A Study of an Organic Bottom Antireflective Coating for 157-nm Lithography

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 less than that used in KrF or ArF lithography. This is because conventional BARCs have a lower dry-etching rate than resists with a fluorinated polymer resist for 157-nm lithography and the thickness of the 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 wavelength, 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 during exposure. In this paper, we evaluate newly developed BARC materials for 157-nm lithography. We found that the k-value of one new BARC material (NCA660) was 0.41 (1.6 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 2.0 (twice that of DUV30J). These improvements were achieved by introducing a chromophore containing an I-atom of halogen into a heterocyclic polymer. Furthermore, the film thickness loss (used to evaluate outgassing from this BARC material when irradiated by 157-nm light) was close to 0 nm (irradiation condition: 100 mJ/cm2), and a resist pattern with no footing was obtained in four typical kinds of fluorinated resist on this BARC material. We concluded that this BARC material was suitable for 157-nm lithography.