Note: Descriptions are shown in the official language in which they were submitted.
~ 9523
1047735
This invention is concerned with an improve-
ment on the process described in Canadian Patent
No. 988,275. The process described in that patent
is the disproportionation or redistribution of
chlorosilicon hydrîdes, such as HSiCl3 in contact
with an anion-exchange resin containing tertiary
amino or quaternary ammonium groups to produce
by a multistep process, dichlorosilane, trichloro-
silane and silane ~SiH4~.
Dichlorosilane, monochlorosilane and silane
are sparingly e~ployed in commercial activities.
Dichlorosilane (H2SiCl2~ is being increasingly used as
a source of silicon in the deposition of epitaxial
silicon layers in the manufacture of semi-conductor
de~ices. Silane (SiH4~ is being used as a source, in
a limited number of cases, of silicon metal in the
deposition of polycrystalline silicon metal, from
which single crystal silicon metal is made, and
in making epitaxial silicon layers. Theoretically,
- 20 silane is a superior source of silicon because the sole
products of the decomposition of SiH4 are hydrogen and silicon.
In the case of the deposition of silicon from the de-
: composition of HSiCl3 ~the most popular Si metal source)
~; or H2SiCl2, the primary by-product is HCl. Hydrogen
chloride is a difficult-to-handle material which can
react with deposited metal to produce HSiCl3 and/or
. 2.
104773S 9523
SiC14 thereby reducing the efficiency of the reaction
and the yield of metal produced. Moncchlorosilane is
not presently available in quantities sufflcient to
support commercial activities, but its decomposition
also results in the formation of HCl, but in lesser
a unts.
It is a purpose of this invention to provide
a single step - one pass proces~ for producing silane
(SiH4) from one of the most abundant commercial
sources of silicon, to wit, trichlorosilane (HSiC13).
The proce~s of this invention involves the dispropor-
tionation or redistribution reaction of HSiC13 in a
solid anion exchange resin bed at a temperature
sufficient to cause the lower boiling products of the
reaction to vaporize from the zone of the reaction and
the highe8t boiling liquid product of the reaction,
SiC14, to be condensed and drained away from the zone
of disproportionation. As the lower boiling products
are vaporized up the bed of anion exchange resin, the
temperature of the bed is progressively lowered to a
temperature below the boiling point of trichlorosilane
and above the boiling point of silane (SiH4). In this
manner, only silane vapors concentrate at the top of
the bed while the various chlorosilicon hydrides are
continually refluxed within the bed probably in a pro-
gre~sive manner, sudh as starting with trichlorosilane
at about the zone of initial disproportionation, then
.
10 47 7 35 9523
dichloro8ilane above the zone of initial dleproportion-
ation followed by monochloro6ilane above the zone of
dichlorosllane reflux. However, it seems clear that a
demarcation of the zone8 does not exist in the column.
At the top of the column, SiH4 is vaporized away,
As a result, the reactlon can be ch~racter-
lzed as a combination of the following:-
(A) 2HSiC13 ~ H2SiC12 ~ ~ SiC
(~) 2H25lC12 _ ~- NSiC13 ~ + H3SlCl
(C) 2H3SlCl ~_ ~ SiH4 ~ + H2SiC1
ovarall reaction is
4HSiC13 _ - S~H4 ~ + 3SiC1
which i8 dri~en to the right by the re val of SiH4
vapors from the reactlon zone, It i8 also driven to
the right by the re val of SiC14 (and the other
refluent products) from each reaction.
AB evident fru~ the discussion herein, a
governlng physical property ln determining the oper-
atlon of this process is the boiling point~ of silane
(B.P.-111.9C.), nochlorosilane (B.P.-30.4C),
tichloro~ilane (B.P. 8.3C), trichloro~ilane tB.P.31.5C)
and silicon tetrachloride (57.6C.).
The process in ef~ected by forming a
reflux of HSiC13 in the anion exchange resin bed at a
point spaced from the top of the bed, The temperature
4.
