ECE Semiconductor Device and Material Characterization

Transcription

1 ECE 483 Semiconuctor Device an Material Characterization Dr. Alan Doolittle School of Electrical an Computer Engineering Georgia Institute of Technology As with all of these lecture slies, I am inebte to Dr. Dieter Schroer from Arizona State University for his generous contributions an freely given resources. Most of (>80%) the figures/slies in this lecture came from Dieter. Some of these figures are copyrighte an can be foun within the class text, Semiconuctor Device an Materials Characterization. Every serious microelectronics stuent shoul have a copy of this book! ECE 483 Dr. Alan Doolittle

2 Optical Characterization Optical Microscopy Ellipsometry Transmission Reflection Photoluminescence ECE 483 Dr. Alan Doolittle

3 Optical Excitation Emission Photoluminescence Raman Spectroscopy UV Photoelectron Spectroscopy hν Reflection Optical Microscopy Ellipsometry Reflection Spectroscopy Absorption Photoconuctance Photoelectron Spectroscopy Transmission Absorption Coefficient Infrare Spectroscopy ECE 483 Dr. Alan Doolittle

4 Optical Characterization Photometric Measurements Amplitue of reflecte or transmitte light Optical constants, absorption coefficients ECE 483 Dr. Alan Doolittle

5 Optical Characterization Interference Measurements Phase of reflecte or transmitte light Film thickness, surface structure Two emerging light beams are phase shifte Constructive an estructive interference ' n sinφ n0 sinφ λ n n0 sin φ λ n 0 n φ φ' φ Phase Shift ECE 483 Dr. Alan Doolittle

6 Interference Amplitue 0 Destructive Interference A B C Amplitue 0 Constructive Interference A B C ωt ωt Eye Oxie thickness variations ECE 483 Dr. Alan Doolittle

7 Interference Blue Morpho butterfly gets its bright blue color from interference effects Interference ue to microscopic riges on the wings ECE 483 Dr. Alan Doolittle

8 Optical Characterization Polarization Measurements Ellipticity of reflecte light Optical constants, film thickness, surface structure Polarizer polarizes the light into particular orientation H-sheet; most popular linear polarizer Polyvinyl alcohol (plastic sheet) is heate an stretche Sheet is ippe into ioine solution Ioine impregnates the plastic, attaches to long-chain molecules, forms wire gri Polarizer Horizontal polarization, transmitte Vertical polarization, not transmitte ECE 483 Dr. Alan Doolittle

9 Polarize Light x Electric Fiel y y Magnetic Fiel Circular Polarization x y x y y x x z z Elliptical Polarization z ECE 483 Dr. Alan Doolittle

10 Polarizing Filter Effect Colore light from thin-film iriescence in butterflies is often polarize Left wings: unmoifie Right wings: generate by taking two photographs through a polarizing filter rotate by 90 between exposures, an then proucing the ifference of the two images One shows a pattern of polarize an epolarize regions, the other oes not Wing color important in male attraction to females A. Sweeney et al. Nature 43, 3 (003) ECE 483 Dr. Alan Doolittle

11 Diamons What s so special about iamons? Star of South Africa Diamon 83.5 Carats Taylor Diamon 69 Carats ECE 483 Dr. Alan Doolittle

12 Transmission, Reflection, Refraction A iamon is polishe into a particular shape for maximum light refraction/reflection/transmission 58 Facets ECE 483 Dr. Alan Doolittle

13 Optical Microscopy Light cannot be focuse to an infinitesimally small spot ue to the wave nature of light ECE 483 Dr. Alan Doolittle

14 Optical Microscopy There is no lower limit to the size of an isolate object that can be etecte The minimum separation, s, of two point objects occurs when the first maximum of the iffraction pattern of one object falls on the first minimum of the secon object s 0.6λ 0. 6λ n sinθ NA λ free space wavelength, n refractive inex of immersion meium, θ half the angle subtene by the lens at the object, NA numerical aperture Best resolution about 0.5 µm for λ 0.4 µm, NA ECE 483 Dr. Alan Doolittle

15 Optical Microscopy Different approaches to optical microscopy bring out ifferent features Bright Fiel Dark Fiel Interference Contrast ECE 483 Dr. Alan Doolittle

16 Near Fiel Optical Microscopy Conventional microscopy Images the far fiel, where Raleigh limit prevails Near fiel microscopy Images the near fiel, where solution etermine by aperture, not wavelength Detector must be very close to sample λ Lens λ λ λ/ Aperture λ D Detector Spherically iverging wave Spacing D Evanescent wave Detector ECE 483 Dr. Alan Doolittle

