DE102014110608B4 - Method for connection processing of a silicon layer - Google Patents

Abstract

Method for the connection processing of a silicon layer with a structure generated by liquid phase crystallization (LPC) using a plasma for various successive method steps in at least one process chamber of a plasma system, at least the following method steps being provided: I. Provision of an n- or p-doped crystalline thin silicon absorber layer (01) with a structure produced by liquid phase crystallization (LPC), II. plasma-chemical etching of the thin silicon absorber layer (01) in a fluoride-containing process gas (06) for layer removal of natural surface oxide (05) and defect-rich material (09) in a layer thickness range between 100 nm and 500 nm, 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) in a fluoride-containing process gas (06) to remove the layer of defect-rich material (09) in a layer thickness range between 100 nm and 500 nm.

Description

The invention relates to a method for connection processing of a silicon layer with a structure produced by liquid phase crystallization using a plasma for various successive method steps in at least one process chamber of a plasma system.

The production of solar cells based on silicon layers, especially thin silicon layers, as absorber layers requires a number of complex process steps. Crystalline silicon thin films can be made by various methods, e.g. Epitaxial growth or Solid Phase Crystallization (SPC). The material is also known more generally as poly-silicon (poly-Si). An approach that is currently still in development is the use of liquid phase crystallized silicon (LPC-Si) in thin layers on inexpensive glass substrates. The invention relates to the connection processing of a thin silicon absorber layer for later use in a thin-film solar cell, but not its production from LPC-Si itself. In connection processing, special aspects have to be taken into account, 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, LPC-Si requires a different chain of process steps to improve the absorber quality. In such a process chain, there has so far been frequent changes between plasma-chemical processes in a vacuum and wet-chemical processes under atmospheric pressure, which mean time-consuming transferring the solar module into and out of vacuum systems. In addition, different systems are usually used for the different processes.

State of the art

Liquid phase crystallization is one of the processes for crystallizing amorphous or polycrystalline Si films. A very thin Si film is advantageously applied to an inexpensive substrate. After it has solidified, the Si film is (re) crystallized locally by applying 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 desirable larger and large crystals, which significantly improves the layer quality of the Si thin layer. Sometimes there is also talk of liquid phase recrystallization. The liquid phase crystallization should not be confused with the pulling up of Si crystals from the liquid melt (correct here liquid phase epitaxy, not liquid phase crystallization).

From the DE 10 2007 009 924 A1 a process for the production of crystalline thin films for solar cells is known, in which an amorphous thin silicon absorber layer is deposited on a glass substrate by means of PECVD in a single vacuum chamber of a continuous coating system (all functional layers can be deposited by means of 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 disclosed in US Pat DE 10 2010 044 291 A1 known. In particular, the liquid phase crystallization is discussed. However, further processing steps are not described in either publication.

The prior art closest to the invention is from the publication by M. Moreno, D. Daineka and P. Roca i Cabarrocas: "Plasmas for texturing, cleaning, and deposition: towards a one pump down process for heterojunction solar cells", Phys. Status Solidi C7, No. 3-4, 1112-1115 (2010). The use of a plasma for various successive 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 here. The use of the plasma-assisted process steps is limited exclusively to Si wafers as a silicon thick layer for wafer-based c-Si-HIT solar cells and only includes etching processes. The publication corresponds to the two American patents US 8 592 949 B2 "Method of texturing the surface of a silicon substrate, and textured 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 go beyond 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 2010/0 087 028 A1 a device for the production of crystalline solar cells is known, which comprises a plurality of linearly arranged different process chambers. PECVD, plasma nitriding, plasma etching and plasma cleaning chambers are provided. The substrates to be treated are channeled through the various chambers on conveyors. From the WO 2006/128 247 A1 , which deals with the plasma-assisted hydrogen passivation of thin layers on glass substrates, it is known not to switch off the plasma while the substrate is cooling. After all, it's from the DE 199 62 896 A1 known to carry out a passivation with hydrogen plasma on semiconductor material for solar cells, the hydrogen plasma being induced at some distance from the solar cells and being fed into the plasma chamber via a feed line. Publications on the hydrogen passivation of LPC-Si thin films are not yet state of the art.

