1. The production of crystalline silicon wafers involves multiple steps: quartz is converted to metallurgical grade silicon, then to polysilicon via chemical vapor deposition or fluidized bed reactors, then polysilicon is made into monocrystalline or multicrystalline ingots using Czochralski or float zone methods. 2. Ingots are cut into wafers, typically using sawing which wastes silicon in the kerf, or using ribbon growth which avoids kerf loss. Wafers are further processed for use in solar cells.

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PRODUCTION OF CRYSTALLINE SILICON WAFERS
: A REVIEW
PROF. R. D. PARMAR
Lecturer, Electrical Engineering Department, C.U.Shah Polytechnic, Surendranagar,
Gujarat, India
raghuvir_dhirubha@yahoo.com
ABSTRACT: This review focuses only production of silicon wafers.Silicon which is available in abundant
quantity in the earth’s crust.The stages for manufacturing silicon wafers from quartz are: quartz to
metallurgical grade silicon, refinement of metallurgical grade silicon to polycrystalline silicon via chemical
means or through metallurgical route to solar grade silicon, polysilicon to monocrystalline and multicrystalline
ingots, monocrystalline and multicrystalline ingots to silicon wafers.
Keywords: Quartz, chemical vapour deposition, siemens, fluid bed reactor, Czochralski method, float zone,
sawing, silicon ribbon
1. INTRODUCTION:
Silica (silicon dioxide) is one of the most common
chemical compounds found in the nature. The most
common crystalline silica is quartz.Quartzite or
quartz sand gives us silicon dioxide.Moreover, many
rocks contain quartz crystals.So it can be concluded
that the resources of silicon are abundant.Amorphous
silica is common sand.
Industrial production of silicon is in the form of
ferrosilicon and metallurgical grade
silicon.Metallurgical grade silicon is the preliminary
element for polycrystalline or solar-grade silicon used
inthe photovoltaic industry. metallurgical silicon is
the lowest quality of silicon. Metallurgicalgrade
silicon is mainly used in aluminium and chemical
industries, and a small fraction is used to make
semiconductor-grade silicon (1).
2. CONVERSION OF QUARTZ IN TO
METALLURGICAL GRADE SILICON
Quartzite is the the source material of making
metallurgical silicon. Quartzite is a rock of pure
silicon oxide.By removing the oxide during the
production, the silicon is purified. A submerged
electrode arc furnace is used for this process.
The quartzite is moved in to the furnace where
it is melted.The Quartzite is heated up to a
temperature around 1900 degrees Celsius using an
electrode. Carbon. is mixed with the molted
quartzite. The carbon source is a mixture of coal,
coke and wood chips. The carbon reacts with the
silicon oxide. The molted silicon that is formed is
drawn of the furnace and solidified. The purity
of metallurgic silicon is around 98 up to 99%.
Electrical energy consumption for the production of
metallurgical grade silicon is 11-13 Mwh/ton of
silicon metal.
3. METALLURGICAL GRADE SILICON TO
POLYSILICON
3.1 First method
The silicon material with the next level of
purity is called polysilicon. Rods of polysilicon
are produced out of metallurgical silicon and for
this the source material is powder of metallurgical
silicon. The metallurgical silicon with hydrogen
chloride is then exposed in a reactor at elevated
temperatures in presence of a catalyst.
The Reaction of silicon the hydrogen chloride
forms trichlorosilane.,which is a molecule that
contains one silicon atom, three chlorine atoms
and one hydrogen atoms. The trichlorosilane gas
is cooled and liquified. Distillation process is then
carried out to remove Impurities with higher or lower
boiling points. In a different reactor the purified
trichlorosilane is evaporized and mixed with
hydrogen gas. Trichlorosilane reacts with hot rods
which are at high temperature of 850 up to 1050
degree Celsius.
The silicon atom are deposited on the rod
whereas the chlorine and hydrogen atoms are
desorbed from the surface of the rod back in to
the gas phase. As a result a pure silicon material
is grown and this deposition method is called
chemical vapor deposition.
