In-Situ Transmission Electron Microscopy Studies on Advanced Materials for Micro- and Nano-Electronics

This PhD thesis was focused on the development of in-situ transmission electron microscopy (TEM) methodologies on advanced materials for micro- and nano-electronics. The first in-situ study was focused on time dependent dielectric breakdown (TDDB) degradation kinetics and failure mechanisms in Cu/low-k interconnect stacks. The second study investigated the stretching of patterned graphene ribbons for tuning the bandgap, and consequently the mechanical properties. In the in-situ TDDB study, the electric field was generated using a TEM holder and a source-measurement unit,while TEM imaging and electron spectroscopic imaging (ESI) were selected as techniques of choice to image the test structure and to detect possible Cu traces in the dielectrics during electrical testing. Three major TDDB-induced damage mechanisms in the “tip-to-tip” structures can occur during electrical tests. Cu migration into the low-k dielectric and SiO2 layer was only observed after forming a breach in the TaN/Ta barrier during the electricaltest. The final breakdown location depends on the complex interplay of the various steps in the degradation sequence, i.e. electronic damage,barrier material dissolution and breach, Cu diffusion and agglomeration. The experimental approach opens a novel opportunity to study the TDDB breakdown mechanism in the interconnect stacks of microelectronic products, and it could also be extended to other structures in active devices. The observed degradation mechanisms improve the understanding of reliability-limiting processes in integrated circuits and provide data for the selection of the model used for lifetime estimation. The mechanical response of patterned graphene ribbons under stretching was monitored in-situ in the TEM, and thecorresponding low-loss electron energy loss spectrum (EELS) was recorded as an attempt to reveal the tuning of the bandgap. Chemical vapor deposition (CVD) grown monolayer graphene was transferred onto a “push-to-pull” device by a modified poly (methyl methacrylate) (PMMA) method, and was patterned into ribbons by both focused ion beam (FIB) in a SEM/FIB tool and focused electron beam in a TEM. The elongation was confirmed to be about 3 % by more than 30 focused electron beam patterned graphene ribbons. To our knowledge, this experiment demonstrated here is the first one to directly measure the tensile failure strain of graphene ribbons. No bandgap opening in the in-situ stretched graphene ribbons was detected from the low-loss EELS spectrum even with an energy resolution of about 0.15 eV. Further improvement of the energy resolution may offer the possibility to directly detect the bandgap opening of strained graphene