Analysis of charging effects on highly resistive materials under electron irradiation by using transient-absorbed-current method

Accumulation and relaxation properties of charge in highly resistive materials under electron irradiation were investigated by using an absorption current stimulated by sequential two-pulse electron beams. The amount of absorbed charge corresponding to induced surface charge was obtained from the time integration of the absorption component of the substrate current. The absorbed charge of both highly resistive poly-Si ( 10 9 – 10 10 Ω cm ) and SiO 2 substrates increases to 35 nC / cm 2 with increasing injected charge and saturates; in contrast, there is a significant difference in absorbed charges for the two substrates at low injected charge (i.e., less than 1 μ C / cm 2 ). The time constant of absorbed-charge relaxation is obtained from the analysis of sequential absorbed current, namely, 0.4 ms for poly-Si and 12.5 ms for SiO 2 . A distinct voltage-contrast image of poly-Si plugs buried in a SiO 2 film was successfully obtained by scanning electron microscopy with charging control in accordance with the difference in the charging characteristics of poly-Si and SiO 2 .