Effects of Deposition Temperature on the Microstructure and Electrical Properties of 50 nm High-k BaTiO3 MIM Capacitors Fabricated by Atomic Layer Deposition

Thermal atomic layer deposition (ALD) of BaTiO3 (BTO) is of interest for next-generation microelectronic devices, including RAM and NAND memory. Herein, we investigate the influence of deposition temperature on the microstructure and electronic properties of 50 nm BTO thin films fabricated by ALD at 200, 220, 240, and 280 °C using bis-(1,2,4 triisopropylcyclopentadienyl)-Ba [Ba(iPr3Cp2)], titanium isopropoxide, and water as precursors, and highlight the significance of void formation in films based on this chemistry. Self-limiting ALD behavior is observed, such that the deposition rate and Ba:Ti ratio are independent of prolonged Ba dose times. XRD shows that films deposited at 220 and 240 °C are significantly more crystalline than films deposited at 280 °C after annealing. Scanning electron microscopy reveals a difference in film microstructure depending on deposition temperature, indicative of different “structural zones”. Cross-sectional transmission electron microscopy reveals that annealed, crystallized BTO films are susceptible to void formation, especially when lower ALD deposition temperatures are used. This void formation appears to result from a combination of the microstructure of the as-deposited film and the easily hydrated barium constituent and is identified as an important structural defect that will need to be avoided to achieve desired dielectric performance. Electrical properties, such as capacitance–voltage (CV), dielectric loss, and DC current–voltage (IV), are closely correlated with microstructure. Fifty-nanometer BTO thin films deposited at 220, 240, and 280 °C have relative permittivity values (εr) of 73, 60, and 33, respectively, at 10 kHz after annealing. Dielectric loss (tanδ) is as low as 0.001. A modest dispersion in capacitance is observed across varying sampling frequencies. Future research to further understand and mitigate void formation while retaining proper stoichiometry for this ALD chemistry is recommended to further improve dielectric performance.