Note: Descriptions are shown in the official language in which they were submitted.
D-11856
~G~S~Oo~ OP r~ 3
Fleld of the Invention
.. ... .
The invention relates to the production of
high purity siliconO More particularly, it relates to
the low-cost production of h~gh purity silicon on a
semicontinuous or continuous basis.
escription o~ the Prior Art
.
The current commercial technology f~r the
production of high purity, polycrystalline silicon is
a low volume, batch operation that produces hlgh-cost
polycrystalline silicon rods~ This technology, generally
referred to as the Siemens process, is carried out in
the controlled atmosphere of a quar~z b~ll jar re~c~or
that Gontains silicon rods electrically heated to
about 1100C. Chlorosilanes, in concentrations of less
than 10~ in hydrogen, are ~ed into the reactor under
conditions of gas flow rate~ composition, sll~con rod
temperature~ and bell ~ar temperature ad~u~ted so as to
promote the heterogeneous decomposition o~ the
chlorosilanes on the substrate rod surfaces~ A general
descriptlon of the Siemens type process can be found
ln the Dietze et al patent, US 3~97g;490,
In this conventional process, the s~licon
deposition rate is primarily limited by the diffusion
of ~he chlorosilanes to the substrate rod surface or
the difusion of the re~ction products away from the surace,
As a result, the production rate lncreases as the
-2-
,
1144 739 D~11856
su~strate diameters or surface areas increase. In
operating ~hP bell jar reactor, it is necessary to
endeavor to preven~ bo~h gas - phase pyrol~sis o~ the
chlorosilanes and chemical vapor deposition of silicon
on ~he bell jar~ If a signi~icant amount of silicon
deposits on the quartz bell jar, the jar wil~ break on
cooldown after termination of the deposition run.
A major factor in such conventional processing
is the electri~al power consumption necessary to
maintain the uninsulated substrate rods at 1100 5,
The use of hydrogen as a diluent li~ewise contxibutes
to the high cos~s associa~ed with the low volume
conven~ional ba~ch processing. Additional costs are
incurred since the chlorosilane dacomposition reaction
is a reverslbl-e and incomplete reaction, resulting in
the need or the continual removal and separation of the
corrosive reac~ion produc~s ~rom the unreacted corrosive
reactan s.
A need thus exlsts in the art for a process
~0 for the produ~tion of silicon having the high quality
obt$i~able by the Siemens process, combined with a
capability of achia~7ing high volume on a corl~lnuous
or semicontinuous basis and an appreciable reduction
in the cost of the product polycrystalline silicon.
The aYallablli~y of such low-cost, high purity
polycrystalline silicon would facllitate the use of
silicon in desirable semiconductor and solar cell
applica~ions. ~or silicon solar ~ells employed in spac
craft applications and for industrial and commerclal
applica~ions in general, crystals of high puri~y 9
--3--
~ D-11856
semiconductor grade silicon are prepared by convertlng
metallurgical grade silicon to trichlorosilane, that
is reduced, as by the Siemens process; to polycrystalline,
semiconductor grade silicon from which single crystals
can be grown by known techniques. The amount of
useable ma~erial is grea~ly red~ced by the necessary
processing of single crystal boules to produce polished
silicon wafers. Such processing includes cutting o~f the
~mpure end portions of su~h boules, and the cuttin~,
etching and polishing o~ wafers. With accompanying
losses due to mechanical breakage and electronic
~mperfections, less than 20% of the original polycrystalline,
semiconductor greade silicon is generally recovered in
the form of useable wafers o~ single crystal material.
Because of the very high r~sultant overall cost of such
useable materlal and the relatively large area require-
me~ts involved in solar ccll applications~ material
costs constitute a very signi~ican~ actor in the
overall economics of such applica~ions.
The economic easibility o utilizing solar
cell ~echnology ~or significant por~ions o the present
and prospective ne~ds for replenishable, non-pollu~ing
energy sources would be enhaneed, ~herefore, by the
developmen~ of techniques to reduce the cost of high
purity, high perfection single crystal silicon wafers.
One significan aspect of such development would reside
in the reduction of the cost of producing high purity
polycrystalline silicon ~rom which such single crystal
material can be grownO Techni~ues heretoore generally
disclosed for refining m~tallurgical silicon for other
D-11856
73~3
purposes have not resulted in refined silicons suitable
for solar cell applications although the electronic
characteristics of solar cell materials are less
stringent than that for silicons employed in the
complex circuitry used in the electronics ind~stry.
