Patent Number: 
Section: claims

1. A scanning electron microscope, comprising:an electron source;a lens that focuses an electron beam emitted from the electron source;a power source that applies to a specimen a negative voltage that decelerates the electron beam;a control device that controls the negative voltage; anda detector that detects an electron, wherein:the detector detects an electron that is reflected without reaching the specimen by an electric field formed by the negative voltage applied to the specimen, andthe control device corrects a signal value to be supplied to the lens based on a difference between an output of the detector when a predetermined signal is supplied to the lens and a pre-stored output of the detector when the predetermined signal is supplied to the lens. 2. The scanning electron microscope according to claim 1, wherein the control device:calculates a correlation between the output of the detector when the predetermined signal is supplied to the lens and a signal value thereof, andcalculates a misalignment of the electron source based on a difference between the correlation and a pre-stored correlation between the output of the detector when the predetermined signal is supplied to the lens and the signal value thereof. 3. The scanning electron microscope according to claim 2, wherein the control device stores a plurality of correlations for a respective plurality of signals supplied to the lens. 4. A scanning electron microscope, comprising:an electron source;a scanning deflector that scans across a specimen an electron beam emitted from the electron source;a power source that applies to the specimen a negative voltage that decelerates the electron beam;a control device that controls the negative voltage; anda detector that detects an electron, wherein:the detector detects an electron that is reflected without reaching the specimen by an electric field formed by the negative voltage applied to the specimen, andthe control device corrects a signal value to be supplied to the scanning deflector based on a difference between a detected position of the electron that is detected when the electron beam is scanned and a pre-stored detected position of the electron that is detected when a predetermined signal is supplied to the scanning deflector. 5. The scanning electron microscope according to claim 4, wherein the control device:calculates a correlation between the detected position of the electron that is detected when the electron beam is scanned and a signal value that is supplied to the scanning deflector at the time of the scanning, andcalculates a magnification variation based on a difference between the correlation and a pre-stored correlation between the detected position of the electron that is detected when the predetermined signal is supplied to the scanning deflector and the signal value thereof. 6. The scanning electron microscope according to claim 5, wherein the control device varies the signal to be supplied to the scanning deflector in accordance with the calculated magnification variation.