Patent Number: 
Section: claims

1. A charged particle beam apparatus comprising:a charged particle source;a deflector for scanning a charged particle beam emitted from said charged particle source; anda detector for detecting secondary signals emitted from a scanned region of said charged particle beam, a sample image being formed based on said secondary signals detected by said detector, which further comprises:a control unit for forming a plurality of images based on said detected secondary signals, sharpening said formed images, detecting positional displacement between said sharpened images, and superposing images so as to correct the detected positional displacement. 2. A charged particle beam apparatus according to claim 1, wherein said plurality of images are formed by a unit of two-dimensional scanning performed by said deflector. 3. A charged particle beam apparatus according to claim 1, wherein said plurality of images are acquired in different timing. 4. A charged particle beam apparatus according to claim 1, wherein an image shift deflector for shifting a scanning region of said charged particle beam and a sample stage for moving a sample are provided, wherein said control unit detects directions of positional displacements among said sharpened images, and operates said image shift deflector and said sample stage so that said scanning region is positioned toward directions canceling said positional displacements. 5. A charged particle beam apparatus according to claim 1, wherein said control unit shifts said scanning region using said image shift deflector and said sample stage when an amount of said positional displacement is larger than a preset value, and shifts said scanning region using said image shift deflector when an amount of said positional displacement is smaller than a preset value. 6. A charged particle beam apparatus comprising:a charged particle source;a deflector for scanning a charged particle beam emitted from said charged particle source; anda detector for detecting secondary signals emitted from a scanned region of said charged particle beam, a sample image being formed based on said secondary signals detected by said detector, which further comprises:a control unit for forming a plurality of images on the basis of said detected secondary signals and forming composite images of said formed images, wherein number of pixels of said formed images before being superimposed is larger than number of pixels of said composite images. 7. A charged particle beam apparatus according to claim 6, wherein said plurality of images are formed by a unit of two-dimensional scanning performed by said deflector. 8. A charged particle beam apparatus according to claim 6, wherein said plurality of images are acquired in different timing. 9. A charged particle beam apparatus according to claim 6, wherein an image shift deflector for shifting a scanning region of said charged particle beam and a sample stage for moving a sample are provided, wherein said control unit detects directions of positional displacements among said composite images, and operates said image shift deflector and said sample stage so that said scanning region is positioned toward directions canceling said positional displacements. 10. A charged particle beam apparatus according to claim 6, wherein said control unit shifts said scanning region using said image shift deflector and said sample stage when an amount of said positional displacement is larger than a preset value, and shifts said scanning region using said image shift deflector when an amount of said positional displacement is smaller than a preset value.