US20130112564A1 - Electroplating Solutions and Methods For Deposition of Group IIIA-VIA Films - Google Patents
Electroplating Solutions and Methods For Deposition of Group IIIA-VIA Films Download PDFInfo
- Publication number
- US20130112564A1 US20130112564A1 US13/645,459 US201213645459A US2013112564A1 US 20130112564 A1 US20130112564 A1 US 20130112564A1 US 201213645459 A US201213645459 A US 201213645459A US 2013112564 A1 US2013112564 A1 US 2013112564A1
- Authority
- US
- United States
- Prior art keywords
- layer
- acid
- electroplating
- group iiia
- group
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
- 238000009713 electroplating Methods 0.000 title claims abstract description 121
- 238000000034 method Methods 0.000 title claims abstract description 92
- 230000008021 deposition Effects 0.000 title claims description 31
- 239000000463 material Substances 0.000 claims description 83
- 239000000243 solution Substances 0.000 claims description 63
- 229910052751 metal Inorganic materials 0.000 claims description 61
- 239000002184 metal Substances 0.000 claims description 61
- 239000010408 film Substances 0.000 claims description 59
- 239000006096 absorbing agent Substances 0.000 claims description 56
- 229910052733 gallium Inorganic materials 0.000 claims description 56
- 230000008569 process Effects 0.000 claims description 45
- 229910052711 selenium Inorganic materials 0.000 claims description 44
- 238000000151 deposition Methods 0.000 claims description 39
- 229910052738 indium Inorganic materials 0.000 claims description 35
- 239000000203 mixture Substances 0.000 claims description 32
- 239000010409 thin film Substances 0.000 claims description 28
- 239000000654 additive Substances 0.000 claims description 25
- 229910052717 sulfur Inorganic materials 0.000 claims description 23
- 229910052714 tellurium Inorganic materials 0.000 claims description 21
- 239000003963 antioxidant agent Substances 0.000 claims description 18
- 235000006708 antioxidants Nutrition 0.000 claims description 18
- 239000002904 solvent Substances 0.000 claims description 17
- 229910045601 alloy Inorganic materials 0.000 claims description 14
- 239000000956 alloy Substances 0.000 claims description 14
- -1 ammonium hexafluorophosphate Chemical compound 0.000 claims description 14
- KRKNYBCHXYNGOX-UHFFFAOYSA-N citric acid Chemical compound OC(=O)CC(O)(C(O)=O)CC(O)=O KRKNYBCHXYNGOX-UHFFFAOYSA-N 0.000 claims description 12
- OFOBLEOULBTSOW-UHFFFAOYSA-N Malonic acid Chemical compound OC(=O)CC(O)=O OFOBLEOULBTSOW-UHFFFAOYSA-N 0.000 claims description 10
- 239000003623 enhancer Substances 0.000 claims description 10
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims description 9
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 claims description 9
- QIGBRXMKCJKVMJ-UHFFFAOYSA-N Hydroquinone Chemical compound OC1=CC=C(O)C=C1 QIGBRXMKCJKVMJ-UHFFFAOYSA-N 0.000 claims description 8
- 230000005684 electric field Effects 0.000 claims description 8
- QTBSBXVTEAMEQO-UHFFFAOYSA-N Acetic acid Chemical compound CC(O)=O QTBSBXVTEAMEQO-UHFFFAOYSA-N 0.000 claims description 7
- 230000003078 antioxidant effect Effects 0.000 claims description 7
- 239000008139 complexing agent Substances 0.000 claims description 7
- PEDCQBHIVMGVHV-UHFFFAOYSA-N Glycerine Chemical compound OCC(O)CO PEDCQBHIVMGVHV-UHFFFAOYSA-N 0.000 claims description 6
- MUBZPKHOEPUJKR-UHFFFAOYSA-N Oxalic acid Chemical compound OC(=O)C(O)=O MUBZPKHOEPUJKR-UHFFFAOYSA-N 0.000 claims description 6
- 229910018110 Se—Te Inorganic materials 0.000 claims description 6
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 claims description 6
- YCIMNLLNPGFGHC-UHFFFAOYSA-N catechol Chemical compound OC1=CC=CC=C1O YCIMNLLNPGFGHC-UHFFFAOYSA-N 0.000 claims description 6
- RAXXELZNTBOGNW-UHFFFAOYSA-N imidazole Natural products C1=CNC=N1 RAXXELZNTBOGNW-UHFFFAOYSA-N 0.000 claims description 6
- 150000007522 mineralic acids Chemical class 0.000 claims description 6
- 150000007524 organic acids Chemical class 0.000 claims description 6
- LWIHDJKSTIGBAC-UHFFFAOYSA-K potassium phosphate Substances [K+].[K+].[K+].[O-]P([O-])([O-])=O LWIHDJKSTIGBAC-UHFFFAOYSA-K 0.000 claims description 6
- FEWJPZIEWOKRBE-UHFFFAOYSA-N Tartaric acid Natural products [H+].[H+].[O-]C(=O)C(O)C(O)C([O-])=O FEWJPZIEWOKRBE-UHFFFAOYSA-N 0.000 claims description 5
- 150000007530 organic bases Chemical class 0.000 claims description 5
- 239000004094 surface-active agent Substances 0.000 claims description 5
- 239000011975 tartaric acid Substances 0.000 claims description 5
- 235000002906 tartaric acid Nutrition 0.000 claims description 5
- BJEPYKJPYRNKOW-REOHCLBHSA-N (S)-malic acid Chemical compound OC(=O)[C@@H](O)CC(O)=O BJEPYKJPYRNKOW-REOHCLBHSA-N 0.000 claims description 4
- URDCARMUOSMFFI-UHFFFAOYSA-N 2-[2-[bis(carboxymethyl)amino]ethyl-(2-hydroxyethyl)amino]acetic acid Chemical compound OCCN(CC(O)=O)CCN(CC(O)=O)CC(O)=O URDCARMUOSMFFI-UHFFFAOYSA-N 0.000 claims description 4
- JKMHFZQWWAIEOD-UHFFFAOYSA-N 2-[4-(2-hydroxyethyl)piperazin-1-yl]ethanesulfonic acid Chemical compound OCC[NH+]1CCN(CCS([O-])(=O)=O)CC1 JKMHFZQWWAIEOD-UHFFFAOYSA-N 0.000 claims description 4
- FEWJPZIEWOKRBE-JCYAYHJZSA-N Dextrotartaric acid Chemical compound OC(=O)[C@H](O)[C@@H](O)C(O)=O FEWJPZIEWOKRBE-JCYAYHJZSA-N 0.000 claims description 4
- KCXVZYZYPLLWCC-UHFFFAOYSA-N EDTA Chemical compound OC(=O)CN(CC(O)=O)CCN(CC(O)=O)CC(O)=O KCXVZYZYPLLWCC-UHFFFAOYSA-N 0.000 claims description 4
- LYCAIKOWRPUZTN-UHFFFAOYSA-N Ethylene glycol Chemical compound OCCO LYCAIKOWRPUZTN-UHFFFAOYSA-N 0.000 claims description 4
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 claims description 4
- BAVYZALUXZFZLV-UHFFFAOYSA-N Methylamine Chemical compound NC BAVYZALUXZFZLV-UHFFFAOYSA-N 0.000 claims description 4
- NBIIXXVUZAFLBC-UHFFFAOYSA-N Phosphoric acid Chemical compound OP(O)(O)=O NBIIXXVUZAFLBC-UHFFFAOYSA-N 0.000 claims description 4
- GLUUGHFHXGJENI-UHFFFAOYSA-N Piperazine Chemical compound C1CNCCN1 GLUUGHFHXGJENI-UHFFFAOYSA-N 0.000 claims description 4
- KWYUFKZDYYNOTN-UHFFFAOYSA-M Potassium hydroxide Chemical compound [OH-].[K+] KWYUFKZDYYNOTN-UHFFFAOYSA-M 0.000 claims description 4
- JUJWROOIHBZHMG-UHFFFAOYSA-N Pyridine Chemical compound C1=CC=NC=C1 JUJWROOIHBZHMG-UHFFFAOYSA-N 0.000 claims description 4
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 claims description 4
- KDYFGRWQOYBRFD-UHFFFAOYSA-N Succinic acid Natural products OC(=O)CCC(O)=O KDYFGRWQOYBRFD-UHFFFAOYSA-N 0.000 claims description 4
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 claims description 4
- 229910001215 Te alloy Inorganic materials 0.000 claims description 4
- BJEPYKJPYRNKOW-UHFFFAOYSA-N alpha-hydroxysuccinic acid Natural products OC(=O)C(O)CC(O)=O BJEPYKJPYRNKOW-UHFFFAOYSA-N 0.000 claims description 4
- 150000001412 amines Chemical class 0.000 claims description 4
- KDYFGRWQOYBRFD-NUQCWPJISA-N butanedioic acid Chemical compound O[14C](=O)CC[14C](O)=O KDYFGRWQOYBRFD-NUQCWPJISA-N 0.000 claims description 4
- ZPWVASYFFYYZEW-UHFFFAOYSA-L dipotassium hydrogen phosphate Chemical compound [K+].[K+].OP([O-])([O-])=O ZPWVASYFFYYZEW-UHFFFAOYSA-L 0.000 claims description 4
- 229910000396 dipotassium phosphate Inorganic materials 0.000 claims description 4
- 235000019797 dipotassium phosphate Nutrition 0.000 claims description 4
- LNTHITQWFMADLM-UHFFFAOYSA-N gallic acid Chemical compound OC(=O)C1=CC(O)=C(O)C(O)=C1 LNTHITQWFMADLM-UHFFFAOYSA-N 0.000 claims description 4
- 150000007529 inorganic bases Chemical class 0.000 claims description 4
- 239000001630 malic acid Substances 0.000 claims description 4
- 235000011090 malic acid Nutrition 0.000 claims description 4
- MGFYIUFZLHCRTH-UHFFFAOYSA-N nitrilotriacetic acid Chemical compound OC(=O)CN(CC(O)=O)CC(O)=O MGFYIUFZLHCRTH-UHFFFAOYSA-N 0.000 claims description 4
- 239000003002 pH adjusting agent Substances 0.000 claims description 4
- VDZOOKBUILJEDG-UHFFFAOYSA-M tetrabutylammonium hydroxide Chemical compound [OH-].CCCC[N+](CCCC)(CCCC)CCCC VDZOOKBUILJEDG-UHFFFAOYSA-M 0.000 claims description 4
- WGTYBPLFGIVFAS-UHFFFAOYSA-M tetramethylammonium hydroxide Chemical compound [OH-].C[N+](C)(C)C WGTYBPLFGIVFAS-UHFFFAOYSA-M 0.000 claims description 4
- GETQZCLCWQTVFV-UHFFFAOYSA-N trimethylamine Chemical compound CN(C)C GETQZCLCWQTVFV-UHFFFAOYSA-N 0.000 claims description 4
- 229910001370 Se alloy Inorganic materials 0.000 claims description 3
- FMCUPJKTGNBGEC-UHFFFAOYSA-N 1,2,4-triazol-4-amine Chemical compound NN1C=NN=C1 FMCUPJKTGNBGEC-UHFFFAOYSA-N 0.000 claims description 2
- HYZJCKYKOHLVJF-UHFFFAOYSA-N 1H-benzimidazole Chemical compound C1=CC=C2NC=NC2=C1 HYZJCKYKOHLVJF-UHFFFAOYSA-N 0.000 claims description 2
- ZEVWQFWTGHFIDH-UHFFFAOYSA-N 1h-imidazole-4,5-dicarboxylic acid Chemical compound OC(=O)C=1N=CNC=1C(O)=O ZEVWQFWTGHFIDH-UHFFFAOYSA-N 0.000 claims description 2
- HZNVUJQVZSTENZ-UHFFFAOYSA-N 2,3-dichloro-5,6-dicyano-1,4-benzoquinone Chemical compound ClC1=C(Cl)C(=O)C(C#N)=C(C#N)C1=O HZNVUJQVZSTENZ-UHFFFAOYSA-N 0.000 claims description 2
- IEQAICDLOKRSRL-UHFFFAOYSA-N 2-[2-[2-[2-[2-[2-[2-[2-[2-[2-[2-[2-[2-[2-[2-[2-[2-[2-[2-[2-[2-[2-(2-dodecoxyethoxy)ethoxy]ethoxy]ethoxy]ethoxy]ethoxy]ethoxy]ethoxy]ethoxy]ethoxy]ethoxy]ethoxy]ethoxy]ethoxy]ethoxy]ethoxy]ethoxy]ethoxy]ethoxy]ethoxy]ethoxy]ethoxy]ethanol Chemical compound CCCCCCCCCCCCOCCOCCOCCOCCOCCOCCOCCOCCOCCOCCOCCOCCOCCOCCOCCOCCOCCOCCOCCOCCOCCOCCOCCO IEQAICDLOKRSRL-UHFFFAOYSA-N 0.000 claims description 2
- VHUUQVKOLVNVRT-UHFFFAOYSA-N Ammonium hydroxide Chemical compound [NH4+].[OH-] VHUUQVKOLVNVRT-UHFFFAOYSA-N 0.000 claims description 2
- CTENFNNZBMHDDG-UHFFFAOYSA-N Dopamine hydrochloride Chemical compound Cl.NCCC1=CC=C(O)C(O)=C1 CTENFNNZBMHDDG-UHFFFAOYSA-N 0.000 claims description 2
- PIICEJLVQHRZGT-UHFFFAOYSA-N Ethylenediamine Chemical compound NCCN PIICEJLVQHRZGT-UHFFFAOYSA-N 0.000 claims description 2
- DBVJJBKOTRCVKF-UHFFFAOYSA-N Etidronic acid Chemical compound OP(=O)(O)C(O)(C)P(O)(O)=O DBVJJBKOTRCVKF-UHFFFAOYSA-N 0.000 claims description 2
- 229930091371 Fructose Natural products 0.000 claims description 2
- RFSUNEUAIZKAJO-ARQDHWQXSA-N Fructose Chemical compound OC[C@H]1O[C@](O)(CO)[C@@H](O)[C@@H]1O RFSUNEUAIZKAJO-ARQDHWQXSA-N 0.000 claims description 2
- 239000005715 Fructose Substances 0.000 claims description 2
- WQZGKKKJIJFFOK-GASJEMHNSA-N Glucose Natural products OC[C@H]1OC(O)[C@H](O)[C@@H](O)[C@@H]1O WQZGKKKJIJFFOK-GASJEMHNSA-N 0.000 claims description 2
- 239000007995 HEPES buffer Substances 0.000 claims description 2
- HNDVDQJCIGZPNO-YFKPBYRVSA-N L-histidine Chemical compound OC(=O)[C@@H](N)CC1=CN=CN1 HNDVDQJCIGZPNO-YFKPBYRVSA-N 0.000 claims description 2
- 229920000877 Melamine resin Polymers 0.000 claims description 2
- 239000007832 Na2SO4 Substances 0.000 claims description 2
- 229920002415 Pluronic P-123 Polymers 0.000 claims description 2
- 239000002202 Polyethylene glycol Substances 0.000 claims description 2
- PMZURENOXWZQFD-UHFFFAOYSA-L Sodium Sulfate Chemical compound [Na+].[Na+].[O-]S([O-])(=O)=O PMZURENOXWZQFD-UHFFFAOYSA-L 0.000 claims description 2
- 229910000147 aluminium phosphate Inorganic materials 0.000 claims description 2
- LFVGISIMTYGQHF-UHFFFAOYSA-N ammonium dihydrogen phosphate Chemical compound [NH4+].OP(O)([O-])=O LFVGISIMTYGQHF-UHFFFAOYSA-N 0.000 claims description 2
- 229910000387 ammonium dihydrogen phosphate Inorganic materials 0.000 claims description 2
- HFRHTRKMBOQLLL-UHFFFAOYSA-N azane;diethoxy-sulfanyl-sulfanylidene-$l^{5}-phosphane Chemical compound [NH4+].CCOP([S-])(=S)OCC HFRHTRKMBOQLLL-UHFFFAOYSA-N 0.000 claims description 2
- WQZGKKKJIJFFOK-VFUOTHLCSA-N beta-D-glucose Chemical compound OC[C@H]1O[C@@H](O)[C@H](O)[C@@H](O)[C@@H]1O WQZGKKKJIJFFOK-VFUOTHLCSA-N 0.000 claims description 2
- 239000001506 calcium phosphate Substances 0.000 claims description 2
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- IRDLUHRVLVEUHA-UHFFFAOYSA-N diethyl dithiophosphate Chemical compound CCOP(S)(=S)OCC IRDLUHRVLVEUHA-UHFFFAOYSA-N 0.000 claims description 2
- BNIILDVGGAEEIG-UHFFFAOYSA-L disodium hydrogen phosphate Chemical compound [Na+].[Na+].OP([O-])([O-])=O BNIILDVGGAEEIG-UHFFFAOYSA-L 0.000 claims description 2
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- JRBPAEWTRLWTQC-UHFFFAOYSA-N dodecylamine Chemical compound CCCCCCCCCCCCN JRBPAEWTRLWTQC-UHFFFAOYSA-N 0.000 claims description 2
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- LNOPIUAQISRISI-UHFFFAOYSA-N n'-hydroxy-2-propan-2-ylsulfonylethanimidamide Chemical compound CC(C)S(=O)(=O)CC(N)=NO LNOPIUAQISRISI-UHFFFAOYSA-N 0.000 claims description 2
- GKTNLYAAZKKMTQ-UHFFFAOYSA-N n-[bis(dimethylamino)phosphinimyl]-n-methylmethanamine Chemical compound CN(C)P(=N)(N(C)C)N(C)C GKTNLYAAZKKMTQ-UHFFFAOYSA-N 0.000 claims description 2
- 235000006408 oxalic acid Nutrition 0.000 claims description 2
- ATGAWOHQWWULNK-UHFFFAOYSA-I pentapotassium;[oxido(phosphonatooxy)phosphoryl] phosphate Chemical compound [K+].[K+].[K+].[K+].[K+].[O-]P([O-])(=O)OP([O-])(=O)OP([O-])([O-])=O ATGAWOHQWWULNK-UHFFFAOYSA-I 0.000 claims description 2
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- OQZCJRJRGMMSGK-UHFFFAOYSA-M potassium metaphosphate Chemical compound [K+].[O-]P(=O)=O OQZCJRJRGMMSGK-UHFFFAOYSA-M 0.000 claims description 2
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- AKHNMLFCWUSKQB-UHFFFAOYSA-L sodium thiosulfate Chemical compound [Na+].[Na+].[O-]S([O-])(=O)=S AKHNMLFCWUSKQB-UHFFFAOYSA-L 0.000 description 4
- 238000004544 sputter deposition Methods 0.000 description 4
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Images
Classifications
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- C—CHEMISTRY; METALLURGY
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- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D3/00—Electroplating: Baths therefor
- C25D3/02—Electroplating: Baths therefor from solutions
- C25D3/56—Electroplating: Baths therefor from solutions of alloys
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D3/00—Electroplating: Baths therefor
- C25D3/02—Electroplating: Baths therefor from solutions
- C25D3/54—Electroplating: Baths therefor from solutions of metals not provided for in groups C25D3/04 - C25D3/50
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
- C25D5/10—Electroplating with more than one layer of the same or of different metals
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
- C25D5/18—Electroplating using modulated, pulsed or reversing current
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
- C25D5/60—Electroplating characterised by the structure or texture of the layers
- C25D5/605—Surface topography of the layers, e.g. rough, dendritic or nodular layers
- C25D5/611—Smooth layers
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D7/00—Electroplating characterised by the article coated
- C25D7/12—Semiconductors
- C25D7/123—Semiconductors first coated with a seed layer or a conductive layer
- C25D7/126—Semiconductors first coated with a seed layer or a conductive layer for solar cells
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
- H01L21/02104—Forming layers
- H01L21/02365—Forming inorganic semiconducting materials on a substrate
- H01L21/02518—Deposited layers
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- H—ELECTRICITY
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- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
- H01L21/02104—Forming layers
