1、raising standards worldwideNO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAWBSI Standards PublicationBS ISO 14701:2011Surface chemical analysis X-ray photoelectron spectroscopy Measurement of siliconoxide thicknessBS ISO 14701:2011 BRITISH STANDARDNational forewordThis British S
2、tandard is the UK implementation of ISO 14701:2011.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 inclu
3、de all the necessaryprovisions of a contract. Users are responsible for its correctapplication. BSI 2011ISBN 978 0 580 69624 4ICS 71.040.40Compliance with a British Standard cannot confer immunity fromlegal obligations.This British Standard was published under the authority of theStandards Policy an
4、d Strategy Committee on 31 August 2011.Amendments issued since publicationDate Text affectedBS ISO 14701:2011Surface chemical analysis X-ray photoelectron spectroscopy Measurement of silicon oxide thicknessAnalyse chimique des surfaces Spectroscopie de photolectrons par rayons X Mesurage de lpaisseu
5、r doxyde de silicium ISO 2011Reference numberISO 14701:2011(E)First edition2011-08-01ISO14701INTERNATIONAL STANDARDBS ISO 14701:2011ISO 14701:2011(E)COPYRIGHT PROTECTED DOCUMENT ISO 2011All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any
6、form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing 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 4
7、7E-mail copyrightiso.orgWeb www.iso.orgPublished in Switzerlandii ISO 2011 All rights reservedBS ISO 14701:2011ForewordISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is
8、 normally carried out through ISO 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
9、 in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.The main task of technical committees is to prep
10、are International Standards. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote.Attention is drawn to the possibility that so
11、me of the elements of this document may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights.ISO 14701 was prepared by Technical Committee ISO/TC 201, Surface chemical analysis, Subcommittee SC 7, Xray photoelectron spectroscopy.ISO 14701:2
12、011(E) ISO 2011 All rights reserved iiiBS ISO 14701:2011IntroductionThe measurement of the thickness of silicon oxide at the surface of silicon wafers has been conducted in the past by many methods. These generally apply to oxide layers thicker than 20 nm. It is often important to measure thicknesse
13、s in the range below 10 nm, and this International Standard addresses the range below 8 nm using X-ray photoelectron spectroscopy. Problems arise in measuring film thicknesses in this thickness range since, for a layer to bond well to the substrate, it must form strong inter-atomic bonds at the inte
14、rface so that a monolayer or more of layer and substrate interfacial material exists there. This material would not necessarily be a thermodynamically stable bulk material. Additionally, if the layer is reactive, its outer surface might have reacted with the environment and so be changed between fab
15、rication and measurement. For the particular case of silicon dioxide on silicon, at the interface there is approximately a monolayer of sub-oxides and, at the surface, adsorbed materials containing carbon, oxygen and probably hydrogen atoms. These effects lead to offsets for the thicknesses deduced
16、from many methods that, whilst reliably measuring changes in thickness between one specimen and another, have difficulty in defining an absolute thickness.The procedures described in this International Standard provide methods to measure the thickness with high accuracy (optimally 1 %) and also, mor
17、e rapidly and simply, at lower accuracy (optimally 2 %). It could also form a basis for the measurement of many film thicknesses on substrates, but, without considerable further work, the uncertainties will be undefined.ISO 14701:2011(E)iv ISO 2011 All rights reservedBS ISO 14701:2011INTERNATIONAL S
18、TANDARD ISO 14701:2011(E)Surface chemical analysis X-ray photoelectron spectroscopy Measurement of silicon oxide thickness1 ScopeThis International Standard specifies several methods for measuring the oxide thickness at the surfaces of (100) and (111) silicon wafers as an equivalent thickness of sil
19、icon dioxide when measured using X-ray photoelectron spectroscopy. It is only applicable to flat, polished specimens and for instruments that incorporate an Al or Mg X-ray source, a specimen stage that permits defined photoelectron emission angles and a spectrometer with an input lens that can be re
