Patent Number: 
Section: claims

1. A charged particle beam application apparatus having a stage device used to move a sample in at least three axial directions, a charged particle beam optical system having an optical axis inclined from a surface of said sample to irradiate the sample with a charged particle beam, and a display device that displays an image formed by the charged particle beam optical system, the apparatus comprising:a correction table indicating a relationship between focal distance and a position of said sample and a relationship between optical conditions for said charged particle beam optical system and a position of said sample, and an arithmetic section that calculates the position of said sample, the arithmetic section calculating the amount of three-dimensional correction for the position of said sample using said correction table, so that when the focal distance of said charged particle beam changes, a position of a target on said sample is placed in the center of a visual field of a screen of said display device, wherein said correction table is created by assuming that a position [Z] of said sample in a Z direction is expressed using a linear expression with a position [X] of said sample in an X direction, a position [Y] of said sample in a Y direction, and optical conditions [P] for the charged beam optical system. 2. The charged particle beam application apparatus according to claim 1, wherein said charged particle beam optical system includes a plurality of charged particle beam optical systems, and even when said charged particle beam optical system is switched, the position of the target on said sample remains in the center of the visual field of the screen of said display device. 3. The charged particle beam application apparatus according to claim 2, wherein if the same target on said sample is observed without changing the height of said sample even when said charged particle beam optical system is switched, then the focal distance of said charged particle beam optical system is changed and said sample is moved in the X and Y directions by an amount equal to the following differential (dX, dY),dX=SX(1)−FX(1)dY=SY(1)−FY(1)where FX(1) and FY(1) denote the position of the sample in the charged particle beam optical system before the switching and SX(1) and SY(1) denote the position of the sample in the charged particle beam optical system after the switching.