1047735 9523
of the bed at which HSiC13 i8 provided i8 sufficient
to cause vaporization of HSiC13 and the temperature
at the top of the bed is below the boiling point of
H3SiCl, and the temperature gradient between those
two points is sufficient to form liquid HSiC13 some-
what above the point where HSiC13 i8 provided,
vaporous H2SiC12 at and/or about the refluent
HSiC13, vaporous H3SiCl at and/or about the refluent
H2SiC12, and vaporous SiH4 at and/or about the
10 refluent H3SiCl. However, one may not find signifi-
cant quantities of refluent H2SiC12 and H3SiCl if the
bullc of the bed is at the reflux temperature of HSiC13
It follows that if the bed is a short one and
vaporous HSiC13 is fed to its bottom, the means for
heat removal will be much greater than when the column
is longer. The anion exchange resin bed may be in a
column in which the HSiC13 is fed as a liquid to the
top or as a vapor to the bottom. It may be suspended
or dissolved in an inert gas or liquid diluent, in the
20 state of a vapor or liquid. It may be injected into
the side of the bed, at any level, as a vapor or as a
liquid. If the HSiC13 is added to the bed as a liquid,
then the bed must be externally or internally heated to
effect vaporization. In any event, the bed will require
cooling to effect the desired ~eparation of refluent dis-
proportionated product from the advancing vapor.
Since SiC14,per se,can no longer be dispropor-
5.
1047735 9523
tionated to enhance the production of hydride products,there ls no economic basis for providing a bed in which
SiC14 can dwell. It therefore follows that H2SiC12
vapor is st effectively provided at the bottom of a
bed whose size i8 determined by the repeated dispropor-
tionation reactlon6(A) through (C) above.
The amino ion exchange resins suitable for use
in the practice of this invention are polymeric materials
which are insoluble in silane, nochlorosilane, dichloro-
silane, trichlorosilane, and silicon tetrachloride.
Such insolubility can be achieved, in the case
of linear, thermoplastic ion exchange resins, by using a
resin of sufficiently high molecular weight, viz. greater
than about 10,000 such that the polymers possess the
requisite insolubility. Insolubility can be achieved by
employing a cro~s-linked ion exchange resin, such as one
which i8 infusible as well, However, for the purposes
of this invention, the degree of cross-linking need only
be sufficient to meet the requisite insolubility require-
ments.
The amino functionality in the resin is prefer-
ably a tertiary amino or quaternary ammonium group
attached through carbon to the resin 8tructure. Prefer-
ably, other than the nitrogen atoms or the halide ions of
the amino functionality,all of the resin is composed of
carbon and hydrogen. However, this limitation does not
exclude the presence of impurities in the resin which
6.
104~735 9523
contain other atoms such as oxygen, phosphorus, iron,
boron and the like. ~uring the course of the reaction,
it is believed that ~uch impurities are leached to a
substantial degree from the resin by passage of chloro-
silicon hydride monomer through the resin thereby to
produce a resin free of such impurities or the resin
retains such impurities without contaminating the feed
or reaction products.
Particularly preferred ion exchange resins are
those made from the copolymerization of a monoolefini-
cally unsaturated (halogenated or non-halogenated)
hydrocarbons or a m~noolefinically unsaturated hetero-
amine and a polyolefinically unsaturated hydrocarbon or
polyolefinically unsaturated heteroamine. Illustrative
of such monoolefinically unsaturated compounds are, for
example, styrene, 4-chlorostyrene, 3-chlorostyrene,
vinyltnluene, 4 chloromethylstyreme, vinylnaphthalene,
vinylpyridine, 2-methyl-5-vinyl-pyridine, 2,3-dimethyl-
5-vinylpyridine~ 2-methyl-3-ethyl-5-vinylpyridine,
2-methyl-S-vinylquinoline, 4-methyl~4-vinylquinoline,
l-methyl- or 3-methyl-5-vinylisoquinoline, and the like.
The polyolefinically unsaturated compounds may
be, for example, one of the following: 1,4-divinyl-
benzene, divinylpyridine, divinyltoluenes, divinyl-
naphthalenes, trivinylbenzene, trivinylnaphthalenes,
and the polyvinylanthracenes.
