Hard masks and methods of forming hard masks are described. The hard mask has an average roughness less than 10 nm and a modulus greater than or equal to 400 GPa. The method comprises exposing a substrate to a deposition gas comprising a dopant gas or a precursor (solid (e.g. Alkylborane compounds) or liquid (e.g. Borazine)), a carbon gas and argon at a temperature less than or equal to 550 C, and igniting a plasma from the deposition gas to form an ultrananocrystalline diamond film having an average roughness less than 10 nm and a modulus greater than or equal to 400 GPa.