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Background Statement for SEMI Draft Document 5477D
New Standard: Test Method for Determining B, P, Fe, Al, Ca Contents in Silicon Powder for PV Applications by Inductively-Coupled-Plasma Optical Emission Spectrometry
Notice: This background statement is not part of the balloted item. It is provided solely to assist the recipient in reaching an informed decision based on the rationale of the activity that preceded the creation of this Document.
Notice: Recipients of this Document are invited to submit, with their comments, notification of any relevant patented technology or copyrighted items of which they are aware and to provide supporting documentation. In this context, “patented technology” is defined as technology for which a patent has issued or has been applied for. In the latter case, only publicly available information on the contents of the patent application is to be provided.
Background Statement
Hydrochlorination is a key process for the production of polysilicon. Hydrochlorination uses a mass of silicon powder. The contents ofB, P, Fe, Al,Ca insilicon powder may affect the purity level of produced trichlorosilanesignificantly.Therefore, it is necessary to develop a method to measure the contents ofB, P, Fe, Al, Cain silicon powder.This test method can facilitate a unifying of protocols and test results among worldwide laboratories used for monitoring or qualifying B, P, Fe, Al, Ca in silicon powder.
Review and Adjudication Information
Task Force Review / Committee AdjudicationGroup: / PV Silicon Raw Materials Task Force / China PV Committee
Date: / March 10th, 2015 / March 17th, 2015
Time &Timezone: / 13:30 -15:30 / 09:30 -17:00
Location: / Testing centermeeting room, SINOSICO / Pudong Ballroom 4, Ketty Hotel
Pudong, Shanghai
City, State/Country: / Luoyang, China / Shanghai, China
Leader(s): / Xiaoxia Liu( GCL)
Dongxu Chu(SINOSICO)
Li He (CPVT) / Guangchun Zhang(CanadianSolar)
Jun Liu(CESI)
Standards Staff: / Kris Shen(SEMI China)
/ Kris Shen(SEMI China)
Task force meeting date and time are subject to change, and additional TF review sessions may be scheduled if necessary. Contact the task force leaders or Standards staff for confirmation.
Check for the latest schedule.
If you have any questions, please contact the PV Silicon Raw Materials TF Leader.
Dongxu Chu/SINOSICO
Tel: +86 37968608289
E-mail:
Or contact SEMI Staff, Kris Shen
SEMI Draft Document 5477D
New Standard: Test Method for Determining B, P, Fe, Al, Ca Contents in Silicon Powder for PV Applications by Inductively-Coupled-Plasma Optical Emission Spectrometry
1 Purpose
1.1 Hydrochlorination is a key process for the production of polysilicon. Hydrochlorinationconsumes a large amount of silicon powder. The contents ofB, P, Fe, Al,Ca insilicon powder may affect the purity level of produced trichlorosilanesignificantly.Therefore, it is necessary to develop a method to measure the contents ofB, P, Fe, Al, and Cain silicon powder.
1.2 This test method can facilitate a unifying of protocols and test results among worldwide laboratories used for monitoring or qualifying B, P, Fe, Al, and Cainsilicon powder.
2 Scope
2.1 This Standard specifies a test method fordetermining the B, P, Fe, Al, Cacontents in silicon powder by InductivelyCoupledPlasma Optical Emission Spectrometry.
NOTICE:SEMI Standards and Safety Guidelines do not purport to address all safety issues associated with their use. It is the responsibility of the users of the Documents to establish appropriate safety and health practices, and determine the applicability of regulatory or other limitations prior to use.
3 Limitations
3.1 The element detectionrange of this test methodis shown in Table 1, with reference to SEMI C10.
Table 1Element Detection Range
Element / B / P / Fe / Al / CaMass Percent /% / 0.0005～0.25 / 0.0005～0.50 / 0.02～1.00 / 0.02～0.50 / 0.02～1.00
4 Referenced Standards and Documents
4.1 SEMI Standards and Documents
SEMI C10 — Guide for Determination of Method Detection Limits
SEMI C28–– Specifications for Hydrofluoric Acid
SEMI C35 –– Specifications and Guideline for Nitric Acid
SEMI PV17 — Specification for Virgin Silicon Feedstock Materials for Photovoltaic Applications
SEMI PV49 –– Test Method for the Measurement of Elemental Impurity Concentrations in Silicon Feedstock for Silicon Solar Cells by Bulk Digestion, Inductively Coupled-Plasma Mass Spectrometry
4.2 ASTM Standards[1]
ASTM D1193 — Standard Specification for Reagent Water
ASTM E122 — Standard Practice for Calculating Sample Size to Estimate, With Specified Precision, the Average for a Characteristic of a Lot or Process
4.3 ISO Standard[2]
ISO 5725-2:1994—Accuracy (trueness and precision) of Measurement Methods and Results — Part 2: Basic method for the determination of repeatability and reproducibility of a standard measurement method
NOTICE: Unless otherwise indicated, all documents cited shall be the latest published versions.