The need for a low-cost alternative to
the Siemens process exists, ~here~ore, with respec~
to silicon materials for both solar cell and semiconductor
applications. One approach disclosed in the art for
the relatively large scale production of pol~crystalline
silicon involves the use of a fluidized bed reactor
as disclosed in the Ling patent, US 3,012,861, and in
the Bertrand et al patent, US 3,012,862. In this
approach, a silicon-con~aining vapor 1s injected in~o
a reaction chamber containing particles of elemental
silicon small enough to be fluidized and maintained in
ebullient motion by the v~porized silicon compound. The
reaction chambPr and the fluidized bed of silicon
particles are maintained at a tcmperature within the
thermal decomposition range and below the melting point
of silicon. By the heterogeneous decomposit~on of the
vaporized sillcon compound, silicon produGt is deposi~ed
on the 1uidized bed par~icles, which increase in size
until r~moved from the reaction chamber as product.
Both patents disclose the forming o~ seed particles for
the fluidiæed bed by the grinding of a portion of the
product silicon particles.
The potential for particle contamination
during the grinding or other ~smmi~ion of the hard
product silicon particles b~ conventional means known
--5--
D-11856
~4~739
in the art represents, however, a major operating
factor involved in the consideration of the ~luidized
bed approach. At the hlgh levels of purity required
for semiconductor and solar cell applications, such
contamination during the grindi~g procedure would be
unaccap~able as it would effec~ively preclude the
obtaining of the high purity levels required for
such applications. In addition, the silicon-containing
co~pound injected into the reaction chæmber, particularly
silane, will be subject to homogeneous dec~mposition
upon exposure to the reaction conditions within the
chamber as well as ~he desired heterogeneous
decomposition and deposition o product silico~ on
the seed particles. As a result of the homoganeous
decomposition, considerable ~uantities of silicon
dust are ~ormed, with such dus~ being generally
undesired in the fluid bed process and resulting in
considerable loss of materlal and/or addi~ional
processing expense. Such undesired dust ormation,
~ogether with the considerations of product purity
in the regenera~ion o~ fluldized bed seed partioles
reerred to a~ove, have here~o~ore deterred the
development of the 1uid bed approach as a practical
alternative to the conventional Siemens process. The
need continues, there~ore, for tha development of
technically ~nd economically feasible alte~natives to
~he Si~mens process for tha produc~ion o high purity
silicon fo~ se~iconductor and solar eell applications.
It is an object of the invention, therefore,
to provide a process for the production of low-cost,
high purity polycrys~alline silicon.
D~11856
~ ~ 4~3~
It is another object o~ the invention to
provide a process for the production of high purity
silicon on a contin~ous or semicontinuous basis.
It is another object of the invention to
provide a process ~or the production of silicon
capable of advantageously employing silane as the
silicon-containing feed material,
It is a further object of ~he inv~n~ion
to provide for the production at relatively high
production rates, of high purit~ polycrystalline
silicon suitable for semiconductor and solar cell
applications.
With these and other objects in mind, the
invention is h~reina~ter described in detail, the
novel features th~reo~ being par~cularly pointed out
in the appendcd claims.
SummarY o~ the Invention
High purity polycrystalline powder ls
conveniently produced by introducing a sil~con-containing
gas into the hot free space ~one o a decompo~itlon
reactor maintained at a temperature within the
decomposition range or said gas~ As a resul~ of the
homogeneous dec~mposition o~ thP gas wi~hin the free
spacé reactor, polycrystalline silicon powder ls
formed toge~her wlth by-product gas. The silicon
powder can be readily separated r~m the by-product
gas or subsequent consolidation or o~her txea~m~n~
and use ~hereo~. In one ~mbodiment, silane is
employed as the eed gas stre~m wi~h product silicon
powder and by-product hydrogen being produced. The
D-11856
~ ~ ~ 4~3~
eed gas is preferably introduced into the ~rae
space zone turbulently, as by injector means positioned
at the top of the reactor, wlth the turbulence
tending to minimize heterogeneous decomposition a~
the reac~or wall and consequent silicon wall deposit
build-up.
Brief Description of the Invention
The invention is further described with
reerence to the single figure drawing illustra~ing
an embodiment o the ~ree space reac~or appara~us
suitable for carrying out the process o~ the in~ention.
