Charge trapping in ultrathin hafnium oxide

The charge trapping properties of ultrathin HfO2 in MOS capacitors during constant voltage stress have been investigated. The effects of stress voltage, substrates type, annealing temperature, and gate electrode are presented in this letter. It will be shown that the generation of interface-trap density under constant-voltage stress is much more significant for samples with Pt gate electrode than that with Al gate. The trapping-induced flatband shift in HfO2 with Al gate increases monotonically with injection fluence for p-type Si substrate, while it shows a turnaround phenomenon for n-type Si substrate due to the shift of the charge centroid. The trapping-induced flatband shift is nearly independent of stress voltage for p-type substrate, while, it increases dramatically with the stress voltage for n-type Si substrate due to two competing mechanisms. The trap density can be reduced by increasing the annealing temperature from 500 degreesC to 600 degreesC. The typical trapping probability for JVD HfO2 is similar to that for ALD HfO2.