Scatterometry measurement method for gate CD control of sub-130nm technology

Recently, the scatterometry is becoming more and more popular as a inline metrology tool for lithography process control as well as etching process control because of the advantage of fast measurement with high accuracy. Especially, at the gate patterning that fabricates transistors, the scatterometry can be very powerful because it gives massive volume of CD (Critical Dimension) measurement data and gate poly profile, simultaneously. Those results could help to understand and forecast the performance of transistors. In order to achieve accurate and consistent measurement results by scatterometry, the setup of stable model and library is very crucial since it has nature of indirect measurement. For example, as defining of substrate conditions, modeling range of parameters, target values and type of models, scatterometry (in this paper, we call as OCD; Optical CD) gives different results even if we use same data basis. In this paper we have shown the best practice how to optimize variables of scatterometry to get accurate and stable results. We used the OCD(Optic CD: Accent CDS200) angular scatterometry system which can rotate HeNe laser light source from -47 to +47 degree. In order to investigate the substrate dependency, various silicon wafer substrates having periodic patterned with different materials such as photoresist, BARC, poly silicon, and thermal oxide film has been used. Finally, we observed OCD has the excellent capability for inline process controllability.