Role of polymer structure and ceiling temperature in polymer roughening and degradation during plasma processing: a beam system study of P4MS and PαMS

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The degradation and roughening of polymers during plasma processing are important for the understanding of patterning of critical dimension features for both current and future lithographic techniques. Recently, the role of plasma-generated VUV photons in both the roughening and smoothing of current generation 193 nm photoresist (PR) has been investigated. However, a general understanding of the importance of polymer chemistry and structure on the degradation and roughening of polymers during plasma processing, which could be useful for polymer selection for next generation lithography, is currently lacking. Through the use of a beam system approach, the effects of ion bombardment and VUV radiation during plasma processing are investigated for two polymers with the same composition but different structure: poly(4-methyl styrene) (P4MS) and poly(α-methyl styrene) (PαMS). PαMS degrades under VUV radiation when heated above room temperature while P4MS is stable up to 70 °C, the maximum temperature studied. Both polymers undergo a drastic reduction in ion sputter yield at an ion fluence of 1 × 1016 ions cm−2, associated with the formation of a highly modified near-surface region. Almost no surface roughness is generated after VUV radiation, with moderate surface roughness formed on PαMS after ion bombardment at 70 °C. In contrast, extreme levels of surface roughness (∼10 nm rms) are observed for PαMS after simultaneous exposure to VUV photons and ion bombardment at 70 °C. Similarities to the synergistic roughening of current generation 193 nm PR under simultaneous VUV photons and ion bombardment are discussed.