Such copolymers are well known and a number of
10 4~r73~5 9523
them are commercial products which possess amino
functionality. They may be converted into cross-
linked resins with conventional free radical addition
catalysts such as peroxides. If the monomers employed
contain tertiary amino groups, such as is the case with
the pyridinyl compounds mentioned above, then it is not
necessary to treat the copolymer to introduce the amino
functionality, However, if the copoly~er contains
chloro groups (and is free of amine) then the amine can
be formed by reacting the copolymer with, for example,
ammonia, primary and secondary alkyl and/or aryl amines,
to form the amine by condensation, where the by-product
is HCl. In the preferred practice of this invention,
the amine formed in this manner is the reaction product
of a secondary amine, such as a dialkylamine, a diaryl-
amlne and/or an alkylarylamine, and the chlorinated resi~
Quaternization of the tertiary amine containing
resin can be effected by reaction with a hydrocarbon
halide 8uch as an alk~l halide or aryl halide, to form
the corresponding quaternary amine halide,
Amine anion exchange resins are available
generally in two forms. One form is called a gel
type re8in aod represents the standard type exchangers.
The other form is called a macroreticular type anion
exchange resin. The latter form possesses, within
-the particles, greater porosity for the passage of
lecules. The gel type resins possess collapsed ge~
1047735 9523
structures whereas the ~croreticular resins possess a
non-gel pore structure that is not collapsed. Such
forms of the resins have been thoroughly described in
the published literature, see, for example, JACS,
vol. 84, Jan. 20, 1962 at pages 305 and 306; I & EC
Product Research and Development, vol. 1, No. 2,
June 1962, at pages 140-144; Polymer Letters (1964)
vol. 2, at pages 587-591; U.S. Patent No. 3,037,052,
patented May 29, 1962; and U.S. Patent No. 3,367,889,
patented February 6, 1968. ~he latter patent is
particularly pertinent with respect to the processes
for producing a macroreticular tertiary amine ion
e~change resin, see specifically Example IV therein.
Illustrative of a commercial macroreticular
tertiary amine ion exchange resin is Amberlyst A-21,
a trademark ownled by, and which resin is produced by,
Rohm and Haa~ Company, Philadelphia, Pennsylvania. - -
It has the following physical properties:
Appearance Hard, spherical,
light tan
Water-saturated
beads
Ionic form Free base
Moisture holding capacity, percent 45 to 53
Exchange capacity:
Weight capacity, meq./g. dry resin 4.7 to 5.0
~olume capacity, meq./ml. 1.5 to 1.7
Density, lbs./cu. ft. 38 to 42
Effective size, mm. 0.40 to 0.55
Uniformity coefficient 2.0 maximum
Fine~, by wet sieve analysis through
#50 sieve, percent 1.0 maximum
: 1047735
9523
Hydraulic expansion, free base form
at 2.0 gpm/cu. ft., 30C, percent 120 maximum
Whole bead content, percent 100
Porosity, percen~c 0 35 to 45
Average pore diameter A 700 to 1200
Surface area, m /g. 20 to 30
Solids percent 47 to 55
Percent swelling from dry state to
solvent-saturated state -
Hexane 20
Toluene 25
Diethylether 22
Acetone 22
Absolute ethanol 30
Water 25
These data were obtained using free base form resin
previously conditioned for irreversible swelling by
a two cycle alternate acid-caustic rinse treatment.
- Such swelling may amount to 10 to 15 percent.
- 20 Illustrative of a commercial macroreticular
quaternary amine ion exchange resin is Arrberlyst A-26
a trademark owned by, and which resin is produced by,
Rohm and Haas Company, Philadelphia, Pennsylvania. It
has the following physical properties:
Appearance Hard, spherical, light
tan, water-saturated
beads
Functional group Quaternary Ammonium
Ionic form Chloride
Moisture holding 61-65
capacity, %
Ion exchange capacity:
Weight capacity, meq~ 4.1-4.4
Weight capacity,meq.~ml. 0.95-1.1
Density, lbs/ft. 39-43
Effective size, mm. 0.45-0.55
10.
