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

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 deg C. At 180 deg 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 A cycle-1 at substrate temperatures between 180 and 210 deg C. Growth rates of 0.57 and 0.96 A cycle-1 were observed at 150 and 220 deg C, respectively. In a series of films deposited at 180 deg C, the film thicknesses varied linearly with the number of deposition cycles. Films grown at 180 and 210 deg C exhibited resistivity values between 810 and 4600 mu* 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 W1.0N0.82C0.13O0.26H0.33 at 150 deg C, W1.0N0.74C0.20O0.33H0.28 at 180 deg C, and W1.0N0.82C0.33O0.18H0.23 at 210 deg 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 deg C under a nitrogen atmosphere. X-Ray diffraction patterns suggested that crystallization does not occur at or below 800 deg 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.,0.8, and 0.7 nm for films deposited at 150, 180, and 210 deg C, respectively.