Charge trapping in ultrathin hafnium oxide

Abstract

The charge trapping properties of ultrathin HfO/sub 2/ in MOS capacitors during constant voltage stress have been investigated. The effects of stress voltage, substrate type, annealing temperature, and gate electrode are presented in this letter. It is shown that the generation of interface-trap density under constant-voltage stress is much more significant for samples with Pt gate electrodes than that with Al gates. The trapping-induced flatband shift in HfO/sub 2/ with Al gates increases monotonically with injection fluence for p-type Si substrates, while it shows a turnaround phenomenon for n-type Si substrates due to the shift of the charge centroid. The trapping-induced flatband shift is nearly independent of stress voltage for p-type substrates, while it increases dramatically with stress voltage for n-type Si substrates due to two competing mechanisms. The trap density can be reduced by increasing the annealing temperature from 500/spl deg/C to 600/spl deg/C. The typical trapping probability for JVD HfO/sub 2/ is similar to that for ALD HfO/sub 2/.