Metallization in microelectronics

Abstract

Continued improvements in the design and fabrication of semiconductor devices have led to the introduction of medium and large scale integration of microcircuits. These advances have placed severe demands on metallization techniques, requiring metal contacts to shallow junction devices and definition of metal interconnections that are closely spaced and of a narrow pattern. Aluminum is the most widely used metal in microelectronics for providing the necessary contacts and interconnections. The contact resistance of the SiAl interface is sensitive to surface preparation, the vacuum ambience of the Al film deposition and contact sintering. Controlled contaminations, such as H 2O, CO and O 2, have been introduced during the Al film deposition in order to determine their effects on Al/Si contacts. Extensive studies have shown the interdependence of the film deposition parameters, the physical properties of the Al films and the dominant failure mechanisms, such as electromigration, that limit the reliability of integrated circuit interconnections. For high speed very shallow emitter-base junction devices, Al in silicon contact windows can penetrate to the junction during sintering and can cause leakage. Solutions to this problem include the use of Al + Si films, PtSi contacts with a barrier layer ( e.g. Ti:W) and Al or Au conductors. Metallization must be suited to all the device processing steps beginning with contact sintering, device packaging, testing and also the operating conditions. Highly complex large scale integrated circuits require multilevel interconnections. A two-level metallization scheme (Al/insulator/Al) and its application are presented. Future trends in metallization processing are also discussed.