Junction metrology by cross-sectional atomic force microscopy

In this article we address practical aspects of the extension of cross-sectional atomic force microscopy to junction metrology. Examining an arsenic (As+) ion implantation split lot, four specimens were epoxied into a single stack. Thus, each sample was exposed to the same preparation conditions. Using a noncontact mode of image acquisition, we verified that a 120 keV implantation resulted in deeper doping profiles than a 35 keV implant. A shift of the source and drain junctions with respect to the gate was also observed as the angle of implant was changed. Correlating the measured junction depths of each sample with secondary-ion-mass spectroscopy profiles, we determined that the detection limit of the junction etch was in the range of 1017–1018 cm−3. The absolute accuracy of this technique was partially limited by tip interaction with the large topography introduced by etching.