Study On Mechanical And Electrical Properties Of High-K Al₂O₃ Thin Films

In this paper, Al2O3 thin films were prepared on Si substrate by electron beam evaporation and RF magnetron sputtering technologies which could replace traditional SiO2 gate. Their crystal structure, surface morphology, mechanical and electrical properties were studied to find relationship between them.Firstly, the influence of different sputtering process parameters was discussed.(1) With deposition time increasing, the grain size and surface height of film increases. While film thickness increases, the surface roughness also increases. But the residual stress of film decreases with the deposition time increasing. Doljiak model was used to explain the results.(2) The film deposition rate increases significantly with sputtering power increases. Sputtering power had a big influence on surface roughness and particle size of Al2O3 film. Larger sputtering power led to a bigger surface roughness. But it also brought more residual stress and growth defects.Secondly, the influence of different substrate temperature was discussed. All the films were amorphous phase.(1)With same deposition time, the film thickness increases during the substrate temperature increases. The Al2O3 film film was smoother with small particle and little impurities at 500°C. When the substrate temperature reached 800°C, the grain size and film height became larger. The RMS of film was between 1-6nm. The increasing of film thickness and grain size which came from island growth lead larger surface roughness.(2)The residual stress of films were all tensile stress. Annealing in N2 could reduce the stress value effectively. Before annealing, the film stress was 526 MPa at 500°C. But it reached 1391 MPa at 800°C. Different thermal expansion coefficients was the major cause of stress. Stoney equation was used to analyzed the experiment.Thirdly, the electrical properties of Al2O3 thin films were discussed.(1)Under the same substrate temperature, the leakage current of the thin film rose with increasing the test voltage. Under the same test voltage, the leakage current of Al2O3 film rose with increasing the substrate temperature. It reached maximum value at 800°C. Higher substrate temperature brought more interface defects. And the trap energy levels could reduce the height and width of tunneling barrier. It lead to lager leakage current.(2)At the same testing frequency, the capacitors in the accumulation area increases with substrate temperature The value of capacitance was only 2×10-10 F at 400°C. And the capacitance value reached 7×10-10 F at 800°C. At the same temperature, the value of capacitance decreased with the testing frequency increasing. It is because the different electrode mechanism at different frequency.(3)The dielectric constant of different substrate temperatures is discussed. It raised from 7.4 to 11.3 in this experiment.