A method of forming a barrier layer for a thin film structure on a semiconductor substrate includes forming high aspect ratio openings in a base layer having vertical side walls, depositing a dielectric barrier layer comprising a dielectric compound of a barrier metal on the surfaces of the high aspect ratio openings including the vertical side walls and depositing a metal barrier layer comprising the barrier metal on the first barrier layer. The method further includes reflowing the metal barrier layer by (a) directing light from an array of continuous wave lasers into a line of light extending at least partially across the thin film structure, and (b) translating the line of light relative to the thin film structure in a direction transverse to the line of light.