Characterization of line-edge roughness (LER) propagation from resists: underlayer interfaces in ultrathin resist films

Line edge roughness evolutions in EUV resist patterns are investigated. Three dimensional scanning electron microscopy images show the pattern sidewall roughness to be highly anisotropic and the roughness to be propagating from the resistsubstrate interface up the resist pattern sidewall. In ultrathin resist films, (film thickness ca. 100 nm and below) roughness is found to be fully correlated from the resist-substrate interface to the resist-air interface. This behavior is seen regardless of the resist platforms being used. Underlayer stack roughness contributions to the pattern sidewall roughness leading to resist LER were examined and no correlations between the two were found. At the same time, the chemical properties of the underlayer stacks are shown to have strong influences on the resist roughness and process performance. Exact mechanisms behind this are not clearly understood at present.