PROVE: a photomask registration and overlay metrology system for the 45 nm node and beyond

The continuous progress in semiconductor technology has caused mask feature sizes shrinking to 120 nm for the 45nm node and down to 85 nm for the 32nm node. Along with the smaller features, mask image placement accuracy has to improve to 3.4 nm by 2013. Applying double patterning in particular requires rigorous manufacturing control over level to level registration in order to achieve the specified yield and device speed. There is currently no registration tool that ensures image placement performance at the minimum feature size of current and future technology nodes. This work describes fundamental concepts and working principals of a new metrology tool currently under development at Carl Zeiss for measuring image placement and critical dimension in photomask manufacturing. The design of the instrument will be discussed with special emphasis on its optical components. Benefits and advantages using 193nm illumination as well as contrast simulations on different types of masks are presented.