Atomic layer deposition of rutile-phase TiO2 on RuO2 from TiCl4 and O3: Growth of high-permittivity dielectrics with low leakage current

• Atomic layer deposition of TiO2 from TiCl4 and O3 on RuO2 was studied at 225–450 °C.
• Rutile-type TiO2 films were obtained on RuO2 at temperatures down to 225 °C.
• Relative permittivity values ranging from 106 to 126 were achieved for rutile films.
• Low leakage current densities were observed for films deposited at 250–350 °C.

Crystallization of TiO2 thin films grown by atomic layer deposition from TiCl4 and O3 on RuO2 layers was investigated with the aim to develop alternative methods for preparation of high-permittivity dielectrics with low leakage current density for capacitor structures of memory devices. The lowest substrate temperature allowing reproducible growth of TiO2 with a rate exceeding 0.01 nm per cycle was determined to be around 225 °C. The highest deposition temperature used was limited to 450 °C because of RuO2 decomposition at higher temperatures. The TiO2 films deposited on RuO2 electrodes at substrate temperatures of 225–450 °C contained rutile phase. Reference films deposited on Si substrates were amorphous when deposited at 225 °C and contained anatase when deposited at 250 °C and higher temperatures. At temperatures 250–450 °C, the growth rate values of 10–25 nm thick films ranged from 0.04 to 0.07 nm per cycle being somewhat higher on RuO2 than on Si substrates. The dependence of the mean growth rate on the substrate material was mainly due to differences in nucleation and became weaker with increasing film thickness. Relative permittivity measured for TiO2 in the Pt/TiO2/RuO2 structures at a frequency of 10 kHz ranged from 106 to 126. The TiO2 films with the lowest leakage current densities were grown at 300–350 °C. Leakage current densities as low as (5–7)×10–8 A/cm2 at an applied voltage of 0.8 V were recorded for capacitor structures with capacitance–equivalent dielectric thicknesses of 0.41–0.45 nm.