104~735 9523
Uniformity coefficient 1.8 maximum
Whole bead content, % 100
Average pore diameter A 400-700
Surface area, m2/g. 25-30
Illustrative of a commercial gel type
quaternary ammonium ion exchange resin is Amberlite
IRA-400, a trademark owned by, and which resin is Pro- -
du¢ed by, Rohm and Haas Company, Philadelphia,
Pennsylvania. It has the following physical properties:
Appearance Hard, spherical, dark
tan water saturated
beads
Ionic form Quaternary amine -- - --
hydrochloride
Moisture Holding
Capacity, % 42-48
Exchange Capacity
i Wt. Capacity, meq./g.
dry resin 3.8
Volume Capacity,
me~./ml. 1.4
Density, lbs/cu. ft. 38.0-45
Effective size, mm 0.38-0.45
Uniformity Coefficient 1.75 (max.)
Fines, by wet sieve
analysis through #50
sieve (U.S. Standard),
percent c2.0 (max.)
Whole bead content, percent 100
mean pore, diameter,
Angstroms none
Swelling, conversion from
chloride to hydroxide
form~ % 18-22
11.
1047735 9523
The aforementioned resins are predicated upon
styrene and divinylbenzene copolymers which are chloro-
methylated on the styrene ring followed by amination to
produce the desired amine exchange functionality.
Further alkylation as described above can be employed
to produce the corresponding quaternary ammonium
derivatives.
In the st desirable practice of this inven-
tion, the tertiary amine or quaternary ammonium groups
are dialkyl amino, or aLkyl phenyl or diphenyl or
dicycloalkyl or alkylc~cloalkyl, or further alkylated
derivatives of the above to the quaternary derivative,
where each alkyl contains one to about 18 carbon atoms
and the cycloalkyl contains about 4 ~o about 8 carbon
atoms. The st preferred tertiary amino or quater-
nary ammonium functional groups are those which are
the alkylamino or alkylammonium wherein each alkyl
thereof contains one to about 8 carbon atoms.
j The above described resins are particulate
and in this form can be employed to disproportionate
the HSiCl~ feed by pa8sing liquid or vapors of
H SiC13 through a bed of such particles.
The disproportionation process may be prac-
~iced at temperatures as low as about O~C. to as high
as about 350C., th~ugh the preferred operating
temperatures are typically about 20C. to about 200C.
12.
~ lQ4773~5 9523
The process of this invention, as character-
ized above, can be carried out as a liquid phase
process or as a vapor phase process. Surprisingly, the
maximum equilibrium that one can achieve by such dis-
proportionation reactions is attained more rapidly in a
vapor phase disproportionation reaction as compared to
a liquid phase reaction. Hence, for commercial utiliza-
tion of this proces8, a vapor phase reaction will
probably be preferred.
The process may be carried out under sub- -
atmospheric, atmospheric or superatmospheric pressure.
Pressure plays a practical role in the utilization of
this process as a mechanism for controlling the state of
the feed material and disproportionation products during
conduct of the reaction. It is not, however, a critical
factor to the operability of this process. For example, if
one wi~hes to operate the process at 60C.at the initial re-
flux in the liquid phase rather than the vapor or gas phase,
certain considerations must be made. For exampie, at 60C.,
silane, monochlorosilane, trichlorosilane, dichloro-
silane, and silicon tetrachloride are vaporized at
atmospheric pressure and therefore pressure must be
applied in order to maintain a liquid phase process in
which these materials are present. However, the term
"liquid phase process" does not mean that all of the
products of the disproportionation reaction and the
monomer feed are in the liquid phase. All that is
13.
1047735 9523
necessary for a liquid phase reaction i8 that at least
one of such products be liquid under conditions of
operation.
