1、BSI Standards PublicationBS ISO 14706:2014Surface chemical analysis Determination of surfaceelemental contaminationon silicon wafers by total-reflection X-ray fluorescence(TXRF) spectroscopyBS ISO 14706:2014 BRITISH STANDARDNational forewordThis British Standard is the UK implementation of ISO 14706
2、:2014. Itsupersedes BS ISO 14706:2000 which is withdrawn.The UK participation in its preparation was entrusted to TechnicalCommittee CII/60, Surface chemical analysis.A list of organizations represented on this committee can beobtained on request to its secretary.This publication does not purport to
3、 include all the necessaryprovisions of a contract. Users are responsible for its correctapplication. The British Standards Institution 2014. Published by BSI StandardsLimited 2014ISBN 978 0 580 82725 9ICS 71.040.40Compliance with a British Standard cannot confer immunity fromlegal obligations.This
4、British Standard was published under the authority of theStandards Policy and Strategy Committee on 31 July 2014.Amendments issued since publicationDate Text affectedBS ISO 14706:2014 ISO 2014Surface chemical analysis Determination of surface elemental contamination on silicon wafers by total-reflec
5、tion X-ray fluorescence (TXRF) spectroscopyAnalyse chimique des surfaces Dtermination de la contamination en lments la surface des tranches de silicium par spectroscopie de fluorescence X rflexion totaleINTERNATIONAL STANDARDISO14706Second edition2014-08-01Reference numberISO 14706:2014(E)BS ISO 147
6、06:2014ISO 14706:2014(E)ii ISO 2014 All rights reservedCOPYRIGHT PROTECTED DOCUMENT ISO 2014All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting o
7、n the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below or ISOs member body in the country of the requester.ISO copyright officeCase postale 56 CH-1211 Geneva 20Tel. + 41 22 749 01 11Fax + 41 22 749 09 47E-mail copyrightiso.or
8、gWeb www.iso.orgPublished in SwitzerlandBS ISO 14706:2014ISO 14706:2014(E) ISO 2014 All rights reserved iiiContents PageForeword ivIntroduction v1 Scope . 12 Normative reference . 13 Terms and definitions . 14 Abbreviated terms 25 Principle 26 Apparatus . 37 Environment for specimen preparation and
9、measurement . 38 Calibration reference materials . 39 Safety 410 Measurement procedure 410.1 Preparation for measurement . 410.2 Preparing a calibration curve . 410.3 Measurement of a test specimen . 511 Expression of results 511.1 Method of calculation 511.2 Blank correction 612 Precision . 613 Tes
10、t report . 6Annex A (informative) Reference materials . 8Annex B (informative) Relative sensitivity factor . 9Annex C (informative) Preparation of reference materials6.13Annex D (informative) VPD-TXRF method .16Annex E (informative) Glancing-angle settings 18Annex F (informative) International inter
11、-laboratory test results 22Bibliography .25BS ISO 14706:2014ISO 14706:2014(E)ForewordISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO
12、technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates clo
13、sely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.The procedures used to develop this document and those intended for its further maintenance are described in the ISO/IEC Directives, Part 1. In particular the different approval criteria
14、needed for the different types of ISO documents should be noted. This document was drafted in accordance with the editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives). Attention is drawn to the possibility that some of the elements of this document may be the subject of pat
15、ent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of any patent rights identified during the development of the document will be in the Introduction and/or on the ISO list of patent declarations received (see www.iso.org/patents). Any trade name use
16、d in this document is information given for the convenience of users and does not constitute an endorsement.For an explanation on the meaning of ISO specific terms and expressions related to conformity assessment, as well as information about ISOs adherence to the WTO principles in the Technical Bar
17、riers to Trade (TBT) see the following URL: Foreword - Supplementary informationThe committee responsible for this document is ISO/TC 201, Surface chemical analysis.This second edition cancels and replaces the first edition (ISO 14706:2000), which has been technically revised.iv ISO 2014 All rights
18、reservedBS ISO 14706:2014ISO 14706:2014(E)IntroductionThis International Standard was prepared for the measurement of surface elemental contamination on silicon wafers on the basis of three existing standards: ASTM F 1526, SEMI Standard M33, and a UCS (Ultra-Clean Society) standard published by the
