The Reactive Ion Etching of Molybdenum and Bilayer Metallization Systems Containing Molybdenum

Abstract

Refractory metals such as molybdenum (Mo) are seeing increased usage in VLSI circuit designs, primarily due to their thermal stability. Properties desirable for a VLSI metallization system with contact to silicon include high metal conductivity, good thermal stability, absence of spiking, minimal electromigration, corrosion resistance, good adhesion, and low contact resistance. It is very difficult to fulfill all of these requirements with just a single molybdenum layer. Other metals such as Cr, Ti, Al, or can be used as thin underlayers to obtain the properties desired. We will describe processes for the reactive ion etching of Mo, and recent work in which chloro/fluoro gas mixtures such as , , and have been used to etch bilayer metallization systems containing Mo, particularly . In this study, the effects of different cathode cover plate materials, plasma chemistries, and other processing parameters on the etch rate, selectivities, and sidewall profiles were investigated. An analysis of plasma etch chemistry, using the results of emission spectroscopy, is presented. The methods used for the metal deposition and processing of Mo are also shown to be key factors in determining etching characteristics.