Effect of interfacial SiO2−y layer and defect in HfO2−x film on flat-band voltage of HfO2−x/SiO2−y stacks for backside-illuminated CMOS image sensors

In this study, the effect of oxygen gas fraction during deposition of a hafnium oxide (HfO2−x) film and the influence of the quality of the SiO2−y interlayer on the nature of flat-band voltage (Vfb) in TiN/HfO/SiO2−y/p-Si structures were investigated. X-ray photoemission spectroscopy analysis showed that the non-lattice oxygen peak, indicating an existing oxygen vacancy, increased as the oxygen gas fraction decreased during sputtering. From C–V and J–E analyses, the Vfb behavior was significantly affected by the characteristics of the SiO2−y interlayer and the non-lattice oxygen fraction in the HfO2−x films. The HfO2−x/native SiO2−y stack presented a Vfb of − 1.01 V for HfO2−x films with an oxygen gas fraction of 5% during sputtering. Additionally, the Vfb of the HfO2−x/native SiO2−y stack could be controlled from − 1.01 to − 0.56 V by changing the deposition conditions of the HfO2−x film with the native SiO2−y interlayer. The findings of this study can be useful to fabricate charge-accumulating layers for backside-illuminated image sensor devices.