Layer Mapping

One of the most important aspects of importing a GDSII file is in mapping the GDS streams to your Sonnet project. The GDSII file does not contain the information listed below, which Sonnet requires to translate the GDSII file into a Sonnet project. This information is conveyed to Sonnet through the Layer Mapping settings, found in the Import Wizard.

1.   Which GDS streams are important to translate (for example, text layers are usually not translated)
2.   The physical location and order of the layers (i.e., levels) in the Sonnet project (i.e., the stackup)
3.   The object type that the GDS data type represents (planar metal, via, or dielectric brick)
4.   The material properties of the polygons

Sonnet’s Technology Layers can be used to store items 2, 3 and 4 making translations much more efficient.

Sometimes you do not know some of this information before translating, especially the physical location and order of the layers, and the object type of the stream.   If this is the case, you may need to do a “blind” import, which allows you to look at the resulting polygons to determine the purpose of the GDS stream. Then, do a second import using the knowledge you learned from the first import. However, caution should be used when using this approach since you would not be able to detect if a given stream contains objects that do not translate due to a limitation of the translation (see Not All GDSII Structures are Supported for more information.)

The stream mapping can be accomplished three different ways:

1.  Manually entering the information at the time of import: This is accomplished with the Layer Mapping page of the Import Wizard as shown below.

Often, you only need to enter this information on your first import, then one of the other two methods below can be used for subsequent imports.

2.  Loading an external layer file: The layer file contains the mapping from the GDSII streams to the Sonnet levels, as well as all the other settings in the Layer Mapping dialog box. You use the Save button to create a layer file and the Load button to use a previously saved layer file to enter the settings. This method is generally not as useful as the template method below because the layer file does not contain other useful information, such as material properties.
3.  Using a project file as a template: This is the recommended method. Typically, after your first import, and after setting up all your settings, you would save the file as a template project to be used for subsequent imports. When using a template file, the Layer Mapping dialog box is automatically filled in for you using information included in the template.

Mapping information in your template file is stored in the Technology Layer definitions. Technology Layers allow you to define a group of objects with common properties including the metal level on which they are placed in your Sonnet project; they may also store the import/export settings for GDSII for the project. For more information on Technology Layers, please see Technology Layers.

Sonnet Stackup

In order to properly map the layers in the GDSII file to the Sonnet project, you need to have an understanding of the metal levels convention in Sonnet. Below is a 3D view of a Sonnet project with two metal levels; the stackup manager for the project is also shown. Note that level 0 is the highest metal level and is attached to the bottom of the top dielectric layer. Level numbers increase as you move down through the dielectric layers.

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