US4784840A — Polysilicon fluid bed process and product

Claim 1

Independent Claim 202 words

A process for preparing particulate polysilicon having a reduced amount of silicon dust on surfaces thereof, said process comprising: (I) a productivity mode which comprises contacting in a fluidized bed, silicon seed particles having a size range of about 80 to 400 microns, with a gas comprising from about 10 to 100 mole percent of a thermally decomposable silicon compound, at a temperature above the thermal decomposition temperature of said compound; whereby (i) silicon metal produced from said compound is deposited on said seed particles thereby forming intermediate silicon particles having a size range of about 600 to 800 microns; and (ii) silicon dust, produced by homogeneous decomposition of said silicon compound, is deposited on surfaces of said intermediate particles; (II) a quality mode which comprises contacting in a fluidized bed, said intermediate particles having surface dust thereon, with a gas comprising from about 1 to about 5 mole percent of a thermally decomposable silicon compound, at a temperature above the thermal decomposition temperature of said compound; whereby a silicon layer having a thickness sufficient to cement surface silicon dust to said particles is deposited on said particles thereby reducing the amount of removable silicon dust from the surface of said particles.

Claim 2

Dependent Claim 202 words

A process for preparing particulate polysilicon having a reduced amount of silicon dust on surfaces thereof, said process comprising: (I) a productivity mode which comprises contacting in a fluidized bed, silicon seed particles having a size range of about 80 to 400 microns, with a gas comprising from about 10 to 100 mole percent of a thermally decomposable silicon compound, at a temperature above the thermal decomposition temperature of said compound; whereby (i) silicon metal produced from said compound is deposited on said seed particles thereby forming intermediate silicon particles having a size range of about 600 to 800 microns; and (ii) silicon dust, produced by homogeneous decomposition of said silicon compound, is deposited on surfaces of said intermediate particles; (II) a quality mode which comprises contacting in a fluidized bed, said intermediate particles having surface dust thereon, with a gas comprising from about 1 to about 5 mole percent of a thermally decomposable silicon compound, at a temperature above the thermal decomposition temperature of said compound; whereby a silicon layer having a thickness sufficient to cement surface silicon dust to said particles is deposited on said particles thereby reducing the amount of removable silicon dust from the surface of said particles.

Claim 3

Dependent Claim 22 words

The process of claim 1 wherein the same thermally decomposable silicon compound is employed in said productivity mode and said quality mode.

Claim 4

Dependent Claim 11 words

The process of claim 2 wherein said silicon compound is silane.

Claim 5

Dependent Claim 18 words

The process of claim 3 being conducted at a temperature within the range of 620° to 650° C.

Claim 6

Dependent Claim 20 words

The process of claim 3 wherein said quality mode is conducted using silane admixed with hydrogen as an inert gas.

Claim 7

Dependent Claim 20 words

The process of claim 1 wherein step (I) is conducted in one fluidized bed reactor and step (II) in another.

Claim 8

Dependent Claim 18 words

The process of claim 1 wherein steps (I) and (II) are conducted in the same fluidized bed reactor.

Claim 9

Dependent Claim 49 words

A process of claim 1, comprising conducting said step (I) using seed particles (a) porepared by the process of steps (I) and (II), followed by (b) reducing the particle size of the product of step (II) to an average of 200 microns with an 80 to 400 micron range.

Claim 10

Dependent Claim 109 words

A process for reducing the mount of silicon dust on the surface of particulate silicon particles, said particles (i) having a size range of from about 400 to about 1000 microns and (ii) having a surface dust content greater than about 0.1 weight percent, said process comprising contacting said particles in a fluidized bed with a deposition gas comprising 1 to 5 mole percent silane at a temperature between the thermal decomposition temperature of silane and the melting point of silicon, to deposit on said particle surfaces a layer of metallic silicon of from about 0.1 to about 5 microns, and thereby cement surface siliocn dust to said particles.

Claim 11

Dependent Claim 109 words

A process for reducing the mount of silicon dust on the surface of particulate silicon particles, said particles (i) having a size range of from about 400 to about 1000 microns and (ii) having a surface dust content greater than about 0.1 weight percent, said process comprising contacting said particles in a fluidized bed with a deposition gas comprising 1 to 5 mole percent silane at a temperature between the thermal decomposition temperature of silane and the melting point of silicon, to deposit on said particle surfaces a layer of metallic silicon of from about 0.1 to about 5 microns, and thereby cement surface siliocn dust to said particles.

Claim 12

Dependent Claim 112 words

In a process for produoing particulate silicon by thermal decomposition of a vaporous silicon-containing compound in a fluidized bed, the improvement which comprises reducing the amount of silicon dust in the product by fluidizing (a) a particulate silicon having a size range of from about 400 to 1000 microns with (b) a gaseous stream comprising from about 1 to about 5 mole percent silane in hydrogen, at from about 620° to about 650° C.; such that a layer of metallic silicon is formed on the particulate product sufficient to make silicon dust adhere thereto, thereby reducing the surface dust content of said high purity particulate silicon to below about 0.1 weight percent.