19、Institute of Basic Semiconductor Technology Development.TXRF needs reference materials to perform quantitative analyses. Certified reference materials are not available at low densities of 1010atoms/cm2. Even if they were available, the possibility of contamination from the environment reduces the s
20、helf life of such reference materials.Therefore, the TXRF reference materials are to be prepared and analysed for calibration by each relevant analytical laboratory. Thus, two standards, one for the TXRF measurement procedure and the other for the preparation of reference materials, are necessary. T
21、his International Standard concerns the former part. ISO 2014 All rights reserved vBS ISO 14706:2014BS ISO 14706:2014Surface chemical analysis Determination of surface elemental contamination on silicon wafers by total-reflection X-ray fluorescence (TXRF) spectroscopy1 ScopeThis International Standa
22、rd specifies a TXRF method for the measurement of the atomic surface density of elemental contamination on chemomechanically polished or epitaxial silicon wafer surfaces.The method is applicable to the following: elements of atomic number from 16 (S) to 92 (U); contamination elements with atomic sur
23、face densities from 1 1010atoms/cm2to 1 1014atoms/cm2; contamination elements with atomic surface densities from 5 108atoms/cm2to 5 1012atoms/cm2using a VPD (vapour-phase decomposition) specimen preparation method (see 3.4).2 Normative referenceThe following documents, in whole or in part, are norma
24、tively referenced in this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.ISO 14644-1, Cleanrooms and associated controlled environments
25、Part 1: Classification of air cleanliness3 Terms and definitionsFor the purposes of this document, the following terms and definitions apply.3.1total reflectioncomplete reflection of glancing X-ray radiation into a medium having larger X-ray optical density value at a boundary between two mediaNote
26、1 to entry: The refractive index of silicon for X-rays is less than 1. X-rays which are incident on the surface at a small glancing angle are therefore, totally reflected from the surface at an angle equal to the glancing angle.3.2glancing angleangle between the specimen surface plane and the virtua
27、l plane containing incident X-rays which impinge on the sample surface3.3critical angleglancing angle corresponding to the first point of inflection in the plot of the sample matrix X-ray fluorescence against the glancing angleINTERNATIONAL STANDARD ISO 14706:2014(E) ISO 2014 All rights reserved 1BS
28、 ISO 14706:2014ISO 14706:2014(E)3.4VPD-TXRF methodmethod in which impurities on the surface are collected by the so-called VPD procedure, i.e. the non-volatile products formed by acid decomposition of the oxide at the wafer surface are collected by a droplet of collecting agent, usually ultra-pure h
29、ydrofluoric acid, and dried in a manner which gives the least environmental contamination, the residue from the droplet, subsequently being analysed by TXRF3.5spurious peaksdetected peaks that do not originate from impurities on the silicon waferNote 1 to entry: Spurious peaks are due to fluorescent
30、 X-rays originating from elements in the detector or the X-ray path. The fluorescent X-rays are excited by direct scattering or reflection of incident X-rays. This phenomenon leads to an increase in the measurement error. Spurious peaks seriously affect analytical measurements in the contamination r
31、ange from ca. 1010atoms/cm2to ca. 1011atoms/cm2.4 Abbreviated termsFWHM full width at half maximumRM reference materialSSD solid-state detectorSDD silicon drift detectorTXRF total-reflection X-ray fluorescenceVPD vapour-phase decomposition5 PrincipleWhen a specimen is irradiated with X-rays, fluores
32、cence X-rays at characteristic energies of the elements that constitute the specimen are generated. The intensities of the fluorescence X-rays are proportional to the amounts of each element in the specimen.Total reflection of the incident X-rays on the specimen reduces a penetration depth of the in
33、cident X-rays in the specimen. This allows more selective excitation of the fluorescence X-rays from the surface region, including atoms deposited on the surface of the silicon wafer. Consequently, a spectrum of fluorescence X-rays with a large ratio of signal to background (S/B) and signal to noise
34、 (S/N) can be obtained.The detection limit depends upon the atomic number, the excitation energy, the photon flux, the detector resolution and energy-dependent detection efficiency, the energy bandwidth of the excitation X-rays, the specimen-related shape and statistics of TXRF spectral background,
