DE102014110608A1 - Method for the terminal processing of a silicon layer - Google Patents

Method for the terminal processing of a silicon layer

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Publication number
DE102014110608A1
DE102014110608A1 DE102014110608.3A DE102014110608A DE102014110608A1 DE 102014110608 A1 DE102014110608 A1 DE 102014110608A1 DE 102014110608 A DE102014110608 A DE 102014110608A DE 102014110608 A1 DE102014110608 A1 DE 102014110608A1
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Prior art keywords
plasma
layer
hydrogen
absorber layer
chamber
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DE102014110608.3A
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German (de)
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Onno Gabriel
Bernd Stannowski
Rutger Schlatmann
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Helmholtz Zentrum Berlin fuer Materialien und Energie GmbH
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Helmholtz Zentrum Berlin fuer Materialien und Energie GmbH
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    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01LSEMICONDUCTOR DEVICES; ELECTRIC SOLID STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H01L31/00Semiconductor devices sensitive to infra-red radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and 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 peculiar to the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/18Processes or apparatus peculiar to the manufacture or treatment of these devices or of parts thereof
    • H01L31/186Particular post-treatment for the devices, e.g. annealing, impurity gettering, short-circuit elimination, recrystallisation
    • H01L31/1872Recrystallisation
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01LSEMICONDUCTOR DEVICES; ELECTRIC SOLID STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H01L31/00Semiconductor devices sensitive to infra-red radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and 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 peculiar to the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/18Processes or apparatus peculiar to the manufacture or treatment of these devices or of parts thereof
    • H01L31/186Particular post-treatment for the devices, e.g. annealing, impurity gettering, short-circuit elimination, recrystallisation
    • H01L31/1868Passivation
    • YGENERAL 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
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02EREDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00Energy generation through renewable energy sources
    • Y02E10/50Photovoltaic [PV] energy
    • Y02P70/521

Abstract

For solid-phase crystallized silicon (SPC-Si) in thin film, there are processes with a change between wet-chemical processes under atmospheric pressure and plasma-chemical processes in vacuum. A known method uses sequentially plasma-assisted process steps for the deposition, cleaning and texturing of a silicon wafer. In the method according to the invention, only plasma-chemical process steps are carried out in direct sequence without interruption of the vacuum, whereby the quality of the thin silicon absorber layer (01) of liquid-phase-crystallized silicon (LPC-Si) is increased and the processing costs are lowered. Quality-reducing surface oxide (05) and defect-rich material (09) are removed by plasma-chemical etching (method steps II, IV), a defect passivation (method step III) is effected by means of a hydrogen plasma. Optionally, at the end of the defect passivation, a protective covering layer (15) can be deposited (additional process step IIIa). The method can be carried out in a process chamber (02) or in the formation of the cover layer (15) in two process chambers (02, 16). The process can be completed by the direct subsequent deposition of an intrinsic buffer layer (17) and / or a counter-doped emitter layer (18) (process steps V, VI).

Description

  • The invention relates to a method for the terminal processing of a silicon layer using a plasma for various sequential method steps in at least one process chamber of a plasma system.
  • The production of solar cells based on silicon layers, in particular silicon thin layers, as absorber layers requires a series of complex process steps. Crystalline silicon thin films can be prepared by various methods, e.g. epitaxial growth or solid phase crystallization (SPC). The material is more commonly referred to as poly-silicon (poly-Si). One approach currently under development is the use of Liquid Phase Crystallized Silicon (LPC-Si) in thin films on inexpensive glass substrates. The invention relates to the terminal processing of a thin silicon absorber layer for later use in a thin-film solar cell, but not their production from LPC-Si itself. Special consideration has to be given in connection processing since the LPC-Si crystal structure is fundamentally different from that SPC-Si-crystal structure.
  • In contrast to solid-phase crystallized silicon (SPC-Si), LPC-Si is still in development today and is not yet used commercially in solar modules. LPC-Si is mainly developed by research groups at the University of New South Wales in Sydney / Australia, at HZB / Berlin and IPHT / Jena and used in thin-film solar cells. Compared to SPC-Si, another chain of process steps for improving the absorber quality has to be carried out for LPC-Si. In such a process chain, there have hitherto been frequent changes between plasma-chemical processes under vacuum and wet-chemical processes under atmospheric pressure, which mean a time-consuming introduction and removal of the resulting solar module into or out of vacuum systems. In addition, different systems are usually used for the various processes.
