Low-energy electron (0-100eV) interaction with resists using LEEM

Extreme Ultra Violet (EUV) lithography is a next generation lithographic technique using 13.5 nm wavelength light (91.7eV photon energy) to define sub-20 nm features. This high energy radiation generates lower energy electrons (LEEs) after being absorbed. The mean free path of LEEs increases rapidly below ca. 30 eV allowing them to migrate several nanometers from their point of origin. As LEEs can still have sufficient energy to react with the surrounding resist, this may give rise to pattern blurring, posing a challenge for sub 10 nm features. Here, we introduce Low Energy Electron Microscopy (LEEM) as an extremely useful technique to investigate the interactions of LEEs with EUV resists. Using LEEM we can expose the resist with precise electron energies and doses. We also report the initial results of LEE exposures on poly(methyl methacrylate) PMMA. We have studied the LEE-PMMA interaction depth as a function of electron energy; a distinct exposure threshold is found at ~15 eV, below which the resist responds only very weakly to electron exposure.

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