Silicon Surface Passivation by Atomic Layer Deposited Hafnium Oxide Films: Trap States Investigation Using Constant Voltage Stress Studies

Excellent silicon surface passivation is demonstrated by the HfOx film deposited using optimized atomic layer deposition (ALD) process. For pristine films, surface recombination velocity (SRV) as low as ~29 cm/s is achieved. The highest effective lifetime of 3 ms, corresponding to SRV of ~5 cm/s, is achieved for hydrogen ambient annealed films. Capacitance-voltage and conductance-voltage measurements confirm that the pristine film consists of positive fixed charges, which remain of the same type or change polarity depending on the postdeposition annealing ambient. Constant voltage stress (CVS) measurements reveal that acceptor-like trap states are present in the film. These trap states are intrinsic in nature and are incorporated in the film structure during ALD growth. CVS study gives an insight to the change in fixed charge polarity in nitrogen ambient annealing, which is not the case in hydrogen ambient. The reduction in surface recombination losses is explained as a combined effect of field and chemical passivation where former dominates in nitrogen and later is dominant in hydrogen ambient annealed films.