Embodiments of the present disclosure generally relate to methods for enhancing carbon hardmask to have improved etching selectivity and profile control. In some embodiments, a method of treating a carbon hardmask layer is provided and includes positioning a workpiece within a process region of a processing chamber, where the workpiece has a carbon hardmask layer disposed on or over an underlying layer, and treating the carbon hardmask layer by exposing the workpiece to a sequential infiltration synthesis (SIS) process to produce an aluminum oxide carbon hybrid hardmask which is denser than the carbon hardmask layer. The SIS process includes exposing and infiltrating the carbon hardmask layer with an aluminum precursor, purging to remove gaseous remnants, exposing and infiltrating the carbon hardmask layer to an oxidizing agent to produce an aluminum oxide coating disposed on inner surfaces of the carbon hardmask layer, and purging the process region to remove gaseous remnants.