Furthermore, it is from the US 2009/0 020 154 A1 known to remove surface defects on a previously deposited p-layer with a hydrogen plasma, this plasma also leading to a passivation of the layer. From the US 2011/0 136 286 A1 an etching process for surface structuring for silicon is known. In both cases, however, it is a question of layers produced by vapor deposition in which the defects are only located directly on the surface. As a result, pure hydrogen gas is used as the process gas.

Task

Based on a method for the connection processing of a silicon layer using a plasma for texturing, cleaning and deposition in at least one process chamber of a plasma system, the task of the present invention is to be seen in an optimal method path with sole plasma support for a connection processing of n- or p- indicate doped crystalline thin silicon absorber layers on a substrate, wherein the crystalline structure of the thin silicon absorber layer was generated by liquid phase crystallization. The aim is to increase the quality and thus the efficiency of the special thin silicon absorber layers and reduce the equipment and financial outlay for connection processing. This object is achieved according to the invention 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.

1. I. Bereitstellen einer n- oder p-dotierten kristallinen dünnen Silizium-Absorberschicht mit durch Flüssigphasenkristallisation erzeugter Struktur auf einem Substrat,
2. II. plasmachemisches Ätzen der dünnen Silizium-Absorberschicht in einem fluoridhaltigen Prozessgas zum Schichtabtrag von natürlichem Oberflächenoxid und defektreichem Material in einem Schichtdickenbereich zwischen 100 nm und 500 nm,
3. III. plasmachemische Wasserstoffpassivierung der zuvor plasmachemisch geätzten dünnen Silizium-Absorberschicht in einem Wasserstoffplasma und
4. IV. plasmachemisches Ätzen der zuvor plasmachemisch wasserstoffpassivierten dünnen Silizium-Absorberschicht in einem fluoridhaltigen Prozessgas zum Schichtabtrag von defektreichem Material in einem Schichtdickenbereich zwischen 100 nm und 500 nm.

In the method according to the invention, at least the following method steps are basically provided:

1. I. providing an n- or p-doped crystalline thin silicon absorber layer with a structure produced by liquid phase crystallization on a substrate,
2. II. Plasma-chemical etching of the thin silicon absorber layer in a fluoride-containing process gas for layer removal of natural surface oxide and material rich in defects in a layer thickness range between 100 nm and 500 nm,
3. III. plasma-chemical hydrogen passivation of the previously plasma-chemically etched thin silicon absorber layer in a hydrogen plasma and
4. IV. Plasma-chemical etching of the previously plasma-chemical, hydrogen-passivated thin silicon absorber layer in a fluoride-containing process gas for layer removal of defective material in a layer thickness range between 100 nm and 500 nm.

The invention aims at the use of a direct sequence of different plasma processes to improve an LPC-Si absorber, i.e. an improvement in the quality of thin silicon absorber layers, which are particularly well suited for use in thin-film solar cells, through an integrated sequence exclusively of plasma Processes. The method according to the invention deals with the aftertreatment of thin LPC-Si absorber layers (“All Plasma Processes for a LPC-Silicon Absorber Upgrade Sequence”, acronym APPLAUSE). On the one hand the special sequence of the process steps and on the other hand the application of the process chain to LPC-Si material and thus the application for thin-film solar cells with high efficiency is 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 conceivable 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 cost savings due to reduced use of equipment, materials and time as well as higher reproducibility of the entire manufacturing process of solar cells with thin LPC-Si absorber layers.

Due to the relatively low substrate temperatures to be driven in the process according to the In accordance with the invention, it is possible to introduce the thin silicon absorber layer into the process chamber on a substrate made of glass, which is particularly inexpensive. A barrier and adhesive layer can be located between the thin silicon absorber layer and the substrate made of glass, so that the thin silicon absorber layer adheres particularly well and no atomic impurities from the glass can diffuse into the thin silicon absorber layer.

