Lecture Slides on Semiconductor Materials - Microelectronic Fabrication | ECEN 5843, Study notes of Microelectronic Circuits

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ECEN 5843 Microelectronic Fabrication Semiconductor Materials Weili Zhang School of Electrical and Computer Engineering Oklahoma State University http://wzhang.okstate.edu/ SemiconductorOverview Atomic Structure & Periodic Table Conductor/Dielectric/Semiconductor Semiconductor materials Crystal Orientation Band Model Doping Electron/Hole Conductivity P-N Junction 2 Microelectronic Fabrication Weili Zhang Periodic Table | 1 [2 | 3 4 °5/6 7 8 | | He” ns DENRA oe| «§ a A a 27 — aE 4 ns a http://www.chemicalelements.com | Element Groups (Families) ee Microelectronic Fabrication Weili Zhang SemiconductorStable Atomic Structure Elements with a filled outer ring or eight electrons in the outer ring - stable Atoms seek to combine with other atoms to create the stable conditions of full orbits or eight electrons in their outer ring through sharing Neon Atomic # 10 Silicon He Atomic # 2 Argon Atomic # 18 6 Atomic number 14 Microelectronic Fabrication Weili Zhang SemiconductorConductors Outer orbit is less than half filled. Attractive hold on outer orbit electrons is weak. Electrons are easy to be moved to create an electrical current flow. Most metals are conductors. i hi http://www.chemicalelements.com L t um. Atomic number 3 7 Microelectronic Fabrication Weili Zhang SemiconductorIntrinsic Semiconductors An intrinsic (pure) semiconductor has an electrical resistance between that of an dielectric (e g . ., glass/SiO2) and an conductor (e.g., Au, Ag, Cu). Elemental: B (III), C, Ge, Si, α-Sn (Gray tin, IV), P (V), Se, Te (VI) Compound: GaAs, GaP, GaN, InP (III V) SiGe, SiC (VI) GaAsP (III V V) GaAlAs InGaP (III III V), ZnSe, ZnO, HgTe (II VI) 10 Microelectronic Fabrication Weili Zhang SemiconductorGermanium Predicted in 1871, discovered in 1886 First Transistor (Ge) Diamond structure Melting point 937ºC – high temperature processing limit Electrical Leakage – Lack of natural i id G O G O @1000Koccurr ng ox e; e , e 2 11 Microelectronic Fabrication Weili Zhang SemiconductorSilicon EGS P it f 99 9999999%ur y o . Diamond structure M l i i 1415ºC hi he t ng po nt – g temperature processing allowed Silicon/SiO Planar processing2 – electrical leakage solved > 90% of wafers 12 Microelectronic Fabrication Weili Zhang SemiconductorZnO Direct semiconductor Wurtzite structure 1 10 100 4.2 K 77 K RT u) Melting point 1231ºC Wide energy gap 3.37eV - potential for optoelectronic and electronic devices 0.01 0.1 X( 3) (1 0- 5 e su Candidate for UV diode laser @ 368nm THz generation 364 368 372 376 380 1E-3 Wavelength (nm) ZnO film - high electrical conductivity ZnO ceramics doped - nonlinear 15 20 25 rp tio n (1 /c m ) voltage-current characteristics 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 0 5 10 Po w er A bs or 15 W. Zhang et al., Appl. Phys. Lett., Vol. 75, 3321 (1999) Microelectronic Fabrication Weili Zhang A. K. Azad et al., Appl. Phys. Lett., Vol. 88, 021103 (2006) Frequency (THz) SemiconductorGaN Wid B d G 3 4 Ve an ap: ~ . e High Break down field Large electron saturation velocity: 1.3 x 10-7 cm/s Chemically stable at high T Operate at 400 ºC high temperature Short wavelength light emission and high power electronic applications 16 Microelectronic Fabrication Weili Zhang SemiconductorGaN 200 250 (a) n (1 /c m )K//c, E⊥c THz pulse 6 0 50 100 150 Po w er A bs or pt io n 3 4 5 (b) Re fr ac tiv e In de xc x y z 1.5 2.0 2.5 σ σr (c) ity (1 /Ω c m ) 2 Freestanding, Hydride-vapor-phase epitaxy 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 0.0 0.5 1.0 i Frequency (THz) C on du ct iv i (HVPE) Unintentionally doped n-type 5 mm × 5 mm × 180 µm 17W. Zhang et al., Appl. Phys. Lett., Vol. 82, 2841 (2003) Microelectronic