US20010051387A1 - Method of growing silicon crystal in liquid phase and method of producing solar cell - Google Patents
Method of growing silicon crystal in liquid phase and method of producing solar cell Download PDFInfo
- Publication number
- US20010051387A1 US20010051387A1 US09/198,263 US19826398A US2001051387A1 US 20010051387 A1 US20010051387 A1 US 20010051387A1 US 19826398 A US19826398 A US 19826398A US 2001051387 A1 US2001051387 A1 US 2001051387A1
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- Prior art keywords
- silicon
- melt
- indium
- substrate
- growing
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- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 title claims abstract description 168
- 229910052710 silicon Inorganic materials 0.000 title claims abstract description 168
- 239000010703 silicon Substances 0.000 title claims abstract description 168
- 238000000034 method Methods 0.000 title claims abstract description 63
- 239000013078 crystal Substances 0.000 title claims abstract description 56
- 239000007791 liquid phase Substances 0.000 title claims abstract description 22
- 239000000758 substrate Substances 0.000 claims abstract description 89
- 229910052738 indium Inorganic materials 0.000 claims abstract description 84
- APFVFJFRJDLVQX-UHFFFAOYSA-N indium atom Chemical compound [In] APFVFJFRJDLVQX-UHFFFAOYSA-N 0.000 claims abstract description 84
- 239000000155 melt Substances 0.000 claims abstract description 78
- 239000002019 doping agent Substances 0.000 claims abstract description 43
- 229910052782 aluminium Inorganic materials 0.000 claims abstract description 27
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 claims abstract description 27
- ZOXJGFHDIHLPTG-UHFFFAOYSA-N Boron Chemical compound [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 claims abstract description 17
- 229910052796 boron Inorganic materials 0.000 claims abstract description 17
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 claims abstract description 14
- 229910052698 phosphorus Inorganic materials 0.000 claims abstract description 13
- 239000011574 phosphorus Substances 0.000 claims abstract description 13
- 229910052785 arsenic Inorganic materials 0.000 claims abstract description 11
- RQNWIZPPADIBDY-UHFFFAOYSA-N arsenic atom Chemical compound [As] RQNWIZPPADIBDY-UHFFFAOYSA-N 0.000 claims abstract description 11
- 239000007787 solid Substances 0.000 claims abstract description 10
- 239000007788 liquid Substances 0.000 claims description 14
- 239000002390 adhesive tape Substances 0.000 claims description 4
- 238000002048 anodisation reaction Methods 0.000 claims description 3
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N silicon dioxide Inorganic materials O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 abstract description 37
- 239000010453 quartz Substances 0.000 abstract description 29
- 238000004519 manufacturing process Methods 0.000 abstract description 18
- 229910021419 crystalline silicon Inorganic materials 0.000 abstract description 12
- 239000010409 thin film Substances 0.000 abstract description 6
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 abstract description 4
- 229910052799 carbon Inorganic materials 0.000 abstract description 4
- 229910021421 monocrystalline silicon Inorganic materials 0.000 abstract 1
- 229910021420 polycrystalline silicon Inorganic materials 0.000 description 33
- 239000008188 pellet Substances 0.000 description 29
- 239000012535 impurity Substances 0.000 description 16
- 238000006243 chemical reaction Methods 0.000 description 15
- 239000010408 film Substances 0.000 description 15
- 238000001816 cooling Methods 0.000 description 13
- 229910052751 metal Inorganic materials 0.000 description 12
- 239000002184 metal Substances 0.000 description 12
- 235000012431 wafers Nutrition 0.000 description 11
- 229920006395 saturated elastomer Polymers 0.000 description 10
- ATJFFYVFTNAWJD-UHFFFAOYSA-N Tin Chemical compound [Sn] ATJFFYVFTNAWJD-UHFFFAOYSA-N 0.000 description 9
- 239000002904 solvent Substances 0.000 description 9
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 8
- KRHYYFGTRYWZRS-UHFFFAOYSA-N Fluorane Chemical compound F KRHYYFGTRYWZRS-UHFFFAOYSA-N 0.000 description 8
- 239000000243 solution Substances 0.000 description 8
- 238000004544 sputter deposition Methods 0.000 description 8
- GYHNNYVSQQEPJS-UHFFFAOYSA-N Gallium Chemical compound [Ga] GYHNNYVSQQEPJS-UHFFFAOYSA-N 0.000 description 7
- 238000009826 distribution Methods 0.000 description 7
- 229910052733 gallium Inorganic materials 0.000 description 7
- 239000007789 gas Substances 0.000 description 7
- 239000011521 glass Substances 0.000 description 7
- 229910052739 hydrogen Inorganic materials 0.000 description 7
- 239000001257 hydrogen Substances 0.000 description 7
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 6
- GWEVSGVZZGPLCZ-UHFFFAOYSA-N Titan oxide Chemical compound O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 description 6
- 238000002844 melting Methods 0.000 description 6
- 230000008018 melting Effects 0.000 description 6
- 239000000843 powder Substances 0.000 description 6
- 230000000052 comparative effect Effects 0.000 description 5
- 229910021417 amorphous silicon Inorganic materials 0.000 description 4
- 239000003085 diluting agent Substances 0.000 description 4
- 238000002474 experimental method Methods 0.000 description 4
- 230000002349 favourable effect Effects 0.000 description 4
- 239000004973 liquid crystal related substance Substances 0.000 description 4
- 229910052757 nitrogen Inorganic materials 0.000 description 4
- 239000002994 raw material Substances 0.000 description 4
- 239000004065 semiconductor Substances 0.000 description 4
- 230000002411 adverse Effects 0.000 description 3
- 238000004458 analytical method Methods 0.000 description 3
- 238000000151 deposition Methods 0.000 description 3
- 238000010438 heat treatment Methods 0.000 description 3
- 150000002431 hydrogen Chemical class 0.000 description 3
- 238000000206 photolithography Methods 0.000 description 3
- 238000001004 secondary ion mass spectrometry Methods 0.000 description 3
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 description 2
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 description 2
- 229910052581 Si3N4 Inorganic materials 0.000 description 2
- 229910045601 alloy Inorganic materials 0.000 description 2
- 239000000956 alloy Substances 0.000 description 2
- 230000015572 biosynthetic process Effects 0.000 description 2
- 238000001354 calcination Methods 0.000 description 2
- 229910052804 chromium Inorganic materials 0.000 description 2
- 239000011651 chromium Substances 0.000 description 2
- 230000008021 deposition Effects 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 229920001296 polysiloxane Polymers 0.000 description 2
- 239000000523 sample Substances 0.000 description 2
- 238000007650 screen-printing Methods 0.000 description 2
- HQVNEWCFYHHQES-UHFFFAOYSA-N silicon nitride Chemical compound N12[Si]34N5[Si]62N3[Si]51N64 HQVNEWCFYHHQES-UHFFFAOYSA-N 0.000 description 2
- 229910052814 silicon oxide Inorganic materials 0.000 description 2
- 238000003980 solgel method Methods 0.000 description 2
- 239000004408 titanium dioxide Substances 0.000 description 2
- OGIDPMRJRNCKJF-UHFFFAOYSA-N titanium oxide Inorganic materials [Ti]=O OGIDPMRJRNCKJF-UHFFFAOYSA-N 0.000 description 2
- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical compound [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 description 1
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 1
- BLRPTPMANUNPDV-UHFFFAOYSA-N Silane Chemical compound [SiH4] BLRPTPMANUNPDV-UHFFFAOYSA-N 0.000 description 1
- 239000000853 adhesive Substances 0.000 description 1
- 230000001070 adhesive effect Effects 0.000 description 1
- 150000004703 alkoxides Chemical class 0.000 description 1
- 229910021529 ammonia Inorganic materials 0.000 description 1
- 238000000137 annealing Methods 0.000 description 1
- 239000007864 aqueous solution Substances 0.000 description 1
- 125000004429 atom Chemical group 0.000 description 1
- 238000005229 chemical vapour deposition Methods 0.000 description 1
- 239000011248 coating agent Substances 0.000 description 1
- 238000000576 coating method Methods 0.000 description 1
- 239000003086 colorant Substances 0.000 description 1
- 238000004891 communication Methods 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 229910052802 copper Inorganic materials 0.000 description 1
- 239000010949 copper Substances 0.000 description 1
- 239000002178 crystalline material Substances 0.000 description 1
- 229910001873 dinitrogen Inorganic materials 0.000 description 1
- PZPGRFITIJYNEJ-UHFFFAOYSA-N disilane Chemical compound [SiH3][SiH3] PZPGRFITIJYNEJ-UHFFFAOYSA-N 0.000 description 1
- 238000001312 dry etching Methods 0.000 description 1
- 238000005530 etching Methods 0.000 description 1
- 230000001788 irregular Effects 0.000 description 1
- 229910001338 liquidmetal Inorganic materials 0.000 description 1
- 238000004518 low pressure chemical vapour deposition Methods 0.000 description 1
- ORUIBWPALBXDOA-UHFFFAOYSA-L magnesium fluoride Chemical compound [F-].[F-].[Mg+2] ORUIBWPALBXDOA-UHFFFAOYSA-L 0.000 description 1
- 229910001635 magnesium fluoride Inorganic materials 0.000 description 1
- 230000000873 masking effect Effects 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
- QJGQUHMNIGDVPM-UHFFFAOYSA-N nitrogen group Chemical group [N] QJGQUHMNIGDVPM-UHFFFAOYSA-N 0.000 description 1
- 239000003960 organic solvent Substances 0.000 description 1
- 230000000737 periodic effect Effects 0.000 description 1
- 238000007639 printing Methods 0.000 description 1
- 239000011347 resin Substances 0.000 description 1
- 229920005989 resin Polymers 0.000 description 1
- 229910000077 silane Inorganic materials 0.000 description 1
- 239000005368 silicate glass Substances 0.000 description 1
- 239000000377 silicon dioxide Substances 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- -1 that is Substances 0.000 description 1
- 238000002230 thermal chemical vapour deposition Methods 0.000 description 1
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L27/00—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate
- H01L27/02—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components specially adapted for rectifying, oscillating, amplifying or switching and having potential barriers; including integrated passive circuit elements having potential barriers
- H01L27/12—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components specially adapted for rectifying, oscillating, amplifying or switching and having potential barriers; including integrated passive circuit elements having potential barriers the substrate being other than a semiconductor body, e.g. an insulating body
