Experimental determination of the rates of decomposition and cation desorption from AlN surfaces

The decomposition rate of AlN thin films in vacuum, nitrogen gas and plasma is reported. The AlN thermal decomposition rate in vacuum is found to have an activation energy of 5.4 eV. The evaporation coefficient is inferred to be less than 0.001, indicating that this process is kinetically limited. Large kinetic energy ion bombardment (∼70 eV), which occurs in the plasma at low nitrogen pressures (0.02 mT), is found to enhance the decomposition rate by a factor of ∼2. In contrast, exposure to 0.3 mT nitrogen pressure or low kinetic energy plasmas (∼25 eV) at similar pressures diminishes the AlN evaporation rate by a factor of ∼3. This result can be attributed to the chemical reactivity of the desorption site, presumably at a kink or step edge. Plasmas containing predominantly excited atomic species do not significantly change the decomposition rate. Temperature-dependent measurements of the aluminum surface resident lifetime on AlN surfaces indicate that the Al desorption energy is 3.0 eV.