Manufacturing Process

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ManufacturingProcess
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What is a Semiconductor?

• Low resistivity gt conductor
• High resistivity gt insulator
• Intermediate resistivity gt semiconductor
• conductivity lies between that of conductors and
  insulators
• generally crystalline in structure for IC devices
• In recent years, however, non-crystalline
  semiconductors have become commercially very
  important

polycrystalline amorphous crystalline
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Semiconductor Materials
Phosphorus (P)
Gallium (Ga)
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Silicon

• Si has four valence electrons. Therefore, it can
  form covalent bonds with four of its nearest
  neighbors.
• When temperature goes up, electrons can become
  free to move about the Si lattice.

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Doping (N type)

• Si can be doped with other elements to change
  its electrical properties.
• For example, if Si is doped with phosphorus (P),
  each P atom can contribute a conduction electron,
  so that the Si lattice has more electrons than
  holes, i.e. it becomes N type

Notation n conduction electron
concentration
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Doping (P type)

• If Si is doped with Boron (B), each B atom can
  contribute a hole, so that the Si lattice has
  more holes than electrons, i.e. it becomes P
  type

Notation p hole concentration
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CMOS Process
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A Modern CMOS Process
Dual-Well Trench-Isolated CMOS Process
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Circuit Under Design
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Its Layout View
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The Manufacturing Process
For a great tour through the IC manufacturing
process and its different steps,
check http//www.fullman.com/semiconductors/semico
nductors.html
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Patterning of SiO2
Chemical or plasma
etch
Si-substrate
Hardened resist
SiO
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(a) Silicon base material
Si-substrate
Photoresist
SiO
2
(d) After development and etching of resist,
chemical or plasma etch of SiO
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Si-substrate
Hardened resist
(b) After oxidation and deposition
SiO
of negative photoresist
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Si-substrate
UV-light
Patterned
(e) After etching
optical mask
Exposed resist
SiO
2
Si-substrate
Si-substrate
(f) Final result after removal of resist
(c) Stepper exposure
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Photo-Lithographic Process
optical
mask
oxidation
photoresist coating
photoresist
removal (ashing)
stepper exposure
Typical operations in a single
photolithographic cycle (from Fullman).
photoresist
development
acid etch
process
spin, rinse, dry
step
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CMOS Process at a Glance
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CMOS Process Walk-Through
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CMOS Process Walk-Through
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CMOS Process Walk-Through
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CMOS Process Walk-Through
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Advanced Metallization
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Advanced Metallization
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Implantation

• Diffusion implantation
• The wafers are placed in a quartz tube embedded
  in a heated furnace.
• A gas containing the dopant is introduced in the
  tube. The high temperatures of the furnace,
  typically 900 to 1100 C, cause the dopants to
  diffuse into the exposed surface both vertically
  and horizontally.
• Ion implantation
• Dopants are introduced as ions into the material.
  
• The ion implantation system directs and sweeps a
  beam of purified ions over the semiconductor
  surface.
• The acceleration of the ions determines how deep
  they will penetrate the material, while the beam
  current and the exposure time determine the
  dosage.
• The ion implantation method allows for an
  independent control of depth and dosage.

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Deposition

• Oxidation
• The wafer is exposed to a mixture of high-purity
  oxygen and hydrogen at approximately 1000C.
• The oxide is used as an insulation layer and also
  forms transistor gates.
• Chemical vapor deposition (CVD)
• CVD uses a gas-phase reaction with energy
  supplied by heat at around 850C.
• silicon nitride (Si3N4) ,Polysilicon,
• Sputtering
• The aluminum is evaporated in a vacuum, with the
  heat for the evaporation delivered by
  electron-beam or ion-beam bombarding.

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Etching

• Wet etching
• It uses many types of acid, base and caustic
  solutions to remove a material.
• For instance, hydrofluoric acid buffered with
  ammonium fluoride is typically used to etch SiO2.
• Dry or plasma etching
• A wafer is placed into the etch tool's processing
  chamber and given a negative electrical charge.
• The chamber is heated to 100C and brought to a
  vacuum level of 7.5 Pa,
• It then filled with a positively charged plasma
  (usually a mix of nitrogen, chlorine and boron
  trichloride).
• The opposing electrical charges cause the rapidly
  moving plasma molecules to align themselves in a
  vertical direction, forming a microscopic
  chemical and physical sandblasting action which
  removes the exposed material.
• It creates patterns with sharp vertical contours.