Another element of the process is the "contact
time" or rather the "residence time" between the resin
and the feed materials. For each temperature employed,
there is an independent period of time in which such
nomer feed should be in contact with the anion ex-
change resin to reach ultimate equilibrium. The mole
psr cent of the desired or favored disproportionated
product is dependent upon the process temperature,
where higher temperatures generally yield higher mnle
per cent quantities of such product, and the contact
time. However,if it i8 desired to achieve partial
disproportionation and,hence,achieve less than the
equilibrium of such di~proportionation, then a shorter
contact time will be favored.
EXAMPLE
A 24" by 1-1/2" I.D. vacuum-~acketted dis-
tillation column was packsd with a mixture of 1/8"boros~licate glass helicss and 13 g of anhydrous
Amberlyst A-21 re~in (sieved to ~ 24 mesh),~upplied as
a toluene s~rry. The resin was dried overnight in
place by an nitrogen strean. The packed column was
inserted onto a 1000 ml, round bottom, 3-neck flask
fitted with a 0-52C ASTM thermwmeter and nitrogen
14.
1047735
9523
purgeJ and topped with a Dry-Ice-acetone condenser.
Standard taper ~oints were fitted with TeflonTM
; sleeves wherever po~sible. The outlet of the conden-
ser wa~ connected to the product outlet line consisting
of, in sequence, a mercury manometer, septum sampling T,
a 33.1 grams active carbon trap (Columbia grade LCK,
12/28 mesh) at room temperature, a post-trap septum
~ampling T, ending in A nitrogen blow-by.
Next, 820 g of 99.9VL pure trichlorosilane
wereiatded to the flask along with boiling ceramic
chip~, and the apparatus purged with nitrogen for an
hour. With the pu~ge of~, the column was brought to
; reflux, and kept Just below flooding condition for the
entire run. Silane rate of production was monitored
by clamping o~f the exit line, downstream of the carbon
trap, withdrswing 10 cc vapor via syringe, and record-
- ing the time needed for the manometer to return to 0 mm
pres8ure (2 to 2-1/2 minute~).
Pre- and post-trap gas samples were taken
periodically with a 2-1/2 cc disposable glass syringe,
and in~ected immedlately into an F&M 700 gas chromato-
graph fitted with a 15' x 1/4" SE-30 on Chromosorb
W 80/100 column, held isothermally at -10 + 5C. This
was adequate to separAte N2, SiH4, H3SiGl and H2SiC12
with higher boiling monomer~ being retained on the
colu~n.
. 15.
1~}47735 9523
It was found that if the active carbon trap
was cooled to -72C, no SiH4 passed it. After 10 hours
it was warmed to room temperature (25C), and this
allowed SiH4 to pass, retaining any chlorosilanes.
The apparatus was run for 68 hours over 9
days with 9 shutdown~ to a pot composition of 76%
SiC14, 22% HSiC13 and 1% H2SiC12, No leaks or equip-
ment failures were encountered.
The results of the runs discussed above are
set forth in the following table:
16.
1~477~ 9523
TABLE
;
Product Gas Comp. (Mole %)
Before After
Carbon Carbon Trap Carbon Trap
Time Silane Trap
(Hr8.) (Liter8)* Temp. SiH4 H3SiCl SiH4 H3SiCl
... . .
0.3 -80C 96.3 3.7
2 0.6 -80C 96.2 3.8
3 0.9 -80C 97.2 2.8 Pure N2(warm
trap)
4 1.2 -24C 97.6 2.4
1.5 -21C 97.9 2.1 Pure N2 -
6 1.8 -21C 9~.1 1.9
8 2.4 -21C 98.4 1.6 Pure N2(warm
trap)
3.0 0 98.4 1.6
23 7.0 22C 97.7 2.3 99.9 0.1
24 7.3 22C 97.7 2.3 99.5 0.5
31 9.4 22C 97.8 2.0 99.8 N.D. &
0.2 hvs.
67 20.0 22C 97.7 2.3 99.0 0.3 &
0.7 hvs.
68 20.3 22C Shutdown
:
*Based on an average of 300 cc/hour measured production
rate.
17,
