The influence of varying sputter deposition conditions on the wet chemical etch rate of AlN thin films

Aluminium nitride (A1N) reactively sputter deposited from an aluminium target is an interesting compound material due to-its CMOS compatible fabrication process and its piezoelectric properties. For the implementation in micromachined sensors and actuators an appropriate patterning technique is needed to form A1N-based elements. Therefore, the influence of different sputtering conditions on the vertical etch rate of A1N thin films with a typical thickness of 600 nm in phosphoric acid (H3PO4) is investigated. Under comparable conditions, such as temperature and concentration of the etchant, thin films with a high c-axis orientation are etched substantially slower compared to films with a low degree of orientation. When a high c-axis orientation is present detailed analyses of the etched topologies reveal surface characteristics with a low porosity and hence, low roughness values. From temperature dependant etching experiments an activation energy of 800 (+/- 30) meV is determined showing a reaction-controlled etching regime independent of sputter deposition conditions.