Claim 13

Dependent Claim 112 words

In a process for produoing particulate silicon by thermal decomposition of a vaporous silicon-containing compound in a fluidized bed, the improvement which comprises reducing the amount of silicon dust in the product by fluidizing (a) a particulate silicon having a size range of from about 400 to 1000 microns with (b) a gaseous stream comprising from about 1 to about 5 mole percent silane in hydrogen, at from about 620° to about 650° C.; such that a layer of metallic silicon is formed on the particulate product sufficient to make silicon dust adhere thereto, thereby reducing the surface dust content of said high purity particulate silicon to below about 0.1 weight percent.

Claim 14

Dependent Claim 33 words

A process of claim 10 wherein said stream of vaporous silicon-containing compound is introduced into said bed at a velocity defined by a U/U min ratio of from about 1.5 to about 3.5.

Claim 15

Dependent Claim 22 words

A process of claim 11 wherein said stream consists essentially of from about 2 to about 4 mole percent silane in hydrogen.

Claim 16

Dependent Claim 63 words

A process of claim 12 wherien at least a poriton of said hydrogen is recycled hydrogen previously (a) produced by thermal decomposition of silane in deposition gas intimately contacted with said particle bed (b) subsequently collected after exit form said bed and (c) thereafter incorporated in said deposition gas by admixing with the silane prior to reintroduction onto said bed of silicon particles.

Claim 17

Dependent Claim 227 words

A process of producing elemental silicon, said process comprising the steps of intimately contacting (A) a bed of particles of silicon maintained, (i) in a vertically disposed reaction zone, and (ii) at a reaction temperature higher than the thermal decomposition temperature of silane with (B) silane contained in a first and second deposition gas, each of said deposition gases being introduced into said bed of particles at a flow rate sufficient to maintain said bed in a fluidized state within said reaction zone, said first deposition gas being introduced for a first deposition period and being from about 10 to about 100 mole percent silane in hydrogen, said second deposition gas being introduced for a second deposition period beginning substantially immediately after the termination of said first deposition period, and being a mixture of about 1 to about 5 mole percent silane in hydrogen, said process being further characterized in that (i) said first deposition period is from about 2 to about 5 times as long in time duration as said second deposition period, and (ii) in said second deposition period, a silicon layer having a thickness of about 0.1 to about 5 microns is deposited on particles of about 400 to 1000 microns and silicon dust is adhered thereto, such that the dust content of said product is reduced to less than about 0.1 weight percent.

Claim 18

Dependent Claim 227 words

A process of producing elemental silicon, said process comprising the steps of intimately contacting (A) a bed of particles of silicon maintained, (i) in a vertically disposed reaction zone, and (ii) at a reaction temperature higher than the thermal decomposition temperature of silane with (B) silane contained in a first and second deposition gas, each of said deposition gases being introduced into said bed of particles at a flow rate sufficient to maintain said bed in a fluidized state within said reaction zone, said first deposition gas being introduced for a first deposition period and being from about 10 to about 100 mole percent silane in hydrogen, said second deposition gas being introduced for a second deposition period beginning substantially immediately after the termination of said first deposition period, and being a mixture of about 1 to about 5 mole percent silane in hydrogen, said process being further characterized in that (i) said first deposition period is from about 2 to about 5 times as long in time duration as said second deposition period, and (ii) in said second deposition period, a silicon layer having a thickness of about 0.1 to about 5 microns is deposited on particles of about 400 to 1000 microns and silicon dust is adhered thereto, such that the dust content of said product is reduced to less than about 0.1 weight percent.

Claim 19

Dependent Claim 18 words

The process of claim 14 wherein said reaction temperature is form about 590° C. to about 750° C.

Claim 20

Dependent Claim 18 words

The process of claim 15 wherein said reaction temperatue is from about 620° C. to about 650° C.

Claim 21

Dependent Claim 25 words

The process of claim 16 wherein the deposition gases are introduced at a rate defined by U/U min of from about 1.5 to about 3.5.

Claim 22

Dependent Claim 34 words

The process of claim 16 wherein each of said deposition gases is preheated to a temperature of from about 330° C. to about 350° C. prior to their introduction into said bed of particles.

Claim 23

Dependent Claim 66 words

The process of claim 16 wherein at least a portion of the hydrogen in one or both of said deposition gases is recycled hydrogen that had been produced by the thermal decomposition of silane in said reaction zone, then collected after exit from said zone, and then incorporated in said deposition gas by admixing with silane prior to reintroduction therewith into said bed of seed particles.

Claim 24

Dependent Claim 17 words

The process of claim 16 wherein the pressure within said reaction zone is 1 to 3 atmospheres.

Annuity Stage	Window Opens	Payment Deadline	Surcharge Period Until	Estimated Fee	Status
3.5 Years (Year 4)	1991-11-15	1992-05-16	1992-11-15	$2000.00	Window Closed / Lapsed
7.5 Years (Year 8)	1995-11-15	1996-05-16	1996-11-15	$3760.00	Window Closed / Lapsed
11.5 Years (Year 12)	1999-11-15	2000-05-16	2000-11-15	$7700.00	Window Closed / Lapsed

Polysilicon fluid bed process and product

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