Apparatus and method for controlling irradiation of electron beam at fixed position in electron beam tester system

Claim 1

A fixed position irradiating control apparatus of an electron beam for correcting a deviation of an irradiating position due to a drift of the electron beam (EB) during measurement of a sample to be measured in an electron beam tester system comprising: an electron gun (11) for generating the electron beam (EB); a deflecting coil (13) for deflecting the electron beam (EB) generated from said electron gun (11); the sample (14) to be measured onto which the electron beam (EB) generated from the electron gun (11) is irradiated; a scintillator (17) for detecting a secondary electron generated due to the irradiation of the electron beam (EB) onto the sample (14) to be measured; a current/voltage converter (20) for converting an output current of said scintillator (17) to a voltage corresponding to said current; and an image display device (22) to which an output of said current/voltage converter (20) is supplied and which displays an image which is derived due to the irradiation of the electron beam (EB) onto the sample (14) to be measured, characterized in that said apparatus comprises: binarizing means (23) for binarizing the output voltage of said current/voltage converter (20); reference pattern data memory means (27) for irradiating the electron beam (EB) from said electron gun (11) onto a scanning area (32) including a specific pattern (31) selected from the sample (14) to be measured prior to measuring the sample (14) to be measured, for detecting the secondary electron obtained due to the irradiation of the electron beam (EB) by said scintillator (17), and for storing a binarized signal, as reference pattern data (3lA), which is obtained by said binarizing means (23) by binarizing the image signal derived by converting the output current of said scintillator (17) to the voltage by said current/voltage converter (20); analog/digital converting means (29) for converting an analog deflection current which is supplied to the deflecting coil (13) to digital data; reference deflection current memory means (27) for storing a value of said deflection current converted to the digital data by said analog/digital converting means (29) when said reference pattern data (31A) is obtained; comparison pattern data memory means (27) for interrupting the measurement of said sample (14) to be measured, for deflecting the electron beam (EB) by supplying the deflection current stored in said reference deflection current memory means (27) to said deflecting coil (13), detecting by the scintillator (17) the secondary electron obtained due to the irradiation of the electron beam (EB), and for storing the binarized signal, as comparison pattern data (31A'), obtained by binarizing by said binarizing means (23) the image signal which is obtained by converting the output current of the scintillator (17) to the voltage by said current/voltage converter (20); comparison deflection current memory means (27) for storing the deflection current which is derived by converting the analog deflection current to said deflecting coil (13) when said comparison pattern data (31A') is obtained to the digital data; exclusive OR means (21) for obtaining an exclusive OR between the reference pattern data (31A) stored in said reference pattern data memory means (27) and the comparison pattern data (31A') stored in said comparison pattern data memory means (27); deviation amount calculating means (21) for calculating deviation amounts in X and Y directions of said comparison pattern data (31A') on the basis of said exclusive OR data derived by said exclusive OR means (21) and said reference pattern data (31A); deflection current converting means (21) for converting the deviation amounts calculated by said deviation amount calculating means (21) for said reference pattern data (31A) of the comparison pattern data (31A') to deflection currents of said deflecting coil (13); and digital/analog converting means (30) for converting the digital deviation amounts converted to the deflection currents which are output from said deflection current converting means (21) to the analog data and for supplying as drift correction data to the deflecting coil (13).