Exhaust gas still contains chlorosilanes and
hydrogen, so these gasses are recycled and used
again. Chlorosilane is liquefied and distilled and
reused. Cleanup process is carried out on hydrogen
and is recycled back in to the reactor. This process is
known as Siemens process which require s lot of
energy. Silicon produced from this and similar
processes is called polycrystalline silicon.Because of

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the high resistivity of the silicon seed rods, the
Siemens process requires two power supplies-one for
pre-heating the rods into a conductive state,and the
second for superheating the rods by conduction. Most
of the energy from the hot silicon rods is radiated into
water-cooled bell jars covering the Siemens reactor.
3.2 Second method
Another method for the production of poly silicon
granules is Fluid Bed Reactors. This process
operates at lower temperatures and consumes
much less energy.
In the fluidized bed process, pure silicon pellets are
grown from tiny pure silicon seeds into poly-silicon
granules in a high-temperature reaction vessel. This
process was developed by the Ethyl Corp., which
proposed to use silicon fluoride as a preliminary
material to produce silane, SiH4. Silicon fluoride is
available in abundant quantity from huge fertilizer
industry. Polysilicon consists of small silicon
crystals. The structure is different from single crystal
silicon.
4. POLYSILICON TO MONOCRYSTALLINE
AND MULTICRYSTALLINE INGOTS.
There are two methods to make monocrystalline
silicon ingots. Ingots are large blocks of
crystalline silicon.An ingot has been produced from
electronic grade silicon. One ingot has a silicon
purity of 99.9999%.
4.1 The Czochralski method : It is a method to
grow single crystal silicon. It is developed by
Polish scientist Jan Czochralski in 1918.The
monocrystalline ingots are solids that consist of
one big crystal.
Highly purified silicon is melted in a crucible at
typical temperature of 1500 degree Celsius in this
method. Boron or Phosphorous can be added
intentionally to make p doped or n doped silicon,
respectively. A seed crystal that is mounted on
rotating shaft is dipped in to the molten silicon.
The orientation of this seed crystal is well
defined.
The crystal is rotating and pulled upwards,
allowing the formation of a large, single-‐crystal
cylindrical column from the melt. This big
single--‐crystalline silicon block is called an
ingot. The temperature gradients, rate of pulling
up and speed of rotations are precisely controlled
in this process.
This process is further developed through years
of advances and nowadays crystal ingots of
diameters of 200 mm and 300 mm with lengths
of two 2 meters can be processed. To prevent the
incorporation of impurities this process takes
place in an inert atmosphere, like argon gas. The
crucible is made from quartz, which partly
dissolves in the melt as well. Consequently,
Chozralski monocrystalline silicon has a
relatively high oxygen level.
4.2 Float zone process : This is the second method
to make monocrystalline silicon ingots with
extreme low densities of impurities like oxygen
and carbon. The source material is a
Polycrystalline rod which is processed in the
Siemens process.
The end of the rod is heated up and melted
using a radiofrequent heating coil. The melted
part is put in contact with seed crystals.
As the molten zone is moved along the
polysilicon rod, the single crystal ingot is growing
as well. Many impurities remain in and move
along with the molten zone. Nitrogen is
intentionally added during the process to improve
the control on microdefects and also the
mechanical strength of the wafers.
Molted silicon is not in contact with other
materials like quartz as in the Chozralski method
which is the advantage of the float zone
technique.In the float zone process, the molten
silicon is only in contact with the inert gas like
argon. The silicon can be doped by adding
doping gasses like diborane and phosphine to the
inert gas to get p doped and n doped silicon
respectively.
Next to monocrystalline silicon ingots,
multicrystalline silicon ingots can be processed as
well.Multicrystalline/polycrystalline consists of
many small crystalline grains.
Highly purified silicon undergoes melting process
in a dedicated crucible and then it is poured in
cubic shaped growth crucible. There the molten
silicon solidifies in to multi crystalline ingot. This
process is called silicon casting.If the melting
and solidification occurs in the same crucible it
is referred to as directional solidification.
5. PROCESS TO MAKE SILICON WAFERS
OUT OF MONOCRYSTALLINE AND
MULTICRYSTALLINE INGOTS:
There are two methods to make wafers out of
monocrystalline and multicrystalline ingots. : Sawing
and silicon ribbon. Ingot is cut into individual silicon
discs called wafers.
5.1 Sawing : Surface of wafers is damaged in this
process , so this processing step is followed by an
polishing step.A significant fraction of the silicon
is wasted as a kerf loss which is the disadvantage
of the sawing step.The kerf loss is usually
determined by the thickness of the wire or saw
used for sawing and is in the order of 100
microns of silicon.
