Precision in stereoscopic measurements using a pre-deposition layer

A system for determining a depth of a hole milled into 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 the sample in a processing chamber having a charged particle beam column;
• prior to milling the hole, deposit material directly over a top surface of the sample in a second region of the sample adjacent to the first region so that the material forms an interface with the top surface;
• mill the hole in the first region of the sample using a charged particle beam generated by the charged particle beam column, wherein the milling partially removes the deposited material such that a remaining portion of the material forms a high-contrast boundary with the top surface at an original location of the top surface prior to milling and wherein the hole abuts the material deposited over the top surface and includes a sidewall that extends from a bottom surface of the hole to the high-contrast boundary formed at the interface between the remaining deposited material and the top surface of the sample;
• obtain first and second images of the sidewall from different perspectives;
• and
• calculate a depth of the hole use stereoscopic measurement techniques on distances measured in the first and second images between a first point along the high-contrast boundary between the remaining deposited material and the top surface and a second point along a bottom surface of the hole.

A non-transitory computer-readable memory that stores instructions for determining a depth of a hole milled into a first region of a sample by:

• positioning the sample in a processing chamber having a charged particle beam column;
• prior to milling the hole, depositing material directly over a top surface of the sample in a second region of the sample adjacent to the first region so that the material forms an interface with the top surface;
• milling the hole in the first region of the sample using a charged particle beam generated by the charged particle beam column, wherein the milling step partially removes the deposited material such that a remaining portion of the material forms a high-contrast boundary with the top surface at an original location of the top surface prior to milling and wherein the hole abuts the material deposited over the top surface and includes a sidewall that extends from a bottom surface of the hole to the high-contrast boundary formed at the interface between the remaining deposited material and the top surface of the sample;
• obtaining first and second images of the sidewall from different perspectives;
• and
• calculating a depth of the hole using stereoscopic measurement techniques based on distances measured in the first and second images between a first point along the high-contrast boundary between the remaining deposited material and the top surface and a second point along a bottom surface of the hole.