Film thickness measurements are good to ensure the amount of material is deposited, etched or how much a photoresit was developed. Often used in hand with samples to verify rate of deposition or etch on a tool. Some of the tools below may also be used to determine surface roughness. Surface roughness could affect the adhesion of subsequent layers (mechanical interlocking is the mechanisim).
noncontact, quick to use, esp. good for Oxides and photoresists