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Derived Layers using Boolean Operations

Many of the newer layout files will require a Boolean operation on more than one layer in order to enable correct net tracing. This is due to advanced lithography approaches that start with an array of parallel stripes. A second layer then "cuts" the stripes where needed.

derived poly layer

The net tracing is done on the "derived" layer - not on either of the actual GDSII layers.

The client controls this behavior by defining it in the stackup file.

Derived Layer Specification

So how do we instruct Nettrace to produce and use a "derived" layer. There are actually two steps: a) generate a new derived layer by defining operations on existing layers; b) use the "derived" layer in the conductor (METAL) stackup or in other sections.

  1. A derived layer number must be represented as 00N (N > 0) and 00N uniquely identifies a single derived layer. e.g 001, 0031 etc.

  2. Every derived layer MUST be represented by a '00' number and the presence of a '00' number in any of the sections of the technology (.tlib) file will be interpreted as a derived layer.

  3. A derived layer can be used anywhere a standard layer & datatype (L:D) or a set of layers with the same layer number (L) can be used in the technology file.

  4. All derived layers MUST have a definition.

Defining a Derived Layer

A derived layer is defined inside of a block known as a SYNTHESIZE block.

#Derived_Layer_Tag    Operation
0017                  17:20 - 17:30

In the example above, a derived layer called 0017 is "built" by subtracting the data found on 17:20 from the data found on 17:30. This might be done if boundaries on 17:20 represented the vertical stripes used for poly and boundaries on 17:30 represented boundaries cut away from those stripes.

If one needs to generate multiple derived layers, additional lines can be entered into a single SYNTHESIZE block as shown below:

#Derived_Layer_Tag    Operation
0017                  17:20 - 17:30
0020                  20 | 120 | 122 | 124


Available operations between layers are:

    ' + ' (BINARY UNION)

    ' - ' (DIFFERENCE)

    ' & ' (INTERSECTION)

    ' ^ ' (XOR)