Electron Cyclotron Resonance Plasma-Assisted Radio Frequency Sputtering of Strontium Titanate Thin Films for Dynamic Random Access Memory Application.

Strontium titanate thin films were deposited by electron cyclotron resonance plasma assisted radio frequency magnetron sputtering. A deposition atmosphere of 90% argon/10% oxygen at a pressure of 5 mTorr was determined to be the optimal conditions to obtain a high density plasma containing activated oxygen species. An applied microwave power level of 100 W yielded SrTiO_3 films exhibiting improved physical and electrical properties over those deposited using rf magnetron sputtering alone. It was found that both the structure and composition improve with the application of microwave plasma during the deposition. Films on platinum coated silicon substrates show good dielectric properties when deposited using in-situ heating at 550 ^circC. The dielectric constant and dissipation factor at a frequency of 100 kHz were 170 and 0.033, respectively. A charge storage density of 28 fC/mum^2 and unit area capacitance of 3.7 fF/mum ^2 were obtained at an applied electric field of 200 KV/cm. Films showed a leakage current density on the order of rm 10^{-8} A/cm^2 at an applied electric field of 50 KV/cm. The use of rapid thermal annealing at 600 ^circC for 30 sec was most effective in crystallizing films deposited on bare silicon substrates. The highest quality films exhibited a dielectric constant and dissipation factor of 90 and 0.049, respectively, at 100 kHz. The reduction in dielectric constant is a result of the formation of a thin, low dielectric constant interfacial layer of SiO_2. Analysis of the capacitance-voltage characteristics of metal-insulator -semiconductor devices revealed that the quality of the film/substrate interface is dependent on the pressure, atmosphere and temperature of the deposition. The charge storage density and current-voltage characteristics are of a sufficient level to allow SrTiO_3 thin films to be a candidate material for use as a gate dielectric in DRAM application.