| 摘要 |
PURPOSE:To perform correct focal point alignment even when astigmatism is not accurately corrected by presetting the strength of a focusing lens so that the conversion signal of beam diameter on the surface of a sample can be set to a specified value. CONSTITUTION:The surface of a sample 5 is irradiated with a particle beam 2 generated from a charged particle beam source 1 so that a small beam diameter can be formed on the surface of the sample 5 by a focusing lens 4 and then is scanned. A scanning picture is displayed on a picture display means 7 that synchronizes with this scanning using a picture signal detected from the sample 5. Such a device is provided with a means that obtains a conversion signal corresponding to the beam diameter on the surface of the sample 5 of the charged beam 2 based on the picture signal. In addition, the device is provided with a means that fixes the lens strength L1 and L2 of the focusing lens 4 by which a conversion signal lower by a specified amount than the maximum value of the said conversion signal that can be obtained when the lens strength of the focusing lens 4 is varied sequentially and a means that sets the lens strength of the focusing lens 4 to (L1+L2)/2. |
