Methods to print optical images at low-k 1 factors

Abstract

The minimum half pitch for optical projection lithography in manufacturing has been held to 0. 8 A/NA or larger. This is supported by the experience gained by semiconductor manufacturers worldwide yet the reasons are not clearly understood. Three main causes for the high-k1 requirement are identified in this paper. First imperfections in the imaging system can reduce the processing margin. Subsequently the k1 factor has to be raised to compensate for the loss. Vibration and stray light are two examples. Secondly even a perfect imaging system can be limited by an unoptimized coherence factor and by optical proximity effects which are increasingly dominant as k1 is reduced. These are basic limitations imposed by the diffraction phenomenon. Thirdly the conditions at the recording media i. e. the photoresist and the substrate can require unsuspectedly large processing margins which necessitate a high k1. Experimental and theoretical results are given to substantiate the above and to lead to methods for low-k1 manufacturing. 1.