A TOP ANTIREFLECTOR PROCESS FOR IMPROVED LINEWIDTH CONTROL AND ALIGNMENT

Thin film interference plays a destructive role in optical photolithography in two regards. (1) Large linewidth variations can occur from tiny changes in the thickness of resist or underlying thin films. (2) Asymmetric flow of resist over alignment mark topography can cause optical fringes which result in poor alignment signal profiles. In this paper, a new approach is described which can address both of these issues. A thin, low index, transparent film analogous to a lens antireflector (AR) coat is placed on top of the photoresist film before exposure. The ideal top antireflector (TAR) film would have thickness T = lambda/(4n') and n' = square-root n where n and n' are the refractive indices of resist and TAR, respectively. Experimental results are presented which show how various TAR layers can improve linewidth control and reduce notching as lines are patterned over topographic steps. In addition, simulations are presented which demonstrate how a TAR layer can improve the alignment signal, for certain types of alignment systems. The TAR process has great potential for high volume, economical semiconductor manufacturing.