Process for preparing polysilicon with diminished hydrogen content by using a fluidized bed with a two-step heating process
First Claim
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1. A method for producing polysilicon particles having a reduced hydrogen content, said process comprising:
- (a) forming polysilicon particles which have a size within the size range of from about 150 to about 3000 microns, the formation being by a process which comprises thermally decompositing silane in a first fluidized bed comprised of silicon particles whereby the silane metal produced from the thermal decomposition of the silane is deposited on the particles; and
(b) subjecting the formed particles to heat in a second fluidized bed or a moving bed in the presence of a non-contaminating inert gas for a time and at a temperature of from about 890°
C. to about 1200°
C., which temperature exceeds the first fluidized bed temperature, whereby the combination of the time and the temperature in the second fluidized bed are sufficient to reduce the hydrogen content of the formed particles but insufficient to melt-consolidate the particles.
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Abstract
The hydrogen content of polysilicon can be reduced by heat treatment. The process is preferably conducted on polysilicon particles in bead-like form produced by chemical vapor deposition in a fluidized bed. The heat treatment is preferably conducted at a temperature of 1020°-1200° C. for a time from about 6 hours to about 1 hour sufficient to reduce the hydrogen content, and insufficient to cause agglomeration of the particles being treated. In order to reduce the tendency of particles to agglomerate at the process temperature employed, the particle bed is preferably maintained in motion during the dehydrogenation. The products produced by the process can have a hydrogen content of 30 ppma or less. These improved products can be used to produce monocrystalline silicon for the production of semiconductor devices.
45 Citations
30 Claims
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1. A method for producing polysilicon particles having a reduced hydrogen content, said process comprising:
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(a) forming polysilicon particles which have a size within the size range of from about 150 to about 3000 microns, the formation being by a process which comprises thermally decompositing silane in a first fluidized bed comprised of silicon particles whereby the silane metal produced from the thermal decomposition of the silane is deposited on the particles; and (b) subjecting the formed particles to heat in a second fluidized bed or a moving bed in the presence of a non-contaminating inert gas for a time and at a temperature of from about 890°
C. to about 1200°
C., which temperature exceeds the first fluidized bed temperature, whereby the combination of the time and the temperature in the second fluidized bed are sufficient to reduce the hydrogen content of the formed particles but insufficient to melt-consolidate the particles. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. A method for producing polysilicon particles having a reduced silicon dust and hydrogen content, said process comprising:
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(a) forming polysilicon particles which have at least a portion of their surface covered with fine silicon dust, the formation being by a process which comprises thermally decomposing silane in a first fluidized bed comprised of silicon particles whereby the silane metal produced from the thermal decomposition of the silane is deposited on the particles; and (b) subjecting the formed particles to heat in a second fluidized bed or a moving bed in the presence of a non-contaminating inert gas for a time and at a temperature of from about 890°
C. to about 1200°
C., which temperature exceeds the first fluidized bed temperature, whereby the combination of the time and the temperature in the second fluidized bed are sufficient to reduce the amount of fine silicon dust covering the particle surfaces and are sufficient to reduce the hydrogen content of the formed particles but insufficient to melt-consolidate these particles. - View Dependent Claims (15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26)
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27. In a process for preparing particulate polysilicon, which process comprises:
- (a) a productivity mode in which silicon seed particles are contacted, in a fluidized bed, with a gas comprising from about 10 to about 100 mol % silane at a temperature which causes the thermal decomposition of the silane whereby silicon metal resulting from such decomposition is deposited on the seed particles to yield intermediate silicon particles and whereby silicon dust is formed which deposits on the surfaces of such intermediate silicon particles; and
(b) a quality mode which comprises contacting, in a fluidized bed, the intermediate particle having surface dust with a gas comprising from about 1 to about 5 mol % silane at a temperature above the thermal decomposition temperature of the silane whereby a silicon metal layer is deposited on the intermediate particles which cements at least a portion of the silicon dust to the intermediate particles, the improvement which comprises subjecting the intermediate particles which have at least a portion of the silicon dust cemented thereto to heat a fluidized bed or a moving bed in the presence of a non-contaminating inert gas for a time and at a temperature which exceeds the fluidized bed temperatures used in forming such cemented intermediate particles so that the hydrogen content of such cemented intermediate particles is reduced, the temperature however being insufficient to melt-consolidate the cemented intermediate particles. - View Dependent Claims (28, 29, 30)
- (a) a productivity mode in which silicon seed particles are contacted, in a fluidized bed, with a gas comprising from about 10 to about 100 mol % silane at a temperature which causes the thermal decomposition of the silane whereby silicon metal resulting from such decomposition is deposited on the seed particles to yield intermediate silicon particles and whereby silicon dust is formed which deposits on the surfaces of such intermediate silicon particles; and
Specification
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Current AssigneeSunEdison, Inc.
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Original AssigneeEthyl Corporation (Newmarket Corporation)
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InventorsBoone, James E., Allen, Robert H.
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Primary Examiner(s)Chaudhuri, Olik
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Assistant Examiner(s)HORTON, KENNETH
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Application NumberUS07/791,882Time in Patent Office664 DaysField of Search423/348, 423/349, 423/350, 427/213US Class Current423/349CPC Class CodesC01B 33/029 by decomposition of monosilaneC01B 33/037 Purification by zone-meltin...
