Modeling of substrate current measurement and charge transfer in insulators

We compare substrate current (SC) values for thin SiO2 films, with thicknesses ranging from 2 nm to 200 nm, between modeled simulation results and actual measurements made by EB-SCOPE, a Substrate current measuring instrument. The simulation models use Monte Carlo methods to model the generation of secondary electrons (SE) and holes, and use 1-D charge transfer to simultaneously model SE yield and SC values to quantify thin film thickness in order to predict if a high aspect ratio contact or via hole is closed or open. The simulation results show a strong match with the measurement data. The SC value can be used for assessing process uniformity as well as detecting process related failures, in this case a closed contact hole which can be seen in the qualitative SC images. We can also apply this modeling to monitoring of surface preparation and clean processes to detect residual films such as SiO2. The method can detect changes in surface state conditions, such as residue or oxide formation, as changes in SC values.