| 摘要 |
<p>An apparatus and a method for monitoring the functioning of an integrated circuit (1) in operation using an electron beam directed to a particular node of the circuit which is of interest and measuring the energy of the secondary electrons (2) emitted, in which the energy measurement is made using a filter grid (3), the bias (18) on which is set by comparing a voltage representing the rate of receipt of secondary electrons (2) past the filter grid (3) with a reference voltage and adjusting the bias (18) in response to the comparison so as to reduce the number of electrons received. A current is produced proportional to the difference between the two voltages and applied to charge a capacitor, the voltage on which is used to set the voltage on the filter grid (3). The electron beam may be pulsed and the comparison gated in synchronism with the pulsing but delayed relative to it so that the control of the filter grid bias is effected only when the signal due to the secondary electrons emitted in response to the beam pulse is received by the comparator. A second but similar channel using different reference and fitter bias voltages may be provided and the voltage on the fitter grid taken altemately from the two channels to eliminate certain errors in the setting of the filter grid voltage. The different voltages may altematively be switched into a single channel altemately with the first voltages.</p> |
