Some foundries request that each layer occupy a minimum percentage of the chip. To enforce such rules, additional pieces of geometry must be placed around the chip to fill that layer.

To check for proper minimum layer coverage, use the Check Area Coverage command (in menu Tools / DRC). To control the coverage rules, use the Coverage Preferences (in menu File / Preferences..., "Tools" section, "Coverage" tab). Each layer in the technology has a minimum percentage of coverage that is needed.

The coverage check proceeds in a "tiled" manner, checking rectangular areas of the cell. For example, to check each 100x100 unit area of the cell, set "Width" and "Height" to 100, and set "DeltaX" and "DeltaY" to 100.

The List Layer Coverage on Cell command is another way to compute the percentage of the cell that is covered by each layer. This command examines the entire cell without breaking it into tiled rectangles.

Use the Fill (MoCMOS)... command (in menu Tools / Generation) to automatically generate fill (see Section 9-8-2).