20、stricted to less than a 6 cone semi-angle. For thermal oxides in the range 1 nm to 8 nm thickness, using the best method described in this International Standard, uncertainties, at a 95 % confidence level, could typically be around 2 % and around 1 % at optimum. A simpler method is also given with s
21、lightly poorer, but often adequate, uncertainties.2 Symbols and abbreviations2.1 AbbreviationsHPLC high-purity liquid chromatographyIPA isopropyl alcohol2.2 SymbolsThe term intensity is used below and elsewhere. This refers to a measurement of peak area in the spectrum after relevant background subt
22、raction.nulloxidetotal oxide thicknessnullSi O2thickness contribution to the Si2O peaknullSiOthickness contribution to the SiO peaknullSi O23thickness contribution to the Si2O3peaknullSiO2thickness contribution to the SiO2peaknullSiintensity of the Si contribution to the Si 2p peaknullSi O2intensity
23、 of the Si2O contribution to the Si 2p peaknullSiOintensity of the SiO contribution to the Si 2p peaknullSi O23intensity of the Si2O3contribution to the Si 2p peaknullSiO2intensity of the SiO2contribution to the Si 2p peakLSiattenuation length for Si 2p electrons in Si ISO 2011 All rights reserved 1
24、BS ISO 14701:2011LSi O2attenuation length for Si 2p electrons in Si2OLSiOattenuation length for Si 2p electrons in SiOLSi O23attenuation length for Si 2p electrons in Si2O3LSiO2attenuation length for Si 2p electrons in SiO2nullSi O2intensity normalization parameter for the Si2O contribution to the S
25、i 2p peaknullSiOintensity normalization parameter for the SiO contribution to the Si 2p peaknullSi O23intensity normalization parameter for the Si2O3contribution to the Si 2p peaknullSiO2intensity normalization parameter for the SiO2contribution to the Si 2p peaknullnuncertainty contribution, at a 9
26、5 % confidence level, for the spectrum measurement statisticsnulluncertainty contribution, at a 95 % confidence level, for nullAuncertainty contribution, at a 95 % confidence level, for the analyser electron optics defining the solid angle of acceptancenullEuncertainty contribution, at a 95 % confid
27、ence level, for the validity of the equations for thicknessesnullFuncertainty contribution, at a 95 % confidence level, for peak synthesis without the intermediate oxidesnullLuncertainty contribution, at a 95 % confidence level, for the attenuation length angle of emission of electrons measured from
28、 the surface normal3 Outline of methodHere, the method is outlined so that the detailed procedure, given in Clause 4, can be understood in context. Typical spectra are available in the literature and given later in Figures 3 and 4.The initial step of cleaning the specimens, if necessary, is given in
29、 4.1. In 4.2 and 4.3, the specimens are mounted and suitable spectrometer settings chosen. In 4.4 and 4.5, the procedures for recording the data and measuring the intensities are given. Finally, in 4.6 and 4.7, the oxide thickness and its uncertainty at a confidence level of 95 % are calculated. In
30、4.5 and 4.6, two methods are provided for calculating the oxide thicknesses from the data: a more complex method with better uncertainties and a simpler method with poorer uncertainties. The more complex method might achieve uncertainties as low as 1 %, but the simpler method is restricted to uncert
31、ainties that are greater than 2 %. This greater figure is often adequate for many purposes, however. The sequence of steps is illustrated in the flowchart in Figure 1. It might be useful to refer to this during use of this International Standard.ISO 14701:2011(E)2 ISO 2011 All rights reservedBS ISO
32、14701:2011Figure 1 Flowchart of the measurement process (Y and N at decision points are the usual “yes” and “no”, respectively)Subclause 4.3 requires the angle of emission to be set accurately, and it is often the accuracy of this setting that limits the final accuracy. Users of this procedure will
33、have to ensure that the accuracies of these settings are known in order to evaluate the final uncertainty. The settings can be checked to an adequate level using reflectors mounted on the specimen stage, a laser beam and standard geometrical relationships12.ISO 14701:2011(E) ISO 2011 All rights rese
34、rved 3BS ISO 14701:20114 Method for measuring the oxide thickness4.1 Cleaning and preparing the specimen4.1.1 For cleaning and preparing the specimens, gloves and uncoated stainless-steel tweezers are required. In selecting gloves, care shall be taken to avoid those with talc, silicone compounds or
35、similar contaminants. “Powder-free” gloves have no talc, and fresh polyethylene gloves, or gloves of a higher quality, shall be used in specimen handling. Do not use moulded gloves, for example vinyl, which will probably be covered with highly contaminating release agents. Tweezers that are of uncoa
