Patent ID: 8405026

Claim:
A charged particle beam apparatus, comprising: a charged particle beam source; a scanning device for irradiating a desired region of a sample with a primary charged particle beam; a display device for displaying secondary charged particles generated from the desired region irradiated by the primary charged particle beam as an image; a first condenser lens for focusing the primary charged particle beam; a second condenser lens disposed closer to the sample than the first condenser lens; an objective aperture disposed between the first and second condenser lenses; a movable mechanism for taking off the objective aperture from the charged particle beam apparatus; a first lens setting device and a second lens setting device for setting an excitation value for the first and second condenser lenses, respectively; a controller configured for controlling the first and second lens setting devices; an alignment coil disposed closer to the charged particle beam source than the objective aperture for scanning the primary charged particle beam on the objective aperture; a length measuring device for measuring a diameter of the objective aperture from an image scanned by the alignment coil; an ammeter for measuring an amount of the charged particle beam, an input device for inputting probe current, dim level, and focal depth; a memory device for storing images displayed on the display device, and storing inputted probe current, dim level, focal depth, and the diameter of the objective aperture; and a computing device configured for calculating the image dim level of stored images, detecting focal depth as the difference between calculated image dim level and inputted dim level, taking the difference between the detected probe current and its inputted value, and taking the difference between the detected focal depth and its inputted value, wherein the computing device orders the controller to control the first lens setting device until the difference between the detected probe current and its inputting value converges within a desired range, and wherein the computing device orders the controller to control the second lens setting device until the difference between the detected focal depth and its inputting value converges within a desired range.