Debugging Requires Knowledge of Driver Location

An engineer in the failure analysis laboratory has generally highlighted a net because there is some sort of temperature or radiation anomaly physically detected by a camera or probe in the same region as the net. In order to convert this location into a circuit component and pin identification he often needs to know where the driver is located on the net as there many be many component and pin connections on the net. Nettrace can speed up this identification by doing a fairly simple computation. The computation consists of searching for all coordinates on the net where M1 is located over CONTACT and over DIFF.

Metal over Contact over Diffusion

The basic building block in digital IC’s is a pair of stacked FETs whose output are hooked together. This is built by first creating your diffusion regions. Two different diffusions are performed - a NDIFF (for N channel FETS) and a PDIFF (for P channel FETS).

Then openings in the insulating layer above the diffusions are created to form contacts to the diffusion.

Polysilicon is deposited next. It forms the gate of a FET where it lies over the diffusion regions.

Metal layer 1 is now deposited.

By performing a boolean (actually many times as needed) one can detect all the regions on the net where M1 is found over a contact and also over either a PDIFF or NDIFF area. These are the source or drain connections and are driver outputs.

Merging Multiple Contacts for a Single Driver

You can see that this driver consists of a stacked P and N device. There are a total of 7 locations where we identify the combination of M1|CONTACT|DIFF. But if this many locations were highlighted in a large design the display would be unecessarily confusing.

To address this we will define a "gap" value that generates a box around the center of each region.

A box is drawn around each of the seven contact locations.

Overlapping or touching boxes are merged and a bounding box is generated. In this case, the choice of the gap parameter generated two bounding boxes but a slightly larger value would produce a single bounding box and hence a single highlight for the driver.