  • State of the art
  • Liquid phase crystallization is one of the processes of crystallization of amorphous or polycrystalline Si films. In this case, a very thin Si film is advantageously applied to a low-cost substrate. After solidification, the Si film is locally (re) crystallized by introducing energy via a laser or electron beam. If the melting point of the silicon is exceeded, it is a liquid phase crystallization. The Si layer melts locally and crystallizes in a controlled manner in desirably larger and larger crystals, thereby significantly improving the film quality of the Si thin film. In part, it is also spoken of a liquid phase recrystallization. Not to be confused with the liquid phase crystallization but with the deposition of Si crystals from the liquid melt (correct here Flüssigphasenepitaxie, not liquid phase crystallization).
  • From the DE 10 2007 009 924 A1 is a method for producing crystalline thin films for solar cells is known in which deposited in a single vacuum chamber of a continuous coating plant, an amorphous thin silicon absorber layer on a glass substrate by means of PECVD (all occurring functional layers can be deposited by PECVD) and then by means of a laser-induced crystallization process from the liquid phase is crystallized. These process steps can be repeated several times. All functional layers can be subjected to hydrogen passivation after the last laser crystallization. A method for producing a silicon thin-film solar cell based on LPC-Si is known from DE 10 2010 044 291 A1 known. In particular, attention is paid to the liquid-phase crystallization. Further processing steps are not described in both documents.
  • The closest prior art to the invention is known from the publication of M. Moreno, D. Daineka, and P. Roca i Cabarrocas: "Plasmas for texturing, cleaning, and deposition: towards a single pump down process for heterojunction solar cells," Phys. Status Solidi C7, No. 3-4, 1112-1115 (2010) known. Here, the use of a plasma for various sequential process steps in the form of deposition, cleaning and texturing of a silicon layer in at least one process chamber of a plasma system is described. However, the application of the plasma-supported method steps is limited exclusively to Si wafers as a silicon thick film for wafer-based c-Si-HIT solar cells and includes only etching processes. The publication corresponds to the two American patents US Pat. No. 8,592,949 B2 "Method of texturing the surface of a silicon substrate, and structured silicon substrate for a solar cell" and US 8 404 052 B2 "Method for cleaning the surface of a silicon substrate", the disclosure content of which in relation to the invention does not exceed that of the aforementioned publication. The wet-chemical etching of LPC-Si is known, for example, from the publication of Q. Wang, T. Soderstrom, K. Omaki, A. Lennon and S. Varlamov: "Etch-Back Silicon Texturing for Light Trapping in Electron Beam Evaporated Thin-Film Polycrystalline Silicon Solar Cells", Energy Procedia 15, 220-228 (2012) ,
  • From the US 2010/0087028 A1 For example, an apparatus for producing crystalline solar cells is known which comprises a multiplicity of linearly arranged different process chambers. These include PECVD, plasma nitriding, plasma etching and plasma cleaning chambers. The substrates to be treated are conveyed on conveyors through the various chambers. From the WO 2006/128 247 A1 In the field of plasma assisted hydrogen passivation of thin films on glass substrates, it is known not to turn off the plasma during cooling of the substrate. Finally it is off the DE 199 62 896 A1 known to make a passivation of hydrogen plasma with semiconductor material for solar cells, wherein the hydrogen plasma is induced at some distance from the solar cells and fed via a feed line into the plasma chamber. Publications on the hydrogen passivation of LPC-Si thin films are not yet state of the art.
  • task
  • Starting from a method for the terminal processing of a silicon layer using a plasma for texturing, cleaning and deposition in at least one process chamber of a plasma system according to the closest prior art described above, the object for the present invention is to see an optimal process path with sole plasma support for to provide a terminal processing of n- or p-doped crystalline thin silicon absorber layers on a substrate, wherein the crystalline structure of the thin silicon absorber layer was produced by liquid-phase crystallization. The aim is to increase the quality and thus the efficiency of the special thin silicon absorber layers and to reduce the apparatus and financial expense for the connection processing. This object is achieved by the features of claim 1. Advantageous embodiments of the method according to the invention can be found in the dependent claims, which are explained in more detail below together with the invention.
