Considerations in the Setting up of Industry Standards for Photolithography Process, Historical Perspectives, Methodologies, and Outlook

Photolithography has been the driving force for the continuous design rule shrink where the manufacturing linewidth has been evolving from the early a few micrometers in the 1970's to the current several tens of nanometers and is due to develop into the future single-digit-nanometer technologies. Throughout the past years, both the Front-End-Of-the-Line (FEOL) device performance and the Back-End-Of-the-Line (BEOL) metal routing performance have been related to the photolithography process quality. There are several key parameters that we use to characterize the quality of a lithography process, such as, Exposure Latitude (EL), Depth of Focus (DoF), and relatively later added Mask Error Factor (MEF). All of these parameters are related to the linewidth uniformity, including, the within exposure field uniformity, the across wafer uniformity, and the across pattern uniformity (Optical Proximity Effect, OPE). For photoresists, the important parameters are the photo-sensitivity, the photoacid diffusion length, the PhotoAcid Generator (PAG) loading, the dissolution contrast, etc. Among all the parameters, there are trade-offs and possible areas for mutual compensation. The industry standard is a set of rules or practices that can best reflect the needs for performance, reliability, cost, and short time- to- market. In this paper, we will present our studies on the setting up of industry standards for photolithography with the analysis of the photolithographic process at typical past technology nodes and Extreme Ultra-Violet (EUV) technology nodes with future outlook and proposal.