1. Field of the invention
The present invention relates to the field of multilevel integrated circuits, and more specifically, to the field of ULSI multilevel interconnection structures and their methods of fabrication.
2. Discussion Of Related Art
Modem integrated circuits are made up of literally millions of active devices such as transistors and capacitors. These devices are initially isolated from one another but are later interconnected together to formed functional circuits. The quality of the interconnection structure drastically affects the performance and reliability of the fabricated circuit. Interconnections are increasingly determining the limits of performance and density of modern ultra large scale integrated (ULSI) circuits.
FIG. 1 is a cross-sectional illustration of an interconnection structure which is presently used in the semiconductor industry. Formed in a silicon substrate or well 102 are active devices (not shown) such as transistors and capacitors. Interconnection lines 104 and 106, which are typically aluminum or aluminum alloys, are used to couple active devices into functional circuits. Metal interconnections 104 and 106 and substrate 102 are electrically isolated from one another by interlevel dielectric""s (ILDs) 108 and 110, respectively. Electrical connections are made between metal interconnections 104 and 106 through the use of metal vias 112.
The interconnection structure of FIG. 1 experiences several problems. As integrated circuit dimensions decrease, in order to increase circuit density and complexity, vias are becoming smaller by the square of the dimension decrease. Such small vias can cause both reliability and performance problems in a fabricated integrated circuit. Reliability problems are caused by high concentrations of current or current crowding at the corners 114 of via 112, as shown in FIG. 1. Current crowding in area 114 can cause self-heating effects which can cause electromigration. Electromigration can cause voids and open circuits and other reliability problems. Performance of small dimensioned vias is decreased due to an increase in contact resistance caused by a reduction of the interfacial contact area between via and interconnections. It is to be appreciated that contact resistance is becoming the major portion of the total interconnection resistance.
Another problem with the interconnection structure of FIG. 1 is the aluminum metal used for interconnections 104 and 106. Aluminum interconnections are known to suffer from electromigration. Electromigration in interconnections are known to cause voids which can cause open circuits and failures. Aluminum interconnections are also known to form hillocks which can result in nonplanar interconnection structures and can cause interlevel shorts with interconnections formed above and intralevel shorts with neighboring interconnection lines from the same level of metalization. These problems are magnified as line widths decrease and packing densities increase as in the case of future ULSI circuits.
Thus, what is desired is a ULSI compatible interconnection structure which exhibits excellent performance and reliability.
A novel, high performance, high reliability, high density, ULSI manufacturable, multilevel interconnection structure is described. The interconnection structure of the present invention is formed on a first insulating layer of an integrated circuit. A first multilayer interconnection comprising a first aluminum layer, a first refractory metal layer, and a second aluminum layer is formed on the first insulating layer. A second insulating layer is formed over the first multilayer interconnection. A conductive via of, for example, tungsten, aluminum, copper or TiN, is formed through the second insulating layer and into the multilayer interconnection wherein the via is formed down to at least the first refractory metal layer of the multilayer interconnection to form a high surface area contact with the first multilayer interconnection. A portion of the conductive via extends above the second insulating layer so that a high surface area contact can be made to a second interconnection which is formed on the second insulating layer and on and around the portion of the via extending above the second insulating layer.
A goal of the present invention is to form an interconnection structure which exhibits excellent performance and reliability even when formed to the small dimensions necessary for modern ULSI circuits.
Another goal of the present invention is to provide an interconnection structure which provides decreased current crowding around vias.
Still another goal of the present invention is to provide an interconnection structure which exhibits redundant current carrying capabilities.
Still yet another goal of the present invention is to provide an interconnection structure which is resistant to electromigration and related failures.
Still other goals and advantages of the present invention will become obvious from the detailed description of the present invention which follows.