Suppression of defect formation in atomic-layer deposited Al₂O₃ thin films by addition of AlF₃ cycles

Aluminum oxyfluoride (AlO_xF_y) nanolaminate thin films with various compositions were grown by alternating atomic layer deposition (ALD) cycles of aluminum oxide (Al₂O₃) and aluminum fluoride (AlF₃) at different ratios. The addition of the AlF₃ cycles significantly reduced the defects in the ALD-grown Al₂O₃ films. The defects inside the AlO_xF_y nanolaminate films were analyzed by exposing the defects inside the films by plasma etching after depositing them on a silicon (Si) substrate so that the etching gases penetrating through these defects etch the Si substrate and leave the etching traces. It was confirmed that the defect density inside the AlO_xF_y films was significantly reduced when the ALD cycle ratio of Al₂O₃ and AlF₃ was optimal. These results were experimentally verified by observing the changes in the characteristics of indium-gallium-zinc-oxide (IGZO) thin-film transistors (TFTs) when AlO_xF_y films were covered over the TFTs and hydrogen gas was allowed to permeate the films for a certain period of time. When the ALD cycle ratio of Al₂O₃ and AlF₃ was 5:1, hydrogen penetration was the lowest and the change in characteristics of the IGZO TFTs was also the smallest.