The Development Of Metal Layer OPC Model In 28nm Node IC Technology

With minimum half-pitch shrinking to 28 nm technology node according to "Moore's law",problem of diffraction in photography is getting more serious,Thus,OPC(Optical Proximity Correction)technique plays much more important role.OPC helps lithography to enhance the exposure resolution and enlarge the process window.In 28 nm process,due to the smaller tolerance to CD(Critical Dimension)variation,the precision of OPC model must be reduced as much as possible.In addition,due to the smaller process window,OPC model needs to have the ability to predict the patterning defects when expose dose and focus drift in a normal amount,to ensure patterns can be correctly formed through lithography process window.This paper selected 28 nm metal layers,which have the most complex pattern routing.To study the characteristics of the 28 nm OPC model,we analyzed the factors which affects the model accuracy,took the corresponding method to improve the accuracy of the model.Also,new OPC techniques were investigated and applied.Firstly,mask model was studied.The parameters of mask model were analyzed,and the optimization method of these parameters was summarized through the experiment.The experiment mask model showed great improvement to the OPC model accuracy.Secondly,PWOPC(Process Window OPC)model was also built.In this paper,the gauge sensitivity to energy/focus variation was defined,by which the screening sensitive data points helped to establish an accurate PWOPC model with a much shortening runtime.Then,the modeling of photoresist top loss was investigated.A compact etch CD model was built to predict the pattern contour after etch.The experiment model error was controlled within 3 nm which can meet the process requirement.With the application of this photoresist top loss model,several patterning defects were successfully detected on the real layout before OPC tape out.