- H01L21/02365—Forming inorganic semiconducting materials on a substrate
- H01L21/02612—Formation types
- H01L21/02614—Transformation of metal, e.g. oxidation, nitridation
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- H—ELECTRICITY
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- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
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- H01L21/02617—Deposition types
- H01L21/02623—Liquid deposition
- H01L21/02628—Liquid deposition using solutions
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L31/00—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
- H01L31/0248—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 characterised by their semiconductor bodies
- H01L31/0256—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 characterised by their semiconductor bodies characterised by the material
- H01L31/0264—Inorganic materials
- H01L31/032—Inorganic materials including, apart from doping materials or other impurities, only compounds not provided for in groups H01L31/0272 - H01L31/0312
- H01L31/0322—Inorganic materials including, apart from doping materials or other impurities, only compounds not provided for in groups H01L31/0272 - H01L31/0312 comprising only AIBIIICVI chalcopyrite compounds, e.g. Cu In Se2, Cu Ga Se2, Cu In Ga Se2
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L31/00—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
- H01L31/0248—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 characterised by their semiconductor bodies
- H01L31/036—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 characterised by their semiconductor bodies characterised by their crystalline structure or particular orientation of the crystalline planes
- H01L31/0392—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 characterised by their semiconductor bodies characterised by their crystalline structure or particular orientation of the crystalline planes including thin films deposited on metallic or insulating substrates ; characterised by specific substrate materials or substrate features or by the presence of intermediate layers, e.g. barrier layers, on the substrate
- H01L31/03923—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 characterised by their semiconductor bodies characterised by their crystalline structure or particular orientation of the crystalline planes including thin films deposited on metallic or insulating substrates ; characterised by specific substrate materials or substrate features or by the presence of intermediate layers, e.g. barrier layers, on the substrate including AIBIIICVI compound materials, e.g. CIS, CIGS
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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
- Y02E10/00—Energy generation through renewable energy sources
- Y02E10/50—Photovoltaic [PV] energy
- Y02E10/541—CuInSe2 material PV cells
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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
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
- Y02P70/50—Manufacturing or production processes characterised by the final manufactured product
Definitions
- This application relates to electroplating methods and solutions and, more particularly, to methods and electroplating solution chemistries for electrodeposition of Group IIIA-VIA layers on a conductive surface for solar cell applications.
- Solar cells are photovoltaic devices that convert sunlight directly into electrical power.
- the most common solar cell material is silicon, which is in the form of single or polycrystalline wafers.
- the cost of electricity generated using silicon-based solar cells is higher than the cost of electricity generated by the more traditional methods. Therefore, since early 1970's there has been an effort to reduce cost of solar cells for terrestrial use.
- One way of reducing the cost of solar cells is to develop low-cost thin film growth techniques that can deposit solar-cell-quality absorber materials on large area substrates and to fabricate these devices using high-throughput, low-cost methods.
- Group IBIIIAVIA compound semiconductors comprising some of the Group IB (Cu, Ag, Au), Group IIIA (B, Al, Ga, In, Tl) and Group VIA (O, S, Se, Te, Po) materials or elements of the periodic table are excellent absorber materials for thin film solar cell structures.
- compounds of Cu, In, Ga, Se and S which are generally referred to as CIGS(S), or Cu(In,Ga)(S,Se) 2 or CuIn 1-x Ga x (S y Se 1-y ) k , where 0 ⁇ x ⁇ 1, 0 ⁇ y ⁇ 1 and k is approximately 2, have already been employed in solar cell structures that yielded conversion efficiencies approaching 20%.
- FIG. 1 The structure of a conventional Group IBIIIAVIA compound photovoltaic cell such as a Cu(In,Ga,Al)(S,Se,Te) 2 thin film solar cell is shown in FIG. 1 .
- the device 10 is fabricated on a substrate 11 , such as a sheet of glass, a sheet of metal, an insulating foil or web, or a conductive foil or web.
- the absorber film 12 which includes a material in the family of Cu(In,Ga,Al)(S,Se,Te) 2 is grown over a conductive layer 13 , which is previously deposited on the substrate 11 and which acts as the electrical contact to the device.
- Various conductive layers comprising Mo, Ta, W, Ti, and stainless steel etc.
- the substrate itself is a properly selected conductive material, it is possible not to use a conductive layer 13 , since the substrate 11 may then be used as the ohmic contact to the device.
- a transparent layer 14 such as a CdS, ZnO or CdS/ZnO stack is formed on the absorber film. Radiation 15 enters the device through the transparent layer 14 .
- Metallic grids may also be deposited over the transparent layer 14 to reduce the effective series resistance of the device. A variety of materials, deposited by a variety of methods, can be used to provide the various layers of the device shown in FIG. 1 .
- Cu(In,Ga)(S,Se) 2 a more accurate formula for the compound is Cu(In,Ga)(S,Se) k , where k is typically close to 2 but may not be exactly 2. For simplicity we will continue to use the value of k as 2.
- Cu(In,Ga) means all compositions from CuIn to CuGa.
- Cu(In,Ga)(S,Se) 2 means the whole family of compounds with Ga/(Ga+In) molar ratio varying from 0 to 1, and Se/(Se+S) molar ratio varying from 0 to 1.
- One technique employed for growing Cu(In,Ga)(S,Se) 2 type compound thin films for solar cell applications is a two-stage process where at least two ingredients or elements or components of the Cu(In,Ga)(S,Se) 2 material are first deposited onto a substrate, and then reacted with S and/or Se in a high temperature annealing process.
- CuInSe 2 or CIS film growth thin layers of Cu and In are first deposited on a substrate and then this stacked precursor layer is reacted with Se at elevated temperature to form CIS. If the reaction atmosphere also contains sulfur, then a CuIn(S,Se) 2 or CIS(S) layer can be grown. Addition of Ga in the precursor layer, i.e. use of a Cu/In/Ga stacked film precursor, allows the growth of a Cu(In,Ga)(S,Se) 2 or CIGS(S) absorber.
- Cu(In,Ga)(Se,S) 2 or CIGS(S) films which are the most advanced compound absorbers for polycrystalline thin film solar cells.
- An exemplary plating process includes first electroplating a thin In layer on a Cu layer, and then reacting this Cu/In precursor stack with Se to form a CuInSe 2 , or a CIS absorber.
- Ga can also be included in the precursor stack by plating it on the In layer or by including it in the In layer.
- the solar cell efficiency is a strong function of the molar ratio of the IB element(s) to IIIA element(s), i.e. the IB/IIIA molar ratio. If there are more than one Group IIIA materials in the composition, the relative amounts or molar ratios of these IIIA elements also affect the solar cell efficiency and other properties.
- the efficiency of the device is a function of the molar ratio of Cu/(In+Ga).
- the Ga/(Ga+In) molar ratio In general, for good device performance Cu/(In+Ga) molar ratio is kept at or below 1.0. For ratios higher than 1.0, a low resistance copper selenide phase, which may introduce electrical shorts within the solar cells may form. Increasing the Ga/(Ga+In) molar ratio, on the other hand, widens the optical bandgap of the absorber layer, resulting in increased open circuit voltage and decreased short circuit current. A CIGS material with a Ga/(Ga+In) molar ratio higher than about 0.3 is electronically poor.
- the sunlight-to-electricity conversion efficiency of a CIGS type solar cell first increases as the Ga/(Ga+In) molar ratio in the absorber is increased from 0 to 0.3, and then the efficiency starts to decrease as the molar ratio is further increased towards 1 .
- the electrodeposition process is used to introduce In into the composition of a CIGS(S) precursor material, it is essential that the electroplated In films have smooth morphology and uniform thickness, in micro-scale. If micro-structure of an In film or a In—Ga film electroplated on a Cu and optionally Ga containing precursor layer is rough and includes protrusions and valleys or discontinuities, the localized micro-scale Ga/(In+Ga) ratio at the protrusions would be lower than the Ga/(In+Ga) ratio at the valleys. Even the Cu/(In+Ga) molar ratio would be different at these two locations.
- this kind of micro-scale non-uniformity would yield a CIGS(S) absorber with non-uniform electrical and optical properties after reaction of the precursor stack with Se and/or S.
- the same argument also holds for the other thin film layers (such as Cu and Ga) within the precursor stack.
- electroplating a smooth Cu layer is relatively easy and the problem usually lies with Ga and In electrodeposition due to the tendency of these low melting, high surface tension elements forming droplets rather than continuous layers when deposited in thin film form.
- Thin film CIGS(S) solar cell absorbers typically have a thickness range of 1000-3000 nm.
- the amount of In that needs to be included in such a thin absorber is equivalent to an In layer thickness which is in the range of about 200-700 nm.
- an In layer thickness which is in the range of about 200-700 nm.
- CIGS absorber with a final Cu/(In+Ga) ratio of 0.85-0.9 and a Ga/(Ga+In) ratio of about 0.3
- the thickness of the In film in the above example gets reduced to about 200-300 nm level.
- the Ga layer thickness goes down even lower to the 75-100 nm range. Therefore, in a two stage CIGS(S) absorber formation approach employing an electroplated In layer, the electroplated In film thickness will have to be much less than 1000 nm, preferably less than 700 nm, most preferably less 500 nm. This requirement presents many challenges for prior art In electroplating methods and chemistries. Although these issues will be discussed with respect to In electrodeposition, it should be understood that they are also applicable to Ga and In—Ga alloy electrodeposition.
- Low melting Group IIIA materials such as In and Ga have high surface tension and they grow in the form of islands or droplets when deposited on a substrate surface in thin film form. This behavior has been observed in prior work carried out on electroplated In films (see for example, Chen et al., Solar Cells, 30 (1991) 451; Kim et al, Proceedings of the 1 st World Conf. on Photovoltaic Energy Conversion, 1994, p. 202; Calixto and Sebastian, J.
- FIGS. 2A-2B schematically show a prior art structure in perspective and side views, respectively.
- the structure includes a typical prior art In layer 37 , with sub-micron thickness which may be electrodeposited on a surface 36 of an under-layer 33 .
- the under-layer 33 is formed over a base 30 having a substrate 31 and a contact layer 32 .
- the under-layer 33 may, for example, include Cu and Ga and be formed on the contact layer 32 .
- the sub-micron thick In layer 37 is discontinuous and it includes islands 34 of In, separated by valleys 35 through which the surface 36 of the under-layer 33 is exposed. The width of the islands may be in the range of 500-5000 nm. If the structure of FIGS.
- a CIGS solar cell absorber 40 may be formed on the base 30 as shown in FIG. 3 .
- the CIGS solar cell absorber 40 has compositional non-uniformities caused by the morphological non-uniformity of the sub-micron thick In layer 37 . Accordingly, the CIGS solar cell absorber 40 has a first region 41 and a second region 42 .
- the first region 41 corresponds to the islands 34 of In of the structure of FIG. 2A , and is an In-rich, Ga-poor region.
- the second region 42 corresponds to the valleys 35 of the structure of FIG. 2A , and is an In-poor, Ga-rich region.
- the Cu(In+Ga) molar ratio in the first region 41 is lower than the Cu(In+Ga) molar ratio in the second region 42 .
- the solar cell would act like two separate solar cells, one made on the first region 41 and the other made on the second region 42 and then interconnected in parallel. Since the Ga/(Ga+In) as well as the Cu/(In+Ga) molar ratios in the two regions are widely different the quality of the separate solar cells on these regions would also be different. The quality of the overall solar cell would then suffer from the poor I-V characteristics of the separate solar cells formed on either one of the first and second regions.
- Highly efficient CIGS solar cells can be fabricated on 1000 nm thick CIGS absorbers. Using a 3000 nm thick CIGS absorber in a solar cell structure increases materials usage three time and wastes effectively 67% of the materials used in forming the CIGS absorber structure.
- the embodiment described herein relate to electroplating methods and plating electrolyte solutions.
- a method of forming an absorber layer over a surface of a base comprising: forming a metal layer over the surface of the base, wherein the metal layer comprises a Group IIIA material; co-depositing Group IIIIA and Group VA materials to form a Group IIIA-VIA layer on the metal layer using pulse electroplating that varies an electroplating pulse between a first higher value and a second lower value, wherein at the first higher value electroplating of at least one of Ga and In predominates, and wherein at the second lower value electroplating of one of Se, Te and S predominates, wherein the step of co-depositing the Group IIIA-VIA layer uses a roll-to-roll electroplating process wherein the base having the metal layer is continuously advanced within an electroplating solution held in a deposition chamber as at least one electric field is formed between at least one anode to deposit the Group IIIA-VIA layer onto the metal layer; and reacting the metal layer and the Group IIIA-VIA layer
- an electroplating solution for deposition of a Group IIIA-Group VIA thin film on a Group IIIA material surface comprising: a solvent; a Group IIIA material source that provides Ga in ionic form in the solvent; a Group VIA material source that dissolves in the solvent and provides Se in ionic form; an anti-oxidant; an anti-flocculant; a pH adjuster including at least one of an organic acid, an inorganic acid, an organic base and an inorganic base; additives including at least one of a surface-active compound, a complexing agent and an ionic conductivity enhancer; wherein the pH of the solution is in the range of 0.5-13.
