Precision in stereoscopic measurements using a pre-deposition layer

1 . A method of determining a depth of a hole milled into a first region of a sample, the method comprising:

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 partially removes the material deposited over the top surface 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 original top surface and a second point along a bottom surface of the hole.

2 . The method of determining a depth of a hole milled into a first region of a sample set forth in claim 1 wherein the each of the first and second images are obtained using a scanning electron microscopy (SEM) technique.

3 . The method of determining a depth of a hole milled into a first region of a sample set forth in claim 1 wherein the charged particle beam column is a focused ion beam (FIB) column and the charged particle beam is a focused ion beam.

4 . The method of determining a depth of a hole milled into a first region of a sample set forth in claim 3 wherein depositing the material comprises:

injecting a deposition precursor gas into the second region of the sample;

generating a focused ion beam with the focused ion beam column and focusing the ion beam within the second region of the sample; and

scanning the focused particle beam across the second region of the sample to activate molecules of the deposition gas that have adhered to the sample surface in the deposition region and deposit material on the sample within the second region.

5 . The method of determining a depth of a hole milled into a first region of a sample set forth in claim 1 wherein the stereoscopic measurement techniques comprise:

obtaining the first image of the sidewall of the hole, the first image obtained from a first perspective associated with a first angle relative to the sample;

measuring, using the first image, a first distance between a first point on the sidewall at the interface between the deposited material and the top surface of the sample and a second point on the sidewall corresponding to a bottom surface of the hole;

obtaining the second image of the sidewall of the hole, the second image obtained from a second perspective associated with a second angle relative to the sample, wherein the first angle and first perspective are different from the second angle and the second perspective;

measuring, using the second image, a second distance between the first point on the sidewall corresponding to the interface between the deposited material and the top surface of the sample and the second point on the sidewall corresponding to the bottom surface of the hole, wherein the first point and the second point fall approximately on a line extending vertically through the milled hole; and

determining a depth of the hole using the first distance, the first angle associated with the first perspective, the second distance, and the second angle associated with the second perspective.

6 . The method of determining a depth of a hole milled into a first region of a sample set forth in claim 5 wherein the each of the first and second images are obtained using a scanning electron microscopy (SEM) technique.

7 . The method of determining a depth of a hole milled into a first region of a sample set forth in claim 1 wherein the processing chamber is a vacuum chamber that includes both a focused ion beam (FIB) column and a scanning electron microscope (SEM) column.

8 . The method of determining a depth of a hole milled into a first region of a sample set forth in claim 1 wherein the sample is a semiconductor wafer.

9 . 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.

10 . The system for determining a depth of a hole milled into a first region of a sample set forth in claim 9 wherein the each of the first and second images are obtained using a scanning electron microscopy (SEM) technique.

11 . The system for determining a depth of a hole milled into a first region of a sample set forth in claim 9 wherein the charged particle beam column is a focused ion beam (FIB) column and the charged particle beam is a focused ion beam.

12 . The system for determining a depth of a hole milled into a first region of a sample set forth in claim 11 wherein depositing the material comprises:

injecting a deposition precursor gas into the second region of the sample;

generating a focused ion beam with the focused ion beam column and focusing the ion beam within the second region of the sample; and

scanning the focused particle beam across the second region of the sample to activate molecules of the deposition gas that have adhered to the sample surface in the deposition region and deposit material on the sample within the second region.

13 . The system for determining a depth of a hole milled into a first region of a sample set forth in claim 9 wherein the processing chamber is a vacuum chamber that includes both a focused ion beam (FIB) column and a scanning electron microscope (SEM) column.

14 . 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.

15 . The non-transitory computer-readable memory that stores instructions for determining a depth of a hole milled into a first region of a sample according to claim 14 wherein the each of the first and second images are obtained using a scanning electron microscopy (SEM) technique.

16 . The non-transitory computer-readable memory that stores instructions for determining a depth of a hole milled into a first region of a sample according to claim 14 wherein the charged particle beam column is a focused ion beam (FIB) column and the charged particle beam is a focused ion beam.

17 . The non-transitory computer-readable memory that stores instructions for determining a depth of a hole milled into a first region of a sample according to claim 14 wherein depositing the material comprises:

injecting a deposition precursor gas into the processing chamber at a location adjacent to the deposition region;

generating a focused ion beam with the focused ion beam column and focusing the ion beam within the deposition region of the sample; and

scanning the focused particle beam across the deposition region of the sample to activate molecules of the deposition gas that have adhered to the sample surface in the deposition region and deposit material on the sample within the deposition region.