SEMASPEC Test Method for Auger Electron Spectroscopy … · SEMASPEC Test Method for Auger Electron Spectroscopy (AES) Analysis of Surface and Oxide Composition of Electropolished

SEMATECHTechnology Transfer 91060573B-STD

SEMASPEC Test Method for AugerElectron Spectroscopy (AES)

Analysis of Surface and OxideComposition of Electropolished

Stainless Steel Tubing for GasDistribution System Components

© 1996 SEMATECH, Inc.

SEMATECH and the SEMATECH logo are registered service marks of SEMATECH, Inc.

SEMASPEC Test Method for Auger Electron Spectroscopy (AES)Analysis of Surface and Oxide Composition of Electropolished

Stainless Steel Tubing for Gas Distribution System ComponentsTechnology Transfer # 91060573B-STD

SEMATECHFebruary 22, 1993

Abstract: This SEMASPEC defines a method of testing the interior surface of chromium enhanced stainlesssteel tubing, fittings, and valves to determine the surface composition and chemistry and therebymeasure the effectiveness of electropolishing. The purpose of this procedure is to evaluatecomponents considered for use in ultra-high purity gas distribution systems. Application of this testmethod is expected to yield comparable data among components tested for the purposes ofqualification for installation. The purpose of this SEMASPEC is to provide a document thatmember companies can use to correlate Research Triangle Institute (RTI) test data with the testmethod that was used. This document is in development as an industry standard by SemiconductorEquipment and Materials International (SEMI). When available, adherence to the SEMI standardis recommended.

Keywords: Stainless Steel Tubing, AES, Surface Composition, Defect Sources, Facilities, Gas DistributionSystems, Specifications, Components, Component Testing

Authors: Jeff Riddle

Approvals: Jeff Riddle , Project ManagerVenu Menon , Program ManagerJackie Marsh, Director of Standards ProgramGene Feit, Director, Contamination Free ManufacturingJohn Pankratz, Director, Technology TransferJeanne Cranford, Technical Information Transfer Team Leader

Technology Transfer # 91060573B-STD SEMATECH

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SEMASPEC #91060573B-STD

SEMASPEC Test Method for Auger Electron Spectroscopy (AES) Analysis ofSurface and Oxide Composition of Electropolished Stainless Steel Tubing for GasDistribution System Components

1. Introduction

Semiconductor cleanrooms are serviced by high-purity gas distribution systems. This documentpresents a test method that may be applied for the evaluation of one or more componentsconsidered for use in such systems.

1.1 Purpose

1.1.1 The purpose of this document is to define a method for testing components being considered forinstallation into a high-purity gas distribution system. Application of this test method isexpected to yield comparable data among components tested for the purposes of qualification forthis installation.

1.1.2 This document defines a method of testing the interior surface of chromium enhanced stainlesssteel tubing, fittings, and valves to determine the surface composition and chemistry and therebymeasure the effectiveness of electropolishing.

1.1.3 The objective of this method is to describe a general set of instrument parameters and conditionsthat will achieve precise and reproducible measurements of important surface chemistry withinthe chromium-enriched oxide layer.

1.2 Scope

1.2.1 This document describes a test method to characterize "as-received" surface composition, andoxide composition and thickness encompassing all interior chromium enhanced stainless steelsurfaces on tubing, connectors, regulators, and valves of all sizes.

1.2.2 This procedure describes measurement of surface composition of the outer "as-received surfaceand a depth composition profile for C, O, Cr, Fe, and Ni in the outer 150 Å of the near surfaceoxide film. These measurements quantify the maximum Cr/Fe elemental ratio in theelectropolished oxide film and establish a figure of merit oxide film thickness in theelectropolished surface. This method also describes the measurement of elemental surfacecomposition including P, S, Si, and surface-adsorbed carbon.

1.2.3 This method includes 1) an initial survey scan at the "as-received surface" to determinecomposition, 2) a compositional depth profile to determine elemental distribution and thicknessof the oxide layer, and 3) a survey scan at the end of the profile to determine composition of thebulk material (150 Å).

1.3 Limitations

1.3.1 This methodology assumes an AES analyst with skill level typically achieved over a twelve-month period and familiarity with the AES technique and instrumentation.

1.3.2 The accuracy and precision of all measurements described in this method require that theinstrument be calibrated and maintained to all manufacturer's specifications. In addition,sensitivity factors for all pertinent elements must be determined from appropriate referencestandards to ensure accuracy and reproducibility of composition data. Calibration proceduresare described in detail in Annex A1.

1.3.3 The methodology and instrumentation described in this procedure are not intended to precludethe use of any particular brand or model of surface analysis equipment. While most of the test

SEMATECH Technology Transfer # 91060573B-STD

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methodology has been developed using specific instrumentation, the method can be adapted tomost state-of-the-art surface analytical instrumentation.