  • In the method according to the invention, at least the following method steps are basically provided:
    • I. providing an n- or p-doped crystalline thin silicon absorber layer on a substrate, wherein the crystalline structure of the thin silicon absorber layer has been previously produced by liquid-phase crystallization,
    • II. Plasma-chemical etching of the thin silicon absorber layer for layer removal of natural surface oxide and defect-rich material,
    • III. Plasma-chemical hydrogen passivation of the previously plasma-chemically etched thin silicon absorber layer in a hydrogen plasma and
    • IV. Plasma-chemical etching of the previously plasma-chemically hydrogen-passivated thin silicon absorber layer for layer removal of defect-rich material.
  • The invention aims to use a direct sequence of different plasma processes for improving an LPC-Si absorber, ie a quality improvement of thin silicon absorber layers, which are particularly well suited for use in thin-film solar cells, by an integrated sequence exclusively of plasma Processes. The process according to the invention is concerned with the after-treatment of thin LPC-Si absorber layers ("All Plasma Processes for a LPC-Silicon Absorber Upgrade Sequence", acronym APPLAUSE). On the one hand, the special consequence of the process steps and, on the other, the application of the process chain to LPC-Si material and thus the application for thin-film solar cells with high efficiency are new and surprising. A simplified sequence of process steps with a direct sequence of different plasma processes improves the quality of the thin silicon absorber layer and the pn junction during the connection processing to the solar cell. Compared to a possible further processing of the LPC-Si absorber with a mixture of wet-chemical and plasma-chemical process steps, the APPLAUSE process represents a significant simplification of the process chain. This simplification leads to a cost saving due to a reduced use of equipment, materials and time as well as to a higher reproducibility of the entire production process of solar cells with thin LPC-Si absorber layers.
  • Due to the relatively low moving substrate temperatures in the method according to the invention, it is possible to introduce the thin silicon absorber layer on a substrate made of glass in the process chamber, which is particularly inexpensive. In this case, a barrier and adhesive layer between the thin silicon absorber layer and the substrate made of glass, so that the thin silicon absorber layer adheres particularly well and can not diffuse atomic impurities from the glass into the thin silicon absorber layer.
  • Solar cells with special thin LPC-Si absorber layers are not yet commercially available. A complete manufacturing process of a solar cell based on LPC-Si is not state of the art and has so far only been tested in individual laboratories of the abovementioned developers. Of the Conventional production process used there is conceivable as a combination of wet-chemical process steps under atmospheric pressure for layer removal and for structuring and plasma-chemical process steps in vacuum at least for layer deposition and for hydrogen passivation, wherein the wet-chemical and the plasma-chemical process steps must imperatively be carried out in different process chambers.
  • All of the process steps of the process of the present invention can be carried out in a typical PECVD process chamber, as have been in widespread use industrially for many years. Therefore, APPLAUSE is easily applicable to large areas of several square meters. The advantages of APPLAUSE over a conceivable mixed, conventional process chain are:
    • • Less equipment, since all processes can take place in one or two vacuum or PECVD process chambers. Since the hydrogen passivation anyway requires such a chamber, eliminating all wet chemical plants. Also for the PECVD of the intrinsic buffer layer (optional) and the emitter layer then no separate equipment is required,
    • • significantly higher process speed, ie increased throughput. In the conventional process chain it is necessary to insert or remove from a vacuum chamber twice, whereas in APPLAUSE this only has to be done once.
    • • less material consumption as the plasma-based processes do not require chemical acids or bases. The use of the process gases for etching can be minimized if the plasma etching is used simultaneously with the chamber cleaning, which is necessary in any case.
  • In the case of plasma-chemical etching of the surface of the thin absorber layer, a marked removal of material takes place deliberately in the invention. This is particularly important when using thin LPC-Si absorber layers, because significant oxide layers are formed during (re) crystallization. Basically, in the invention, the plasma-chemical etching is therefore carried out to remove oxide layers and defect-rich material from the entire surface of the thin silicon absorber layer, which would severely limit their functionality. It is furthermore advantageous and preferred if, in addition, a texture is etched into the surface of the thin absorber layer by means of plasma-chemical etching. The texture serves as a result of the effect of light scattering a further increase in absorption. This method step can also be carried out with plasma support in one and the same process chamber. Also in the same process chamber can advantageously and preferably subsequently a plasma-chemical thin-layer deposition of an intrinsic buffer layer and / or a p- or n-doped emitter layer are performed. All process steps are performed costly and time-saving without complex input and output with venting and subsequent re-evacuation.
