Download Microlithography Chapter 2 E Beam Lithography b

There are 64 available Layers, numbered 0 to 63. Each primitive object (Boundary, etc.) lies on one of
these layers. Each layer number typically represents one mask or electron-beam exposure step in a
process.
A specification of GDSII format appears in the appendix to this chapter, portions of which are reprinted
by permission of Cadence Design Systems.
2.6.5.2 CIF
The Caltech Intermediate Format, or CIF 2.0, is specified officially in A Guide to LSI Implementation,
Second Edition, by R. W. Hon and C. H. Sequin, [110] and a nearly identical description appears in
Introduction to VLSI Systems, by C. Mead and L. Conway. [111] This format is far simpler than GDSII
and has the advantage that it is readable, using only ASCII characters. While providing nearly all of
the functionality of GDSII, there are a few differences:
•
•
•
•
Names of cells are not supported. Instead, cells are numbered.
Datatypes are not supported. These are commonly used to assign different doses within a
pattern. Therefore, proximity effect correction requires patterns to be split into multiple layers.
There is no limit on the number of vertices in a polygon; therefore, CIF interpreters either set
arbitrary values or simply run out of memory.
The array structure (a square array of cells of n m elements) is not supported and so the users
of CIF have invented extensions to the format. These extensions have not been added to the
CIF standard.
CIF is widely used by universities using the Berkeley CAD tools to design circuits for the MOSIS
integrated circuit foundry service. [112] MOSIS requires a number of sensible restrictions on CIF data:
[113]
•
•
•
•
•
•
•
•
•
•
Polygons (P) must have at least three points; other than this, arbitrary polygons are accepted.
Wires (W) must have at least one point.
Round Flashes (R) must have a non-zero diameter.
The "delete definition" (DD) command is not allowed.
Symbols (cells) may not be redefined.
Lines are limited to 509 characters of text.
The following ASCII characters should not be used as "blanks": square brackets ([]), single
quotes ('), and periods (.).
User extensions are allowed but ignored. Wires are extended beyond the two extreme
endpoints by half the wire width.
The comment layer has a name ending with the letter "X". All geometry on this layer is read by
MOSIS but is totally ignored; however, any syntax error in this layer may cause the CIF file to
be rejected.
The bonding pad layer is named "XP" in all technologies.
2.6.5.3 DXF
DXF format is produced by the program AutoCAD as well as by a number of other inexpensive CAD
programs for Windows/DOS and the Macintosh. These programs were not designed for lithography
and so contain structures (e.g. three-dimensional figures) that have no meaning in this area. Also, the
common jargon (e.g., "cell") has been replaced with less familiar terminology (e.g. "block"). Like CIF,
this format does not support datatype numbers. DXF is useful only after it has been translated into
GDSII by a program such as that sold by Artwork Conversion Software [108] or those of various mask
vendors.
In DXF there can be considerable confusion over such issues as whether an enclosed line represents
a polygon or an actual line. Translation programs support different subsets of DXF and translate the
structures into GDSII using various sets of rules. Users of DXF are advised to submit sample patterns
for conversion before investing a lot of time in CAD work, and to bear in mind that the DXF file used for