Gradient-based milling for segmented endpointing during lamellae thinning

A system comprising:

• a vacuum chamber;
• a sample stage disposed in the vacuum chamber and configured to receive a sample in the vacuum chamber;
• an ion beam column configured to provide an ion beam into the vacuum chamber;
• and
• a controller comprising one or more processors and one or more memories storing computer-executable instructions that, when executed by the one or more processors, configure the controller to:
• cause the ion beam column to remove a first layer of material from a sample by at least directing a charged particle beam toward a surface of the sample in a pattern, the pattern corresponding to a segment of the sample;
• process, after the first layer is removed, a first image that shows at least the segment;
• determine, based on the image, a variation in material removal between at least two sections of the segment;
• determine, based on the variation in material removal, a control parameter that varies one or more properties of the charged particle beam across the at least two sections;
• and
• cause removal of a second layer of material from the sample by at least directing the charged particle beam in the pattern according to the control parameter.

A controller comprising:

• one or more processors;
• and
• one or more memories storing computer-executable instructions that, when executed by the one or more processors, configure the controller to:
• cause an ion beam column to remove a first layer of material from a sample by at least directing a charged particle beam toward a surface of the sample in a pattern, the pattern corresponding to a segment of the sample;
• cause, after the first layer is removed, a first image to be generated, the image showing at least one segment;
• determine, based on the image, a variation in material removal between at least two sections of the segment;
• determine, based on the variation in the material removal, a control parameter that varies one or more properties of the charged particle beam across the at least two sections;
• and
• cause removal of a second layer of material from the sample by at least directing the charged particle beam in the pattern according to the control parameter.