2. Reference Documents

2.1 ASTM E 1078–851 Standard Guide for Specimen Handling in Auger Electron SpectroscopyX-Ray Photoelectron Spectroscopy and Secondary Ion Mass Spectrometry.1985.

2.2 Briggs, D. and M.P. Seah, ed. Practical Surface Analysis: by Auger and X-Ray Photo–ElectronSpectroscopy. John Wiley and Sons, 1983.

2.3 Palmberg, P.W., et.al. Handbook of Auger Electron Spectroscopy: A reference book of standarddata for identification and interpretation of Auger electron spectroscopy data. PhysicalElectronics Industries, Inc. Second Edition. 1983.

3. Terminology

3.1 AES—auger electron spectroscopy.

3.2 electron escape depth—the depth in a surface from which the electron can escape.

3.3 ion sputtering—removing material from a surface by bombardment with ions.

3.4 SAM—scanning auger microscope.

3.5 CMA—cylindrical mirror analyzer.

3.6 standard conditions—101.3 kPa, 0.0 °C (14.73 psia, 32.0 °F).

4. Test Protocol

4.1 Test Conditions—The etch rate calibration is to be done on a weekly basis or prior to analysis oftest specimens. Typical etch rate standards include materials such as 1000Å (electrolyticallygrown) Ta2O5 on Ta or 1000 Å SiO2 thermal oxide on silicon. Calibration of appropriatesensitivity factors for estimating surface composition using survey or depth profilemeasurements are described in Annex A1. The etch rates measured with Ta2O5 or SiO2 provideonly relative calibration of the sputter rate.

4.1.1 Precautions

4.1.1.1 This test method may involve hazardous materials, operations, and equipment. This test methoddoes not purport to address the safety considerations associated with its use. It is theresponsibility of the user to establish appropriate safety and health practices and determine theapplicability of regulatory limitations before using this method.

4.1.1.2 All normal and acceptable precautions regarding the use of high voltage, vacuum, and X-rayproducing equipment should be observed.

4.1.2 Sample preparation

4.1.2.1 The samples should be prepared and mounted for analysis using standard practices consistentwith high vacuum surface analytical procedures. Samples should be cut down to ~1 cm squareusing a clean, dry hack saw or low speed band saw. Any mechanical cutting must not introduceorganic or inorganic contamination onto the sample surface.

1 American Society for Testing and Materials, 1916 Race St., Philadelphia, PA 19103.


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4.1.2.2 Sample preparation shall be done in a manner that avoids excessive heating; i.e., the surfacetemperature should remain at or below 50 °C, so as to avoid artifactual growth of the oxidethickness or change in surface composition.

4.1.2.3 Unless specifically requested, such as when only chromium and iron will be analyzed, thesample surface is not to be cleaned with organic solvent or with water. Residual particles fromthe cutting process will be removed aerodynamically by chemically inert particle-free flow suchas dry nitrogen.

4.1.2.4 Mounting of the samples onto AES-compatible mounts shall be done in a manner consistentwith high vacuum practices to avoid contamination of the surface to be analyzed.

4.2 Apparatus

4.2.1 Materials—See Annex A1 for etch rate and sensitivity factor calibration standards.

4.2.2 Instrumentation

4.2.2.1 Auger spectrometer—A scanning Auger spectrometer (SAM) is typically used for thesemeasurements, although static beam instruments can also be used. The spectrometer must beequipped with an ion gun and must use a high purity argon or xenon gas for sputter etching. Adifferentially pumped ion gun is recommended but not required. The Auger instrument may usea hemispherical or cylindrical mirror analyzer (CMA).

4.2.2.2 Instruments shall be calibrated and maintained using standard laboratory practices andmanufacturers' recommendations. The etch rate and sensitivity factor calibration data are to berecorded and documented in a logbook.


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4.3 Test Procedures

4.3.1 (Summary) The test methodology comprises an initial survey scan of the "as received" surface todetermine overall composition, followed by a depth profile to determine the relative abundanceof C, O, Cr, Fe, and Ni within the outer 150 Å, followed by a 0 to 2000 eV survey scan todetermine "bulk" composition at the end of the profile (150 Å).

4.3.2 Place the sample into the instrument. Pump down to acceptable vacuum levels consistent withmanufacturer's recommendations. The surface area to be analyzed should be free of visibleparticles and should be an area representative of the overall surface.

4.3.3 Acquire a "survey scan," a 0 to 2000 eV spectrum for quantifying the composition of the as-received surface.

4.3.4 Acquire a depth composition profile of the outer 150 Å to determine the relative abundances ofC, O, Cr, Fe, and Ni, as described in Sections 4.3.4 through 4.3.5.

