Robust lithography application to prevent resist poisoning in BEOL

Abstract

As feature sizes become increasingly smaller in integrated circuits, the occurrence of resist-pattern defects (resist poisoning) has become a serious problem in Back End Of Line (BEOL) Dual Damascene (DD) processing. Against this background, we have researched a bi-layer silylation process as one type of multi-layer process and evaluated its effectiveness as a countermeasure to resist poisoning. In the bi-layer silylation process, two layers of chemically amplified resist (CAR) are formed on novolac, and after wet-developing the upper CAR layer by an alkali developer, a silylation reaction is generated to make the resist pattern resistant to O2 reactive ion etching (RIE). We found that the bi-layer silylation process was an effective countermeasure to resist poisoning in a methylsilsesquioxane (MSQ) DD structure with a 160-nm via, and that a 160-nm MSQ DD structure could be formed. We also found that the occurrence of resist poisoning depended greatly on the surface conditions of the via structure and on the resist-ashing technique.