System and method for uniform ion milling

A system for delayering of a sample consisting of generally planar, parallel layers, comprising:

• a. a movable sample stage supporting a sample at a plurality of locations in a vacuum chamber;
• b. an ion beam source within said vacuum chamber having at least one ion source generating a generally columnar ion beam;
• c. a deflector diverting said charged ion beam from an initial beam path to raster said ion beam in at least one direction directly upon and along a surface of said sample over a raster range;
• d. at least one detector within said vacuum chamber for generating an output signal including data indicative of the elemental composition of an area of interest portion of said sample surface, said detector selected from the group consisting of an optical microscope, a CCD camera, a CMOS camera, a scanning electron microscope, a secondary electron detector, a backscatter electron detector, an energy dispersive spectrometer, a secondary ion mass spectrometer and an auger probe;
• and
• e. a control circuit in electronic communication with said deflector, said ion beam source and said at least one detector, said control circuit:
• i. generating said charged ion beam with said ion beam source and operating said deflector to cause said charged ion beam to remove material from said sample surface associated with said area of interest portion;
• ii. obtaining elemental composition data from said at least one detector output signal relative to said area of interest portion,
• iii. determining whether said area of interest portion has been appropriately exposed generally planar to at least one of said parallel layers of said sample based upon the identification of said elemental composition of said area of interest portion;
• and
• iv. modifying at least one of:
• accelerating voltage, ion flux density, spot size, raster rate, raster dimension and dwell time of said ion beam source based upon said identification of said elemental composition to provide a time-averaged flux of ions per unit area as a function of position and time on said sample surface to realize substantially planar material removal at said area of interest portion.