  • In terms of process technology, it is preferred and advantageous for the plasma-chemical etching to be carried out in a fluoride-containing process gas having a process pressure of less than 1000 Pa and a substrate temperature of between 200 ° C. and 600 ° C., which is advantageously and preferably the removal of a layer thickness range between 100 nm and 500 nm. For plasma-chemical hydrogen passivation with a hydrogen process gas, it is advantageous to passivate at a process pressure of less than 1000 Pa and a substrate temperature of between 400 ° C. and 600 ° C.
  • In order to reliably prevent a deeper damage of the thin absorber layer during plasma etching, it is advantageous and preferred to carry out the plasma-chemical etching with the plasma gas of a plasma source which is spatially remote from the thin absorber layer in an external plasma chamber (RPS Remote Plasma Source). In this case, only process gas radicals, in particular fluorine radicals, and no process gas ions enter the process gas chamber, which could damage the thin absorber layer in a direct plasma. RPS processes are typically used for chamber cleaning, ie they are already present in many PECVD process chambers. In the method according to the invention can advantageously and preferably a NF 3 : Ar process gas mixture in a ratio of 1:10 are used. In this case, preferably and advantageously, a process pressure between 10 Pa and 100 Pa at a process duration between 30 s and 300 s and a substrate temperature between 200 ° C and 400 ° C is driven. An RPS plasma with the mentioned special process gas mixture has hitherto not been used in any plasma-chemical silicon etching process. Also, the use of NF 3 as a process gas is unusual (for plasma processes usually SF 6 or SiF 4 is used), this gas is used so far rather in connection with the cleaning of the process chambers. Particularly in the case of the important material removal of defect-rich silicon from the thin LPC-Si absorber layer, the use of an RPS process has particular advantages over plasma etching with active direct plasma sources because it leads to less damage in the thin absorber layer.
  • The process step of the plasma-chemical hydrogen passivation can be preferred and advantageously be carried out by means of capacitively coupled RF plasma with 13.56 MHz excitation frequency of the hydrogen process gas in a parallel plate arrangement. Here, the process pressure between 100 Pa and 1000 Pa, the substrate temperature between 400 ° C and 600 ° C, the process duration between 5 min and 30 min and the RF power density between 0.02 W / cm 2 and 0.2 W / cm 2 be selected. Furthermore, in the case of plasma-chemical hydrogen passivation, the substrate temperature at the end of the hydrogen passivation may preferably be lowered to 200 ° C., the hydrogen plasma being switched off only when the substrate temperature has fallen below 300 ° C.
  • In the above-described type of passivation of silicon defects by means of hydrogen plasma may also be advantageous and preferably provided that SiH 4 (silane) is added to the hydrogen process gas with a ratio H 2 : SiH 4 of 1:10 at the end of the hydrogen passivation, in which case a 10 nm to 200 nm cover layer of amorphous, hydrogen-saturated silicon is deposited on the thin absorber layer by means of PECVD. This takes place advantageously and preferably at a process pressure between 100 Pa and 1000 Pa. The RF plasma remains active until the end of the deposition and is then switched off. Only after switching off the RF plasma is the substrate temperature lowered to 200 ° C. The deposition of a 10 to 200 nm thick top layer of amorphous silicon (a-Si: H) by PECVD on the passivated thin silicon absorber layer is also new in such a plasma-chemical process and guarantees a good passivation of the thin absorber layer. The cover layer prevents outward diffusion of hydrogen, which normally occurs at temperatures above 400 ° C., out of the thin absorber layer. Since the diffusion is prevented by the cover layer, in this embodiment, a cooling process without active plasma take place, which is very advantageous from a production point of view.
  • Preferably and advantageously all process steps can be carried out in a single process chamber. The time-consuming locks in different chambers is eliminated. However, the substrate is in the process chamber in each case to heat to different temperatures, this is especially true for the hydrogen passivation with the formation of a cover layer. It is therefore preferred and advantageous for this embodiment if the method steps without the hydrogen passivation in a first process chamber and the method steps of the hydrogen passivation are carried out with the formation of a cover layer in a second process chamber. Further details and advantageous embodiments of the invention can be found in the embodiments described below.