- H01L27/1214—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components specially adapted for rectifying, oscillating, amplifying or switching and having potential barriers; including integrated passive circuit elements having potential barriers the substrate being other than a semiconductor body, e.g. an insulating body comprising a plurality of TFTs formed on a non-semiconducting substrate, e.g. driving circuits for AMLCDs
- H01L27/1259—Multistep manufacturing methods
- H01L27/1296—Multistep manufacturing methods adapted to increase the uniformity of device parameters
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- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B19/00—Liquid-phase epitaxial-layer growth
- C30B19/02—Liquid-phase epitaxial-layer growth using molten solvents, e.g. flux
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- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
- C30B29/02—Elements
- C30B29/06—Silicon
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- H01L21/02367—Substrates
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- H01L21/02381—Silicon, silicon germanium, germanium
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- H01L29/66—Types of semiconductor device ; Multistep manufacturing processes therefor
- H01L29/66007—Multistep manufacturing processes
- H01L29/66075—Multistep manufacturing processes of devices having semiconductor bodies comprising group 14 or group 13/15 materials
- H01L29/66227—Multistep manufacturing processes of devices having semiconductor bodies comprising group 14 or group 13/15 materials the devices being controllable only by the electric current supplied or the electric potential applied, to an electrode which does not carry the current to be rectified, amplified or switched, e.g. three-terminal devices
- H01L29/66409—Unipolar field-effect transistors
- H01L29/66477—Unipolar field-effect transistors with an insulated gate, i.e. MISFET
- H01L29/66742—Thin film unipolar transistors
- H01L29/6675—Amorphous silicon or polysilicon transistors
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- H01L31/04—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices
- H01L31/06—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices characterised by potential barriers
- H01L31/068—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices characterised by potential barriers the potential barriers being only of the PN homojunction type, e.g. bulk silicon PN homojunction solar cells or thin film polycrystalline silicon PN homojunction solar cells
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- H01L31/18—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof
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- H01L31/18—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof
- H01L31/1892—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof methods involving the use of temporary, removable substrates
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
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- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
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Definitions
- the present invention relates to a method of growing a silicon crystal in a liquid phase.
- a silicon crystal produced by the method of the present invention can be used in silicon devices having a large area such as solar cells and picture element driving circuits for liquid crystal display devices.
- Solar cells are prevailing as electric power sources which are systematically linked with driving power sources for various kinds of appliances and commercial line power. It is desirable that solar cells can be manufactured at low costs. For example, it is desired to produce solar cells on inexpensive substrates at a low cost.
- Silicon is generally used as a semiconductor for composing solar cells.
- Single crystalline silicon is extremely excellent from a viewpoint of efficiency of converting a light energy into electric power, that is, photoelectric conversion efficiency. From a viewpoints of enlargement of areas and reduction of manufacturing costs, on the other hand, amorphous silicon is advantageous. In the recent years, it has come to use polycrystalline silicon for the purpose of obtaining a cost as low as that of amorphous silicon and a photoelectric conversion efficiency as high as that of the single crystalline silicon.
- the expensive crystalline materials are sufficiently utilized by a method which is conventionally adopted to manufacture silicon devices using single crystalline silicon or polycrystalline silicon since the method is configured to slice a lump crystal to form plate-like substrates and hardly capable of preparing substrates which have thickness of 0.3 mm or smaller, thereby allowing the substrates to have thicknesses larger than a thickness (20 ⁇ m to 50 ⁇ m) generally required to absorb incident rays.
- the spin method of forming a silicon sheet by flowing drops of melted silicon into a template has a quality insufficient for use as a semiconductor and cannot provide a photoelectric conversion efficiency which is so high as that in the case of using a general crystalline silicon.
- a silicon crystal of a good quality is generally grown by the thermal CVD method of thermally decomposing a raw material gas such as silane chloride.
- a raw material gas such as silane chloride.
- it is general to use the so-called epitaxial growing furnace.
- such a growing furnace is not only unsuited to mass production since it can treat 10 wafers at most at one batch but also requires a high raw material cost since it utilizes a raw material gas at a low efficiency.
- this furnace also provides a crystal insufficient in a quality thereof and allows the crystal to grow at a rate only on the order of 0.01 ⁇ m/minute, thereby being low in productivity.
- a liquid phase growing method of supersaturating a liquid metal solution in which silicon is dissolved and allowing a crystal to deposit from the solution onto a substrate is known.
- This liquid phase growing method is capable of growing a crystal of a high quality at a high rate on the order of 1 ⁇ m/minute and treating 100 or more wafers at one batch, thereby being suited to mass production.
- the liquid phase growing method is not generally used for growing silicon and has some technical problems to be solved though it widely prevails as a method of growing compound semiconductors.
- a metal which is to be used as a solvent It is desirable that a metal to be used for this purpose has a solubility for silicon which is as high as possible and can hardly be incorporated into deposited silicon. Furthermore, a metal having a lower melting point and a lower vapor pressure can be handled easier. Tin is used most generally as a solvent for silicon. Tin can be handled relatively easily since it has allow melting point and a relatively high solubility for silicon. It has been considered that tin is a preferable solvent since tin and silicon belong to the same IV group of the Periodic Table, and tin is inactive as a dopant even when it is incorporated into deposited silicon.
- tin is incorporated into silicon in a prettily large amount when growth conditions (in particular, a growth temperature) are inadequate, thereby deforming a lattice of a silicon crystal and adversely affecting electric characteristics of a semiconductor probably due to the atomic size of tin very different from that of silicon though they are atoms belonging to the IV group. From this viewpoint, there is posed a doubt in aptitude of tin as a solvent which is used to grow a crystal for a solar cell with high efficiency.
- gallium, indium and aluminum which belong to the III group can be mentioned as metals which are usable as solvents.
- Gallium and indium, in particular, having a low melting point can be handled easily. Since gallium is extremely expensive, indium is hopeful for use as a practical melt.
- indium posed a problem which is described later in controlling by introducing dopant a conductivity type of a silicon crystal which is grown using an indium melt.
- gallium is used as p-type dopant in combination with an indium melt (G. F. Zheng et al.: Solar Energy Materials and Solar Cells. 40 (1996) 231-238).
- gallium is usable at relatively low concentrations, it cannot be used for doping at high concentrations since a solid of gallium can be dissolved into silicon at concentrations within a relatively low solubility and is extremely expensive.
- examples which use n-type dopants in combination with indium melts are disclosed by Japanese Patent Application Laid-Open Nos. 9-183695 and 9-183696.
- Thin films of silicon crystals are also used as devices for driving picture elements of liquid crystal displays and so on.
- Progresses made in the mass communication media have produced increasing demands for a display having a larger screen and capable of more minutely driving at a higher speed.
- the TFTs (thin film transistors) of amorphous silicon have hitherto been utilized as a driving circuit for picture elements to cope with the demands for a display having a larger screen, the amorphous silicon cannot meet any longer the demands for a display which can be more minutely driven at a higher speed, and it is becoming to use TFTs of polycrystalline silicon.
- polycrystalline silicon which has higher carrier mobility and other characteristics.
- the liquid phase growing method is also suited for growing such crystalline silicon of a high quality on a large substrate such as a glass plate.
- a glass plate or the like makes it unallowable to heat a solution to a high temperature, it is possible to grow a crystal of a good quality by using indium as a solvent.
- indium As a solvent, it is impossible to grow a thick crystal at a low growth temperature which lowers a solubility of silicon into indium, there is no problem in formation of a crystal to be used as a TFT having a thickness of the order of 0.1 to 0.5 ⁇ m which is far smaller than that of a solar cell.
- indium is used as a solvent for production of a TFT, a problem related to reproducibility may be posed.
- a concentration of a dopant must be precisely controlled in order to enhance reproducibility of characteristics of the TFT.
- an ununiform distribution of a dopant concentration is not preferable which produces an ununiform distribution of characteristics of TFT, thereby producing variations in image density on a display device.
- indium was used as a dopant, it was impossible to sufficiently prevent the dopant from being distributed ununiformly on surfaces.
- the present invention has been achieved in view of the current circumstances described above, and an object of the present invention is to provide a method of precisely controlling a dopant to be incorporated into crystalline silicon which is grown in a liquid phase using indium as a solvent, thereby enabling mass production of solar cells having a high efficiency and a light weight as well as driving circuits for a high precision and high speed display having a large area.