5 Terminology
5.1 Abbreviations and Acronyms
5.1.1 ICP-OES —Inductively Coupled Plasma Optical Emission Spectrometer
5.2 Definitions
5.2.1 acid blank—asolution of acid used to establish the background spectrum and trace metal contamination of the acid mixture used in the procedure.
5.2.2 analytical line—theoptical emission line used for analyzing the specimen.
5.2.3 method blank—a solution of acid prepared using the preparation method without a specimen or test sample used to establish the contribution of trace metal contamination from the laboratory environment, reagents or laboratory ware to the background.
5.2.4 silicon powder—siliconsolid materials in accordance to SEMI PV17.
5.2.5 Certified Reference Material (CRM) — reference material, one or more of whose property values are certified by a technically valid procedure, accompanied by or traceable to a certificate or other documentation issued by a certifying body.
6 Summary of Test Method
6.1 Usemannitolto form complex reaction with boronin the sample(the recovery of boron is 90~110%).Remove the silicon matrixwithhydrofluoric acid and nitric acidby smoking reaction.Dissolve the residue with nitric acid solution, and useICP-OESto measure theB, P, Fe, Al, and Cacontents in the preparedsolution.
6.2 Key Points ofTestAccuracyControl
6.2.1 Drop the nitric acidslowly in the processof sampledissolving, and control the reaction rate to avoid boiling; the sample dissolution temperature shall not exceed 140°C, to preventoverevaporation.
6.2.2 Repeat the standard curve before each sample measurement, and ensure the linear correlation coefficient isnoless than 0.9995.
6.2.3 The purity of Argon gas shallbe over than 99.99% (v/v).
6.2.4 Prevent contamination andsamplelossesduring the sample treatment.
6.2.5 Flush the injection pipethoroughly, since there is a memory effect when the boron content is high.
6.2.6 Mannitolhas the best complex reactionwith the boron when the boron content is 0.0005-0.25%(m/m).
6.2.7 The processof sampledissolving shall be carried out in aPTFE (polytetrafluoroethylene) or other hydrofluoric acid corrosion-resistant plastic volumetric flask.
6.2.8 Flasks for differentreagentsor samplesshall not be cross-used; and flasks fordifferent concentration of the samereagent or sample shall not be cross-used. Whenit is necessary, performa blank analysis test.
7 Apparatus
7.1 ICP-OES, and associated equipment and supplies.
7.2 ElectronicBalance with0.1 mg accuracy.
7.3 Platinum crucibleorhydrofluoric acid corrosion-resistant container.
7.4 Electric hot plate,capable oftemperature control, can heat the solution and keepit at 140 ℃.
7.5 Plastic volumetric flask-PTFE (polytetrafluoroethylene) material or other hydrofluoric acid corrosion-resistant material.
8 Reagents and Materials
8.1 Ultra-Pure Water—Unlessotherwise indicated, references to water shall be understood to mean reagent water conforming to specification ASTM D1193.
8.2 Reagents
8.2.1 Mannitol (10g/L), guaranteed reagent grade.
8.2.2 Hydrofluoric acid:in accordance with Grade 2 hydrofluoric acid of SEMI C28.
8.2.3 30% (v/v) nitric acid solution: prepared by nitric acid in accordance with Grade 2 of SEMI C35 and ultra-pure water(¶8.1).
8.2.4 2%(v/v) nitric acid solution: prepared by nitric acid in accordance with Grade 2 of SEMI C35 and ultra-pure water(¶8.1).
8.3 Standard Solution —To the extent available, standards will be used to assess the calibration linearity and elemental recovery efficiency on the ICP-OES.
8.3.1 Boron standard solution, CRM, 1000mg/L
8.3.2 Phosphorus standard solution, CRM, 1000mg/L
8.3.3 Iron standard solution, CRM, 1000mg/L
8.3.4 Aluminumstandard solution, CRM, 100mg/L
8.3.5 Calciumstandard solution, CRM, 100mg/L
9 Sampling
9.1 No general sampling procedure is included as part of this test method, because the most suitable sampling plan will vary considerably depending upon individual conditions.For referee purposes, a sampling plan should be agreed upon before conducting the test. See ASTM E122 for suggested choices of sampling plans.
10 Preparation of Reference Solutions, Test Specimens, and Method Blank Solutions
10.1 Clean all containers, including those used to run the blanks, to avoid erroneous results due to different levels of contamination.
10.2 Preparation of Reference Solutions
10.2.1 Mix the standard solutions(¶8.3) in a set of 100mLPTFE (polytetrafluoroethylene) or other hydrofluoric acid corrosion-resistantplastic volumetric flasks, and dilute with 2% (v/v) nitric acid (¶8.2.4)to a set of appropriate concentrations of reference solutions (the lowest concentration for boron and phosphorus is no less than 0.05μg/mL).
