Method for Al thin film surface nanostructuring using Al imprinting and anodic oxidation: Application to a high capacitance density metal-insulator-metal capacitor

A method for Al thin film surface nanostructuring using Al imprinting with a silicon insert and subsequent anodic oxidation and selective oxide removal for nanostructure thinning and surface smoothing is presented. Al imprinting results in direct pattern transfer of the Si insert pattern, while anodic oxidation results in an increase of the nanostructure pattern aspect ratio due to the observed anodic oxidation anisotropy between the vertical direction and sidewalls. Al lines of 120 nm width and height-to-width ratio of 6 were thus achieved, starting from a Si insert of 500 nm wide lines with a height-to-width ratio of 1, resulting in an effective surface area increase × 2.4, confirmed by a corresponding capacitance density increase of a MIM capacitor using the nanostructured Al thin film as the bottom electrode. The developed method is simple, fast, versatile, and does not require any expensive equipment for its realization. It can be used for the formation of a variety of different nanostructures on the Al surface, for use in a large variety of applications.