- the present invention therefore provides a method of growing a silicon crystal, which comprises using a melt prepared by dissolving a solid of silicon containing a dopant at a predetermined concentration into liquid indium. Furthermore, the present invention provides a method of growing a silicon crystal, which comprises using a melt prepared by dissolving a solid of indium containing a dopant at a predetermined concentration into liquid indium.
- the present invention provides a method of producing a solar cell, which comprises the steps: preparing a melt by dissolving a solid of silicon containing a dopant at a predetermined concentration into liquid indium; forming a first silicon layer of a first conductivity type on a substrate by bringing the substrate into contact with the melt; and forming a second silicon layer of a second conductivity type on the first silicon layer of the first conductivity type.
- the present invention provides a method of producing a solar cell, which comprises the steps of: preparing a melt by dissolving a solid of indium containing a dopant at a predetermined concentration into liquid indium and further dissolving silicon into the melt; forming a first silicon layer of a first conductivity type on a substrate by bringing the substrate into contact with the melt; and forming a second silicon layer of a second conductivity type on the first silicon layer of the first conductivity type.
- FIG. 1 is a sectional view for showing one example of a solar cell according to the present invention
- FIGS. 2A, 2B and 2 C are sectional views for showing one example of production steps of a solar cell according to the present invention.
- FIG. 3 is a sectional view for showing one example of an apparatus used for carrying out a method of producing a silicon crystal according to the present invention
- FIG. 4 is a sectional view for showing one example of an apparatus used for carrying out the method of producing a silicon crystal according to the present invention
- FIG. 5 is a sectional view for showing one example of an apparatus used for carrying out the method of producing a silicon crystal according to the present invention.
- FIGS. 6A, 6B, 6 C, 6 D, 6 E and 6 F are sectional views for showing one example of production steps of a thin film transistor (TFT) of polycrystalline silicon to which the method of the present invention is applied.
- TFT thin film transistor
- silicon was grown using a melt which was prepared by dissolving silicon into highly pure indium until it was saturated and then dissolving pellets of boron and aluminum.
- specific resistance of silicon grown as described above was low in reproducibility.
- the result of SIMS analysis indicated variations in concentrations of boron and aluminum in the silicon.
- silicon was grown using a melt which was prepared by dissolving silicon into highly pure indium until it was saturated, and then dissolving powders of phosphorus and arsenic.
- the silicon grown as described above was certainly of the n-type but its specific resistance was low in reproducibility.
- the result of SIMS analysis indicated variations in concentrations of phosphorus and arsenic in the silicon.
- Indium can be used as a first example of adequate diluent.
- An alloy prepared by dissolving impurities into indium at a predetermined concentration makes it possible to more accurately control concentrations of the impurities and prevent adverse influences from being produced by a diluent incorporated into silicon. Further, such an alloy is advantageous also from a viewpoint of having a slight different density from that of a solvent, that is, liquid indium.
- a solvent that is, liquid indium.
- Silicon can be used as a second example of adequate diluent.
- the elements of the impurities are preliminarily diluted with silicon, the elements of the impurities are always and simultaneously dissolved into indium with silicon, thereby facilitating to maintain concentrations of the elements constant relative to that of silicon.
- a crucible 301 made of quartz glass is filled with a dissolved indium melt 302 .
- the apparatus is accommodated as a whole in a quartz bell-jar 303 and heated to a desired temperature from outside with electric furnaces 304 .
- Hydrogen gas is always introduced into the quartz bell-jar 303 to maintain a reducing atmosphere in the bell-jar 303 .
- a reference numeral 305 represents a substrate susceptor made of quartz glass which holds ends of a substrate 300 of a highly pure polycrystalline silicon or the substrate 101 of the metal grade polycrystalline silicon 101 having a diameter of 4 inches.
- the substrate 100 or 300 of the polycrystalline silicon is held obliquely so as to go and come smoothly into and out of the melt 302 .
- a reference numeral 306 designates a load lock chamber which can be partitioned from the quartz bell-jar 303 with a gate valve 307 .
- the susceptor 305 is hoisted up with a hoist mechanism 308 and the gate valve 307 is closed to prevent an interior of the quartz bell-jar 303 from being exposed to atmosphere.
- a reference numeral 309 represents a dopant introducer which is configured also as a load lock mechanism and allows pellets 310 containing a dopant to be put into the indium melt 302 in a condition where the gate valve 307 is opened and the susceptor 305 is hoisted up.
- the method of growing the layer 102 of the p-type polycrystalline silicon will be described concretely.
- the indium melt 302 was heated to 1000° C. and pellets 310 of highly pure indium containing 1% by weight of aluminum were put into the indium melt 302 . Since the indium pellets had a density which was nearly the same as that of indium, it was considered that the indium pellets were to uniformly disperse in the melt.
- the substrate 300 of highly pure polycrystalline silicon was submerged as shown in FIG. 3. The substrate 300 was maintained in this condition for 30 minutes to dissolve silicon into the indium melt 302 until it is saturated.
- the gate valve 307 was closed, the substrate 300 of the highly pure polycrystalline silicon was removed from the susceptor 305 , and a substrate 101 of metal grade polycrystalline silicon having the diameter of 4 inches was placed in the susceptor.
- the gate valve 307 was opened and the susceptor 305 was hoisted down to a preheating position (not shown in the drawings) over the melt 302 to wait for temperature rise of the substrate 101 .
- cooling of the interior of the quartz bell-jar was started at a rate of 1° C./minute. When temperature reached 990° C., the substrate 101 was submerged into the melt 302 .
- the susceptor 305 was hoisted up and the load lock chamber 306 was closed with the gate valve 307 . After replacing an internal gas of the load lock chamber 306 with nitrogen, the substrate 101 was taken outside. A p-type polycrystalline silicone layer 102 having a thickness of 30 ⁇ m had been grown on the substrate 101 .
- the characteristic of the solar cell 1 was evaluated with an AM-1.5 solar simulator to obtain a photoelectric conversion efficiency of 13%. Furthermore, 21 subcells each having an area of 1 cm 2 were formed on the substrate 101 and checked for a distribution of the photoelectric conversion efficiency. The result indicated a distribution within ⁇ 2% which was a favorable result. Moreover, a silicon crystal was grown successively five times while replenishing aluminum and silicon in the same procedures as those for the first growth in the amount of aluminum and silicon lost in each growth due to the deposition from the melt. This experiment indicated the variation of the photoelectric conversion efficiency within ⁇ 3% at one and the same location of each substrate, which was a favorable result.
- FIG. 4 shows an apparatus for growing single crystalline silicon which was used in Example 2.
- Reference numerals 401 and 402 represent members which compose a carbon boat.
- the member 401 is provided with a cavity for dropping substrates 403 , 403 a and 403 b for dissolving and a cavity for dropping a substrate 404 for growing.
- the member 402 is provided with a hole in which an indium melt 405 is to be accommodated.
- the members 401 and 402 are configured to slide relative to each other.
- a polycrystalline silicon substrate 403 for dissolving silicon into a melt and a single crystalline silicon substrate 404 having a porous layer 202 formed on the surface for growing a crystal were arranged in the member 401 .
- the member 402 was laid on the member 401 and a predetermined amount of highly pure indium pellets were placed in the hole of the member 402 .
- the indium pellets were heated in a hydrogen flow, they were melted into a melt 405 as shown in FIG. 4. After maintaining the growing apparatus at 1050° C. for five minutes, the temperature was adjusted to 1000° C. and the melt 405 was brought into contact with the substrate 403 for dissolving by sliding the member 402 .
- a p-type polycrystalline silicon substrate doped with boron having specific resistance of 0.01 ⁇ cm was used as the substrate 403 for dissolving.
- cooling of the apparatus as a whole was started at a rate of 1° C./minute.
- temperature reached 980° C. the member 402 was slid to bring the melt 405 into contact with a surface of the porous layer 202 and cooled for one minute to form a p + -type silicon layer 203 having a thickness of approximately 1 ⁇ m.
- the melt was returned to its initial position by sliding the member 402 once again and left standing for cooling.
- a titanium dioxide film 207 having a thickness of 600 ⁇ and a magnesium fluoride film 208 having a thickness of 1000 ⁇ were stacked as antireflection layers 207 and 208 by sputtering. In sputtering of the antireflection layers, grid tabs were masked so that the antireflection layers were not deposited thereon.
- Example 3 shows steps for mass production of solar cells having a structure which is basically the same as that of the solar cell produced in Example 2 and proves that the method of the present invention is preferably applicable to mass production.
- a melt was prepared by placing highly pure indium pellets in a crucible of a second quartz bell-jar, heating and melting the pellets at 1000° C. Then, ten substrates of polycrystalline silicon doped with boron and having a specific resistance of 0.05 ⁇ cm were attached to a susceptor 505 , submerged into the indium melt, kept in this condition for 30 minutes to dissolve silicon until the indium melt was saturated, thereby preparing a melt for growing a p-type silicon layer.
- a melt was prepared by placing highly pure indium pellets in a crucible of a third quartz ball-jar, heating and melting the pellets at 1000° C. Highly pure indium pellets containing 1% by weight of arsenic were put into the melt, and a polycrystalline silicon substrate for dissolving was submerged into the melt and kept in this condition for 30 minutes to dissolve silicon into the indium melt until it was saturated, thereby preparing a melt for growing an n + -type silicon layer.
- the gate valves With the gate valves kept closed, the polycrystalline silicone substrate for dissolving was removed from the susceptor 505 and a silicon wafer 201 (hereinafter simply referred to “substrate”) having a diameter of six inches and a porous layer 202 formed on a surface thereof was set in the susceptor.
