Defects Generation in SIO2/HFO2 Studied with Variable TCHARGE-TDIScharge Charge Pumping (VT2CP)

Abstract

A variable t_CHARGE-t_DISCHARGE charge pumping (VT²CP) is used to investigate the creation of traps in the SiO₂ and HfO₂ separately in an ALD SiO₂/HfO₂ metal gate stack. It is shown that by independently controlling the pulse low timing "discharging time" and high level timing "charging time", we are able to separate the traps in the interfacial SiO₂ from the traps in the HfO₂ and observe the creation of new traps in both constituent layers. During degradation the increase of traps, both in the SiO₂ as well as in the HfO₂, follows a power law behavior as a function of time with an exponent ~0.32 and ~0.34 respectively independent of stress voltage. The voltage acceleration of creation of HfO₂ traps (-30) found using VT²CP is nearly identical of the TDDB (-27) confirming the earlier published model that TDDB occurs when the density of traps in the HfO₂ reaches a critical value. VT²CP can accurately detect degradation down to a much lower voltage than the dielectric breakdown measurement range and only one stress experiment combined with VT²CP is sufficient to determine the degradation at a given voltage, while a TDDB test requires many measurements in order to construct an accurate distribution of failure times.