- FIG. 1 is a schematic view of a prior art solar cell structure.
- FIG. 2A is a perspective top view of a prior art precursor structure formed by electroplating a sub-micron thick In layer on a sub-layer.
- FIG. 2B is a cross-sectional view of the structure of FIG. 2A taken along the line AA.
- FIG. 3 is a CIGS layer formed after reaction of the structure of FIG. 2B with Se.
- FIGS. 4A-4C schematically shows electrodeposition of a uniform In-rich layer over a continuous interlayer thus forming a uniform stack.
- FIG. 5 shows a Group IBIIIAVIA compound layer formed on a base using the stack of FIG. 4 .
- FIG. 6A is a schematic view of a precursor stack including a Group IB-IIIA meta layer on a base, a Group IIIA-VIA alloy layer on the metal layer and a Group VIA layer on the alloy layer;
- FIG. 7A is an electroplating voltage-time graph
- FIG. 7B is an electroplating current density-time graph
- FIGS. 9A-9B various electroplating voltage-time and electroplating current density-time graphs
- FIG. 10 is a pulsed electroplating voltage-time graph
- FIG. 11 is a pulsed electroplating current density-time graph
- FIG. 13A is a schematic view of an embodiment of a second electroplating system
- FIG. 13B is a process graph showing voltage or current density variation along the length of an electroplating chamber of the second system shown in FIG. 13A ;
- FIG. 14A is a schematic view of an embodiment of a third electroplating system.
- FIG. 14B is a process graph showing voltage or current density variation along the length of an electroplating chamber of the third system shown in FIG. 14A .
- the interlayer is formed on a conductive surface which may be the top surface of a base or a precursor stack.
- the group IIIA material thin film may then be formed by electrodeposition on the exposed surface of the interlayer.
- the interlayer comprises 20-90 molar percent, preferably 40-80 molar percent of at least one of In and Ga.
- the balance of the interlayer composition comprises an additive material.
- the additive material of the interlayer includes at least one of Cu, Se, Te, Ag and S, preferably at least one of Cu and Te. Other materials or impurities may also be present in the additive material as long as their molar content does not exceed about 10 molar percent of the total additive material composition.
- the process used to form the Group IIIA material thin film on the interlayer is electrodeposition; however, in the following description the words electroplating, plating and deposition may be used to refer to the electrodeposition process of the In and/or Ga layer.
- FIG. 4A exemplifies a first structure 100 including a first layer 102 formed on a base 104 to initiate the precursor stack forming process.
- the first layer 102 may preferably be formed using an electrodeposition process; however, other deposition processes such as evaporation, sputtering and the like may also be used to form the first layer 102 .
- the base 104 may be a conductive base including a substrate 106 and a contact layer 108 , which will eventually form an electrical contact to the CIGS(S) absorber after the reaction step.
- the substrate 106 may be a continuous conductive material such as a metal or alloy foil, preferably a stainless steel foil.
- FIG. 4B shows a second structure 200 formed as the process proceeds.
- a second layer 112 or an interlayer is formed on the top surface 110 of the first layer 102 , using preferably an electrodeposition process.
- the interlayer 112 is a conditioned conductive layer so that it establishes a conditioned surface for the following Group IIIA thin film deposition.
- the word conditioned refers to establishing a mate composition that not only helps forming a thin and continuous Group IIIA layer on the interlayer but also includes constituents that do not affect negatively the overall composition of the resulting precursor stack and do not deteriorate the quality of the CIGS(S) absorber to be formed.
- the interlayer 112 is a continuous layer with a substantially uniform thickness which is less than 100 nm, preferably less than 50 nm.
- Surface 114 of the interlayer 112 functions as an active deposition site to allow a Group IIIA material to continuously and uniformly deposit onto the surface 114 in the subsequent step, thereby eliminating the discontinuity problems of the prior art described above.
- the interlayer 112 comprises 20-90 molar percent, preferably 40-80 molar percent of at least one of In and Ga. Presence of In and/or Ga in the interlayer composition is important for the interlayer to provide effective nucleation to the In and/or Ga rich layer that will be electroplated on top of it. However, the In and/or Ga content of the interlayer cannot be more than 90% because the interlayer needs to be continuous to be able to provide the effective nucleation sites. If the interlayer becomes near pure In and/or Ga layer then it would be in the form of islands or droplets as discussed before.
- the balance of the interlayer composition is an additive material.
- the additive material in the interlayer includes at least one of Cu, Se, Te, Ag and S.
- the most preferred additives are Cu and Te. These additives assist in making the interlayer a continuous film, and at the same time the In and/or Ga in the interlayer provide high density of nucleation sites for the In and/or Ga layer that would be electroplated on the interlayer. Since the Group IBIIIAVIA absorber layer (compound layer) fabrication is specifically targeted, the additive materials are the materials that will not damage the electronic quality of the CIGS(S) absorber. Other materials or impurities may also be present in the additive material without exceeding about 10 molar percent of the total additive material composition.
- the composition of the interlayer is largely determined by the chemical composition of the Group IIIA material layer (layer 116 in FIG. 4C ) that will be electrodeposited onto the interlayer 112 and any other layer that may be present in the resulting precursor stack.
- the interlayer 112 may be electrodeposited out of plating electrolytes comprising at least one of In and Ga as well as at least one additive such as Cu and Te. By co-depositing these additives and including them into the interlayer 112 , a continuous interlayer may be obtained even at a thickness as low as 10 nm.
- the thickness of the interlayer 112 depends on the thickness of the Group IIIA material layer that will be electrodeposited onto the interlayer, a preferable thickness of it may be for example less than about 50 nm so that the amount In, Ga and other materials that it may contain do not become a determining factor in the overall composition, i.e.
- the thickness of the interlayer is less than or equal to about 20%, preferably less than about 10% of the thickness of the Group IIIA material-rich layer that is deposited over the interlayer, so that the effect of the interlayer on determining the overall composition of the resulting precursor stack is limited. This is important for manufacturability and repeatability of the process.
- FIG. 4C shows a third structure 300 formed after electrodepositing a third layer 116 which is a substantially pure Group IIIA material layer onto the interlayer 112 .
- the third layer 116 is a continuous thin film.
- very thin Group IIIA material layers having uniform thickness may be formed on the interlayer 112 .
- the thickness of the third layer 116 may be less than about 700 nm, preferably less than about 500 nm, whereas the thickness of the interlayer is less than about 20% of these values, i.e. less than about 140 nm, preferably less than about 100 nm.
- the thickness of the interlayer is less than about 10% of the thickness of the third layer 166 , i.e. less than about 70 nm.
- the Group IIIA material deposited on the interlayer may be a substantially pure In—Ga binary alloy electrodeposited from an electrolyte comprising In and Ga ions.
- the interlayer 112 is cathodically polarized with respect to an anode so that the third layer comprising In and Ga deposits onto the surface 114 of the interlayer in a uniform manner.
- the chemical composition of the third layer 116 may preferably comprise at least 90 molar percent In and/or Ga, preferably at least 95 molar percent In and/or Ga.
- the stack of the first layer 102 , the second layer 112 or interlayer and the third layer 116 forms a precursor stack containing Group IB and Group IIIA elements on the base 104 .
- the precursor stack 118 is reacted with at least one Group VIA material such as Se, Te or S to form an absorber layer 120 on the base 104 .
- the precursor stack 118 comprises Cu, In, and Ga, and therefore reacting them with a Group VIA material forms the absorber 120 which is a compositionally uniform Group IBIIIAVIA compound layer.
- IIIA-VIA Group IIIA-Group VIA
- the IIIA-VIA layer may be a part of a precursor stack that is reacted to form a Group IBIIIAVIA compound semiconductor absorber layer (CIGS layer).
- the IIIA-VIA layer may comprise any one of a Ga—Se binary alloy, an In—Se binary alloy or an In—Ga—Se ternary alloy.
- the IIIA-VIA layer may comprise any one of a Ga—Te binary alloy, an In—Te binary alloy or an In—Ga—Te ternary alloy.
- the IIIA-VIA layer may be formed, using a PVD process, such as sputter deposition, evaporation deposition, or an electrodeposition process, on an In film or a Ga film of a precursor stack including Cu, Ga and In films.
- the electroplating process includes an electroplating solution coupled with galvanic (constant current), potentiostatic (constant voltage) or pulsed galvanic or potentiostatic electroplating techniques to provide more control over the electroplated film morphology and quality.
- Electroplating process may be performed in a roll-to-roll electroplating system including an electroplating tank containing an electroplating solution and at least one electrode (anode). As shown in FIG. 6A , a first layer 302 or metal layer may be formed on a base 304 to initiate the precursor stack forming process.
- the metal layer 302 may preferably be formed using an electroplating process; however, other deposition processes such as evaporation, sputtering and the like may also be used to form the metal layer 302 .
- the base 304 may be a conductive base including a substrate 306 and a contact layer 308 , which will eventually form an electrical contact to the CIGS(S) absorber after the reaction step.
- the substrate 306 may be a continuous conductive material such as a metal or alloy foil, preferably a stainless-steel foil.
- the contact layer 308 may comprise conductive materials such as Mo, W, metal nitrides, Ru, Os and Ir, which make ohmic contact to CIGS(S) type absorber films.
- the metal layer 302 is a conductive layer comprising Cu, In and Ga.
- the metal layer 302 may preferably be in the form of a stack including multiple films of Cu and at least one of In and Ga.
- Exemplary stacks forming the metal layer 302 include, but are not limited to, Cu/Ga, Cu/In, Cu/In/Ga, Cu/Ga/In, and the like, stacks.
- the metal layer is a stack with an In-film, i.e., the top surface of the metal layer 302 is In metal.
- a second layer 312 or a IIIA-VIA layer is formed on a top surface 310 of the metal layer 302 , using preferably an electroplating process.
- the IIIA-VIA layer 312 may be electrodeposited from a IIIA-VIA electroplating solution or electrolyte onto the metal layer 302 .
- the IIIA-VIA layer may be an alloy with the predetermined compositions of non-alloyed 111 A and VIA materials, a mixture of alloys of IIIA and VIA materials or a mixture of alloyed and non-alloyed IIIA and VIA materials. In the preferred embodiment IIIA and VIA materials are co-electrodeposited to form the IIIA-VIA layer.
- the IIIA-VIA layer 312 is a Ga—Se binary alloy layer or a layer of mixed Ga and Se materials co-electrodeposited from a Ga—Se electroplating solution on the top surface 310 of the metal layer 302 .
- the metal layer 302 and the IIIA-VIA layer 312 form a CIGS precursor stack 314 .
- a cap layer 316 that preferably includes a Group VIA layer including at least one of Se, Te and S and a dopant layer including at least one of Na, K and L is deposited onto the CIGS precursor stack 314 and the stack is reacted to form an absorber layer 320 on the base 304 , as shown in FIG. 6B .
- the cap layer 316 and the IIIA-VIA layer 312 there may be one or more films of Cu, In and Ga.
- the CIGS precursor stack 314 comprises Cu, In, Ga and Se and therefore reacting the precursor stack 314 with Group VIA material forms the absorber layer 320 which is a compositionally uniform Group IBIIIAVIA compound semiconductor layer.
- the electroplating process of the IIIA-VIA layer 312 utilizes precise chemistry control coupled with a waveform deposition profile in either a galvanic mode or a potentiostatic mode to precisely control the co-deposition of Group IIIA and Group VIA materials, i.e. Ga and Se.
- a stable multi-composition electroplating solution with an increased lifetime was formulated.
- the electrolyte solution includes several distinctive additives such as anti-oxidants, anti-flocculants, surface-active compounds, organic-water solvent pairs (non-aqueous solvents) to facilitate defect-free, continuous and device-quality layers containing IIIA and VIA elements.
- the waveform deposition profile provides a flexible platform for the deposition of IIIA-VIA layers with different electroplating redox potentials such that alloys, intermetallics, or mix-metal films can be electrodeposited.
- a Cu—In—Ga layer can be deposited, preferably with the use of plating.
- Precursor formation can be completed by plating a graded In—Se or Ga—Se layer on the top of this layer with an In/Ga-rich bottom region and a Se-rich top region. If the potentiostatic (voltage) mode is used, a high plating voltage followed by a low plating voltage can be used to obtain a layer grading.
- FIG. 8A shows a constant voltage V 1 for duration T 1 followed by V 2 for duration T 2 , where V 2 >V 1 .
- IIIA-VIA electroplating solutions are prepared by dissolving a IIIA source material and a VIA source material in a solvent.
- the amount of IIIA source can be in the range of 0-100%.
- the solution composition can be in any range from a pure VIA solution to a mixture of IIIA and VIA source at any ratio, to a pure IIIA solution.
- the amount of VIA source can be in the range of 0-100%.
- the solution composition can be in any range from a pure IIIA solution to a mixture of VIA and IIIA source at any ratio, to a pure VIA solution.
- an exemplary pure Se solution to deposit to a IIIA-VIA layer with 0% IIIA material may contain a selenium source, inorganic and organic acids and bases, complexing agents, additive groups such as anti-oxidants, anti-flocculants, surface-active compounds ionic conductivity enhancers and organic-water solvent pairs or non-aqueous solvents.
- Selenium oxide may provide Se source.
- compounds of Se such as acids of Se as well as oxides, chlorides, sulfates, nitrates, perchlorides, and phosphates of Se can be used.
- Exemplary Ga—Se electroplating solutions to deposit the IIIA-VIA layer 312 may include a gallium source, a selenium source, inorganic and organic acids and bases, complexing agents, additive groups such as anti-oxidants, anti-flocculants, surface-active compounds ionic conductivity enhancers and organic-water solvent pairs or non-aqueous solvents.
- Ga source in this plating bath composition may comprise stock solutions prepared by dissolving Ga metals into their ionic forms as well as by dissolving soluble Ga salts, such as sulfates, chlorides, acetates, sulfamates, carbonates, nitrates, phosphates, oxides, perchlorates, hydroxides.
- Examples of a gallium source may include one of GaCl 3 , Ga(NO 3 ) 3 , Ga 2 (SO 4 ) 3 , Ga-Oxides, gallium (III) acetylacetonate, gallium bromide, gallium iodine, gallium (III) trifluoromethane sulfonate, gallium trichloride-phosphorus oxychloride, or gallium oxychloride.
- Selenium oxide may provide Se source.
- compounds of Se such as acids of Se as well as oxides, chlorides, sulfates, nitrates, perchlorides, and phosphates of Se can be used.
- Examples of a selenium source may include one of a selenus acid, selenic acid, selenium oxide, selenium (IV) bromide, selenium chloride (I, IV), selenium (IV) sulfide selenourea, N,N-dimethylselenourea, selenosemicabazide, sodium selenite, silver selenite or selenium disulfide.
- the electroplating solution may also be prepared to electroplate other IIIA-VIA layers including other materials such as indium and tellurium to form an In—Te alloy layer or a layer of mixed In and Te.
- indium salts may be dissolved in an above described Ga—Se solution to formulate an In—Ga—Se electroplating solution to deposit an In—Ga—Se alloy layer or a layer of mixed In, Ga and Se materials.
- In and Ga source in this plating bath composition may comprise stock solutions prepared by dissolving In and Ga metals into their ionic forms as well as by dissolving soluble In and Ga salts.
- Indium salts may include indium-chloride, indium-sulfate, indium-sulfamate, indium-acetate, indium-carbonate, indium-nitrate, indium-phosphate, indium-oxide, indium-perchlorate, and indium-hydroxide.
- Te sources such as telluric acid (H 6 TeO 6 ), tellurium dioxide (TeO 2 ) may be included in the above described Ga—Se solutions to formulate a Ga—Se—Te electroplating solution to deposit a Ga—Se—Te alloy layer or a layer of mixed Ga, Se and Te materials.
- Both In and Te salts may also be added to prepare an In—Ga—Se—Te solution to deposit an In—Ga—Se Te alloy or a layer of mixed In, Ga, Se and Te materials.
- another group VIA element sulfur may also be incorporated into the electrodeposited IIIA-VIA layer if S sources are added into the electroplating solution specified above.
- Exemplary sulfur sources include selenium sulfides (Se 4 S 4 , SeS 2 , Se 2 S 6 ), thiourea (CSN 2 H 4 ), and sodium thiosulfate (Na 2 S 2 O 3 ).
- An exemplary In—Ga—Se—Te—S electroplating solution to deposit the IIIA-VIA layer 312 may include a gallium source, an indium source, a selenium source, a tellurium source, a sulfur source, inorganic and organic acids and bases, complexing agents, additive groups such as anti-oxidants, anti-flocculants, surface-active compounds ionic conductivity enhancers and organic-water solvent pairs or non-aqueous solvents.
