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How to Describe the Geometry of Your Target

 

The simulation geometry may be defined either by using the PED (PIF Editor), a graphically supported tool for geometry specification embedded into VISTA (Viennese Integrated System for Technology CAD Applications), or by writing a geometry file containing all vertex coordinates, lines, faces, etc. using any text editor. The binary PIF (Profile Interchange Format) files which have the format used within VISTA (PED) have the default extension .pbf and cannot directly read by SESAME. But these files can be automatically converted after their generation by means of the PED within the graphical user interface for input deck generation (see Chapter 5.2). Only ASCII files using the format which is described in this chapter can be specified in the input deck by means of the CGFILE variable in the &TARGET namelist.

If the VISTA system (or the necessary parts of it) is (are) installed, the PIF Editor (PED) can then be used to generate a geometry with the corresponding material description (for further information about the PED please refer to Chapter 5.3 or the appropriate VISTA manual). The resulting PIF file may then be transformed, as already mentioned, within the GUI.

When defining the geometry by hand, two main points have to be obeyed for the geometry description:

In the geometry file first the faces describing the different regions of the structure have to be defined. The number of faces (NFC) is the first entry in the geometry file; it must be the same as defined by NREG in the input file in the &TARGET record (see chapter 9.4). Then the faces are described. A face is defined by

Every entry has to be written on a separate line. This leads to the following structure:

NLNS[,ISEG]
P_1
P_2
.
.
.
P_NLNS

The face is assumed to go from point P_1 via the following points P_2 ... to point P_NLNS and it is closed automatically; so every point must only be referenced once. The index of the points is automatically generated from the order of the specification of the points.

Note: The order of the faces must correspond to the order of the regions in the input file!

The definition of the points is the next task. First the number of points (NPTS) has to be given and then every point is defined on a separate line by its x- and z-coordinate:

NPTS
x_1, z_1
x_2, z_2
.
.
.
x_NPTS, z_NPTS

Note: The unit of the coordinates is Å!

Here follows an example for a geometry file. The geometry consists of a nitride mask, an oxide spacer, a thin (15 Å) screening oxide and the crystalline substrate. It is shown in Figure 6.8.

  
Figure: Geometry for the example consisting of three regions: I nitride mask, II silicon substrate, III spacer and screening oxide. The coordinates are in Å.

3                       number of regions (faces)
4                       number of points for region 1
 1                      point number
 2
 3
 4
5                       number of points for region 2
 4
 3
 5
 6
 7
6                       number of points for region 3
 2
 8
 9
 10
 5
 3
10                      total number of points
0.0 0.0	                coordinates (x,z) of point 1
1000.0 0.0              coordinates (x,z) of point 2
1000.0 1000.0           etc.
0.0 1000.0
4000.0 1000.0
4000.0 6000.0
0.0 6000.0
1500.0 500.0
1500.0 985.0
4000.0 985.0

As already mentioned the geometry consists of three faces: The first region consists of 4, the second one of 5 and the third one of 6 points. Altogether ten points are required for this geometry.



next up previous contents
Next: How to Specify Up: How to Specify Previous: How to Describe



Horst Wagner
Tue Mar 19 10:24:55 MET 1996