This is a large fraction of the ingot if we
consider that typical crystalline silicon
wafers used in solar cells nowadays are in the
order of 150 up to 200 microns.
5.2 Silicon ribbon : Kerf losses is not the problem in
this method .Silicon ribbon is based on a high
temperature resistant string, which is pulled up
from a silicon melt.
The silicon solidifies on the string and a sheet
of crystalline silicon is pulled out of the melt

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like this. The ribbon is then cut into wafers. The
surface is further treated before they are further
processed in to solar cells.
A crystalline silicon solar cell produces a voltage of
about 0.5 volts.Individual cells are usually
interconnected to produce a voltage useful for
practical application.These interconnected solar cells
are encapsulated for protection, and in this way a
solar module (panel) is produced. Such a solar
module can be used directly for electricity generation
or incorporated into a photovoltaic system.
CONCLUSION :
Silicon is dominant material in Photovoltaic industry
particularly in its crystalline form. Availability in
abundant quantity, environmental friendly,
production at low cost, higher conversion efficiency
are the main factors to be considered for PV industry
and at present all are fulfilled by silicon. Future could
see some more material better than silicon as it is
proved that still silicon is not the best material as far
as energy conversion efficiency is concerned.
REFERENCES:
(1) “Float zone silicon for high volume production of
solar cells” by Jan Vedde, Thomas Clausen and Leif
Jensen ,Topsil A/S, Linderupvej 4, DK-3600
Frederikssund, Denmark dated May 11-18,2003
(2) Advanced material and process/october 2008
Powering the future Solar silicon
partII,Dr.OlegS.Fishman Inductotherm group
,Rancocas, Newjersey,www.inductotherm.com
(3) J.Zhao,A.Wang,andM.Green,“24,5%Efficiency
Silicon PERT Cells on MCZ Substrates and 24.7%
Efficiency PERL Cells on FZ
substrates”,Progress in Photovoltaics,7,1999,pp.471-
474.
(4)A.Münzer,KH.Eisenrith,W.W.Krühler,RE.Schloss
er, M.G.Winstel,and F.G. Kragh .“Progress of large
area 18%-PEBSCO Silicon solar cells”. WCPEC-3,
these proceedings.
(5)M.J.Cudzinovic,K.R.McIntosh,W.P.Mulligan,Dav
idSmith,andR.M.Swanson.“The choice of silicon
wafer for the production of low-costrear-contact solar
cells”.WCPEC-3,these proceedings.
(6)A.Luedge,H.Riemann,B.Hallmann,H.Wawra,L.Je
nsen,T.L.LarsenandA.Nielsen,“HIGH-SPEED
GROWTH OF FZ SILICON FOR
PHOTOVOLTAICS”Proc.High purity silicon
VII.,The electrochemical soc.
(7) Retrieved from :
http://en.wikipedia.org/wiki/czochralski_process
(8)7Retrieved from : www.solarbuzz.com
(9) Retrieved from : www.first solar.com
(10) Retrieved from : www.us.sunpowercorp.com
(11) Retrieved from : www.epia.org
(12) Proceedings NREL/BK-520-38573, November
2005 of National Renewable Energy Laboratory
(13) Characterisation of polycrystalline silicon grown
in a fluidized bed reactor - A thesis submitted in
partial fulfillment of the requirements for the degree
of Master of science in material science and
engineering at washington state university by
Megan mureen Dahl,May 2009
(14) ch.4 ,crystalline silicon solar cell byMartin
A.Green,photovoltaic special research
centre,Univesity of new south
wales,sydney,N.S.W.,Australia,24/04/2001
(15) Silicon wafer processing by Dr.Seth
P.Bates,Apllied materials,summer 2010
(16) ELEG620:Solar Electric Systems,University of
Delaware,ECE spring 2009,S.Bremner
(17) High quality polysilicon – The basis for high
wafer yields and high efficiency solar cells by
WACKER POLYSILICON,capital markets
day,Burghausen,July 25,2007
(18)Manufacturing processes for engineering
materials,5th
ed.Kalpakjian,schmid,2008,pearson
education.
REVIEW PAPER PUBLISHED ON : 05/07/2010