Abstract
In optical lithography it is likely that 0.5 μm feature sizes can be obtained with the current positive wet developable resists in combination with i-line steppers with high N.A. lenses (0.42). The next generation of I.C.s. with 0.35 μm dimensions will probably be processed with DUV-lithography. A considerable change in resist chemistry will be needed since suitable sensitizers and low absorption resins are required. Besides, the sub half-micron regime can also become the turning point for dry developable lithography. Therefore this paper presents a new positive dry developable photoresist ( SUPER) which is particularly suitable for DUV-lithography. The resist is a three component system containing a phenolic resin, a crosslinker and an acid-forming sensitizer. After a patternwise exposure (NUV, DUV or X-ray) a PEB is carried out during which the exposed resist areas are crosslinked. The silylation reaction is hindered in the crosslinked areas but a good conversion in the un-crosslinked areas can be reached (selectivity: ≈30). After selective silylation of the resist layer, the patterns are developed with an oxygen plasma (O 2-RIE, or Magnetron). The SUPER system makes use of the principle of top-imaging. The silylated resist areas, which form a mask for the dry development step, are only present in a thin top layer. The exposure step is therefore less critical for problems such as the bulk effect and the limited depth of focus. This makes SUPER particularly suitable for DUV-lithography. Because it is also positive working, DUV induced crosslinking of novolak as a possible side-reaction during the exposure is not a problem and SUPER can be used for critical mask steps such as for printing contact holes.
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