One metric to rule them all: new k4 definition for photoresist characterization

As feature sizes continue to shrink, low-k₁ lithographic processes are required to advance chip technologies. In this context, both advances in optical systems and imaging capabilities as well as improvements in EUV photoresist have led to practical gains in resolution. This work focusses on our latest attempt to characterize photoresist performance by a metric that can effectively exclude all other contributors (e.g. scanner) and quantify the true photoresist capabilities. By a cautious analysis of the previous k₄ metric for several use cases and resist platforms (chemically amplified vs. metal-oxide resist), we propose an improved formula that incorporates key resist attributes.