A Study of Interfacial Reactions in  W  / WSi x  / Al ( Si , Ti )  Via Hole Metallization

Abstract

Planar vertical interconnects and low resistivity track lines are stringent requirements for future very large scale integrated (VLSI) and ultra large scale integrated (ULSI) multilevel metallizations schemes. A blanket chemically vapor deposited tungsten-plug technique involving an adhesion promoting layer of WSi., in combination with an aluminum track scheme is a very promising choice. Stability and metallurgical interactions of such a metallization system are of major concern. Many investigations have focused on the interface W/AI(Si, Ti), elucidating the barrier function of W against indiffusion of A1. Equivalent investigations regarding possible interfacial reactions of the triple-layer system W/WSiJAI(Si, Ti) are rare. By using transmission electron microscopy (TEM), energy-dispersive x-ray spectroscopy (EDX), and Auger electron spectroscopy (AES) a detailed analysis of samples deposited at 400 and 450~ respectively, and of samples additionally annealed at 450~ was performed. The WSi.~. forms an amorphous matrix with small crystalline precipitates identified as ~-tungsten. The interfaces AI(Si, Ti)/WSi,. and WSiJW are free from any detrimental layer. Indiffusion of A1 into the amorphous WSix layer is found to take place at typical VLSI annealing temperatures of 450~ resulting in a high A1 concentration within this layer. Extensive voids in the adjacent A1 regions are the consequence of this mass flow leading to reliability risks due to electromigration at the remaining contact areas.