Plan view TEM sample preparation using the focused ion beam lift-out technique

Abstract

Localized plan view TEM samples have been prepared from silicon semiconductor wafers using the focused ion beam lift-out technique. Two different methods of sample preparation before FIB machining were found to be successful: mounting cleaved samples sandwiched together or adding silver paint and cleaving through paint and samples. The plan view technique offers site specific TEM capability from a horizontal section rather than a vertical cross section. The sections can be taken from any layer and can be angled if desired. Results have been obtained from metal layers in a semiconductor device structure. TEM micrographs of tungsten plug arrays show non-uniform barrier layer coverage and tungsten grain size across the via. Hundreds of plugs have been cut through in one sample, thereby offering statistical as well as specific structural information. Metal and polysilicon lines have been examined for grain size and uniformity in a single micrograph. Plan view samples from continuous metal layers can also be made.