H₂ Plasma and PMA Effects on PEALD-Al₂O₃ Films with Different O₂ Plasma Exposure Times for CIS Passivation Layers

In this study, the electrical properties of Al₂O₃ film were analyzed and optimized to improve the properties of the passivation layer of CMOS image sensors (CISs). During Al₂O₃ deposition processing, the O₂ plasma exposure time was adjusted, and H₂ plasma treatment as well as post-metallization annealing (PMA) were performed as posttreatments. The flat-band voltage (V_fb) was significantly shifted (ΔV_fb = 2.54 V) in the case of the Al₂O₃ film with a shorter O₂ plasma exposure time; however, with a longer O₂ plasma exposure time, V_fb was slightly shifted (ΔV_fb = 0.61 V) owing to the reduction in the carbon impurity content. Additionally, the as-deposited Al₂O₃ sample with a shorter O₂ plasma exposure time had a larger number of interface traps (interface trap density, D_it = 8.98 × 10¹³ eV^-1·cm^-2). However, D_it was reduced to 1.12 × 10¹² eV^-1·cm^-2 by increasing the O₂ plasma exposure time and further reduced after PMA. Consequently, we fabricated an Al₂O₃ film suitable for application as a CIS passivation layer with a reduced number of interface traps. However, the Al₂O₃ film with increased O₂ plasma exposure time deteriorated owing to plasma damage after H₂ plasma treatment, which is a method of reducing carbon impurity content. This deterioration was validated using the C-V hump and breakdown characteristics.