Comparison of mechanical properties and composition of magnetron sputter and plasma enhanced atomic layer deposition aluminum nitride films

Comparative study of mechanical properties and elemental and structural composition was made for aluminum nitride thin films deposited with reactive magnetron sputtering and plasma enhanced atomic layer deposition (PEALD). The sputtered films were deposited on Si (100), Mo (110) and Al (111) oriented substrates to study the effect of substrate texture to the film properties. For the PEALD trimethylaluminum-ammonia (TMA/NH3) films, the effects of process parameters such as temperature, bias voltage, and plasma gas (NH3 vs. N2/H2) on the AlN properties were studied. All the AlN films had a nominal thickness of 100 nm. Time-of-flight elastic recoil detection analysis (ToF-ERDA) showed the sputtered films to have lower impurity concentration with an Al/N ratio of 0.95, while the Al/N ratio for the PEALD films was 0.81-0.90. The mass densities were ~3.10 g/cm3 and ~2.70 g/cm3 for sputtered and PEALD AlN, respectively. Only the sputtered films were crystalline, as determined by x-ray diffraction (XRD). Nanoindentation experiments showed the elastic modulus and hardness to be 250 GPa and 22 GPa, respectively, for sputtered AlN on (110) substrate, whereas with PEALD AlN, values of 180 GPa and 19 GPa, respectively, were obtained. The sputtered films were under tensile residual stress (61 to 421 MPa) whereas PEALD films had a residual stress ranging from tensile to compressive (846 to -47 MPa) and high plasma bias resulted in compressive films. The adhesion of both films was good on Si, although sputtered films showed more inconsistent critical load behaviour. Also, the substrate underneath the sputtered AlN did not withstand as high wear forces as with the PEALD AlN. The coefficient of friction was determined to be ~0.2 for both AlN types and their wear characteristics were almost identical.