Patent Number: 
Section: claims

1. An apparatus for inspecting patterns, comprising:an electron source for generating an electron beam;focusing means for focusing the electron beam and irradiating the electron beam onto a specimen with one of the patterns formed thereon;a detector for detecting electrons generated from a surface of the specimen with the electron beam irradiated thereon;imaging means for forming an electron beam image of said one of the patterns based on a signal detected by the detector;determining means for determining a charge state of the specimen which allows the specimen to be inspected stably;potential adjusting means for changing at least one of a potential of the specimen and a potential of an electrode provided on a side of the electron source with respect to the specimen, to maintain the determined charge state of the specimen; andimage evaluation value computation means for obtaining the electron beam image formed by the imaging means at each of a plurality of potentials adjusted by the potential adjusting means and determining an image evaluation value of the electron beam image. 2. The apparatus for inspecting patterns according to claim 1, further comprising: display means for displaying the image evaluation value and said each of the potentials corresponding to the image evaluation value. 3. The apparatus for inspecting patterns according to claim 1, wherein the image evaluation value indicates at least one of contrast of the electron image and brightness of the electron beam image. 4. An apparatus for inspecting patterns, comprising:an electron source for generating an electron beam;focusing means for focusing the electron beam and irradiating the electron beam onto a specimen with one of the patterns formed thereon;a detector for detecting electrons generated from a surface of the specimen with the electron beam irradiated thereon;imaging means for forming an electron beam image of said one of the patterns based on a signal detected by the detector;determining means for determining a charge state of the specimen which allows the specimen to be inspected stably; andpotential adjusting means for changing at least one of a potential of the specimen or a potential of an electrode provided on a side of the electron source with respect to the specimen; to maintain the determined charge state of the specimen;the electron beam image formed by the imaging means at each of a plurality of potentials adjusted by the potential adjusting means being obtained, and one of the potentials with brightness of the electron beam image corresponding to said one of the potentials starting to decrease being set as an inspecting condition potential for the potential adjusting means. 5. The apparatus for inspecting patterns according to claim 1, wherein when the potential of the specimen or the potential of the electrode above the specimen is changed by the potential adjusting means, a setting condition range is set so that the potential is changed from positive to negative. 6. A method for inspecting patterns using an inspection apparatus, the inspection apparatus comprising means for irradiating an electron beam onto a surface of a specimen with one of the patterns formed thereon and scanning the specimen, means for detecting a signal secondarily generated from the specimen by the electron beam, and means for imaging the detected signal, for display, the method comprising the steps of:determining a charge state of the specimen which allows the specimen to be inspected stably,changing a potential of the specimen or a potential of an electrode set above the specimen with respect to the specimen, to maintain the determined charge state of the specimen,obtaining an electron beam image at each potential, andperforming numeric conversion on information indicating at least one of contrast of the obtained electron beam and brightness of the obtained electron beam image, for display. 7. A method for inspecting patterns using an inspection apparatus, the inspection apparatus comprising means for irradiating an electron beam onto a surface of a specimen with one of the patterns formed thereon and scanning the specimen, means for detecting a signal secondarily generated from the specimen by the electron beam, and means for imaging the detected signal, for display, the method comprising the steps of:determining a charge state of the specimen which allows the specimen to be inspected stably,changing a potential of the specimen or a potential of an electrode set above the specimen of the electron source with respect to the specimen, to maintain the determined charge state of the specimen,obtaining an electron beam image at each potential, andsetting a point of change with brightness of the electron beam image starting to decrease when the potential of the specimen or the potential of the electrode is changed. 8. The method for inspecting patterns according to claim 7, wherein the step of changing the potential of the specimen or the potential of the electrode comprises the steps of:extensively changing the potential in several stages, thereby obtaining the electron beam image in each of the stages;obtaining the point of change with the brightness of the obtained electron beam image starting to decrease;changing the potential in finer stages in the vicinity of the point of change, thereby obtaining the electron beam image in each of the finer stages again; andobtaining a point of change again from information on the electron beam image obtained again. 9. The method for inspecting patterns according to claim 6, wherein when the potential of the specimen or the potential of the electrode is changed, the potential is changed so that a charged condition of the specimen is changed from positive to negative. 10. The apparatus for inspecting patterns according to claim 2, wherein the image evaluation value indicates at least one of contrast of the electron beam image and brightness of the electron beam image. 11. The apparatus for inspecting patterns according to claim 2, wherein when the potential of the specimen or the potential of the electrode above the specimen is changed by the potential adjusting means, a setting condition range is set so that the potential is changed from positive to negative. 12. The apparatus for inspecting patterns according to claim 3, wherein when the potential of the specimen or the potential of the electrode above the specimen is changed by the potential adjusting means, a setting condition range is set so that the potential is changed from positive from negative. 13. The apparatus for inspecting patterns according to claim 4, wherein when the potential of the specimen or the potential of the electrode above the specimen is changed by the potential adjusting means, a setting condition range is set so that the potential is changed from positive to negative. 14. The method for inspecting patterns according to claim 7, wherein when the potential of the specimen or the potential of the electrode above the specimen is changed by the potential adjusting means, potential is changed so that a charged condition of the specimen is changed from positive to negative.