- substrate silicon wafer 201
- the gate valve of the first quartz bell-jar was opened, the susceptor 505 was hoisted down to its preheating position, an interior of the quartz bell-jar was maintained at 1050° C. for ten minutes and then cooled to 1000° C., and gradual cooling of the interior of the quartz bell-jar was started at a rate of 0.2° C./minute.
- an adhesive tape 209 was bonded to a surface of the antireflection layer, the layers of the p + -type silicon layer 203 from the upper layers were peeled from the substrate 201 by applying a force to the substrate 201 so as to destroy the porous layer 202 , and the tape 209 was peeled off with an organic solvent. Thereafter, a back surface of the p + -type silicon layer 203 was coated with an electroconductive ink, bonded to an aluminum support plate 210 and calcined for setting, thereby producing solar cells 5 .
- Example 4 Used in Example 4 was a growing apparatus having a structure which was similar to that of the apparatus shown in FIG. 3 except that two quartz bell-jars were connected to a common load lock chamber by way of gate valves.
- an n-type polycrystalline silicon substrate doped with arsenic having a specific resistance of 0.5 ⁇ cm and a size of 4-inch square was submerged into an indium melt 302 in a crucible of a first quartz bell-jar as shown in FIG. 3 and maintained in this condition for thirty minutes to dissolve silicon into the melt 302 until it was saturated, thereby preparing a melt for an n-type silicon layer for dissolving.
- the gate valve was closed, the polycrystalline silicon substrate was dismounted from a susceptor, and the glass substrate 601 on which the gate insulating film 603 had been formed was set in the susceptor.
- the gate valve of the first quartz bell-jar was opened, and the susceptor was hoisted down to its preheating position and held at 600° C. for ten minutes to wait for temperature rise of the substrate 601 . Thereafter, gradual cooling of an interior of the quartz bell-jar was started at a rate of 0.2° C./minute. When temperature reached 595° C., the substrate 601 was submerged into the melt.
- the substrate was maintained in this condition for 30 minutes until an n-type polycrystalline silicon layer 604 having a thickness of 3000 ⁇ was grown on the gate insulating film 603 . Then, the susceptor was hoisted up, the gate valve was closed, the gate valve of the second quartz bell-jar was opened while maintaining the hydrogen atmosphere, and the susceptor was hoisted down to its preheating position and kept at 600° C. for ten minutes, whereafter gradual cooling of an interior of the quartz bell-jar was started at a rate of 0.2° C./minute.
- the substrate 601 When temperature reached 595° C., the substrate 601 was submerged in the melt and maintained in this condition for five minutes, whereby a p + -type silicon layer 605 having a thickness of 500 ⁇ was grown on the n-type silicon layer 604 (see FIG. 6C). Though silicon was grown at a very low rate in Example 4 due to the use of the glass substrate which did not allow the melt to be heated to a high temperature, the growth could be completed in a time within a range similar to that for the other examples since a necessary layer thickness was small.
- a source electrode 606 and a drain electrode 607 were patterned by photolithography (see FIG. 6D). Using the electrodes 606 and 607 as masks, unnecessary portions of the p + -type layer at a channel portion 608 were removed by dry etching (see FIG. 6E). Furthermore, a silicon oxide layer 609 was deposited on the surface by sputtering for surface protection (see FIG. 6F).
- a dopant was supplied as pellets or powders each singly composed of a dopant element.
- on/off ratios of TFTs were distributed within a wide range of 10 2 , whereby the TFTs could not be expected to be usable for driving display devices.
- the method of the present invention is capable of growing silicon crystals of a high quality having a dopant concentration favorably controlled, thereby making it possible to produce high performance solar cells, driving circuits for liquid crystal display devices and so on at a low cost and with a high reproducibility.
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Abstract
The method of the present invention of growing single crystal silicon in a liquid phase comprises preparing a melt by dissolving a solid of silicon containing boron, aluminum, phosphorus or arsenic at a predetermined concentration into indium melted in a carbon boat or a quartz crucible, supersaturating the melt, and submerging a substrate into the melt, thereby growing a silicon crystal containing a dopant element. This method can provide a method of growing a thin film of crystalline silicon having a high crystallinity and a dopant concentration favorably controlled, thereby serving for mass production of inexpensive solar cells which have high performance as well as image displays which have high contrast and are free from color ununiformity.
Description
- 1. Field of the Invention
- The present invention relates to a method of growing a silicon crystal in a liquid phase. A silicon crystal produced by the method of the present invention can be used in silicon devices having a large area such as solar cells and picture element driving circuits for liquid crystal display devices.
- 2. Related Background Art
- Solar cells are prevailing as electric power sources which are systematically linked with driving power sources for various kinds of appliances and commercial line power. It is desirable that solar cells can be manufactured at low costs. For example, it is desired to produce solar cells on inexpensive substrates at a low cost. Silicon is generally used as a semiconductor for composing solar cells. Single crystalline silicon is extremely excellent from a viewpoint of efficiency of converting a light energy into electric power, that is, photoelectric conversion efficiency. From a viewpoints of enlargement of areas and reduction of manufacturing costs, on the other hand, amorphous silicon is advantageous. In the recent years, it has come to use polycrystalline silicon for the purpose of obtaining a cost as low as that of amorphous silicon and a photoelectric conversion efficiency as high as that of the single crystalline silicon.
- However, it cannot be said that the expensive crystalline materials are sufficiently utilized by a method which is conventionally adopted to manufacture silicon devices using single crystalline silicon or polycrystalline silicon since the method is configured to slice a lump crystal to form plate-like substrates and hardly capable of preparing substrates which have thickness of 0.3 mm or smaller, thereby allowing the substrates to have thicknesses larger than a thickness (20 μm to 50 μm) generally required to absorb incident rays. Furthermore, there has recently been proposed the spin method of forming a silicon sheet by flowing drops of melted silicon into a template. However, a silicon sheet formed by this method has a quality insufficient for use as a semiconductor and cannot provide a photoelectric conversion efficiency which is so high as that in the case of using a general crystalline silicon.
- There has been proposed and actually applied to trial production of a solar cell under the circumstances described above, an idea of growing on an inexpensive substrate a silicon crystal of a good quality until it has a required and sufficient thickness, and form an active region (for example, a photoelectric conversion region) thereon. Moreover, there has been proposed an idea of growing a silicon crystal epitaxially on a substrate of a good quality and then peel off the silicon crystal and reuse the substrate.
- On a premise that large area devices such as solar cells are to be produced in mass, however, it is not so easy to grow a silicon crystal until it has a thickness required for absorbing incident rays. A silicon crystal of a good quality is generally grown by the thermal CVD method of thermally decomposing a raw material gas such as silane chloride. In order to grow a single crystal at a high rate on the order of 1 μm/minute in particular, it is general to use the so-called epitaxial growing furnace. However, such a growing furnace is not only unsuited to mass production since it can treat 10 wafers at most at one batch but also requires a high raw material cost since it utilizes a raw material gas at a low efficiency. Though it is possible to treat 100 or more wafers at one batch by utilizing the so-called low pressure CVD furnace, this furnace also provides a crystal insufficient in a quality thereof and allows the crystal to grow at a rate only on the order of 0.01 μm/minute, thereby being low in productivity.
- As another method of growing a silicon crystal, there is known a liquid phase growing method of supersaturating a liquid metal solution in which silicon is dissolved and allowing a crystal to deposit from the solution onto a substrate. This liquid phase growing method is capable of growing a crystal of a high quality at a high rate on the order of 1 μm/minute and treating 100 or more wafers at one batch, thereby being suited to mass production. However, the liquid phase growing method is not generally used for growing silicon and has some technical problems to be solved though it widely prevails as a method of growing compound semiconductors.
- One of important problems lies in selection of a metal which is to be used as a solvent. It is desirable that a metal to be used for this purpose has a solubility for silicon which is as high as possible and can hardly be incorporated into deposited silicon. Furthermore, a metal having a lower melting point and a lower vapor pressure can be handled easier. Tin is used most generally as a solvent for silicon. Tin can be handled relatively easily since it has allow melting point and a relatively high solubility for silicon. It has been considered that tin is a preferable solvent since tin and silicon belong to the same IV group of the Periodic Table, and tin is inactive as a dopant even when it is incorporated into deposited silicon.
- However, the inventors have recently found that tin is incorporated into silicon in a prettily large amount when growth conditions (in particular, a growth temperature) are inadequate, thereby deforming a lattice of a silicon crystal and adversely affecting electric characteristics of a semiconductor probably due to the atomic size of tin very different from that of silicon though they are atoms belonging to the IV group. From this viewpoint, there is posed a doubt in aptitude of tin as a solvent which is used to grow a crystal for a solar cell with high efficiency.
- In addition to tin, elements such as gallium, indium and aluminum which belong to the III group can be mentioned as metals which are usable as solvents. Gallium and indium, in particular, having a low melting point can be handled easily. Since gallium is extremely expensive, indium is hopeful for use as a practical melt. However, indium posed a problem which is described later in controlling by introducing dopant a conductivity type of a silicon crystal which is grown using an indium melt. There are known examples wherein gallium is used as p-type dopant in combination with an indium melt (G. F. Zheng et al.: Solar Energy Materials and Solar Cells. 40 (1996) 231-238). Though gallium is usable at relatively low concentrations, it cannot be used for doping at high concentrations since a solid of gallium can be dissolved into silicon at concentrations within a relatively low solubility and is extremely expensive. On the other hand, examples which use n-type dopants in combination with indium melts are disclosed by Japanese Patent Application Laid-Open Nos. 9-183695 and 9-183696.
