Footing reduction in the organic bottom anti-reflective coating implementation

Abstract

During the implementation of organic bottom anti-reflective coating (BARC) for i-line 0.35 μn critical layer fabrication, footing was observed after the development of the photoresist due to the reduction of reflectivity by the organic BARC. Footing was undesirable since it created difficulties in the subsequent etching steps. Two methods were attempted to reduce the footings. One method was to increase the reflectivity of the substrates by changing the thickness of the organic BARC. Another method was to carry out a descrum process after the lithographic processes. The nominal thickness of organic BARC in the manufacturing process was 1520 Å with a reflectivity of less than 5%. However, by increasing the organic BARC thickness to 2000 Å and 2500 Å, the reflectivity of the polycide substrates were increased to 13% and 8%, respectively. Experimental results showed that the increased reflectivity indeed helped to reduce the amount of footings. In the case of 2000 Å organic BARC, the footing was almost completely gone. Since these two different values of thickness were the local maximum and minimum on the thickness vs. reflectivity curves, they provided relatively wide processing latitudes for manufacturing. For the descrum experiments to reduce the footings, the photoresist profiles were significantly thinned down laterally while the heights of the developed photoresist were only slightly affected. Unfortunately, the magnitudes of the footings remained unchanged. Therefore, the descrum process did not seem to help to resolve the footing problems in the implementation of organic BARC.