E. Lyumkis

MOSFET degradation kinetics and its simulation

In this work, the time-dependence of Si/SiO/sub 2/ interface trap formation is considered by solving an improved set of Si-H defect kinetics equations that take into account interface disorder and the Si-H bond activation energy evolution as the bonds are broken. This model is applied to the simulation of metal oxide semiconductor field effect transistor (MOSFET) high field and hot carrier degradation, and then verified with various experimental data. An estimation of the potential barrier of the Si/SiO/sub 2/ interface is given.

Random dopant fluctuation modelling with the impedance field method

We discuss an approach for the modelling of random dopant fluctuations based on the impedance field method that has been recently integrated into DESSIS. The method is easy to use and orders of magnitudes more efficient than the statistical method.

Gate Current Calculations Using Spherical Harmonic Expansion of Boltzmann Equation

A physics-based gate current model has been de- veloped based on nonequilibrium electron energy distributions obtained from the spherical harmonic expansion of the Boltz- mann equation. The model accounts for band structure effects, relevant microscopic scattering mechanisms, and electron injec- tions caused by tunneling and thermionic emission processes with parallel momentum conservation and image potential barrier lowering. Obtained distribution functions and injection currents agree well with Monte Carlo simulations and experiments. I. INTRODUCTION Hot carrier injection into the gate oxide in MOSFETs is responsible for gate leakage and oxide degradation, and it has been used in the write operation in NOR flash memories. In order to model the hot carrier injection current, accurate knowledge of the nonequilibrium electron energy distribution is required. Although the Monte Carlo (MC) method would be the most rigorous tool to study hot electron transport (1), the MC method involves large statistical noise in the tail distribution that is important in the gate current calcu- lation. This paper describes a gate current model based on the Spherical Harmonic Expansion (SHE) of the Boltzmann Transport Equation (BTE) (2), (3), (4), (5) that we have implemented in the device simulator Sentaurus Device (6). The implemented SHE model accounts for the full band structure obtained from the empirical pseudopotential method (EPM) (7) and microscopic scattering mechanisms caused by acoustic and intervalley phonons, ionized impurities, and impact ionization. The implemented gate current model covers tunneling and thermionic emission components, and it takes into account parallel momentum conservation, image potential induced barrier lowering, and scattering probability within the image force potential well (1). We validate our model by com- paring obtained distribution functions and gate currents with MC simulations and experiments, and provide a gate current simulation example for a long-channel MOSFET where the hot electron injection is the dominant gate current mechanism.

Investigation of the Statistical Variability of Static Noise Margins of SRAM Cells Using the Statistical Impedance Field Method

The statistical variability of the static noise margin of a six-transistor bulk complementary metal-oxide-semiconductor static random access memory (SRAM) cell due to random doping fluctuations (RDFs) is investigated via 3-D technology computer-aided design simulations. The SRAM cell is created through 3-D process simulations of the entire cell as a single structure. The process flow is based on a typical 32-nm technology. The effects of RDFs on the cell performance are investigated using the highly efficient statistical impedance field method.

Simulations of ultrathin, ultrashort double-gated MOSFETs with the density gradient transport model

We report the results of numerical simulation of nanoscale SOI structures under highly non-equilibrium conditions with the Density Gradient model. The simulations have been carried out with the general purpose device simulator DESSIS. We show that 2D quantum mechanical effects are important for the structures under investigation. We demonstrate that our implementation of the DG model is robust and enables efficient simulation far from equilibrium, for both the drift-diffusion and hydrodynamic transport model.

Phase-change memory simulations using an analytical phase space model

In this paper, an analytical phase transition model is coupled self-consistently with the electro-thermal transport model. The phase space model and the transition dynamic is described. The resulting phase-electro-thermal simulation model is applied to an illustrative example structure. The self-consistency of the approach and its resulting simulation speed and robustness provide a useful TCAD tool for design studies of phase change memory devices.

Integration of the Density Gradient Model into a General Purpose Device Simulator

A generalized Density Gradient model has been implemented into the device simulator Dessis [DESSIS 7.0 reference manual (2001). ISE Integrated Systems Engineering AG, Balgriststrasse 102, CH-8008

Investigation of Proximity Effects in a 6T SRAM Cell Using Three-Dimensional TCAD Simulations

In this paper, we study the impacts of proximity effects on the electrical characteristics Id-Vg and the static noise margin of a six-transistor (6T) bulk complementary metal-oxide-semiconductor (MOS) static random access memory (SRAM) cell using 3-D process and device technology computer-aided design (TCAD) simulations. We show that when a 6T SRAM cell is simulated as a single continuous 3-D structure, effective stresses in channels are reduced due to close proximity of n-channel and p-channel MOS transistors in the cell with respect to simulations of transistors as discrete 3-D structures. Furthermore, we find that doping in channels of SRAM transistors is reduced by well proximity and implant shadowing. Stress and doping proximity effects have opposite contributions to device performance. We estimate the influence of proximity effects for typical 32-nm technology to be more than 10% for certain electrical cell characteristics. We thus conclude that, to accurately predict electrical cell behavior via TCAD simulations, the 6T SRAM cell should be a single continuous 3-D structure, instead of a set of six discrete transistors, which are simulated as individual 3-D devices and connected via a netlist.

Simulations of quantum transport in HEMT using density gradient model

In this paper, quantum transport simulations for AlGaAs/InGaAs HEMT devices based on the density gradient model are presented. It is shows that size quantization effects have a pronounced influence on the electrical characteristics.

Three-dimensional TCAD Process and Device Simulations

Shrinking feature sizes, novel device designs as well as stress engineering increase the need for three- dimensional process and device simulations. We present several application examples for full 3D process and device simulations using Sentaurus TCAD, including a 3D NMOSFET with shallow trench isolations (STI), a PMOSFET device with SiGe pockets for stress engineering (similar to the structure presented in Ref. [1]) and a Omega-FinFET (similar to structures presented in Refs. [2,3]). TCAD simulations of the full process flow as well as of the electrical device characteristics are performed. We also show examples of 3D oxidation simulations with Sentaurus Process.