Current limited stresses of SiO2 gate oxides with conductive atomic force microscope

Current limitation effects on the breakdown (BD) of ultrathin SiO2 layers have been analyzed at a nanometric scale with a conductive atomic force microscope (C-AFM). Bare oxide regions have been stressed and broken down using the tip of the C-AFM as the metal electrode of a metal-oxide-semiconductor (MOS) structure. BD induced negative charge (BINC) has been observed at the BD location, which has been related to the structural damage generated by the BD event. Moreover, BD, although triggered at one point, is electrically propagated to neighbor regions. The area affected by BD and the amount of BINC (the structural damage) depend on the breakdown hardness. In particular, it is shown that both magnitudes are smaller when the current through the structure is limited during BD transient. Based on the results, a qualitative picture of the breakdown process is presented, which accounts for the current limitation effects.