Patent ID: 7557921

Claim:
A method of monitoring a characteristic associated with a product feature on a semiconductor product, the method comprising: providing a proxy target formed from at least one substructure that corresponds to a product feature, wherein the substructure is not individually resolvable by an optical tool; determining a characteristic of the proxy target based on optically monitoring the proxy target using the optical tool, wherein the characteristic of the proxy target is an amount of overlay error that is present between two sets of structures of the proxy target; and based on the determined characteristic of the proxy target, determining whether the corresponding product feature has a characteristic that is a line shortening effect that is within a predetermined specification, wherein it is determined whether the line shortening effect is within a predetermined specification when the overlay error determined for the proxy target is not within a predetermined specification, wherein the predetermined specification of the line shortening effect corresponds to whether the corresponding product feature will likely result in a faulty device that decreases yield, wherein the proxy target comprises a first set of anchor structures that have shape and position characteristics that remain substantially the same when a process for fabricating the proxy target changes and a second set of structures that are sensitive to line shortening.