Chapter 2 : Semiconductor Materials & Devices (I)

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1 Chapter 2 : Semiconductor Materials & Devices (I) 1

2 Reference 1. SemiconductorManufacturing Technology: Michael Quirk and Julian Serda (2001) 3. ULSI Technology : C. Y. Chang, S. M. Sze (1996) 4. Semiconductor Physics and Devices- Basic Principles (3/e) : Donald A. Neamen (2003) 5. Semiconductor Devices - Physics and Technology (2/e) : S. M. Sze (2002) 2

3 Semiconductor Materials - The Crystal Structure of Solids : 10 4 ~10-10 (Ωcm) -1 (impurity) (carrier) 3

4 What is Semiconductor What is Semiconductor Conductivity between conductor and insulator 4

5 Element Semiconductors Why Silicon Can Dominate the IC Industry? Silicon devices exhibit better properties at room temperature, and high-quality silicon dioxide can be grown thermally. There is also an economic consideration. Device-grade silicon costs much less than any other semiconductor material. 5

6 6

7 Silicon Structure Covalence band Shared electrons Silicon Atom Quadrivalent element Four valence electron Atomic number = 14 4 valence electron Covalent bond 7

8 Silicon Structure Diamond Structure 8

Schematics of three general types of crystals:(a) amorphous, (b) polycrystalline, (c) single crystal. Amorphous materials have order only within a few atomic or molecular dimensions.

9 Schematics of three general types of crystals:(a) amorphous, (b) polycrystalline, (c) single crystal. Amorphous materials have order only within a few atomic or molecular dimensions. Polycrystalline materials have a high degree of order over many atomic or molecular dimensions. These ordered regions, or single-crystal regions, vary in size and orientation with respect to one another. The single-crystal regions are called grains and are separated from one another by grain boundaries. Single-crystal materials, ideally, have a high degree of order, or regular geometric periodicity, throughout the entire volume of the material. The advantage of a single-crystal material is that, in general, its electrical properties are superior to those of a non-single crystal material, since grain boundaries tend to degrade the electrical characteristics 9

10 Preparation of Single Crystal Silicon Wafers 1. Crystal Growth Polysilicon Crucible Seed crystal 6. Edge Rounding Heater 7. Lapping 2. Single Crystal Ingot 8. Wafer Etching 3. Crystal Trimming and Diameter Grind Slurry Polishing head 4. Flat Grinding 9. Polishing Polishing table 5. Wafer Slicing 10. Wafer Inspection 10

11 General Characteristics of Silicon Wafer Diameter: 10~30cm, 20cm(8-inch) Thickness: 400~600µm Resistivity: 0.05~0.1 cm 11

12 SiO 2 Si HCl SiHCl3 Si Bridgman) (Czochralski) > 50% market for growing GaAs Schematic of a horizontal Bridgman growth system Simplified schematic drawing of the Czochralski puller. Clockwise (CW), counterclockwise (CCW). 12

13 Czochralski Growth Time lapse sequence of boule being pulled from the melt in a Czochralski growth A 200-mm silicon growth facility 13

14 Carriers of Semiconductor Conduction electron Electron and Hole Covalent band is broken at room temperature Produce the free electron Empty position hole Both electron and hole are called carriers Hole Covalent band broken 14

15 Carriers of Semiconductor Electrons negative charge Holes positive charge The movement of carriers cause current in semiconductor 15

16 Ways of Doping Intrinsic semiconductor Bad conductivity Doping Substitutional impurity Interstitial impurity Interstitial-Substitutional impurity 16

17 Doping Type Extrinsic semiconductor Doped the impurities into intrinsic semiconductor Acceptor p-type Donor n-type 17

18 p-type Semiconductor Acceptor Adding the element of Group III (B, Al) Accept electron Majority carrier holes Acceptor 18

19 n-type Semiconductor Donor Adding the element of Group V (P, As) Supply electron Majority carrier electrons Donor 19

20 Energy Band Diagram Schematic energy band representations of (a) a conductor with two possibilities (either the partially filled conduction band shown at the upper portion or the overlapping bands shown at the lower portion), (b) a semiconductor, and (c) an insulator. 20

