| 摘要 |
PURPOSE:To obtain high contrast by making larger a number of bist of A/D converter for digitizing the strobe secondary elecrron signal than the number of bits for required resolution and extracting the required number of bits from the additional average of such output. CONSTITUTION:A sample such as LSI, etc. which are operated by a driver 12 is irradiated with a pulse wise electron beam in the strobe scanning type electron microscope, the secondary electron is detected by a detector 8 and it is then converted to a digital signal by a signal processing circuit 11. In this case, an output of the detector 8 is applied to a quantizing A/D converter 32 of 8 bits which is larger than a number of bits corresponding to the desired resolution through an amplifier 22, calculation for additional average is carried out by the additional average circuit 24, and thereafter an output is obtained as the digital secondary signal of 4 bits corresponding to the required resolution from an extraction circuit 26. Thereby, the A/D converter is saturated by noise and decrease of contrast can be prevented. |
