Atomically controlled growth of tungsten and tungsten nitride using sequential surface reactions

Thin films of tungsten (W) and tungsten nitride (W2N) were grown with atomic layer control using sequential surface reactions. Tungsten atomic layer deposition was accomplished by separating the reaction WF6 + Si2H6 --> W + 2SiHF(3) + 2H(2) into two half-reactions. The tungsten nitride atomic layer growth was performed by dividing the reaction 2WF(6) + NH3 --> W2N + 3HF + 9/2F(2) into two half-reactions. Successive exposure to WF6 and Si2H6 (NH,) in an ABAB... reaction sequence produced W (W2N) deposition at substrate temperatures between 425-600 K (600-800 K). The W deposition rate was 2.5 Angstrom/AB cycle for WF6 and Si2H6 reactant exposures > 800 and 3000 L, respectively. The W2N deposition rate was also 2.5 Angstrom/AB cycle for WF6 and NH3 reactant exposures > 3000 and 10,000 L, respectively. Atomic force micrographs of the deposited films on Si(100) were remarkably flat indicating smooth deposition. X-ray diffraction investigations revealed that the deposited tungsten and tungsten nitride films were either amorphous or composed of very small crystalline grains. X-ray photoelectron spectroscopy demonstrated that the films contained very low impurity concentrations. The results for tungsten represent the first demonstration of atomic layer deposition (ALD) of smooth single-element films using sequential surface reactions. (C) 2000 Elsevier Science B.V. All rights reserved.