A low valent metalorganic precursor for the growth of tungsten nitride thin films by atomic layer deposition

Abstract

The atomic layer deposition growth of tungsten nitride films was demonstrated using the precursors W₂(NMe₂)₆ and ammonia with substrate temperatures between 150 and 250 °C. At 180 °C, surface saturative growth was achieved with W₂(NMe₂)₆ pulse lengths of ≥2.0 s. The growth rates were between 0.74 and 0.81 Å cycle⁻¹ at substrate temperatures between 180 and 210 °C. Growth rates of 0.57 and 0.96 Å cycle⁻¹ were observed at 150 and 220 °C, respectively. In a series of films deposited at 180 °C, the film thicknesses varied linearly with the number of deposition cycles. Films grown at 180 and 210 °C exhibited resistivity values between 810 and 4600 μΩ cm. Time-of-flight elastic recoil detection analysis on tungsten nitride films containing a protective AlN overlayer demonstrated slightly nitrogen-rich films relative to W₂N, with compositions of W_1.0N_0.82C_0.13O_0.26H_0.33 at 150 °C, W_1.0N_0.74C_0.20O_0.33H_0.28 at 180 °C, and W_1.0N_0.82C_0.33O_0.18H_0.23 at 210 °C. In the absence of an AlN overlayer, the oxygen and hydrogen levels were much higher, suggesting that the films degrade in the presence of ambient atmosphere. The as-deposited films were amorphous. Amorphous films containing a protective AlN overlayer were annealed to 600–800 °C under a nitrogen atmosphere. X-Ray diffraction patterns suggested that crystallization does not occur at or below 800 °C. Similar annealing of films that did not contain the AlN overlayer afforded X-ray diffraction patterns that were consistent with orthorhombic WO₃. Atomic force microscopy showed root-mean-square surface roughnesses of 0.9, 0.8, and 0.7 nm for films deposited at 150, 180, and 210 °C, respectively.