4.3.4.1 The depth composition profile can be acquired in a "continuous" etch/data acquisition mode oralternating etch/data acquisition mode. In either case, measurements for each element should bemade at a frequency of at least one data point every 5 Å within the first 50 Å, and one data pointeach 10 Å from a depth of 50 Å to 150 Å. A depth profile obtained in this mode is acquired intwo sections. The first section of the profile is typically measured at an etch rate of 10 Å perminute for the first 5 minutes, to maximize sensitivity to elemental composition changes withinthe outer 50 Å. In the second section, data can be collected at roughly 20 Å per minute for 5minutes, to a total depth of approximately 150 Å.

4.3.4.2 Scan times are one to three sweeps per element (acquisition time of 5 to 10 seconds) in narrowwindows around the dN(E)/dE peaks. Each spectral window should have at least ten data points,with eV/step adjusted to optimize resolution and signal to noise ratio.

4.3.5 Following the depth profile, measure a survey scan from 0 to 2000 eV, using conditions similarto those described in 4.3.3 above (or adjusted for the particular AES instrument used), todetermine the relative elemental compositions in the bulk (150 Å) of the material.

4.4 Data Analysis

4.4.1 Survey data—The 0 to 2000 eV survey data acquired at the "as-received" and 150 Å depths aredisplayed as the first derivative of the N(E) signal (number of counts) versus energy. A typical 0to 2000 eV dN(E)/dE AES survey scan (at a depth of 150 Å to show the Cr, Fe, and Ni peakswith greater clarity) is shown in Figure 1. Quantitation of composition (for elements heavierthan helium) is facilitated using peak-to-peak measurements of the dN(E)/dE signal corrected bysensitivity factors as determined from reference standards. [Note: Quantification of survey datameasured in the N(E) mode would follow analogous procedures; i.e., the area under the curvewould be measured and corrected using sensitivity factors determined for that instrument.]

4.4.2 Profile data—The depth profile data are typically displayed in two methods. First, theuncorrected signal intensity of each element (y–axis) is plotted as a function of depth (x–axis).Second, an atomic composition plot (ACP) is calculated by adjusting the uncorrected signalintensities for the appropriate sensitivity factor and number of sweeps, which yields the relativeatomic composition at each data point. The relative elemental abundance of C, O, Cr, Fe, and Niis then plotted (y–axis) as a function of depth (x–axis) percentage, to yield the atomiccomposition depth profile. All oxide thicknesses estimated from this procedure are expressed asSiO2 and/or Ta2O5 ion etch equivalents. A representative AES profile of the outer 150 Å isshown in Figure 2.


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4.4.3 The thickness of the chromium enriched oxide layer is estimated from the depth profile data asthe depth at which the oxygen signal decreases to one half of the maximum peak height. Thedepth profile spectra should be clearly marked to show how the oxide thickness was estimated.

4.4.4 The maximum Cr/Fe ratio within the chromium enriched oxide layer, as determined from theatomic composition depth profile, is also an important figure of merit. As in Section 4.4.3above, the profile spectra should clearly be marked to indicate the value and depth of maximumelemental Cr/Fe ratio.

4.4.5 Data presentation—The key measurements from this procedure are 1) determination of the as-received surface composition, 2) acquisition of a depth composition profile showing the depthand value of the maximum Cr/Fe ratio in the oxide layer and the thickness of the oxide layer,and 3) determination of the surface composition at the end of the profile (150 Å).

4.4.5.1 All hard copy reports must clearly show sample identification, outline experimental details,describe all spectral labelling, and include all pertinent numerical results in tables. Figuresshould be mounted with captions, and worksheets or appendices that explain how any and allvalues were calculated should be included. All reports must indicate who actually did theanalyses and when and must include those signatures within the text. It is also recommendedthat each report include a table that describes the exact instrument model used and records allexperimental parameters, i.e., beam voltage, magnification, raster size, sample angle, ion etchgas, beam acceleration, ion etch rate, and all pertinent sensitivity factors, calibration, andcalculations.

4.4.6 Accuracy and precision of results—For results to be comparable between and among equipmentof different manufacturers, it is important to thoroughly describe the key data acquisitionconditions including sample geometry with respect to the electron beam and analyzer andmagnification (which, combined with sample angle, describes the dimensions of the areaanalyzed). Use standard reference materials for calibration. Document all calibration results ina log book.

