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A. Ababneh, H. Kreher, U. Schmid:
"Etching Behaviour of Sputter-Deposited Aluminium Nitride Thin Films in H3P04 and KOH Solutions";
Microsystem Technologies - Micro- and Nanosystems - Information Storage and Processing Systems, 14 (2008), 4-5; 567 - 573.

Aluminium nitride (AlN) 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
elements made of AlN. Therefore, the influence of different
sputtering conditions on the vertical etch rate of
AlN thin films with a typical thickness of 600 nm is
investigated in an etch mixture based on phosphoric acid.
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 (002) orientation. When a high
c-axis orientation is present detailed analyses of the
etched topographies 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. For comparison, AlN films synthesized
under the same conditions were etched in potassium
hydroxide (KOH) at room temperature revealing
comparable etching characteristics as a function of deposition
parameters. Depending on the degree of (002)
orientation the topography of the etched samples show a
strong increase in surface roughness with time due to a
selective etching behaviour between (002) and residual
crystallographic planes.

http://dx.doi.org/10.1007/s00542-007-0450-x