Mechanism of the Trefonas effect (polyphotolysis) in Novolak-diazonaphthoquinone resists

Polyphotolysis, namely the behavior of polyfunctional photoactive component s (PACs), is an important aspect of dissolution inhibition resists. Polyfun ctional PACs produce higher lithographic contrast and lead to higher line r esolution. The effect is so important that trifunctional diazonaphthoquinon e PACs have become the industry standard, virtually eliminating the use of the corresponding monofunctional inhibitors. We believe that polyphotolysis depends on an interaction between phenolic strings emanating from the acce ptor groups of PACs located on the same backbone molecule. In the coating s olution the strings of the PACs meet and connect with each other, and these connections survive into the solid resist film. After partial exposure som e of the strings are severed from their anchors and would lose their inhibi ting power, were it not for an unexpected effect that allows the severed st rings to be reconnected to still polarized, "living" strings. In this proce ss of reconnection the living strings increase in length, and the final res ult of exposure is the replacement of two shorter polarized strings by a si ngle longer one. Inhibition depends on the overall number of phenolic units taking part in polarized strings. If there is only a small change in the o verall length of the phenolic strings in the system, there will be only a s mall change in dissolution rate. That is precisely what Trefonas and Daniel s observed.