Detailed Description of the Invention
The objects of the invention are accomplished
by the production of silicon powder in a free space
zone of a decomposition chamber and ~he separa~ion
of such sil~con powder fr~m by-pr~duct gas~ While
the homogeneous decomposition of a silicon-contalning
gas under gas dec~mposi~ion condi~ons is known, ~he
invention represents a significan~ ad~ance in the artg
enabling high purity polycrystalline silicon to be
produced a~ relatively high production rates and at
low-cost, while avoiding obstacles tha~ hav~ heretofore
deterred the de~elopment of a prac~ical alternati~e to
th~ conventional~ high-cost, relati~ely low production
Siemens processO The in~ention is particularly
advantageous in that it is highly suitable or use
with silane as the ~eed gas stre~m~ Despite the
inhexent advantages realized by the use of silane,
ne~ther the conventional Siemens process or the
_~_
D-11856
~ 73~
fluidized bed approach re~erred to abov~ are suitable
to capitalize on such advantages that are referred
to below with respect to the sub~ect invention.
! The invention may be used with any suitable
silicon-containing gas stream capable o~ being thermally
pyrolyzed or reduced in gas phase. Illustrative of
the gases that may be employed are silane and the
halosilanes o~ chlorine, bromine and iod~ne. While
the chlorosilanes, such as mono-, di-, tri-, and
tetrachlorosilane; bromosilanes, such as mono-, tri-
and dibromosilane and including silicon tetrabromide;
and iodosilanes such as SiHI3 and including iodides
such as SiI4 and Si2I6, may thus be employed, particular
advantages are realized through the use of silane 9 i. e.
SiH4, as the source of high purity silicon. ~The
exothermic silane pyrolysis reaction goes to completion,
is irreversible and starts at a somewhat lower
~emperature, i.e. about 390C~ than the chloros~lanes.
In addition, silane and its decompostlon products,
~.eO sllicon and hydrogen~ are noncorrosive and
nonpolluting. The by-product hydrogen generated upon
dacomposition of silane may be used as a carrier gas,
re~irculated as a pr~heater gas~ or bottled and sold
or otherwise employed in the overall process for
producing high purity silicon from me~allurgical
grade silicon. The chlorosilane decomposition, on
the other hand, is a re~ersi~le and incomplete
~ 73~ D-ll8s6
reaction and both the chlorosilanes and their
decomposition by-products are corrosive in nature.
The overall advantages of utilizing silane are
accompanied by some disad~antages as will be
appreciate~ by those skilled în the art, however,
namely in the spontaneous combustion of
9a
D-11856
~ 7 3 ~
silane with air and in the higher current pr~ce
of silane c~mpared to that of the chlorosilanes,
The silicon-containing gas can be
introduced into the hot free space zone of the
decomposition reactor as essentially 100% silicon-
containing gas without dilution or said gas may be
diluted with inert gases, such as argon, hel~m or
the like, or wi~h hydrogen or other silicon-containing
gases. For op~mum product and production control,
it may be advantageous to dilute the silane or
other s~licon-containing gas with a suitable carrier
prior to injection into the free space reactor.
In tha decomposition of s~lane, by-product hydrogen
can conveniently be recycled ~or use as a carrier
gas for additional quantities of silane feed gas in
the semicon~inuous or continuous operations convenien~ly
carried out in the free space reactor.
Reerring to the drawing, the illustrated
embod~ment of the decomposi~ion reac~or employed
i~ the pxactice of the invention is represen~ed by
the numeral 1, with the hot free space zone 2 thereof
being positioned over set~ling cham~er 3 in which
silicon product is separa~ed fr~m by-produc~ gases.
Gas injector means 4 is located at the tap of reactor
1 and is shown extending down~ard into free space zone
2 essentially to the upper-most end of the hea~ed
section thereofO As shown, th~ heated section of zone
2 is wrapped with a suitable layer of insulation 5 and
is inductively heated by means of induction heatlng
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D-11856
~ 73 ~
coil 6. Settling chamber 3 having support members
7 secured thereto contai~s a dust collector 8
and exhaust lin~ 9 through ~hich by-product gases
are withdrawn. A preheater 10 may be employed,
i~ desired, ~or prehea~ing the silane or other
~ilicon-containing ~eed gas supplied fr~m a source
11 thereof through l~ne 12. Settling chamber 3 has
opening 13 at the bottom ~hereof for withdrawal of
product silicon.
