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

A variable t
_CHARGE
-t
_DISCHARGE
charge pumping (VT
²
CP) is used to investigate the creation of traps in the SiO
₂
and HfO
₂
separately in an ALD SiO
₂
/HfO
₂
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 SiO
₂
from the traps in the HfO
₂
and observe the creation of new traps in both constituent layers. During degradation the increase of traps, both in the SiO
₂
as well as in the HfO
₂
, 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 HfO
₂
traps (-30) found using VT
²
CP is nearly identical of the TDDB (-27) confirming the earlier published model that TDDB occurs when the density of traps in the HfO
₂
reaches a critical value. VT
²
CP can accurately detect degradation down to a much lower voltage than the dielectric breakdown measurement range and only one stress experiment combined with VT
²
CP 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.