20-12-2012, 12:19 PM
Design Rules
Design Rules.ppt (Size: 336.5 KB / Downloads: 157)
Design rules are a set of geometrical specifications that dictate the design of the layout masks
A design rule set provides numerical values
For minimum dimensions
For minimum line spacings
Design rules must be followed to insure functional structures on the fabricated chip
Design rules change with technological advances (www.mosis.org)
Silicon Foundry
A standard
A foundry allows designers to submit designs using a state-of-the-art process
Each foundry state simpler set of design rules called lambda design rules
All widths, spacings, and distances are written in the form
Value =
TSMC (Thailand Semiconductor Manufacturing Corporation)
Physical Limitations
Line width limitation of an imaging system
The reticle shadow projected on the photoresist does not have sharp edges due to optical diffraction
Etching process problem
Undercutting of the resist due to lateral etching decreases the resolution
Electrical Capacitive Coupling
This occurs between closely spaced conducting lines
This leads to a problem called crosstalk
A portion of the electrical energy is coupled to another causing noise
This is a major problem in high-density design
Electrical Rules
An example of an electrical rule is the allowed width of a metal interconnect line
To avoid electromigration effects
The design rule set will stipulate the maximum current flow level permitted
Metal Vs PolySi/Diffusion
Metal lines can pass over both diffusion and polySi without electrical effect
It is recommended practice to leave between a metal edge and a polySi or diffusion line to which it is not electrically connected