2.1 Overview
2.2 Reinitializing Sentaurus Structure Editor
2.3 Exact Coordinates Mode
2.4 Selecting Materials
2.5 Selecting the Default Boolean Expression
2.6 Creating Rectangular Regions
2.7 Rounding Edges
2.8 Defining Contacts
2.9 Setting Contacts at Existing Edges
2.10 Adding Vertices
2.11 Defining a Region as a Contact
2.12 Saving the Model
2.13 Assignment
This section is intended to familiarize you with some fundamental functions that Sentaurus Structure Editor supports. For this purpose, a 2D SOI MOSFET device, similar to the one shown in Figure 1, will be created using basic 2D geometric operations.
To start a new object and discard all objects that have been previously defined:
The corresponding Scheme command is:
(sde:clear)
This command restarts the Sentaurus Structure Editor environment and resets most of the internal variables to their default values. However, some internal variables might remain defined at their previously set values.
In Sentaurus Structure Editor, geometric objects can be drawn manually. However, for most applications, it is convenient (and sometimes necessary) to specify explicitly the coordinates of the object, for example, to allow for precise alignment of different regions.
To do this, you must activate the Exact Coordinates mode. This mode is deactivated by default when Sentaurus Structure Editor initially starts.
To activate the mode, choose Draw > Exact Coordinates.
A check mark now precedes the Exact Coordinates command indicating the mode is active. When the mode is active, all subsequent command operations that involve the placement of any object will display a dialog box in which exact coordinate values can be entered for the object being edited.
All materials used by Sentaurus Structure Editor are accessible from the Material list.
To set the material to be used for new objects:
Until a new material type is selected, all newly added regions consist of the material type that is currently being selected.
In some applications, a device has only one region. In most other cases, a device has multiple regions. When you use the GUI to build a device with multiple regions, the later-added regions might intersect existing regions. If this occurs, a predefined scheme is required to resolve the overlapping region.
Sentaurus Structure Editor includes several predefined schemes. For example, to select the New Replaces Old scheme in which newly added regions replace old regions where they overlap:
The corresponding Scheme command is:
(sdegeo:set-default-boolean "ABA")
To create a rectangular, silicon substrate region:
The corresponding Scheme command for the drawing operation is:
(sdegeo:create-rectangle (position -0.5 0.2 0.0) (position 0.5 1.0 0.0)
Other device regions can be created in a similar way as the substrate region. However, different regions often consist of different material types. Therefore, before drawing a region, select the required material type from the Material list (see Section 2.4 Selecting Materials).
Follow these rules to create the gate oxide region, the nitride spacer region, the polysilicon gate region, and the buried oxide region. Use the coordinates as follows:
Region | Material | Coordinates |
---|---|---|
Gate oxide | SiO2 | (-0.2 -40e-4), (0.2 0.0) |
Nitride spacer | Si3N4 | (-0.2 -0.2), (0.2 -40e-4) |
Polysilicon gate | PolySi | (-0.1 -0.2), (0.1 -40e-4) |
Buried oxide | SiO2 | (-0.5 0.1), (0.5 0.2) |
After these steps, the device structure is shown as in Figure 4.
The corresponding Scheme commands are:
(sdegeo:create-rectangle (position -0.5 0.2 0.0) (position 0.5 1.0 0.0) "Silicon" "R.Substrate" ) (sdegeo:create-rectangle (position -0.5 0.1 0.0) (position 0.5 0.2 0.0) "Oxide" "R.Box" )
In this example, the later-defined polysilicon gate region overlaps the previously defined spacer region. Since the New Replaces Old option has been set to be the default Boolean, the overlap is resolved in such a way that the gate region replaces the spacer region where the two regions overlap. Likewise, the later-defined buried oxide takes up the overlapped substrate region. Although this given structure also can be defined precisely without any overlap, the process would take more steps as more regions would have to be defined.
Sentaurus Structure Editor includes functions that round the corners and the edges of a structure.
To round the two outside corners of the nitride spacers:
Figure 6 shows the result.
