Scanning tunneling microscopy of the topology of vapour-deposited and electro-deposited metal films

Abstract

The fracture and subsequent spontaneous delamination of thin metal films under the influence of excessive internal stresses, resulting from low temperature deposition and processing, can be extremely deleterious to the long term serviceability of IC devices. The conditions for fracture are determined by the magnitude of the residual stress, which can be measured by x-ray diffraction techniques, the fracture toughness of the thin film material and the size of any internal or sinface flaws that may be present.In order to establish the size and depth of microcracks at the surface, high resolution scanning (SEM) and transmission electron microscopy (TEM) and scanning tunneling microscopy (STM) are being used to define the topology of the surfaces of vapour-deposited films for comparison with electroplated films of the same metal. Direct knowledge of the surface relief is required to predict the onset of through-thickness cracking or to derive the fracture energy of the film material by detecting the critical conditions for cracking. Detailed knowledge of surface structures also is useful for understanding the mechanisms of film growth, including information on the crystallography of surface facets and growth steps.