Removal of Interfacial Layer in HfO2 Gate Stack by Post-Gate Cleaning Using NF3/NH3 Dry Cleaning Technique

HfO2 gate stack has been one of the most popular subjects of research in recent years due to its outstanding material properties, such as high-k (20~25), wide band gap (~5.68eV), and the compatibility with Si-based semiconductor process technology. However, the interfacial layer (IL) with a reduced k-value between HfO2 dielectric and Si channel is still a critical issue for future ultra large scale integration (ULSI) technology application of the HfO2 gate stack. Various ways have been studied to improve the IL properties of HfO2 gate stack and to achieve ~1nm-thick equivalent oxide thickness (EOT) of the gate stack. Recently, fluorine incorporations into the HfO2 gate stack have been suggested for improvement of the electrical properties of the gate stack by defect passivation.1,2 However, it was reported that the SiOx IL grows during the fluorine treatment of HfO2 film, which finally led to degradation of electrical characteristics.2 In this paper, we present interesting findings on the IL removal effect of fluorine incorporation into the HfO2 gate stack where a post-gate dry cleaning technique is used with the NF3/NH3 plasma.