Mathematical model of thermomigration of liquid inclusions through a crystal under stationary and non-stationary thermal conditions is presented. It is assumed that the mass-transfer is provided by diffusion only, the crystallization and dissolution processes are carried out in accordance with the diffuse interface mechanism for atomic-rough (non-singular) interfaces and screw-dislocation or two-dimension nucleation mechanisms for singular interfaces.

The package of computer programs based on this model enables simulation of the evolution of the cross-sectional shape of cylindrical liquid inclusions. It is possible to simulate the cases of various inclusion sizes, various relationship between the interface and volume mass-transfer restrictions, various liquid phase composition, thermal gradient under stationary and non-stationary thermal conditions as well. The main results of the simulation are presented.

Chemical reactions in the gas-phase and on surfaces are important in the deposition and etching of materials for microelectronic applications. A general software framework for describing homogeneous and heterogeneous reaction kinetics utilizing the Chemkin suite of codes is presented. Experimental, theoretical and modeling approaches to developing chemical reaction mechanisms are discussed. A number of TCAD application modules for simulating the chemically reacting flow in deposition and etching reactors have been developed and are also described.

A simple gas-phase and surface kinetic model describing the Metalorganic Vapor Phase Epitaxy (MOVPE) of GaAs from trimethyl-gallium (TMG) and arsine has been extracted from reported reaction mechanisms through sensitivity analysis. This model was coupled with fundamental descriptions of the flow, heat and mass transfer in MOVPE reactors. All the uncertainties of the model were lumped into the two rate constants of the surface growth reaction. Finite element simulations of GaAs growth in a rotating-disk MOVPE reactor reported in the literature were used to fit the two unknown rate constants. Without any adjustment, the model could predict observed growth rates at higher susceptor rotational rates. A more serious robustness test was the fully coupled 2-D simulation of GaAs growth in a horizontal MOVPE reactor by using a state-of-the-art code (MPSalsa) developed at Sandia National Laboratories. The model predicted observed growth rates reasonably well in 2-D fully coupled simulations of flow, heat and mass transfer. Further development of the kinetic model by testing different kinetic scenaria in 2- and 3-d simulations and by using data obtained at kinetically-limited growth conditions is planned in order to develop a reactor-independent simulator of the MOVPE of GaAs. Such a model will be essential for the development of a conceptual virtual MOVPE reactor, which can be used for reactor design, optimization and model-based control.

An approach for optimal design of vertical stagnation flow Metalorganic Vapor Phase Epitaxy (MOVPE) reactors that minimizes parasitic pre-reactions between the film precursors is presented. The use of axisymmetric multi-aperture inlets (e.g. tube-in-tube or concentric-ring inlets) enables the separation of incompatible precursors, while preserving the axial symmetry of the reactor. A careful selection of the inlet velocity of each stream and the distance between the inlet and the susceptor (reactor height) can lead to complete mixing just above the substrate, while keeping the contact time between the precursors in the gas phase low enough to suppress pre-reactions. This idea has been used by our group for growing high quality ZnSe films on GaAs substrates from (CH3)2Zn:N(C2H5)3 and H2Se diluted in H2 in a stagnation flow MOVPE reactor with an axisymmetric split inlet. A transport model describing the MOVPE of ZnSe, for conditions at which the growth rate is limited by the precursors' arrival rate at the surface, has been developed. A parametric study was performed aiming at identifying operating conditions in industrial-scale reactors that maximize film thickness uniformity while minimizing precursor contact time. Operation atGr/Re2<100 eliminated flow recirculations in the region above the substrate. Such recirculations may lead to formation of particulates by trapping reactants. Optimal conditions correspond to equal velocities of the inlet streams, satisfying the above criterion, and to the minimum possible reactor height leading to uniform film thickness across the substrate.

