ASTM_F_1404_-_92_2007.pdf

Designation:F140492(Reapproved 2007)Test Method forCrystallographic Perfection of Gallium Arsenide by MoltenPotassium Hydroxide(KOH)Etch Technique1This standard is issued under the fixed designation F1404;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()indicates an editorial change since the last revision or reapproval.1.Scope1.1 This test method is used to determine whether an ingotor wafer of gallium arsenide is monocrystalline and,if so,tomeasure the etch pit density and to judge the nature of crystalimperfections.To the extent possible,it follows the corre-sponding test method for silicon,Test Method F47.TestMethod F47 also presents the definition of many crystallo-graphic terms,applicable to this test method.1.2 This procedure is suitable for gallium arsenide crystalswith etch pit densities between 0 and 200 000/cm2.1.3 Gallium arsenide,either doped or undoped,and withvarious electrical properties,may be evaluated by this testmethod.The front surface normal direction of the sample mustbe parallel to the within 6 5 and must be suitablyprepared by polishing or etching,or both.Unremoved process-ing damage may lead to etch pits,obscuring the quality of thebulk crystal.1.4 This standard does not purport to address all of thesafety problems,if any,associated with its use.It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and to determine theapplicability of regulatory limitations prior to use.Specifichazard statements are given in Section 8.2.Referenced Documents2.1 ASTM Standards:2D1125 Test Methods for Electrical Conductivity and Resis-tivity of WaterE177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsF26 Test Methods for Determining the Orientation of aSemiconductive Single Crystal(Withdrawn 2003)3F47 Test Method for Crystallographic Perfection of Siliconby Preferential Etch Techniques33.Summary of Test Method3.1 The determination of the etch pit density is onlymeaningful for monocrystalline material.After a mechanical orchemical polish,or both,of the sample surface,the sample isetched in molten KOH.This agent preferentially attacks thegallium arsenide surface in regions of crystal imperfections,such as low angle grain boundaries,twin lamellae,precipitates,slip lines,and dislocations.The etched surface is examinedmicroscopically to characterize these imperfections,and deter-mine their density.3.2 Viewed through an optical microscope,etch pits appearas dark elongated hexagonal pits.The etch pit density(EPD)isdetermined by counting these pits at nine different standardizedlocations across the sample along and directions.A lens micrometer or a grid installed in the microscope is usedto define the sampling area.The reported EPD is obtained byaveraging the EPD values in the nine counted areas.3.2.1 The orientation of the elongated KOH etch pits mayalso be used to determine the crystal orientation prior to theaddition of flats to gallium arsenide(GaAs)wafers or crystals.4.Significance and Use4.1 The use of GaAs for semiconductor devices requires aconsistent atomic lattice structure.However,lattice or crystalline defects of various types and quantities are always present,and rarely homogeneously distributed.It is important todetermine the mean value and the spatial distribution of theetch pit density.5.Characteristics of Revealed Imperfections5.1 The KOH etch of the specimen surface reveals patternsthat are characteristic for several of the crystalline defectsdescribed in detail in Test Method F47.5.1.1 Dislocations on 100 GaAs surfaces are character-ized by microscopic anisotropic six-sided etch pits.The size of1This test method is under the jurisdiction of ASTM Committee F01 onElectronics and is the direct responsibility of Subcommittee F01.15 on CompoundSemiconductors.Current edition approved Dec.1,2007.Published January 2008.Originallyapproved in 1992.Last previous edition approved in 1999 as F1404-92(1999).DOI:10.1520/F1404-92R07.2For referenced ASTM standards,visit the ASTM website,www.astm.org,orcontact ASTM Customer Service at serviceastm.org.For Annual Book of ASTMStandards volume information,refer to the standards Document Summary page onthe ASTM website.3The last approved version of this historical standard is referenced onwww.astm.org.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 the pits depends on the consistency of the etch and the etchingtime and will be typically 25 to 50 m for the proceduredescribed in Section 9.Because the sides of these pits are notnormal to the incident light,they appear dark under verticalfield illumination.The use of a Nomarski microscope isoptional.5.1.2 Lineage,a precursor to a low-angle boundary,appearsas a linear array of etch pits with a density greater th