Energy-Band Diagram Donor & Acceptor Energy State E d : the

showing (a) the discrete donor energy state and (b) the effect

E a : the energy state of the acceptor electron Energy-band

21 Energy-Band Diagram Donor & Acceptor Energy State E d : the energy state of the donor electron The energy-band diagram showing (a) the discrete donor energy state and (b) the effect of a donor state being ionized. E a : the energy state of the acceptor electron Energy-band diagram showing (a) the discrete acceptor energy state and (b) the effect of a acceptor state being 21

22 Mobility and Resistivity Mobilities and diffusivities in Si and GaAs at 300 K as a function of impurity concentration. Resistivity versus impurity concentration for Si and GaAs ρ = σ 1 q ( nµ + pµ ) n p 22

23 23 Measurement of Resistivity ( ) IR I A L V L V E A I J p n q E E p n q J p n p n drf = = = = Ω + = = + = ) ( ; cm) - ( ) ( 1 1 σ µ µ σ ρ σ µ µ Current conduction in a uniformly doped semiconductor bar with length L and cross-sectional area A. Measurement of resistivity using a four-point probe.

24 Semiconductor Devices - Components on Printed Circuit Board Circuit types: Analog & Digital Circuits Component types: Passive & Active 24

25 Passive Component Structures - IC Resistor Structures: Parasitic Resistor Structures Integrated circuit resistors. All narrow lines in the large square area have the same width W, and all contacts are the same size. 1 L 1 R = G W g where1/g : sheet resistance Example: L=90 µm; W=10 µm; (Ω/ ) /g=1 kω/ R=(9+0.65*2)* 1 kω/ =10.3 kω Examples of Resistor Structures in ICs 25

26 Resistor Polysilicon resistor is doped on an IC chip Linear Resistance is determined by length, area, and the resistivity of the material type Silicide Block Poly FOX Silicided Poly P-substrate l area=a symbol 26

27 Resistor Interconnect Resistance 27

28 Passive Component Structures Examples of Capacitors Structures in ICs (a) Integrated MOS capacitor. (b) Integrated p-n junction capacitor. ox C = d where 0 ox ( F / cm 2 ) ; ox : dielectricpermittivi ty of :dielectricconstant of SiO r = = = 3.9 SiO : permittivi ty of freespace( r F/cm) Si 3 4 r 28 Ta 2 N O 5 Increase the dielectric constant ( = 7) or ( r = 25 )

29 Capacitor Charge storage device Memory Devices, esp. DRAM Two boards of semiconductor material as a capacitor Capacitances are proportional to the area (A=h*l) are inverse proportional to the distance d l h symbol C hl = r 0 ( F) d 29

30 Capacitor Poly poly (double poly process) Middle value Better noise immunity MMC (metal/metal capacitor) M5 VIA VIA MMC Metal M4 M3 30

Passive Component Structures Examples of Inductors Structures in ICs Quality factor: Q = Lω/R The higher the Q values; the lower the loss from resistance, hence the better the performance of the

31 Passive Component Structures Examples of Inductors Structures in ICs Quality factor: Q = Lω/R The higher the Q values; the lower the loss from resistance, hence the better the performance of the circuits. There are some approaches to improve the Q values: (1) Reduce C p : use low Є ox material (2) Reduce R 1 : use thick film metal (e.g. Cu, Au) (3) Reduce R sub loss : use insulating substrate (SOI, quartz) An estimated inductance of the square planar spiral inductor : L µ n 0 where µ 2 r : permeability in n : the 6 = (4π 10 7 number n 2 r H / m) of vacuum turns (a) Schematic view of a spiral inductor on a silicon substrate. (b) Perspective view along A-A 31

32 Active Component Structures The pn Junction Diode The Bipolar Junction Transistor (BJT) The Metal-Oxide-Semiconductor FET (MOSFETs) Complementary MOSFET (CMOS) 32

Space charge region in thermal equilibrium Also called depletion region No mobile

33 PN Junction Diode p region Doped with acceptor impurities The positive charges atoms left n region Doped with donor impurities The negative charges atoms left Space charge region in thermal equilibrium Also called depletion region No mobile carrier exists Two forces exactly balance each other No current Metallurgical junction 33

