OMOG mask topography effect on lithography modeling of 32nm contact hole patterning

The topography effect of Opaque MoSi on Glass (OMOG) mask on 32nm contact hole patterning is analyzed by examining the difference of image intensity profile between thin mask approximation and rigorous electro-magnetic field (EMF) simulation. The study shows that OMOG topography results in more than a 20% decrease of image intensity. The impact of OMOG mask topography on lithography modeling of a 32nm contact hole process is explored by fitting lithography simulation with experimental results for both thin mask model and EMF model. This study shows that thin mask modeling is a good approximation of EMF modeling for a contact pitch larger than 120nm, but yields about 10nm prediction error for a 110nm contact pitch. Thin mask modeling is shown to be inaccurate in predicting critical dimension of contact arrays with sub-resolution assistant feature (SRAF). In addition, thin mask modeling is too pessimistic in predicting SRAF printability. In contrast, EMF model shows good prediction of contact arrays with and without sub-resolution feature. A modified thin mask modeling technique utilizing an effective SRAF size is proposed and verified with experimental results.