Solar cells with special thin LPC-Si absorber layers have not yet been commercially available. A complete manufacturing process for 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 developers mentioned above. The conventional manufacturing process used there is conceivable as a combination of wet-chemical process steps under atmospheric pressure for layer removal and structuring and plasma-chemical process steps in a vacuum, at least for layer deposition and hydrogen passivation, with the wet-chemical and plasma-chemical process steps necessarily having to be carried out in different process chambers.

• • weniger apparativer Aufwand, da alle Prozesse in einer oder zwei Vakuum- bzw. PECVD-Prozesskammern stattfinden können. Da die Wasserstoffpassivierung ohnehin eine solche Kammer erfordert, entfallen alle nasschemischen Anlagen. Auch für die PECVD der intrinsischen Pufferschicht (optional) und der Emitterschicht ist dann keine gesonderte Apparatur mehr erforderlich,
• • deutlich höhere Prozessgeschwindigkeit, d.h. erhöhter Durchsatz. In der konventionellen Prozesskette ist zweimaliges Ein- bzw. Ausschleusen in bzw. aus einer Vakuumkammer erforderlich, während dies in APPLAUSE nur einmalig geschehen muss,
• • weniger Materialverbrauch, da die plasmagestützten Prozesse keine chemischen Säuren bzw. Basen erfordern. Der Einsatz der Prozessgase zum Ätzen kann minimiert werden, wenn das Plasmaätzen gleichzeitig zur ohnehin notwendigen Kammerreinigung genutzt wird.

All process steps of the process according to the invention can be carried out in a typical PECVD process chamber, as they have been used successfully in industry for many years. Therefore, APPLAUSE can easily be applied to large areas of several square meters. The advantages of APPLAUSE compared to a conceivable mixed, conventional process chain are:

• • Less expenditure on equipment, since all processes can take place in one or two vacuum or PECVD process chambers. Since the hydrogen passivation requires such a chamber anyway, there is no need for any wet chemical systems. Separate apparatus is no longer required for the PECVD of the intrinsic buffer layer (optional) and the emitter layer either,
• • Significantly higher process speed, ie increased throughput. In the conventional process chain, it is necessary to transfer in and out of a vacuum chamber twice, while in APPLAUSE this only needs to be done once,
• • Less material consumption, as the plasma-based processes do not require chemical acids or bases. The use of process gases for etching can be minimized if the plasma etching is used at the same time for cleaning the chamber, which is necessary anyway.

With the plasma-chemical etching of the surface of the thin absorber layer, the invention specifically results in a noticeable material removal in a layer thickness range between 100 nm and 500 nm. This is particularly important when using thin LPC-Si absorber layers, because during the (re) crystallization Form oxide layers. In principle, the plasma-chemical etching is carried out in the invention in order to remove oxide layers and defect-rich material from the entire surface of the thin silicon absorber layer, which would severely limit its functionality. It is also advantageous and preferred if a texture is additionally etched into the surface of the thin absorber layer by means of plasma-chemical etching. The texture serves to further increase absorption through light scattering. This process step can also be carried out with plasma support in one and the same process chamber. A plasma-chemical thin-layer deposition of an intrinsic buffer layer and / or a p- or n-doped emitter layer can also advantageously and preferably then be carried out in the same process chamber. All process steps are carried out in a cost-saving and time-saving manner without laborious transferring in and out with ventilation and subsequent renewed evacuation.

In terms of process technology, it is preferred and advantageous if the plasma-chemical etching is carried out in the fluoride-containing process gas with a process pressure of less than 1000 Pa and a substrate temperature between 200 ° C. and 600 ° C. For the plasma chemical hydrogen passivation with a hydrogen process gas, it is advantageous if passivation is carried out at a process pressure of less than 1000 Pa and a substrate temperature between 400 ° C. and 600 ° C.

