Investigation of Residual Stress Profiles and Fracture Properties of Thin Films

Stefan Massl

Research output: ThesisDoctoral Thesis

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Abstract

A method for the determination of residual stress distributions in near-surface structures and a technique for evaluating the fracture properties of thin films are developed. The new technique for the determination of residual stress profiles, called ion beam layer removal method (ILR method), is based on the fabrication of a microcantilever and the subsequent gradual reduction of the film thickness using a focused ion beam workstation (FIB). The method developed can be applied to crystalline as well as amorphous materials and features a depth resolution on a nanoscale. The method is presented by investigating the depth profile of residual stresses in an 840nm thick Ni film deposited on (100) Si. The influence of experimental errors and parameters is investigated by means of a 1.16 microns thick TiN film on (100) Si and four model stress distributions. The most important measures to assure small errors are the choice of adequate cantilever substrate thicknesses to avoid fracture or plastic deformation and the gradual reduction of the film thickness in small steps in order to reproduce the stress profiles well. A further development of the ILR method is the 3D-ILR method, which allows the determination of spatial stress profiles in near-surface structures. This technique is presented by investigating the lateral and depth distribution of residual stresses in and around the plastic zone induced by a scratch with a ball-shaped indenter in a 840nm thick Ni film on (100) Si. The method used for the determination of fracture properties of thin films is based on the determination of the depth profile of residual stresses followed by the fabrication of a microcantilever by means of a FIB workstation and the subsequent testing with an in-situ cube corner indenter. The strength and mode I fracture toughness are evaluated by superimposing the residual stresses and the stresses induced by the loading. The investigations of a magnetron-sputtered 1.1 microns thick TiN film shows a fracture toughness of 2.8MPam^0.5 and a fracture strength of 4.4GPa. SEM-images of the fracture surface reveal that the crack propagates mainly along the grain boundaries, which leads to the conclusion that besides compressive residual stresses, the high grain boundary strength contributes significantly to structural integrity of such coated systems.
Translated title of the contributionUntersuchung von Eigenspannungsprofilen und bruchmechanischen Eigenschaften von dünnen Schichten
Original languageEnglish
QualificationDr.mont.
Supervisors/Advisors
  • Clemens, Helmut, Assessor C (internal)
  • Pippan, Reinhard, Assessor A (internal)
Publication statusPublished - 2008

Bibliographical note

embargoed until null

Keywords

  • Residual stress Stress profile Thin film ILR method Parameters
  • fracture cantilever FIB

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