Search

Atomic layer deposition (ALD) and pulsed chemical vapor deposition (p-CVD) of Ru-based films, such as Ru, RuO2, and SrRuO3, were examined for their application to advanced dynamic random access memory capacitor with a design rule of < 20 nm. Growth characteristics and film properties of Ru grown by ALD and p-CVD using (DMPD)(EtCp)Ru and RuO4, respectively, were comparatively examined. Furthermore, deposition of RuO2 and SrRuO3 electrodes was explored by p-CVD and combined ALD/CVD processes using RuO4 and Sr(iPr3Cp)2 as Ru and Sr precursors, respectively. The leakage current density and equivalent oxide thickness of metal-insulator-metal capacitor, where Ru based electrodes and higher-k dielectrics were adopted, were also studied.

SrTiO3 (STO) thin films were deposited by an atomic layer deposition at a higher temperature (370 oC) in order to improve the crystallinity and density of the film using Ti(O-iPr)2(thd)2 and Sr(thd)2 as Ti-, and Sr-precursors, respectively, and H2O as the oxidant. With the help of the crystallized seed-layer, in-situ crystallized STO film could be deposited even at the as-deposited state with the excellent electrical performances. The process conditions including the annealing temperature and the thickness of the seed-layer were crucial for achieving the high dielectric constant. From a planar capacitor structure consisting of Pt/20-nm-thick STO/Ru(bottom) Tox of 0.72 nm (dielectric constant of 108) and a low leakage current density (~ 10-7 A/cm2 at 0.8 V) were achieved. The Schottky conduction mechanism mainly contributed to the electrical conduction process in the low electric field region (< ~ 0.3 MV/cm) with a Schottky barrier height of 0.47 eV between Ru and STO. The Fowler-Nordheim tunneling was appeared as the primary conduction mechanism in the high electric field region (0.3~0.5 MV/cm).

Ru and RuO2 thin films were grown on Si, SiO2 and TiN substrates by pulsed chemical vapor deposition using RuO4 and 5%H2/95%N2 as the precursor and reducing gas, respectively. Ru film showed an excellent thermal stability, high growth rate of 0.18nm/pulse (0.43nm/min), low impurity concentration, conformal step coverage and very smooth surface. The TiO2 film grown on this Ru electrode showed much improved electrical performance compared to those on the other Ru electrode. RuO2 thin film can be deposited by decreasing the H2/N2 gas supply rate. RuO2 thin film has excellent conformal step coverage on a hole structure with an opening diameter of 100nm and a depth of 1000nm. With ¬RuO2 thin film as sub-electrode of MIM capacitor, the equivalent oxide thickness of TiO2 film could be decreased to 0.56nm within the specification of DRAM leakage current.

SrTiO3 (STO) thin films were deposited by atomic-layer- deposition (ALD) at a higher temperature (370{degree sign}C) using Ti(O-iPr) 2(thd)2 and Sr(thd)2 as Ti-, and Sr-precursors, respectively, and H2O as the oxidant, in order to improve the crystallinity and film density. With these precursors, the ALD process window of the STO film could be extended up to 400{degree sign}C. With the help of a seed-layer, more dense and well-crystallized STO films could be obtained even in the as-deposited state. The adoption of a seed-layer and the seed-layer annealing temperature are the crucial factors for obtaining high capacitance. In the case of a planar capacitor structure consisting of Pt/STO (27nm)/Ru(bottom), an equivalent oxide thickness of 0.73nm and leakage current density of 1x10-7 A/cm2 at 1V were achieved.