The Filmetrics F40 is used to measure the thickness and optical constants (n and k) of transparent thin films. The F40 uses a microscope to provide a square measurement spot size as small as 1 micron. Commonly measured films include semiconductor process films such as oxides, nitrides, resists, and polysilicon, optical coatings such as hardness and anti-reflection coatings, flat panel display films such as polyimides, resist, and cell gaps, and the various coatings used in CD and DVD manufacture. Films that cannot be measured include very rough films and opaque films.