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Part 3 of crystal growth sums up the properties of Silicon, describes the identity marks of Silicon Wafers in terms of Semiconductor Type and in terms of Crystal Orientation and this part defines the crystal orientation and its relevance in IC fabrication.

CRYSTAL GROWTH

Silicon, (Si) :The most common semiconductor, atomic number 14,

energy gap Eg= 1.12 eV- indirect bandgap;

crystal structure- diamond, lattice constant 0.543 nm,

atomic concentration 5 x 10 22 atoms/cm -3 ,

index of refraction 3.42, density 2.33 g/cm 3 , dielectric constant 11.7,

intrinsic carrier concentration 1.02 x 10 10 cm -3 ,

bulk mobility of electrons and holes at 300°K: 1450 and 500 cm 2 /V-s,

thermal conductivity 1.31 W/cm°C,

thermal expansion coefficient 2.6 x 10 -6 °C -1 ,

melting point 1414°C; excellent mechanical properties (MEMS applications);

single crystal Si can be processed into wafers up to 300mm in diameter.

In future this diameter will be 450mm.

P type= Always Boron (B) Doped N type= Dopant typically as follows:Res: .001-.005 Arsenic (As)Res: .005-.025 Antimony (Sb)Res:>.1 Phosphorous (P)

EPITAXIAL CRYSTAL GROWTH

The substrate or the wafer only constitutes the strong base of the integrated circuit. The actual active and passive components fabrication and there integration are carried out in overlay films which are grown by epitaxial technique.

EPITAXY is a Greek word meaning : ‘epi’ (upon)&‘taxy’ (ordered). That is an epitaxial film, a few μm thick, is an orderly continuation of the substrate crystal. It grows very slowly layer by layer. Hence the dimension , defects and doping magnitude as well as uniformity can be precisely and accurately controlled in the crystal growth direction.

This precise control is obtained in Molecular Beam Epitaxy (MBE) but not in Liquid Phase Epitaxy(LPE) or in Chemical Vapour Phase Epitaxy (CVPE). The thickness accuracy is within ±3À which is essential for growing Quantum Photonic Devices namely Quantum Dots, Quantum Wells and Super-lattices

Table 2. Identity marks of the Wafer to identify its orientation and semiconductor type.

α (angle between primary and secondary flats as indicated in Figure 9) Type Orientation
45º N <111>
90º P <100>
180º N <100>
P <111>

The normal to the plane along which crystals cleaves is the cleavage plane orientation. Suppose the cleavage plane orientation is<111>. Miller Index is being used to define the planes and their normal. Figure 10 illustrates the Plane’s Miller Index and how the normal to the plane is represented. If the exposed surface of the Si wafer, which is known as major flat, is parallel to cleavage plane then the given wafer has a crystal orientation<111>.

If the cleavage plane orientation is<100>and the wafer major flat is parallel to YZ plane then the crystal orientation is<100>. In this case cleavage plane lies in YZ plane i.e. [100] plane and its orientation is perpendicular to YZ plane i.e. x-axis. Hence Wafer Crystal Plane orientation is<100>

Scribing the wafer along cleavage planes allows it to be easily diced into individual chips (‘die”) so that billions of individual circuits or systems on an average wafer can be separated into individual dies. Each individual die is eutectic ally bonded on ceramic substrate. The substrate is bonded to the header.The gold wire is connected to the bonding pads of the die on one end and to the chip terminals on the header by Thermo-compression bonding or by Ultra-sonic bonding. Next the die is hermetically sealed into Dual-in-Line(DIP) package or TO5 package

In<100>crystal orientation, scribed pieces form rectangle whereas in<111>crystal orientation, scribed pieces form triangles. Here we have to scribe from the base of the triangle to the apex.

For MOS fabrications, wafers with crystal orientation<100>are used. This helps achieve a lower threshold voltage. For BJT and other applications wafers with orientation<111>are preferred.

Silicon Crystal Bulk is isotropic to diffusion of dopents and to etchents used for etching the oxide layer. This is because of the symmetric property of Cubic Structure of Si. But real devices are built near the surface hence the orientation of the crystal does matter.

In 111 crystal terminates on 111 plane and in 100 it terminates on 100 plane. 111 plane has largest number of Si atoms per cm2 whereas 100 has the least number of atoms per cm2. Because of this difference 111 planes oxidize much faster because the oxidation rate is proportional to the Silicon atoms available for reaction.

