Metal to Diffusion

In the 6561 die shot, a metal to diffusion contact is recognisable by its white colour. It appears as a circle on a metal line with a black edge and pure white middle.

As can be seen from the above example, it is usually within an area that is green in colour. That is due to thin film effects and, if present, are usually associated with diffusion. This cannot always be relied on though when identifying a contact, particularly when the diffusion area is large and/or when most of the diffusion area is not under metal.

The larger diffusion areas might show a hint of green around the edges, but when the edges are not under metal, this appears as only a shade of grey. For this reason it is better to use the colour of the metal contact as the first indicator that it is a contact to diffusion. It's usually fairly obvious that there is no poly around the contact and therefore through elimination we deduce that it is a metal to diffusion contact, but in some cases the poly does get a bit close and its difficult to work out by any method other than the contact colour what it is connected to.