Electrical Properties of Compositional Al<sub>2</sub>O<sub>3</sub> Supplemented HfO<sub>2</sub> Thin Films by Atomic Layer Deposition

Abstract

With advanced research for dielectrics including capacitors in DRAMs, decoupling filters in microcircuits and insulating gates in transistors, a lot of demand for the new challenging of high-k materials in semiconductor industries has been emerged. This study explores and addresses the experimental approach for composite materials with one of the major concerns of high capacitance, and low leakage, as well as ease of integration technology. The characteristics of Al2O3 supported HfO2 (AHO) thin films for a series of different Hf ratios with Al2O3 dielectrics by atomic layer deposition demonstrated as a candidate material. A composite AHO films with the homogeneous compositions of Al and Hf atoms into the Al-Hf-O mixed oxide system could stabilize the polycrystalline structure with increasing of dielectric constant (k) and decreasing of leakage current density, as well as a higher breakdown voltage than HfO2 film on its own. 70 nm thick AHO thin films with different composition of Al and Hf contents were prepared by atomic layer deposition technique on titanium nitride (TiN) and silicon dioxide (SiO2) coated Si substrates. Photolithography and metal lift-off technique were used for the device fabrication of the metal-insulator-metal (MIM) capacitor structures. AHO films on TiN/SiO2/Si were measured by semiconductor analyzer and source/ measure system with probe station in the voltage range from -5 to 5 V with a frequency range from 10 kHz to 1 MHz were used to conduct capacitance-voltage (C-V) measurements with low/medium frequency range and current-voltage (I-V) measurements. It was found that Au/AHO/TiN/SiO2/Si MIM capacitors demonstrate a capacitance density of 1.5 - 4.5 fF/μm2 at 10 kHz, a loss tangent of 0.02 - 0.04 at 10 kHz, dielectric constant of 11.7 - 35.5 depending on the composition and a low leakage current of 1.7 × 10-9 A/cm2 at 0.5 MV/cm at room temperature. The acquired experimental results could show the possibility of compositional alloy thin films that could potentially replace or open new market for high-k challenges in semiconductor technology.