Method of inspecting a circuit pattern and inspecting instrument

A circuit pattern inspecting instrument comprising:

• a first electron-optical system including
• a first cathode for emitting a first electron beam,
• a first objective lens having a first focal length for focusing the first electron beam on a sample positioned at a first sample position, and
• a first scanning deflector for scanning the first electron beam on the sample positioned at the first sample position;
• a first detector for detecting secondary charged particles generated from the sample positioned at the first sample position;
• a second electron-optical system including
• a second cathode for emitting a second electron beam,
• a second objective lens having a second focal length shorter than the first focal length for focusing the second electron beam on a sample positioned at a second sample position, and
• a second scanning deflector for scanning the second electron beam on the sample positioned at the second sample position;
• a second detector for detecting secondary charged particles generated from the sample positioned at the second sample position;
• an image-forming device for imaging the sample positioned at the first sample position based on an output of the first detector, and for imaging the sample positioned at the second sample position based on an output of the second detector;
• and
• a stage for moving a sample between the first sample position and the second sample position;
• wherein the first electron-optical system, the second electron-optical system, the first detector, the second detector, and the stage are housed in a single vacuum chamber;
• and
• wherein the circuit pattern inspecting instrument is configured so that
• first the sample is observed at the first sample position with a current of the first electron beam being set to a first value and the first electron beam being scanned at a first speed,
• then a particular position on the sample is selected based on image data produced by an output of the first detector,
• then the particular position on the sample is moved to the second sample position by moving the stage, and
• then the particular position on the sample is observed by enlarging the particular position on the sample using the second electron-optical system with a current of the second electron beam being set to a second value smaller than the first value and the second electron beam being scanned at a second speed slower than the first speed.

A method of inspecting a circuit pattern comprising the steps of:

• (a) providing
• an electron-optical system for irradiating and scanning a sample having a circuit pattern thereon by a focused electron beam,
• a detector for detecting back-scattered electrons or secondary electrons from an electron beam-irradiated portion of the sample,
• an image forming unit for forming an image of the sample based on a detected signal from the detector, and
• a difference detecting circuit for comparing an image signal obtained by the image forming unit with a reference image signal and thereby detecting a difference between the two image signals;
• (b) amplifying an output from the detector using an amplifier having a first amplification factor, the output being obtained by scanning a relatively large region of the sample with the electron beam of a relatively large electric current at a relatively high speed;
• (c) then supplying the thus-amplified output to the image forming unit to form an image signal;
• (d) comparing the image signal with a similar image signal obtained from another region of the sample, so as to detect a difference between the image signals;
• (e) determining coordinates of a position where the difference has occurred;
• (f) scanning a region of a smaller area than the relatively large region, including the position of occurrence of the difference, with the electron beam of a smaller electric current than the relatively large electric current and at a lower speed than the relatively high speed;
• (g) then supplying the resulting output from the detector to the image forming unit via a circuit provided with an amplifier which amplifies the output at a larger amplification factor than the first amplification factor and is provided with a high-frequency component cut-off filter, to form an image signal;
• and
• (h) observing the difference-generating position.