ASTM_F_391_-_96.pdf

Designation:F 391 96Standard Test Methods forMinority Carrier Diffusion Length in ExtrinsicSemiconductors by Measurement of Steady-State SurfacePhotovoltage1This standard is issued under the fixed designation F 391;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 These test methods cover the measurement of minoritycarrier diffusion lengths in specimens of extrinsic single-crystalsemiconducting materials or in homoepitaxial layers of knownresistivity deposited on more heavily doped substrates of thesame type,provided that the thickness of the specimen or layeris greater than four times the diffusion length.1.2 These test methods are based on the measurement ofsurface photovoltage(SPV)as a function of energy(wave-length)of the incident illumination.The following two testmethods are described:1.2.1 Test Method AConstant magnitude surface photo-voltage(CMSPV)method.1.2.2 Test Method BLinear photovoltage,constant photonflux(LPVCPF)method.1.3 Both test methods are nondestructive.1.4 The limits of applicability with respect to specimenmaterial,resistivity,and carrier lifetime have not been deter-mined;however,measurements have been made on 0.1 to 50Vcm n-and p-type silicon specimens with carrier lifetimes asshort as 2 ns.1.5 These test methods were developed for use on singlecrystal specimens of silicon.They may also be used to measurean effective diffusion length in specimens of other semicon-ductors such as gallium arsenide(with suitable adjustment ofthe wavelength(energy)range of the illumination and speci-men preparation procedures)and an average effective diffusionlength in specimens of polysilicon in which the grain bound-aries are normal to the surface.1.6 These test methods also have been applied to thedetermination of the width of the denuded zone in siliconwafers.1.7 These test methods measure diffusion lengths at roomtemperature(22C)only.Lifetime and diffusion length are afunction of temperature.1.8This 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.2.Referenced Documents2.1 ASTM Standards:D 1193 Specification for Reagent Water2F 28 Test Method for Minority-Carrier Lifetime in BulkGermanium and Silicon by Measurement of Photoconduc-tivity Decay3F 84 Test Methods for Measuring Resistivity of SiliconWafer with an In-Line Four-Point Probe3F 95 Test Method for Thickness of Lightly Doped SiliconEpitaxial Layers on Heavily Doped Silicon SubstratesUsing an Infrared Dispersive Spectrophotometer3F 110 Test Method for Thickness of Epitaxial or DiffusedLayers in Silicon by the Angle Lapping and StainingTechnique3F 533 Test Method for Thickness and Thickness Variationof Silicon Slices3F 673 Test Methods for Measuring Resistivity of Semicon-ductor Slices or Sheet Resistance of Semiconductor Filmswith a Noncontact Eddy-Current Gage32.2SEMI Standards:C 1 Specification for Reagents4C 2 Specifications for Etchants43.Summary of Test Method3.1 Test Method AThe specimen surface is illuminatedwith chopped monochromatic radiation of energy slightlygreater than the band gap of the semiconductor sample.Electron-hole pairs are produced and diffuse to the surface ofthe specimen where they are separated by the electric field ofa depletion region to produce the SPV.The depletion regioncan be created by surface states,surface barrier,p-n junction,or liquid junction.The SPV signal is capacitively or directlycoupled into a lock-in amplifier for amplification and measure-ment.The photon intensity is adjusted to produce the same1This test method is under the jurisdiction of ASTM Committee F-1 onElectronics and is the direct responsibility of Subcommittee F01.06 on SiliconMaterials and Process Control.Current edition approved Feb.10,1996.Published April 1996.Originallypublished as F 391 73 T.Last previous edition F 391 90a.2Annual Book of ASTM Standards,Vol 11.01.3Annual Book of ASTM Standards,Vol 10.05.4Available from Semiconductor Equipment and Materials International,805East Middlefield Road,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 ASTMvalue of SPV for all energies of the illuminating radiation.Thephoton intensity at each selected energy is plotted against thereciprocal absorption coefficient for the energy.The resultantlinear plot is extrapolated to zero intensity;the(negative)intercept value is the effective diffusion length.By usingfeedback from the detector to the light source,and a steppingmotor for the monochromator,the procedu