David A. Kewley

Characterization of array CD uniformity with respect to pattern density in 193nm dry photolithography

As we move toward printing sub-100nm features using 193nm dry photolithography with high-contrast photoresists, effects of mask transmission and pattern density start to play an important role in critical dimension uniformity (CDU). With these two factors in existence, the linewidth for a dense feature block gradually increases from the center to the edge of the array of the block. This change in CD is typically observed for low-transmission reticles. In this paper, we have characterized variables, such as reticle tone and resist processing parameters, which have an effect on the CD uniformity. Use of high-contrast photoresist can increase the effect of chemical flare and can have higher CDU. We have further shown that by using a topcoat or by making changes in the resist bake temperature and time, the effect of chemical flare can be reduced. We also propose a mechanism by which resists exhibit this characteristic and show that both the photoacid generator and quencher can contribute to chemical flare.