Norihiko Kotani

Three-dimensional topography simulation model: etching and lithography

An etching model in which topography is derived by solving a modified diffusion equation is introduced. This model is simple and makes it possible to simulate three-dimensional (3-D) topography accurately and quickly. Based on this model, a 3-D topography simulator which can be applied in the development of photolithography and isotropic/anisotropic etching has been developed. With this simulator, it is possible to simulate the series processes and multilayer etching, such as contact hole and trench etching. By simulating photolithography, diffraction and standing-wave effects can be found clearly in the 3-D topography of the developed photoresist. In the case of an etching process which is restricted by diffusion, the dependence of the etch front topography on the window width of the mask is examined. >

Reverse short-channel effect due to lateral diffusion of point-defect induced by source/drain ion implantation

Presents a physical model of reverse short-channel effects on threshold voltage caused by lateral diffusion of the Frenkel pairs (interstitial-vacancy) induced by ion implantation in source/drain region of n-channel MOS devices. Based on the process and device simulation, it is shown that lateral diffusion of the Frenkel pairs enhances diffusion of channel dopant, and results in nonuniform lateral distribution. This phenomenon causes the threshold voltage increase in the short-channel devices. The authors extracted parameters on point-defect diffusion from the comparison of calculated results with experimental data on threshold voltage. Calculated arsenic profile in the source/drain region using those parameters shows good agreement with the experimental data measured by secondary ion mass spectroscopy (SIMS). The close agreement between simulation and experimental results both on the arsenic profile in source/drain region and threshold voltage confirms the validity of the model and extracted parameters. >

A complete substrate current model including band-to-band tunneling current for circuit simulation

A simple and accurate substrate current model that is valid in the whole operation region of a MOSFET with various dimensions is presented. The theory is based on hot-carrier induced impact ionization and band-to-band tunneling (BTBT). All the parameters in the model can be assigned proper physical meanings and are easily extracted from the measurement data. The model is incorporated in a Mitsubishi Circuit Simulator (MICS). Both the accuracy and the efficiency of the model are shown by experiment and simulation, and hence make the simulator useful for designers who care about low power applications. >

3-D numerical modeling of thermal flow for insulating thin film using surface diffusion

This paper presents a three-dimensional (3-D) numerical surface diffusion model of BPSG glass flow of surface tension. The analysis region is divided into small cubic cells. Material surface is described as an equi-concentration (equi-existence rate) area which is obtained by linear interpolation between the cells. 3-D surface curvature is defined as the ratio of the increment of surface area to that of volume in a small interface area. Flux of flow is proportional to gradient of the surface curvature, and the direction is from positions of larger curvature to that of small curvature. The flow algorithm is that particles move from the mass-center of the equi-concentration area of a cell to that of the neighbor cells across the contact lines of the cell boundary and the equi-concentration area. This paper presents two 3-D simulations of flow which show that this model can be applied for not only cylindrical symmetry but also general 3-D topography. Also, the surface diffusion coefficient for the total concentration (C/sub imp/: P/sub 2/O/sub 5/ and B/sub 2/O/sub 3/) is derived using the model by fitting 2-D simulations to the experiments at 850/spl deg/C. >

A simulation of plastic deformation of silicon during thermal oxidation

Plastic deformation of silicon during thermal oxidation has been simulated using the finite element method. The von Mises yield criterion is assumed for the plastic deformation of silicon. In order to solve a pure elasto-plastic problem, an elasto-visco-plastic algorithm is used with stationary conditions. As an application example, local oxidation of silicon has been simulated, and the result demonstrates that plastic deformation is initiated at the edge of the nitride mask, and expands into substrate silicon as oxidation proceeds.<<ETX>>

New topography expression model and 3D topography simulation of Al sputter deposition, etching, and photolithography

It is shown that the material surface can be described by the constant concentration area (the contour surface), by using the continuity principle at the material surface and considering the essential property of the material surface. Based on this model and the conservation of mass, the authors present a simulation algorithm and develop a 3D topography simulator (3D MULSS: Three-Dimensional Multi Layer Shape Simulator). It is demonstrated that this simulator can simulate the coverage of Al sputter deposition accurately, by comparing simulations and experimental results. 3D MULSS can also simulate the sequential processes of deposition, etching, and photolithography in three dimensions. In addition, it is shown that the proposed model can be applied to the surface tension by the 2D simulation of reflow.<<ETX>>

Three dimensional topography simulation model using diffusion equation

An etching model for three-dimensional topography simulation is proposed in which the topography is deduced by solving the diffusion equation. A 3-D topography simulator called 3-D MULSS (multilayer shape simulator) has been developed on the basis of this model. Using this program, contact hole and trench etching was simulated exactly, and the computation was extremely fast.<<ETX>>