Delta Effects on the Contacts

When the contact holes are etched, there is some real world uncertainty about the actual dimensions. If you over-etch the edges evens lightly, that hole will get much bigger. Consequently, the size and width you use for your contact is in reality variable. You need to make sure when you design your resist or you know enough about the way the resistor is built in order to account for this physical discrepancy.

The manufacturers will give you the process variation numbers. They'll measure these for you. You might ask, for example, "If I draw it at 1 micron wide, how big will it end up on the mask?" They might reply, for instance, "If you draw it like this it might oversize by 0.1 micron."

This difference between drawn and real world dimensions is what we call the delta on this width (also called tolerance, error, variation, change in dimension, slop or change). The delta could be positive or negative, over-processed...