1、Designation: F 1438 93 (Reapproved 2005)Standard Test Method forDetermination of Surface Roughness by ScanningTunneling Microscopy for Gas Distribution SystemComponents1This standard is issued under the fixed designation F 1438; the number immediately following the designation indicates the year ofo
2、riginal adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.INTRODUCTIONSemiconductor clean rooms are serviced by high-purity gas d
3、istribution systems. This test methodpresents a procedure that may be applied for the evaluation of one or more components considered foruse in such systems.1. Scope1.1 The purpose of this test method is to define a method foranalyzing the surface texture of the above-mentioned compo-nents using a s
4、canning tunneling microscope (STM). STM is anoncontact method of surface profiling that can measurethree-dimensional surface features in the nanometer size range,which can then be used to represent the surface texture or toprovide figures of merit.Application of this test method, wheresurface textur
5、e is used as a selection criterion, is expected toyield comparable data among different components tested.1.2 Limitations:1.2.1 This test method is limited to characterization ofstainless steel surfaces that are smoother than Ra= 0.25 m, asdetermined by a contact-stylus profilometer and defined byAN
6、SI B46.1. The magnifications and height scales used in thistest method were chosen with this smoothness in mind.1.2.2 Intentional etching or conductive coating of the sur-face are considered modifications of the gas-wetted surface andare not covered by this test method.1.2.3 This test method does no
7、t cover steels that have anoxide layer too thick to permit tunneling under the testconditions outlined in 11.3.1.3 This technique is written with the assumption that theSTM operator understands the use of the instrument, itsgoverning principles, and any artifacts that can arise. Discus-sion of these
8、 points is beyond the scope of this test method.1.4 The values stated in SI units are to be regarded as thestandard.1.5 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate
9、 safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:E 691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method22.2 ANSI Standard:ANSI B.46.1-85, “Surface Texture (Surface
10、 Roughness,Waviness, and Lay),” ANSI/ASME, 198533. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 artifactany contribution to an image from other thantrue surface morphology. This could include such examples asvibration, electronic noise, thermal drift, or tip imperfections.3.1.
11、2 center line (graphical center line)line parallel to thedirection of profile measurement, such that the sum of the areascontained between it and the profile contained on either sideare equal (see Calculation Section).3.1.3 cutoff length (lc)for profiles in this context, thesampling length, that is,
12、 the length of a single scan, innanometers (see Calculation Section).1This test method is under the jurisdiction of ASTM Committee F0-1 onElectronics and is the direct responsibility of Subcommittee F01.10 on Contamina-tion Control.Current edition approved Jan. 1, 2005. Published January 2005. Origi
13、nallyapporved in 1993. Last previous edition approved in 1999 as F 143893(1999).2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page
14、onthe ASTM website.3Available from American National Standards Institute, 13th Floor, 11 W. 42ndSt., New York, NY 10036.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.1.4 current in this context, the tunneling current (ex-pressed
15、in nanoamperes) that flows in either direction betweenthe tip and surface, under the conditions specified.3.1.5 feature heightdatum (height in the z-direction) ofany point in the scan area, relative to the lowest point in thescan area, as derived from tunneling current during tip raster-ing.3.1.6 fi
16、lterprocess of modification of surface data forpurposes of numerical analysis or data presentation. Examplesinclude high or low pass filters and plane-fitting.3.1.7 gold ruled gratinggold surface having uniformlyspaced grooves of known depth and separation; used formicrometer scale x-y calibration.3
17、.1.8 illuminated surfacethree-dimensional image repre-sentation that simulates a reflective surface illuminated ob-liquely or from overhead.3.1.9 imagesurface topography represented by plottingfeature height as a function of tip position. The feature heightdata is derived from the amount of tunnelin
18、g current flowingbetween the tip and surface during rastering.3.1.10 line plotthree-dimensional image given as side-by-side surface profiles.3.1.11 mean roughness (Ra)average deviation from themean of all profile heights (see algebraic definition in theCalculation Section).3.1.12 peakhighest point b
19、etween two crossing points ofa profile and its center line.3.1.13 profilethe cross-sectional data that has been highpass filtered with a two-pole filter having a gain of 75 % at thecutoff length lc(in nanometers).3.1.14 rasterrepetitive scanning in the x-direction whilemoving stepwise in the y-direc
20、tion; also the area defined bysuch action.3.1.15 scana single, continuous movement in one direc-tion (defined as the x-direction) of the tip relative to samplesurface.3.1.16 scan areaarea covered by successive, side by sidescans.3.1.17 scan lengthdistance from start to end of a singlescan, without m
