Caltech Intermediate Form - Geometry

Geometry

The LAYER statement (or the letter L) sets the mask layer to be used for all subsequent geometry until the next such statement. Following the LAYER keyword comes a single layer-name parameter. For example, the command:

L CC;

sets the layer to be the CMOS contact cut (see Fig. B.1 for some typical MOS layer names).

NM nMOS metal NP nMOS polysilicon ND nMOS diffusion NC nMOS contact NI nMOS implant NB nMOS buried NG nMOS overglass CMF CMOS metal 1 CMS CMOS metal 2 CPG CMOS polysilicon CAA CMOS active CSG CMOS select CWG CMOS well CC CMOS contact CVA CMOS via COG CMOS overglass

FIGURE B.1 CIF layer names for MOS processes.

The BOX statement (or the letter B) is the most commonly used way of specifying geometry. It describes a rectangle by giving its length, width, center position, and an optional rotation. The format is as follows:

B length width xpos ypos ;

Without the rotation field, the four numbers specify a box the center of which is at (xpos, ypos) and is length across in x and width tall in y. All numbers in CIF are integers that refer to centimicrons of distance, unless subroutine scaling is specified (described later). The optional rotation field contains two numbers that define a vector endpoint starting at the origin. The default value of this field is (1, 0), which is a right-pointing vector. Thus the rotation clause 10 5 defines a 30-degree counterclockwise rotation from the normal. Similarly, 10 -10 will rotate clockwise by 45 degrees. Note that the magnitude of this rotation vector has no meaning.

The WIRE statement (or the letter W) is used to construct a path that runs between a set of points. The path can have a nonzero width and has rounded corners. After the WIRE keyword comes the width value and then an arbitrary number of coordinate pairs that describe the endpoints. Figure B.2 shows a sample wire. Note that the endpoint and corner rounding are implicitly handled.

The ROUNDFLASH statement (or the letter R) draws a filled circle, given the diameter and the center coordinate. For example, the statement:

R 20 30 40;

will draw a circle that has a radius of 10 (diameter of 20), centered at (30, 40).

The POLYGON statement (or the letter P) takes a series of coordinate pairs and draws a filled polygon from them. Since filled polygons must be closed, the first and last coordinate points are implicitly connected and need not be the same. Polygons can be arbitrarily complex, including concavity and self-intersection. Figure B.3 illustrates a polygon statement.