Ca-Doped CuO Diffusion Barrier for High-Performance a -IGZO Transistors With Cu-Based Source/Drain Material

A thermally stable Ca-doped CuO x (CuCaO x ) diffusion barrier to prevent the migration of Cu to amorphous InGaZnO ( ${a}$ -IGZO) was developed by reactive sputtering and subsequent annealing. Insertion of a 5-nm-thick CaCuO x between the Ca-doped Cu (CuCa) and a-IGZO channel films in the source/drain contact regions provided the resulting transistors with superior charge transport and lower trap density compared to the diffusion barrier-free CuCa/a-IGZO transistors. The fabricated a-IGZO transistors with the CuCa/CuCaO x stack contact exhibited a high mobility of 20.8 cm $^{\textsf {2}}/\textsf {V}\cdot \textsf {s}$ and an Ion/off ratio of 108. Simultaneously, very stable behavior against the external positive/negate gate bias stress was observed for the a-IGZO thin-film transistors with the CuCa/CuCaO x stack contact. This was attributed to suppression of Cu-related acceptor-like traps due to the conformal formation of CuCaO x film with excellent barrier properties.