- Group IIIA material source in this plating bath composition may comprise stock solutions prepared by dissolving In and Ga metals into their ionic forms as well as by dissolving soluble In and Ga salts, such as sulfates, chlorides, acetates, sulfamates, carbonates, nitrates, phosphates, oxides, perchlorates, and hydroxides.
- Selenium oxide and Te oxide may provide the Group VIA source.
- Group VIA compounds of Se and Te such as acids of Se and Te as well as oxides, chlorides, sulfates, nitrates, perchlorides, and phosphates of Se and Te can be used.
- Sulfur can be provided from source including selenium sulfides (Se 4 S 4 , SeS 2 , Se 2 S 6 ), thiourea (CSN 2 H 4 ), and sodium thiosulfate (Na 2 S 2 O 3 ).
- Some of the anti-oxidant that can be used to control the selenium oxidation state includes, but not limited to, one of organic anti-oxidants such as hydroquinone, pyrocatechol, gallic acid; cycloamines such as 4-amino-4H-1,2,4-triazole, 4,5-imidazoledicarboxylic acid; sugars such as dextrose, saccharin, fructose; organic-sulfonates such as hydroquinone sulfonic; alcohols such as ethanol, methanol, glycerol, ethyleneglycol and phenolic compounds such as 1,1-Diphenyl-2-picryl hydrazyl, dihydric phenols, catechol, resorcinol, 4-(N-alkylated) aminophenols, etc.
- organic anti-oxidants such as hydroquinone, pyrocatechol, gallic acid
- cycloamines such as 4-amino-4H-1,2,4-triazole, 4,5-
- Anti-flocculants are compounds used to reduce the interaction between metal metal-oxides or other metal based particulates such that they do not aggregate and precipitate. Anti-flocculants can be used to increment the lifetime of the solution and reduce defect formation by reducing flocculation which could cause shadowing effects during electroplating due to particle formation on the working electrode/electrolyte interface; this effect would impact the integrity of the film and reduce the overall performance efficiency of the particular spot where flocculation has created a plating defect.
- Anti-flocculants may include phosphates including one of simple phosphates including dipotassium phosphate, ammonium dihydrogen phosphate, ammonium hexafluorophosphate, calcium phosphate, potassium metaphosphate, potassium phosphate, potassium triphosphate, potassium hexafluorophosphate, potassium hydrogen phosphate and sodium hydrogen phosphate; phosphate-thiols such as diethyl dithiophosphate; phosphate-ammonium such as diethyl dithiophosphate, ammonium salt; organic phosphates such as tetrabutylammonium hexafluorophosphate.
- simple phosphates including dipotassium phosphate, ammonium dihydrogen phosphate, ammonium hexafluorophosphate, calcium phosphate, potassium metaphosphate, potassium phosphate, potassium triphosphate, potassium hexafluorophosphate, potassium hydrogen phosphate and sodium hydrogen phosphate
- Anti-flocculants may also include one of: glycols such as polyethylene glycol; organic compounds including acids and esters, such as tannic acid as an acid and ether as an ester; phosphonic acids such as organo-phosphates for example, 1-hydroxyethylidenebis(phosphonic acid) or methylenediphosphonic acid; and amines such as diethylenediamine or amino-phosphonic-organic acid, for example, (aminomethyl)phosphonic acid.
- glycols such as polyethylene glycol
- organic compounds including acids and esters, such as tannic acid as an acid and ether as an ester such as tannic acid as an acid and ether as an ester
- phosphonic acids such as organo-phosphates for example, 1-hydroxyethylidenebis(phosphonic acid) or methylenediphosphonic acid
- amines such as diethylenediamine or amino-phosphonic-organic acid, for example, (aminomethyl)phosphonic acid.
- Surface active compounds are compounds that will bind to the surface of the working electrode (e.g., the surface 310 of the metal layer 302 in FIG. 6A ) and will modify the growth by either binding to the surface and preventing growth or binding to the surface and aiding in the growth.
- the surface active components can be non-ionic such that they will only change the surface tension of the solid-liquid interface and this effect will change the hydrodynamics at the surface which will in turn change the growth rate and diffusion limitations.
- Exemplary surface active compounds may include one of: amine such as melamine; amine-hydroxide such as dopamine hydrochloride; sulfonic such as (HEPES) 4-(2-hydroxyethyl)piperazine-1-ethanesulfonic acid; triazine-thiol such as 1,3,5-triazine-2,4,6-trithiol trisodium; anioninc surfactants such as SDS; cationic surfactants such as n-dodecylamine or sodium n-octyl sulfate; tri-block-polymers such as ethylene oxide(EO)-propylene oxide-EO, for example, pluronic P123, pluronic F127 (pluronic is a trade name from BASF but this should include similar type of polymers that are not a trademark, but a similar family of compounds); polyglycol the polymers such as Brij 35 or other Brij Polymers (Trademark of Croda).
- HEPES 4-(
- Ionic conductivity enhancers are any family compounds that will form ionic compounds when dissolved in the electroplating bath medium (water or organic-water solvent pairs) that can increase the conductivity of the plating bath. Such compounds can range from inorganic salts such as NaCl or Na 2 SO 4 .
- Organic-solvent pairs can be used to improve the solubility of the metal precursor or additive, decrease the temperature at which the plating can be performed to prevent the melting of Ga and/or In in the precursor stack, decrease the H 2 evolution and increase the plating faradaic efficiency.
- the following solvents may be considered as water-solvent pairs: alcohols such as ethanol, methanol, iso-propanol, butanol, 2-butanol or tert-butanol, amongst other soluble alcohols; dimethysulfoxide; acetone; and other organic solvents in which water constitutes less than 5% of the total volume, for example, acetonitrile, dichloromethane, pyrrolidimome or tetrahydrofuran.
- the pH of the electroplating solutions can be either in the acidic, neutral or alkaline regime, but pH's above 13 are not preferred as electrochemical reduction of Se becomes very difficult in this highly alkaline pH regime.
- the preferred pH regime is 0.5 to 4.
- a more preferred pH range is 0.8-2.5.
- Plating solutions can be prepared at a pH range between 4 to 13, and more preferably at a pH range between 7 to 12.
- Complexing agents such as such as tartaric acid, citric acid, acetic acid, malonic acid, malic acid, succinic acid, ethylenediamine, ethylenediaminetetraacetic acid, nitrilotriacetic acid, and hydroxyethylethylenediaminetriacetic acid, etc.
- the pH of the solution can be adjusted by incorporation of acids such as sulfuric acid, hydrochloric acid, phosphoric acid, ethylenediaminetetraacetic acid, malonic acid, malic acid, nitrilotriacetic acid, succinic acid, maleic acid, oxalic acid, tartaric acid, citric acid, sulfamic acid, hydroxyethylethylenediaminetriacetic acid etc.
- acids such as sulfuric acid, hydrochloric acid, phosphoric acid, ethylenediaminetetraacetic acid, malonic acid, malic acid, nitrilotriacetic acid, succinic acid, maleic acid, oxalic acid, tartaric acid, citric acid, sulfamic acid, hydroxyethylethylenediaminetriacetic acid etc.
- inorganic and organic bases such as NaOH, KOH, NH 4 OH, organic amines such as methylamine and trimethylamine etc.
- organic hydroxides such as tetramethylammonium hydroxide and tetrabutylammonium hydroxide
- other organic bases such as pyridine, imidazole, benzimidazole, histidine and phosphazene bases can also be used to adjust the pH of the plating solutions.
- the electroplating solution may be employed by various electroplating processes to electroplate the above described Ga—Se layer on metal layers.
- a potential between the metal layer 302 which becomes the working electrode or cathode, and an anode, which is the counter electrode, is applied and controlled by either monitoring the voltage between the electroplated metal layer 302 and the anode or monitoring the voltage between the metal layer and a reference electrode such as a SHE (standard hydrogen electrode) or a Ag/AgCl saturated electrode.
- FIG. 10 is a voltage-time graph showing a potential mode electrodeposition to deposit the IIIA-VIA layers.
- the applied potential between the anode and the metal layer 302 is modulated, i.e., pulsed, between a first voltage V 1 for a T 1 time or first voltage application period (pulse 1 ) and a second voltage V 2 for a T 2 time or second voltage application period (pulse 2 ).
- TT is a total deposition time of the IIIA-VIA layer 312 onto the metal layer 302 , based upon a cumulative amount of pulses. In some cases, more than two pulses might be advantageous. For example, a third Voltage V 3 and T 3 can be applied such that the 3 pulses are repeated until TT the total deposition time is reached.
- a third pulse can be used when dissolution of the Ga—Se compound is preferred such that the first pulse would be a nucleation pulse, the second pulse would correspond to a growth regime and the third pulse would partially dissolve the alloy layer portion that was previously deposited during the second pulse.
- the voltage range for any of the pulses used in the waveform can be between 0 V and 20 V but more preferably between 0 and 10 V, and most preferably between 0 and 4 V.
- the duration of any of the pulses (pulse width in time) can be between 1E-7 sec to 360 sec but more preferably in the range of 1E-5 sec to 10 sec, and most preferably in the range of 1E-3 to 5 sec.
- the total electroplating time TT can be in the range of seconds to hours; this TT time can also be terminated once a total charge (Coulomb [A/cm2]) has been applied to the electroplated layer such that a desired thickness range can be obtained.
- the voltage-time graph is a potentiostatic wave form in the form of a step function; however any other functional waveforms (sine, cosines, ramped profile, etc.) can also be used.
- a pulsed potential Ga will predominantly be deposited at a higher deposition potential while Se will be deposited at a lower deposition potential to form the Ga—Se layer.
- the Selenium distribution in the Ga—Se layer as a function of thickness can be controlled by simply changing the time that the voltage is maintained at V 1 ; therefore the Ga profile can be controlled independently of the overall Ga/Se atomic overall layer composition.
- potential or galvanic modulation the conductivity of the deposition receiving cathode layer may be better controlled.
- a Ga film may first be pulse electroplated on a Se film, which is a semiconductor, and then the deposition may continue with Ga—Se layer pulse electroplating to form thicker Ga—Se layers.
- Ga—Se layers electrodeposited with the potential modulation may have a more uniform Ga—Se distribution than the Ga—Se layers electrodeposited with a galvanic modulation.
- FIG. 11 is a current density-time graph showing a galvanic mode electrodeposition to form the IIIA-VIA layer.
- a defined amount of current density [mA/cm 2 ] is passed between the metal layer 302 (cathode) and an anode to deposit a Ga—Se layer onto the metal layer 302 .
- the applied current density between the anode and the metal layer 302 is modulated, i.e., pulsed, between a first current density J 1 for a T 1 time or first current density application period and a second current density J 2 for a T 2 time or second current density application period.
- the current density range for J 1 and J 2 is from 0 to 200 mA/cm 2 , but more preferably from 0 to 50 mA/cm 2 most preferably between 0.0 mA/cm 2 and 20 mA/cm 2 . In some cases, more than two pulses might be advantageous. For example, a third pulse J 3 with a duration of T 3 can also be included.
- the current density range for any of the pulses used in the waveform can be from 0 mA/cm 2 to 80 mA/cm 2 but most preferably between 0 and 40 mA/cm 2 .
- the duration of any of the pulses (pulse width in time) can be between 1E-7 sec to 60 sec but more preferably in the range of 1E-5 sec to 10 sec, and most preferably in the range of 1E-3 to 5 sec.
- the application of a constant current density permits a more precise control of the thickness of the deposited Ga—Se layer since the current density will be proportional to a deposition thickness; therefore a quasi-constant rate of Ga—Se can be deposited at each pulse of J 1 and J 2 .
- the low current density pulse can serve as a nucleation pulse while the second pulse allows the Ga—Se layer to grow, however, one of the pulses may also be used as a dissolution pulse where a portion of the deposited Ga—Se layer is etched (anodic current) and some material is deposited on the cathodic pulse.
- the Ga distribution on the Ga—Se layer will be less controllable on a galvanostatic method since the resulting voltage between the working and counter electrode will vary due to the change in conductivity of the deposited layers.
- the conductivity of the Ga—Se layer will be a function of the Ga and Se distribution as well as the Ga/Se ratio in the layer.
- a complex waveform in which the applied potential is varied as a function of time is used to deposit the Ga—Se compound.
- the waveform can be in any functional form such as a sine or cosine waveform, a linear ramp (known in electrochemistry as: Linear Sweep voltammetry), cyclic voltammetry and/or staircase voltammetry.
- electroplating under a constant current or constant voltage for a predetermined amount of time is the most straightforward way of depositing the IIIA-VIA layers using the electrodeposition electrolytes.
- pulse electroplating might be preferable due to several advantages pulse plating provides.
- First the morphology of the electroplated layer might be controlled more closely with pulse plating which is advantageous for photovoltaic applications.
- the ratio of Ga/Se (on any other metal in solution) might also be controlled by the pulse deposition parameters.
- better intermixing of the deposited metals might be achieved since diffusion control deposition of the metal species with the highest deposition rate can be controlled (coupled with the concentration in solution of such species).
- FIGS. 12A , 13 A and 14 A illustrate exemplary electroplating systems 400 A- 400 C to achieve a high throughput continuous fashion electrodeposition at constant voltage or constant current mode to electroplate a IIIA-VIA layer onto a metal layer, including a Cu film and at least one of an In film and Ga film, on a continuous base.
- the roll-to roll systems 400 electroplate a compound film or IIIA-VIA layer 412 onto a continuous metal layer 402 , formed on a continuous base 404 or substrate in a continuous fashion.
- the IIIA-VIA layer and metal layer have described above.
- the metal layer 402 As the metal layer 402 is advanced in a process direction P, it passes through the electroplating chamber 430 including a group IIIA-VIA electroplating solution, such as a Ga—Se electroplating solution 432 and at least one anode 434 immersed into the electroplating solution 432 .
- the continuous base 404 including the continuous metal layer will be referred as a web 405 .
- the web 405 will be unwrapped from a web supply roll SR; continuously advanced in the process direction ‘P’ and through the electroplating chamber 430 to form the IIIA-VIA layer 412 on a top surface 406 of the web 405 , and the web 405 with the IIIA-VIA layer 412 is wound around as take-up roll TR.
- a DC power supply 440 anodically polarizes the at least one anode 434 and cathodically polarize the web 405 through a conductive brush touching the web during the electroplating process.
- FIG. 12A shows a roll-to-roll electroplating system 400 A which may be used in either constant voltage or constant current density mode.
- the web 405 may be electroplated at a constant voltage V 1 as it is advanced for a total distance TD which is the length of the electroplating chamber 430 .
- the residence time of the web will be TD/web velocity.
- a first process graph 450 A shows the voltage (V)-distance (D) variation or the voltage profile along the cell length TD.
- the system 400 A may be used to electroplate in the current density mode by replacing the constant voltage V 1 with a constant current (J 1 ). In the current mode the first process graph 450 A shown in FIG. 12B will become the current density (J) distance (D) variation or the current density profile along the cell length TD.
- FIGS. 13A and 14A exemplary pulsed voltage or pulsed current density electroplating in a high throughput continuous fashion.
- FIG. 13A shows a roll-to-roll electroplating system 400 B which may be used in either pulsed voltage or current density mode.
- the system 400 B may have a plurality of anodes preferably isolated from one another.
- a second process graph 450 B shows the voltage (V)-distance (D) variation or the voltage profile along the length TD of the chamber 430 .
- the anodes 434 A- 434 C are held at a constant voltage V 1 creating a constant voltage pulsed profile with the first and second regions with no applied potential.
- the applied electric field from the anodes is limited by the dividers 442 that delimit the applied potential in the first and second regions resulting in no applied potential.
- Multiple anodes 434 may be placed along the electroplating chamber 430 , which are kept at the same voltage; however the spacing between the anodes, i.e. D 1 , D 2 distances, can be changed such that the extend of the region where the electroplating is performed is varied.
- the dividers 442 delimit the region where the applied potential is reflected over the moving web delimiting the area where the constant potential will be applied.
- the constant potential at the edges of the anodes 434 will decay very fast and the applied potential will be stopped by the dividers 442 .
- a second process graph 450 B shows the voltage (V)-distance (D) variation or the voltage profile along the length TD of the chamber 430 .
- the anodes 434 A- 434 C are held at a constant voltage V 1 creating a constant voltage pulsed profile with the first and second regions with no applied potential.
- the system 400 B may be used to electroplate in the current density mode by replacing the constant voltage V 1 with a constant current J 1 .
- the second process graph 450 B shown in FIG. 13B will become the current density (J)-distance (D) variation or the current density profile along the length TD of the chamber 430 .