In order to reliably prevent deeper damage to 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 that is active in an external plasma chamber (RPS remote plasma source) spatially remote from the thin absorber layer. Only process gas radicals, in particular fluorine radicals, and no process gas ions, which could damage the thin absorber layer in a direct plasma, then get into the process gas chamber. RPS processes are usually used for chamber cleaning, ie they are already present in many PECVD process chambers. In the method according to the invention, an NF ₃ : Ar process gas mixture in a ratio of 1:10 can advantageously and preferably be used. A process pressure between 10 Pa and 100 Pa is preferred and advantageous for a process time between 30 s and 300 s and a substrate temperature driven between 200 ° C and 400 ° C. An RPS plasma with the aforementioned special process gas mixture has not yet been used in any plasma-chemical silicon etching process. The use of NF ₃ as a process gas is also unusual (SF ₆ or SiF ₄ is usually used for plasma processes); this gas has so far been used more in connection with cleaning the process chambers. In particular with 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 to the thin absorber layer.

The process step of the plasma-chemical hydrogen passivation can preferably 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. The process pressure can be between 100 Pa and 1000 Pa, the substrate temperature between 400 ° C and 600 ° C, the process time between 5 min and 30 min and the RF power density between 0.02 W / cm ² and 0.2 W / cm ^{2 must be} selected. Furthermore, in the case of plasma-chemical hydrogen passivation, the substrate temperature at the end of the hydrogen passivation can preferably be lowered to 200 ° C., the hydrogen plasma only being switched off when the substrate temperature has fallen below 300 ° C.

In the previously described type of passivation of silicon defects by means of hydrogen plasma, it can also advantageously and preferably be provided that SiH ₄ (silane) is added to the hydrogen process gas with a ratio of 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 made 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 only 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 cover layer of amorphous silicon (a-Si: H) using PECVD on the passivated thin silicon absorber layer is also new in such a plasma-chemical process and guarantees good passivation of the thin absorber layer. The cover layer prevents hydrogen from diffusing out of the thin absorber layer, which normally occurs at temperatures above 400 ° C. Since diffusion through the cover layer is prevented, in this embodiment a cooling process can also take place without active plasma, 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. There is no need for time-consuming locks in different chambers. However, the substrate must be heated to different temperatures in the process chamber; this applies in particular to hydrogen passivation with the formation of a cover layer. It is therefore preferred and advantageous for this embodiment if the process steps are carried out without hydrogen passivation in a first process chamber and the process steps with hydrogen passivation with formation of a cover layer are carried out in a second process chamber. Further details and advantageous configurations of the invention can be found in the exemplary embodiments described below.

Figure list

• 1 eine schematische Darstellung der prinzipiellen Anschlussprozessierung,
• 2 ein Detail der Anschlussprozessierung mit RPS-Plasma für das Plasmaätzen,
• 3 ein Detail der Anschlussprozessierung mit RF-Plasma für die Plasma-Defektpassivierung,
• 4 ein Detail der Anschlussprozessierung mit RF-Plasma für die Plasma-Defektpassivierung und Deponieren einer Deckschicht,
• 5 eine Variante der Anschlussprozessierung in zwei Prozesskammern und
• 6 eine schematische Darstellung der Anschlussprozessierung bis zur Dünnschicht-Solarzelle mit Absorber-Textur und Hetero-Puffer- und -Emitterschicht.

Forms of embodiment of the method for the connection processing of thin LPC-Si absorber layers according to the invention are explained in more detail below with reference to the schematic figures that are not to scale for a further understanding of the invention. It shows:

• 1 a schematic representation of the basic follow-up processing,
• 2 a detail of the connection processing with RPS plasma for plasma etching,
• 3 a detail of the connection processing with RF plasma for the plasma defect passivation,
• 4th 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
• 6th a schematic representation of the connection processing up to the thin-film solar cell with absorber texture and hetero buffer and emitter layer.

