Multiple patterning (or multi-patterning) is a class of technologies for manufacturing integrated circuits (ICs), developed for photolithography to enhance the feature density. The simplest case of multiple patterning is double patterning, where a conventional lithography process is enhanced to produce double the expected number of features. The resolution of a photoresist pattern begins to blur at around 45 nm half-pitch. For the semiconductor industry, therefore, double patterning was introduced for the 32 nm half-pitch node and below, mainly using state-of-the-art 193 nm immersion lithography tools.There are several types of double patterning. In combination, these may be used for multiple patterning.