File formats

CleWin supports the three main file formats used for photomask design, i.e. CIF, GDS-II and OASIS:

  • CIF – Caltech Intermediate Format
    A human readable text file format developed for the design of VLSI chips in the 1970’s and 80’s, see e.g.┬áCarver A. Mead and Lynn A. Conway, Introduction to VLSI Systems, Addison-Wesley, 1980.
    CIF is CleWin’s default file format because it can be easily extended to support additional features.
  • GDS-II – Graphic Data System
    A binary database format developed by Calma Company in the 1970’s. It has been the de-facto industry standard since the mid-1980’s.
  • OASIS™ – Open Artwork System Interchange Standard
    The OASIS format is trademark of Semiconductor Equipment and Materials International (SEMI). It was introduced in 2004 as a more efficient replacement for GDS-II.

CIF, GDS-II and OASIS are all hierarchical file formats. That is, objects can be combined into “symbols” (or “cells”) and placed in a design many times (“symbol instances”). This is very useful for repeating structures: changing the symbol definition will change all instances simultaneously. Furthermore, it can significantly reduce file size because data for the symbol definition is only stored once.

A photomask design typically corresponds to a “layer” in the file, although layers can also be used for other purposes (e.g. for guidelines or showing chip outlines).

Each file format imposes specific limitations on a design. For example, the CIF format only allows rectangles, polygons, wires and circles as basic shapes and the GDS-II format only allows polygons and wires.