36、ted stainless steel shall be used.4.1.2 To manipulate specimens, the gloves are used to hold the tweezers and not the specimen. Avoid any wiping materials, sometimes used to handle specimens, as they might result in unwanted contamination of the specimen surface. Unnecessary contact of the specimen
37、with the gloves shall be avoided. Specimen mounts and other materials used to hold specimens shall be cleaned regularly whenever there is a possibility of cross-contamination of specimens. The use of tapes containing silicones and other mobile species shall be avoided.34.1.3 Specimens shall be prepa
38、red and mounted with clean tweezers to ensure that the surface is not altered prior to analysis and that the best possible vacuum conditions are maintained in the analytical chamber. Use the gloves to handle the tweezers to avoid contaminating them or any cleaning equipment with finger grease. Clean
39、 the tweezers by one of the following two methods:a) Immerse the tweezers before use for 16 h in high-purity liquid chromatography (HPLC), or equivalent, grade (99,5 %) isopropyl alcohol (IPA) that leaves no significant residue. Next, remove the liquid, renew the IPA, agitate ultrasonically for 1 mi
40、n, rinse in fresh IPA and remove the excess liquid using a jet of pure, dry argon or another inert gas.b) Boil the tweezers in ultra-high-purity water for 10 min.Grip the specimen at the edge only, in a region that will not be analysed. Avoid breathing or speaking over the specimen. Keep these tweez
41、ers in a clean, glass container for future use. Tools shall not unnecessarily touch the specimen surface to be analysed.4.1.4 Inspect the specimens for any scratches, blemishes or marks on the polished surfaces. Finger marks should not be present but, if they are, may be removed as described in 4.1.
42、6. Note the condition of the surface. It should be featureless. Identify the side of the specimen for analysis. This is usually the polished side. If the unpolished side is to be analysed, this International Standard is not applicable. If the specimen is too large for insertion into the instrument,
43、a smaller portion will need to be cut from it. To do this, material with a (100)-orientated surface may be cut to form a suitably sized rectangular portion by cleavage along (111) planes. In this way, a square of side 10 mm, bounded by directions, may be conveniently produced. For those specimens wi
44、th a (111)-orientated surface, a similar cleaving along (111) planes forms equilateral triangles, also bounded by directions. Triangle sides of length 15 mm are convenient. The scribing for cleaving often leaves very small fragments of Si on the specimens. These fragments shall, as far as possible,
45、be removed. The cleaning procedure described in 4.1.6 is often found sufficient for this purpose.NOTE The directions are usually indicated by flats cut into the sides of (100)- and (111)-orientated wafers.4.1.5 Analyses show that wafers and many other materials such as metals accumulate organics, hy
46、drocarbons, silanes and phthalates from the environment. During storage of wafers, the thickness of these adsorbed layers increases to around 0,35 nm on the polished surface in normal, uncirculated laboratory air after 100 days, but is kept below 0,2 nm if a wafer container is used that has been kep
47、t closed and has not been exposed to excessive heat4(i.e. has been kept below 35 C). In either case, the specimens should be analysed without cleaning. If, however, there is evidence that they have been contaminated by organic contaminants (e.g. finger grease) or the specimens have been cut to reduc
48、e their size, the contamination can be reduced to a thickness of about 0,14 nm by cleaning as described in 4.1.6.4.1.6 If the specimens require cleaning, immerse them in a cleaned glass container in HPLC (or equivalent) quality (99,5 %) isopropyl alcohol (IPA) for 16 h (e.g. overnight). The top of t
49、he test tube can be conveniently ISO 14701:2011(E)4 ISO 2011 All rights reservedBS ISO 14701:2011closed by a piece of clean aluminium foil. Next, remove the liquid, renew the IPA, agitate ultrasonically for 1 min, rinse in fresh IPA and remove the excess liquid using a jet of pure (99,9 % purity), dry (0,01 % water) argon or an equivalent rare gas. If IPA is not available, HPLC-quality chloroform or dichloromethane may be used. The specimens are now ready for analysis.NOTE The procedure using 16 h immersion in solvent leaves
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