Fabrication Weili Zhang SemiconductorMiller Indices <XXX> Miller Indices (hkl) (hkl) = (1/s1 1/s2 1/s3) = (1/1 1/∞ 1/∞) = (100) a3 <110> a1 <111><100> a2 20 Microelectronic Fabrication Weili Zhang SemiconductorCrystal Orientation Orientation Slice the single crystalline unit <100> i ti l l - n ver ca p ane; <111> - corner-to-corner; Application <100> - MOS devices; <111> - Bipolar devices; 21 Microelectronic Fabrication Weili Zhang SemiconductorBand Model Electron shells: 1s; 2s, 2p; 3s, 3p, 3d; 4s, 4p, 4d, … Each shell corresponds to a certain energy - energy levels; Many atoms - Energy band; High energy band corresponds higher energy 22 Microelectronic Fabrication Weili Zhang SemiconductorComparison Fermi level Metal: Dielectric: Conduction band empty Semiconductor: Conduction band empty l b d fill dConduction band partly filled Valence band filled. Valence band filled Large band gap Va ence an e Small band gap 25http://www.chembio.uoguelph.ca/educmat/chm729/band/fl.htm Microelectronic Fabrication Weili Zhang SemiconductorSemiconductor Band gap is small enough that electrons can be moved from valence band to the conduction band (by applying a voltage, illumination, heating, etc). Both bands partly filled material can conduct electricity. 26 Microelectronic Fabrication Weili Zhang SemiconductorSemiconductor Doping Increases the conductivity of intrinsic semiconductors Precise resistivity control through doping. Resistivity range: 10-3 to 103 ohm·cm depending on the amount and type of dopant. Dopant concentration: 10-6 – 0.1% 27 Microelectronic Fabrication Weili Zhang Semiconductorp-type & n-type Band Model Semiconductor: Conduction band empty Valence band filled Phosphorus doped silicon (n-type). Aluminum doped silicon (p-type). Small band gap 30 Microelectronic Fabrication Weili Zhang SemiconductorElectron/Hole Conductivity Electron conduction in n-type semiconductors (and metals) e- e- e- e-(-) (+) Hole conduction in p-type semiconductor (+)( )- e- e- e- e- e- e- e- e- e- e- e- e- e-e- e- 31 Microelectronic Fabrication Weili Zhang SemiconductorResistivity vs. Carrier Concentration - Si 32 Microelectronic Fabrication Weili Zhang Semiconductorp-n Junction p n p n Conduction Band Conduction Band electrons Conduction Band Conduction Band electronsBand gap l tr Valence Bandholes Band gap Band gap EFp EFn Valence Band holes Band gap EFp= EFn Valence Band Valence Band 35http://jas.eng.buffalo.edu/education/pn/pnformation/pnformation.html Microelectronic Fabrication Weili Zhang SemiconductorForward Biased Junction p n p n (+) (-) Conduction Band Conduction Band electronsBand gap l trEFp= EFn Conduction Band Conduction Band electrons Band gap Band gap l tr Valence Band Valence Band holes Band gap Valence Band Valence Band holes 36 Microelectronic Fabrication Weili Zhang http://jas.eng.buffalo.edu/education/pn/biasedPN/index.html SemiconductorReverse Biased Junction p n p n ( )( ) +- Conduction Band Conduction Band electronsBand gap l trEFp= EFn Conduction Band Conduction Band electrons Band gap Valence Band Valence Band holes Band gap Valence Band holes Band gap electrons Valence Band 37http://jas.eng.buffalo.edu/education/pn/biasedPN/index.html Microelectronic Fabrication Weili Zhang SemiconductorWhy Silicon for Microelectronics? Elements are easier to fabricate than compounds Si or Ge. Ge’s melting (937ºC) doesn’t allow high temp processing (Si 1415 ºC). SiO2 is the main component of sand lots of it! An electrically mechanically and chemically , , stable dielectric (SiO2) is available (not for Ge). Tremendous technological base and infrastructure exists for Si. 40 Microelectronic Fabrication Weili Zhang SemiconductorReading Assignment Textbook: Microchip Fabrication 5th Edition (2004) by Peter Van Zant , McGraw Hill, ISBN 0-07-143241-8 PAGE 25 - 49 41 Microelectronic Fabrication Weili Zhang