The important intermediates in the Ti plasma-enhanced CVD using TiCl4/Ar/H2 are investigated by ab initio molecular orbital (MO) calculations. From the experimental point of view, it is pointed out that'TiCls is a key species for the Ti deposition reaction. So, its reactivity with the Si and SiO2 substrates is estimated theoretically from the stabilization energy. The difference of the stabilization energies of TiCl3 between them, which is 12.3kcal/mol in Hartree-Fock level calculations with using the on-top deposition reaction model, indicates a longer existing time by the factor of 102 on SiO2 than on Si. In addition to these calculations, the stabilization energies on the suicide substrates are also calculated and compared with the results on the Si and Si02 substrates. But other reaction paths may have to be considered because the growth rates of Ti thin films onto between Si and SiO2 don't necessarily coincide with the tendency of calculated results.

A rigorous three-dimensional lithography simulator based on a recently developed single integral equation formulation for electromagnetic scattering is used in a simulation study of the effectiveness of using pre-distortions of mask patterns to compensate for linewidth variations in the resist patterns on nonplanar substrate topography. An efficient simulation methodology is used to reduce the number of required scattering calculations. Simulation results for different mask shapes and defocus conditions are presented.

Global model of oxygen transport in the melt and inert gas is proposed which is based on coupled two-dimensional stationary modeling of global heat transfer, laminar flow of inert gas and turbulent flow in Si melt, and transport of dissolved oxygen in the melt and SiO vapor in the gas. The model allows to study effects of process parameters like flow rate and pressure of inert gas, and rotation of the crucible on incorporation of oxygen into Si crystal.

In this work, the epitaxial silicon deposition by SiHCl3-hydrogen mixtures in a AMT 7700 barrel reactor was analyzed through a detailed model where a three dimensional flow dynamic was solved by reduction to a two dimensional geometry under cylindrical coordinates. The model was used to investigate the role of the reactor geometry and of the process parameters on the axial deposition uniformity. A comparison with industrial experimental data was also performed.

A 2-D axisymmetric finite element analysis has been performed on a vertical MOCVD reactor having a close-spaced water-cooled injector for which the gas is injected only 1.6 cm above the rotating disk. The analysis showed that the system has a much higher flow stability, in terms of suppression of unwanted thermally driven convection, than conventional reactors. In addition, the flow study has identified two kinds of flow recirculation, a purely thermally driven convection and a geometry assisted one. The former is initiated with gas flowing upward near the center of the disk circulating clockwise, the latter one is located near the chamber wall circulating counterclockwise. This result is important in interpreting experiments.

After discussing topography simulation, we summarize two approaches used to move surfaces in topography simulators used in virtual semiconductor wafer fabs; “front tracking” and “level set”. Front tracking is presented for two dimensional (2d) surfaces, and a number of examples are shown to demonstrate the approach. The level set approach is presented for three dimensional (3d) surfaces, and examples are shown. Though either approach could be used in both 2d and 3d topography simulators, this is by and large the current usage. Transport and reaction submodels needed for physically based process simulations will continue to be developed using experiments performed on structures that are inherently 2d, combined with three dimensional 3d transport simulations; i.e., “3d/2d” simulations. Three dimensional device structures will be generated using “3d/3d” topography simulations, using robust codes. Plasma enhanced deposition of silicon dioxide from TEOS is used as an example of how 3d/2d and 3d/3d simulations are used.

Starting from the Ising model for the bond-breaking algorithm associated to the problem of anisotropie etching of crystals, a method is used to write the discrete master equation for etching normally to indefinite large planes. This equation links the values of the absence probabilities for bonds placed in neighbouring lattice planes and can be transformed to describe a continuous spatial field of probabilities. The method allows the calculation of the etching rate angular diagrams. Examples are shown for several orientations and sets of parameters governing the bond-breaking scheme at atomic level. Comparisons with experimental results are provided.

We have extended a 2D simulation of grain growth to treat the effects of precipitates on the evolution of interconnect grain structures during post-patterning processing. It is known from experiments that different annealing histories result in different precipitate sizes and locations. Precipitates capture and effectively pin grain boundaries and inhibit grain growth and evolution toward bamboo structures. We find that even a small volume fraction of precipitates prevent an interconnect strip from reaching the fully bamboo structure by retarding grain growth and lowering the average grain size. At a late stage of evolution, cluster regions are pinned by precipitates on both sides, preventing further transformation to the by far more reliable bamboo structure. The results from grain growth simulations have been used with our electromigration simulator MTT/EmSim to investigate the dependence of interconnect reliability on linewidth and precipitate distribution. We find that in lines with precipitates the bamboo structure is not reached during post-pattern annealing even if the line width is smaller than the average grain diameter. Furthermore, it is found that while Cu in solid solution improves interconnect reliability, Al2Cu precipitates can inhibit post-patterning grain structure evolution to more reliable bamboo or near-bamboo structures so much that similar lines made of pure Al would be more reliable. Linked grain structure evolution and electromigration simulations allow process optimization for maximum interconnect reliability.

