Current 193-nm optical lithography and commercially available 193-nm resists have been pushed far beyond the previously expected critical dimension by using process extension technology for resolution enhancement technology. This paper deals with three kinds of process extension technologies, thermal treatment, polarization, and double patterning. These technologies are modeled and analyzed. If a 50 \% pattern shrinkage due to thermal treatment, a 25 \% resolution enhancement due to polarization, and a 50 \% pattern shrinkage due to double patterning are supposed, an effective combination can generate a sub-50-nm pattern. When the pattern size is smaller, optical proximity effects are more severe. After describing optical proximity effects for each of these technologies, we discuss optical proximity correction methods.