Background material science ideas that may be of use.

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Background material science ideas that may be of
use.
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A) Starting Materials
Start with Sand
Finish with EGS
Electronic Grade solid silicon
Poly-crystalline
(Quartzite)
Chemical Vapor Deposition Reactor
Si
liquid
hot
Coke Furnace
gas
HCl
Fuel gas
Hydrogen gas
Heat Exchanger
Fluidized Bed
Metallugical grade silicon
pure
Si
Trichorosilane
Solid
MGS
Micron sized particles
Pulverizer
Distillation Column
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B) Unit Process Models for Proper Control
(Process control is best achieved when the
equipment follows the model)
Crystal growth is an excellent example of how
equipment and model cooperate to accomplish the
task
Crystal Growth
Model
Temperature gradient in solid crystal near the
solid crystal interface
Temperature gradient in liquid at a location near
the liquid interface
The small change in solid crystal mass because
of a small change in time
"
(dT/dx)
- (dT/dx)
liquid
Solid
Growth Approach Adjustments to Model Constraints

(Three adjustments to equipment to make growth
process match simplify model)
1)
0
2)
Slow Pull Rates. (This makes (dx) small value and
allows use of calculus)
3)
Crucible Surface Area Approximates A
and Crystal Rotates Slowly.
s
(This makes heat of fusion the only new heat
source and (dT/dx)
predictable)
S
This Gradient has Known Shape and Values
'
s
Thermal Conductivity for Crystal Near Liquid
Interface
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Density of Crystal Near Melt Interface
Czechralski Method (CZ Growth)


Linear Pull Rate
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Impurity Sources ( PPM)
Note
CZ Growth used over 99 of time. Other option
is Float Zone Crystal Growth Process.
Good reference for CZ growth,
Characterization Engineering of the Antimony
Hero-Antisite Defect in LEC Gallium Arsenide,
Ph.D. Dissertation, Marshall Wilson, U. South Fl.
1997
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C)Wafer Material Performance Adjustments
Gallium
Arsenic
Lewis diagrams show the atom as its symbol plus
its electrons in the outer orbit
Every atom in a Group has the same number
electrons in outer orbit.
Impurities the Crystal Structure
Although unwanted impurities exist within a
crystal structure, in most
micro and nano applications, a special
impurity, the dopant, is added
to the crystal structure.
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Two views of a cubic crystal structure
3 D Perspective
Interstitial
Location
Lattice Point
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Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
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Doping During Crystal Growth
Equilibrium Segregation Coefficient
Equilibrium Segregation Coefficient
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Effective Segregation Coefficient
Segregation Coefficient
With

B Boundary Layer
Note
D Diffusion Coefficient
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Summary Two Views of a Doped Cubic Crystal
Structure
Phosphorus atom on a substitutional lattice
location
Boron atom on a substitutional lattice location
n-type Doped Arrangement
p-type Doped Arrangement
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Local and Universal Charge Characteristics
1) At Low Temperatures
Both of these Slabs (n-type and p-type) Remain
Overall Neutral
p-type Doped Arrangement
n-type Donor Arrangement
Number Density of Acceptors
Number Density of Donors
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Local and Universal Charge Characteristics
2) Raise the temperature of the lattice
Ionized acceptor
ionized donor atom
Density of Charged Donors
Concentration of ions Concentration of carrier
3) Add ion to slab so it finally exchanges with a
lattice location
An Ion
Lattice with new ion becomes charged
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D) Wafer Issues
Orientation
Surface planes and directions based on Miller
Indices
(001)
(001)
(111)
(100)
(110)
(010)
(100)
(100)
(The 111 perspective)
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Concentration of Constituents
Typical Intrinsic Densities
Number Density of Constituents
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Important Parameters
Conductivity
(Charge/Carrier)(Mobility of Carrier)(Density of
Carrier)
Resistivity
Conductivity (1/ Resistivity)
When Dopant is a p-type Material
When Dopant is an n-type Material
Resistively Ohm-Cm
-3
10
14
15
17
18
19
20
16
10
10
10
10
10
10
10
(Sometimes before the first process step the
wafer may have an
excess amount of dopant that defines the
wafers resistivity.)
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Example- Epitaxial Film Concentration
How many Boron (dopant) atoms should be put into
an epi layer with a resistivity of
A) 1 ohm-cm
B) 10 ohm-cm
Resistance of a Material
Resistance (resistivity) ((length material)/
(cross-section area))
R
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E) Electronic Influence of Contaminates
Energy Level Approximate Values for Isolated Atom
in Space
Energy of Orbit closest to nucleus
Energy Levels from Bohrs Model
Not to Scale
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E
(1/n)
(13.6 ev)

n
( -0.55 - -0.85 ) 0.30 ev
-3.40 ev
Higher Negative Values
Energy Values
With n being integer energy levels and 13.6
electron volts being Bohrs energy value for the
first orbit of a hydrogen atom
-1.51 ev
-0.85 ev
-0.21 ev
-0.55 ev
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2
3
4
5
6
7
8
9
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Energy Levels
(levels further away from the nucleus)
Related Position of Silicon Energy Levels
More Positive Energy Values
More Positive Energy Values
Valance Band
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Compensated Device
(If both n-type and p-type materials are present,
the device is said to be compensated)
Mask Protecting a Piece of Boron Doped Silicon
Phosphorous in Interstital Spaces
Note
Charge neutrality occurs when


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Number of ionized acceptors
Phosphorous in Substitutional Spaces
Number of holes
p-type Dopent at Substitutional Sites
Metallurgical Junction
(Equal Density of Positive and Negative Entities)
indicates that all of the items in the region of
interested are added together.)
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Image Triggering Vocabulary
Metallurgical Grade Silicon (MSG)
Electronic Grade Silicon (ESG)
CZ Growth
Lattice
Interstitial Locations
Substitutional Locations
Lewis Diagrams
Miller Indicies
Resistivity
Epitaxial Film
Compensated Device
Donors
Acceptors
Equal Charge Density
Metallurigical Junction
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