Substrate heating by sputter-deposition of AlN: the effects of dc and rf discharges in nitrogen atmosphere

The power density at the substrate during sputter deposition of AlN was measured by a calorimetric method. Deposition was performed by either a dc discharge or a 13.56-MHz rf discharge in a pure nitrogen atmosphere. The combination with measurements of the atomic deposition rate resulted in the determination of the total amount of the energy input per incorporated atom. For rf discharges in N2 atmosphere there is a monotonic increase of energy input with increasing pressure and decreasing power. The energy input is in the range between 0.4 and 15.7 keV per atom. For dc discharges, the energy flux is (under identical conditions) significantly smaller and in the range between 270 and 720 eV. With increasing nitrogen pressure, there is a general increase of the energy, proportional to the logarithm of pressure. The hypothetical bombardment of an aluminum target by nitrogen ions was simulated by tridyn Monte Carlo calculations. The surface of the target was under steady-state conditions covered by a 2-nm-thick layer of stoichiometric AlN. The calculations further resulted in sputtering yields, reflection coefficients and average energies of sputtered atoms and reflected nitrogen-neutrals. These data were used to calculate the energy input at the substrate. The calculations indicate the strong effect of reflected nitrogen, but cannot account for the high experimental values of energy input. It is argued that the contributions of charged particles and AlN dimers are the origin of the discrepancy.