- the pulse width T 1 , T 2 , etc will now be related to the length of the electric field (length of the anode) divided by the speed of the moving web. For example an anode with a length of 0.1 meter with a web speed of 1 meter/sec will be equivalent to a pulse time of a residence time of 0.1 sec.
- the total electroplating time will be equal to the number of anodes times the residence time.
- FIG. 14A shows another roll-to-roll electroplating system 400 C which may be used in either pulsed voltage or current density mode.
- the system 400 C may have a plurality of anodes preferably isolated from one another. Each anode may be kept in a unique potential that is different from the potential of the rest of the anodes if the voltage mode is used, or each anode may be kept in a unique current density that is different from the current density of the rest of the anodes if the current mode is used.
- first anodes 434 A, 434 C and 434 E may be held at a first potential V 1
- second anodes 434 B, 434 D and 434 F may be held at a second potential V 2 .
- the first potential V 1 applied to the first anodes is different from the second potential V 2 applied to the second anodes.
- first regions with the length D 1 include the first anodes 434 A, 434 C and 434 E and the second regions with the length D 2 includes the second anodes 434 B, 434 D and 434 F.
- the lengths D 1 and D 2 may be the lengths of the first and second anodes respectively.
- a third process graph 450 C shows the voltage (V)-distance (D) variation or the voltage profile along the length TD of the chamber 430 .
- the anodes 434 A- 434 F are held at the constant voltages V 1 and V 2 as described above to from a constant voltage pulsed profile.
- the voltage is constant at the center position of each anode 434 ; however, there is a voltage drop near edges of the anodes adjacent the dividers 442 .
- the dividers 442 utilized in this embodiment confine the voltage to a specific region and decrease the possibility of anode cross talk which may create a region where electrochemical reactions between the neighboring anodes may arise.
- a total deposition time can be determined by the web travel speed/TD.
- the system 400 C may be used to electroplate in the current density mode by replacing the constant voltages V 1 and V 2 with constant currents densities J 1 and J 2 , where J 1 is different from J 2 .
- the third process graph 450 C shown in FIG. 14B will become the current density (J)-distance (D) variation or the current density profile along the cell length TD.
- the anodes 434 A- 434 F are held at the constant current densities J 1 and J 2 from a constant current density pulsed profile.
- the current density is constant at the center position of each anode 434 ; however, there is a current density drop near edges of the anodes adjacent the dividers 442 .
- the Ga—Se solution used was comprised of GaCl 3 and H 2 SeO 3 with a pH between 1 and 2.5.
- the solution also included at least one of the following additive groups of (a): anti-oxidants, (b) anti-floculants, (c) surface-active compounds (d) ionic conductivity enhancers.
- Electroplating of the Ga—Se layer was conducted on a stainless steel substrate having an Indium terminated top metal layer. The electroplating was done in a batch mode and the cathode was titanium covered with IrO 2 .
- the deposition profile consisted of an applied constant voltage of 3.4 V between the anode and the cathode. The total deposition time was 60 sec.
- the Ga/Se ratio of the resulting film was 1.48.
- the deposited Ga—Se layers had a smooth and continuous surface with good adhesion properties.
- the Ga—Se solution used was comprised of GaCl 3 and H 2 SeO 3 with a pH between 1 and 2.5.
- the solution also included at least one of the following additive groups of (a): anti-oxidants, (b) anti-flocculants, (c) surface-active compounds (d) ionic conductivity enhancers.
- Electroplating of the Ga—Se layer was conducted on a stainless steel substrate having an Indium terminated top metal layer. The electroplating was done in a batch mode and the cathode was titanium covered with IrO 2 . This time a pulsed voltage was applied during plating. The applied potential was modulated between 3.4 V for 500 milliseconds and 2.2 V for 50 milliseconds for a total deposition time of 54 sec.
- the deposited Ga—Se layers had a smooth and continuous surface with good adhesion properties.
- the Ga/Se ratio deposited in this case is 1.6.
Abstract
Description
- This application is a continuation-in-part of U.S. patent application Ser. No. 13/347,540 filed Jan. 10, 2012, which is a continuation of U.S. patent application Ser. No. 12/143,609 filed Jun. 20, 2008 (now U.S. Pat. No. 8,092,667), and is a continuation-in-part of U.S. patent application Ser. No. 13/306,863 filed Nov. 29, 2011, which is a continuation of U.S. patent application Ser. No. 12/123,372 filed May 19, 2008 (now U.S. Pat. No. 8,066,865), and is a continuation-in-part of U.S. patent application Ser. No. 12/121,687 filed May 15, 2008, and the entire contents of these applications are incorporated herein by reference.
- 1. Field of the Art
- This application relates to electroplating methods and solutions and, more particularly, to methods and electroplating solution chemistries for electrodeposition of Group IIIA-VIA layers on a conductive surface for solar cell applications.
- 2. Description of the Related Art
- Solar cells are photovoltaic devices that convert sunlight directly into electrical power. The most common solar cell material is silicon, which is in the form of single or polycrystalline wafers. However, the cost of electricity generated using silicon-based solar cells is higher than the cost of electricity generated by the more traditional methods. Therefore, since early 1970's there has been an effort to reduce cost of solar cells for terrestrial use. One way of reducing the cost of solar cells is to develop low-cost thin film growth techniques that can deposit solar-cell-quality absorber materials on large area substrates and to fabricate these devices using high-throughput, low-cost methods.
- Group IBIIIAVIA compound semiconductors comprising some of the Group IB (Cu, Ag, Au), Group IIIA (B, Al, Ga, In, Tl) and Group VIA (O, S, Se, Te, Po) materials or elements of the periodic table are excellent absorber materials for thin film solar cell structures. Especially, compounds of Cu, In, Ga, Se and S which are generally referred to as CIGS(S), or Cu(In,Ga)(S,Se)2 or CuIn1-xGax(SySe1-y)k, where 0≦x≦1, 0≦y≦1 and k is approximately 2, have already been employed in solar cell structures that yielded conversion efficiencies approaching 20%. Absorbers containing Group IIIA element Al and/or Group VIA element Te also showed promise. Therefore, in summary, compounds containing: i) Cu from Group IB, ii) at least one of In, Ga, and Al from Group IIIA, and iii) at least one of S, Se, and Te from Group VIA, are of great interest for solar cell applications.
- The structure of a conventional Group IBIIIAVIA compound photovoltaic cell such as a Cu(In,Ga,Al)(S,Se,Te)2 thin film solar cell is shown in
FIG. 1 . Thedevice 10 is fabricated on asubstrate 11, such as a sheet of glass, a sheet of metal, an insulating foil or web, or a conductive foil or web. Theabsorber film 12, which includes a material in the family of Cu(In,Ga,Al)(S,Se,Te)2 is grown over aconductive layer 13, which is previously deposited on thesubstrate 11 and which acts as the electrical contact to the device. Various conductive layers comprising Mo, Ta, W, Ti, and stainless steel etc. have been used in the solar cell structure ofFIG. 1 . If the substrate itself is a properly selected conductive material, it is possible not to use aconductive layer 13, since thesubstrate 11 may then be used as the ohmic contact to the device. After theabsorber film 12 is grown, atransparent layer 14 such as a CdS, ZnO or CdS/ZnO stack is formed on the absorber film.Radiation 15 enters the device through thetransparent layer 14. Metallic grids (not shown) may also be deposited over thetransparent layer 14 to reduce the effective series resistance of the device. A variety of materials, deposited by a variety of methods, can be used to provide the various layers of the device shown inFIG. 1 . It should be noted that although the chemical formula for a CIGS(S) layer is often written as Cu(In,Ga)(S,Se)2, a more accurate formula for the compound is Cu(In,Ga)(S,Se)k, where k is typically close to 2 but may not be exactly 2. For simplicity we will continue to use the value of k as 2. It should be further noted that the notation “Cu(X,Y)” in the chemical formula means all chemical compositions of X and Y from (X=0% and Y=100%) to (X=100% and Y=0%). For example, Cu(In,Ga) means all compositions from CuIn to CuGa. Similarly, Cu(In,Ga)(S,Se)2 means the whole family of compounds with Ga/(Ga+In) molar ratio varying from 0 to 1, and Se/(Se+S) molar ratio varying from 0 to 1. - One technique employed for growing Cu(In,Ga)(S,Se)2 type compound thin films for solar cell applications is a two-stage process where at least two ingredients or elements or components of the Cu(In,Ga)(S,Se)2 material are first deposited onto a substrate, and then reacted with S and/or Se in a high temperature annealing process. For example, for CuInSe2 or CIS film growth, thin layers of Cu and In are first deposited on a substrate and then this stacked precursor layer is reacted with Se at elevated temperature to form CIS. If the reaction atmosphere also contains sulfur, then a CuIn(S,Se)2 or CIS(S) layer can be grown. Addition of Ga in the precursor layer, i.e. use of a Cu/In/Ga stacked film precursor, allows the growth of a Cu(In,Ga)(S,Se)2 or CIGS(S) absorber.
- Sputtering and evaporation techniques have been used in prior art approaches to deposit the layers containing the Group IB and Group IIIA components of the precursor stacks. In the case of CulnSe2 growth, for example, Cu and In layers were sequentially sputter-deposited on a substrate and then the stacked film was heated in the presence of gas containing Se at elevated temperature for times typically longer than about 30 minutes, as described in U.S. Pat. No. 4,798,660. More recently U.S. Pat. No. 6,048,442 disclosed a method comprising sputter-depositing a stacked precursor film comprising a Cu—Ga alloy layer and an In layer to form a Cu—Ga/In stack on a metallic back electrode layer and then reacting this precursor stack film with one of Se and S to form the absorber layer. Such techniques may yield good quality absorber layers and efficient solar cells, however, they suffer from the high cost of capital equipment, and relatively slow rate of production.
- One prior art method described in U.S. Pat. No. 4,581,108 utilizes a low cost electrodeposition approach for metallic precursor preparation. In this method a Cu layer is first electrodeposited on a substrate. This is then followed by electrodeposition of an In layer and heating of the deposited Cu/In stack in a reactive atmosphere containing Se. Various other researchers have reported In electroplating approaches for the purpose of obtaining In-containing precursor layers later to be converted into CIS absorber films through reaction with Se (see for example, Lokhande and Hodes, Solar Cells 21 (1987) 215; Fritz and Chatziagorastou, Thin Solid Films, 247 (1994) 129; Kim et al Proceedings of the 1st World Conf. on Photovoltaic Energy Conversion, 1994, p. 202; Calixto and Sebastian, J. Materials Science, 33 (1998) 339; Abedin et al., Electrochemica Acta, 52 (2007) 2746, and, Valderrama et al., Electrochemica Acta, 53 (2008) 3714).
- A number of In electroplating baths used for depositing In layers on various conductive substrates have been disclosed in several references. For example, In plating baths containing sulfamate (U.S. Pat. No. 2,458,839), cyanide (U.S. Pat. No. 2,497,988), alkali hydroxides (U.S. Pat. No. 2,287,948), tartaric acid (U.S. Pat. No. 2,423,624), and fluoborate (U.S. Pat. No. 3,812,020, U.S. Pat. No. 2,409,983) have been developed. Some details on such chemistries may be found in the review paper of Walsh and Gabe (Surface Technology, 8 (1979) 87). Although it is possible to deposit In layers using various electroplating chemistries employing standard plating practices, unless these layers have sub-micron thickness and smooth morphology, they cannot be effectively used in thin film Group IBIIIAVIA compound solar cell fabrication.
- As described above, one recent application of electroplated In films involves the formation of Cu(In,Ga)(Se,S)2 or CIGS(S) films, which are the most advanced compound absorbers for polycrystalline thin film solar cells. An exemplary plating process includes first electroplating a thin In layer on a Cu layer, and then reacting this Cu/In precursor stack with Se to form a CuInSe2, or a CIS absorber. Furthermore, to form a CIGS or CIGS(S) type of compound absorber, Ga can also be included in the precursor stack by plating it on the In layer or by including it in the In layer. Zank et al. (Thin Solid Films, 286 (1996) 259), for example, electrodeposited an In—Ga alloy layer on a Cu film forming a Cu/In—Ga precursor stack and then obtained a CIGS absorber layer by reacting the precursor stack with Se vapor. The CIGS absorber was then used to fabricate a thin film solar cell having a structure similar to the one shown in
FIG. 1 . - In a thin film solar cell employing a Group IBIIIAVIA compound absorber such as CIS or CIGS, the solar cell efficiency is a strong function of the molar ratio of the IB element(s) to IIIA element(s), i.e. the IB/IIIA molar ratio. If there are more than one Group IIIA materials in the composition, the relative amounts or molar ratios of these IIIA elements also affect the solar cell efficiency and other properties. For a Cu(In,Ga)(S,Se)2 absorber layer, for example, the efficiency of the device is a function of the molar ratio of Cu/(In+Ga). Furthermore, some of the important parameters of the cell, such as its open circuit voltage, short circuit current and fill factor vary with the molar ratio of the IIIA elements, i.e. the Ga/(Ga+In) molar ratio. In general, for good device performance Cu/(In+Ga) molar ratio is kept at or below 1.0. For ratios higher than 1.0, a low resistance copper selenide phase, which may introduce electrical shorts within the solar cells may form. Increasing the Ga/(Ga+In) molar ratio, on the other hand, widens the optical bandgap of the absorber layer, resulting in increased open circuit voltage and decreased short circuit current. A CIGS material with a Ga/(Ga+In) molar ratio higher than about 0.3 is electronically poor. It is for this reason that the sunlight-to-electricity conversion efficiency of a CIGS type solar cell first increases as the Ga/(Ga+In) molar ratio in the absorber is increased from 0 to 0.3, and then the efficiency starts to decrease as the molar ratio is further increased towards 1.
- In light of the above discussion, it should be appreciated that if the electrodeposition process is used to introduce In into the composition of a CIGS(S) precursor material, it is essential that the electroplated In films have smooth morphology and uniform thickness, in micro-scale. If micro-structure of an In film or a In—Ga film electroplated on a Cu and optionally Ga containing precursor layer is rough and includes protrusions and valleys or discontinuities, the localized micro-scale Ga/(In+Ga) ratio at the protrusions would be lower than the Ga/(In+Ga) ratio at the valleys. Even the Cu/(In+Ga) molar ratio would be different at these two locations. As will be described next, this kind of micro-scale non-uniformity would yield a CIGS(S) absorber with non-uniform electrical and optical properties after reaction of the precursor stack with Se and/or S. The same argument also holds for the other thin film layers (such as Cu and Ga) within the precursor stack. However, electroplating a smooth Cu layer is relatively easy and the problem usually lies with Ga and In electrodeposition due to the tendency of these low melting, high surface tension elements forming droplets rather than continuous layers when deposited in thin film form.
- Thin film CIGS(S) solar cell absorbers typically have a thickness range of 1000-3000 nm. The amount of In that needs to be included in such a thin absorber is equivalent to an In layer thickness which is in the range of about 200-700 nm. For example, for the formation of about 2000 nm thick CIGS absorber with a final Cu/(In+Ga) ratio of 0.85-0.9 and a Ga/(Ga+In) ratio of about 0.3, one needs to deposit about 250-300 nm thick Cu film, about 150 nm thick Ga layer and about 450-500 nm thick In film to form a precursor which may then be reacted with Se. Since cost lowering in CIGS solar cell fabrication as well as the need to reduce stress in the CIGS layer grown by the two-stage processes dictate the use of an absorber thickness which is in the range of 1000-1500 nm, the thickness of the In film in the above example gets reduced to about 200-300 nm level. The Ga layer thickness goes down even lower to the 75-100 nm range. Therefore, in a two stage CIGS(S) absorber formation approach employing an electroplated In layer, the electroplated In film thickness will have to be much less than 1000 nm, preferably less than 700 nm, most preferably less 500 nm. This requirement presents many challenges for prior art In electroplating methods and chemistries. Although these issues will be discussed with respect to In electrodeposition, it should be understood that they are also applicable to Ga and In—Ga alloy electrodeposition.
- Low melting Group IIIA materials such as In and Ga have high surface tension and they grow in the form of islands or droplets when deposited on a substrate surface in thin film form. This behavior has been observed in prior work carried out on electroplated In films (see for example, Chen et al., Solar Cells, 30 (1991) 451; Kim et al, Proceedings of the 1st World Conf. on Photovoltaic Energy Conversion, 1994, p. 202; Calixto and Sebastian, J. Materials Science, 33 (1998) 339; Abedin et al., Electrochemica Acta, 52 (2007) 2746, and, Valderrama et al., Electrochemica Acta, 53 (2008) 3714), and in work carried out on In—Ga alloy films (see for example Zank et al., Thin Solid Films, 286 (1996) 259). As stated before, lack of planarity in sub-micron thick In and/or Ga-rich layers presents problems for application of such non-uniform layers to thin film solar cell manufacturing.
