29 June 1998 Conformality of photoresist and antireflective coatings over topography
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Scanned probe microscopy (SPM) and optical thickness measurements were used to study conformality of a 0.5 micrometer-thick photoresist and two different ARCs (75 nm thick). One ARC (ARC A) was a thermally stable system as applied. (The molecular weight did not change with the normal post-apply bake.) The other ARC (ARC B) was a thermally cross- linking system. (Cross-linking occurs on the wafer during post-apply bake, thus increasing molecular weight.) Three different step heights, ranging from 44 to 150 nm, were studied. Two measures of conformality were used: the 'planarization length' or distance from an edge for which the material reaches nominal thickness, and the film thickness loss over a given feature width. For the photoresist, the planarization length was 30 - 50 micrometer, and a 1 micrometer-wide ridge was almost completely planarized. (Resist thickness loss was 70 - 80% of the step height, vs 100% for complete planarization.) As expected, the much thinner ARC films were more conformal than the resist film; however, each behaved quite differently: the thermally stable system (ARC A) was more conformal than the thermally cross- linking system (ARC B). The planarization length for ARC A was 5 - 10 micrometer while, for ARC B, it was 20 - 40 micrometer. ARC A also showed less thickness loss for 1 to 10 micrometer- wide ridges. For a 1 micrometer-wide ridge, ARC A showed a thickness loss of 40% of the step height; for ARC B, the loss was 50%. For a 10 micrometer-wide ridge, the thickness losses were 5% and 15% for ARCs A and B, respectively.
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James A. Bruce, Ellen Wallander, "Conformality of photoresist and antireflective coatings over topography", Proc. SPIE 3334, Optical Microlithography XI, (29 June 1998); doi: 10.1117/12.310799; https://doi.org/10.1117/12.310799

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