The influence of N2/H2 and ammonia N source materials on optical and structural properties of AlN films grown by plasma enhanced atomic layer deposition
The influence of N2/H2 and ammonia as N source materials on the properties of AlN films grown by plasma enhanced atomic layer deposition using trimethylaluminum as metal source has been studied. The -2Θ grazing-incidence X-ray diffraction, high resolution transmission electron microscopy, and spectroscopic ellipsometry results on AlN films grown using either NH3 or N2/H2 plasma revealed polycrystalline and wurtzite AlN layers. The AlN growth rate per cycle was decreased from 0.84 to 0.54 Å/cycle when the N source was changed from NH3 to N2/H2. Growth rate of AlN remained constant within 100200 °C for both N precursors, confirming the self-limiting growth mode in the ALD window. AlAl bond was detected only near the surface in the AlN film grown with NH3 plasma. AFM analysis showed that the RMS roughness values for AlN films grown on Si(100) substrates using NH3 and N2/H2 plasma sources were 1.33 nm and 1.18 nm, respectively. The refractive indices of both AlN films are similar except for a slight difference in the optical band edge and position of optical phonon modes. The optical band edges of the grown AlN films are observed at 5.83 and 5.92 eV for ammonia and N2/H2 plasma, respectively. According to the FTIR data for both AlN films on sapphire substrates, the E1(TO) phonon mode position shifted from 671 cm -1 to 675 cm-1 when the plasma source was changed from NH3 to N2/H2. © 2011 Elsevier B.V. All Rights Reserved.