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

Thin films of tungsten (W) and tungsten nitride (W2N) were grown with atomi c layer control using sequential surface reactions. Tungsten atomic layer d eposition was accomplished by separating the reaction WF6 + Si2H6 --> W + 2 SiHF(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 t emperatures between 425-600 K (600-800 K). The W deposition rate was 2.5 An gstrom/AB cycle for WF6 and Si2H6 reactant exposures > 800 and 3000 L, resp ectively. The W2N deposition rate was also 2.5 Angstrom/AB cycle for WF6 an d NH3 reactant exposures > 3000 and 10,000 L, respectively. Atomic force mi crographs of the deposited films on Si(100) were remarkably flat indicating smooth deposition. X-ray diffraction investigations revealed that the depo sited tungsten and tungsten nitride films were either amorphous or composed of very small crystalline grains. X-ray photoelectron spectroscopy demonst rated that the films contained very low impurity concentrations. The result s 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.