Positive Tone, Low-k Polynorbornene Dielectric Crosslinking

Abstract

The effect of pH on film properties is studied in epoxy-based polynorbornene dielectrics. During normal processing, the negative tone films exhibit a highly acidic pH prior to cure, whereas the positive tone films exhibit a neutral or basic pH. Films with the exposed photo acid generator were swelled with base to achieve a comparable pH to the positive tone material. Despite the contrast in film acidity, a peak modulus of 3.0 GPa at a 140ºC cure temperature was observed, declining to 2.4 GPa at 220ºC for both negative tone pH conditions. In a neutral pH positive tone material, crosslinking occurred with DNQ acting as the cross-linker, providing a modulus of 4.0 GPa. When developed, DNQ-loaded films showed a decline in modulus to 2.6 GPa, likely due to the reactions of DNQ with aqueous base. An epoxy cross-linker added to the developed positive tone film helped crosslinking by inhibiting base uptake.