ASTM F1438-93(2005)
(Test Method)Standard Test Method for Determination of Surface Roughness by Scanning Tunneling Microscopy for Gas Distribution System Components
Standard Test Method for Determination of Surface Roughness by Scanning Tunneling Microscopy for Gas Distribution System Components
SIGNIFICANCE AND USE
The use of STM images and data is for purposes of textural quality assessment and calculation of figures of merit, and for high purity gas system clean room components.
This test method defines a standard data presentation format and suggests figures of merit that utilize STM’ability to analyze three-dimensional surface features.
SCOPE
1.1 The purpose of this test method is to define a method for analyzing the surface texture of the above-mentioned components using a scanning tunneling microscope (STM). STM is a noncontact method of surface profiling that can measure three-dimensional surface features in the nanometer size range, which can then be used to represent the surface texture or to provide figures of merit. Application of this test method, where surface texture is used as a selection criterion, is expected to yield comparable data among different components tested.
1.2 Limitations:
1.2.1 This test method is limited to characterization of stainless steel surfaces that are smoother than Ra = 0.25 [mu]m, as determined by a contact-stylus profilometer and defined by ANSI B46.1. The magnifications and height scales used in this test method were chosen with this smoothness in mind.
1.2.2 Intentional etching or conductive coating of the surface are considered modifications of the gas-wetted surface and are not covered by this test method.
1.2.3 This test method does not cover steels that have an oxide layer too thick to permit tunneling under the test conditions outlined in 11.3.
1.3 This technique is written with the assumption that the STM operator understands the use of the instrument, its governing principles, and any artifacts that can arise. Discussion of these points is beyond the scope of this test method.
1.4 The values stated in SI units are to be regarded as the standard.
1.5 This standard does not purport to address all of the safety problems, 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: F1438 − 93(Reapproved 2005)
Standard Test Method for
Determination of Surface Roughness by Scanning
Tunneling Microscopy for Gas Distribution System
Components
This standard is issued under the fixed designation F1438; 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.
INTRODUCTION
Semiconductor clean rooms are serviced by high-purity gas distribution systems. This test method
presentsaprocedurethatmaybeappliedfortheevaluationofoneormorecomponentsconsideredfor
use in such systems.
1. Scope 1.5 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
1.1 Thepurposeofthistestmethodistodefineamethodfor
responsibility of the user of this standard to establish appro-
analyzing the surface texture of the above-mentioned compo-
priate safety and health practices and determine the applica-
nents using a scanning tunneling microscope (STM). STM is a
bility of regulatory limitations prior to use.
noncontact method of surface profiling that can measure
three-dimensionalsurfacefeaturesinthenanometersizerange,
2. Referenced Documents
which can then be used to represent the surface texture or to
2.1 ASTM Standards:
providefiguresofmerit.Applicationofthistestmethod,where
E691Practice for Conducting an Interlaboratory Study to
surface texture is used as a selection criterion, is expected to
Determine the Precision of a Test Method
yield comparable data among different components tested.
2.2 ANSI Standard:
1.2 Limitations:
ANSI B.46.1-85,“Surface Texture (Surface Roughness,
1.2.1 This test method is limited to characterization of
Waviness, and Lay),” ANSI/ASME, 1985
stainless steel surfaces that are smoother than R =0.25 µm, as
a
3. Terminology
determined by a contact-stylus profilometer and defined by
ANSI B46.1.The magnifications and height scales used in this
3.1 Definitions of Terms Specific to This Standard:
test method were chosen with this smoothness in mind.
3.1.1 artifact—anycontributiontoanimagefromotherthan
1.2.2 Intentional etching or conductive coating of the sur-
true surface morphology. This could include such examples as
faceareconsideredmodificationsofthegas-wettedsurfaceand
vibration, electronic noise, thermal drift, or tip imperfections.
are not covered by this test method.
3.1.2 center line (graphical center line)—lineparalleltothe
1.2.3 This test method does not cover steels that have an
directionofprofilemeasurement,suchthatthesumoftheareas
oxide layer too thick to permit tunneling under the test
contained between it and the profile contained on either side
conditions outlined in 11.3.
are equal (see Calculation Section).
1.3 This technique is written with the assumption that the
3.1.3 cutoff length (l )—for profiles in this context, the
c
STM operator understands the use of the instrument, its
sampling length, that is, the length of a single scan, in
governing principles, and any artifacts that can arise. Discus-
nanometers (see Calculation Section).
sion of these points is beyond the scope of this test method.
3.1.4 current— in this context, the tunneling current (ex-
1.4 The values stated in SI units are to be regarded as the
pressed in nanoamperes) that flows in either direction between
standard.
the tip and surface, under the conditions specified.
1 2
This test method is under the jurisdiction of ASTM Committee F01 on For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Electronicsand is the direct responsibility of Subcommittee F01.10 on Contamina- contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
tion Control. Standards volume information, refer to the standard’s Document Summary page on
Current edition approved Jan. 1, 2005. Published January 2005. Originally the ASTM website.
apporvedin1993.Lastpreviouseditionapprovedin1999asF1438–93(1999).DOI: Available fromAmerican National Standards Institute, 13th Floor, 11 W. 42nd
10.1520/F1438-93R05. St., New York, NY 10036.
