A CASE STUDY - RESIST POISONING IN COPPER AND LOW-K DUAL DAMASCENE PROCESS

摘要

The processes giving rise to resist poisoning while patterning of trench structures in copper and low-k using dual damascene architecture was investigated in this paper. The low-k film used for this study was organo silicate glass (OSG) type deposited by plasma enhanced chemical vapor deposition (PECVD) technique. A 'via first' method of dual damascene fonnation was used. While via patterning showed no issues, scumming and uneven resist pattern fonnation (resist poisoning) were observed when the trench was patterned on top of the etched via structures. The inter-level dielectric, comprised of an OSG stack followed by a cap layer of undoped silicate glass (USG) was found to give severe poisoning. At the same time an OSG stack without the USG cap layer showed very minimum poisoning to no poisoning. A number of surface treatments were tried out after via etch process to surmount this problem. Some of these treatments were helium plasma treatment and vacuum degas treatment. Isolation of resist by using thicker bottom anti reflective layer was also tried. However, none of the treatments could give good patterning performance. Since severe poisoning was found limited to stacks with USG hard mask, the deposition process was examined. When low-k materials are exposed to nitrogen containing plasmas during deposition, etch and strip, it may form amine impurities in the film which are difficult to desorb due to presence of USG hard mask. At a subsequent patterning level photo acid was quenched by the base that is formed possibly due to amine impurities in the film. Hence resist which came in contact with the OSG film could not fully develop out, giving rise to uneven patterns. Experiments were also carried out on resist rework steps to find out a suitable chemistry, which did not give poisoning at a subsequent patterning step.