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Proceedings Paper

Nelative-Working Electron Beam Resist Based on Poly(methylmethacrylate)
Author(s): Yarrow M. N. Namaste; S. Kay Obendorf; Bernard C. Dems; F. Rodriguez
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Paper Abstract

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 (Mn 22,500) and 20 wt. % DPEPA exhibit an electron sensitivity of 4 μC/cm2 (based on 50% of exposed film remaining) and a contrast (γ) of 1.2. Resolution of 0.25 μm 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 (Mw) increases the sensitivity to 1 μC/cm2, but results in poorer resolution. Use of nearly monodisperse PMMA (Mn ≈ Mw = 29,000) improves the contrast to a γ value of 2.3 without affecting resolution or sensitivity relative to the blends with low molecular weight PMMA. Image formation in these blends is largely controlledby differential dissolution rates, with reactive plasticizer (DPEPA) enhancing dissolution in unexposed regions and inhibiting dissolution after exposure. The degree of polymerization and crosslinking of the plasticizer necessary for inhibiting dissolution rates is less than that required for complete insolubilization of the resist film. Thus, exposure at moderate doses results not only in a non-swelling image, but also one that is easily stripped with developing solvent after processing. This mechanism differs greatly from that of conventional crosslinking negative electron beam resists for which exposure renders the exposed regions insoluble in any developing solvent.

Paper Details

Date Published: 1 August 1989
PDF: 9 pages
Proc. SPIE 1089, Electron-Beam, X-Ray, and Ion-Beam Technology: Submicrometer Lithographies VIII, (1 August 1989); doi: 10.1117/12.968542
Show Author Affiliations
Yarrow M. N. Namaste, Cornell University (United States)
S. Kay Obendorf, Cornell University (United States)
Bernard C. Dems, Cornell University (United States)
F. Rodriguez, Cornell University (United States)

Published in SPIE Proceedings Vol. 1089:
Electron-Beam, X-Ray, and Ion-Beam Technology: Submicrometer Lithographies VIII
Arnold W. Yanof, Editor(s)

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