21、oving in the y-direction (see cutoff length).3.1.18 scan ratethe speed at which the tip moves relativeto the surface.3.1.19 shaded height plotimage representing featureheight as dark or light shades (any color) over a two-dimensional area. Higher features are shaded lighter and lowerfeatures are sha
22、ded darker.3.1.20 thermal driftmovement of the surface with respectto the tip due to a lack of thermal equilibrium.3.1.21 tilted surfacethree-dimensional image showingsurface tilted away from viewer, as opposed to a topview.3.1.22 tip crashtouching of tip to surface, during rasteringor attempts to i
23、nitiate tunneling, usually resulting in damage toone or both.3.1.23 top viewimage represented as a surface viewedfrom overhead.3.1.24 tunnelingin this context, the flow of currentbetween the tip and surface (see current); more discussion canbe found in additional references.43.1.25 valley lowest poi
24、nt between two crossing points ofa profile and its center line.3.1.26 voltagebias voltage, expressed in volts (V) ormillivolts (mV), applied between the tip and the surface.3.2 Abbreviations:Abbreviations and Symbols:3.2.1 HOPGhighly ordered pyrolytic graphite; used foratomic scale x-y calibration o
25、f the scanning tunneling micros-copy.3.2.2 STMscanning tunneling microscopy (or micro-scope).3.2.3 nAnanoamperes (1 3 109amperes).3.2.4 Pt/Irplatinum and iridium alloy wire used to maketunneling tips.3.2.5 Rasee mean roughness.3.2.6 Rmaxmaximum height difference between the high-est and the lowest p
26、oints on the profile over the length of theprofile (see Calculation Section).3.2.7 root mean square (RMS)see algebraic definition inCalculation Section.3.2.8 Rzthe 10-point mean roughness; that is, the averagedifference in height between the five highest peaks and the fivelowest valleys over the len
27、gth of the profile (see CalculationSection).3.2.9 x-directionsee scan.3.2.10 y-directionthe direction, in the sample plane, overwhich successive scans are taken, orthogonal to the scandirection.3.2.11 z-directionthe direction perpendicular to thesample plane. Also referred to as the feature height d
28、irection.3.2.12 Zisame as feature height (see Calculation Section).3.2.13 Zmaxmaximum height difference over entire sur-face (see Calculation Section).3.2.14 Zrmsroot-mean-square of all surface heights (seeCalculation Section).4. Summary of Test Method4.1 In this test method a sharp, conductive tip
29、is scannedover very closely but not in contact with a conductive surface;that is, they are separated by a gap of several angstroms.Abiasvoltage present between them causes a flow of electronsthrough, rather than over, the energy barrier represented by thistip-surface gap. This flow is referred to as
30、 the tunnelingcurrent. The manner in which the current fluctuates during thescanning process is used to indicate the surfaces topography.Though the tip or sample can be scanned, the method describedhere considers only the tip to be in motion. A more extensivediscussion of the operating principles ca
31、n be found in otherliterature.4.2 In this test method, stainless steel tubing is used as anexample of a component surface. An area of the surface is firstscanned at a width of 500 nA, then 2000 nA. Even though4Binning, G., et al., “Surface Studies by Scanning Tunneling Microscopy,”Physical Review Le
32、tters, Vol 49, No. 1, July 1982, pp. 5761.F 1438 93 (2005)2larger areas can be scanned by most instruments, these mag-nifications are chosen to show surface texture in a size rangebeyond that measured by contact stylus type surface profilinginstruments, but not at an atomic scale. The surface scans
33、arethen compared for damage, artifacts, etc. Numerical analysiscan then proceed using these data for roughness or surface areaor both, following the model of other standards such as ANSIB46.1.5. Significance and Use5.1 The use of STM images and data is for purposes oftextural quality assessment and
34、calculation of figures of merit,and for high purity gas system clean room components.5.2 This test method defines a standard data presentationformat and suggests figures of merit that utilize STMs abilityto analyze three-dimensional surface features.6. Interferences6.1 Some (stainless steel) compone
35、nt surfaces have an oxidelayer that prevents tunneling from occurring under any condi-tions without affecting tip or surface morphology. This resultsin ambiguous surface data. Such surfaces require the use ofother techniques for topographic measurement.6.2 This test method assumes that the images ob
36、tained areunperturbed by very thin, non-solid layers (for example,hydrocarbons, moisture) on the surface.6.3 Operation with the surface in air, vacuum, or under inertliquids is permissible. (The liquids must be suitably inert andfluid, so as to not modify the apparent surface topography orintroduce
37、artifacts into the image.) Water is not recommended.6.4 The tip shall be made from platinum/iridium or tung-sten.NOTE 1Caution: The tip must not have previously touched anysurface (see 11.7).7. Apparatus7.1 Scanning Tunneling Microscope, capable of the follow-ing may be used:7.1.1 Scanning lengths u
38、p to at least 50 m,7.1.2 Substaining 6 3 V between the tip and sample,7.1.3 Monitoring tunneling current as low as 0.05 nA,7.1.4 Traversing feature height variations as great as 2 mwithout touching the tip to the surface, and7.1.5 Providing the surface topography as a shaded heightplot or line plot.
