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

概要

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The progressive miniaturization and integration of electronic devices has made interfacial fracture between thin films of several nanometers thickness an important consideration. The present paper attempts to clarify the mechanism of the damage process along an interface between multi-layered films during nanoscratch tests. Using the edge of a Berkovich-type indenter, a nanoscratch test was performed on sub-micron films of Si3N4/Cu/TaN fabricated on a silicon substrate. Initiation of damage occurs near the Si3N4/Cu interface before the tip of indenter reaches the interface. This implies that Si3N4 is weak in terms of interfacial resistance to failure. A spot-like damaged area appears under the scratched line, and the size of this area is several nanometers or less. Critical values measured in the nanoscratch tests and three-dimensional non-linear finite element analysis reveal that shear stress concentration appears behind the indenter; this agrees qualitatively with the behavior of the spot-like damage area as observed under an optical microscope. In order to examine the validity of the damage mechanism, another nanoscratch test was performed by moving the indenter in the opposite direction. Critical load is greater than that in the original test due to the difference in the shape of the indenter, but stress analysis reveals that initiation of spot-like damage occurs when the two tests are equal in terms of peak stress acting on the interface.