1. I. Bereitstellen einer dünnen Silizium-Absorberschicht 01 in einer ersten Prozesskammer 02. Die kristalline Struktur der dünnen Silizium-Absorberschicht 01 wurde durch Flüssigphasenkristallisation LPC erzeugt (LPC-Si). Die dünne Silizium-Absorberschicht 01 ist unter Zwischenlage einer Barriere- und Haftschicht 03 auf einem Substrat 04 aus Glas angeordnet. Auf der Oberfläche der dünnen Silizium-Absorberschicht 01 befindet sich durch den Luftkontakt eine Schicht aus einem natürlichen Oberflächenoxid 05. Die Prozesskammer 02 wird evakuiert (Vakuum).
2. II. Plasmachemisches Ätzen der Oberfläche der dünnen Silizium-Absorberschicht 01 zum Schichtabtrag von dem natürlichen Oberflächenoxid 05, gefolgt von einem Abtrag von defektreichem Material 09 der obersten 100 nm bis 500 nm von der Oberfläche der dünnen Silizium-Absorberschicht 01 unter Nutzung von fluorhaltigen Prozessgasen 06, Gasdrücken unter 1000 Pa und einer Substrattemperatur zwischen 200°C und 600°C.
3. III. Plasmachemische Wasserstoffpassivierung der vom natürlichen Oberflächenoxid 05 und defektreichem Material 09 befreiten Oberfläche der dünnen Silizium-Absorberschicht 01 in einem Wasserstoffplasma zur Passivierung von Defekten im Silizium unter Nutzung von Wasserstoff-Prozessgas 08 und Gasdrücken unter 1000 Pa und einer Substrattemperatur zwischen 400 und 600°C. Unterhalb der Oberfläche der dünnen Silizium-Absorberschicht 01 bildet sich wiederum ein Bereich aus defektreichem Material 09 aus.
4. IV. Plasmachemisches Ätzen der Oberfläche der dünnen Silizium-Absorberschicht 01 zum Schichtabtrag von defektreichem Material 09. Es erfolgt ein direkt auf Verfahrensschritt III folgender erneuter Abtrag von defektreichem Material 09 von der Oberfläche der dünnen Silizium-Absorberschicht 01 wie in Schritt II beschrieben.

In the 1 the basic follow-up processing is shown. It presents itself as a method for 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 the preferred use in thin-film solar cells and modules. The subsequent processing includes at least the following process steps:

1. 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 through Liquid phase crystallization LPC generated (LPC-Si). The thin silicon absorber layer 01 is interposed with a barrier and adhesive layer 03 on a substrate 04 arranged from glass. On the surface of the thin silicon absorber layer 01 there is a layer of natural surface oxide due to contact with air 05 . The process chamber 02 is evacuated (vacuum).
2. II. Plasma-chemical etching of the surface of the thin silicon absorber layer 01 for removing layers from the natural surface oxide 05 , followed by the removal of defective material 09 the top 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.
3. III. Plasma chemical hydrogen passivation of the natural surface oxide 05 and defective material 09 freed surface of the thin silicon absorber layer 01 in a hydrogen plasma to passivate 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.
4. IV. Plasma-chemical etching of the surface of the thin silicon absorber layer 01 for layer removal of defective material 09 . There is a renewed removal of defect-rich material directly following process step III 09 from the surface of the thin silicon absorber layer 01 as described in step II.

Method steps II and IV can also be used as an alternative to the plasma source 10 directly within the process chamber 02 with an external plasma source 11 outside the process chamber 02 in an external plasma chamber 22nd 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 it does remove layers of surface oxide 05 and defective material 09 comes, the deeper-lying thin silicon absorber layer 01 but remains undamaged in its structure.

Process step III (hydrogen defect passivation) can be performed by means of a capacitively coupled RF plasma (RF radio frequency) with an excitation frequency of 13.56 MHz in a parallel plate arrangement 14th be carried out (compare 3 ), 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 takes between 5 and 30 minutes, with the substrate temperature between 400 and 600 ° C. At the end of the process, the substrate temperature T is _substrate to 200 ° C lowered, wherein the RF plasma remains active only at temperatures T _substrate below 300 ° C is turned off. Process step IV is then carried out. The parallel plate arrangement 14th for the RF plasma for process step III or IIIa and the plasma torch 10 for PECVD deposition of further functional layers according to 6th can also be used outside the process chamber 2 or. 15th arranged and thus designed as an RPS.

