Method to more precisely calibrate the mechanical tilt and rotation angles of an sem column

A method of precisely calibrating mechanical tilt and rotation angles of a charged particle column, the method comprising:

• positioning a test structure with known dimensions in a processing chamber having a charged particle column tilted at a first tilt angle and first rotational angle;
• determining the first tilt angle and first rotational angle by:
• taking an image of the test structure with the charged particle column tilted at the first tilt angle and the first rotational angle;
• measuring, based on the image, distances between multiple edges of the test structure aligned with each other along a vector;
• determining ratios between the measured distances;
• and
• determining a calculated tilt angle and a calculated rotational angle of charged particle column from the ratios and the known dimensions of the structure.

A system for determining a depth of a feature formed in a first region of a sample, the system comprising:

• a vacuum chamber;
• a sample support configured to hold a sample within the vacuum chamber during a milling process;
• a charged particle beam column configured to direct a charged particle beam into the vacuum chamber;
• a processor and a memory coupled to the processor, the memory including a plurality of computer-readable instructions that, when executed by the processor, cause the system to:
• position a test structure with known dimensions on the sample support with the charged particle column tilted at a first tilt angle and first rotational angle;
• determine the first tilt angle and first rotational angle by:
• taking an image of the test structure with the charged particle column tilted at the first tilt angle and the first rotational angle;
• measuring, based on the image, distances between multiple edges of the test structure aligned with each other along a vector;
• determining ratios between the measured distances;
• and
• determining a calculated tilt angle and a calculated rotational angle of charged particle column from the ratios and the known dimensions of the structure;
• transfer the test structure out of the processing chamber and positioning the sample in the processing chamber such that the first region is under a field of view of the charged particle column;
• take a first image of the feature with the column tilted at the first tilt angle and first rotational angle and taking a second image of the feature with the column is tilted at a second tilt angle, different than the first tilt angle, and a second rotational angle;
• and
• use stereoscopic measurement techniques to determine the depth of the feature based on the first and second images and the calculated tilt angle and calculated rotational angle.