Advanced/3D Packaging and Materials Integrity: Stress-Induced Effects and Mechanical Properties of New Ultra Low-k Dielectrics for On-Chip Interconnect Stacks

摘要

The reliability-limiting effects in 3D IC structures using TSVs including mechanical stress distributions and the resulting effects on material integrity (e.g. failure modes like interface .delamination, cohesive cracking, metallurgical degradation at joints, and chip-package interaction)and finally on device performance degradation are challenges in advanced 3D integration technologies and product development [1]. Managing internal mechanical stress is a key task to ensure high reliability of products manufactured in advanced CMOS technology nodes, and it is a highly ranked concern for 3D TSV technologies [2]. It requires the determination of materials properties, including Young's modulus, Poisson ratio and coefficient of thermal expansion (CTE), for each material used. Particularly for sub-m structures, materials properties change depending on the size of the structure. For some materials, especially the materials used in packaging, these characteristics are a non-linear function of temperature, i. e. temperature-dependent materials data have to be determined [3]. For. polycrystalline materials, their microstructure has to be considered. In this talk, the determination of mechanical properties like Young's modulus, and fracture toughness will be discussed for the elements of Cu/Low-k interconnect stacks, but also cohesive and adhesive failure in thin film stacks. Double cantilever beam (DCB) testing provides the energy release rate of thin films. Nanoindentation experiments are usually used to measure the elastic modulus of thin films, however, this technique is able to provide fracture toughness information as well. A wedge-shape indenter is used to delaminate ULK films locally. The fracture energy associated with the indentation induced delamination is evaluated considering the pore densification process. The fragile nature of ultra low-k dielectrics, particularly nanoporous organosilicate glasses (OSGs), and the packaging-induced mechanical stress are reliability concerns for advanced/3D packaged products. We demonstrate that novel synthesis approaches to manufacture nanoporous materials with optimized topology, particularly self-assembly processes, are able to control pore size and pore topology. Particularly, elastic modulus values close to the Hashin-Shtrikman upper bound can be reached for thin films with periodically arranged pore structures with constant pore size [4].