The aim of this work is to compare several methods for
the determination of very thin films Young's modulus and stress state: the
nanoindentation test, the bulge test and the point-deflection method. The
tested structures were silicon nitride and silicon nitride/silicon oxide
bilayer membranes with different shapes (square or rectangular) and
dimensions (from 1 mm to 3 mm). We report new experimental results on
submicron thick dielectric membranes with thicknesses down to 100 nm. A
Young's modulus of 217 ± 14 GPa have been found for silicon nitride
membranes with a residual stress of 411 ± 30 MPa using the bulge test.
Using nanoindentation experiments, a Young's modulus higher than 190 GPa has
been estimated. The bulge test is still valid for the studied high dimension
to thickness ratio membranes and more appropriate to determine the Young's
modulus. A mixture law was shown to be possibly applied for
Si3N4/SiO2 bilayer membranes for the Young's modulus and
stress determination. The point deflection method is limited by the very low
stiffness of these structures and only the residual stress can be accurately
extracted. As the Young's modulus and membrane geometry have no significant
influence on the stress determination by means of the point deflection
method for the studied membranes (with a high lateral dimension to thickness
ratio), more reliable results have been obtained such as 487 ± 40 MPa
using an AFM cantilever for load-deflection experiments, for Si3N4
thin films.