Atomic Layer Deposition of SrTiO3 Thin Films with Highly Enhanced Growth Rate for Ultrahigh Density Capacitors

The ever-shrinking dimensions of dynamic random access memory (DRAM) require a high quality dielectric film for capacitors with a sufficiently high growth-per-cycle (GPC) by atomic layer deposition (ALD). SrTiO3 (STO) films are considered to be the appropriate dielectric films for DRAMs with the design rule of similar to 20 nm, and previous studies showed that STO films grown by ALD have promising electrical performance. However, the ALD of STO films still suffers from much too slow GPC to be used in mass-production. Here, we accomplished a mass-production compatible ALD process of STO films using Ti(O-Pr-i)(2)-(tmhd)(2) as a Ti-precursor for TiO2 layers and Sr((Pr3Cp)-Pr-i)(2) as a Sr-precursor for SrO layers. O-3 and H2O were used as the oxygen sources for the TiO2 and SrO layers, respectively. A highly improved GPC of 0.107 nm/unit-cycle (0.428 nm/supercycle) for stoichiometric STO films was obtained at a deposition temperature of 370 degrees C, which is similar to 7 times higher than previously reported. The origin of such high GPC values in this STO films could be explained by the partial decomposition of the precursors used and the strong tendency of water adsorption onto the SrO layer in comparison to the TiO2 layer. The STO film grown in this study also showed an excellent step coverage (similar to 95%) when deposited inside a deep capacitor hole with an aspect ratio of 10. Owing to the high bulk dielectric constant (similar to 146) of the STO film, an equivalent oxide thickness of 0.57 nm was achieved with a STO film of 10 nm. In addition, the leakage current density was sufficiently low (3 x 10(-8) Acm(-2) at +0.8 V). This process is extremely promising for fabrication of the next generation DRAMs.