Bulk deposition for tilted mill protection
To reduce artifacts in a surface exposed by a focused ion beam for viewing, a trench is milled next to the region of interest, and the trench is filled to create a bulkhead. The ion beam is directed through the bulkhead to expose a portion of the region of interest for viewing. The trench is filled, for example, by charged particle beam-induced deposition. The trench is typically milled and filled from the top down, and then the ion beam is angled with respect to the sample surface to expose the region of interest.
1. A method of using a charged particle beam to expose a feature of interest in a sample, including:
milling a trench adjacent to the feature of interest in a surface of the sample;
filling the trench with a material using beam-induced deposition;
directing an ion beam to expose the feature of interest from an angle that requires milling through the deposited material, the angle being an angle between the surface and the ion beam that is less than or equal to 45°; and
observing the exposed feature of interest.
2. The method of claim 1 in which filling the trench with a material using beam-induced deposition comprises depositing material adjacent to but not on top of the feature of interest.
3. The method of claim 1 in which the angle is an angle between the surface and the ion beam that is less than or equal to 10°.
4. The method of claim 1 in which:
the filled trench comprises a bulkhead;
the bulkhead has a proximal edge closest to the feature of interest; and
the bulkhead is configured such that directing an ion beam to expose the feature of interest causes each point on the proximal edge to be milled to a different depth.
5. The method of claim 4 in which the region of interest contains multiple identical features and in which directing an ion beam exposes multiple features of interest adjacent to the bulkhead at different depths in one exposed face.
6. The method of claim 1 in which directing an ion beam to expose the feature of interest from an angle that requires milling through the deposited material comprises exposing a vertical face parallel to the beam direction to provide a side view of the feature of interest.
7. The method of claim 1 in which directing an ion beam to expose the feature of interest from an angle that requires milling through the deposited material comprises exposing a face less than 10 degrees from the horizontal and parallel to the beam direction to provide a nearly top-down view of the feature of interest.
8. The method of claim 7 in which the steps of directing an ion beam to expose the feature of interest from an angle that requires milling through the deposited material; and observing the exposed feature of interest are repeated to provide information about the feature of interest at multiple depths below the original surface.
9. A method of exposing a feature of interest in a sample with a charged particle beam, the sample comprising a first material, the method comprising:
milling a hole adjacent to the feature of interest in a surface of the sample;
filling the hole with a second material; and
directing an ion beam from an angle that requires milling through the second material to expose the feature of interest, wherein the angle is an angle between the surface and the ion beam that is less than or equal to 45°.
10. The method of claim 9 in which milling a hole adjacent to the feature of interest comprises milling the hole in a direction normal to the surface.
11. The method of claim 9 in which filling the hole with a material comprises filling the hole using charged particle beam deposition.
12. The method of claim 9 in which directing an ion beam to expose the feature of interest comprises performing a glancing angle mill.
13. The method of claim 12 further comprising:
re-orienting the sample before performing the glancing angle mill; and
imaging the sample with a scanning electron microscope.
14. The method of claim 9 in which the second material used to fill the hole has an etch rate within 30% of the etch rate of the first material.
15. The method of claim 9 in which the feature of interest is a high aspect ratio structure.
16. The method of claim 9 in which the second material used to fill the hole comprises tungsten, platinum, or an oxide.
17. The method of claim 13 further comprising repeating, at least once, the steps of performing a glancing angle mill and imaging the sample with a scanning electron microscope.
18. The method of claim 17 in which information obtained from imaging the sample is combined to create three-dimensional information of the sample.
19. The method of claim 9 in which milling a hole adjacent to the feature of interest comprises milling the hole to have a proximal edge that is angled with respect to the feature of interest.
20. A system for exposing a feature of interest in a sample, comprising:
an ion optical column for providing a focused beam of ions;
an electron optical column for providing a focused beam of electrons;
a particle detector for detecting secondary particles emitted from the sample; and
a controller communicating to a computer memory, the computer memory storing instructions for:
milling a hole adjacent to the feature of interest in a surface of the sample;
filling the hole with a second material using charged particle beam deposition;
directing an ion beam to expose the feature of interest from an angle that requires milling through the deposited second material, the angle being an angle between the surface and the ion beam that is less than or equal to 10°, wherein milling through the deposited second material comprises performing a glancing angle mill and re-orienting the sample before performing the glancing angle mill; and
imaging the sample using a scanning electron microscope.