Gate leakage current reduction and improved reliability with an ultra-thin Ti layer for low-power applications

• Published in: Thin solid films 2020-08, Vol.708, p.138102, Article 138102
• Main Authors: Park, Jungmin, Choi, Pyungho, Kim, Soonkon, Kang, Heesung, Ku, Jahum, Choi, Byoungdeog
• Format: Article
• Language: English
• Subjects: Composition; Metal gate; Oxygen vacancy; Sputtering; Thin films; Titanium; Titanium nitride
• ISSN: 0040-6090; 1879-2731
• DOI: 10.1016/j.tsf.2020.138102

•Physical vapor deposition method was used for metal gate deposition.•Physical and electrical properties of TiN were analyzed with various Ar/N2 ratios.•TiN deposited with low N2 partial pressure showed an improved gate oxide leakage.•Blockade of up-diffusion of oxygen from gate oxide induces oxide quality improvement.•Ti insertion prior to TiN improved oxide quality without changing gate work function. This study analyzed the physical and electrical characteristics of the interface reactions between hafnium-based high-k gate dielectrics and a TiN-based metal gate. Decreasing the N2 gas flow ratio (RN2 = N2/Ar+N2) from the physical-vapor-deposited TiN decreased the gate leakage current (JG) and the effective work function (EWF) of the metal gate. X-ray photoelectron spectroscopy analysis confirmed that TiN deposited with a lower RN2 condition can be easily oxidized to form TiOx at the gate oxide and metal gate interface after annealing at 1050 °C. This newly created oxide layer can prevent oxygen diffusion from the gate oxide through TiN to the TiN/poly-silicon interface, resulting in improved gate oxide quality. Inserting a thin Ti layer (< 1 nm) on the gate oxide formed a TiOx layer without a change in EWF, indicating that TiN composition variation followed the same trend as capacitance equivalent thickness (CET) versus JG. Therefore, an oxygen-blocking layer can have the same effect as gate oxide quality improvement for both scenarios—low RN2 of TiN and the thin Ti insertion—due to decreased oxide charge density. The Ti insertion process was associated with improved gate oxide leakage, negligible CET increase (0.2 Å), and gate oxide reliability, including time-dependent dielectric breakdown characteristics due to the blockage of oxygen up-diffusion.