Abstract
The minimum half pitch for optical projection lithography in manufacturing has been held to 0.8 λ/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-k 1 requirement are identified in this paper. First, imperfections in the imaging system can reduce the processing margin. Subsequently, the k 1 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 k 1 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 k 1 . Experimental and theoretical results are given to substantiate the above and to lead to methods for low-k 1 manufacturing.