# Johann CervenkaTU Wien | TU Wien · Institute for Microelectronics

Johann Cervenka

## About

50

Publications

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250

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Introduction

**Skills and Expertise**

## Publications

Publications (50)

We discuss boundary value problems for the characteristic stationary von Neumann equation (stationary sigma equation) and the stationary Wigner equation in a single spatial dimension. The two equations are related by a Fourier transform in the non-spatial coordinate. In general, a solution to the characteristic equation does not produce a correspon...

The Wigner formalism is a convenient way of describing quantum mechanical effects through a framework of distribution functions in phase space. Currently, there are stochastic and deterministic approaches in use. In our deterministic method, the critical discretization of the diffusion term is done through the utilization of an integral formulation...

The Wigner equation describing stationary quantum transport has a singularity at the point \(k=0\). Deterministic solution methods usually deal with the singularity by just avoiding that point in the mesh (e.g., Frensley’s method). Results from such methods are known to depend strongly on the discretization and meshing parameters.

The development of novel nanoelectronic devices requires methods capable to simulate quantum-mechanical effects in the carrier transport processes. We present a deterministic method based on an integral formulation of the Wigner equation, which considers the evolution of an initial condition as the superposition of the propagation of particular fun...

We introduce a simulation technique suitable to model the tunneling leakage current in the metal(polySi)/CaF2/Si(111) MIS structures using TCAD simulators Minimos-NT and ViennaSHE. The simulations are performed using the real physical parameters of the CaF2/Si tunnel barrier. The results obtained for the case of near-equilibrium carrier transport a...

We model the main characteristics of metal-insulator-silicon field-effect transistors (MISFETs) with different gate insulators using the carrier energy distribution function calculated with a Spherical Harmonics Expansion method. In addition to standard devices with Silicon Dioxide or Oxynitride we study a hypothetical MISFET with a rather new crys...

Hot-carrier degradation is associated with the buildup of defects at or near the silicon/silicon dioxide interfaced of a metal-oxide-semiconductor transistor. However, the exact location of the defects, as well as their temporal buildup during stress, is rarely studied. In this work we directly compare the experimental interface state density profi...

To investigate the electrical on-chip-transistor behavior at different temperatures usually the transistor area on the wafer is heated by external heat sources to operate at a specific temperature. To avoid using external heat sources a heatring structure was developed which directly controls the temperature of the investigated transistor area on t...

We perform a comparative study of various macro-scopic transport models against multisubband Monte Carlo (MC) device simulations for decananometer MOSFETs in an ultra-thin body double-gate realization. The transport parameters of the macroscopic models are taken from homogeneous subband MC simulations, thereby implicitly taking surface roughness an...

The potential of strained DOTFET technology is demonstrated. This technology uses a SiGe island as a stressor for a Si capping layer, into which the transistor channel is integrated. The structure information of fabricated samples is extracted from atomic force microscopy (AFM) measurements. Strain on the upper surface of a 30 nm thick Si layer is...

To provide simulation software in the field of TCAD with the utmost flexibility regarding generation and adaptation of meshes, a generic and high-quality meshing library, ViennaMesh, has been developed. The library is coded in C++ and utilizes modern programming techniques to wrap tasks, like mesh generation and mesh adaptation, into functional obj...

Models for the local anodic oxidation of silicon using scanning tunneling microscopy and non-contact atomic force microscopy are implemented in a generic process simulator, using the Level Set method. The advantage of the presented implementation is the ease with which further processing steps can be simulated in the same environment. An empirical...

With the modern transistor size shrinking below 45 nm the classical drift-diffusion model to describe transport in the conducting channel is loosing its validity. In short-channel devices carriers get accelerated by the driving field and do not thermalize before they reach the drain contact. Thus, the assumption underlying the classical transport m...

We refine our approach for hot-carrier degradation modeling based on a thorough evaluation of the car-rier energy distribution by means of a full-band Monte–Carlo simulator. The model is extended to describe the linear current degradation over a wide range of operation conditions. For this purpose we employ two types of interface states, either cre...

