Vol.:(0123456789) 1 3 Applied Physics A (2018) 124:259 https://doi.org/10.1007/s00339-018-1659-5 Efect of interfacial SiO 2−y layer and defect in HfO 2−x flm on fat-band voltage of HfO 2−x /SiO 2−y stacks for backside-illuminated CMOS image sensors Heedo Na 1  · Jimin Lee 1  · Juyoung Jeong 1  · Taeho Kim 1  · Hyunchul Sohn 1 Received: 8 August 2017 / Accepted: 7 February 2018 © Springer-Verlag GmbH Germany, part of Springer Nature 2018 Abstract In this study, the efect of oxygen gas fraction during deposition of a hafnium oxide (HfO 2−x ) flm and the infuence of the quality of the SiO 2−y interlayer on the nature of fat-band voltage (V fb ) in TiN/HfO/SiO 2−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 V fb behavior was signif- cantly afected by the characteristics of the SiO 2−y interlayer and the non-lattice oxygen fraction in the HfO 2−x flms. The HfO 2−x /native SiO 2−y stack presented a V fb of − 1.01 V for HfO 2−x flms with an oxygen gas fraction of 5% during sputtering. Additionally, the V fb of the HfO 2−x /native SiO 2−y stack could be controlled from − 1.01 to − 0.56 V by changing the depo- sition conditions of the HfO 2−x flm with the native SiO 2−y interlayer. The fndings of this study can be useful to fabricate charge-accumulating layers for backside-illuminated image sensor devices. 1 Introduction Complementary metal–oxide–semiconductor image sensors (CISs) of high density have recently become an essential component in mobile device applications. High-performance CISs require high quantum efciency, excellent low-light sensitivity, low-crosstalk between cells, a wide incident ray angle, and small pixel size. To address these requirements, the backside illumination (BI) scheme has been suggested as an alternative to the front illumination scheme for image sensors [1]. However, backside-illuminated metal–oxide–semicon- ductor image sensors (BI-CISs) sufer from a high dark current due to defects from broken bonds formed on the backside surface during the wafer-thinning process of BI devices [2]. It was reported that such high dark current could be diminished by forming a thin p + -Si layer at the back- side surface through the reduction of the electron lifetime [3]. However, the high thermal energies required for dopant activation impair the interfaces and primary devices on the front side, hindering its application in BI-CISs [4–6]. Hence, processes such as laser annealing [7], low-temperature epi- taxial growth [8], and charge accumulation technology [9, 10] have been investigated as an alternative to the conven- tional dopant activation and p + -Si layer formation to reduce the high dark current. Charge accumulation technology utilizes the electric feld generated by charges within the oxide layers near the backside. This process could bend the silicon energy band as p + -Si layers form at the surface of the backside [11]. Moreover, the shift value of the fat-band volt- age should be above 0.9 V for stable CIS operation without dark current [10]. The behavior of fxed charges within an oxide flm is very important in this technology, because the amount of the fxed charge could determine the shift of the fat-band voltage. Previous works reported that the quantity of defects, such as oxygen vacancies in HfO 2 and ZrO 2, was controllable by annealing process [12–14]. HfO 2 is the most favorable mate- rial for the charge accumulation layer in CISs, because it has the optimal refractive index for an anti-refection layer. This prevents refection of visible light near the Si surface at the backside [15–17]. Oxygen vacancies near the interface of HfO 2 /Si can act as fxed charges and infuence the fat-band voltage (V fb ) level. However, the relationship between V fb and properties such as the chemical composition of HfO 2 * Hyunchul Sohn hyunchul.sohn@yonsei.ac.kr 1 Department of Materials Science and Engineering, Yonsei University, 50 Yonsei-ro, Seodaemun-gu, Seoul 03722, Republic of Korea