Impact of PFIB Gas Assisted Delayering on MOSFET Degradation

Delayering is an essential sample preparation step in physical failure analysis (PFA) of integrated circuits (IC). During delayering it is crucial to precisely control the endpoint and uniformity of the region of interest (ROI). Furthermore, to perform SEM based nanoprobing it is also required to end the delayering process without residues on the surface that will reduce conductivity of, or induce shorts between, isolated contacts. Delayering via mechanical polishing has been the main approach for PFA and nanoprobing. However, as the shrinkage of the interconnect layer thickness reduced below 100 nm, it has become very challenging to control the polish endpoint and to achieve robustly controlled process. Recently gas assisted Xe+ Plasma FIB (PFIB) has demonstrated uniform delayering of the metal and dielectric layers, achieving a planar surface of heterogeneous materials. The purpose of this study is to analyze the PFIB ion beam interaction with MOSFET devices, addressing ion beam damage related device degradation. We explored the final surface treatment required for nanoprobing and the impact on MOSFETs. For this purpose, we monitored device parameters after PFIB delayering final steps with different beam conditions and compare PFIB prepared samples to polished prepared samples. Consequently, we summarize the considerations of parameters for ion beam on final surface treatment.