34 PN Junction (a) (b) Simplified geometry of a pn junction; Doping profile of an ideal uniformly doped pn junction The space charge region, the electric field, and the forces acting on the charged carriers. 34

35 Energy Band Diagram of the PN Junction (a) (a) Uniformly doped p-type and n-type semiconductors before the junction is formed. (b) The energy band diagram of a p-n junction in thermal equilibrium. Build-in voltage : V bi t 35 kt q Drift Diffusion (b) Drift N a N d N a N ln = V ln 2 ni ni = 2 d Diffusion

36 Space Charge Density & Electric Field/Potential uniformly doped pn junction (a) d ( x) ( x) de( x) Poisson' s Eq.: φ = ρ = 2 dx dx s (b) E ( x) = ρ dx = = s s s qn qn a d ( x + x ( x n p ) ; ( x p x 0) x) ; (0 x x n ) φ( x ) = E( x) dx (a) The space charge density in a uniformly doped pn junction assuming the abrupt junction approximation (c) (b) Electric field in the space charge region in a uniformly doped pn junction (c) Electric potential through the space charge region in a uniformly doped pn junction 36

37 Space Charge Density & Electric Field/Potential One-sided abrupt junction (a) One-sided abrupt junction (with N A >> N D ) in thermal equilibrium. (b) Space charge distribution. (c) Electric-field distribution. (d) Potential distribution with distance, where V bi is the built-in potential. W 2 s V = q x = bi 2 Na + N NaNd V d 1/ 2 s bi n qn d 37

38 38 The Uniformly Doped pn Junction Diode 2 1 / 2 + = d a d a bi s N N N N q V W 2 1/ ) ( 2 + = d a d a a bi s N N N N q V V W 2 1/ ) ( = d a d a R bi s N N N N q V V W Schematic representation of depletion layer width and energy band diagrams of a p-n junction under various biasing conditions. (a) Thermal-equilbrium condition.

Ideal Current-Voltage Relationship of Diode (a) (b) A pn junction with an applied forwardbias voltage showing the directions of the electric field induced by V a and the space

39 Ideal Current-Voltage Relationship of Diode (a) (b) A pn junction with an applied forwardbias voltage showing the directions of the electric field induced by V a and the space charge electric field. Energy-band diagram of the forwardbiased pn junction Excess minority carrier concentrations at the space charge edges generated by the forward-bias voltage 39

40 Ideal PN Junction Current Steady-state minority carrier concentrations in a pn junction under forward bias J J J p n D ( x ( x J ) J ) ( x qd p p = [ L = = n s p = p = qd p n Ideal electron and hole current components through a pn junction under forward bias SOC a 論 a ) 1] J exp( ) s 40 [exp( qd ) L n 0 p + p p n L + qv kt n 0 n n J p 0 n [exp( [exp( ( x qd n L n n p ) p 0 qv kt a qv kt ][exp( ) 1] a ) 1] qv kt a qv kt ) 1] J Q J s : the diode reverse saturation current density r d 1 = slope dv = di a D Vt = I Diffusion resistance Ideal I-V characteristic of a pn junction diode Q

41 PN Junction Diode P N Switch Forward biased (Va > 0) Short Current Reverse biased (Va < 0) Open No current Ohm contact Ohm contact 41

42 Fabrication Processes of PN Junction Diode (a) The wafer after the development. (b) The wafer after SiO 2 removal. (c) The final result after a complete lithography process. (d) A p-n junction is formed in the diffusion or implantation process. (e) (f) The wafer after metallization. A p-n junction after the compete process. 42

43 Application of Diode Diode Used for protection circuit In substrate Remain reverse biased In n-well Prevent forward pn junction Substantial current flow p + n + p + n + n-well p-substrate 43

Microsoft PowerPoint - Ch5 The Bipolar Junction Transistor

Microsoft PowerPoint - Ch5 The Bipolar Junction Transistor O2005: Electronics The Bipolar Junction Transistor (BJT) 張大中中央大學通訊工程系 dcchang@ce.ncu.edu.tw 中央大學通訊系張大中 Electronics, Neamen 3th Ed. 1 Bipolar Transistor Structures N P 17 10 N D 19 10 N D 15 10 中央大學通訊系張大中