Forming an image while milling work piece

Dual beam instruments, comprising a Scanning Electron Microscope (SEM) column for imaging and a Focused Ion Beam (FIB) column for milling, are routinely used to extract samples (lamellae) from semiconductor waters. By observing the progress of the milling with the SEM column, end pointing of the milling process can be performed. The invention offers an alternative solution to this problem, in which an instrument with only a FIB column is used. For milling a lamella (105) to its final thickness of, for example, 30 nm, the focused ion beam (100), is scanned repeatedly along the lamella. It is found that while milling the lamella a signal can be derived from the lamella that is sufficient for end pointing. No additional electron beam for inspection is needed.