CA1047735A - Process of making silane - Google Patents

Abstract

PROCESS FOR MAKING SILANE

ABSTRACT OF THE DISCLOSURE

There is a process for manufacturing SiH4 by the disproportionation or redistribution of HSiCl3 which comprises feeding HSiCl3 into a bed of insoluble solid anion exchange resin containing tertiary amino or quaternary ammonium groups bonded to carbon therein, refluxing the HSiCl3 to vaporize dispropor-tionated products to the upper portion of the bed and condensing liquid SiCl4 from the area in which HSiCl3 is refluxed, maintaining the temperature at the top of the bed above the boiling point of SiH4 and below the boiling point of H3SiCl, and recovering SiH4 from the bed substantially free of chlorosilanes.
S P E C I F I C A T I O N

1.

Description

~ 9523 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.

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 .

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.

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.

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~

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 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.

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.

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.

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,

Claims (4)

WHAT IS CLAIMED IS:

1. The process of producing SiH4 which comprises providing HSiCl3 in a bed of an insoluble, solid anion exchange resin containing tertiary amino or quaternary ammonium groups bonded to carbon thereof, maintaining the temperature of the bed where HSiCl3 is provided sufficient to cause said HSiCl3 to be disproportionated to form vaporous products which rise in the bed, and SiCl4, which is condensed, maintaining the temperature at the top of the bed above the boiling point of SiH4 and below the boiling point of H3SiCl and recovering SiH4 which is sub-stantially free of chlorosilicon hydrides from the bed.

2. The process of claim 1 wherein the resin is macroreticular and contains tertiary amino groups.

3. The process of claim 2 wherein the resin is derived from the reaction of a styrene and divinyl-benzene.

4. The process of claim 1 wherein liquid HSiCl3 is vaporized and the vapors are passed to said bed.

18.