ASTM_F_576_-_00.pdf

Designation:F 576 00Standard Test Method forMeasurement of Insulator Thickness and Refractive Indexon Silicon Substrates by Ellipsometry1This standard is issued under the fixed designation F 576;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.INTRODUCTIONWhen this test method was developed in the mid-1970s,manual-null ellipsometers,which are thebasis of this test method,were in routine use.More recently,faster,automated instruments havereplaced manual-null ellipsometers for all common use in the semiconductor industry.There are twobasic types of such automated instruments commonly used:the rotating element null ellipsometer andthe rotating element photometric ellipsometer.For each of these,microprocessors or microcomputersare used to operate the instrument and to analyze the data.Details of the procedures utilized in theseinstruments are usually considered to be proprietary by the instrument manufacturers.Despite the fact that this test method is not commonly used in its present form,it embodies all thebasic elements of this test method and a simple analysis of data.Thus,it provides useful guidance inthe fundamentals and application of ellipsometry to film thickness measurements.Until a test method,or test methods,can be developed that cover the newer,automated instruments,this test methodprovides the only such information that is available in a standard test procedure.It also contains resultsof a test of interlaboratory precision on silicon dioxide films from 20 to 280 nm using manual nullellipsometers,and of a test of interlaboratory precision of films of 5 to 550 nm using both manual nullellipsometers as well as automated ellipsometers of both types just mentioned.Two major changes have occurred since this test method was initially adopted.First,referencematerials certified for the thickness of silicon dioxide layers on silicon are available both from theNational Institute of Standards and Technology and from commercial sources.These can be used toevaluate the performance of automated ellipsometers.Second,significantly improved materials andprocedures have been developed for storage of reference wafers needed for long term testing ofbaseline performance of ellipsometers.It is not uncommon for reference wafers simply to be stored“clean”with no further wafer-cleaning utilized.If cleaning steps are in fact,utilized,they are not thosedescribed in this test method.The cleaning steps detailed in this test method are retained,however,toprovide background information on procedures used for the first of the interlaboratory tests.1.Scope1.1 This test method covers the measurement by ellipsom-etry of the thickness and refractive index of an insulator grownor deposited on a silicon substrate.1.2 This test method uses monochromatic light.1.3 This test method is nondestructive and may be used tomeasure the thickness and refractive index of any film notabsorbing light at the measurement wavelength on any sub-strate(1)not transparent to light at the measurement wave-length,and(2)of a material for which both the refractiveindex and the absorption coefficient are known at the measure-ment wavelength.1.4 The precision of this test method is reduced by varia-tions,over regions smaller than the light-beam spot size,insubstrate flatness,insulator thickness,and index of refraction.1.5 Film thickness measurements determined by ellipsometry are not unique.When the film thickness is greater than thatcalculated from the expression Nl/2(n2 sin2f0)1/2,whereN is an integer,l the measurement wavelength,n the index ofrefraction,and f0the angle of incidence,the thickness valuedetermined by this expression must be added to the thicknessvalue determined by ellipsometry to obtain the correct filmthickness.The value of N must be obtained by anotherprocedure.1.6 Two procedures for computing the results are provided.If the graphical procedure is used,the measuring wavelengthshall be either 546.1 or 632.8 nm,and the angle of incidenceshall be 70 6 0.1.1.7 This test method may be used for referee measurements1This test method is under the jurisdiction of ASTM Committee F01 onElectronics and is the direct responsibility of Subcommittee F01.06 on Electricaland Optical Measurements.Current edition approved Dec.10,2000.Published February 2001.Originallypublished as F 576 78.Last previous edition F 576 95.1Copyright ASTM,100 Barr Harbor Drive,West Conshohocken,PA 19428-2959,United States.with computer calculations.1.8 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 hazardst