A part of the high-energy electrons which impact on the substrate is stopped and cannot be conducted at all or only very slowly toward ground, especially in the case of insulating substrates such as quartz. The substrate and respectively the resist charges itself negatively and the electron beam is deflected uncontrollably from the desired position during exposure. The distracting excessive charge can be discharged by application of a thin metal layer or a conductive polymer layer (e.g. conductive resist AR-PC 5090.02, Electra 92). For low-energy electron beams, the application of conductive layers is more efficient than it is for high-energy beams (>50keV), since these can pass the layer mostly unobstructedly and continue to accumulate in the substrate.
Such charges may also play a part in scanning electron microscopy (SEM). The occuring charges spoil the contrast of the micrograph. Electra 92 or a metal layer may be used here as well in order to eliminate the effect.
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