It will be understood that various
modifications to decomposition reactor 1 can be
made with the various embGdiments oE the reactor
being suitable for, or even advantageous in, the
practice o~ the process of the invention, For
ex~mple, gas injector means 4 may be loca~ed so
as to in;ect ~he silicon-containing gas upward fr~m
the bott~m of zone 2, and the injector may be positioned
so as to extend to various dlst~nces wi~hi~ zone 2,
It may also be advantageous to employ several injectors
or multiple orfice injectors of either water-cooled
or uncooled designO Means for employing elevated
reac~on pressures may also be provided al~hough the
invention can readily be practiced at essentially
atmospheric pressure conditionsO
In the practice of the invention, a silicon-
con~aining gas stream from source 11 ls passed
through line 12 a~d preheater 10, if desired, to
injector means 4 through which said gas is introduced
into hot free space zone 2 of dec~mposition reactor 1
D-1185
~ 3~
Said free space zone is maintained at the de~ired
operating temperature by means of induction h~ating
coil 6 and reactor insulation 5. Upon exposure
to the rPaction conditions in free space zone 2,
the silicon-containing feed gas s~ream will rapidly
be converted b~ homogeneous decomposition to fine
silicon powder and by-product gas. The thus - formed
silicon particles constitute silicon nuclei that
react heterogeneously with the silicon-containing
gas and thereby grow to submicron or low micron size
that can conveniently be separated from the by-product
gas.
The decomposition products thus ormed are
passed to settling chamber 3 in which the silicon powder
product is found to be of sufficient size to
conveniently separate from the by-product gas that
is thereupon exhausted from settling chamber 3 through
line 9 for further disposition as indicated above.
To assure that essentially all of the silicon powder
produced in zone 2 is recovered and to minimize the
entraiNment of silicon powder in the ~y-product gas,
sa~d gas is advantageously passed through dus~ collec-
tion means 8 so that essentially all of the silicon
product may be contained in the settling chamber
or the auxiliary dust collector. A discharge opening
13 in settling chamber 3 i5 used to remove and recover
product silicon from decomposition reactor 1.
The sllicon containing gas in introduced into
the hot free space zone o~ the reactor maintained
at a temperature within the decomposition temperature
-12-
D 11856
~ 3~
range of the particular silicon-containlng gas and
below the melting point te~pera~ure of silicon,
i.e. about 1420C. For efficient dec~mpos~tion o
the feed gas and sllicon powder ormation, it has
been found desirable to employ a tempera~ure within
the range of from about 390C up to about 1400C
~lth preerable temp~xatures being within ~he range of
from about 800C to about lOOO~C. The silicon containing
gas may be passad into ~ee ~pace zone 2 without preheat,
as by use o~ a wa~er-cooled injector means, or may
be preheated to a temperature less than the decompos~tion
temperature ~hereo~. Such preheat will ordinarily
occur upon passage o the gas ~hrough the portion
of injection means 4 extending into said zone 2
in the absence of cool-ing, or may be accomplished
by the use of preheatar 10 ~o which ho~ by-produc~
gas may ~e passed if desiredO It should be noted
that, by preheating the ln~ec~ed ~eed gas, it may
be possible to maintain the reac~or walls a~ a
somewhat cooler ~empera~ure th~n otherwise, thareby
reducing heat losses during the silicon produc~ion
operation. Alternately, the reac~or walls may be
m~in~ained ho~er in co~junction with such prehea~ing
so as to achieve an increase in productio~ rates
under the particular reactox conditions employed.
The invention may be carried out at
essentially atmospheric condi~ions or, al~erna~ely;
at elevated reaction pressures, e.g. up to 100 psi
or above. The use of elevated reactor pressures
may tend ~o favor higher s:ilicon production ra~es
-13~
D-11856
~'1473~
and he formation of larger particles of silicon.
The use of lower reactor pressures may tend to
favor reduction in pxoduct particle size. As
indicated above~ the product silicon is ob~ained
as a powder of sufficient size to permit convenient
separation ~r~m by~product gases, with the silicon
powder size ranging from submicron to low micron
size, e.g. 5 u. It will be und0rstood that, in any
particular embodiment or example o~ the invention,
particles of silicon having a range of particle size
will be obtained. The particle sizes are not
determined directly, but are calculated, ass~ming
spherical particles, from suxface area values. In
illustrative examples of the invention, the actual
average surface areas determined were found to vary
fr~m approx~mately 0.5m2/gm to about 32m2/gm.
