Semiconductor Manufacturing Technology

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EE-354
Integrated Circuit Technology
Characteristics of Semiconductor Materials and
Basic Device Physics(Part 1)

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Elementary Model of the Carbon Atom
Figure 2.1
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Electron Shells for Sodium and Chlorine Atoms
Figure 2.3
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Energy Band Gaps
Figure 2.4
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The Periodic Table of the Elements
Figure 2.6
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Group IVA Elemental Semiconductors
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Silicon Crystal Structure
Silicon crystallizes in the same pattern as
Diamond, in a structure called "two
interpenetrating face-centered cubic" primitive
lattices. The lines between silicon atoms in the
lattice illustration indicate nearest-neighbor
bonds. The cube side for silicon is 0.543 nm.
Germanium has the same diamond structure with a
cell dimension of .566 nm.
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Silicon Crystal Structure
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Covalent Bonding of Pure Silicon
Figure 2.19
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Electrons in N-Type Silicon with Phosphorus Dopant
Figure 2.23
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Conduction in n-Type Silicon
Figure 2.24
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Holes in p-Type Silicon with Boron Dopant
Figure 2.25
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Hole Movement in Silicon
                 Boron is neutral, butnearby
electron mayjump to fill bond site.
                  Boron is now a  negative
ion.
                 Only thermal energy to kick
electronsfrom atom to atom.
The empty silicon bond sites (holes) are thought
of as being  positive, since their presence
makes that region positive.
                  Hole moved from 2  to 3 to
4, and will move to 5.
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Conduction in p-Type Silicon
Figure 2.26
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Silicon Dopants
Items in RED form chemical reactions with silicon
and cant be used for doping.
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Silicon Resistivity Versus Dopant Concentration
Redrawn from VLSI Fabrication Principles, Silicon
and Gallium Arsenide, John Wiley Sons, Inc.
Figure 2.27
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N- and P-Type Silicon
Important Facts Not shown are the silicon
atoms, which are present in vastly greater
numbers than either arsenic or boron. Typical
doping concentrations are 1016 arsenic or boron
atoms per cm3. The concentration of silicon
atoms is about 1022 atoms per cm3.   For every
"dopant" atom, there are about a million silicon
atoms.
 The dominant charge carrier in n-type Si is
the electron.
The dominant charge carrier in p-type Si is
the hole
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  P- and N-Type Silicon Joined
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 Charges in the Interface Region  
Most of the arsenic (As) ions on the nside are
covered by an electron.
Near the interface, these ions areuncovered.
Most of the boron  (B-) ions on the p side are
"covered", meaning that swimming about them, on
the average, is one hole.
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Depletion Region
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PN Junction Under Reverse Bias
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Negligible Current in Reverse Bias
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Thermally Generated Reverse Current
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Forward-Biased PN Junction   
 
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A Forward-Biased PN Junction
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 I-V Characteristic Curve
This is the "characteristic" curveof a pn
junction diode.  It showsthe slow, then abrupt,
rise ofcurrent as the voltage is raised.Under
reverse bias, even verylarge voltages will cause
onlyvery small currents, essentiallyconstant
reverse bias currents.
Reverse current exaggerated typical reverse
current  10 uA.
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Turn-On Voltage
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A PN Junction Diode and Its Symbol
 
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Semiconductor Devices

• MOS Device Metal/Oxide/Semiconductor. The heart
  of modern Integrated Circuits
• BiPolar Device Back-to-back diodes. The highest
  speed devices, but they produce heat.
• Schottky Barrier Diodes Used since 1900 for
  electrical rectification. Also called Point
  Contact.

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The MOS Transistor
Polysilicon
Aluminum
Gate is insulated from substrate and all
components. NO current flows from Gate under ANY
bias.
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Two Types of MOSFETs
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Biasing Circuit for an NMOS Transistor
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MOS Device Physics

• Gate is TOTALLY insulated from Semiconductor
• Three components are Source (S), Gate (G) and
  Drain(D)
• Current will be Minority Carriers of substrate
  under Gate!
• Quiescent State Gate is reverse voltage of
  substrate (- for p-type and for n-type.) This
  repels/depletes silicon below gate (between S and
  D) of any minority carriers.
• Conducting State Gate is same as substrate (
  for p-type and for n-type substrate).
• Gate pulls minority carriers from substrate to
  thin layer (5nm) connecting Source and Drain with
  their majority carriers.
• Forward bias of Source/Gate injects majority
  carriers into thin layer.
• Bias of Gate/Drain creates field that pulls
  majority carriers into Drain.

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NMOS Transistor in Conduction Mode
Figure 3.17
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PMOS Transistor in Conduction Mode
Figure 3.20
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Enhancement and Depletion MOSFETs
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MOS Transistors -Types and Symbols
D
D
G
G
S
S
Depletion
NMOS
Enhancement
NMOS
D
D
G
G
B
S
S
NMOS with
PMOS
Enhancement
Bulk Contact
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Future Perspectives
25 nm FINFET MOS transistor
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Bipolar Device Physics

• Three components are Emitter (E), Base (B) and
  Collector(C)
• Gate is connected to Semiconductor (produces
  heat)
• Current will be Minority Carriers of substrate!
• Emitter doping gtgt Base doping. Base is very
  narrow. This means electric field penetrates deep
  into base region, almost to B/C junction.
• Quiescent State Emitter/Gate at same bias. No
  current. E/B current is limited by intrinsic
  field, B/C junction is reverse-biased.
• Conducting State VE lt VB ltlt VC (NPN type)
• Emitter/Base Forward Biased. Base/Collector
  Reverse Biased.
• This Bias is the same as for MOS device.
• Emitter/Base field extends almost to Collector.
  Forward bias injects minority carriers into
  narrow Base. These carriers immediately drift to
  B/C junction, and the B/C electric field
  accelerates them into Collector.

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  The PNP Bipolar Transistor
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  The PNP Bipolar Transistor
The Collector                                   
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Schottky Barrier Diode

• Known since 1900 as Point Contact Diode. Used
  for power current rectification (AC ? DC). Used
  for early radio receivers.
• Made by contacting metal directly to n-type
  silicon. Potential barrier is typically 0.3-0.7V
  (depends on metal)
• Uses only Majority Carriers (electrons). Is a
  diode above potential barrier and forward bias.
• Effect disappears for silicon doping gt 1016cm-3.
  Then get ohmic contact and no diode effect.

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The Schottky Diode
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  Photovoltaic Devices 
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Appendix
The following slides are to remind you of some
basic physics.
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How Sizes Affect Resistance
Figure 2.12
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Battery Charges a Capacitor
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Capacitor Holds a Charge