Controllability of Mesoscopic Surface Roughness of Sputtered Al and Al–N Films

Abstract

There is a concept that the surface roughness is the structure-type of the optical gradient function because the material volume fraction gradually changes along the surface normal from the vacuum (or air) to the material. In this sense, the controlling the surface undulations corresponds to the controlling the gradient-profile.
Sputtered Al film, AlN film, and incompletely-nitrided Al film (Al–N film) has been investigated from the view point of forming the mesoscopic scaled surface roughness because it can be applied to, e.g., the solar absorption coating, the solar cell and/or the diffusive coloring. The surface structures have been characterized and the growth condition dependence, such as the degree of nitriding which is controlled by changing mixing ratio of N₂ and Ar sputtering gases, the film thickness (d_f), and the substrate temperature (T_sub), are systematically investigated. The following controllable factors about surface structure are confirmed. The characteristic of the form of protuberances on the surface depends on the degree of nitriding. The height and the width of the protuberances can be controlled by d_f and/or T_sub.