The corresponding Scheme commands for the rounding operations are:
(sde:define-parameter "fillet-radius" 0.08 0.0 0.0 ) (sdegeo:fillet-2d (find-vertex-id (position -0.2 -0.2 0.0)) fillet-radius) (sdegeo:fillet-2d (find-vertex-id (position 0.2 -0.2 0.0)) fillet-radius)
In the command-line window, the displayed rounding command is (sdegeo:fillet-2d (list(car(find-vertex-id (position -0.2 -0.2 0.0)))) 0.08). In the above commands, a simplified expression applicable for a single vertex is used. The vertex to be rounded is selected using the command (find-vertex-id (position x y z)) instead of using mouse operations.
Contacts can be defined to allow the constructed device to be connected to outside power sources.
To define a contact:
Contacts become effective only after they are associated with part of the device structure. To associate a contact with a particular edge of a device:
The corresponding Scheme commands are:
(sdegeo:set-contact (find-edge-id (position -0.4 0.0 0.0)) "source") (sdegeo:set-contact (find-edge-id (position 0.4 0.0 0.0)) "drain")
The script version allows edges to be selected using explicit coordinates with the (find-edge-id (position x y z)) command instead of using mouse operations.
For the simulation of 2D SOI MOSFETs, artificial body-tied contacts are sometimes useful. These contacts are placed typically at the interface between the silicon epilayer and the buried oxide near the source side of the gate corner. Before such a contact can be defined, two additional vertices must be introduced.
To add vertices:
Figure 9 shows the device viewed in the Wireframe mode with all the contacts that have been defined.
The corresponding Scheme commands are:
(sdegeo:insert-vertex (position -0.1 0.1 0.0)) (sdegeo:insert-vertex (position -0.05 0.1 0.0)) (sdegeo:set-contact (find-edge-id (position -0.07 0.1 0.0)) "bodytie")
In some applications, a contact can cover the entire body of a (2D) region of the device. For example, the metal and polysilicon regions of a MOS device are often treated, as a whole, as ideal contacts.
To define such a contact:
The corresponding Scheme commands are:
(sdegeo:set-contact (find-body-id (position 0.0 -0.1 0.0)) "gate" "remove")
To save a model, choose File > Save Model, or press Ctrl+S, or click the corresponding toolbar button.
If the model has not been saved up to this point, the command displays a standard dialog box in which you can enter the file name for the output. Only the root name is required. Sentaurus Structure Editor appends implicitly all the extensions corresponding to different file formats.
The corresponding Scheme command is:
(sde:save-model "n@node@_geo")
This command saves the model geometry in the native ACIS format file n@node@_geo.sat, according to the specified file name n@node@_geo, where @node@ is replaced by the corresponding node number of Sentaurus Workbench. The Ref/Eval windows and parameters are saved in the Scheme script file n@node@_geo.scm, the mesh-related refinement and doping-related information is saved in the file n@node@_geo_msh.cmd, and the TDR boundary representation is saved in the file n@node@_geo_bnd.tdr.
In this example, no Ref/Eval windows have been created, so only the setting of the variable fillet-radius appears in the file n@node@_geo.scm.
Click to view all the commands discussed in this section in the command file geometry_dvs.cmd.
The complete project can be investigated from within Sentaurus Workbench in the directory Applications_Library/GettingStarted/sde/soifet.
In this assignment, you are encouraged to build a bipolar transistor structure as shown in Figure 12.
The tools discussed so far should allow you to work out most of the structure. However, to complete the assignment, you might need to be familiar with some additional tools that are explained here.
To move a vertex:
The corresponding Scheme command is:
(sdegeo:move-vertex (car (find-vertex-id (position Xold Yold Zold))) (position Xnew Ynew Znew))
To create a polygonal region:
The corresponding Scheme commands are:
(sdegeo:create-polygon (list (position -0.45 0.6 0.0) (position 1.2 0.6 0.0) ...)
"Silicon" "Substate")
Click to view the command file sigehbt_dvs.cmd.
The complete project can be investigated from within Sentaurus Workbench in the directory Applications_Library/GettingStarted/sde/sigehbt.
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