Investigating metal oxide resists for patterning 28-nm pitch structures using single exposure extreme ultraviolet: defectivity, electrical test, and voltage contrast study

Abstract

BackgroundTo keep up with the logic area scaling, back-end-of-line (BEOL) structures are reduced to smaller pitches, requiring faster and reliable metrology and defect detection solution.AimMetrology and detailed defect inspection at the early phases of process optimization.ApproachSingle exposure (SE) 0.33NA extreme ultraviolet (EUV) lithography was used along with a bright field mask for patterning in a metal damascene process flow of BEOL structures. We also used a dual damascene process flow for voltage contrast (VC) metrology study.ResultsScatterometry technique, together with machine learning (ML), allowed us to have fast and accurate measurements of line-space (LS) and tip-to-tip (T2T) critical dimension (CD), and prediction of electrical performance. We demonstrated characterization results of stochastic defects across various test structures of 28-nm pitch devices. We used a large-area electron beam (e-beam) tool for high-speed large-area inspection which provided us with the quick feedback on defect signatures and scope for further root cause analysis. On a separate dual damascene integration flow, we used VC metrology to capture different failure modes in the patterning process of metal trenches with tight T2T and corresponding overlapping vias.ConclusionsWe studied the impact of stochastic resist defects on electrical measurements of meander (MR) and fork-fork (FF) structures, and showed that large electrical test structures, built with a relatively simple patterning flow, can be used at the early stages of resist and patterning development, as the electrical failures are almost exclusively caused by the resist defects. In the dual damascene flow, we demonstrated that VC metrology is useful to determine the design rule parameters and capture different failure mechanisms.