-
FIGS. 2A-2B schematically show a prior art structure in perspective and side views, respectively. The structure includes a typical prior art Inlayer 37, with sub-micron thickness which may be electrodeposited on asurface 36 of an under-layer 33. The under-layer 33 is formed over a base 30 having asubstrate 31 and acontact layer 32. The under-layer 33 may, for example, include Cu and Ga and be formed on thecontact layer 32. As can be seen fromFIGS. 2A and 2B , the sub-micron thick Inlayer 37 is discontinuous and it includesislands 34 of In, separated byvalleys 35 through which thesurface 36 of the under-layer 33 is exposed. The width of the islands may be in the range of 500-5000 nm. If the structure ofFIGS. 2A and 2B is reacted with a Group VIA material such as Se, a CIGSsolar cell absorber 40 may be formed on the base 30 as shown inFIG. 3 . The CIGSsolar cell absorber 40 has compositional non-uniformities caused by the morphological non-uniformity of the sub-micron thick Inlayer 37. Accordingly, the CIGSsolar cell absorber 40 has afirst region 41 and asecond region 42. Thefirst region 41 corresponds to theislands 34 of In of the structure ofFIG. 2A , and is an In-rich, Ga-poor region. Thesecond region 42 corresponds to thevalleys 35 of the structure ofFIG. 2A , and is an In-poor, Ga-rich region. Furthermore, the Cu(In+Ga) molar ratio in thefirst region 41 is lower than the Cu(In+Ga) molar ratio in thesecond region 42. It should be appreciated that when a solar cell is fabricated on the CIGSsolar cell absorber 40, the efficiency of the solar cell would be determined by both thefirst region 41 and thesecond region 42. The solar cell would act like two separate solar cells, one made on thefirst region 41 and the other made on thesecond region 42 and then interconnected in parallel. Since the Ga/(Ga+In) as well as the Cu/(In+Ga) molar ratios in the two regions are widely different the quality of the separate solar cells on these regions would also be different. The quality of the overall solar cell would then suffer from the poor I-V characteristics of the separate solar cells formed on either one of the first and second regions. - It should be noted that such non-uniformity problems may not be important in applications where the electroplated In layer is not used for the fabrication of an active electronic device such as a solar cell. It should also be noted that the In films when electrodeposited to thicknesses larger than about 1000 nm they may start forming continuous layers. In such cases the
islands 34 inFIG. 2A grow horizontally as well as vertically and eventually merge, eliminating thevalleys 35. However, such thick electroplated In layers are not useful for thin film solar cell fabrication since they yield CIGS absorbers that are too thick (thicker than about 3000 nm). Thick absorber layers cause excessive stress and delamination from the base. They also add to the cost of processing, which is not in line with the cost-lowering targets of thin film photovoltaics. Highly efficient CIGS solar cells can be fabricated on 1000 nm thick CIGS absorbers. Using a 3000 nm thick CIGS absorber in a solar cell structure increases materials usage three time and wastes effectively 67% of the materials used in forming the CIGS absorber structure. - As can be seen from the foregoing discussion it is necessary to develop new Group IIIA material electroplating approaches that can yield continuous layers at thicknesses less than about 700 nm, preferably less than about 500 nm. Such thin layers can be used in electronic and semiconductor applications such as in processing thin film CIGS type solar cells.
- The embodiment described herein relate to electroplating methods and plating electrolyte solutions.
- In one embodiment is described a method of forming an absorber layer over a surface of a base, the method comprising: forming a metal layer over the surface of the base, wherein the metal layer comprises a Group IIIA material; co-depositing Group IIIIA and Group VA materials to form a Group IIIA-VIA layer on the metal layer using pulse electroplating that varies an electroplating pulse between a first higher value and a second lower value, wherein at the first higher value electroplating of at least one of Ga and In predominates, and wherein at the second lower value electroplating of one of Se, Te and S predominates, wherein the step of co-depositing the Group IIIA-VIA layer uses a roll-to-roll electroplating process wherein the base having the metal layer is continuously advanced within an electroplating solution held in a deposition chamber as at least one electric field is formed between at least one anode to deposit the Group IIIA-VIA layer onto the metal layer; and reacting the metal layer and the Group IIIA-VIA layer to form the absorber layer.
- In another embodiment is described an electroplating solution for deposition of a Group IIIA-Group VIA thin film on a Group IIIA material surface, the electroplating solution comprising: a solvent; a Group IIIA material source that provides Ga in ionic form in the solvent; a Group VIA material source that dissolves in the solvent and provides Se in ionic form; an anti-oxidant; an anti-flocculant; a pH adjuster including at least one of an organic acid, an inorganic acid, an organic base and an inorganic base; additives including at least one of a surface-active compound, a complexing agent and an ionic conductivity enhancer; wherein the pH of the solution is in the range of 0.5-13.
- Other embodiments and aspects are described herein.
- These and other aspects and features will become apparent to those of ordinary skill in the art upon review of the following description of specific embodiments in conjunction with the accompanying figures, wherein:
-
FIG. 1 is a schematic view of a prior art solar cell structure. -
FIG. 2A is a perspective top view of a prior art precursor structure formed by electroplating a sub-micron thick In layer on a sub-layer. -
FIG. 2B is a cross-sectional view of the structure ofFIG. 2A taken along the line AA. -
FIG. 3 is a CIGS layer formed after reaction of the structure ofFIG. 2B with Se. -
FIGS. 4A-4C schematically shows electrodeposition of a uniform In-rich layer over a continuous interlayer thus forming a uniform stack. -
FIG. 5 shows a Group IBIIIAVIA compound layer formed on a base using the stack ofFIG. 4 . -
FIG. 6A is a schematic view of a precursor stack including a Group IB-IIIA meta layer on a base, a Group IIIA-VIA alloy layer on the metal layer and a Group VIA layer on the alloy layer; -
FIG. 6B is a schematic view of a precursor layer formed after reacting the precursor stack shown inFIG. 6A ; -
FIG. 7A is an electroplating voltage-time graph; -
FIG. 7B is an electroplating current density-time graph; -
FIG. 8A is a pulsed electroplating voltage-time graph; -
FIG. 8B is a pulsed electroplating current density-time graph; -
FIGS. 9A-9B various electroplating voltage-time and electroplating current density-time graphs; -
FIG. 10 is a pulsed electroplating voltage-time graph; -
FIG. 11 is a pulsed electroplating current density-time graph; -
FIG. 12A is a schematic view of an embodiment of a first electroplating system; -
FIG. 12B is a process graph showing voltage or current density variation along the length of an electroplating chamber of the first system shown inFIG. 12A ; -
FIG. 13A is a schematic view of an embodiment of a second electroplating system; -
FIG. 13B is a process graph showing voltage or current density variation along the length of an electroplating chamber of the second system shown inFIG. 13A ; -
FIG. 14A is a schematic view of an embodiment of a third electroplating system; and -
FIG. 14B is a process graph showing voltage or current density variation along the length of an electroplating chamber of the third system shown inFIG. 14A . - Described are methods for forming a Group IIIA material thin film on a conductive layer which is coated by an interlayer to facilitate a uniform Group IIIA material thin film growth with thickness less than about 700 nm. The Group IIIA material film, the interlayer and the conductive layer may be a part of a precursor stack that will eventually be reacted and transformed into a Group IBIIIAVIA solar cell absorber. The Group IIIA material thin film may comprise any one of a substantially pure In material, a substantially pure Ga material, or an In—Ga binary alloy. The Group IIIA material thin film is a continuous film having a thickness less than about 700 nm. In one embodiment, the Group IIIA material thin film may be formed by an electrodeposition process on the surface of the interlayer. Accordingly, the interlayer is formed on a conductive surface which may be the top surface of a base or a precursor stack. The group IIIA material thin film may then be formed by electrodeposition on the exposed surface of the interlayer. The interlayer comprises 20-90 molar percent, preferably 40-80 molar percent of at least one of In and Ga. The balance of the interlayer composition comprises an additive material. The additive material of the interlayer includes at least one of Cu, Se, Te, Ag and S, preferably at least one of Cu and Te. Other materials or impurities may also be present in the additive material as long as their molar content does not exceed about 10 molar percent of the total additive material composition. The process used to form the Group IIIA material thin film on the interlayer is electrodeposition; however, in the following description the words electroplating, plating and deposition may be used to refer to the electrodeposition process of the In and/or Ga layer.
- An electrodeposition process which forms a Group IIIA material layer, or thin film, for the manufacture of a Group IBIIIAVIA solar cell precursor structure will be described using
FIGS. 4A-4C .FIG. 5 shows the structure with the Group IBIIIAVIA solar cell absorber, which is formed from the precursor stack ofFIG. 4C . -
FIG. 4A exemplifies afirst structure 100 including afirst layer 102 formed on a base 104 to initiate the precursor stack forming process. Thefirst layer 102 may preferably be formed using an electrodeposition process; however, other deposition processes such as evaporation, sputtering and the like may also be used to form thefirst layer 102. The base 104 may be a conductive base including asubstrate 106 and acontact layer 108, which will eventually form an electrical contact to the CIGS(S) absorber after the reaction step. Thesubstrate 106 may be a continuous conductive material such as a metal or alloy foil, preferably a stainless steel foil. Thecontact layer 108 may comprise conductive materials such as Mo, W, metal nitrides, Ru, Os, and Ir, which make ohmic contact to CIGS(S) type absorber films. Thefirst layer 102 is a conductive layer comprising Cu. Thefirst layer 102 may be a pure Cu layer or it may comprise In and/or Ga. Thefirst layer 102 may be homogeneous or it may be in the form of a stack. Exemplary stacks forming thefirst layer 102 include, but are not limited to, Cu/Ga, Cu/Ga/Cu, Cu—Ga/Cu, and the like, stacks. -
FIG. 4B shows asecond structure 200 formed as the process proceeds. In thesecond structure 200, asecond layer 112 or an interlayer is formed on thetop surface 110 of thefirst layer 102, using preferably an electrodeposition process. Theinterlayer 112 is a conditioned conductive layer so that it establishes a conditioned surface for the following Group IIIA thin film deposition. In the context of this application, the word conditioned refers to establishing a mate composition that not only helps forming a thin and continuous Group IIIA layer on the interlayer but also includes constituents that do not affect negatively the overall composition of the resulting precursor stack and do not deteriorate the quality of the CIGS(S) absorber to be formed. Theinterlayer 112 is a continuous layer with a substantially uniform thickness which is less than 100 nm, preferably less than 50 nm.Surface 114 of theinterlayer 112 functions as an active deposition site to allow a Group IIIA material to continuously and uniformly deposit onto thesurface 114 in the subsequent step, thereby eliminating the discontinuity problems of the prior art described above. - The
interlayer 112 comprises 20-90 molar percent, preferably 40-80 molar percent of at least one of In and Ga. Presence of In and/or Ga in the interlayer composition is important for the interlayer to provide effective nucleation to the In and/or Ga rich layer that will be electroplated on top of it. However, the In and/or Ga content of the interlayer cannot be more than 90% because the interlayer needs to be continuous to be able to provide the effective nucleation sites. If the interlayer becomes near pure In and/or Ga layer then it would be in the form of islands or droplets as discussed before. - Besides In and/or Ga, the balance of the interlayer composition is an additive material. The additive material in the interlayer includes at least one of Cu, Se, Te, Ag and S. The most preferred additives are Cu and Te. These additives assist in making the interlayer a continuous film, and at the same time the In and/or Ga in the interlayer provide high density of nucleation sites for the In and/or Ga layer that would be electroplated on the interlayer. Since the Group IBIIIAVIA absorber layer (compound layer) fabrication is specifically targeted, the additive materials are the materials that will not damage the electronic quality of the CIGS(S) absorber. Other materials or impurities may also be present in the additive material without exceeding about 10 molar percent of the total additive material composition. Examples of such impurities include Sb and As. The composition of the interlayer is largely determined by the chemical composition of the Group IIIA material layer (
layer 116 inFIG. 4C ) that will be electrodeposited onto theinterlayer 112 and any other layer that may be present in the resulting precursor stack. - In one embodiment, the
interlayer 112 may be electrodeposited out of plating electrolytes comprising at least one of In and Ga as well as at least one additive such as Cu and Te. By co-depositing these additives and including them into theinterlayer 112, a continuous interlayer may be obtained even at a thickness as low as 10 nm. Although the thickness of theinterlayer 112 depends on the thickness of the Group IIIA material layer that will be electrodeposited onto the interlayer, a preferable thickness of it may be for example less than about 50 nm so that the amount In, Ga and other materials that it may contain do not become a determining factor in the overall composition, i.e. the Cu/(In+Ga) molar ratio or Ga/(Ga+In) molar ratio, of the resulting structure after the Group IIIA material deposition. In one embodiment, the thickness of the interlayer is less than or equal to about 20%, preferably less than about 10% of the thickness of the Group IIIA material-rich layer that is deposited over the interlayer, so that the effect of the interlayer on determining the overall composition of the resulting precursor stack is limited. This is important for manufacturability and repeatability of the process. -
FIG. 4C shows athird structure 300 formed after electrodepositing athird layer 116 which is a substantially pure Group IIIA material layer onto theinterlayer 112. As opposed to the discontinuity problems of the prior art In and/or Ga films, thethird layer 116 is a continuous thin film. By employing an electrodeposition process that uses theinterlayer 112 as a cathode, very thin Group IIIA material layers having uniform thickness may be formed on theinterlayer 112. The thickness of thethird layer 116 may be less than about 700 nm, preferably less than about 500 nm, whereas the thickness of the interlayer is less than about 20% of these values, i.e. less than about 140 nm, preferably less than about 100 nm. Most preferably the thickness of the interlayer is less than about 10% of the thickness of the third layer 166, i.e. less than about 70 nm. In one embodiment, the Group IIIA material deposited on the interlayer may be a substantially pure In—Ga binary alloy electrodeposited from an electrolyte comprising In and Ga ions. During the electrodeposition process, in an electrodeposition chamber containing the electrodeposition electrolyte, theinterlayer 112 is cathodically polarized with respect to an anode so that the third layer comprising In and Ga deposits onto thesurface 114 of the interlayer in a uniform manner. The chemical composition of thethird layer 116 may preferably comprise at least 90 molar percent In and/or Ga, preferably at least 95 molar percent In and/or Ga. - Referring back to
FIG. 4C , as will be appreciated, in thethird structure 300, the stack of thefirst layer 102, thesecond layer 112 or interlayer and thethird layer 116 forms a precursor stack containing Group IB and Group IIIA elements on thebase 104. - As shown in
FIG. 5 , in the following process step, theprecursor stack 118 is reacted with at least one Group VIA material such as Se, Te or S to form anabsorber layer 120 on thebase 104. As mentioned above theprecursor stack 118 comprises Cu, In, and Ga, and therefore reacting them with a Group VIA material forms theabsorber 120 which is a compositionally uniform Group IBIIIAVIA compound layer. - Described also are methods for forming a Group IIIA-Group VIA (IIIA-VIA) material layers or films on a conductive layer. The IIIA-VIA layer may be a part of a precursor stack that is reacted to form a Group IBIIIAVIA compound semiconductor absorber layer (CIGS layer). The IIIA-VIA layer may comprise any one of a Ga—Se binary alloy, an In—Se binary alloy or an In—Ga—Se ternary alloy. Alternatively, the IIIA-VIA layer may comprise any one of a Ga—Te binary alloy, an In—Te binary alloy or an In—Ga—Te ternary alloy. The IIIA-VIA layer may be formed, using a PVD process, such as sputter deposition, evaporation deposition, or an electrodeposition process, on an In film or a Ga film of a precursor stack including Cu, Ga and In films.