4.4.7 The use of the AVS AES/XPS Contributors Form (Abbreviated Version), reproduced inAppendix X1 is optional.


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5. Illustrations

Figure 1 Auger Survey


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Figure 2 Auger Profile

8 ANNEX(Mandatory Information)


A1. Reference Standards for Calibration of AES Spectrometers

A1.1 Purpose—This section describes sample materials and procedures for ensuring that compositionmeasurements from auger electron microscopy (AES), especially Cr, Fe, and Ni, are as accurate andprecise as possible.

A1.2 In addition to the sensitivity factors typically supplied with the instrument by the manufacturer,sensitivity factors for chromium (Cr), iron (Fe), and nickel (Ni) should be determined using aNational Institute of Standards and Technology (NIST, formerly NBS) traceable type 316stainless steel standard.

The above standard should be polished, cleaned, and lightly ion etched (~ 50 Å) to removesurface adsorbed hydrocarbons and the native oxide film. Survey scan and/or multiplexmeasurements should be acquired on the appropriate spectral lines to establish sensitivity factorsthat result in the proper stoichiometric ratios for the standard's composition as supplied in thestandard's certification.

A1.3 The AES spectrometer must be calibrated for ion etch rate using either a thermal oxide film ofSiO2 on a silicon wafer and/or Ta2O5 electrolytically grown on Ta metal. These films aretypically 1000 Å thick and can be obtained from several sources, typically suppliers of SEMcalibration standards.

A1.4 Where AES determination of surface composition is determined from survey scanmeasurements, the data typically are displayed as the first derivative of the N(E) data (number ofcounts versus energy), dN(E)/dE. Quantification of composition (relative elemental percentagewithin the escape depth) is facilitated using peak-to-peak heights of the dN(E)/dE signalcorrected by sensitivity factors.

These sensitivity factors are typically supplied by the instrument manufacturer and areapplicable to a specific model. However, in order to produce composition data which areaccurate and reproducible, standard reference materials should be analyzed to establishsensitivity factors that yield stoichiometrically correct ratios for metal alloy compounds. Thesestandards include, but are not limited to, sputtered transition metal alloys of Cr, Fe, Co, and Ni,which have had the composition determined. These standards should be lightly ion etched priorto analysis to remove any surface adsorbed carbon or metal oxidation. Care should be taken notto etch too deeply as differential sputter yields will alter the alloy ratio of the deposited films.

APPENDIX(Optional Information)


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X1. AVS AES/XPS Contributors Form for Reporting Test Results

X1.1 The AES/XPS Contributors Form (Abbreviated Version) by the Database Committee of theAmerican Vacuum Society (Editors: Charles E. Bryson III and Gary E. McGuire) may be usedto report test results. The original purpose of this form is to provide a standard form forsubmitting AES/XPS data records to Surface Science Spectra, an international journalelectronically archiving surface science spectra of technological and scientific interest anddistributing hard copies of selected surface spectroscopy data files quarterly. The goal of theform is to adequately describe the conditions under which the reported spectra were collected sothat others can repeat them from the information provided on the form alone. Because of itsthoroughness and the desire to promote uniform reporting of results, the major sections of thisform are recommended as the format for reporting the test results of this test method. (SectionsA & G of the AVS Contributors Form are not deemed necessary for reporting test results and areomitted.)

X1.2 The form lists five levels of entries keyed as follows:

Level 1: Mandatory entry - An entry must be made, even if the only valid entry is N/A(not applicable). The absence of an entry is not equivalent to entering zero, none, orN/A.

Level 2: Mandatory entry - An entry must be made unless there are specialconsiderations. Failure to make an entry would be acceptable only if the data recordwere of such unusual technical importance that it should be archived, even in the absenceof some data entries at this level. All entries in the form at this level are usually requiredto establish the utility or significance of a data record.

Level 3: Recommended entry - An entry, though not required, is important to readerswho wish to have a complete interpretation of the data record.

Level 4: Recommended entry - An entry allows the most critical uses of the data record.

Level 5: Optional entry - An entry should be made at the author’s discretion (e.g., seeField 16, Section B).

All level 1 and 2 entries should be completed in reporting the test method results. Level 3-5entries are optional.

X1.3 Figure X1.1 reproduces the sheets of the AVS AES/XPS Contributors Form (AbbreviatedVersion) recommended for reporting the test results of this test method.

10 APPENDIX(Optional Information)


Figure X1.1 AVS AES/XPS Contributors Form (Page 1 of 19)



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NOTICE: SEMATECH DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED,INCLUDING THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FORA PARTICULAR PURPOSE. SEMATECH MAKES NO WARRANTIES AS TO THESUITABILITY OF THIS METHOD FOR ANY PARTICULAR APPLICATION. THEDETERMINATION OF THE SUITABILITY OF THIS METHOD IS SOLELY THERESPONSIBILITY OF THE USER.

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