The Ion Beam Etching (IBE) model is developed assuming the analogy between the evolution of hydrodynamic surfaces and that of vacuum-solid interfaces. The main physical phenomenon in the IBE is the ion sputtering where the transfer of ion energy to the surface allows to eject the surface atoms. The local etching rate is thus proportional to the energetic flux and to the sputtering yield. Mask erosion and shadowing are taken into account in the model. The angular dependence of the sputtering yield permits to underscore the faceting and trenching phenomena which respectively represent the formation of the facets in mask comers and the overetching in the trench sides. Besides, the effect of mask erosion on pattern transfer of both trench and mesa structures is studied. In comparison with the experimental profile, the simulated etching profile of the mesa, based on the IBE model, shows a good agreement.

This study calculates the threshold voltage (VT) roll-off behavior caused by short channel effect (SCE) as a result of scaling and the reverse short-channel effect (RSCE) due to B segregation around source and drain junctions by using the 2D device simulator - SILVACO™-ATLAS. The simulation results are comparable with the experimental data. It suggests that the drift diffusion physics can predict SCE and RSCE very well to sub-0.25μ Si n-MOSFET devices. The modeling results indicate the VT roll off at shorter channel length for devices with higher substrate doping concentration. VT increases if the local p-dopant segregation exists around the source and drain junction. It is observed that RSCE is more significant for devices with lower substrate doping concentration and shorter channel length.

This paper presents a numerical-simulation-based investigation of drain current transients in floating body partially and fully depleted n-channel SOI MOSFETs. For both Zerbst-type and overshoot transients, analytical models are developed and validated. An original contribution concerns the detailed study of drain and source junction influences on the transient regime.

We discuss an improved quantitative mobility spectrum analysis (i-QMSA) of magnetic-field-dependent Hall and resistivity data, which can determine multiple electron and hole densities and mobilities. A fully automated computer implementation of i-QMSA is applied to a variety of synthetic and real data sets. The results show that the new algorithm increases the information available from a given data set and is suitable for use as a standard tool in the characterization of semiconductor materials and devices.

The three-dimensional Poisson's equation is solved by iterative methods and the resulting electric field is used in Newton's equation to simulate electron transfer in a charge-coupled device (CCD). The time dependence of charge transfer is studied through a random walk simulation of Newton's equation. Potential obstacles of the order of 0.03 V are seen to slow charge transfer. Electron motion is also followed in two spatial dimensions through Newton's equation in order to probe a more varied set of potential obstacles.

We present the modelling of a new two-terminal and low-voltage operating optoelectronic device based on MIS silicon structure with multichannel insulator and having as gate a transparent metallic tin-doped indium oxide (ITO) layer deposited by spray pyrolysis technique over the insulator layer. ITO layer has a multiple non-rectifier electrical contact with silicon substrate, in the SiO2 channel's region. Construction details of the process, together with its operating characteristics are given. The devices developed do not require external active electronic components (transistors, microschemes) to execute their functions and to transform analogue input optical signals to digital output form, highly important for a wide range of optoelectronic applications.

Theoretical modeling of ZT of (111) and (001) oriented PbTe/Pb1-xEuxTe multiple-quantum-wells (MQWs) is carried out assuming parabolic energy bands and the constant relaxation time approximation. The model calculation for the (111) oriented MQWs is compared with the recently obtained experimental results for the Seebeck coefficient and the Hall carrier concentration. The thermoelectric properties for (001) oriented PbTe MQWs are expected to have even better thermoelectric properties than the (111) oriented PbTe MQWs.