- An electroplating process which forms a IIIA-VIA layer or thin film to manufacture a Group IBIIIAVIA solar cell precursor structure will be described using
FIG. 6A . The electroplating process includes an electroplating solution coupled with galvanic (constant current), potentiostatic (constant voltage) or pulsed galvanic or potentiostatic electroplating techniques to provide more control over the electroplated film morphology and quality. Electroplating process may be performed in a roll-to-roll electroplating system including an electroplating tank containing an electroplating solution and at least one electrode (anode). As shown inFIG. 6A , afirst layer 302 or metal layer may be formed on a base 304 to initiate the precursor stack forming process. Themetal layer 302 may preferably be formed using an electroplating process; however, other deposition processes such as evaporation, sputtering and the like may also be used to form themetal layer 302. The base 304 may be a conductive base including asubstrate 306 and acontact layer 308, which will eventually form an electrical contact to the CIGS(S) absorber after the reaction step. Thesubstrate 306 may be a continuous conductive material such as a metal or alloy foil, preferably a stainless-steel foil. Thecontact layer 308 may comprise conductive materials such as Mo, W, metal nitrides, Ru, Os and Ir, which make ohmic contact to CIGS(S) type absorber films. Themetal layer 302 is a conductive layer comprising Cu, In and Ga. Themetal layer 302 may preferably be in the form of a stack including multiple films of Cu and at least one of In and Ga. Exemplary stacks forming themetal layer 302 include, but are not limited to, Cu/Ga, Cu/In, Cu/In/Ga, Cu/Ga/In, and the like, stacks. In the preferred embodiment, the metal layer is a stack with an In-film, i.e., the top surface of themetal layer 302 is In metal. - As shown in
FIG. 6A , asecond layer 312 or a IIIA-VIA layer is formed on atop surface 310 of themetal layer 302, using preferably an electroplating process. The IIIA-VIA layer 312 may be electrodeposited from a IIIA-VIA electroplating solution or electrolyte onto themetal layer 302. The IIIA-VIA layer may be an alloy with the predetermined compositions of non-alloyed 111A and VIA materials, a mixture of alloys of IIIA and VIA materials or a mixture of alloyed and non-alloyed IIIA and VIA materials. In the preferred embodiment IIIA and VIA materials are co-electrodeposited to form the IIIA-VIA layer. In the preferred exemplary embodiment the IIIA-VIA layer 312 is a Ga—Se binary alloy layer or a layer of mixed Ga and Se materials co-electrodeposited from a Ga—Se electroplating solution on thetop surface 310 of themetal layer 302. In one embodiment, themetal layer 302 and the IIIA-VIA layer 312 form aCIGS precursor stack 314. Before the reaction step, acap layer 316 that preferably includes a Group VIA layer including at least one of Se, Te and S and a dopant layer including at least one of Na, K and L is deposited onto theCIGS precursor stack 314 and the stack is reacted to form anabsorber layer 320 on thebase 304, as shown inFIG. 6B . Between thecap layer 316 and the IIIA-VIA layer 312, there may be one or more films of Cu, In and Ga. As also mentioned above theCIGS precursor stack 314 comprises Cu, In, Ga and Se and therefore reacting theprecursor stack 314 with Group VIA material forms theabsorber layer 320 which is a compositionally uniform Group IBIIIAVIA compound semiconductor layer. - The electroplating process of the IIIA-
VIA layer 312 utilizes precise chemistry control coupled with a waveform deposition profile in either a galvanic mode or a potentiostatic mode to precisely control the co-deposition of Group IIIA and Group VIA materials, i.e. Ga and Se. A stable multi-composition electroplating solution with an increased lifetime was formulated. The electrolyte solution includes several distinctive additives such as anti-oxidants, anti-flocculants, surface-active compounds, organic-water solvent pairs (non-aqueous solvents) to facilitate defect-free, continuous and device-quality layers containing IIIA and VIA elements. The waveform deposition profile provides a flexible platform for the deposition of IIIA-VIA layers with different electroplating redox potentials such that alloys, intermetallics, or mix-metal films can be electrodeposited. - The composition of the IIIA-
VIA layer 312 of the Group IIIA and Group VIA material can also be controlled by the ratio of Group IIIA/Group VIA,.e, Ga/Se ratio, in the electroplating solution. A waveform deposition profile, e.g., pulsing either the deposition voltage or current density, provides a flexible platform for the deposition of IIIA-VIA alloys. In its simplest form, the waveform might be a constant current or a constant voltage that is applied for the required duration to electroplate the desired thickness and composition of IIIA-VIA alloys as illustrated inFIGS. 7A-7B .FIG. 7A shows a constant voltage V1 for duration T1 whileFIG. 7B shows a constant current density J1 for duration T1. In addition, intentional grading can be employed in the electrodeposition of IIIA-VIA layers to distribute the elemental species throughout the layer thicknesses to obtain desirable precursor structures. For example, in the preparation of the precursor first a Cu—In—Ga layer can be deposited, preferably with the use of plating. Precursor formation can be completed by plating a graded In—Se or Ga—Se layer on the top of this layer with an In/Ga-rich bottom region and a Se-rich top region. If the potentiostatic (voltage) mode is used, a high plating voltage followed by a low plating voltage can be used to obtain a layer grading.FIG. 8A shows a constant voltage V1 for duration T1 followed by V2 for duration T2, where V2>V1. - The film grading can also be accomplished in a galvanostatic (current) mode by applying a high current density initially to obtain an In/Ga-rich layer and then lowering the current density to incorporate more selenium into the growing layer, these approach is shown in
FIG. 8B where a constant current density J1 for duration T1 is followed by J2 for duration T2, where J2>J1. Yet another way to achieve such type of graded structure in either a potentiostatic and galvanostatic modes is by application of a waveform (pulse).FIGS. 9A-9B illustrate one of many types of waveforms for gradual grading in potentiodynamic and galvanodynamic modes.FIG. 9A shows a constant voltage increasing from V1 to V2 for duration from T1 to T2 andFIG. 9B shows a current density increasing from J1 to J2 for duration from T1 to T2 in linear or parabolic fashions. - The IIIA-VIA electroplating solutions are prepared by dissolving a IIIA source material and a VIA source material in a solvent. In these solutions the amount of IIIA source can be in the range of 0-100%. In other words, the solution composition can be in any range from a pure VIA solution to a mixture of IIIA and VIA source at any ratio, to a pure IIIA solution. Similarly, the amount of VIA source can be in the range of 0-100%. In other words, the solution composition can be in any range from a pure IIIA solution to a mixture of VIA and IIIA source at any ratio, to a pure VIA solution. In an exemplary pure Se solution to deposit to a IIIA-VIA layer with 0% IIIA material may contain a selenium source, inorganic and organic acids and bases, complexing agents, additive groups such as anti-oxidants, anti-flocculants, surface-active compounds ionic conductivity enhancers and organic-water solvent pairs or non-aqueous solvents. Selenium oxide may provide Se source. In addition, compounds of Se such as acids of Se as well as oxides, chlorides, sulfates, nitrates, perchlorides, and phosphates of Se can be used.
- Exemplary Ga—Se electroplating solutions to deposit the IIIA-
VIA layer 312 may include a gallium source, a selenium source, inorganic and organic acids and bases, complexing agents, additive groups such as anti-oxidants, anti-flocculants, surface-active compounds ionic conductivity enhancers and organic-water solvent pairs or non-aqueous solvents. Ga source in this plating bath composition may comprise stock solutions prepared by dissolving Ga metals into their ionic forms as well as by dissolving soluble Ga salts, such as sulfates, chlorides, acetates, sulfamates, carbonates, nitrates, phosphates, oxides, perchlorates, hydroxides. Examples of a gallium source may include one of GaCl3, Ga(NO3)3, Ga2(SO4)3, Ga-Oxides, gallium (III) acetylacetonate, gallium bromide, gallium iodine, gallium (III) trifluoromethane sulfonate, gallium trichloride-phosphorus oxychloride, or gallium oxychloride. Selenium oxide may provide Se source. In addition, compounds of Se such as acids of Se as well as oxides, chlorides, sulfates, nitrates, perchlorides, and phosphates of Se can be used. Examples of a selenium source may include one of a selenus acid, selenic acid, selenium oxide, selenium (IV) bromide, selenium chloride (I, IV), selenium (IV) sulfide selenourea, N,N-dimethylselenourea, selenosemicabazide, sodium selenite, silver selenite or selenium disulfide. - The electroplating solution may also be prepared to electroplate other IIIA-VIA layers including other materials such as indium and tellurium to form an In—Te alloy layer or a layer of mixed In and Te. Further, indium salts may be dissolved in an above described Ga—Se solution to formulate an In—Ga—Se electroplating solution to deposit an In—Ga—Se alloy layer or a layer of mixed In, Ga and Se materials. In and Ga source in this plating bath composition may comprise stock solutions prepared by dissolving In and Ga metals into their ionic forms as well as by dissolving soluble In and Ga salts. Indium salts may include indium-chloride, indium-sulfate, indium-sulfamate, indium-acetate, indium-carbonate, indium-nitrate, indium-phosphate, indium-oxide, indium-perchlorate, and indium-hydroxide. Te sources such as telluric acid (H6TeO6), tellurium dioxide (TeO2) may be included in the above described Ga—Se solutions to formulate a Ga—Se—Te electroplating solution to deposit a Ga—Se—Te alloy layer or a layer of mixed Ga, Se and Te materials. Both In and Te salts may also be added to prepare an In—Ga—Se—Te solution to deposit an In—Ga—Se Te alloy or a layer of mixed In, Ga, Se and Te materials. In addition to Te, another group VIA element sulfur may also be incorporated into the electrodeposited IIIA-VIA layer if S sources are added into the electroplating solution specified above. Exemplary sulfur sources include selenium sulfides (Se4S4, SeS2, Se2S6), thiourea (CSN2H4), and sodium thiosulfate (Na2S2O3).
- An exemplary In—Ga—Se—Te—S electroplating solution to deposit the IIIA-
VIA layer 312 may include a gallium source, an indium source, a selenium source, a tellurium source, a sulfur source, inorganic and organic acids and bases, complexing agents, additive groups such as anti-oxidants, anti-flocculants, surface-active compounds ionic conductivity enhancers and organic-water solvent pairs or non-aqueous solvents. Group IIIA material source in this plating bath composition may comprise stock solutions prepared by dissolving In and Ga metals into their ionic forms as well as by dissolving soluble In and Ga salts, such as sulfates, chlorides, acetates, sulfamates, carbonates, nitrates, phosphates, oxides, perchlorates, and hydroxides. Selenium oxide and Te oxide may provide the Group VIA source. In addition, Group VIA compounds of Se and Te such as acids of Se and Te as well as oxides, chlorides, sulfates, nitrates, perchlorides, and phosphates of Se and Te can be used. Sulfur can be provided from source including selenium sulfides (Se4S4, SeS2, Se2S6), thiourea (CSN2H4), and sodium thiosulfate (Na2S2O3). - Antioxidants are compounds which can be used to regulate the oxidation potential of the solution to control the oxidation state, and thus the relative amounts of dissolved selenium ions from +4 to +6. For example, inclusions of appropriate anti-oxidants can provide the ability to regulate the ratio of selenite (SeO32-) ion, where Se has an oxidation state of +4, to selenate (SeO42-) ion, where Se has an oxidation state of +6. The oxidation states of ionic selenium ions for +4 and +6 will be designated as Se(+4) and Se(+6) from here on. In the absence of any anti-oxidants, the oxidation of Se (+4) to Se (+6) ions is mainly controlled by the dissolved oxygen in the electroplating baths. Several categories of anti-oxidants operating under different mechanisms can be considered to prevent the oxidation of Se(+4) to Se(+6). For example, in one category, additives that reduce the oxygen solubility in the electroplating bath can be used. These will reduce the rate of oxidation of selenium. In another category, additives that sequester the dissolved oxygen can be used to reduce the dissolved oxygen and to decrease the oxidation rate. In another category, that reduce the selenium (+4) to Selenium (+6) by oxidizing themselves can be considered. Controlling the Se (+4)/Se (+6) ratio can provide an increase and stable faradaic plating efficiency. An increase in the faradaic efficiency might be possible as the reduction of Se (+4) to elemental Se will require four electrons as compared to 6 electrons needed for Se(+6). Having a constant Se (+4)/Se(+6) ratio can provide a constant faradic efficiency which will yield films with a better Se thickness control in the film over time. As a result, the ratio of Ga/Se in the Ga—Se films can be controlled more precisely since the faradaic efficiency for selenium plating, will be constant. Any anti-oxidant that can assist to provide a better control over the Ga/Se ratio in the resulting Ga—Se film can be included in the Ga Se electrolytes. Some of the anti-oxidant that can be used to control the selenium oxidation state includes, but not limited to, one of organic anti-oxidants such as hydroquinone, pyrocatechol, gallic acid; cycloamines such as 4-amino-4H-1,2,4-triazole, 4,5-imidazoledicarboxylic acid; sugars such as dextrose, saccharin, fructose; organic-sulfonates such as hydroquinone sulfonic; alcohols such as ethanol, methanol, glycerol, ethyleneglycol and phenolic compounds such as 1,1-Diphenyl-2-picryl hydrazyl, dihydric phenols, catechol, resorcinol, 4-(N-alkylated) aminophenols, etc.
- Anti-flocculants are compounds used to reduce the interaction between metal metal-oxides or other metal based particulates such that they do not aggregate and precipitate. Anti-flocculants can be used to increment the lifetime of the solution and reduce defect formation by reducing flocculation which could cause shadowing effects during electroplating due to particle formation on the working electrode/electrolyte interface; this effect would impact the integrity of the film and reduce the overall performance efficiency of the particular spot where flocculation has created a plating defect. Anti-flocculants may include phosphates including one of simple phosphates including dipotassium phosphate, ammonium dihydrogen phosphate, ammonium hexafluorophosphate, calcium phosphate, potassium metaphosphate, potassium phosphate, potassium triphosphate, potassium hexafluorophosphate, potassium hydrogen phosphate and sodium hydrogen phosphate; phosphate-thiols such as diethyl dithiophosphate; phosphate-ammonium such as diethyl dithiophosphate, ammonium salt; organic phosphates such as tetrabutylammonium hexafluorophosphate. Anti-flocculants may also include one of: glycols such as polyethylene glycol; organic compounds including acids and esters, such as tannic acid as an acid and ether as an ester; phosphonic acids such as organo-phosphates for example, 1-hydroxyethylidenebis(phosphonic acid) or methylenediphosphonic acid; and amines such as diethylenediamine or amino-phosphonic-organic acid, for example, (aminomethyl)phosphonic acid.
- Surface active compounds are compounds that will bind to the surface of the working electrode (e.g., the
surface 310 of themetal layer 302 inFIG. 6A ) and will modify the growth by either binding to the surface and preventing growth or binding to the surface and aiding in the growth. Furthermore the surface active components can be non-ionic such that they will only change the surface tension of the solid-liquid interface and this effect will change the hydrodynamics at the surface which will in turn change the growth rate and diffusion limitations. Exemplary surface active compounds may include one of: amine such as melamine; amine-hydroxide such as dopamine hydrochloride; sulfonic such as (HEPES) 4-(2-hydroxyethyl)piperazine-1-ethanesulfonic acid; triazine-thiol such as 1,3,5-triazine-2,4,6-trithiol trisodium; anioninc surfactants such as SDS; cationic surfactants such as n-dodecylamine or sodium n-octyl sulfate; tri-block-polymers such as ethylene oxide(EO)-propylene oxide-EO, for example, pluronic P123, pluronic F127 (pluronic is a trade name from BASF but this should include similar type of polymers that are not a trademark, but a similar family of compounds); polyglycol the polymers such asBrij 35 or other Brij Polymers (Trademark of Croda). - Ionic conductivity enhancers are any family compounds that will form ionic compounds when dissolved in the electroplating bath medium (water or organic-water solvent pairs) that can increase the conductivity of the plating bath. Such compounds can range from inorganic salts such as NaCl or Na2SO4.
- Organic-solvent pairs can be used to improve the solubility of the metal precursor or additive, decrease the temperature at which the plating can be performed to prevent the melting of Ga and/or In in the precursor stack, decrease the H2 evolution and increase the plating faradaic efficiency. The following solvents may be considered as water-solvent pairs: alcohols such as ethanol, methanol, iso-propanol, butanol, 2-butanol or tert-butanol, amongst other soluble alcohols; dimethysulfoxide; acetone; and other organic solvents in which water constitutes less than 5% of the total volume, for example, acetonitrile, dichloromethane, pyrrolidimome or tetrahydrofuran.
