A Further Analysis of the Forbidden Pitch in Photolithography in Advanced Technology Nodes

Starting at the 0.13 μm technology node, optical proximity effect becomes significant. One parameter that describes the difficulty level of the photolithography process is the k
1
factor. When the k
1
factor is less than 0.4, Optical Proximity Correction (OPC) technique needs to be used to compensate for the linewidth loss due to the diffraction effects and to improve the process window to some extent. In advanced technology nodes, such as 28 nm technology node and below, even after OPC, there still exists a pitch range (1.4~2 times that of dense pitches) within which the process window of some critical layers is relatively small, known as the "forbidden pitch".