Average particle diameters calculated ~rom the
values range from about 800 ~ to about 5 microns.
The silicon product is obtained as a high purity,
polycrystalline powder that, upon discharge from the
decomposition reactor, may be consolidated or mel~ed
for further processing by con~entional means to produce
a low~cos , high pu~i~y single crystal material for
solar cell and/or semi~onductor applica~ion p~rposes.
In a highly desir~ble embodiment of the
invention, the silicon-containing feed gas is
in~roduced turbulently~ tha~ is under condi~ions
of turbulent gas flow, into the free space zone
of the decomposition reactor. By means of such
tur~ulence the dec~mposition o~ the sillcon-containing
gas occurs rapidly in a diverging region near the
-14
D- 11856
~4~39
injection nozzle xather than at further distances
from the injector.
As a result, the heterogeneous decomposition
of the silane or other silicon-containing feed gas
at the reactor wall, with consequent silicon wall
deposit build-up can be minimized. It will be
apprecia~ed by ~hose skilled in the art that
condltions of turbulent flow are obtained at a
Reynolds No~ of above about 2,000, with the
\~ :
14a
D- 11856
3~
Reynolds No. being a ~unction of the particular
nozzle diameter, and the inje~tion gas velocity,
density, viscosity and the temperature of the
injected gas. While turbulent injection of the
eed gas is not an essential feature of the
inv~ntion, it is o~ particular advantage and is
generally preferred in practical silicon production
operations in accordance with the process of the
inventionO
The benefits of the invention were
illustrated in an ex~mple in which silane was fed
into the top of a decomposition reactor at the rate
of 4 l/min, employing an injec~or with a 2mm. diameter
orifice. The calculated room temperature velocity
of the gas passing through the injector was 21.2 m /sec.
With the reactor wall at the center of the ~xee space
zone maintained at approximately 800C, the silane
inside ~he inj ector reached a tempera~ure oE
approximately 350~C. By the time the gas was hea~ed
to said 350Cg it would undergo, assuming ideal gas
conditicns, a volume expansion of abou~ 2.1 ~imes,
resulting in an orifice exit veloclty o~ æbout
44.6 m/sec~ and a Reynolds No~ of about 3,000.
In another run, the reactox wall temperature was
approximately 800C and a water-cooled injector was
employed to assure against heating the silane to
above its decompositlon temperature while in the
inj ector. Silane was -Eed at the rate of 2 l/min. to
the injectox and through a 2mm. dlzmeter orlEice~
resulting in an injection velocity of about 10,6 m~sec.
-15-
D-11856
~ 7 3 ~
and a Reynolds No. of about 2700. In both cases,
the decomposition products were silicon powder
and by-product hydrogen gas. In both runs9 which
were carried ou~ at near atmospheric pressure,
decomposition of the silane at the reactor wall,
and consequent silicon wall build-up were minimized
by injecting the silane turbulently into the hot
reactor.
In other examples using a larger reactor,
silane flow rates up to 61 l/min, were achieved,
employing a 4 . 6 mm. orifice, with an inj ection gas
velocity of 61.6 m/sec. and a Reynolds No. o 36,000.
15a
~ 4~ 3~ D~11856
Reactor wall deposit build-up was again minlmi~ed
by injecting the silane ~urbulently into the
reactor. At a silane flow r~te of 61 l/min.,
the reactor wall temperature at the center of the
hot zone was controlled at between 995 and
1030C. A silane decomposltion efficiency o
~8% was obtained, wlth the average particle size
of the high purity, polycrystalline silicon powder
product being 0.30 um. ~o measurable impurities
are detectable iR the product upon examination
us~ng the cathode layer emission spectroscopic
technique.
The invention represents a significant
development in the silicon production field. In
overcoming the disadvantages o~ the conventiona
Siemens process and the difficulties encountered
in other ef~orts to provide a process for the
high volume production of high purity silicon,
the invention achisves the production o~ high purity
siliconj in a recoverable form, with minimum
pyrolysis ef~iciencies of 80% readily ob~ained
and exceeded, and with the injection o~ undiluted
as well as diluted feed gas s~reams. The
decomposition of the silicon-containing gas
readil~ occuxs in the ~ree re ctor space and can
be achieved without building up re~ctor wall deposit~
of silicon to the extent tha~ undesired blockage
of the free space zone of the reac~or occ~rs. In
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D-11856
~ ~ ~ 4~3 ~
this regard, it should be noted that the mlnimal
deposit o silicon likely ~o occur in ~he practice
of the invention is of advantage as a very thin
liner of high purity silicon on ~he surface of the
quar~z, graphite, stai~le~s steel or other sui~able
reactor wall material. While the silicon powd2r
produced in the free space reactor is generally
less desirable than the rod-shaped silicon
produced in a Siemens bell jar, the homogeneous
decomposition of the feed gas and the heterogeneous
grow~h of the resultant silicon powders to a
readily recoverable size enables ~he process of
the inven~ion to provide highly important advan~ages
over the currently practiced technology.