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F1438 − 93 (2005)
3.1.5 feature height—datum (height in the z-direction) of 3.1.24 tunneling—in this context, the flow of current be-
any point in the scan area, relative to the lowest point in the tweenthetipandsurface(see current);morediscussioncanbe
scan area, as derived from tunneling current during tip raster- found in additional references.
ing.
3.1.25 valley— lowest point between two crossing points of
a profile and its center line.
3.1.6 filter—process of modification of surface data for
purposes of numerical analysis or data presentation. Examples
3.1.26 voltage—bias voltage, expressed in volts (V) or
include high or low pass filters and plane-fitting.
millivolts (mV), applied between the tip and the surface.
3.1.7 gold ruled grating—gold surface having uniformly
3.2 Abbreviations and Symbols:
spaced grooves of known depth and separation; used for
3.2.1 HOPG—highly ordered pyrolytic graphite; used for
micrometer scale x-y calibration.
atomic scale x-y calibration of the scanning tunneling micros-
copy.
3.1.8 illuminated surface—three-dimensional image repre-
sentation that simulates a reflective surface illuminated 3.2.2 STM—scanning tunneling microscopy (or micro-
obliquely or from overhead. scope).
−9
3.2.3 nA—nanoamperes (1×10 amperes).
3.1.9 image—surface topography represented by plotting
feature height as a function of tip position. The feature height
3.2.4 Pt/Ir—platinum and iridium alloy wire used to make
data is derived from the amount of tunneling current flowing
tunneling tips.
between the tip and surface during rastering.
3.2.5 R —see mean roughness.
a
3.1.10 line plot—three-dimensional image given as side-by-
3.2.6 R —maximum height difference between the high-
max
side surface profiles.
est and the lowest points on the profile over the length of the
profile (see Calculation Section).
3.1.11 mean roughness (R )—average deviation from the
a
mean of all profile heights (see algebraic definition in the 3.2.7 root mean square (RMS)—see algebraic definition in
Calculation Section). Calculation Section.
3.1.12 peak—highestpointbetweentwocrossingpointsofa
3.2.8 R —the 10-point mean roughness; that is, the average
z
profile and its center line.
differenceinheightbetweenthefivehighestpeaksandthefive
lowest valleys over the length of the profile (see Calculation
3.1.13 profile—the cross-sectional data that has been high
Section).
pass filtered with a two-pole filter having a gain of 75% at the
cutoff length l (in nanometers).
3.2.9 x-direction—see scan.
c
3.2.10 y-direction—the direction, in the sample plane, over
3.1.14 raster—repetitive scanning in the x-direction while
which successive scans are taken, orthogonal to the scan
moving stepwise in the y-direction; also the area defined by
direction.
such action.
3.2.11 z-direction—the direction perpendicular to the
3.1.15 scan—a single, continuous movement in one direc-
sample plane. Also referred to as the feature height direction.
tion (defined as the x-direction) of the tip relative to sample
surface. 3.2.12 Z—same as feature height (see Calculation Section).
i
3.2.13 Z —maximum height difference over entire sur-
3.1.16 scan area—area covered by successive, side by side
max
face (see Calculation Section).
scans.
3.2.14 Z —root-mean-square of all surface heights (see
rms
3.1.17 scan length—distance from start to end of a single
Calculation Section).
scan, without moving in the y-direction (see cutoff length).
3.1.18 scan rate—the speed at which the tip moves relative
4. Summary of Test Method
to the surface.
4.1 In this test method a sharp, conductive tip is scanned
3.1.19 shaded height plot—image representing feature
over very closely but not in contact with a conductive surface;
height as dark or light shades (any color) over a two-
thatis,theyareseparatedbyagapofseveralangstroms.Abias
dimensional area. Higher features are shaded lighter and lower
voltage present between them causes a flow of electrons
features are shaded darker.
through,ratherthanover,theenergybarrierrepresentedbythis
tip-surface gap. This flow is referred to as the tunneling
3.1.20 thermal drift—movement of the surface with respect
current. The manner in which the current fluctuates during the
to the tip due to a lack of thermal equilibrium.
scanning process is used to indicate the surface’s topography.
3.1.21 tilted surface—three-dimensional image showing
Thoughthetiporsamplecanbescanned,themethoddescribed
surface tilted away from viewer, as opposed to a topview.
here considers only the tip to be in motion. A more extensive
discussion of the operating principles can be found in other
3.1.22 tip crash—touchingoftiptosurface,duringrastering
orattemptstoinitiatetunneling,usuallyresultingindamageto literature.
one or both.
3.1.23 top view—image represented as a surface viewed
Binning, G., et al., “Surface Studies by Scanning Tunneling Microscopy,”
from overhead. Physical Review Letters, Vol 49, No. 1, July 1982, pp. 57–61.