We propose and verify a model for hot carrier degradation based on the exhaustive evaluation of the energy distribution function for charge carriers in the channel by means of a full-band Monte-Carlo device simulator. This approach allows us to capture the interplay between “hot” and “colder” electrons and their contribution to the damage build-up....

Using a physics-based model for hot-carrier degrada-tion we analyze the worst-case conditions for long-channel transis-tors of two types: a relatively low voltage n-MOSFET and a high-voltage p-LDMOS. The key issue in the hot-carrier degradation model is the information about the carrier energetical distribution function which allows us to asses the...

We refine our approach for hot-carrier degradation modeling based on a thorough evaluation of the carrier energy distribution by means of a full-band Monte-Carlo simulator. The model is extended to describe the linear current degradation over a wide range of operation conditions. For this purpose we employ two types of interface states, namely, cre...

The electromigration failure development in typical copper dual-damascene interconnect structures is analyzed based on numerical simulations. The origin of the lognormal distribution of electromigration times to failure is investigated. Also, electromigration-induced void formation and evolution in advanced 0.18 μm dual-damascene lines are simulate...

The nano-era of semiconductor electronics introduces the necessity of simulation methods which describe the electron transport in ultra-small devices in a mixed mode where quantum-coherent processes are considered along with the de-coherence processes of scattering. The latter can be conveniently described in the Wigner picture of quantum mechanics...

We investigate the influence of the statistical distribution of copper grain sizes on the electromigration time-to-failure distribution. We have applied a continuum multiphysics electromigration model which incorporates the effects of grain boundaries for stress build-up. The peak of tensile stress develops at the intersection of copper grain bound...

We study the impact of microstructure on nucleation and evolution of electromigration induced voids. The grain boundaries are described with a comprehensive model which includes the dynamics of mobile and immobile vacancies in dependence of mechanical stress. The surface of an evolving void is modeled by a three-dimensional level-set algorithm. Sim...

The effect of the microstructure on the electromigration failure development is analyzed. We investigate the influence of the statistical distribution of copper grain sizes on the electromigration time to failure distribution. Also, the effect of the microstructure on the formation and development of an electromigration-induced void is studied by s...

We present the application of a state of the art electromigration model on a dual damascene interconnect with typical copper microstructure. The influence of the microstructure on the formation and development of an electromigration induced void is studied by simulation and the results are compared with experiments. A close investigation has shown...

In this work we analyze the influence of the statistical distribution of copper grain sizes on the electromigration time to failure distribution based on numerical simulations. We have applied a continuum multi-physics electromigration model which incorporates the effects of grain boundaries for stress build-up. It is shown that the lognormal distr...

With the modern transistor size shrinking below 45 nm the traditionally used classicall drift-diffusion model to describe transport in the conducting channel is gradually loosing its validity.

Modern interconnect structures are exposed to high mechanical stresses during their operation. These stresses have their sources in interconnect process technology and electromigration. The mechanical properties of passivating films and the choice of process technology influence electromigration reliability. In this paper we analyze the interplay b...

The demanding task of assessing long-time interconnect reliability can only be achieved by combination of experimental and technology computer-aided design (TCAD) methods. The basis for a TCAD tool is a sophisticated physical model which takes into account the microstructural characteristics of copper. In this paper, a general electromigration mode...

We have developed a two-dimensional non-parabolic macroscopic transport model up to the sixth order. To model higher-order transport parameters with as few simplifying assumptions as possible, we apply an extraction technique from Subband Monte Carlo simulations followed by an interpolation within these Monte Carlo tables through the whole inversio...

The standard electromigration model is extended by introducing an anisotropic diffusivity which depends on the general stress tensor and a new model of grain boundaries which describes dynamics of mobile vacancies and vacancies trapped in grain boundaries. The application scenario for electromigration simulation is presented. The new calibration an...

a b s t r a c t In order to describe carrier transport in inversion layers we have developed a two-dimensional non-par-abolic macroscopic transport model up to the sixth order. To model the transport parameters with as few simplifying assumptions as possible, we apply an extraction technique from Subband Monte Carlo sim-ulations followed by an inte...