17 Near Fiel Optical Microscopy The light is confine to a small aperture Drawn or etche glass fiber Topography Transmission Fluorescence Light Al Coat Glass Fiber Polymer Sample Physics.nist.gov/Divisions/Div844/facilities/nsom/nsom.html ECE 483 Dr. Alan Doolittle

18 Definition Ellipsometry Measurement of the state of polarization of a polarize light wave General Scheme A polarize light wave probe interacts with an "optical system", this interaction changes the state of polarization, measurement of the initial an final states is performe this yiels information about the optical constants of the "system" E S E E S Incient E P E P Reflecte ECE 483 Dr. Alan Doolittle

19 Null Ellipsometer Angles P, C, an A lea to ellipsometer quantities ρ, Ψ an Laser Polarizer Unpolarize P Compensator Linearly Polarize ρ tanψe C Incient j φ φ The ellipsometry equation! n 0 n -jk Transmitte Reflecte A Extinguishe Analyzer Detector Elliptically Polarize Sample Linearly Polarize ECE 483 Dr. Alan Doolittle

20 Nonestructive technique Ellipsometry Film thickness measurement; can measure film thicknesses own to nm Refractive inex etermination; can measure refractive inex of thin films of unknown thickness Azimuth angles can be measure with great accuracy Measures a ratio of two values Highly accurate an reproucible (even in low light levels) No reference sample necessary Not as susceptible to scatter, lamp or purge fluctuations Surface uniformity assessment Composition eterminations Can be use for in situ analysis ECE 483 Dr. Alan Doolittle

21 Null ellipsometry Ellipsometer Polarizer-Compensator-Sample-Analyzer Polarizer an Compensator Angles ajuste for linear polarization upon reflection Analyzer is ajuste to extinguish reflecte light Rotating Analyzer Ellipsometry Analyzer rotates ( θ ) I [ + a cosθ sinθ ] I + 0 b Ψ cos Spectroscopic Ellipsometry ( a ); Uses several wavelengths Can also use several angles cos b a ECE 483 Dr. Alan Doolittle

22 Ellipsometry Measure change of polarization state of light reflecte from a surface Ep( reflecte ) Rp ; Rs E ( incient ) p Es( reflecte ) E ( incient ) s ρ R R p s tanψe j For an air-soli with an absorbing substrate n [ cos Ψ sin Ψ sin ] tan φ k n0 sin φ + [ + sinψ cos ] n k n 0 sin φ tan φ sin4ψ sin [ + sinψ cos ] ECE 483 Dr. Alan Doolittle

23 Definition Transmission / Absorption Absorption - the loss of a photon from an incient flux by the process of exciting an electron from a lower- to a higher-energy state General Scheme Light is incient on a thin sample part of the light is reflecte an the remainer is absorbe or transmitte; a measurement is mae of the transmitte intensity The experiment can be carrie out as a function of temperature, externally applie fiels, sample thickness, etc. I i I t ECE 483 Dr. Alan Doolittle

24 Transmission Optical transmission measurements Sample thickness Absorption coefficient Impurities in semiconuctors (oxygen an carbon in Si) I i I r I r R R A B C D n, k, α n 0 n 0 0 x I t I t T I I t i + R R e For R R : R T ( R )( R ) + R e α ( R) α ( n0 n) + k ( n + n ) + k 0 e R R e e Re α α α α cosφ 4πn φ λ cosφ ECE 483 Dr. Alan Doolittle

25 ECE 483 Dr. Alan Doolittle Transmission If etector has insufficient resolution ( ) φ α α α cos R e e R e R T + ( ) cosφ R R R T + ( ) R R R R T + ( ) e R e R T α α ( ) φ φ π π π α α α e R e R T + cos Re If α 0 T /λ

26 ECE 483 Dr. Alan Doolittle Transmission Gives absorption coefficient, impurity ensity (e.g., oxygen, carbon in Si), thickness ( ) ( ) ( ) λ α ; 4 ln n T R T R R

27 ECE 483 Dr. Alan Doolittle Thickness Oscillations are etermine by ; / 4 cos λ πn Has maxima at n i m n m n m i ) (... ) ( ; 0 λ λ λ + + i o i i m λ λ λ ) / (/ ) ( λ λ λ λ λ λ i i i n i n ) (/ ) / (/ : 0 λ λ λ n n i For (/λ) /λ: Wave number

28 Instrumentation Two types of instruments are use Monochromator Source Entrance Slit Interferometer Source N θ φ Grating L Movable Mirror Beam Splitter L Sample Detector Exit Slit Fixe Mirror mλ sin(θ)cos(φ) m,, 3..; line spacing of grating ECE 483 Dr. Alan Doolittle

