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Titanium Overlay on Metallurgy

IP.com Disclosure Number: IPCOM000072876D
Original Publication Date: 1970-Oct-01
Included in the Prior Art Database: 2005-Feb-22
Document File: 1 page(s) / 11K

Publishing Venue

IBM

Related People

Gniewek, JJ: AUTHOR [+2]

Abstract

The use of a titanium overlay in the range of a few hundred to several thousand angstroms thick over Al or Al/Cu metallization reduces the amount of current induced mass transport with resultant increase in stripe lifetime. While it is possible that there is an alloy effect between the overlay and the metallization, it is more probable that the resultant advantages occur as a result of the mechanical strength of the titanium film which forms a surface barrier layer, and thereby effectively removes the free surface of the covered film. This effect removes the vacancy source at the surface and prevents accumulation of vacancies, via mass transport, in the form of voids with subsequent metallization failure.

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Titanium Overlay on Metallurgy

The use of a titanium overlay in the range of a few hundred to several thousand angstroms thick over Al or Al/Cu metallization reduces the amount of current induced mass transport with resultant increase in stripe lifetime. While it is possible that there is an alloy effect between the overlay and the metallization, it is more probable that the resultant advantages occur as a result of the mechanical strength of the titanium film which forms a surface barrier layer, and thereby effectively removes the free surface of the covered film. This effect removes the vacancy source at the surface and prevents accumulation of vacancies, via mass transport, in the form of voids with subsequent metallization failure. The properties of the overlay film require high mechanical strength, minimum amount of alloying with the host metallization to keep resistivity low, and a low electromigration rate. In addition to titanium, other materials useful for overlays include nickel, niobium, vanadium, tantalum, molybdenum, tungsten and zirconium.

The overlay is deposited immediately over the metallization prior to subetch, or the overlay can be deposited after subetch to totally enclose the stripe. However, the latter modification requires a double photoresist process.

In addition to the characteristics of the described overlay, the diffusion rates of Al and Cu into the overlay film should be small, and the overlay film should form a protective oxide on it...