Development of organic bottom antireflective coating for 157-nm lithography

Abstract

In 157-nm lithography, an organic bottom-antireflective-coating (BARC), which has been mainly used as an antireflective technology in KrF or ArF lithography, is needed to reduce reflection from the substrate under the resist. To apply a conventional BARC to 157-nm lithography, the BARC thickness must be thinner than the BARC thickness used in KrF or ArF lithography. Because conventional BARCs have a lower dry-etching rate than resists with a fluorinated polymer for 157-nm lithography and the thickness of remaining resist after BARC dry-etching may be greatly reduced. Moreover, the substrate reflection under a conventional thin BARC cannot be completely controlled since the k-value of the extinction coefficient at a 157-nm wavelength is small. Therefore, a BARC material for 157-nm lithography must have a higher k-value at the 157-nm, a higher dry-etching rate than resists with a fluorinated polymer, good matching between the fluorinated resist and the BARC material to ensure a good resist pattern shape, and low outgassing from the BARC material. In this paper, we evaluate a newly developed BARC material (NCA646) for 157-nm lithography. We found that the k-value of this BARC material was 0.45 (1.8 times that of a conventional BARC (DUV30J; Brewer Science, Inc)), and the ratio of the dry-etching rate to that of a KrF resist was 1.53 (1.6 times that of DUV30J). These improvements were achieved by introducing a new chromophore into a BARC polymer of novolak resin. Furthermore, the amount of outgassing from the BARC material when irradiated by 157-nm light was close to 0 ng (irradiated condition; 100 mJ/cm²), and resist patterns with no footing were obtained with four kinds of fluorinated resist on this BARC material. We concluded that this BARC material was suitable for 157-nm lithography.