Eliminating Sidewall Damage During Etch Process for Ultra Low-k Film

Abstract

There is a growing concern over the side wall damage caused by plasma etching in low-k interconnect process development. The extended vertical irregularities termed as “striations” is one such plasma damage resulting in a very rough surface on trench side walls. In the present work, mechanism of striation formation was studied in the trench etching process of ultra low-k (ULK) “spin-on type” film in Cu/ULK interconnects for 130 nm technology node. Reactive ion etch process was carried out to form trenches in the ultra low-k film capped with a dual hard mask deposited by chemical vapor deposition (CVD) technique. The ultra low-k film thickness was 5000 Å and critical dimension target of trench was 180 nm. Very obvious trench side wall striations were seen after etching the trenches with the conventional etch chemistry containing C4F8/CO gas mixture and stripping with O2 gas. An alternate method using different etch chemistry containing CHF3 gas mixture was proposed which greatly minimized the side wall striations. The mechanism of striation formation on trench side walls and successful elimination by modified etch process was studied and correlation of results was obtained through surface roughness measurements on blanket film. The alternate method of etching provided valuable solutions to trench etch of ultra low-k material. Several advantages evolved from this method of etching will also be discussed in this paper.