- Boron and aluminum are generally used as p-type dopants, whereas phosphorus and arsenic are often used as n-type dopants. It is therefore conceivable to use these dopants for growing silicon crystals in liquid phase with the indium melt. In practice, however, problems were posed in conductivity types or reproducibility of conductivities of grown silicon crystals in certain cases. Furthermore, it is feared that a metal of the III group such as indium which is originally active by itself as a dopant may control a crystal to a strong p-type when incorporated into silicon and may be incapable of controlling it to p−-type or n-type.
- The problems described above makes it still impossible to judge whether or not the liquid phase method has a true aptitude for growth of silicon crystals on scales of mass production and whether or not solar cells utilizing thin films of silicon crystals have practical utility.
- Thin films of silicon crystals are also used as devices for driving picture elements of liquid crystal displays and so on. Progresses made in the mass communication media have produced increasing demands for a display having a larger screen and capable of more minutely driving at a higher speed. Though the TFTs (thin film transistors) of amorphous silicon have hitherto been utilized as a driving circuit for picture elements to cope with the demands for a display having a larger screen, the amorphous silicon cannot meet any longer the demands for a display which can be more minutely driven at a higher speed, and it is becoming to use TFTs of polycrystalline silicon. In addition, there has been increasing demands for polycrystalline silicon which has higher carrier mobility and other characteristics.
- The liquid phase growing method is also suited for growing such crystalline silicon of a high quality on a large substrate such as a glass plate. Though use of a glass plate or the like makes it unallowable to heat a solution to a high temperature, it is possible to grow a crystal of a good quality by using indium as a solvent. Though it is impossible to grow a thick crystal at a low growth temperature which lowers a solubility of silicon into indium, there is no problem in formation of a crystal to be used as a TFT having a thickness of the order of 0.1 to 0.5 μm which is far smaller than that of a solar cell. When indium is used as a solvent for production of a TFT, a problem related to reproducibility may be posed. Therefore, a concentration of a dopant must be precisely controlled in order to enhance reproducibility of characteristics of the TFT. In formation of a film having a large area, an ununiform distribution of a dopant concentration is not preferable which produces an ununiform distribution of characteristics of TFT, thereby producing variations in image density on a display device. In certain cases where indium was used as a dopant, it was impossible to sufficiently prevent the dopant from being distributed ununiformly on surfaces.
- The present invention has been achieved in view of the current circumstances described above, and an object of the present invention is to provide a method of precisely controlling a dopant to be incorporated into crystalline silicon which is grown in a liquid phase using indium as a solvent, thereby enabling mass production of solar cells having a high efficiency and a light weight as well as driving circuits for a high precision and high speed display having a large area.
- The present invention therefore provides a method of growing a silicon crystal, which comprises using a melt prepared by dissolving a solid of silicon containing a dopant at a predetermined concentration into liquid indium. Furthermore, the present invention provides a method of growing a silicon crystal, which comprises using a melt prepared by dissolving a solid of indium containing a dopant at a predetermined concentration into liquid indium.
- Moreover, the present invention provides a method of producing a solar cell, which comprises the steps: preparing a melt by dissolving a solid of silicon containing a dopant at a predetermined concentration into liquid indium; forming a first silicon layer of a first conductivity type on a substrate by bringing the substrate into contact with the melt; and forming a second silicon layer of a second conductivity type on the first silicon layer of the first conductivity type.
- In addition, the present invention provides a method of producing a solar cell, which comprises the steps of: preparing a melt by dissolving a solid of indium containing a dopant at a predetermined concentration into liquid indium and further dissolving silicon into the melt; forming a first silicon layer of a first conductivity type on a substrate by bringing the substrate into contact with the melt; and forming a second silicon layer of a second conductivity type on the first silicon layer of the first conductivity type.
- FIG. 1 is a sectional view for showing one example of a solar cell according to the present invention;
- FIGS. 2A, 2B and2C are sectional views for showing one example of production steps of a solar cell according to the present invention;
- FIG. 3 is a sectional view for showing one example of an apparatus used for carrying out a method of producing a silicon crystal according to the present invention;
- FIG. 4 is a sectional view for showing one example of an apparatus used for carrying out the method of producing a silicon crystal according to the present invention;
- FIG. 5 is a sectional view for showing one example of an apparatus used for carrying out the method of producing a silicon crystal according to the present invention; and
- FIGS. 6A, 6B,6C, 6D, 6E and 6F are sectional views for showing one example of production steps of a thin film transistor (TFT) of polycrystalline silicon to which the method of the present invention is applied.
- The present invention has been achieved on the basis of knowledge obtained by experiments which are described below.
- First, commercially available indium pellets were put into a carbon crucible, heated and melted at 1000° C. in a hydrogen gas flow to obtain liquid indium. A melt was prepared by bringing non-doped polycrystalline silicon into contact with the liquid indium and dissolving silicon into the liquid indium until it was saturated. Then, the melt was gradually cooled until it was supersaturated. When the melt was cooled to 980° C., a substrate of non-doped polycrystalline silicon was brought into contact with the melt, whereby a silicon crystal having a thickness of 10 μm was epitaxially grown on the substrate. A measurement of specific resistance of the silicon crystal by the four-probe method indicated approximately 0.2 Ωcm. Specific resistance was varied within a range from 0.1 to 0.5 Ωcm in similar experiments which were carried out using three different lots of commercially available indium as the melt.
- A similar experiment was carried out using indium pellets refined to a high purity (6N), whereby a grown silicon layer on the substrate has an extremely high resistance (a difference in resistance between the grown silicon and the substrate could not be evaluated). By secondary ion mass spectrometry (SIMS) analysis of impurities contained in the grown silicon layer, no indium itself was unanticipatedly detected in any sample (below measurable limit). However, it was found that various kinds of impure elements such as gallium and aluminum of the III group in particular other than indium were contained in samples which were grown using commercially available indium. From this result, it is presumed that indium itself can hardly be incorporated into a silicon crystal grown in a liquid phase, but the elements of the III group other than indium which were contained in the commercially available indium pellets were easily incorporated into the silicon crystals, thereby lowering resistance. In other words, it is necessary for precise control of conductivity of silicon to precisely control impurities, in particular, elements of the III group which are contained in indium.
- Then, silicon was grown using a melt which was prepared by dissolving silicon into highly pure indium until it was saturated and then dissolving pellets of boron and aluminum. However, specific resistance of silicon grown as described above was low in reproducibility. The result of SIMS analysis indicated variations in concentrations of boron and aluminum in the silicon. Furthermore, silicon was grown using a melt which was prepared by dissolving silicon into highly pure indium until it was saturated, and then dissolving powders of phosphorus and arsenic. The silicon grown as described above was certainly of the n-type but its specific resistance was low in reproducibility. The result of SIMS analysis indicated variations in concentrations of phosphorus and arsenic in the silicon.
- The inventors considered a cause for these variations as described below. Since boron (density=2.23), aluminum (density=2.70), phosphorus (density=2.69) and arsenic (density=3.9) which are used as the dopants are prettily lighter than indium (density=7.28), a solution of the dopant tends to be concentrated on a surface of the indium melt, whereby the indium solution can hardly be uniform as a whole. Furthermore, solubilities of impurities which are subsequently dissolved into indium are influenced at a high possibility by a concentration of silicon which has already been dissolved in indium. In particular, when indium is nearly saturated with silicon, a slight variation in the saturation remarkably produces influences on the solubilities of the impurities, whereby the elements which are put into the melt as impurities are not always dissolved actually and concentrations of the elements of the impurities may be unstable in the melt.
- It is possible to dissolve the elements of the impurities before dissolving silicon into indium by reversing the dissolving order. In this case, since pellets or powders of the impurities are to be put in trace amounts as compared with that of silicon, it is difficult to uniformly distribute the elements of the impurities in the melt as a whole.
- For the reason described above, it is considered that indium makes it hard to obtain a high reproducibility of doping though indium itself has an excellent property as a melt that it can hardly be incorporated into silicon crystals and facilitates to obtain silicon crystals of high qualities. The inventors therefore considered to dilute and then dissolve impurities into liquid indium. However, a diluent to be used for this purpose must be a substance which can hardly be incorporated into grown silicon crystals or produces no adverse influence even when it is incorporated into the silicon crystals.
- Indium can be used as a first example of adequate diluent. An alloy prepared by dissolving impurities into indium at a predetermined concentration makes it possible to more accurately control concentrations of the impurities and prevent adverse influences from being produced by a diluent incorporated into silicon. Further, such an alloy is advantageous also from a viewpoint of having a slight different density from that of a solvent, that is, liquid indium. When the diluted impurities are dissolved before dissolving silicon, it is possible to prevent the influence due to a concentration of silicon and use pellets or powders in large amounts, thereby uniformly dissolving the elements of the impurities into the melt.
- Silicon can be used as a second example of adequate diluent. When the elements of the impurities are preliminarily diluted with silicon, the elements of the impurities are always and simultaneously dissolved into indium with silicon, thereby facilitating to maintain concentrations of the elements constant relative to that of silicon.
- The present invention which has been achieved on the idea described above will be described in details below with reference to effects and preferred embodiments thereof. However, the present invention is not limited to the following examples.