  • embodiments
  • Embodiments of the method for the terminal processing of thin LPC-Si absorber layers according to the invention are explained in more detail below with reference to the non-scale, schematic figures for further understanding of the invention. Showing:
  • 1 a schematic representation of the basic connection processing,
  • 2 a detail of the terminal processing with RPS plasma for plasma etching,
  • 3 a detail of the connection processing with RF plasma for the plasma defect passivation,
  • 4 a detail of the connection processing with RF plasma for the plasma defect passivation and depositing a cover layer,
  • 5 a variant of the connection processing in two process chambers and
  • 6 a schematic representation of the connection processing to the thin-film solar cell with absorber texture and hetero-buffer and emitter layer.
  • In the 1 the basic connection processing is shown. It presents itself as a method of improving the quality of a liquid phase crystallized silicon (LPC-Si) based, n- or p-doped thin absorber layer with a layer thickness between 5 μm and 20 μm for preferred use in thin-film solar cells and modules. The connection processing comprises at least the following method steps:
    • I. Providing a thin silicon absorber layer 01 in a first process chamber 02 , The crystalline structure of the thin silicon absorber layer 01 was generated by liquid phase crystallization LPC (LPC-Si). The thin silicon absorber layer 01 is with the interposition of a barrier and adhesive layer 03 on a substrate 04 arranged from glass. On the surface of the thin silicon absorber layer 01 is due to the air contact a layer of a natural surface oxide 05 , The process chamber 02 is evacuated (vacuum).
    • II. Plasmachemisches etching of the surface of the thin silicon absorber layer 01 for removing the layer from the natural surface oxide 05 , followed by a removal of defective material 09 the uppermost 100 nm to 500 nm from the surface of the thin silicon absorber layer 01 using fluorine-containing process gases 06 , Gas pressures below 1000 Pa and a substrate temperature between 200 ° C and 600 ° C.
    • III. Plasma-based hydrogen passivation of natural surface oxide 05 and defective material 09 liberated surface of the thin silicon absorber layer 01 in a hydrogen plasma for passivation of defects in silicon using hydrogen process gas 08 and gas pressures below 1000 Pa and a substrate temperature between 400 and 600 ° C. Below the surface of the thin silicon absorber layer 01 In turn, an area of defect-rich material is formed 09 out.
    • IV. Plasmachemisches etching of the surface of the thin silicon absorber layer 01 for removing layers of defective material 09 , There follows a directly subsequent to step III subsequent removal of defective material 09 from the surface of the thin silicon absorber layer 01 as described in step II.
  • The method steps II and IV can also be used as an alternative to the plasma source 10 directly inside the process chamber 02 with an external plasma source 11 outside the process chamber 02 in an external plasma chamber 22 with a diluted process gas 12 (NF 3 : Ar), compare 2 , The advantage of the RPS plasma lies in the gentle bombardment of the surface of the thin silicon absorber layer 01 only with radicals (not with ions), so while it removes layers of surface oxide 05 and defective material 09 comes, the deeper-lying thin silicon absorber layer 01 but remains undamaged in its structure.
  • The process step III (hydrogen defect passivation) can by means of a capacitively coupled RF (RF RF) plasma with 13 , 56 MHz excitation frequency in a parallel plate arrangement 14 be carried out, (cf. 3 ), wherein the thin silicon absorber layer 01 is arranged between the plates. The pressure is between 100 and 1000 Pa and the RF power density between 0.02 and 0.2 W / cm 2 . The process lasts between 5 and 30 minutes, with the substrate temperature between 400 and 600 ° C. At the end of the process, the substrate temperature is T substrate to 200 ° C lowered, wherein the RF plasma remains active only at temperatures T substrate below 300 ° C is turned off. Subsequently, the method step IV is performed. The parallel plate arrangement 14 for the RF plasma for process step III or IIIa and the plasma torch 10 for PECVD deposition of further functional layers according to 6 can also be outside the process chamber 2 respectively. 15 arranged and thus be designed as RPS.
  • Alternatively, in the above-described process step III (passivation of silicon defects by means of hydrogen plasma), the substrate 03 not be cooled at the end of the process step, but instead directly at the end of the process step silane (SiH 4 ) to the hydrogen process gas 08 mixed and in this way a 10-200 nm thick topcoat 15 of amorphous silicon (a-Si: H) by PECVD on the passivated silicon absorber 01 be separated (see 4 , additional process step IIIa). Between H 2 passivation and a-Si: H deposition, the RF power remains active, ie the RF plasma is active without interruption. The process pressure remains between 100 and 1000 Pa, the H 2 : SiH 4 ratio is 1:10 during the a-Si: H deposition. Only after the deposition of the topcoat 15 The RF plasma is turned off and the substrate temperature is lowered and the thin silicon absorber layer 01 further treated with method step IV. Alternatively, the cover layer 15 Of course, with a simple plasma source 10 (comparison 1 ) be generated.
