Atomic layer deposition of tungsten using sequential surface chemistry with a sacrificial stripping reaction

Abstract

Tungsten (W) films were grown with atomic layer control using a novel sequence of self-limiting surface reactions. The tungsten film growth was achieved by dividing the binary reaction WF 6+Si 2H 6→W+2SiHF 3+2H 2 into two separate half-reactions. Alternating exposures to WF 6 and Si 2H 6 in an ABAB… sequence produced tungsten deposition at temperatures between 425 and 600 K. The Si 2H 6 reactant served only a sacrificial role to strip fluorine from tungsten without incorporating into the film. FTIR spectroscopic investigations demonstrated that the WF 6 and Si 2H 6 half-reactions were complete and self-limiting at T>400 K. In situ spectroscopic ellipsometry measurements determined a tungsten growth rate of 2.5 Å/AB cycle with WF 6 and Si 2H 6 reactant exposures sufficient for complete half-reactions. The surface topography of the deposited tungsten films was flat indicating smooth film growth. The tungsten films were either amorphous or composed of very small crystalline grains and contained no measurable silicon or fluorine. These results represent the first demonstration of atomic layer deposition of smooth single-element metal films using sequential surface chemistry.