Even with the latest lithography tool, there is a limit to the minimum feature size that can be patterned for a given lithography technology. Nevertheless, there is one clever and widely used technique which allows for patterning of the dimension that is actually smaller than what is capable with just using lithography. This technique requires the formation of a spacer. Yes, the formation of this spacer is exactly the same as the spacer that is formed before the deep source/drain doping that we discussed in class. However, for this case, its use is a bit different. Please do a search on this technique and explain (with diagrams or cross-section drawings) how sub-lithography resolution can be achieved with the help of a spacer.