IMAGING SPATIAL VARIATIONS IN RESISTANCE ALONG ELECTRICAL CONDUCTORS

A nondestructive, noncontact method of imaging resistance variations a long electrical conductors is described. It is especially suitable for locating resistance variations in interconnect lines buried beneath l ayers of passivation. In its implementation, an intensity modulated la ser beam is scanned over the circuit carrying a de current and the vol tage induced in the circuit at the modulation frequency is used to var y the intensity of a synchronously scanned display. Resistance variati ons, such as caused by defects, produce variations in the image thereb y identifying their spatial location. Under certain circumstances, oth er features in the immediate vicinity of the conductors, such as reman ent photoresist and decohered interfaces, can also be imaged. An advan tage of the method is that the electrical circuitry in the device or p ackage call be used. (C) 1998 American Institute of Physics.