Primary electron pulse shape evaluation in an EBT system

The time resolution of an electron beam testing system (EBT) is mainly related to the primary electron (PE) sampling pulse width. Signal deconvolution techniques are available to enhance the time resolution of the system, provided the PE pulse shape is known with high accuracy. While for high energies this shape has already been evaluated, for the low energies commonly used in MOS IC testing, some additional difficulties must be accounted for, such as increased PE beam spot dispersion, charge trapping into passivation oxides, and lower SIN ratio at the detector. Here, we describe the direct measurement of the PE current used to sample internal voltage waveforms through the use of a fast avalanche photodiode. A numerical simulation has also been performed to help in the correct interpretation of the results. Using a known signal as an input to a matched-impedance microstrip line, a numerical deconvolution technique has been applied to the signal sampled by finite-duration current pulses to evaluate the goodness of the restoration of the original signal.<
>