10.3 Preparation of Test Specimens
10.3.1 Separate the silicon powder samplebya standard 0.149mm sieve.
10.3.2 Weigh 0.3000g (accurate to 0.0001g) test sample (¶9.1), then loadthe test sample into a clean platinum crucible or hydrofluoric acid corrosion-resistant container (Do a sample blank at the same time).Add 0.25mL mannitol (¶8.2.1) to the crucible orcontainer.Add 5mL hydrofluoric acid (¶8.2.2), and then slowly drop 5mL 30% (v/v)nitric acid (¶8.2.3) to dissolve the test sample, cover the crucible with a lid.
10.3.3 Heat the sample solution with an electric hot plateat 140℃ to dissolve the test sample completely, open the lid of the crucible, rinse the mist on the lid to the crucible or the container with 30% (v/v) nitric acid (¶8.2.3).Heatthe sample solution to the state of dryness like wet salt and re-dissolvethe sample with 0.5mL hydrofluoric acid (¶8.2.2), then re-heat it to completely dry.
10.3.4 After the evaporation process is completed, add 1.5mL 30% (v/v)nitric acid (¶8.2.3) to dissolve the test sample completely again by heating. Allow the test sample solution to cool down to room temperature,transfer the solution to a 25mLPTFE (polytetrafluoroethylene) or other hydrofluoric acid corrosion-resistant plastic volumetric flask, and dilute with ultra-pure water(¶8.1) to 25mL.
10.4 Preparation of Method Blank Solutions
10.4.1 Prepare a method blank with the elements of interest below the expected detection limits.
10.4.2 Use 2% (v/v) nitric acid (¶8.2.4) as the acid blank solution.
11 Preparation of Apparatus
11.1 Boot in accordancewiththe operating procedure of the ICP-OES.Afterthe instrument is stabilized,edit appropriate detection method corresponding to different detection elements.
11.2 If the instrument uses different spectrometer settings to measure ion counts during the same test process, the measurementaccuracy of each setting relative to the others should be determined based on necessary frequency to guarantee proper performance of the detection system.
11.2.1 Table 2liststhe preferredanalytical linesfor some elements.
Table 2Wavelengths of the PreferredAnalytical Linesfor some Elements
Element / B / P / Fe / Al / CaWavelength/nm / 249.677 / 213.617 / 259.910 / 396.152 / 317.933
12 Procedure
12.1 Preparation of Standard Curves
12.1.1 The number of reference solution series is determined by the experimental precision, usually the number is 3 to 5.
12.1.2 Ensure that the element content in the test specimen is within the range of the working curve and that the linear correlation coefficient of standard curve is at least 0.9995.
12.1.3 Introduce the series ofreferencesolutions to the ICP-OES, input optimal determination conditions and establish thestandard curves.
12.2 Measurement of the Test Specimen
12.2.1 Introduce the method blank solution and the test specimen to the ICP-OES, and then read the measured result.
12.3 After the measurement, flush the piping with 5% (v/v) hydrofluoric acid and nitric acid for 10 minutes, then flushwith ultra-pure waterfor 10 minutes.
12.4 Shut down the ICP-OES.
NOTE 1:If available,use SiliconStandard Reference Materials (Certified Reference Material) to verify the accuracy of the method.
13 Calculations
13.1 Mass fraction of each element in test sample:
%(1)
Where:
w (X) —mass fraction of element in test sample, %;
Cx— mass concentration of element in test sample, μg/mL;
C0— mass concentration ofAcid Blank solution, μg/mL;
m —mass of the sample, g;
V0— volume of sample solution, mL;
R—dilution factor.
14 Report
14.1 Report the arithmetic mean of the parallel determination results for each elementtothree significant digits. The relative deviation of the parallel determination results shall be no more than 10%.
15 Precision
15.1 Repeatability—Onelaboratory repeated this method 43 times, using the same lot for the test sample and under the same conditions. The results obtained were treated statistically in accordance with IS0 5725. The standard deviation of repeatabilityisshown in Table 3:
Table 3Standard Deviation of Repeatability
Element / B / P / Fe / Al / CaSr(% m/m) / 0.0001 / 0.0005 / 0.0259 / 0.0106 / 0.0038
15.2 Reproducibility—A round-robin test of this method was carried out by 4 laboratories, each laboratory respectively determinedthe contents of B, P, Fe, Al, Ca in 7 samples from different producers, and repeated 2-3 times determinations for each sample. The results obtained were treated statistically in accordance with IS0 5725. The standard deviation of reproducibilityis shown in Table 4:
Table 4Standard Deviation of Reproducibility
Element / B / P / Fe / Al / CaSR(% m/m) / 0.0002 / 0.0005 / 0.0279 / 0.0108 / 0.0040
NOTICE:Semiconductor Equipment and Materials International (SEMI) makes no warranties or representations as to the suitability of the Standards and Safety Guidelines set forth herein for any particular application. The determination of the suitability of the Standard or Safety Guideline is solely the responsibility of the user. Users are cautioned to refer to manufacturer’s instructions, product labels, product data sheets, and other relevant literature, respecting any materials or equipment mentioned herein. Standards and Safety Guidelines are subject to change without notice.
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