35、the instrument-related noise magnitude, the integration time, and the accuracy of calibration of the RM and the blank value. For constant instrumental parameters, the interference-free detection limits vary over two orders of magnitude as a function of the atomic number of the analyte element.NOTE T
36、he depth of measurement can vary with the glancing angle, but in the case of film-type contamination it is usually less than 5 nm. The area of measurement consists of a circle of ca. 10 mm in diameter, though it varies depending on the relative position of the X-ray detector and the specimen. In the
37、 case of particulate-type contamination on a clean surface, the yield of fluorescence X-rays varies depending on the sizes, distribution, and constituent elements of the particles.2 ISO 2014 All rights reservedBS ISO 14706:2014ISO 14706:2014(E)6 Apparatus6.1 The apparatus for TXRF shall include at l
38、east the following components: an X-ray source; a monochromator; a specimen stage capable of movement in three orthogonal directions; an X-ray detector (SSD or SDD); and a computerized signal-processing system.6.2 X-rays which have been monochromatized shall be used as the incident X-rays.6.3 The fl
39、uorescence X-ray detector shall have sufficient energy resolution to analyse the Mn-K-LII,IIIline with an FWHM of 200 eV or less.6.4 The specimen stage, which sets the glancing angle, shall be controlled to a reproducibility within 0,17 mrad (0,01) in the range between 0 mrad (0) and 8,7 mrad (0,5).
40、6.5 The atmosphere in the specimen chamber shall be able to be brought to a reduced pressure or replaced with helium gas or nitrogen gas, as required.7 Environment for specimen preparation and measurement7.1 The local environment (i.e. airborne particles, temperature, humidity) for specimen preparat
41、ion and measurement shall be equal to or better than ISO Class 4 in accordance with ISO 14644-1.NOTE The unwanted deposition of airborne particles which are composed of the elements that are being measured will cause an increase in the error of measurement.7.2 The mechanical vibration at the locatio
42、n where the apparatus is installed shall be as small as possible and shall not be greater than 5 103m/s2(0,5 Gal).NOTE The mechanical vibration will degrade the energy resolution of the detection system, which will, in turn, degrade the detection limits and peak deconvolution.8 Calibration reference
43、 materials8.1 Calibration reference materials (RMs) used to establish a reliable calibration procedure shall consist of an RM on which known amounts of impurities have been deposited and a blank RM used to determine the level of contamination of the calibration RM (see Annex A).8.2 The RMs shall be
44、prepared from a chemomechanically polished wafer with a certain quantity of Ni or Fe uniformly deposited on its surface as the RM element. The atomic surface density of the RM element shall be ca. 1 1012atoms/cm2to 1 1013atoms/cm2(see Annex C).8.3 How the RM element is located on the RM surface shal
45、l be verified by an anglescan (see Annex E).8.4 The amount of RM element deposited on the surface of the wafer shall be determined by a reliable quantitative method of analysis.8.5 The blank RM shall be a chemomechanically polished or epitaxial wafer. The magnitude of contamination of the surface re
46、gion of the blank RM shall be below the detection limit for specified elements. The crystallographic orientation of the blank RM shall be the same as that of the RM.8.6 The RM and the blank RM shall be stored in the same container. ISO 2014 All rights reserved 3BS ISO 14706:2014ISO 14706:2014(E)9 Sa
47、fetyThis test method uses X-ray radiation. Consequently, it is absolutely essential to avoid exposing any part of the body to the X-rays produced by the apparatus. It is especially important to keep hands and fingers out of the path of the X-rays and to protect the eyes from scattered secondary X-ra
48、y radiation. Each country has its own safety regulations and requirements concerning X-rays. These shall be observed.10 Measurement procedure10.1 Preparation for measurement10.1.1 All specimens shall be chemomechanically polished or epitaxial wafers.10.1.2 For the VPD-TXRF method, the impurities on
49、the surface are collected by VPD, i.e. acid decomposition in a droplet which is then dried in a manner that produces the least environmental contamination (see Annex D).10.1.3 For a series of measurements, including the calibration measurements, the crystal orientation of the specimen on the specimen stage shall be the same for each specimen.10.1.4 Set the glancing angle at between 25 % and 75 % of the critical angle.NOTE 1 Due to the physical form of particulate-type contamination, an angle that is too low will cause a l
