Advanced inspection technique for deep-submicron and high-aspect-ratio contact holes

We developed a technique using electron beams for inspecting contact holes immediately after dry etching and detecting incomplete contact failures. Wafers with deep-submicron contact holes that had high aspect ratios of 10 could be detected during practical inspection time by controlling the charging effect on the wafer surfaces. Measurements of the energy distribution in the secondary electrons exhausted from the bottom of the holes indicated that they were accelerated by the charge-up voltage on the wafer surfaces. Our analysis showed that high-density electron beams must be used to charge the surfaces when the aspect ratio is high. The minimum thickness of the residual SiO2 that could be detected at the bottom of the contact holes was 2 nm using an aspect ratio of 8. Applying this mechanism to optimize the dry etching process in semiconductor manufacturing showed that we could achieve reliable process control. (C) 2003 Society of Photo-Optical Instrumentation Engineers.