and inter-valley phonon scattering mechanisms. This simulator was applied to a 70 nm n-MOSFET transistor, and we found that current mostly flows through the lowest subband and transport is quasi-ballistic near the source junction. To quantitatively estimate the performance of advanced devices, we have developed an inversion carrier transport simulator based on a full-band model. Our simulation method enables us to evaluate device characteristics and analyze the transport properties of ultra-small MOSFETs.

Coupled atomistic 3D process/device simulation considering both line-edge roughness and random-discrete-dopant effects

We developed new simulation tools for the precise design of sub-100nm MOSFETs. The intrinsic statistical nature of these devices is expressed as fluctuations in device characteristics. Line-edge-roughness (LER) is incorporated in the structural variations in polysilicon gate masks for halo and source/drain-extensions implantations. The statistical nature of these discrete dopant distributions can be automatically included in the simulation by using Monte Carlo procedures for ion implantation and dopant diffusion/activation processes with different computationally generated LER patterns for each individual device. Our 3D device simulations were based on the classical drift-diffusion approach in which electrostatic potentials are constructed from the long-range Coulombic components of individual dopant atom potentials. Using a 3D atomistic approach to both process and device simulation enabled us to closely examine the coupling effects of the most significant sources of fluctuation, i.e. line-edge-roughness and random-discrete-dopants in the context of practical fabrication processes.