Microscale
and
Si Wafer
From macro to nano…
Scaling laws of small
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Laws of physics make the small world look different.
Some small scale phenomena
Surface tension
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Surface tension force for 100 µm opening = 5.7 µN
Typical force for 100 µm device is 10 nN
Surface tension over 500x greater!
Some small scale phenomena
Laminar flow
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Reynolds Number (Re)scales as length.
Typical Reynolds Number for 100 µm device is Re ~ 0.1
Onset of turbulence is at Re ~ 2000
Some small scale phenomena
Surface area/volume
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Surface area to volume is large at small scales.
Mass flow saturates quickly in small volumes.
Equilibrium can be reached very quickly.
Mass flows through small devices
quickly.
Hard to maintain concentration
gradient.
 Micro-scale systems must
utilize physical barriers (cell
walls) to maintain
concentration gradients.
 Surface contamination is a
serious issue at small scales.
Some small scale phenomena
Loss of continuity
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At sizes below ~50 µm, granularity of nature becomes
relevant.
Many bulk-scale physical laws no longer accurate.
 Typical grain size is ~10 µm.
Affects physical, thermal and
electrical properties.
 Mean free path of N2 at
atmosphere
is 60 nm. Affects dynamics in
air. Example: Paschen effect.
Micromachining Materials
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Substrates:
• Silicon
• GaAs
• Other elemental or compound semiconductors
• Metals (bulk and foils)
• Glasses
• Quartz
• Sapphire
• Ceramics
• Plastics, polymers and other organics
Silicon Crystallography
Cubic Lattices
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Simplest arrangements of atoms in three dimension in
which the unit cell is a cubic volume
• Simple Cubic (sc) structure has an atom located at
each corner of the unit cell
• Body Centered Cubic (bcc) has an additional atom at
the center of the cube
• Face Centered Cubic (fcc) unit cell has atoms at the
eight corners and on the six faces.
Cubic Lattices
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How is the arrangement of atoms in Silicon?
• Silicon has fcc + (1/4x, 1/4y, 1/4z) fcc structure
Si crystal structure
Planes and directions
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Lattice vector R= r*a+ s*b+ t*c, r, s & t are integers
We can define a plane in a crystal lattice with three integer,
called Miller indices
Planes and directions
[1 0 0 ]
[1 1 0 ]
[1 1 1 ]
Czochralski Method (CZ)
Si-Wafer fabriaction
Floating Zone Method (FZ)
懸浮帶區法(FZ法)
CZ法和FZ法比較
CZ法和FZ法比較
晶圓的備製
晶塊修整
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Miller indices indicated by
ground edges called “flats”.
“n”-type and “p”-type refer to
“doping”. N means “negative”
(phosphorous) and P means
“positive” (boron).
Clean Room
Clean room classifications and
applications
Clear room classification
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‡ lass 1000: fewer than 1,000 particles (>0.5μm) in 1 cubic foot of air
C
‡
Class 100: fewer than 1,00 particles (>0.5μm) in 1 cubic foot of air