ASTM E986-04(2010)
(Practice)Standard Practice for Scanning Electron Microscope Beam Size Characterization
Standard Practice for Scanning Electron Microscope Beam Size Characterization
SIGNIFICANCE AND USE
The traditional resolution test of the SEM requires, as a first step, a photomicrograph of a fine particulate sample taken at a high magnification. The operator is required to measure a distance on the photomicrograph between two adjacent, but separate edges. These edges are usually less than one millimetre apart. Their image quality is often less than optimum limited by the S/N ratio of a beam with such a small diameter and low current. Operator judgment is dependent on the individual acuity of the person making the measurement and can vary significantly.
Use of this practice results in SEM electron beam size characterization which is significantly more reproducible than the traditional resolution test using a fine particulate sample.
SCOPE
1.1 This practice provides a reproducible means by which one aspect of the performance of a scanning electron microscope (SEM) may be characterized. The resolution of an SEM depends on many factors, some of which are electron beam voltage and current, lens aberrations, contrast in the specimen, and operator-instrument-material interaction. However, the resolution for any set of conditions is limited by the size of the electron beam. This size can be quantified through the measurement of an effective apparent edge sharpness for a number of materials, two of which are suggested. This practice requires an SEM with the capability to perform line-scan traces, for example, Y-deflection waveform generation, for the suggested materials. The range of SEM magnification at which this practice is of utility is from 1000 to 50 000 × . Higher magnifications may be attempted, but difficulty in making precise measurements can be expected.
1.2 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation: E986 − 04 (Reapproved 2010)
Standard Practice for
Scanning Electron Microscope Beam Size Characterization
This standard is issued under the fixed designation E986; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 3.2.1 Y-deflection waveform—the trace on a CRT resulting
from modulating the CRT with the output of the electron
1.1 This practice provides a reproducible means by which
detector. Contrast in the electron signal is displayed as a
one aspect of the performance of a scanning electron micro-
changein Y(vertical)ratherthanbrightnessonthescreen.This
scope (SEM) may be characterized. The resolution of an SEM
operating method is often called Y-modulation.
depends on many factors, some of which are electron beam
voltage and current, lens aberrations, contrast in the specimen,
4. Significance and Use
and operator-instrument-material interaction. However, the
4.1 The traditional resolution test of the SEM requires, as a
resolution for any set of conditions is limited by the size of the
first step, a photomicrograph of a fine particulate sample taken
electron beam. This size can be quantified through the mea-
at a high magnification. The operator is required to measure a
surement of an effective apparent edge sharpness for a number
distance on the photomicrograph between two adjacent, but
ofmaterials,twoofwhicharesuggested.Thispracticerequires
separate edges. These edges are usually less than one millime-
an SEM with the capability to perform line-scan traces, for
tre apart. Their image quality is often less than optimum
example, Y-deflection waveform generation, for the suggested
limited by the S/N ratio of a beam with such a small diameter
materials. The range of SEM magnification at which this
and low current. Operator judgment is dependent on the
practice is of utility is from 1000 to 50000×. Higher
individual acuity of the person making the measurement and
magnifications may be attempted, but difficulty in making
can vary significantly.
precise measurements can be expected.
4.2 Use of this practice results in SEM electron beam size
1.2 This standard does not purport to address all of the
characterization which is significantly more reproducible than
safety concerns, if any, associated with its use. It is the
the traditional resolution test using a fine particulate sample.
responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica-
5. Suggested Materials
bility of regulatory limitations prior to use.
5.1 SEM resolution performance as measured using the
procedurespecifiedinthispracticewilldependonthematerial
2. Referenced Documents
used; hence, only comparisons using the same material have
2.1 ASTM Standards:
meaning. There are a number of criteria for a suitable material
E7Terminology Relating to Metallography
to be used in this practice. Through an evaluation of these
E766Practice for Calibrating the Magnification of a Scan-
criteria, two samples have been suggested. These samples are
ning Electron Microscope
nonmagnetic; no surface preparation or coating is required;
thus, the samples have long-term structural stability. The
3. Terminology
sample-electron beam interaction should produce a sharply
3.1 Definitions: For definitions of terms used in this
rising signal without inflections as the beam scans across the
practice, see Terminology E7.
edge. Two such samples are:
3.2 Definitions of Terms Specific to This Standard: 5.1.1 Carbon fibers, NIST—SRM 2069B.
5.1.2 Fracture edge of a thin silicon wafer, cleaved on a
(111) plane.
This practice is under the jurisdiction of ASTM Committee E04 on Metallog-
6. Procedure
raphy and is the direct responsibility of Subcommittee E04.11 on X-Ray and
Electron Metallography.
6.1 Inspect the specimen for cleanliness. If the specimen
Current edition approved April 1, 2010. Published May 2010. Originally
appears contaminated, a new sample is recommended as any
approved in 1984. Last previous edition approved in 2004 as E986–04. DOI:
10.1520/E0986-04R10.
cleaningmayadverselyaffectthequalityofthespecimenedge.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on Available from National Institute of Standards and Technology (NIST), 100
the ASTM website. Bureau Dr., Stop 1070, Gaithersburg, MD 20899-1070, http://www.nist.gov.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E986 − 04 (2010)
6.2 Ensure good electrical contact with the specimen by
using a conductive cement to hold the specimen on a SEM
stub, or by clamping the specimen on the stage of the SEM.
MountthespecimenrigidlyintheSEMtominimizeanyimage
degradation caused by vibration.
6.3 Verify magnification calibration for both X and Y direc-
tions. This can be accomplished by using Practice E766.
−2 −4
6.4 Use a clean vacuum of 1.33 by 10 Pa (10 mm Hg)
or better to minimize specimen contamination resulting from
electron beam and residual hydrocarbons interacting during
examination. The presence of a contamination layer has a
deleterious effect on image-edge quality.
6.5 Allow a minimum of 30 min for stabilization of elec-
tronic components, vacuum stability, and thermal equilibrium
fortheelectrongunandlenses.TheselectionofoptimumSEM
parameters is at the discretion of the operator. For measuring
the ultimate resolution, these will typically be: high kV
(~30max.), short working distance (5 to 10 mm), smallest spot
size, and long scan time.
6.6 Anyalternativesetofconditionscanbeusedtomeasure
probe size, but they will measure beam diameter under those
FIG. 1 Edge of Graphitized Natural Cellulose Fiber Used to Pro-
specific conditions, not ultimate resolution.
duce Line
...
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