F1438 − 93 (2005)
4.2 In this test method, stainless steel tubing is used as an using a diamond blade saw is recommended over high speed
example of a component surface.An area of the surface is first abrasive cutting or hacksaws.
scanned at a width of 500 nA, then 2000 nA. Even though
8.2 This sampling must not modify the surface topography,
larger areas can be scanned by most instruments, these mag-
such as effects due to stress, heat, corrosion, or combination
nifications are chosen to show surface texture in a size range
thereof, from its condition as found in the component.
beyond that measured by contact stylus type surface profiling
8.3 Cleaning the surface using an inert fluid to remove
instruments, but not at an atomic scale. The surface scans are
cutting contamination is permitted.
then compared for damage, artifacts, etc. Numerical analysis
canthenproceedusingthesedataforroughnessorsurfacearea
9. Calibration
or both, following the model of other standards such asANSI
B46.1.
9.1 Calibration frequency may vary with different instru-
ment manufacturers. It should be performed, at least initially,
5. Significance and Use
then yearly, and after any repair or addition to the instrument’s
hardware and software.
5.1 The use of STM images and data is for purposes of
textural quality assessment and calculation of figures of merit,
9.2 Following the manufacturer’s recommendations, the
and for high purity gas system clean room components.
STMwillbecalibratedusingtheHOPG,goldruledgrating,or
some other suitable dimensional standard, depending upon the
5.2 This test method defines a standard data presentation
size range to be used and the accuracy of the standard.
format and suggests figures of merit that utilize STM’s ability
to analyze three-dimensional surface features.
10. Conditioning
6. Interferences
10.1 Aconductive path for the sample shall be provided for
6.1 Some(stainlesssteel)componentsurfaceshaveanoxide voltage biasing of the sample with respect to the tip.
layer that prevents tunneling from occurring under any condi-
10.2 Mount the sample so the tip will scan an arbitrarily
tions without affecting tip or surface morphology. This results
chosen representative area.
in ambiguous surface data. Such surfaces require the use of
10.3 Bring the sample and microscope to thermal equilib-
other techniques for topographic measurement.
rium.
6.2 This test method assumes that the images obtained are
unperturbed by very thin, non-solid layers (for example,
11. Procedure
hydrocarbons, moisture) on the surface.
11.1 As stated in 1.2.3, this test method does not cover
6.3 Operationwiththesurfaceinair,vacuum,orunderinert
steels that have an oxide layer too thick to permit tunneling
liquids is permissible. (The liquids must be suitably inert and
under the test conditions outlined in this test method.
fluid, so as to not modify the apparent surface topography or
11.2 Make sure that a minimum of 200 data points is
introduce artifacts into the image.)Water is not recommended.
collected in the x-direction, and at least 200 scans per raster is
6.4 The tip shall be made from platinum/iridium or tung-
in the y-direction (200×200=40000 data points).
sten.
11.3 Initiate tunneling between a Pt/Ir tip and the sample in
NOTE 1—Caution: The tip must not have previously touched any
accordance with the manufacturer’s instructions under condi-
surface (see 11.7).
tionstoprovideartifactfreeimages.Suggestedstartingvalues:
voltage bias of 1800 mV, and current levels monitored at 0.1
7. Apparatus
nA (Standard Test Conditions—Room temperature and ambi-
7.1 Scanning Tunneling Microscope ,capableofthefollow-
ent pressure (101.3 kPa, 25° 6 2°C)).
ing may be used:
11.4 Scan an area 500-nm across at a rate of approximately
7.1.1 Scanning lengths up to at least 50 µm,
2 s/µm (or slow enough to prevent the tip from touching the
7.1.2 Substaining 6 3 V between the tip and sample,
surface during rastering), collecting at least 200 data points
7.1.3 Monitoring tunneling current as low as 0.05 nA,
with each x-direction scan.
7.1.4 Traversing feature height variations as great as 2 µm
without touching the tip to the surface, and
11.5 Collect area scans so that comparisons can be made
7.1.5 Providing the surface topography as a shaded height
between the first two successive rasters. Ensure that the area
plot or line plot.
has not drifted more than 10% of the scan width in any
direction. If it has, discontinue scanning for sufficient time to
7.2 Inert atmospheres, temperature controls, acoustic isola-
allow thermal equilibrium to be obtained. Determine this by
tion, and vibration isolation are to be provided as necessary to
repeating 11.3 through 11.5.
obtain artifact-free images.
11.6 Scan the selected 500-nm area for at least five full,
8. Sampling
successive rasters and then store at least the last (fifth) image
8.1 Many components are too large or irregularly shaped to of that scan area. Fig. 1, Fig. 2, and Fig. 3 show an example of
permit STM analysis without cutting a sample from the such an area after the fifth successive raster (see data presen-
component. Low speed cutting, preferably without lubricants, tation section for explanation of format shown).
F1438 − 93 (2005)
FIG. 1 Shaded Height Topview of Electropolished 316L Stainless Steel, 500-nm Across
FIG. 2 Line Plot of Same Scan as Shown in Fig. 1
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