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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

what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
Daniel
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
Maciej
characteristics of micro business
Abigail
for teaching engĺish at school how nano technology help us
Anassong
Do somebody tell me a best nano engineering book for beginners?
s. Reply
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
s.
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
Tarell
what is the actual application of fullerenes nowadays?
Damian
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
Tarell
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
Virgil
is Bucky paper clear?
CYNTHIA
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Harper
Do you know which machine is used to that process?
s.
how to fabricate graphene ink ?
SUYASH Reply
for screen printed electrodes ?
SUYASH
What is lattice structure?
s. Reply
of graphene you mean?
Ebrahim
or in general
Ebrahim
in general
s.
Graphene has a hexagonal structure
tahir
On having this app for quite a bit time, Haven't realised there's a chat room in it.
Cied
what is biological synthesis of nanoparticles
Sanket 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
what is the k.e before it land
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
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, Solid state physics and devices-the harbinger of third wave of civilization. OpenStax CNX. Sep 15, 2014 Download for free at http://legacy.cnx.org/content/col11170/1.89
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