Study of the Reliability Impact of Chlorine Precursor Residues in Thin Atomic-Layer-Deposited HfO2 Layers

Atomic layer deposition (ALD) with HfCl₄ as a precursor is widely used for HfO₂ fabrication. Due to the nature of the precursor under study, i.e., HfCl₄ and H₂O, the presence of chlorine residues in the film due to insufficient hydrolysis is eminent. Obviously, the chlorine residue in the HfO₂ film is suspected to affect the quality of the HfO₂ film. In this paper, The authors reduced the concentration of chlorine residues by increasing the H₂O oxidant pulse time in between the deposition cycles from 0.3 to 10 and 90 s. Time-of-flight secondary ion mass spectrometry analysis shows that this decreases the chlorine concentration in the HfO₂ film by more than one order of magnitude. However, time-dependent dielectric breakdown analysis shows that the lifetime remains quasi unaffected (within identical error bars) for the different injection cycles. Charge pumping analysis was done by varying both pulse frequency and amplitude to investigate the creation of defects, but negligible differences were observed. Therefore, the presence of chlorine residues has no significant impact on the trap generation and reliability of ALD HfO₂ layers, and this result corresponded with the mobility result. The experimental picture is confirmed with first-principle calculations that show that the presence of chlorine residues does not induce defect levels in the bandgap of HfO₂