Ph.D. Proposal Presentation by
Monday, July 11, 2005
(Dr. Suresh K. Sitaraman, Chair)
"Monotonic and Fatigue Interfacial Delamination Characterization of Nano-Scale Thin Films"
Delamination is an important reliability concern for thin film interfaces. The objective of this work is to develop innovative monotonic and fatigue interfacial decohesion tests to characterize the dissimilar material interfaces.
A fixtureless superlayer based delamination test has been developed to measure the interfacial fracture toughness of a nano-scale thin film deposited on a substrate. This test uses common IC fabrication techniques and overcomes the shortcomings of available methods. A stress-engineered superlayer is used to initiate and drive the interfacial delamination between the thin-film and the substrate. An etchable release layer of varying width between the thin-film and the substrate is applied to control the amount of energy available for delamination propagation. Interfacial fracture toughness for thin films with thickness ranging from a few nanometers to several hundred nanometers can be measured by the proposed decohesion test over a wide range of mode mixities. The developed test will be used to measure the interfacial fracture toughness for two material pairs: low-k dielectric and barrier layer, Si and Ti. Numerical models will be developed, in parallel to the experiments, to obtain the fracture parameters such as the critical energy release rate and mode mixity. In addition to the monotonic decohesion test, a fixtureless fatigue test will be developed. The proposed test will fabricate a micro-cantilever with permanent magnetic material deposited on the tip region on top of the cantilever. An external electromagnet interacts with the cantilever to drive the interface crack initiation and crack propagation along the interface of the cantilever and the supporting base. Fatigue crack growth can be monitored by E-beam lithography patterning metal trace lines that are separated by a few nanometers. The crack initiation and propagation can be monitored through electrical resistance measurement. Through metal trace lines the crack length can be measured and an empirical relationship correlating da/dN with the energy release rate range will be developed. The proposed technique can be effectively used to understand the fatigue crack initiation and nano-scale crack propagation of thin films on a substrate.