Highly selective, high rate tungsten deposition

An experimental reactor has been built which is capable of depositing tungsten films selectively on exposed silicon or metal surfaces at rates in excess of 2000 A per minute without deposition on silicon dioxide or silicon nitride surfaces. It is a cold-wall, low pressure system using the hydrogen reduction of tungsten hexafluoride. With this system selective deposition in excess of two microns of tungsten is readily achieved. It has been used to fill vias between metal levels in a VLSI process. With a Mo/W/Al system a high yield of low resistance contact strings has been obtained. No satisfactory model to describe the reaction of tungsten hexafluoride and hydrogen on either tungsten or silicon dioxide has been developed. In the absence of such models no definitive statement about the reasons for observed selectivity and deposition rates can be made