8.20 Ssspd_chapter 6_part 7_introduction to athena_process simulator  (Page 3/5)

7.7.2.: Creatinga Device Structure Using ATHENA

7.7.2.1: Procedure Overview

ATHENA is designed as a process simulation framework. The framework includes simulator independent operations and simulator specific functions that simulate different process steps (e.g., implant, RIE, or photoresist exposure). This section describes ATHENA input/output and the following basic operations for creating an input file:

• Developing a good simulation grid

• Performing conformal deposition

• Performing geometric etches

• Structure manipulation

• Saving and loading structure information

• Interfacing with device simulators

• Using different VWF INTERACTIVE TOOLS

7.7.2.2: Creating An Initial Structure

This section will describe how to use DECKBUILD’s Commands menu to create a typical ATHENA input file. The goal of this section is not to design a real process sequence, but to demonstrate the use of specific ATHENA statements and parameters, as well as some DECKBUILD features, to create a realistic input file. You can find many realistic process input files among the examples and use them as a starting point in your process simulation.

Once DECKBUILD is running and the current simulator is set to ATHENA (see the VWF AUTOMATION, CALIBRATION, AND PRODUCTION TOOLS USER ’S MANUAL for more information), open and pin the Commands menu as shown in Table 7.5.. Then, select Mesh Define.... and the ATHENA Mesh Define Menu will appear. We recommend that you pin this popup because it will be used often in designing an initial mesh.

Table 7.5 Commands Menu

Defining Initial Rectangular Grid.

Now, you can specify the initial rectangular grid. The correct specification of a grid is critical in process simulation. The number of nodes in the grid Np has a direct influence on simulation accuracy and time. A finer grid should exist in those areas of the simulation structure where ion implantation will occur, where p-n junction will be formed, or where optical illumination will change photoactive component concentration. The number of arithmetic operations necessary to achieve a solution for processes simulated, using the finite element analysis method could be estimated as (Np) ^a , where a is of order 1.5 - 2.0. Therefore, to maintain the simulation time within reasonable bounds, the fine grid should not be allowed to spill over into unnecessary regions. The maximum number of grid nodes is 20,000 for ATHENA simulations, but most practical simulations use far fewer nodes than this limit.

To create a simple uniform grid in a rectangular 1 µm by 1 µm simulation area, click on the Location field and enter a value of 0.0. Then, click on the Spacing field and enter a value of 0.10. Then, click on the Insert button and the line parameters will appear in the scrolling list.

Note: ATHENA coordinate system has positive x axis pointed to the right along the structure surface and positive y axis pointed down to the depth of the structure.