Properties of silicon and silicon wafers 
Silicon material properties  Silicon wafer properties 
1. Crystal properties  1. Properties 
2. Band structure properties  2. Typical Sizes of Semiconductor Wafers 
3. Thermal properties  3. Wafer Flats 
4. Electrical properties  4. Cleaving 
5. Silicon etching  
5. Mechanical properties 
PROPERTY 
VALUE 
UNITS 
Structure 
Cubic 

Space Group 
Fd3m 

Atomic weight 
28.0855 

Lattice spacing (a_{0} ) at 300K 
0.54311 
nm 
Density at 300K 
2.3290 
g/cm^{3} 
Nearest Neighbour Distance at 300K  0.235  nm 
Number of atoms in 1 cm^{3} 
4.995 · 10^{22} 

Isotopes 
28 (92.23%) 29 ( 4.67%) 30 ( 3.10%) 

Electron Shells 
1s^{2}2s^{2}2p^{6}3s^{2}3p^{2} 

Common Ions  Si ^{4 +}, Si ^{4 }  
Critical Pressure  1450  atm 
Critical Temperature  4920  °C 
PROPERTY 
VALUE 
UNITS 
Dielectric Constant at 300 K 
11.9 

Effective density of states 
2.8x10^{19} 
cm^{3} 
Effective density of states (valence, N_{v }T=300 K ) 
1.04x10^{19} 
cm^{3} 
Electron affinity 
133.6 
kJ / mol 
Energy Gap E_{g} at 300 K (Minimum Indirect Energy Gap at 300 K) 
1.12 
eV 
Energy Gap E_{g} at ca. 0 K (Minimum Indirect Energy Gap at 0K) 
1.17 (at 0 K) 
eV 
Minimum Direct Energy Gap at 300 K 
3.4 
eV 
Energy separation (E_{ΓL}) 
4.2 
eV 
Intrinsic Debye length 
24 
um 
Intrinsic carrier concentration 
1·10^{10} 
cm^{3} 
Intrinsic resistivity 
3.2·10^{5} 
Ω·cm 
Auger recombination coefficient C_{n} 
1.1·10^{30} 
cm^{6} / s 
Auger recombination coefficient C_{p} 
3·10^{31} 
cm^{6} / s 
Temperature dependence of the energy gap:
E_{g} = 1.17  4.73·10^{4}·T^{2}/(T+636) (eV)
where: T is temperature in degrees K.
PROPERTY 
VALUE 
UNITS 
Melting point 
1414 1687 
°C K 
Boiling point 
3538 
K 
Specific heat 
0.7 
J / (g x °C) 
Thermal conductivity [300K] 
148 
W / (m x K) 
Thermal diffusivity 
0.8 
cm^{2}/s 
Thermal expansion, linear 
2.6·10^{6} 
°C ^{1} 
Debye temperature 
640 
K 
Temperature dependence of band gap  2.3e4  eV/K 
Heat
of: fusion / vaporization / atomization 
39.6 / 383.3 / 452 
kJ / mol 
PROPERTY 
VALUE 
UNITS 
Breakdown field 
≈ 3·10^{5} 
V/cm 
Index of refraction 
3.42 

Mobility electrons 
≈ 1400 
cm^{2} / (V x s) 
Mobility holes 
≈ 450 
cm^{2} / (V x s) 
Diffusion coefficient electrons 
≈ 36 
cm^{2}/s 
Diffusion coefficient holes 
≈ 12 
cm^{2}/s 
Electron thermal velocity 
2.3·10^{5} 
m/s 
Electronegativity  1.8  Pauling`s 
Hole thermal velocity 
1.65·10^{5} 
m/s 
Optical phonon energy 
0.063 
eV 
Density of surface atoms  (100)
6.78
(110) 9.59 (111) 7.83 
10^{14}/cm^{2}
10^{14}/cm^{2} 10^{14}/cm^{2} 
Work function (intrinsic)  4.15  eV 
Ionization Energies for Various Dopants 
Donors Sb 0.039 P 0.045 As 0.054 Acceptors
Al 0.067 Ga 0.072 In 0.16 
eV eV eV
eV eV eV eV 
PROPERTY  VALUE  UNITS  
Bulk modulus of elasticity  9.8·10^{11}  dyn/cm^{2}  
Density  2.329  g/cm^{3}  
Hardness  7  on the Mohs scale  
Surface microhardness (using Knoop's pyramid test)  1150  kg/mm^{2}  
Elastic constants 
C_{11} = 16.60·10^{11}
C_{12} = 6.40·10^{11} C_{44} = 7.96·10^{11} 
dyn/cm^{2}_{ }
dyn/cm^{2}_{ } dyn/cm^{2}_{ } 

