Patent ID: 6979820

Claim:
A method of focusing a scanning electron microscope, comprising: providing a magnetic lens, an image detector, and a wafer holder; providing means for adjusting the position of said wafer holder; providing means for supplying a focus current to said magnetic lens; providing means for supplying a retarding voltage to said wafer holder; placing a wafer on said wafer holder; adjusting the position of said wafer holder, thereby adjusting the distance between the wafer placed on said wafer holder and said magnetic lens to a desired focus distance; adjusting the retarding voltage supplied to said wafer holder to achieve a best focus image of the wafer placed on said wafer holder at said image detector, after adjusting the distance between the wafer placed on said wafer holder and said magnetic lens to said desired focus distance; and adjusting said focus current to achieve a final focus image of the wafer placed on said wafer holder at said image detector, after adjusting the retarding voltage supplied to said wafer holder.