Mechanism of Damage Process on the Si₃N₄/Cu Interface in Nanoscratch Test

Abstract

As the shrinkage and integration of electric devices, an interfacial fracture between thin films with several nanometers becomes most important. This paper aims that the mechanism of damage process along the interface between multi-layered films during nanoscratch tests. Using the edge of indenter of Berkovich type, nanoscratch test was conducted in sub-micron films of Si₃N₄/Cu/TaN fabricated on silicon substrate. Initiation of damage takes place near the Si₃N₄/Cu interface which has poor interfacial strength before fracture of Si₃N₄. Damaged spot appears under the scratched line and its size is within several nanometers. Measured critical values in nanoscratch tests and three dimensional non-linear finite element analysis reveal that shear stress concentration appears backward the indenter and it agree with the behavior of spot-like damage area from observation by means of microscope qualitatively. In order to examine the validity of damage mechanism, another nanoscratch test in the opposite direction of scratch was carried out. The value of critical load takes the larger one than that in the original test due to the difference of the shape of indenter, but the stress analysis reveals that initiation of spot-like damage takes place when the values of peak stress acting on the interface reach the same in both tests.