Partial rim: a new design of rim phase shift mask for submicron contact holes
Cui Z., Prewett PD., Martin B.
The reduction of image intensity in a rim phase shift mask (PSM) for contact holes has been investigated by computer simulation and experimental lithography. The reduction occurs at contact hole size below 1.0λ/NA. The smaller the size the severer the reduction. A new design of rim PSM called partial rim PSM, is proposed to overcome the problem. Computer simulation of aerial images has shown that the partial rim PSM can enhance image intensity. The enhancement is more significant for smaller size of contact holes while the degradation of image quality is much less than a biased rim PSM proposed previously. The partial rim PSM has been fabricated using the same self-aligned process as for conventional rim PSM fabrication. The contact holes with partial rims and with conventional rims have been printed on a wafer by a g-line stepper. The experimental result has confirmed the improvement in image intensity achieved by the partial rim PSM.