But because the atom surface density is the highest the dangling bond surface density is also the highest in 111 hence Si/SiO2 has superior electrical properties in terms of interface states in 100. Interface states give rise to 1/f noise or flicker noise. Because of this superiority all MOS devices use 100 crystal orientation. But historically BJT have used 111 because 111 crystal growth is easier to grow by Czochralski method. But as we move to sub-micron and deep and ultra-deep sub-micron BJT, 100 crystal orientation seems to be the crystal orientation of choice for BJT also.

Questions & Answers

how do they get the third part x = (32)5/4
kinnecy Reply
can someone help me with some logarithmic and exponential equations.
Jeffrey Reply
sure. what is your question?
ninjadapaul
20/(×-6^2)
Salomon
okay, so you have 6 raised to the power of 2. what is that part of your answer
ninjadapaul
I don't understand what the A with approx sign and the boxed x mean
ninjadapaul
it think it's written 20/(X-6)^2 so it's 20 divided by X-6 squared
Salomon
I'm not sure why it wrote it the other way
Salomon
I got X =-6
Salomon
ok. so take the square root of both sides, now you have plus or minus the square root of 20= x-6
ninjadapaul
oops. ignore that.
ninjadapaul
so you not have an equal sign anywhere in the original equation?
ninjadapaul
Commplementary angles
Idrissa Reply
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Sherica
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Uday
what is a good calculator for all algebra; would a Casio fx 260 work with all algebra equations? please name the cheapest, thanks.
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a perfect square v²+2v+_
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Abdirahman Reply
algebra 2 Inequalities:If equation 2 = 0 it is an open set?
Kim Reply
or infinite solutions?
Kim
The answer is neither. The function, 2 = 0 cannot exist. Hence, the function is undefined.
Al
y=10×
Embra Reply
if |A| not equal to 0 and order of A is n prove that adj (adj A = |A|
Nancy Reply
rolling four fair dice and getting an even number an all four dice
ramon Reply
Kristine 2*2*2=8
Bridget Reply
Differences Between Laspeyres and Paasche Indices
Emedobi Reply
No. 7x -4y is simplified from 4x + (3y + 3x) -7y
Mary Reply
is it 3×y ?
Joan Reply
J, combine like terms 7x-4y
Bridget Reply
how do you translate this in Algebraic Expressions
linda Reply
Need to simplify the expresin. 3/7 (x+y)-1/7 (x-1)=
Crystal Reply
. After 3 months on a diet, Lisa had lost 12% of her original weight. She lost 21 pounds. What was Lisa's original weight?
Chris Reply
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
China
Cied
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
Porter
many many of nanotubes
Porter
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Yasmin
what is the function of carbon nanotubes?
Cesar
I'm interested in nanotube
Uday
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
what is nano technology
Sravani Reply
what is system testing?
AMJAD
preparation of nanomaterial
Victor Reply
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
Himanshu Reply
good afternoon madam
AMJAD
what is system testing
AMJAD
what is the application of nanotechnology?
Stotaw
In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
Azam
anybody can imagine what will be happen after 100 years from now in nano tech world
Prasenjit
after 100 year this will be not nanotechnology maybe this technology name will be change . maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
Azam
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
Prasenjit
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
Damian
silver nanoparticles could handle the job?
Damian
not now but maybe in future only AgNP maybe any other nanomaterials
Azam
Hello
Uday
I'm interested in Nanotube
Uday
this technology will not going on for the long time , so I'm thinking about femtotechnology 10^-15
Prasenjit
can nanotechnology change the direction of the face of the world
Prasenjit Reply
At high concentrations (>0.01 M), the relation between absorptivity coefficient and absorbance is no longer linear. This is due to the electrostatic interactions between the quantum dots in close proximity. If the concentration of the solution is high, another effect that is seen is the scattering of light from the large number of quantum dots. This assumption only works at low concentrations of the analyte. Presence of stray light.
Ali Reply
the Beer law works very well for dilute solutions but fails for very high concentrations. why?
bamidele Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, Electrical and electronic materials science. OpenStax CNX. May 01, 2014 Download for free at http://cnx.org/content/col11615/1.14
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