Detection of metallic buried void by effective density contrast mode

Abstract

For sub-2Xnm technology nodes, metallic buried voids in metal contacts have become critical yield and reliability issue for high volume semiconductor device manufacturing. Especially as the scaling continues, void-free metal filling becomes more challenging for advanced technology development, which poses great need for effective in-line detection methodology. In this paper we demonstrate comprehensive study of a special buried metallic void detection mode by backscatter electron (BSE) signals based on effective density contrast (EDC), especially for the case of partial conduction while the conventional voltage contrast (VC) mode has no detection due to minimum detectable resistance difference requirement. Successful application of EDC mode in buried metallic void detection by in-line electron beam inspection (EBI) is presented on various metal contact chemical mechanical planarization (CMP) layers, together with Monte Carlo simulations and other characterization methodology which show consistent correlation with experimental observations. Thus an extrapolation based on simulation result is illustrated to predict the detection capability of EDC mode in buried metallic void detection for the popular metal contact material systems including tungsten and copper. Despite of the detection limitation as well as potential damage by the charged particle exposure, EDC mode is demonstrated as a very effective detection methodology for buried metallic void in advanced technology development.