Negative-Working Electron Beam Resist Based on Poly(methyl methacrylate)
CORNELL UNIV ITHACA NY SCHOOL OF CHEMICAL ENGINEERING
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Blends of polymethylmethacrylate PMMA and dipentaerythritol pentaacrylate DPEPA respond to electron beam exposure as negative resists, with sensitivity that increases with increasing DPEPA concentration. Blends of 80 wt. PMMA and 20 wt. DPEPA exhibit an electron sensitivity of 4 microcoulombssq cm and a contrast gamma of 1.2. Resolution of 0.25 micrometers has been demonstrated with this blend without the use of non-solvent rinses or plasma de-scumming. This superior resolution for a negative electron resist is attributed to the small degree of swelling of the PMMA host polymer. Increasing the molecular weight of the PMMA component to 450,000 increases the sensitivity to 1 microcoulombsq cm improves the contrast to a gamma value of 2.3 without affecting resolution or sensitivity relative to the blends with low molecular weight PMMA.
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