Improvement in linewidth roughness by postprocessing
Top down SEM images of photoresist before and after trim etch, post-HM, and polyetch (above). SEM bar scale is . before and after trim (below left); before and after trim (below right). Increasing etch tool chuck temperature could reduce LWR.
CD (top left) and LWR (top right) measurements as a function of vapor smoothing time. Optimum vapor smoothing time is ; longer times increase the CD due to swelling. SEM images as a function of vapor smoothing time (below). SEM bar scale is .
Top down SEM images as a function of hard bake temperature (above). SEM bar scale is . Change in LWR (bottom left) and CD (bottom right) as a function of hard bake temperature. hard bake temperature shows the most smoothing but accompanied with larger CD due to reflow of the resist.
SEM images before and after ozonation with HCl for . SEM bar scale is . LWR decrease by ozonation is .
LWR (left) and SEM images (right)Vs half-pitch with and without rinse on Si. SEM bar scale is . The impact of rinse is greater at smaller pitches. However, at half-pitch, top loss started to occur.
LWR through defocus (left) and CD through pitch (right) with and without rinse. LWR is reduced uniformly through focus. No change in CD was observed through pitch after rinse.
SEM images after rinse process for 50 and half-pitch features on HM showing LWR of . SEM bar scale is .
Power spectral density of the roughness for some of the smoothing techniques at low spatial frequencies (left) and low-medium spatial frequencies (right). Ozonation and rinse show improvement in low spatial frequency roughness. Reflow (hardbake) and rinse show reduction in midspatial frequency roughness.
Variation in roughness as a function of line length (inverse of frequency) for the data shown in Fig. 8 . The roughness values are an indication of the noise levels in the data and the trends agree with power spectral density analysis.
Cross-section SEM images of half-pitch features (top left clockwise): no postprocessing, after reflow (hardbake), after ozonation, and after rinse. Reflow degrades the sidewall angle (profile) of large features as indicated on the top right image.
Summary of the reduction in LWR for half-pitch features.
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