Paper TF+EM-MoM10
Development of a Reduction-resistant Oxide Electrode for Dynamic Random Access Memory Capacitor

Monday, October 30, 2017, 11:20 am, Room 20

Rutile phase TiO₂/RuO₂ structures have attracted great interests as a new material system for next-generation dynamic random access memories (DRAM) capacitors because of the high dielectric constant (> 80) of the rutile TiO₂. A conducting oxide electrode, RuO₂, enables the TiO₂ dielectric to be crystallized into a rutile phase at low temperatures (< 300 ^oC). Since RuO₂ has a high work function, it is effective to suppress leakage current by Schottky emission which is a main conduction mechanism of TiO₂/RuO₂. However, the RuO₂ electrode is easily reduced during the post-annealing under forming gas atmosphere for trap passivation at the gate oxide/Si interface. Subsequently, the dissociated oxygen ions from RuO₂ cause problems such as the oxidation of W plug. The oxidation of W plug causes a fatal deterioration in device operation because the W plug acts as a path through which the charges of the capacitor move. Also, physical damage such as cracks will also occur when RuO₂(rutile) is reduced to Ru(hexagonal close-packed, HCP). For these reasons, we suggest a SnO₂-based electrode, which is a reduction-resistant material, as a new oxide electrode for DRAM capacitors. The reduction reaction of SnO₂ is thermodynamically more difficult than that of RuO₂. Also, a small amount of Ta ions is incorporated into the SnO₂ films to enhance the conductivity of the electrode. The resistivity of SnO₂ is reported to reach down to 10^-4Ω·cm by Ta doping, which is sufficient for use as an electrode of DRAM capacitor. Furthermore, the Ta-doped SnO₂ films are well crystallized into a rutile phase, thereby leading to the formation of rutile TiO₂ at a low growth temperature (< 270 ^oC). Therefore, we demonstrate that Ta-doped SnO₂ would be a promising candidate for the electrodes for next-generation DRAM capacitors.