- In Example 1, a solar cell having a structure shown in FIG. 1 was produced using a metal grade silicon substrate which had a low purity and was inexpensive due to the low purity.
- Meant by the metal grade silicon is silicon which has a purity on the order of 99% and is obtained by metallurgically reducing silica. A
substrate 101 of a metal grade polycrystalline silicon which was 0.1 mm thick and 4 inches in diameter was produced by dissolving a metal grade silicon nugget and gradually cooling it in a carbon die coated with silicon nitride. Thesubstrate 101 contained boron at a high concentration and was of a strong p-type. Using a liquid phase growing apparatus which had a configuration shown in FIG. 3, alayer 102 of a p-type polycrystalline silicon was grown on thesubstrate 101. - In the apparatus shown in FIG. 3, a
crucible 301 made of quartz glass is filled with a dissolvedindium melt 302. The apparatus is accommodated as a whole in a quartz bell-jar 303 and heated to a desired temperature from outside withelectric furnaces 304. Hydrogen gas is always introduced into the quartz bell-jar 303 to maintain a reducing atmosphere in the bell-jar 303. Further, areference numeral 305 represents a substrate susceptor made of quartz glass which holds ends of a substrate 300 of a highly pure polycrystalline silicon or thesubstrate 101 of the metal gradepolycrystalline silicon 101 having a diameter of 4 inches. The substrate 100 or 300 of the polycrystalline silicon is held obliquely so as to go and come smoothly into and out of themelt 302. Areference numeral 306 designates a load lock chamber which can be partitioned from the quartz bell-jar 303 with agate valve 307. When setting silicon in thesusceptor 305 or replacing silicon with another, thesusceptor 305 is hoisted up with a hoistmechanism 308 and thegate valve 307 is closed to prevent an interior of the quartz bell-jar 303 from being exposed to atmosphere. Areference numeral 309 represents a dopant introducer which is configured also as a load lock mechanism and allowspellets 310 containing a dopant to be put into theindium melt 302 in a condition where thegate valve 307 is opened and thesusceptor 305 is hoisted up. - Now, the method of growing the
layer 102 of the p-type polycrystalline silicon will be described concretely. First, theindium melt 302 was heated to 1000° C. andpellets 310 of highly pure indium containing 1% by weight of aluminum were put into theindium melt 302. Since the indium pellets had a density which was nearly the same as that of indium, it was considered that the indium pellets were to uniformly disperse in the melt. Then, the substrate 300 of highly pure polycrystalline silicon was submerged as shown in FIG. 3. The substrate 300 was maintained in this condition for 30 minutes to dissolve silicon into theindium melt 302 until it is saturated. - Then, the
gate valve 307 was closed, the substrate 300 of the highly pure polycrystalline silicon was removed from thesusceptor 305, and asubstrate 101 of metal grade polycrystalline silicon having the diameter of 4 inches was placed in the susceptor. After replacing an internal gas of theload lock chamber 306 first with nitrogen and then with hydrogen, thegate valve 307 was opened and thesusceptor 305 was hoisted down to a preheating position (not shown in the drawings) over themelt 302 to wait for temperature rise of thesubstrate 101. Thereafter, cooling of the interior of the quartz bell-jar was started at a rate of 1° C./minute. When temperature reached 990° C., thesubstrate 101 was submerged into themelt 302. Thirty minutes later, thesusceptor 305 was hoisted up and theload lock chamber 306 was closed with thegate valve 307. After replacing an internal gas of theload lock chamber 306 with nitrogen, thesubstrate 101 was taken outside. A p-typepolycrystalline silicone layer 102 having a thickness of 30 μm had been grown on thesubstrate 101. - A PSG layer (phosphor silicate glass layer) having a thickness of 200 Å was deposited on the surface of the p-type
polycrystalline silicon layer 102 at a temperature of 560° C. using a CVD apparatus (not shown in the drawings). An n+-type silicon layer 103 was formed on the surface side by annealing the PSG layer in a nitrogen gas flow at a temperature of 1050° C. for 30 minutes and diffusing phosphorus (P). The remaining PSG was eliminated by etching with an aqueous solution of hydrofluoric acid. Furthermore, aluminum was deposited to a thickness of 2 μm on the surface of the n+-type silicon layer 103 by sputtering and comb-teeth likegrid electrodes 104 were formed by photolithography. Successively, a titanium oxide film having a thickness of 600 Å was deposited by sputtering as anantireflection film 105. At this stage, pads of thegrid electrodes 104 were masked to prevent titanium oxide from being deposited thereon. A solar cell produced as described above will hereinafter referred to as a solar cell 1. - The characteristic of the solar cell1 was evaluated with an AM-1.5 solar simulator to obtain a photoelectric conversion efficiency of 13%. Furthermore, 21 subcells each having an area of 1 cm2 were formed on the
substrate 101 and checked for a distribution of the photoelectric conversion efficiency. The result indicated a distribution within ±2% which was a favorable result. Moreover, a silicon crystal was grown successively five times while replenishing aluminum and silicon in the same procedures as those for the first growth in the amount of aluminum and silicon lost in each growth due to the deposition from the melt. This experiment indicated the variation of the photoelectric conversion efficiency within ±3% at one and the same location of each substrate, which was a favorable result. - As a comparative example, a solar cell2 was produced in the same procedures as those for the solar cell 1, except that pellets of pure aluminum were used as the
pellets 310 containing the dopant. In this case, aluminum could hardly be incorporated into a p-typepolycrystalline silicon layer 102 even when a dopant was replenished in a theoretically adequate amount. When the dopant was replenished in an amount exceeding the adequate amount, however, irregular spots were generated on the surface of thesubstrate 101 and the p-typepolycrystalline silicon layer 102, which were considered to be formed by reaction between silicon and aluminum. It is presumed that a layer of melted aluminum was formed on a surface of the melt and reacted with thesubstrate 101 or thesilicon layer 102. The solar cell 2 had remarkably ununiform photoelectric conversion efficiencies which were and certain subcells exhibited no photoelectric conversion efficiencies at all. Thus, the effects of the present invention was clarified by this comparison. - Example 2 shows a principle of a method of producing a light-weight and highly efficient solar cell at a low cost by repeatedly using an expensive silicon wafer in steps shown in FIGS. 2A to2C. First, a
porous layer 202 which was 5 μm thick was formed on a surface of a p+-type (100) singlecrystalline silicon wafer 201 having a diameter of 2 inches by the so-called anodization which applies a positive voltage in hydrofluoric acid. The porous layer is composed of a large number of micropores having a diameter of 100 Å which are formed by ununiformly dissolving silicon due to electrochemical action of hydrofluoric acid and extend in a direction of a film thickness while complicatedly tangling with one another. It is possible to epitaxially grow a single crystalline silicon on this layer since a portion remaining as a skeleton maintains a property of a single crystal. Methods of forming a porous layer and application of the porous layer to solar cells are detailed by Japanese Patent Application Laid-Open Nos. 5-283722 and 7-302889. - FIG. 4 shows an apparatus for growing single crystalline silicon which was used in Example 2.
