Rate-dependent responses of electroless plated and sputtered copper layer during nanoindentation loading

摘要

A thin copper layer is an integral part of a Through-Silicon via (TSV) structure. The copper layer experiences mechanical stressing through the temperature excursion, thus raising reliability concern of the component. Such reliability assessment calls for the determination of the mechanical properties of the thin layer. In this respect, this paper discusses the experimental study to establish the loading rate-dependent behavior of the Cu layer deposited on SiO2-coated Si substrate. A series of nanoindentation tests are performed on sputtered and electroless plated copper layer. The tests cover a range of probe displacement rates from 80-400 nm/s and indentation depths up to 400 nm. Load-displacement (depth) data pairs are recorded for each test. Results show that an indentation depth of 3% of the Cu layer thickness is sufficient to eliminate the effect of surface morphology on the indentation load-displacement response. The load-displacement response of the electroless plated copper layer significantly decreases with the test speed, while a minor increase in similar effect is observed for the sputtered layer. The elastic modulus of both the electroless and sputtered copper layer is insensitive to the displacement rates up to 320 nm/s, while the hardness measure of the electroless copper layer linearly decreases with increasing rates.