Development of a conductive atomic force microscope with a logarithmic current-to-voltage converter for the study of metal oxide semiconductor gate dielectrics reliability

A new configuration of conductive atomic force microscope (CAFM) is presented, which is based in a conventional AFM with a logarithmic current-to-voltage (log I-V) amplifier. While a standard CAFM allows to measure a current dynamic range of typically three orders of magnitude (0.1–100 pA), with the new setup it is possible to measure up to nine orders of magnitude. The extended current range allows to evaluate the reliability of gate dielectrics in a single electrical test, overcoming the limitations of standard CAFM configurations. The setup has been tested by analyzing breakdown (BD) spots induced in SiO₂ and high-k layers. For current measurements, the results show that I-V characteristics and current images (measured at a constant voltage) can be easily obtained in a wide dynamic range, which can reveal new details of the BD mechanisms. In particular, the setup was used to investigate the area electrically affected by the breakdown event in SiO₂ and HfO₂/SiO₂ stacks.