Alternatively, the substrate can be used in the previously explained method step III (passivation of silicon defects by means of hydrogen plasma) 03 are not cooled at the end of the process step, but instead, directly at the end of the process step, silane (SiH ₄ ) is added to the hydrogen process gas 08 mixed in and in this way a 10-200 nm thick top layer 15th made of amorphous silicon (a-Si: H) using PECVD on the passivated silicon absorber 01 are deposited (compare 4th , additional process step IIIa). The RF power remains active between H ₂ passivation and a-Si: H deposition, ie the RF plasma is active without interruption. The process pressure remains between 100 and 1000 Pa, the H2: SiH4 ratio is 1:10 during the a-Si: H deposition. Only after the top layer has been deposited 15th the RF plasma is switched off and the substrate temperature is lowered and the thin silicon absorber layer 01 treated further with step IV. Alternatively, the top layer 15th of course with a simple plasma source 10 (comparison 1 ) be generated.

1. a. Aufheizen des Substrats 03 auf 200°C
2. b. Schichtabtragen mittels RPS-Prozess und NF₃:Ar Prozessgas 12 wie in 2 beschrieben
3. c. Aufheizen des Substrats 03 auf 400°bis 600°C
4. d. Defektpassivieren mittels RF-Plasma einschließlich dem integrierten Abkühlen des Substrats 03 auf 200°C, wie in 3 beschrieben
5. e. Schichtabtragen mittels RPS-Prozess und NF₃:Ar Prozessgas 12 wie in 2 beschrieben

Process steps I to IV can be performed one after the other in the process chamber 02 be carried out as the only process chamber. This then comprises the following sequence of procedural steps:

1. a. Heating the substrate 03 to 200 ° C
2. b. Layer removal using the RPS process and NF ₃ : Ar process gas 12 as in 2 described
3. c. Heating the substrate 03 to 400 ° to 600 ° C
4. d. Defect passivation using RF plasma including integrated cooling of the substrate 03 to 200 ° C, as in 3 described
5. e. Layer removal using the RPS process and NF ₃ : Ar process gas 12 as in 2 described

1. a. Aufheizen des Substrats 03 in der Prozesskammer 02 auf 200°C.
2. b. Schichtabtragen mittels RPS-Prozess und NF₃:Ar Prozessgas 12 wie in 2 beschrieben.
3. c. Überführen des Substrats 03 in die Prozesskammer 16 und Aufheizen des Substrats 03 auf 400°bis 600°C.
4. d. Defektpassivieren mittels RF-Plasma in Prozesskammer 16 einschließlich des direkt folgenden Abscheidens der a-Si:H-Deckschicht 15, wie in 4 beschrieben
5. e. Rücküberführen des Substrats 03 in die Prozesskammer 02 und Abkühlen des Substrats 03 auf 200°C in der Prozesskammer 02
6. f. Schichtabtragen mittels RPS-Prozess und NF₃:Ar Prozessgas 12 wie in 2 beschrieben.

Alternatively, two process chambers can also be used 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 comprises the following sequence of procedural steps:

1. a. Heating the substrate 03 in the process chamber 02 to 200 ° C.
2. b. Layer removal using the RPS process and NF ₃ : Ar process gas 12 as in 2 described.
3. c. Transferring the substrate 03 into the process chamber 16 and heating the substrate 03 to 400 ° to 600 ° C.
4. d. Defect passivation using RF plasma in the process chamber 16 including the immediately following deposition of the a-Si: H top layer 15, as in FIG 4th described
5. e. Transferring the substrate back 03 into the process chamber 02 and cooling the substrate 03 to 200 ° C in the process chamber 02
6. f. Layer removal using the RPS process and NF ₃ : Ar process gas 12 as in 2 described.

Following process step IV (process step III - only hydrogen passivation - or process step IIIa - hydrogen passivation with deposition of the top layer) was optional 15th - carried out) can according to method step V in the process chamber 02 a texture using plasma-chemical etching 20th into the surface (after previous plasma-chemical etching and thus removal of an optionally available cover layer 15th ) the thin silicon absorber layer 01 be introduced, compare 6th . Then, according to method step VI, further functional layers of the solar cell, in particular an amorphous intrinsic buffer layer 17th and / or a thin silicon absorber layer 01 counter-doped emitter layer 18th deposited by means of PECVD and thus an i / n or i / p hetero emitter can be generated, see also 6th . The layer thicknesses are 5-10 nm for the amorphous intrinsic buffer layer 17th as 5 to 20th nm for the n- or p-doped emitter layer 18th at pressures from 100 to 1000 Pa, RF power densities from 0.01 to 0.05 W / cm ² and a substrate temperature between 150 and 250 ° C.

