Patent Number: 
Section: claims

1. A scanning electron microscope comprising:electron beam illumination means for irradiating an electron beam on a desired region of a specimen while scanning the electron beam thereon;digital image acquisition means for detecting secondary charged particles generated from a surface of the desired region of said specimen under scanning irradiation of the electron beam by said electron beam illumination means and digitizing a detected signal at a predetermined sampling clock so as to acquire a digital image of the desired region of said specimen;image processing means for processing the digital image acquired by said digital image acquisition means; andcontrol means for controlling said electron beam illumination means, said digital image acquisition means and said image processing means;wherein said digital image acquisition means obtains images of a plurality of frames by scanning the electron beam plural times on the desired region of said specimen, such that frame images acquired in sampling positions are added to frame images acquired at positions displaced or shifted by under 1 pixels from the frame images acquired in the sampling positions in a X-direction, Y-direction or diagonal direction; andwherein said image processing means processes said images of said plurality of frames. 2. A scanning electron microscope according to claim 1, wherein said digital image acquisition means obtains the frame images for which the timing of said sampling clock is shifted by a smaller interval than that of said sampling clock and applies to the frame images for which timing of said sampling clock is shifted. 3. A scanning electron microscope according to claim 1, wherein said image processing means performs a frame addition process in which odd and even frame images are added to create an image in which individual pixel values are averages of pixel values at the same pixels of the plural frame images, a densification process in which said plural frame images are used to densify an image having a large number of pixels, an image improvement process in which a degraded image is restored, and a thin-out process in which pixels of an image are thinned out to prevent aliasing. 4. A scanning electron microscope according to claim 1, wherein said scanning electron microscope is any one of a SEM including a unit which measures dimensions or size of the pattern formed on the specimen, a SEM including a unit which detects defects of the pattern formed on the specimen and a SEM including a unit which reviews defects of the pattern formed on the specimen. 5. A scanning electron microscope according to claim 1, wherein said digital image acquisition means obtains images of a plurality of frames by scanning the electron beam plural times on the desired region of said specimen, such that frame images acquired in sampling positions are added to frame images acquired at positions displaced or shifted by 0.5 pixels from the frame images acquired in the sampling positions in a X-direction, Y-direction or diagonal direction. 6. A scanning electron microscope according to claim 1, wherein said control means controls said electron beam illumination means to scan the electron beam plural times on the desired region of said specimen, and controls said image acquisition means to obtain images of a plurality of frames such that frame images acquired in sampling positions are added to frame images acquired at positions displaced or shifted by 0.5 pixels from the frame images acquired in the sampling positions in a X-direction, Y-direction or diagonal direction. 7. A scanning electron microscope comprising:electron beam illumination means for irradiating a focused electron beam on a desired region of a specimen while scanning the electron beam thereon;digital image acquisition means for detecting secondary charged particles generated from a surface of the desired region of said specimen under scanning irradiation of the electron beam by said electron beam illumination means and digitizing a detected signal so as to acquire a digital image of the desired region of said specimen;image processing means for processing the digital image acquired by said digital image acquisition means; andcontrol means for controlling said electron beam illumination means, said digital image acquisition means and said image processing means;wherein said digital image acquisition means obtains images of a plurality of frames of the desired region of said specimen by scanning the electron beam plural times on the desired region of said specimen, such that frame images acquired in sampling positions are added to frame images acquired at positions displaced or shifted by under 1 pixels from the frame images acquired in the sampling positions in a X-direction, Y-direction or diagonal direction; andwherein said image processing means processes said images of said plurality of frames. 8. A scanning electron microscope according to claim 7, wherein said image processing means performs a frame addition process in which odd and even frame images are added to create an image in which individual pixel values are averages of pixel values at the same pixels of the plural frame images, a densification process in which plural frame images are used to densify an image having a large number of pixels, an image improvement process in which a degraded image is restored, and a thin-out process in which pixels of an image are thinned out to prevent aliasing. 9. A scanning electron microscope according to claim 7, wherein said scanning electron microscope is any one of a SEM including a unit which measures dimensions or size of the pattern formed on the specimen, a SEM including a unit which detects defects of the pattern formed on the specimen and a SEM including a unit which reviews defects of the pattern formed on the specimen. 10. A scanning electron microscope according to claim 7, wherein said digital image acquisition means obtains images of a plurality of frames of the desired region of said specimen by scanning the electron beam plural times on the desired region of said specimen, such that frame images acquired in sampling positions are added to frame images acquired at positions displaced or shifted by 0.5 pixels from the frame images acquired in the sampling positions in a X-direction, Y-direction or diagonal direction. 11. A scanning electron microscope comprising:an electron beam illumination unit arranged to illuminate an electron beam on a desired region of a specimen while scanning the electron beam thereon;an image acquisition unit arranged to detect secondary charged particles generated from a surface of the desired region of said specimen and to acquire a digital image of the desired region of said specimen;an image processor arranged to perform a dimension or size measurement of a pattern representing said specimen using an acquired image; anda controller to control the operation of the electron beam illumination unit, the image acquisition unit and the image processor,wherein the controller controls the electron beam illumination unit to scan the electron beam plural times on the desired region of said specimen, the image acquisition unit to obtain images of a plurality of frames such that frame images acquired in sampling positions are added to frame images acquired at positions displaced or shifted by under 1 pixels from the frame images acquired in the sampling positions in a X-direction, Y-direction or diagonal direction, and the image processor processes said images of said plurality of frames. 12. A scanning electron microscope according to claim 11, wherein the image processor is configured to perform:a frame addition process in which odd and even frame images are added to create an image in which individual pixel values are averages of pixel values at the same pixels of the plural frame images;a densification process in which said plural frame images are used to densify an image having a large number of pixels;an image improvement process in which a degraded image is restored; anda thin-out process in which pixels of an image are thinned out to prevent aliasing. 13. A scanning electron microscope according to claim 11, wherein said scanning electron microscope is any one of a SEM including a unit which measures dimensions or size of the pattern formed on the specimen, a SEM including a unit which detects defects of the pattern formed on the specimen and a SEM including a unit which reviews defects of the pattern formed on the specimen. 14. A scanning electron microscope according to claim 11, wherein the digital image acquisition unit obtains images of a plurality of frames of the desired region of said specimen by scanning the electron beam plural times on the desired region of said specimen, such that frame images acquired in sampling positions are added to frame images acquired at positions displaced or shifted by 0.5 pixels from the frame images acquired in the sampling positions in a X-direction, Y-direction or diagonal direction. 15. A scanning electron microscope according to claim 11, wherein the controller controls the electron beam illumination unit to scan the electron beam plural times on the desired region of said specimen, and controls the image acquisition unit to obtain images of a plurality of frames such that frame images acquired in sampling positions are added to frame images acquired at positions displaced or shifted by 0.5 pixels from the frame images acquired in the sampling positions in a X-direction, Y-direction or diagonal direction.