Frequency dependent Kelvin probe force microscopy on locally doped Si

Failure analysis and optimization of nanoelectronic devices require knowledge of their electrical properties. Kelvin probe force microscopy (KPFM) is a standard technique for the investigation of the surface potential. We present its applicability to buried doped regions in cross-sectionally prepared Si epilayer structures and to shallow doped regions in a conventional dynamic random access memory (DRAM) cell. Frequency dependent KPFM measurements were performed under ambient conditions by means of an Anfatec Level-AFM with a 2nd amplifier and p- and n-type conductive NSC15 probes from MikroMasch. Using an active mixer, the excitation amplitude of the NSC15 probes is almost independent of the operation frequency. The frequency dependence of the Kelvin bias above differently doped regions is discussed with respect to surface states and trapped charges in the thin oxide layer. As a result, KPFM measurements have to be performed at frequencies high enough so that the electrical properties of the locally doped Si are probed.