Reference numerals 401 and 402 represent members which compose a carbon boat. The member 401 is provided with a cavity for dropping substrates 403, 403 a and 403 b for dissolving and a cavity for dropping a substrate 404 for growing. Themember 402 is provided with a hole in which anindium melt 405 is to be accommodated. Themembers 401 and 402 are configured to slide relative to each other. - A polycrystalline silicon substrate403 for dissolving silicon into a melt and a single crystalline silicon substrate 404 having a
porous layer 202 formed on the surface for growing a crystal were arranged in the member 401. Themember 402 was laid on the member 401 and a predetermined amount of highly pure indium pellets were placed in the hole of themember 402. When the indium pellets were heated in a hydrogen flow, they were melted into amelt 405 as shown in FIG. 4. After maintaining the growing apparatus at 1050° C. for five minutes, the temperature was adjusted to 1000° C. and themelt 405 was brought into contact with the substrate 403 for dissolving by sliding themember 402. As the substrate 403 for dissolving, a p-type polycrystalline silicon substrate doped with boron having specific resistance of 0.01 Ωcm was used. After keeping this state for one hour, cooling of the apparatus as a whole was started at a rate of 1° C./minute. When temperature reached 980° C., themember 402 was slid to bring themelt 405 into contact with a surface of theporous layer 202 and cooled for one minute to form a p+-type silicon layer 203 having a thickness of approximately 1 μm. Thereafter, the melt was returned to its initial position by sliding themember 402 once again and left standing for cooling. - When the apparatus was cooled to room temperature, the hardened melt and the substrate403 for dissolving were removed, whereafter highly pure indium pellets and the substrate 403 a for dissolving made of the p-type polycrystalline silicon doped with boron and having specific resistance of 1 Ωcm were newly arranged and heated in a manner similar to that at the preceding stage. After bringing the
melt 405 into contact with the substrate 403 a for dissolving at a temperature of 1000° C., keeping it in this condition for one hour, cooling of the apparatus as a whole was started at a rate of 1° C./minute. When temperature was lowered to 980° C., themelt 405 was brought into contact with the surface of the p+-type silicon layer 203 by sliding themember 402 once again and cooled for thirty minutes, thereby forming a p-type silicon layer 204 which was approximately 30 μm thick. Then, the melt was returned to its initial position by sliding themember 402 once again and left standing for cooling. - When the melt was cooled to room temperature, the hardened melt and the substrate403 a for dissolving were removed, whereafter highly pure indium pellets, and a substrate 403 a for dissolving made of n-type polycrystalline silicon doped with phosphorus and having specific resistance of 0.01 Ωcm were newly disposed and heated in a manner similar to that at the preceding stage. After bringing the
melt 405 into contact with the substrate 403 b for dissolving at a temperature of 1000° C. and keeping it in this condition for one hour, cooling of the apparatus as a whole was started at a rate of 1° C./minute. When temperature was lowered to 980° C., themelt 405 was brought into contact with the surface of the p-type silicon layer 204 by sliding themember 402 and cooled for thirty seconds, thereby forming an n+-type silicon layer 205 which was approximately 0.5 μm thick. Thereafter, the melt was returned to its initial position by sliding themember 402 once again and left standing for cooling. - Furthermore, aluminum was deposited to form 2 μm thick layer on the n+-
type silicon layer 205 by sputtering while masking thelayer 205, thereby forminggrid electrodes 206. Atitanium dioxide film 207 having a thickness of 600 Å and amagnesium fluoride film 208 having a thickness of 1000 Å were stacked asantireflection layers - A transparent
adhesive tape 209 was bonded to a surface of the antireflection layer thus formed. After a stacked body from the p+-type silicon layer 203 to theantireflection layer 208 was peeled from thesilicon wafer 201 by destroying theporous layer 202 by applying forces in directions indicated by arrows in FIG. 2B, analuminum sheet 210 was bonded to a back surface of the p+-type silicon layer 203 with an electroconductive adhesive, thereby forming a solar cell 3. - The characteristic of the solar cell3 was evaluated with an AM-1.5 solar simulator to obtain a photoelectric conversion efficiency of 18%. Furthermore, 26 subcells each having an area of 0.25 cm2 were formed on a
substrate 210 of an aluminum sheet and checked for a distribution of photoelectric conversion efficiencies. This result indicated a distribution within ±3%, which was a favorable result. - As a comparative example, a solar cell4 was produced in the same procedures as in the case of the solar cell 3, except that a melt was prepared by arranging powders of boron and phosphorus as dopants in the hole of the
member 402 together with indium pellets and that a non-doped polycrystalline silicon was used as the silicon for dissolving. Possibly due to a fact that boron and phosphorus were not uniformly distributed in the melt in the liquid phase growth, photoelectric conversion efficiencies of subcells were 10% at most and distributed within a broad range, and certain subcells exhibit no photoelectric conversion efficiency at all. - Example 3 shows steps for mass production of solar cells having a structure which is basically the same as that of the solar cell produced in Example 2 and proves that the method of the present invention is preferably applicable to mass production.
- A
porous layer 202 having a thickness of 2 μm were formed on each 6-inch silicon wafer 201. In this case, theporous layers 202 could be formed on each of the wafers at a time and a working efficiency could be remarkably enhanced by connecting tensilicon wafers 210 in series in a solution of hydrofluoric acid and supplying a current to the wafers. - An apparatus for growing silicon crystal according to the present invention was based on the same principle as that of the apparatus adopted for Example 1 shown in FIG. 3, provided that a
substrate susceptor 505 was used which is made of quartz glass and configured to be capable of accommodating ten substrates.Quartz glass crucibles 501 and quartz bell-jars (not shown in the drawings) are deepened correspondingly. The apparatus can be configured so as to accommodate a larger number of substrates to enhance a production efficiency. Three quartz bell-jars having similar internal structures are connected to a common load lock chamber by way of gate valves so that substrates can move from one bell-jar into another without being exposed to atmosphere. - First, a melt was prepared by placing highly pure indium pellets in a
crucible 501 of a first quartz bell-jar, heating and melting the pellets at 1000° C. Highly pure indium pellets containing 1% by weight of aluminum were put into the melt, and then a polycrystalline silicon substrate for dissolving was submerged into the melt and kept in this condition for 30 minutes to dissolve silicon into the indium melt until it was saturated, thereby preparing a melt for growing a p+-type silicon layer. - Then, a melt was prepared by placing highly pure indium pellets in a crucible of a second quartz bell-jar, heating and melting the pellets at 1000° C. Then, ten substrates of polycrystalline silicon doped with boron and having a specific resistance of 0.05 Ωcm were attached to a
susceptor 505, submerged into the indium melt, kept in this condition for 30 minutes to dissolve silicon until the indium melt was saturated, thereby preparing a melt for growing a p-type silicon layer. - Further, a melt was prepared by placing highly pure indium pellets in a crucible of a third quartz ball-jar, heating and melting the pellets at 1000° C. Highly pure indium pellets containing 1% by weight of arsenic were put into the melt, and a polycrystalline silicon substrate for dissolving was submerged into the melt and kept in this condition for 30 minutes to dissolve silicon into the indium melt until it was saturated, thereby preparing a melt for growing an n+-type silicon layer.
- With the gate valves kept closed, the polycrystalline silicone substrate for dissolving was removed from the
susceptor 505 and a silicon wafer 201 (hereinafter simply referred to “substrate”) having a diameter of six inches and aporous layer 202 formed on a surface thereof was set in the susceptor. After replacing an internal gas of the load lock chamber first with nitrogen and then with hydrogen, the gate valve of the first quartz bell-jar was opened, thesusceptor 505 was hoisted down to its preheating position, an interior of the quartz bell-jar was maintained at 1050° C. for ten minutes and then cooled to 1000° C., and gradual cooling of the interior of the quartz bell-jar was started at a rate of 0.2° C./minute. When temperature reached 995° C., the substrate was submerged into themelt 502 as shown in FIG. 5. After keeping this condition for ten minutes, thesusceptor 505 was hoisted up. A p+-type silicon layer 203 having a thickness of approximately 2 μm was grown on theporous layer 202. Since this apparatus treated a large number of substrates and required a time for pulling the susceptor into and out of the melt, a crystalline silicon growing rate was set at a low level in order not to vary the thickness of the p+-type silicon layer 203 of each substrate. - After completely hoisting up the susceptor, the first quartz bell-jar was closed to maintain a hydrogen atmosphere in the load lock chamber, the gate valve of the second bell-jar was opened, the
susceptor 505 was hoisted down to its preheating position and an interior of the bell-jar was maintained at 1000° C. for ten minutes. Then, gradual cooling of the interior of the quartz bell-jar was started at a rate of 1° C./minute. When temperature reached 980° C., the substrate was submerged into themelt 502 as shown in FIG. 5. After keeping this condition for 30 minutes, thesusceptor 505 was hoisted up and the load lock chamber was closed. A p-type silicon layer 204 having a thickness of approximately 30 μm was grown on the p+-type silicon layer 203. - While keeping the hydrogen atmosphere in the load lock chamber, the gate valve of the third quartz bell-jar was opened, the
susceptor 505 was hoisted down to its preheating position, an interior of the quartz bell-jar was maintained at 1000° C. for ten minutes and then gradual cooling was started at a rate of 0.2° C./minute. When temperature reached 995° C., the substrate was submerged into themelt 502. After maintaining this condition for two minutes, thesusceptor 505 was hoisted up and the load lock chamber was closed. An n+-type silicon layer 205 having a thickness of approximately 0.4 μm was grown on the p-type silicon layer 204. - Thereafter, comb-teeth like
grid electrodes 206 were formed on the surface of the n+-type silicon layer 205 by printing a copper paste by the screen printing method and calcining the paste. Successively, atitanium dioxide film 207 having a thickness of 600 Å was formed by coating a metal alkoxide solution by the sol-gel method and calcining the solution, and a film (208) of silicon oxide 800 Å thick was formed in the similar procedures as twoantireflection layers adhesive tape 209 was bonded to a surface of the antireflection layer, the layers of the p+-type silicon layer 203 from the upper layers were peeled from thesubstrate 201 by applying a force to thesubstrate 201 so as to destroy theporous layer 202, and thetape 209 was peeled off with an organic solvent. Thereafter, a back surface of the p+-type silicon layer 203 was coated with an electroconductive ink, bonded to analuminum support plate 210 and calcined for setting, thereby producing solar cells 5. - Ten solar cells5 were evaluated with an AM-1.5 solar simulator to obtain photoelectric conversion efficiencies of 17±0.3%, which were favorable and uniform. Furthermore, a solar cell module 1 was produced by connecting the ten solar cells in series and bonding them to a heat-resistant glass plate having a thickness of 3 mm with a PVC resin. This solar cell module 1 had an output of approximately 30 W.
- Successively to the module1, a module 2 was produced in similar procedures. During the producing, the melts were not cooled but kept in melted conditions. However, the polycrystalline silicon substrate for dissolving was submerged again into the melt in each of the quartz bell-jars to dissolve silicon until the melt was saturated since silicon concentration was lowered by deposition of a silicon crystal on the substrate. Boron was supplied together with silicon into the melt in the second quartz bell-jar. Since dopant concentrations were lowered in the melts in the first and third quartz bell-jars, pellets containing a predetermined amount of aluminum or arsenic were replenished into the melts in the first and third quartz bell-jars before replenishing silicon. The method of the present invention is capable of uniformly supplying a dopant with a high repeatability even when using a large crucible for mass production, whereby the module 2 also exhibited a characteristic equalled to that of the module 1.
- As a comparative example, ten solar cells were produced at a batch by replenishing the melts with pellets or powders each containing a single element of aluminum, boron or phosphorus. These solar cells exhibited remarkably variable characteristics, and therefore a solar cell module3 composed of these solar cells in series had an output characteristic of 5 W, clarifying that the method of the present invention is extremely excellent in mass production of modules connecting in series.