  • The process steps I to IV can successively in the process chamber 02 be carried out as the only process chamber. This then includes the following sequence of process steps:
    • a. Heating the substrate 03 at 200 ° C
    • b. Layer removal by RPS process and NF 3 : Ar process gas 12 as in 2 described
    • c. Heating the substrate 03 at 400 ° to 600 ° C
    • d. Defect passivation using RF plasma including the integrated cooling of the substrate 03 to 200 ° C, as in 3 described
    • e. Layer removal by RPS process and NF 3 : Ar process gas 12 as in 2 described
  • Alternatively, two process chambers 02 . 16 are used, the process steps I, II and IV are in the process chamber 02 , the process step IIIa is in the process chamber 16 performed, compare 5 , This then includes the following sequence of process steps:
    • a. Heating the substrate 03 in the process chamber 02 at 200 ° C.
    • b. Layer removal by RPS process and NF 3 : Ar process gas 12 as in 2 described.
    • c. Transferring the substrate 03 in the process chamber 16 and heating the substrate 03 at 400 ° to 600 ° C.
    • d. Defect passivation by means of RF plasma in process chamber 16 including the direct subsequent deposition of the a-Si: H overcoat 15 , as in 4 described.
    • e. Returning the substrate 03 in the process chamber 02 and cooling the substrate 03 to 200 ° C in the process chamber 02 ,
    • f. Layer removal by RPS process and NF 3 : Ar process gas 12 as in 2 described.
  • Following process step IV (optional, process step III-only hydrogen passivation-or process step IIIa-was previously Hydrogen passivation with deposition of the cover layer 15 - Performed) can according to step V in the process chamber 02 by plasmachemic etching a texture 20 in the surface (after previous plasma-chemical etching and thus removal of an optional existing cover layer 15 ) of the thin silicon absorber layer 01 to be introduced, cf. 6 , Subsequently, according to method step VI, further functional layers of the solar cell, in particular an amorphous intrinsic buffer layer 17 and / or to the thin silicon absorber layer 01 counter doped emitter layer 18 by PECVD deposited and thus an i / n or i / p hetero emitter are generated, see also 6 , The layer thicknesses are 5 to 10 nm for the amorphous intrinsic buffer layer 17 and 5 to 20 nm for the n- or p-doped emitter layer 18 at pressures of 100 to 1000 Pa, RF power densities of 0.01 to 0.05 W / cm 2 and a substrate temperature of between 150 and 250 ° C.
  • For the completion of a thin-film solar cell then done a cell contacting and possibly. A module interconnection, but they are not part of the claimed method.
  • LIST OF REFERENCE NUMBERS
  • 01
     thin silicon absorber layer (LPC-Si)
    02
     first process chamber
    03
     Barrier and adhesive layer
    04
     substratum
    05
     surface oxide
    06
     process gas
    08
     Hydrogen process gas
    09
     Defective material
    10
     internal plasma source
    11
     external plasma source (RPS)
    12
     Process gas mixture
    14
     Parallel plate arrangement
    15
     topcoat
    16
     second process chamber
    17
     intrinsic buffer layer
    18
     emitter layer
    20
     texture
    22
     external plasma chamber for RPS
  • QUOTES INCLUDE IN THE DESCRIPTION
  • This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.
  • Cited patent literature
    • DE 102007009924 A1 [0005]
    • DE 102010044291 A1 [0005]
    • US 8592949 B2 [0006]
    • US 8404052 B2 [0006]
    • US 2010/0087028 A1 [0007]
    • WO 2006/128247 A1 [0007]
    • DE 19962896 A1 [0007]
  • Cited non-patent literature
    • M. Moreno, D. Daineka, and P. Roca i Cabarrocas: "Plasmas for texturing, cleaning, and deposition: towards a single pump down process for heterojunction solar cells," Phys. Status Solidi C7, No. 3-4, 1112-1115 (2010) [0006]
    • Q. Wang, T. Soderstrom, K. Omaki, A. Lennon and S. Varlamov: "Etch-Back Silicon Texturing for Light Trapping in Electron Beam Evaporated Thin-Film Polycrystalline Silicon Solar Cells", Energy Procedia 15, 220-228 (2012) [0006]

Claims (13)

  1. Process for the connection processing of a silicon layer using a plasma for various successive process steps in at least one process chamber of a plasma system, characterized by at least the following process steps: I. Provision of an n- or p-doped crystalline thin silicon absorber layer ( 01 ) on a substrate ( 04 ), wherein the crystalline structure of the thin silicon absorber layer ( 01 ) was previously produced by liquid-phase crystallization (LPC), II. plasma-chemical etching of the thin silicon absorber layer ( 01 ) for the layer removal of natural surface oxide ( 05 ) and defective material ( 09 ), III. Plasma-chemical hydrogen passivation of the previously plasma-chemically etched thin silicon absorber layer ( 01 ) in a hydrogen plasma ( 08 ) and IV. Plasma-chemical etching of the previously plasma-chemically hydrogen-passivated thin silicon absorber layer ( 01 ) for layer removal of defective material ( 09 ).
