From "Microelectronics Technology Alert"

Copyright (c) 1997, Technical Insights/John Wiley & Sons, Inc., New York NY

Used with Permission....

A software package developed by Silvaco International, Inc. provides sophisticated treatments for a surprising range of semiconductor processes, including lithography with optical proximity correction, film deposition with keyhole voids, and plasma etching. By covering virtually all deep submicrometer processes, chip developers have a way of checking design and process variations without resorting to fabrication of test wafers.

The Athena software package integrates several separate models developed by the company. Ssuprem4 is a cousin of Stanford's famous Suprem IV package, where both models originated from the same early Stanford product. Ssuprem4 handles diffusion, implantation, oxidation and silicidation. Optolith models the lithography processes. Elite is an etch model that includes a plasma-etch treatment. The models are primarily executed with finite-difference and finite-element analysis.

A number of factors make lithography simulation especially difficult. Printed images never exactly reproduce the mask pattern because of diffraction from mask edges and interference between adjacent features. Such proximity effects cause corner rounding, line shortening and nonuniform linewidths, and are corrected by mask modifications like adding serifs to corners. Optolith incorporates recently developed algorithms that perform optical proximity correction to allow evaluation of proximity effects.

An improved analytical ion implantation technique handles and saves time over the more accurate but cumbersome Monte Carlo method, and provides more accuracy than previous analytical models and look-up tables.

The plasma-etch model in Elite includes calculation of ion- angular dependencies, and concentration and stress-dependent etch rates over complex topologies.

The company's next step is to provide a full suite of 3D models, using volume-based grids with tetrahedral elements. Most process models attempting 3D simulation use prismatic elements, which provide less accurate results in contemporary device geometries, especially in surface topography and sidewalls. The full 3D models are expected in 1998.

The Athena version 4.0 1D and 2D process-simulation software package is available commercially.

Copyright 1997, John Wiley & Sons, Inc., New York, NY 10158

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