Method for positioning a focal plane of a light imaging device and apparatus arranged for applying said method.

摘要

The invention relates to a method for positioning a focal plane of a light imaging device at a surface of a substrate, wherein the substrate emits light when irradiated with charged particles. The method comprises the steps of: i. irradiating the substrate with a beam of charged particles having a set charged particle beam energy; ii. moving the focal plane of the light imaging device at least in a direction towards or away from the substrate and measuring an intensity of the emitted light as a function of the position of said focal plane with respect to the substrate; and iii. setting the focal plane at a focal position with respect to the substrate, said focal position being determined using the measured dependence of the intensity of the light signal as a function of the position. Preferably the method steps are subsequently repeated using a reduced charged particle beam energy.