AR-P 8100 (Phoenix 81) thermal pattern-able positive resist

High-contrast, thermal pattern-able resist for integrated circuit and holographic structure

Patterning of PPA with e-beam Lithography

PPA layers can also be positively patterned directly by electron irradiation. Similar to the irradiation of common- ly used e-beam resists like CSAR 62 or PMMA, electron beam exposure induces fragmentation of the polymer chains. Polymer fragments resulting from PPA are how- ever unstable and decompose into the volatile ortho- phthalaldehyde.

Only very small amounts of monomeric phthalaldehyde are directly released in the device during e-beam expo- sure; only the subsequent PEB leads to an almost com- plete thermal development. But even in the range of the dose to clear (approx. 30 - 40 μC/cm2), a resist layer with a thickness of a few nanometres will remain. A residue- free substrate surface can nevertheless be obtained if a short plasma etching step is added. The gradation passes through a minimum, but with increasing dose, also the concurrent cross-linking processes become increasingly important. This undesirable side reaction is due to radicals which are generated during electron irradiation and stabilise the layer by cross-linking. These effects also occur in PMMA layers, but only at much higher exposure doses, and are here used to produce negative PMMA architectures. To determine the resolution limits of AR-P 8100, line patterns were examined in detail at the company Raith. Lines of different width were written into the PPA layer. After PEB and subsequent platinum metallisation, metal bridges of < 20 nm width were obtained. The highest resolution that could be achieved was 16 nm.