29 Interferometer Let source be cosπfx f: frequency of light x: movable mirror location L L Constructive interference Maximum etector output L L + λ/4 Destructive interference Zero etector output L Movable Mirror Source Beam Splitter L Fixe Mirror Sample Detector L L L L + λ/4 ECE 483 Dr. Alan Doolittle

30 Fourier Transform Infrare Spectroscopy Fourier transform infrare spectroscopy (FTIR) I ( x ) B( f )[ + cosπxf ] I f ( x ) Acosπxf f B 0 I f ( x ) 0 B( f )[ cosπxf ]f + Af ( f ) I( x ) cosπxf x ω ω sinπxf πxf Amplitue f f Spectrum f (siny/y) 0.8 f 0 3 cm x0 3 cm x (cm) Interferogram ECE 483 Dr. Alan Doolittle

31 Interferogram - Spectrum Interferogram Spectrum ECE 483 Dr. Alan Doolittle

32 FTIR Applications Determine oxygen an carbon ensity by transmission ip ECE 483 Dr. Alan Doolittle

33 ECE 483 Dr. Alan Doolittle Reflection Reflection measurements Film thickness Reflectivity φ n 0 n n λ φ φ Reflection Transmission Refraction cos cos φ φ α α α α r r e r r e r r e r e r R sin sin cos 4 ; n n n n n n n r n n n n r φ φ λ φ π φ

34 Reflection Examples Rearview Mirror ECE 483 Dr. Alan Doolittle

35 Total Internal Reflection Snell s law: n 0 sinθ 0 n sinθ For θ θ c sin - (n 0 /n ) (critical angle) θ 0 90 Total internal reflection ECE 483 Dr. Alan Doolittle

36 Reflection R versus λ yiels plots with unequal wavelength spacings R versus /λ (wavenumber) gives equal spacings n φ cos λ( max) m n m,, 3 n iλ λ ( λ λ ) cosφ ( λ λ ) cosφ 0 i i: number of complete cycles from λ 0 to λ i i 0 o i i Reflectance Reflectance λ 0 λ λ λ Wavelength (cm) λ 3 - λ - λ - λ Wavenumber (cm - ) ECE 483 Dr. Alan Doolittle

37 Reflection FTIR Applications FTIR is use in may soli state an chemical applications ECE 483 Dr. Alan Doolittle

38 Line With Scatterometry uses scattere or iffracte light From iffracte signature can etermine Line height Line with Corner rouning Siewall slope/angle Special test structure Light 300 (variable λ) Variable θ i Variable θ Detector SEM CD (nm) Measurements Scatterometry CD (nm) C.J. Raymon in Hanbook of Si Semiconuctor Metrology (A.C. Diebol, e.) Marcel Dekker, 00. ECE 483 Dr. Alan Doolittle

39 Luminescence Luminescence is the emission of light ue to: Incanescence: energy supplie by heat Photoluminescence: energy supplie by light Fluorescence: energy supplie by ultraviolet light Chemiluminescence: energy supplie by chemical reactions Bioluminescence: energy supplie by chemical reactions in living beings Electroluminescence: energy supplie by electric current/voltage Cathooluminescence: energy supplie by electron beams. Raioluminescence: energy supplie by nuclear raiation Phosphorescence: elaye luminescence or "afterglow" Triboluminescence: energy supplie by mechanical action Thermoluminescence: energy supplie by heat ECE 483 Dr. Alan Doolittle

40 Photoluminescence Incient laser creates electron-hole pairs (ehp) When the ehp recombine, they emit light Si Sample Light Detector E C E D hν E A E V hν E G E D -E V E C -E A E D -E A Exciton ECE 483 Dr. Alan Doolittle

41 How Does PL Work An How Can It Be Use? Carrier generation epth Wavelength epth information Recombination Shockley-Rea-Hall (impurities) impurity information Auger (high carrier ensities) oping ensity information Surface (surface states, impurities) surface information Raiative (light emission) etection mechanism This is what we want! Moulate Light Carrier Generation Diffusion Recombination ECE 483 Dr. Alan Doolittle

42 Depth Depenent PL Signals ECE 483 Dr. Alan Doolittle

43 Iron In Si by PL An PCD PL PCD Fe Mean: 465 mv Dev.: 7.74 mv Mean: 75 µs Dev.: 0 µs Mean:.4x0 cm -3 Dev.:.9x0 cm Signal (mv) Lifetime (µs) N Fe (cm -3 ) ECE 483 Dr. Alan Doolittle

44 Review Questions What etermines the resolution limit in conventional optical microscopy? What is near fiel optical microscopy? What are the basic elements of ellipsometry? How oes FTIR work? Where are transmission measurements use? Where are reflection measurements use? What is luminescence? How can photoluminescence be use in Si characterization? ECE 483 Dr. Alan Doolittle