The demands and solutions for ultra-precision metrology in the manufacturing of lithography masks for the display industry are indeed challenging. Specification demands to be overcome are a measurement repeatability of 10 nm (3 σ) and an absolute accuracy of better than 100 nm (3 σ) on a scale of more than 1.5 m in the X and Y directions. The design of a measurement system that meets these requirements calls for careful selections of materials such as metal, ceramic composites, quartz or glass as they at this precision level are highly affected by the surrounding temperature. Also the fact that the refractive index of air in the interferometers measuring absolute distances is affected by temperature, pressure, humidity and CO2 content make the reference measurements really challenging [1].

As in many other areas in the industry high quality metrology is the key for success in developing high accuracy production tools. This paper will therefore start by introducing the metrology requirements of mask making for display screens and end with the state-of-the-art results we have achieved.