8.25 Sspd_chapter 6_part 7_introduction to athena 6_process simulator  (Page 28/7)

SSPD_Chapter 6_Part 7_Introduction to ATHENA 6_Process Simulator.

7.7. Background of ATHENA.

7.7.3. Choosing Models In SSUPREM4

This section describes how to simulate process steps (e.g., implantation, diffusion/oxidation, epitaxy, and silicidation) specific to the SSUPREM4 module of ATHENA. Also discussed, are the SSUPREM4 model statements, such as METHOD, OXIDE, MATERIAL, and IMPURITY.

When simulating any process involving dopant or its diffusion or both, it is absolutely critical for simulation accuracy to use the appropriate model. Process steps where correct choice of models are vital include implantation, diffusion, rapid thermal annealing, oxidation, and epitaxy . This section provides specific advice on which models should be used for each process step.

7.7.3.1: The Reason for Multiple Models for Each Process

The key to simulating any dopant related process is to accurately account for damage in the semiconductor. For example, in silicon processing, typical implantation doses can cause sufficient damage to the substrate to enhance dopant diffusion rates by three orders of magnitude or more, so choosing the wrong model in this instance will result in inaccurate results.

Well known device anomalies such as the Reverse Short Channel Effect in MOS processing or the emitter push effect in bipolar processing are wholly the result of such damage enhanced diffusion.

Other processes that consume the semiconductor, such as oxidation and silicidation also inject damage into the substrate. This must be accounted for if accurate dopant profiles are a requirement.

This section aims to provide you with a set of rules outlined, indicating the correct model that can be used most of the time without you having a detailed knowledge of the physics involved. The usual rules of model selection apply here. The more complicated the model, the greater the simulation time. There is always a compromise between simulation accuracy and simulation time. The following sections describe when to use the hierarchy of models so that the most complicated models are only used when you make a significant difference to the result.

7.7.3.2.: Choosing an Appropriate Model Using the Method Statement

The hierarchy of diffusion and damage models available is broadly related to the maximum level of damage already in the semiconductor or the maximum level of damage that the next process step is likely to introduce at any particular time during the process flow. The level of damage in the semiconductor at any one time is not a static quantity but will depend on when and how much damage was induced by a process step and how much annealing has occurred in subsequent thermal steps. The range of models available to you can account for all of the above effects and allows accurate simulation of dopant diffusion if appropriate models have been chosen.