ASTM_F_1708_-_96.pdf

Designation:F 1708 96Standard Practice forEvaluation of Granular Polysilicon by Melter-ZonerSpectroscopies1This standard is issued under the fixed designation F 1708;the number immediately following the designation indicates the year oforiginal 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.1.Scope1.1 This practice describes a procedure to consolidategranular polysilicon into a solid rod and then to convert thepolysilicon rod into a single crystal by a float-zone technique.The resultant single crystal ingot is used for the determinationof trace impurities in the polysilicon.These impurities areacceptor and donor components(usually boron,aluminum,phosphorus,arsenic,and antimony)as well as substitutionalcarbon.1.2 The useful range of impurity concentration covered bythis practice is 0.002 to 100 parts per billion atomic(ppba)foracceptor and donor impurities,and 0.03 to 5 parts per millionatomic(ppma)for carbon.The acceptor and donor impuritiesare analyzed in a slice taken from the single crystal ingot byphotoluminescence or infrared spectroscopies.The carbonimpurity is determined by analysis of a slice by infraredspectroscopy.1.3 This practice is applicable only to evaluation of poly-silicon granules as produced by thermal deposition of silane,orone of the chlorosilanes,onto high purity seeds of polysiliconin a continuous fluid bed reactor.The granules are nearspherical in shape and range in size from 200 to 2500 m witha mean size of about 900 m.1.4 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 safety and health practices and determine the applica-bility of regulatory limitations prior to use.Specific hazardstatements are given in Section 9 and in 12.1.1.2.Referenced Documents2.1 ASTM Standards:D 5127 Guide for Electronic Grade Water2F 1241 Terminology of Silicon Technology3F 1389 Test Methods for Photoluminescence Analysis ofSingle Crystal Silicon for III-V Impurities3F 1391 Test Method for SubstitutionalAtomic Carbon Con-tent of Silicon by Infrared Absorption3F 1630 Test Method for Low Temperature FT-IR Analysisof Single Crystal Silicon for III-V Impurities32.2SEMI Standards:Specification for Gases4Specification for Process Chemicals43.Terminology3.1 Most terms used in this practice are defined in Termi-nology F 1241.3.2 Definitions of Terms Specific to This Practice:3.2.1 granular polysilicon,nnearly spherical,granules(200 to 2500 m)of polysilicon as produced in a fluidized bedreactor.3.2.2 melter/zoner,nan apparatus designed to melt granu-lar polysilicon to a solid rod and then convert the polycrystal-line rod to a single crystal ingot by an rf coupled coil.3.2.3 PTFEan acronym for polytetrafluoroethylene,achemically resistant polymer.3.2.4 silicon pedestal,na piece of single crystal siliconcut from a high purity silicon ingot.4.Summary of Practices4.1 Granular polysilicon is converted into a single crystalsilicon rod in a two-step procedure.4.1.1 First,the silicon granules are consolidated into apolysilicon rod by melting fluidized granules into the molten(bottom)end of a silicon pedestal during a downward pass ofthe coil of the zone furnace.After about 12 g of polysilicon hasbeen melted and cooled in the zone process,a polysilicon rodabout 0.9 by 6 cm is obtained.4.1.2 In the second step,a single crystal silicon seed ismelted into the tail end of the polycrystalline rod and a singlezone pass is done in the upward direction to level the impuritiesand to convert the silicon to a single crystal rod.This producesa single crystal silicon ingot about 0.9 cm in diameter by 5 cmin length from which a section is sliced for measurement ofimpurities.The entire consolidation and zoning requires about30 min to accomplish.4.1.3 A slice of 2 to 4-mm thick is taken from the centerone-third of the single crystal silicon ingot for measurement ofimpurities by infrared or photoluminescence spectroscopies.1This practice is under the jurisdiction of ASTM Committee F-1 on Electronicsand is the direct responsibility of Subcommittee F01.06 on Silicon Materials andProcess Control.Current edition approved June 10,1996.Published August 1996.2Annual Book of ASTM Standards,Vol 11.01.3Annual Book of ASTM Standards,Vol 10.05.4Available from Semiconductor Equipment and Materials International,805 E.Middlefield Rd.,Mountain View,CA 94043.1AMERICAN SOCIETY FOR TESTING AND MATERIALS100 Barr Harbor Dr.,West Conshohocken,PA 19428Reprinted from the Annual Book of ASTM Standards.Copyright ASTM5.Significance and Use5.1 Polycrystalline silicon is used as the starting material forgrowth of large single crystal ingots by the Czochralskimethods.This procedure provides a means to determine theimpurity levels in granular polysilicon to be used for crystal