A coating system for forming an atomic layer deposition (ALD) or a molecular layer deposition (MLD) barrier coating on interior fluid wetted surfaces of a fluid handling component for a vacuum chamber of a semiconductor substrate processing apparatus. The coating system includes the fluid handling component, wherein the interior fluid wetted surfaces define a process region of the coating system, a gas supply system in fluid communication with the process region of the component wherein the gas supply system supplies process gases to the process region of the component through the inlet port thereof such that an ALD or MLD barrier coating can be formed on the fluid wetted surfaces of the fluid handling component, and an exhaust system in fluid communication with the process region of the component wherein the exhaust system exhausts the process gases from the process region of the component through the outlet port thereof.