Patent Number: 
Section: claims

1. An electron-beam size measuring apparatus comprising:electron beam irradiating means that irradiates an electron beam on a surface of a sample;detection means that detects electrons emitted from the sample;distance measurement means that measures the distance between the sample and a secondary electron control electrode of the detection means;a stage on which the sample is mounted; andcontrol means which adjusts the height of the stage so that the distance measured by the distance measurement means would be equal to a predetermined fixed distance, which applies a control voltage to the secondary electron control electrode of the detection means, the control voltage predetermined so as to allow the sample surface potential to become constant level when the sample is positioned at the fixed distance, and which causes the electron beam to be irradiated by applying a predetermined accelerating voltage. 2. The electron-beam size measuring apparatus according to claim 1, wherein the control voltage is a voltage at a time when a first measured value and a second measured value are equal to each other, the first measured value obtained by measuring a dimension of a calibration sample with the surface thereof not charged, the calibration sample made of the same material as that of the sample, and the second measured value being a value at a time when the measured value of the calibration sample does not vary any more, while the calibration sample is irradiated with the electron beam and is measured in dimension, alternately, from a state in which the surface of the calibration sample is charged at the beginning. 3. The electron-beam size measuring apparatus according to claim 1, wherein the stage includes holding means that does not electrically connect the sample thereto, and moving means that moves the sample up and down. 4. The electron-beam size measuring apparatus according to claim 1, wherein the control means causes the electron beam irradiating means to irradiate the entire surface of the sample with the electron beam. 5. The electron-beam size measuring apparatus according to claim 1, wherein the control means causes the electron beam irradiating means to irradiate, with the electron beam, an area to which a conductor on the sample is exposed. 6. The electron-beam size measuring apparatus according to claim 1, wherein the control means causes the electron beam irradiating means to adjust an electron irradiation amount of the electron beam to be larger than an irradiation amount of electrons at a time of measuring a dimension. 7. The electron-beam size measuring apparatus according to claim 1, wherein the control means measures a dimension of the sample after adjusting the potential of the surface of the sample to a fixed level. 8. A size measuring method with electron beams comprising the steps of:figuring out a control voltage to be applied to a secondary electron control electrode for adjusting the charge potential of the sample to become constant when the distance between a sample and the secondary electron control electrode is kept fixed, and also when an accelerating voltage for an electron beam to be irradiated on the sample is set to a predetermined value;adjusting the distance between the sample and the secondary electron control electrode to be the predetermined distance;irradiating the sample with an electron beam at the accelerating voltage by applying the control voltage to the secondary electron control electrode; andmeasuring a dimension of the sample after irradiating the electron beam. 9. The size measuring method with electron beams according to claim 8, wherein the control voltage is a voltage at a time when a first measured value and a second measured value are equal to each other, the first measured value obtained by measuring a dimension of a calibration sample with the surface thereof not charged, the calibration sample made of the same material as that of the sample, and the second measured value being a value at a time when the measured value of the calibration sample does not vary any more, while the calibration sample is irradiated with the electron beam and is measured in dimension, alternately, from a state in which the surface of the calibration sample is charged at the beginning. 10. The size measuring method with electron beams according to claim 8, wherein the electron beam is irradiated on the entire surface of the sample. 11. The size measuring method with electron beams according to claim 8, wherein the electron beam is irradiated on an area to which a conductor on the sample is exposed. 12. The size measuring method with electron beams according to claim 8, wherein an electron irradiation amount of the electron beam is larger than an irradiation amount of electrons at a time of measuring a dimension.