Young's Modulus (E)  [100] [110] [111] 
129.5 168.0 186.5 
GPa GPa GPa 
Shear Modulus  64.1  GPa  
Poisson's Ratio  0.22 to 0.28   
Silicon wafers propertiesSilicon, Si  the most common semiconductor, single crystal Si can be processed into wafers up to 300 mm in diameter. Wafers are thin (thickness depends on wafer diameter, but is typically less than 1 mm), circular slice of singlecrystal semiconductor material cut from the ingot of single crystal semiconductor. All lattice planes and lattice directions are described by a mathematical description known as a Miller Index. In the cubic lattice system, the direction [hkl] defines a vector direction normal to surface of a particular plane or facet. A crystal can always be divided into a fundamental shape with a characteristic shape, volume, and contents. As a crystal is periodic, there exist families of equivalent directions and planes. Notation allows for distinction between a specific direction or plane and families of such. Miller convention:
Planes configurations for (100) and (110) wafers:
Angles Between Planes
Stereographic projection of silicon crystal:
TTV = A  B
GTIR = A + B
An ntype (negativetype) extrinsic silicon semiconductor is a semiconducting material that was produced by doping silicon with an ntype element of Group V A, such as P, As, or Sb. Consequently, electrons are the majority charge carriers of the material. A ptype (positivetype) extrinsic silicon semiconductor is a semiconducting material that was produced by doping silicon with an ptype element of group III A, such as B, Al, or Ga. Since the dopants are acceptor atoms, holes are the majority charge carriers of the material. Measurement of wafer characteristics  dark field and bright field detection
1. Typical Sizes of Semicoductor Wafers(The Diameter of a wafer is measured through its center and not through any flats): 1 inch or 25mm
2. Wafer Flats  orientation for automatic equipment and indicate type and orientation of crystal.Primary flat – The flat of longest length located in the circumference of the wafer. The primary flat has a specific crystal orientation relative to the wafer surface; major flat. Secondary flat – Indicates the crystal orientation and doping of the wafer.
3. CleavingCleaves will run according to the crystal orientations. If the crystal orientation of the Si is <100> cleave at 90 deg. angles. If the crystal orientation of the Si is <111> cleave at 60 deg. angles.
5. Silicon etchingIn general, there are two classes of etching processes:
Wet etchingWet etching is a blanket name that covers the removal of material by immersing the wafer in a liquid bath of the chemical etchant. Wet etchants fall into two broad categories; isotropic etchants and anisotropic etchants. Silicon, exhibit anisotropic etching in certain chemicals. Anisotropic etching in contrast to isotropic etching means different etch rates in different directions in the material. The classic example of this is the <111> crystal plane sidewalls that appear when etching a hole in a <100> silicon wafer in a chemical such as potassium hydroxide (KOH). The result is a pyramid shaped hole instead of a hole with rounded sidewalls with a isotropic etchant.
Plane hkl etching speed: V_{hkl} =d_{hkl} / t where: d_{hkl}  etching deep, t  etching time
EXAMPLE: Silicon membrane


Dry etchingThe most common form of dry etching is reactive ion etching (RIE). Ions are accelerated towards the material to be etched, and the etching reaction is enhanced in the direction of travel of the ion. RIE is an anisotropic etching technique. RIE is not limited by the crystal planes in the silicon.
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