To complete a thin-film solar cell, cell contacting and, if necessary, module interconnection then take place, but these are not part of the claimed method.

List of reference symbols

01

thin silicon absorber layer (LPC-Si)

02

first process chamber

03

Barrier and adhesive layer

04

Substrate

05

Surface oxide layer

06

Process gas

08

Hydrogen process gas

09

Defective material

10

internal plasma source

11

external plasma source (RPS)

12

Process gas mixture

14th

Parallel plate arrangement

15th

Top layer

16

second process chamber

17th

intrinsic buffer layer

18th

Emitter layer

20th

texture

22nd

external plasma chamber for RPS

Claims (12)

Method for the connection processing of a silicon layer with a structure generated by liquid phase crystallization (LPC) using a plasma for various successive method steps in at least one process chamber of a plasma system, at least the following method steps being provided: I. providing an n- or p-doped crystalline thin silicon absorber layer (01) with a structure produced by liquid phase crystallization (LPC), II. Plasma-chemical etching of the thin silicon absorber layer (01) in a fluoride-containing process gas (06) to remove the layer of natural surface oxide (05) and defect-rich material (09) in a layer thickness range between 100 nm and 500 nm, 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-chemical hydrogen-passivated thin silicon absorber layer (01) in a fluoride-containing process gas (06) to remove the layer of defect-rich material (09) in a layer thickness range between 100 nm and 500 nm. Procedure according to Claim 1 , characterized by the following process step: V. plasma-chemical etching of a texture (20) in the thin silicon absorber layer (01) freed from the defect-rich material. Procedure according to Claim 1 or 2 , characterized by the following process step: VI. plasma-chemical thin-layer deposition of an intrinsic buffer layer (17) and / or a p- or n-doped emitter layer (18). Method according to one of the preceding claims, characterized by the plasma-chemical etching according to method steps II and IV in the fluoride-containing process gas (06) with a process pressure of less than 1000 Pa and a substrate temperature between 200 ° C and 600 ° C. Method according to one of the preceding claims, characterized by plasma-chemical hydrogen passivation according to method 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. 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) which is active in an external plasma chamber (22) spatially remote from the thin silicon absorber layer (01), with only Process gas radicals get into the process gas chamber (02). Procedure according to Claim 6 , characterized by the use of an 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 time between 30 s and 300 s and a substrate temperature between 200 ° C and 400 ° C. 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 between 100 Pa and 1000 Pa, a Substrate temperature 400 ° C and 600 ° C, a process time between 5 min and 30 min, an RF power density between 0.02 W / cm ² and 0.2 W / cm ² . Procedure according to Claim 8 , 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 fallen below 300 ° C. Procedure according to Claim 8 , characterized by the additional process step after process step III: IIIa. Mixing SiH ₄ to the hydrogen process gas (08) with a ratio of H ₂ : SiH ₄ of 1:10 at the end of the hydrogen passivation according to process step III and plasma-assisted vapor deposition of a 10 nm to 200 nm cover layer (15) made of amorphous, hydrogen-saturated silicon on the thin silicon absorber layer (01) at a process pressure between 100 Pa and 1000 Pa, the RF plasma being active until the end of the deposition of the cover layer (15) and the substrate temperature being lowered to 200 ° C only after the RF plasma has been switched off becomes. Method according to one of the Claims 1 to 9 , characterized by the implementation of all process steps I to VI in a single process chamber (02). Method according to one of the Claims 1 to 7th and after Claim 10 , characterized by performing method steps I, II, IV to VI without hydrogen passivation in a first process chamber (02) and performing hydrogen passivation in accordance with additional method step IIIa with the combined formation of a cover layer (15) in a second process chamber (16).

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