High Speed Field Programmable LSI Using Current-Drive Silicidation

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The antifuse device, that enables to drastically shorten the development cycle time of LSI circuits, was developed using tantalum/amorphous silicon/tantalum structure. We have shown that the silicidation reaction, that usually occurs only at temperatures higher than 700ﾟC,can be carried out at room temperature by the "current-drive silicidation" allowing a very fast programming of the antifuse. Antifuse devices made by ultraclean plasma process can be programd by "current drive silicidation" in the short time of less than 1 nsec, that is equivalent to a reaction speed of 5000m/sec, unimaginable in usual thermal reaction. The contact resistance after the silicidation is less than 30 OMEGA, and before the silicidation, the amorphous silicon, when deposited at temperature in the range of 200-250ﾟC,limits the leakage current at a level low enough to separate the on and off states. We have shown that by depositing the amorpous silicon over the tantalum film in sequence in a multi chamber de … More position system, without exposing the tantalum surface to the clean room air, there is no degradation of the antifuse up to a temperature as high as 400ﾟC.In order to characterize the origin of the leakage current under the operation bias and the mechanism of the current drive silicidation, we have studied antifuse structures using tantalum, titanium, and aluminum as the metal. In addition, we have formed Schottky diodes of the type tantalum/amorphous silicon/crystalline silicon, using silicon substrates of both, n and p type, with the purpose of characterizing the barrier height and the diode characteristics. We have also clarified many of the cilicidation mechanism by studying the contact resistance as a function of the programming parameter, as well as by analyzing SEM and TEM pictures of the cross sections at the contact region. Finally, in order to establish design rules of practical LSI circuits, TEG's were carefully designed to minimize the parasitic capacitances and resistances, using nMOS technology. From the results obtained in this research, the fundamentals of the fabrication process of antifuse structures of the type tantalum/amorphous silicon/tantalum, which allows high speed programming and very low on state resistance, were established. Less