This invention relates to the fabrication of thin film and hybrid integrated circuits, and in particular to the formation of crossover connections on said circuits.
Thin film and hybrid circuits presently enjoy extensive use in a wide variety of applications, such as filter circuits and memories switching and transmission systems. This extensive use has recently prompted the development of a new interconnect multilayer metallization system for such circuits comprising layers of titanium-copper-nickel-gold with an optional layer of palladium between the titanium and copper layers. See U.S. patent application of Lesh, Morabito and Thomas, Ser. No. 576,711 filed May 12, 1975, which is incorporated by reference herein. The basic advantage of such a system is the requirement of only a minimum amount of gold, resulting in great cost savings over the prior art systems.
One of the problems associated with this new system, however, was that a new fabrication technique was needed for forming "crossover" connections necessary for electrically connecting certain metallization across any intervening elements or metallization in the circuit. In particular it was desirable to utilize at least a portion of said interconnect metallization as a base layer for forming the copper spacing layer commonly utilized for crossover fabrication. This created additional problems in that the removal of the spacing layer would undercut the copper layer of the interconnect metallization.
It is therefore a primary object of the invention to provide a crossover fabrication technique which is fast, simple and economical and which is compatible with the constraints imposed by interconnect metallization systems which utilize layers of copper.