- The pH of the electroplating solutions can be either in the acidic, neutral or alkaline regime, but pH's above 13 are not preferred as electrochemical reduction of Se becomes very difficult in this highly alkaline pH regime. In the acidic regime, the preferred pH regime is 0.5 to 4. A more preferred pH range is 0.8-2.5. Plating solutions can be prepared at a pH range between 4 to 13, and more preferably at a pH range between 7 to 12. Complexing agents such as such as tartaric acid, citric acid, acetic acid, malonic acid, malic acid, succinic acid, ethylenediamine, ethylenediaminetetraacetic acid, nitrilotriacetic acid, and hydroxyethylethylenediaminetriacetic acid, etc. may be employed in the plating solution in the entire pH regime. However, they might be most effective in the In the neutral and alkaline pH regimes to solubilize group III metal ions in the form of complexed species and to prevent them forming oxide and hydroxide species. The pH of the solution can be adjusted by incorporation of acids such as sulfuric acid, hydrochloric acid, phosphoric acid, ethylenediaminetetraacetic acid, malonic acid, malic acid, nitrilotriacetic acid, succinic acid, maleic acid, oxalic acid, tartaric acid, citric acid, sulfamic acid, hydroxyethylethylenediaminetriacetic acid etc. In addition to acids, inorganic and organic bases such as NaOH, KOH, NH4OH, organic amines such as methylamine and trimethylamine etc., organic hydroxides such as tetramethylammonium hydroxide and tetrabutylammonium hydroxide, other organic bases such as pyridine, imidazole, benzimidazole, histidine and phosphazene bases can also be used to adjust the pH of the plating solutions.
- The electroplating solution may be employed by various electroplating processes to electroplate the above described Ga—Se layer on metal layers. In one embodiment of an electroplating process, a potential between the
metal layer 302, which becomes the working electrode or cathode, and an anode, which is the counter electrode, is applied and controlled by either monitoring the voltage between the electroplatedmetal layer 302 and the anode or monitoring the voltage between the metal layer and a reference electrode such as a SHE (standard hydrogen electrode) or a Ag/AgCl saturated electrode. - In addition to waveforms described above, modulated or pulsed voltage and current (or current density) waveforms might be used in order to achieve a desired IIIA-VIA layer composition and morphology. For example
FIG. 10 is a voltage-time graph showing a potential mode electrodeposition to deposit the IIIA-VIA layers. In this embodiment, the applied potential between the anode and themetal layer 302 is modulated, i.e., pulsed, between a first voltage V1 for a T1 time or first voltage application period (pulse 1) and a second voltage V2 for a T2 time or second voltage application period (pulse 2). TT is a total deposition time of the IIIA-VIA layer 312 onto themetal layer 302, based upon a cumulative amount of pulses. In some cases, more than two pulses might be advantageous. For example, a third Voltage V3 and T3 can be applied such that the 3 pulses are repeated until TT the total deposition time is reached. - Applications of a third pulse can be used when dissolution of the Ga—Se compound is preferred such that the first pulse would be a nucleation pulse, the second pulse would correspond to a growth regime and the third pulse would partially dissolve the alloy layer portion that was previously deposited during the second pulse. The voltage range for any of the pulses used in the waveform can be between 0 V and 20 V but more preferably between 0 and 10 V, and most preferably between 0 and 4 V. The duration of any of the pulses (pulse width in time) can be between 1E-7 sec to 360 sec but more preferably in the range of 1E-5 sec to 10 sec, and most preferably in the range of 1E-3 to 5 sec. The total electroplating time TT can be in the range of seconds to hours; this TT time can also be terminated once a total charge (Coulomb [A/cm2]) has been applied to the electroplated layer such that a desired thickness range can be obtained.
- In
FIG. 10 , the voltage-time graph is a potentiostatic wave form in the form of a step function; however any other functional waveforms (sine, cosines, ramped profile, etc.) can also be used. By applying a pulsed potential, Ga will predominantly be deposited at a higher deposition potential while Se will be deposited at a lower deposition potential to form the Ga—Se layer. The Selenium distribution in the Ga—Se layer as a function of thickness can be controlled by simply changing the time that the voltage is maintained at V1; therefore the Ga profile can be controlled independently of the overall Ga/Se atomic overall layer composition. Furthermore by potential or galvanic modulation, the conductivity of the deposition receiving cathode layer may be better controlled. For example, a Ga film may first be pulse electroplated on a Se film, which is a semiconductor, and then the deposition may continue with Ga—Se layer pulse electroplating to form thicker Ga—Se layers. Ga—Se layers electrodeposited with the potential modulation may have a more uniform Ga—Se distribution than the Ga—Se layers electrodeposited with a galvanic modulation. -
FIG. 11 is a current density-time graph showing a galvanic mode electrodeposition to form the IIIA-VIA layer. In this embodiment, a defined amount of current density [mA/cm2] is passed between the metal layer 302 (cathode) and an anode to deposit a Ga—Se layer onto themetal layer 302. The applied current density between the anode and themetal layer 302 is modulated, i.e., pulsed, between a first current density J1 for a T1 time or first current density application period and a second current density J2 for a T2 time or second current density application period. The current density range for J1 and J2 is from 0 to 200 mA/cm2, but more preferably from 0 to 50 mA/cm2 most preferably between 0.0 mA/cm2 and 20 mA/cm2. In some cases, more than two pulses might be advantageous. For example, a third pulse J3 with a duration of T3 can also be included. The current density range for any of the pulses used in the waveform can be from 0 mA/cm2 to 80 mA/cm2 but most preferably between 0 and 40 mA/cm2. The duration of any of the pulses (pulse width in time) can be between 1E-7 sec to 60 sec but more preferably in the range of 1E-5 sec to 10 sec, and most preferably in the range of 1E-3 to 5 sec. - The application of a constant current density permits a more precise control of the thickness of the deposited Ga—Se layer since the current density will be proportional to a deposition thickness; therefore a quasi-constant rate of Ga—Se can be deposited at each pulse of J1 and J2. The low current density pulse can serve as a nucleation pulse while the second pulse allows the Ga—Se layer to grow, however, one of the pulses may also be used as a dissolution pulse where a portion of the deposited Ga—Se layer is etched (anodic current) and some material is deposited on the cathodic pulse. The Ga distribution on the Ga—Se layer will be less controllable on a galvanostatic method since the resulting voltage between the working and counter electrode will vary due to the change in conductivity of the deposited layers. The conductivity of the Ga—Se layer will be a function of the Ga and Se distribution as well as the Ga/Se ratio in the layer.
- In another embodiment of an electroplating process, a complex waveform in which the applied potential is varied as a function of time is used to deposit the Ga—Se compound. The waveform can be in any functional form such as a sine or cosine waveform, a linear ramp (known in electrochemistry as: Linear Sweep voltammetry), cyclic voltammetry and/or staircase voltammetry.
- As described above, electroplating under a constant current or constant voltage for a predetermined amount of time is the most straightforward way of depositing the IIIA-VIA layers using the electrodeposition electrolytes. However, when the constant current density or constant voltage electroplating is compared to pulse electroplating described above, pulse electroplating might be preferable due to several advantages pulse plating provides. First the morphology of the electroplated layer might be controlled more closely with pulse plating which is advantageous for photovoltaic applications. Second the ratio of Ga/Se (on any other metal in solution) might also be controlled by the pulse deposition parameters. Finally, better intermixing of the deposited metals might be achieved since diffusion control deposition of the metal species with the highest deposition rate can be controlled (coupled with the concentration in solution of such species).
-
FIGS. 12A , 13A and 14A illustrateexemplary electroplating systems 400A-400C to achieve a high throughput continuous fashion electrodeposition at constant voltage or constant current mode to electroplate a IIIA-VIA layer onto a metal layer, including a Cu film and at least one of an In film and Ga film, on a continuous base. The roll-to roll systems 400 electroplate a compound film or IIIA-VIA layer 412 onto a continuous metal layer 402, formed on a continuous base 404 or substrate in a continuous fashion. The IIIA-VIA layer and metal layer have described above. As the metal layer 402 is advanced in a process direction P, it passes through theelectroplating chamber 430 including a group IIIA-VIA electroplating solution, such as a Ga—Se electroplating solution 432 and at least oneanode 434 immersed into theelectroplating solution 432. In the following embodiments, the continuous base 404 including the continuous metal layer will be referred as aweb 405. In the following embodiments, theweb 405 will be unwrapped from a web supply roll SR; continuously advanced in the process direction ‘P’ and through theelectroplating chamber 430 to form the IIIA-VIA layer 412 on a top surface 406 of theweb 405, and theweb 405 with the IIIA-VIA layer 412 is wound around as take-up roll TR. ADC power supply 440 anodically polarizes the at least oneanode 434 and cathodically polarize theweb 405 through a conductive brush touching the web during the electroplating process. -
FIG. 12A shows a roll-to-roll electroplating system 400A which may be used in either constant voltage or constant current density mode. As shown inFIG. 12A , theweb 405 may be electroplated at a constant voltage V1 as it is advanced for a total distance TD which is the length of theelectroplating chamber 430. The residence time of the web will be TD/web velocity. InFIG. 12B , afirst process graph 450A shows the voltage (V)-distance (D) variation or the voltage profile along the cell length TD. Alternatively, thesystem 400A may be used to electroplate in the current density mode by replacing the constant voltage V1 with a constant current (J1). In the current mode thefirst process graph 450A shown inFIG. 12B will become the current density (J) distance (D) variation or the current density profile along the cell length TD. - The
systems FIGS. 13A and 14A , exemplary pulsed voltage or pulsed current density electroplating in a high throughput continuous fashion.FIG. 13A shows a roll-to-roll electroplating system 400B which may be used in either pulsed voltage or current density mode. Thesystem 400B may have a plurality of anodes preferably isolated from one another. In theexemplary system 400B, there are four dividers 442 to confine threeanodes 434 as in the manner shown inFIG. 13A . A distance D1 of a first region between thedividers dividers electroplating chamber 430 are not exposed to theanodes 434 and hence the electric field in their confined sections. As shown inFIG. 13A , asecond process graph 450B shows the voltage (V)-distance (D) variation or the voltage profile along the length TD of thechamber 430. As shown in thegraph 450B, theanodes 434A-434C are held at a constant voltage V1 creating a constant voltage pulsed profile with the first and second regions with no applied potential. The applied electric field from the anodes is limited by the dividers 442 that delimit the applied potential in the first and second regions resulting in no applied potential.Multiple anodes 434 may be placed along theelectroplating chamber 430, which are kept at the same voltage; however the spacing between the anodes, i.e. D1, D2 distances, can be changed such that the extend of the region where the electroplating is performed is varied. The dividers 442 delimit the region where the applied potential is reflected over the moving web delimiting the area where the constant potential will be applied. The constant potential at the edges of theanodes 434 will decay very fast and the applied potential will be stopped by the dividers 442. InFIG. 13B , asecond process graph 450B shows the voltage (V)-distance (D) variation or the voltage profile along the length TD of thechamber 430. As shown in thegraph 450B, theanodes 434A-434C are held at a constant voltage V1 creating a constant voltage pulsed profile with the first and second regions with no applied potential. Alternatively, thesystem 400B may be used to electroplate in the current density mode by replacing the constant voltage V1 with a constant current J1. In the current mode, thesecond process graph 450B shown inFIG. 13B will become the current density (J)-distance (D) variation or the current density profile along the length TD of thechamber 430. In the current mode, since theanodes 434A-434C are held at a constant current density, a constant current density pulsed profile with the first and second regions having no applied current will be formed. The implementation of constant voltage or constant current density along a distance over the web will mimic the pulsed electroplating modes such as those shown inFIGS. 10 and 11 . Since the time domain is transferred into a distance, the pulse width T1, T2, etc will now be related to the length of the electric field (length of the anode) divided by the speed of the moving web. For example an anode with a length of 0.1 meter with a web speed of 1 meter/sec will be equivalent to a pulse time of a residence time of 0.1 sec. By employing an adequate number of anodes in the electroplating chamber, the total electroplating time will be equal to the number of anodes times the residence time. -
FIG. 14A shows another roll-to-roll electroplating system 400C which may be used in either pulsed voltage or current density mode. Thesystem 400C may have a plurality of anodes preferably isolated from one another. Each anode may be kept in a unique potential that is different from the potential of the rest of the anodes if the voltage mode is used, or each anode may be kept in a unique current density that is different from the current density of the rest of the anodes if the current mode is used. In theexemplary system 400C, there are five dividers 442 to confine sixanodes 434 as in the manner shown inFIG. 14A . To generate the voltage pulse over the web during the electroplating,first anodes second anodes - The dividers 442 delimit the region where the applied potential is reflected over the moving web delimiting the regions where the constant potentials V1 and V2 will be applied. In this configuration, first regions with the length D1 include the
first anodes second anodes web 405 advances in the solution in the process direction ‘P’, it will encounter alternating V1 and V2 constant potentials from the first and second anodes. The lengths D1 and D2 determine the residence time that the moving web will spend on each of the potentials. In this embodiment, for clarity there are only two constant voltages V1 and V2; however a plurality of constant voltages may be used and it is within the scope intended herein. - In
FIG. 14B , athird process graph 450C shows the voltage (V)-distance (D) variation or the voltage profile along the length TD of thechamber 430. As shown in thegraph 450C, theanodes 434A-434F are held at the constant voltages V1 and V2 as described above to from a constant voltage pulsed profile. As shown in thegraph 450C, the voltage is constant at the center position of eachanode 434; however, there is a voltage drop near edges of the anodes adjacent the dividers 442. The dividers 442 utilized in this embodiment confine the voltage to a specific region and decrease the possibility of anode cross talk which may create a region where electrochemical reactions between the neighboring anodes may arise. As theweb 405 passes through a deposition voltage range between V1 and that of the V2, theweb 405 will experience a voltage modulation; which would mimic a pulsed waveform as shown inFIG. 10 . A total deposition time can be determined by the web travel speed/TD. - Alternatively, the
system 400C may be used to electroplate in the current density mode by replacing the constant voltages V1 and V2 with constant currents densities J1 and J2, where J1 is different from J2. In the current mode, thethird process graph 450C shown inFIG. 14B will become the current density (J)-distance (D) variation or the current density profile along the cell length TD. In the current mode, since theanodes 434A-434F are held at the constant current densities J1 and J2 from a constant current density pulsed profile. The current density is constant at the center position of eachanode 434; however, there is a current density drop near edges of the anodes adjacent the dividers 442. - The Ga—Se solution used was comprised of GaCl3 and H2SeO3 with a pH between 1 and 2.5. The solution also included at least one of the following additive groups of (a): anti-oxidants, (b) anti-floculants, (c) surface-active compounds (d) ionic conductivity enhancers. Electroplating of the Ga—Se layer was conducted on a stainless steel substrate having an Indium terminated top metal layer. The electroplating was done in a batch mode and the cathode was titanium covered with IrO2. The deposition profile consisted of an applied constant voltage of 3.4 V between the anode and the cathode. The total deposition time was 60 sec. The Ga/Se ratio of the resulting film was 1.48. The deposited Ga—Se layers had a smooth and continuous surface with good adhesion properties. The values coefficient of variation (CV=STDEV/Mean Value) were 1.89% and 5.69% of Ga and Se respectively.
- The Ga—Se solution used was comprised of GaCl3 and H2SeO3 with a pH between 1 and 2.5. The solution also included at least one of the following additive groups of (a): anti-oxidants, (b) anti-flocculants, (c) surface-active compounds (d) ionic conductivity enhancers. Electroplating of the Ga—Se layer was conducted on a stainless steel substrate having an Indium terminated top metal layer. The electroplating was done in a batch mode and the cathode was titanium covered with IrO2. This time a pulsed voltage was applied during plating. The applied potential was modulated between 3.4 V for 500 milliseconds and 2.2 V for 50 milliseconds for a total deposition time of 54 sec. The deposited Ga—Se layers had a smooth and continuous surface with good adhesion properties. The Ga/Se ratio deposited in this case is 1.6. The coefficient of variation (CV=STDEV/Mean Value) are 1.71% and 3.78% of Ga and Se respectively.
- Although the embodiments have been particularly described, it should be readily apparent to those of ordinary skill in the art that various changes, modifications and substitutes are intended within the form and details thereof, without departing from their spirit and scope. Accordingly, it will be appreciated that in numerous instances some features will be employed without a corresponding use of other features. Further, those skilled in the art will understand that variations can be made in the number and arrangement of components illustrated in the above figures.
Claims (31)
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US12/121,687 US20090283411A1 (en) | 2008-05-15 | 2008-05-15 | Selenium electroplating chemistries and methods |
US12/123,372 US8066865B2 (en) | 2008-05-19 | 2008-05-19 | Electroplating methods and chemistries for deposition of group IIIA-group via thin films |
US12/143,609 US8092667B2 (en) | 2008-06-20 | 2008-06-20 | Electroplating method for depositing continuous thin layers of indium or gallium rich materials |
US13/306,863 US8444842B2 (en) | 2008-05-19 | 2011-11-29 | Electroplating methods and chemistries for deposition of group IIIA-group via thin films |
US13/347,540 US20120288986A1 (en) | 2008-06-20 | 2012-01-10 | Electroplating method for depositing continuous thin layers of indium or gallium rich materials |
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