- Example 4 shows an example that the method of the present invention was applied to the production of a thin film transistor (TFT) of polycrystalline silicon formed on a glass plate which was to be used in a driving circuit for a liquid crystal display device. FIGS. 6A to6F schematically show production steps. A stacked films of aluminum/chromium having a thickness of 2000 Å were deposited on a
glass substrate 601 having a size of 4-inch square by sputtering. A pattern was formed as agate electrode 602 on these films by photolithography (see FIG. 6A). Using disilane and ammonia as raw material gases, a silicon nitride film having a thickness of 3000 Å was deposited as agate insulating film 603 on thegate electrode 602 by the CVD method (see FIG. 6B). - Used in Example 4 was a growing apparatus having a structure which was similar to that of the apparatus shown in FIG. 3 except that two quartz bell-jars were connected to a common load lock chamber by way of gate valves. First, an n-type polycrystalline silicon substrate doped with arsenic having a specific resistance of 0.5 Ωcm and a size of 4-inch square was submerged into an
indium melt 302 in a crucible of a first quartz bell-jar as shown in FIG. 3 and maintained in this condition for thirty minutes to dissolve silicon into themelt 302 until it was saturated, thereby preparing a melt for an n-type silicon layer for dissolving. After indium pellets containing 2% by weight of boron were dropped in a predetermined amount into a highly pure indium melt in a second quartz bell-jar, a highly pure polycrystalline silicon substrate having a size of 4-inch square was dissolved thereto, thereby preparing a melt for a p+-type silicon layer for dissolving. - Then, the gate valve was closed, the polycrystalline silicon substrate was dismounted from a susceptor, and the
glass substrate 601 on which thegate insulating film 603 had been formed was set in the susceptor. After an internal gas of the load lock chamber was replaced with nitrogen and then with hydrogen, the gate valve of the first quartz bell-jar was opened, and the susceptor was hoisted down to its preheating position and held at 600° C. for ten minutes to wait for temperature rise of thesubstrate 601. Thereafter, gradual cooling of an interior of the quartz bell-jar was started at a rate of 0.2° C./minute. When temperature reached 595° C., thesubstrate 601 was submerged into the melt. The substrate was maintained in this condition for 30 minutes until an n-typepolycrystalline silicon layer 604 having a thickness of 3000 Å was grown on thegate insulating film 603. Then, the susceptor was hoisted up, the gate valve was closed, the gate valve of the second quartz bell-jar was opened while maintaining the hydrogen atmosphere, and the susceptor was hoisted down to its preheating position and kept at 600° C. for ten minutes, whereafter gradual cooling of an interior of the quartz bell-jar was started at a rate of 0.2° C./minute. When temperature reached 595° C., thesubstrate 601 was submerged in the melt and maintained in this condition for five minutes, whereby a p+-type silicon layer 605 having a thickness of 500 Å was grown on the n-type silicon layer 604 (see FIG. 6C). Though silicon was grown at a very low rate in Example 4 due to the use of the glass substrate which did not allow the melt to be heated to a high temperature, the growth could be completed in a time within a range similar to that for the other examples since a necessary layer thickness was small. - After depositing stacked films of chromium/aluminum by sputtering, a
source electrode 606 and adrain electrode 607 were patterned by photolithography (see FIG. 6D). Using theelectrodes channel portion 608 were removed by dry etching (see FIG. 6E). Furthermore, asilicon oxide layer 609 was deposited on the surface by sputtering for surface protection (see FIG. 6F). - In order to check the TFT for its basic characteristic, −5 V and 0 V were applied to the gate electrode while applying 5 V across the source and drain electrodes. This result indicated an on/off ratio of 106. Moreover, a distribution of on/off ratios of b 10 4 TFTs formed in the substrate was within an extremely narrow range of 120%. Accordingly, it is possible to obtain display devices having a high contrast and free from ununiformity in colors by producing a driving circuit of TFTs according to the method of the present invention.
- As a comparative example, a dopant was supplied as pellets or powders each singly composed of a dopant element. In this comparative example, on/off ratios of TFTs were distributed within a wide range of 102, whereby the TFTs could not be expected to be usable for driving display devices.
- As understood from the foregoing description, the method of the present invention is capable of growing silicon crystals of a high quality having a dopant concentration favorably controlled, thereby making it possible to produce high performance solar cells, driving circuits for liquid crystal display devices and so on at a low cost and with a high reproducibility.
Claims (17)
1. A method of growing a silicon crystal in a liquid phase, which comprises using a melt prepared by dissolving a solid of silicon containing a dopant at a predetermined concentration into liquid indium.
2. A method of growing a silicon crystal in a liquid phase according to , wherein the dopant is boron or aluminum.
claim 1
3. A method of growing a silicon crystal in a liquid phase according to , wherein the dopant is phosphorus or arsenic.
claim 1
4. A method of growing a silicon crystal in a liquid phase, which comprises using a melt prepared by dissolving a solid of indium containing a dopant at a predetermined concentration into liquid indium.
5. A method of growing a silicon crystal in a liquid phase according to , further comprising using a melt prepared by further dissolving silicon into the melt in which the dopant is dissolved.
claim 4
6. A method of growing a silicon crystal in a liquid phase according to , wherein the dopant is boron or aluminum.
claim 4
7. A method of growing a silicon crystal in a liquid phase according to , wherein the dopant is boron or aluminum.
claim 5
8. A method of growing a silicon crystal in a liquid phase according to , wherein the dopant is phosphorus or arsenic.
claim 4
9. A method of growing a silicon crystal in a liquid phase according to , wherein the dopant is phosphorus or arsenic.
claim 5
10. A method of producing a solar cell, which comprises the steps of:
preparing a melt by dissolving a solid of silicon containing a dopant at a predetermined concentration into liquid indium;
forming a first silicon layer of a first conductivity type on a substrate by bringing the substrate into contact with the melt; and
forming a second silicon layer of a second conductivity type on the first silicon layer of the first conductivity type.
11. A method of producing a solar cell according to , wherein the substrate is a silicon wafer which has a porous layer formed on a surface thereof by anodization.
claim 10
12. A method of producing a solar cell according to , further comprising a step of separating the silicon wafer from the first silicon layer of the first conductivity type in the porous layer after forming the second silicon layer of the second conductivity type.
claim 11
13. A method of producing a solar cell according to , wherein the separating step is carried out by using an adhesive tape.
claim 12
14. A method of producing a solar cell, which comprises the steps of:
preparing a melt by dissolving a solid of indium containing a dopant at a predetermined concentration into liquid indium and then further dissolving silicon into the liquid indium;
forming a first silicon layer of a first conductivity type on a substrate by bringing the substrate into contact with the melt; and
forming a second silicon layer of a second conductivity type on the first silicon layer of the first conductivity type.
15. A method of producing a solar cell according to , wherein the substrate is a silicon wafer which has a porous layer formed on a surface thereof by anodization.
claim 14
16. A method of producing a solar cell according to , further comprising a step of separating the silicon wafer from the first silicon layer of the first conductivity type in the porous layer after forming the second silicon layer of the second conductivity type.
claim 15
17. A method of producing a solar cell according to , wherein the separating step is carried out by using an adhesive tape.
claim 16
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JP9-328186 | 1997-11-28 |
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US4236947A (en) * | 1979-05-21 | 1980-12-02 | General Electric Company | Fabrication of grown-in p-n junctions using liquid phase epitaxial growth of silicon |
US4818337A (en) * | 1986-04-11 | 1989-04-04 | University Of Delaware | Thin active-layer solar cell with multiple internal reflections |
US4717688A (en) * | 1986-04-16 | 1988-01-05 | Siemens Aktiengesellschaft | Liquid phase epitaxy method |
EP0641029A3 (en) * | 1993-08-27 | 1998-01-07 | Twin Solar-Technik Entwicklungs-GmbH | Element for a photovoltaic solar cell and process of fabrication as well as its arrangement in a solar cell |
CN1132223C (en) * | 1995-10-06 | 2003-12-24 | 佳能株式会社 | Semiconductor substrate and producing method thereof |
JP3717220B2 (en) | 1995-12-28 | 2005-11-16 | 新日本無線株式会社 | Liquid phase epitaxial growth method |
JP3672993B2 (en) | 1995-12-28 | 2005-07-20 | 新日本無線株式会社 | Liquid phase epitaxial growth method |
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1997
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US7459720B2 (en) * | 2000-07-10 | 2008-12-02 | Shin-Etsu Handotai Co., Ltd. | Single crystal wafer and solar battery cell |
US20090142512A1 (en) * | 2007-11-29 | 2009-06-04 | John Forster | Apparatus and method for depositing electrically conductive pasting material |
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US9039833B2 (en) | 2009-02-26 | 2015-05-26 | Harsharn Tathgar | Method for the production of solar grade silicon |
US20110180138A1 (en) * | 2010-01-25 | 2011-07-28 | Hitachi Chemical Company, Ltd. | Paste composition for electrode and photovoltaic cell |
US20110180139A1 (en) * | 2010-01-25 | 2011-07-28 | Hitachi Chemical Company, Ltd. | Paste composition for electrode and photovoltaic cell |
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US9224517B2 (en) | 2011-04-07 | 2015-12-29 | Hitachi Chemical Company, Ltd. | Paste composition for electrode and photovoltaic cell |
Also Published As
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JPH11162859A (en) | 1999-06-18 |
US6429035B2 (en) | 2002-08-06 |
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