As previously noted, the stlicon production
rate in the Siemens process ls limited by the
available sur~ace area. No such restrlction
exists in the ree space decomposition process o~
the in~ention. Upon reaching is decomposition
tempera~ure, the silicon-contalning gas decomposes
homogeneously and heterogeneously within the free
space zone . The ~ree space reactor process has g
as a resul~, a m~ch higher production ratP capability
~han ~he conventional process.
As also indica~ed above~ the concen~ration
of the inj ec~ed silicon-containing feed gas in
the Siemens process should be less than 10% to
prevent the ~ormation o~ silicon particles in the
gas phase and to prevent silicon from ~eposiking
on the quartz bell jar. In the ~ree space reactor
D-11856
~ 73~
procass of the invention, however~ there is no
theoretical composition limit, and the silicsn-
containing feed gas can be utilized in undiluted
form or diluted with a carrier gas if desired.
The expenses involved in using and handling large
volumes o~ a carrier gas are not necessar~,
therefore, in the pra~tice of the in~ention.
The advantages of high production and
reduced carrler gas costs are further enhanced
by the fact that the i~ven~ion can readily be
carried ou~ on a semicontinuous or continuous
basis as in other free space reactor applications
heretofore known, such as in the production of
nickel powder fxom nickel carbonyl as shown in
US 3,367,768.
An additional limitation in the
conventional process rasults from the practical
limit to the size o the bell jar employed in the
Siemens process and the resulting inhibition on
scaleup. There is no kno~ size or scaleup
l~mi~ation applicable to the free space reactor
process of the invention.
An important ~actor in the overall cost
of silicon production is the energy consumption
requlred. The conventional Siemens process is
an energy-intensive process. Energy losses are
kno~n to occur through radiation from the substrate
rods and through gas convection. A large gas
-18-
D-11856
~9f9L739
throughpu~ is malntained ~o prevent the gas
phase from reaching decomposition temperatures
and for cooling the quartz bell jar. By
contrast, the ex~ernal surface of a ree space
reactor may be insulated to prevent radiation
and air convection heat lossasO The internal
gas and particle con~ection mo~ion within the
hot free space zone provides a desirable means
for ~ransferring heat rom the in~ernal surface
of the ~ree space zone to the gas phase ~o
promote the decomposition reac~ion.
The simplicity of ~he free space
reactor design coupled with its desirable
scaleup potential reduces the capital equipment
costs ~hereof compared to a conventional Siemens
process plant~ Such factors also tend to reduce
the manpower opera~ing requiremen~s ~or commercial
embodiments o~ the invention as compared to such
requirements in carrying out the conventional
process.
In addition to all such production and
cos~ advantages of the invention, the abîli~y of
the in~ention to advantageously utili~e sîlane
should again be emphasi~edO Specific advantages
o~ sllane as the feed stock were indica~ed above,
An integxa~ed overall operations or producIng
high purity silicon from metallurgical grade
material~ the by-product hydrogen rom silane
decomposi~lon can be employedg no~ only for carrier
gas purposes as indica~ed above~ bu~ as ~ source of
~ 14 ~ 73 9
hydrogen for use iQ ~he hydroge~a~ion of
.~, CC~4~ Si/~of~ WG~Jro~
metallurgical silicon~to produce trichloros~lane
from which silane can conveniently be produced
~s, for ex~mple, b~ the one-s.t~p p~ess ~l~closed
in US patent No. 3,968,199.
In light of all of the advantages
hereinabove recited, the inven~ion can readily
be appreciated as a highly significant development~
enabling high purity silicon to be prepared at
high production rates and at low-cost on a
continuous or semicontinuous basis. The invention
thus constitu~es a major advance in the
development of low-cost silicon materials and the
utilization of such materials in the deveLopmen~
o~ commercially feasible solar cell technology
and in satisfying the requirements for high
purity silicon for semiconductor applications,
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