  2. Process according to Claim 1, characterized by the subsequent process step: V. Plasma-chemical etching of a texture ( 20 ) in the defect-rich material freed thin silicon absorber layer ( 01 ).
  3. Process according to Claim 1 or 2, characterized by the subsequent process step: VI. Plasmachemic thin-film deposition of an intrinsic buffer layer ( 17 ) and / or a p- or n-doped emitter layer ( 18 ).
  4. Method according to one of the preceding claims, characterized by plasma chemical etching according to method steps II and IV in a fluoride-containing process gas ( 06 ) with a process pressure of less than 1000 Pa and a substrate temperature between 200 ° C and 600 ° C.
  5. Method according to one of the preceding claims, characterized by plasma-chemical hydrogen passivation according to process step III in a hydrogen process gas ( 08 ) with a process pressure of less than 1000 Pa and a substrate temperature between 400 ° C and 600 ° C.
  6. Method according to one of the preceding claims, characterized by plasma chemical etching according to method steps II and IV with a removal of defect-rich material of the thin silicon absorber layer ( 01 ) in a layer thickness range between 100 nm and 500 nm.
  7. Method according to one of the preceding claims, characterized by plasma chemical etching according to method steps II and IV with the plasma gas of an external plasma source ( 11 ) spatially removed from the thin silicon absorber layer (FIG. 01 ) in an external plasma chamber ( 22 ) is active, with only process gas radicals in the process gas chamber ( 02 ) reach.
  8. Process according to Claim 7, characterized by the use of a NF 3 : Ar process gas mixture ( 12 ) in a ratio of 1:10 with a process pressure between 10 Pa and 100 Pa, a process duration between 30 s and 300 s and a substrate temperature between 200 ° C and 400 ° C.
  9. Method according to one of the preceding claims, characterized by plasma chemical hydrogen passivation according to method step III by means of capacitively coupled RF plasma with 13.56 MHz excitation frequency of the hydrogen process gas ( 08 ) in a parallel plate arrangement ( 14 ) with a process pressure of between 100 Pa and 1000 Pa, a substrate temperature of 400 ° C and 600 ° C, a process duration between 5 minutes and 30 minutes, an RF power density between 0.02 W / cm 2 and 0.2 W / cm 2 ,
  10. A method according to claim 9, characterized by lowering the substrate temperature at the end of the hydrogen passivation to 200 ° C and switching off the hydrogen plasma only when the substrate temperature has dropped below 300 ° C.
  11. Process according to claim 9, characterized by the additional process step according to process step III: IIIa. Mixing SiH 4 into the hydrogen process gas ( 08 ) with a ratio H 2 : SiH 4 of 1:10 at the end of the hydrogen passivation according to method step III and plasma-assisted vapor deposition of a 10 nm to 200 nm cover layer ( 15 ) of amorphous, hydrogen-saturated silicon on the thin silicon absorber layer ( 01 at a process pressure of between 100 Pa and 1000 Pa, the RF plasma remaining until the end of the deposition of the top layer ( 15 ) is active and only after switching off the RF plasma, the substrate temperature is lowered to 200 ° C.
  12. Method according to one of claims 1 to 10, characterized by carrying out all method steps I to VI in a single process chamber ( 02 ).
  13. Method according to one of claims 1 to 8 and according to claim 11, characterized by carrying out the method steps I, II, IV to VI without the hydrogen passivation in a first process chamber ( 02 ) and the execution of the hydrogen passivation according to additional process step IIIa with combined formation of a cover layer ( 15 ) in a second process chamber ( 16 ).
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