The demanding task of assessing a long range interconnect reliability can only be achieved by combination of experimental and TCAD methods. A basis for TCAD tools is a sophisticated physical model which takes into account the microstructural characteristics of copper. In this work a general electromigration model is presented with a special focus o...

Sacrificial etching is one of the most important process steps in micro-electro-mechanical systems technology, since it enables
the generation of free-standing structures. These structures are often the main part of micro-mechanical devices, intended
to sense or induce a mechanical movement. The etching process transforms an initial multi-segmented...

We present a two-dimensional tabularized higher-order transport model based on extracted parameters from a Subband Monte Carlo
(SMC) simulator. Important effects like quantum confinement and surface roughness scattering are automatically taken into
account. Device parameters like the electron temperature or the output characteristic of a SOI MOSFET...

The most accurate way to describe carrier transport is to solve the Boltzmann transport equation (BTE), for instance with the very time consuming Monte-Carlo (MC) technique. On an engineering level however macroscopic transport models are more efficient. Multiplication of the BTE with weight functions, approximation of the scattering integral with...

In MEMS fabrication micro-mechanical components have to be partially released from a substrate. Selectively etching away sacrificial layers, such that a free standing structure remains, is a widely used technique for this purpose. Free standing structures allow MEMS devices to induce or to sense mechanical movements or vibrations.
During sacrificia...

For process and device simulation, very high mesh densities are often required to obtain accurate simulation results. Unfortunately, the required mesh densities depend often on a direction. Conventional mesh-refinement strategies generate isotropic meshes with a high amount of mesh points, reaching the memory and time limits in particular for three...

This paper presents an anisotropic adaptation strategy for three-dimensional unstructured tetrahedral meshes, which allows us to produce thin mostly anisotropic layers at the outside margin, i.e., the skin of an arbitrary meshed simulation domain. An essential task for any modern algorithm in the finite-element solution of partial differential equa...

We report an experimental and simulation study for introducing Boron ions into high Ge content relaxed SiGe layers and into Ge wafers. The successful calibration of our Monte Carlo ion implantation simulator for this wide class of materials is demonstrated by comparing the pre- dicted Boron proles with SIMS data. The larger nuclear and electronic s...

We present a Monte Carlo simulation study for introducing boron ions into Ge in the energy range from 5 to 40 keV. The successful calibration of our ion implantation simulator for crystalline Ge is demonstrated by comparing the predicted boron profiles with SIMS measurements. The generation of point defects are calculated with a modified Kinchin-Pe...

The characteristics of modern semiconductor devices are strongly influenced by quantum mechanical effects. Due to this fact,
purely classical device simulation is not sufficient to accurately reproduce the device behavior. For instance, the classical
semiconductor equations have to be adapted to account for the quantum mechanical decrease of the ca...

It is well known that the simulation of time-to-failure for copper (Cu) metal lines requires modeling of vacancy electromigration as well as void nucleation, growth, and movement. Because of the complexity of this problem, different approximate approaches to the physical formulation and solution appear in the literature. Based on our work for two-d...

When cellular based topography simulation is coupled with polygonal data structures it is necessary to extract a triangular representation of the surface of the simulated structure after a deposition or an etching process from the cellular discretization. In this work an advanced multistage cellular postprocessing algorithm is presented which is ca...

Optimizing process- and layout-design in the development of modern electronic devices is key to achieve required characteristics. Coming along with the growing complexity of device structures, associated effects must be considered in an even more complex manner. The use of three-dimensional process- and device-simulation tools is inevitable. Becaus...

We present a methodology for characterization and optimization of SiGe HBTs from our 0.8 μm BiCMOS technology. It involves process calibration, device calibration employing two-dimensional device simulation, and automated Technology Computer Aided Design (TCAD) optimization. The simulation results show a very good agreement with experimental data....

In todays high voltage processes the optimization of process and layout design is a key point to get competitive products. Effects like punch-through between two junctions and breakdown near the surface of the wells make it necessary to ana-lyze complex three-dimensional process steps by simulators which give accurate answers to the process enginee...