What is a GDSII file?

GDSII is a time honored format, used for data transfer of semiconductor physical layout between design tools, computers and mask fabricators. It is universally used and is the most frequently encountered file format in semiconductor work. GDSII was originally a format proprietary to GE Calma, before evolving into an industry standard.

GDSII format is a complete representation of a circuit with cells hierarchically placed on each fabrication layer. The format is binary and platform independent. Cells may contain geometrical objects such as polygons (2-dimensional boundaries), paths or other cells making the design hierarchical.

Databases for wafer level packaging or MCMs are limited in complexity, compared to the billion transistor interconnects common in contemporary wafers. Yet, they both rely on the same elements used to form cells, polygons, paths and arrays hierarchically forming cells and subcells.

Using a GDSII database:

A GDSII database can be transferred to the mask maker using a variety of media, from the obsolete 1/4" magnetic tape to any data disks compatible with the recipient's hardware, or preferably with no media at all by transferring the data directly via the internet.

A mask database is usually designed by drawing lines and filled-in blocks or areas, called polygons. The polygons in the database design may represent chromium on the mask, or clear areas of the masks. The mask designer has to specify to the mask maker how to interpret the database to obtain the desired result. For instance, the filled-in polygons can represent where metal will be applied on the final part, or it may represent holes in a dielectric layer where vias will be opened.