39、7.2 Inert atmospheres, temperature controls, acoustic isola-tion, and vibration isolation are to be provided as necessary toobtain artifact-free images.8. Sampling8.1 Many components are too large or irregularly shaped topermit STM analysis without cutting a sample from thecomponent. Low speed cutti
40、ng, preferably without lubricants,using a diamond blade saw is recommended over high speedabrasive cutting or hacksaws.8.2 This sampling must not modify the surface topography,such as effects due to stress, heat, corrosion, or combinationthereof, from its condition as found in the component.8.3 Clea
41、ning the surface using an inert fluid to removecutting contamination is permitted.9. Calibration9.1 Calibration frequency may vary with different instru-ment manufacturers. It should be performed, at least initially,then yearly, and after any repair or addition to the instrumentshardware and softwar
42、e.9.2 Following the manufacturers recommendations, theSTM will be calibrated using the HOPG, gold ruled grating, orsome other suitable dimensional standard, depending upon thesize range to be used and the accuracy of the standard.10. Conditioning10.1 A conductive path for the sample shall be provide
43、d forvoltage biasing of the sample with respect to the tip.10.2 Mount the sample so the tip will scan an arbitrarilychosen representative area.10.3 Bring the sample and microscope to thermal equilib-rium.11. Procedure11.1 As stated in 1.2.3, this test method does not coversteels that have an oxide l
44、ayer too thick to permit tunnelingunder the test conditions outlined in this test method.11.2 Make sure that a minimum of 200 data points iscollected in the x-direction, and at least 200 scans per raster isin the y-direction (200 3 200 = 40 000 data points).11.3 Initiate tunneling between a Pt/Ir ti
45、p and the sample inaccordance with the manufacturers instructions under condi-tions to provide artifact free images. Suggested starting values:voltage bias of 1800 mV, and current levels monitored at 0.1nA (Standard Test ConditionsRoom temperature and ambi-ent pressure (101.3 kPa, 25 6 2C).11.4 Scan
46、 an area 500-nm across at a rate of approximately2 s/m (or slow enough to prevent the tip from touching thesurface during rastering), collecting at least 200 data pointswith each x-direction scan.11.5 Collect area scans so that comparisons can be madebetween the first two successive rasters. Ensure
47、that the areahas not drifted more than 10 % of the scan width in anydirection. If it has, discontinue scanning for sufficient time toallow thermal equilibrium to be obtained. Determine this byrepeating 11.3 through 11.5.11.6 Scan the selected 500-nm area for at least five full,successive rasters and
48、 then store at least the last (fifth) imageof that scan area. Fig. 1, Fig. 2, and Fig. 3 show an example ofsuch an area after the fifth successive raster (see data presen-tation section for explanation of format shown).11.7 Inconsistent topography from one scan to the next is asign of tip crashing.
49、Fig. 4 shows an example of where the tiptouched the surface during rastering.11.8 Change the scanned width to 2000 nm across, centeredaround the same region, and immediately obtain an image ofthat area. Fig. 5, Fig. 6, and Fig. 7 show an example of a2000-nm wide area.11.9 Observe whether the 2000-nm image shows evidenceof damage from scanning the previous 500-nm (smaller) area.F 1438 93 (2005)3This generally appears as a 500-nm square of very differenttopography or height near the center of the 2000-nm image. Ifthere is such ev
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