TEM sample preparation

Patent metadata

Field	Value
Publication number	US-9378925-B2
Application number	US-201514869553-A
Country	US
Kind code	B2
Filing date	Sep 29, 2015
Priority date	Jan 28, 2011
Publication date	Jun 28, 2016
Grant date	Jun 28, 2016

Abstract

An improved method of preparing ultra-thin TEM samples that combines backside thinning with an additional cleaning step to remove surface defects on the FIB-facing substrate surface. This additional step results in the creation of a cleaned, uniform “hardmask” that controls the ultimate results of the sample thinning, and allows for reliable and robust preparation of samples having thicknesses down to the 10 nm range.

First claim

We claim as follows:

1. A method of preparing a sample for TEM analysis, the method comprising:
positioning a sample having a vertical axis, a top side, and a bottom side so that an ion beam is transverse to the vertical axis of the sample;
milling the bottom side of the sample to remove at least of portion of the bottom surface of the sample to produce a uniformly flat surface;
positioning the sample so that the bottom side of the sample is oriented toward the ion beam source and so that the ion beam is parallel to the vertical axis of the sample;
thinning the sample by directing the ion beam in a milling pattern that thins at least a portion of the sample to a thickness of 30 nm or less.

2. The method of claim 1 further comprising:
rotating the sample about an axis perpendicular to the sample vertical axis to invert the top and bottom sides of the sample; and
attaching the inverted sample to a sample holder.

3. The method of claim 1 in which positioning the sample so that the ion beam is transverse to the vertical axis of the sample comprises positioning the sample so that the angle between the ion beam and the vertical axis of the sample is from 35 to 90 degrees.

4. The method of claim 1 in which thinning the sample by directing the ion beam in a milling pattern comprises thinning at least a portion of the sample to a thickness of 15 nm or less.

5. The method of claim 1 in which milling the bottom side of the sample to remove at least of portion of the bottom surface of the sample to produce a uniformly flat surface comprises removing at least the bottom 25 nm of the sample.

6. The method of claim 1 in which the substrate is a semiconductor wafer or portion thereof and the sample to be extracted is a portion of an integrated circuit that is to be observed using a TEM.

7. The method of claim 2 further comprising, prior to positioning the sample:
separating the sample from the substrate by ion beam milling;
attaching a microprobe to the freed sample;
extracting the sample from the substrate using the attached microprobe; and
in which attaching the sample to a sample holder comprises attaching the sample to a sample holder and separating the microprobe from the attached sample.

8. The method of claim 7 in which rotating the sample about an axis perpendicular to the sample vertical axis to invert the top and bottom sides of the sample comprises inverting the sample by rotating the microprobe so that the orientation of the top and bottom sides is reversed.

9. The method of claim 1 in which milling the bottom side of the sample to remove at least of portion of the bottom surface of the sample to produce a uniformly flat surface comprises milling the bottom side of the sample using an ion beam having a first accelerating voltage and then milling the bottom side of the sample at a second accelerating voltage, the second accelerating voltage being less than half of the first accelerating voltage.

10. The method of claim 1 in which milling the bottom side of the sample to remove at least of portion of the bottom surface of the sample to produce a uniformly flat surface comprises milling the bottom side of the sample using an ion beam having an accelerating voltage of 5 kV or less.

11. The method of claim 1 in which milling the bottom side of the sample to remove at least of portion of the bottom surface of the sample to produce a uniformly flat surface comprises milling the bottom side of the sample using an ion beam having an accelerating voltage of 30 kV or more.

12. An apparatus for carrying out the method of claim 2 .

13. A non-transitory computer-readable storage medium configured with a computer program, where the storage medium so configured causes a computer to control a charged particle beam system to carry out the steps of the method of claim 2 .

14. A method of preparing an ultra thin TEM sample for TEM analysis, the method comprising:
loading a substrate into an ion beam system including an ion beam source and optics for focusing an ion beam along an axis and onto the substrate;
freeing a sample from the substrate by ion beam milling, said sample having a vertical axis, a top side closest to the ion beam source, and a bottom side opposite the ion beam source;
attaching a microprobe to the freed sample;
extracting the sample from the substrate using the attached microprobe;
inverting the sample by rotating the microprobe so that the orientation of the top and bottom sides is reversed;
attaching the inverted sample to a sample holder and separating the microprobe from the attached sample;
positioning the sample holder so that the ion beam axis is at an angle of 30 to 90 degrees relative to the vertical axis of the sample;
removing at least 25 nm from the bottom of the sample to produce a planar surface parallel to the ion beam axis;
positioning the sample holder so that the top side of the sample is oriented opposite the ion beam source and so that the ion beam axis is parallel to the vertical axis of the sample;
thinning the sample by directing the ion beam in a milling pattern that thins at least a portion of the sample to a thickness of 30 nm or less.

15. An apparatus for preparing ultra-thin TEM sample comprising:
an ion beam system including an ion beam source, optics for focusing an ion beam along an axis and onto a substrate, and a micromanipulator for manipulating a sample; and
a computer-readable memory storing computer instructions, the instructions including a program for controlling the apparatus and causing the apparatus to:
position a sample having a vertical axis, a top side, and a bottom side so that the ion beam is transverse to the vertical axis of the sample;
mill the bottom side of the sample to remove at least of portion of the bottom surface of the sample to produce a uniformly flat surface;
position the sample so that the bottom side of the sample is oriented toward the ion beam source and so that the ion beam is parallel to the vertical axis of the sample; and
thin the sample by directing the ion beam in a milling pattern that thins at least a portion of the sample to a thickness of 30 nm or less.

Assignees

• Fei Co

Inventors

• Blackwood Jeffrey
• Bray Matthew
• Senowitz Corey
• Bugge Cliff

Classifications

• H01J37/3056 Primary

  for microworking, e. g. etching of gratings or trimming of electrical components · CPC title

• H01J37/261

  Details · CPC title

• G01N2001/2886

  Laser cutting, e.g. tissue catapult · CPC title

• G01N1/286 Primary

  involving mechanical work, e.g. chopping, disintegrating, compacting, homogenising (microtomes G01N1/06; pulverising in general B02C; mixing in general B01F) · CPC title

• H01J2237/31745

  for preparing specimen to be viewed in microscopes or analyzed in microanalysers · CPC title