Comparative study of binary intensity mask and attenuated phase shift mask using hyper-NA immersion lithography for sub-45nm era

Abstract

In this paper, we will present comparison of attenuated phase shift mask and binary intensity mask at hyper-NA immersion scanner which has been the main stream of DRAM lithography. Some technical issues will be reported for polarized illumination in hyper-NA imaging. One att.PSM (Phase Shift Mask) and three types of binary intensity mask are used for this experiment; those are ArF att.PSM ( MoSi:Å ), thick Cr ( 1030Å ) BIM (Binary Intensity Mask), thin Cr ( 590Å ) BIM and multi layer ( Cr:740Å / MoSi:930Å ) BIM. Simulation and experiment with 1.35NA immersion scanner are performed to study influence of mask structure, process margin and effect of polarization. Two types of DRAM cell patterns are studied; one is an isolation pattern with a brick wall shape and another is a storage node pattern with contact hole shape. Line and space pattern is also studied through 38nm to 50nm half pitch for this experiment. Lithography simulation is done by in-house tool based on diffused aerial image model. EM-SUITE is also used in order to study the influence of mask structure and polarization effect through rigorous EMF simulation. Transmission and polarization effects of zero and first diffraction order are simulated for both att.PSM and BIM. First and zero diffraction order polarization are shown to be influenced by the structure of masking film. As pattern size on mask decreases to the level of exposure wavelength, incident light will interact with mask pattern, and then transmittance changes for mask structure. Optimum mask bias is one of the important factors for lithographic performance. In the case of att.PSM, negative bias shows higher image contrast than positive one, but in case of binary intensity mask, positive bias shows better performance than negative one. This is caused by balance of amplitude between first diffraction order and zero diffraction order light. Process windows and mask error enhancement factors are measured with respect to various design rules, i.e., different k1 levels at fixed NA. In the case of one dimensional line and space pattern, thick Cr BIM shows the best performance through various pitches. But in case of two dimensional DRAM cell pattern, it is difficult to find out the advantage of BIM for sub-45nm. It needs further study for two dimensional patterns. Finally, it was observed that thick Cr binary intensity mask for sub-45nm has advantage for one dimensional line and space pattern.