Atomic layer deposition of Ta-doped SnO2 films with enhanced dopant distribution for thermally stable capacitor electrode applications
Atomic layer deposition (ALD) on Ta-doped SnO2 thin films is proposed as a methodology for the fabrication of capacitor electrodes, for application in dynamic random-access memories (DRAMs). In ALD of doped materials, dopant concentration gradients inevitably occur due to the cyclic process-based characteristics of ALD. In this study, the dopant distribution improves drastically by the decrease in the growth per cycle of TaOx ALD. The modified ALD recipe exploits the low reactivity between Ta and Sn precursors to facilitate a reduction in the growth per cycle. The Ta-doped SnO2 films grown based on this modified ALD recipe exhibit improved crystallinity and conductivity. The ALD process yields excellent conformality of the Ta-doped SnO2 film over a hole structure with a high aspect ratio of ~10, both in terms of physical thickness and composition. Additionally, the Ta-doped SnO2 films serve as a template for the overgrowing dielectric TiO2 film, which induces the formation of a high-temperature phase with a high dielectric constant, rutile TiO2, and exhibit excellent thermal stability even after annealing at 400 °C in forming gas atmosphere. These findings demonstrate that the proposed methodology for the growth of Ta-doped SnO2 can facilitate the fabrication of capacitor electrodes for application in DRAMs.