WO2010034725A2 - Method for the production of a semiconductor component, in particular a solar cell, on the basis of a thin silicon layer - Google Patents

Method for the production of a semiconductor component, in particular a solar cell, on the basis of a thin silicon layer Download PDF

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Publication number
WO2010034725A2
WO2010034725A2 PCT/EP2009/062286 EP2009062286W WO2010034725A2 WO 2010034725 A2 WO2010034725 A2 WO 2010034725A2 EP 2009062286 W EP2009062286 W EP 2009062286W WO 2010034725 A2 WO2010034725 A2 WO 2010034725A2
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Prior art keywords
silicon substrate
silicon
etching
porous layer
layer
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PCT/EP2009/062286
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French (fr)
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WO2010034725A3 (en
WO2010034725A4 (en
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Jan Hensen
Andreas Wolf
Barbara Terheiden
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Institut Für Solarenergieforschung Gmbh
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Publication of WO2010034725A2 publication Critical patent/WO2010034725A2/en
Publication of WO2010034725A3 publication Critical patent/WO2010034725A3/en
Publication of WO2010034725A4 publication Critical patent/WO2010034725A4/en

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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
    • H01L31/18—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof
    • H01L31/1804—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof comprising only elements of Group IV of the Periodic Table
    • 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
    • H01L21/70—Manufacture or treatment of devices consisting of a plurality of solid state components formed in or on a common substrate or of parts thereof; Manufacture of integrated circuit devices or of parts thereof
    • H01L21/71—Manufacture of specific parts of devices defined in group H01L21/70
    • H01L21/76—Making of isolation regions between components
    • H01L21/762—Dielectric regions, e.g. EPIC dielectric isolation, LOCOS; Trench refilling techniques, SOI technology, use of channel stoppers
    • H01L21/7624—Dielectric regions, e.g. EPIC dielectric isolation, LOCOS; Trench refilling techniques, SOI technology, use of channel stoppers using semiconductor on insulator [SOI] technology
    • H01L21/76251—Dielectric regions, e.g. EPIC dielectric isolation, LOCOS; Trench refilling techniques, SOI technology, use of channel stoppers using semiconductor on insulator [SOI] technology using bonding techniques
    • H01L21/76259—Dielectric regions, e.g. EPIC dielectric isolation, LOCOS; Trench refilling techniques, SOI technology, use of channel stoppers using semiconductor on insulator [SOI] technology using bonding techniques with separation/delamination along a porous layer
    • 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
    • Y02E10/547—Monocrystalline silicon PV cells
    • 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

  • the invention relates to a method for the production of a semiconductor component, in particular a solar cell, on the basis of a silicon thin film, i.e. a thin silicon layer.
  • the invention relates to a production method for a silicon solar cell with a layer transfer process according to the introductory clause of Claim 1.
  • Methods are known in the prior art for the production of silicon solar cells, in which firstly a porous silicon layer is produced on a silicon substrate and then a further layer of silicon is deposited over the porous silicon layer, for example epitactically. This further layer can then be separated from the silicon substrate, with the previously produced porous layer serving as a preset breaking point.
  • the separated further layer can be formed for example with a thickness of a few micrometres and can then serve as a thin film substrate for a solar cell, in which in subsequent process steps essential components of the solar cell, such as for example its emitter and/or its contact metallization, can be formed.
  • Such a so-called layer transfer method is described for example in an article by R. Brendel in Solar Energy, 77, 2004, 969-982 and in DE 197 30 975 Al. It makes use of the fact that the thin film which is applied onto the porous layer preferably grows with the same crystalline structure as the silicon substrate adjacent therebeneath.
  • a qualitatively high-grade monocrystalline wafer is used as silicon substrate, in this way qualitatively high-grade silicon thin film can be produced, which can then be used as substrates for solar cells with a high efficiency potential.
  • the silicon substrate is scarcely employed and can be used again several times.
  • the porous layer is produced by anodic etching.
  • the silicon substrate is contacted on its rear side by an electrode.
  • the front side of the silicon substrate is brought into contact with an etching solution which usually contains hydrofluoric acid (HF).
  • the etching solution can be electrically contacted with a further electrode, for example a platinum electrode.
  • a further electrode for example a platinum electrode.
  • the etching rate and hence the structure or porosity of the porous layer can be influenced here, in addition to other factors such as the substrate doping and the composition or temperature of the etching solution, by the choice of the current intensity. In the case of low current intensities, small pores are formed and therefore a low porosity is produced; in the case of greater current intensities, larger pores develop and therefore a greater porosity. Owing to the formation of space charge zones at the surface of the silicon substrate, the etching process continuously advances here in the direction of the interior of the silicon substrate.
  • a porous double layer structure can be produced, in which the pores on the surface of the silicon substrate are smaller than in a layer lying therebeneath.
  • the small-pored layer close to the surface can even close completely due to rearrangement processes during a high temperature step on the surface, so that no more pores at all can be detected on the surface.
  • Such a porous double layer structure can be advantageous in that on the layer having a low or absent porosity, close to the surface, subsequently a homogeneous, continuous silicon thin film can be deposited in a simple manner and the layer lying therebeneath, with a high porosity, can serve as a preset breaking point on the later separation of this siliconthin film.
  • a need can exist for a method for the production of a semiconductor component, in particular a solar cell, on the basis of a silicon thin film using a layer transfer method, in which the processing expenditure is reduced compared with conventional methods.
  • a method for the production of a semiconductor component, in particular a solar cell, on the basis of a silicon thin film.
  • the method here has at least the following process steps: providing of a silicon substrate; forming of a porous layer on a surface of the silicon substrate; depositing of a silicon thin film on the porous layer; and separating the silicon thin film from the silicon substrate, with the porous layer serving as a preset breaking point.
  • the porous layer is formed here by currentless (i.e. electroless) chemical etching of the silicon substrate.
  • the present invention can be regarded as being based on the following perception:
  • the inventors of the present invention have overcome this long-held prejudice and have recognized that with a suitable carrying out of the process, the currentless chemical etching of a silicon substrate can be used perfectly within the scope of a layer transfer process in order to form the necessary porous layer here.
  • the electrical contacting of the silicon substrate and of the etching solution can be dispensed with and therefore the processing for the production of the solar cell can be substantially simplified, so that it can also be converted and used for large-scale use.
  • the silicon substrate provided within the framework of the production method according to the invention can have any desired structure and geometry.
  • a high-quality silicon wafer for example of monocrystalline silicon, is used as silicon substrate.
  • the currentless or electroless chemical etching used for the formation of the porous layer at the surface of the silicon substrate can be characterized in that the silicon substrate does not need to be electrically contacted in any way. Instead, the silicon substrate can be held in any desired, preferably electrically non-conductive holder, whilst it is exposed to an etching solution. No electrical current flows during the etching, in particular through the silicon substrate. In other words, the etching solution which is used for the etching and the silicon substrate can lie at the same electrical potential.
  • the silicon thin film which is deposited on the porous layer can be produced by means of various epitaxy methods.
  • the layer can be deposited by chemical gas- phase deposition (CVD - Chemical Vapour Deposition), physical gas-phase deposition (PVD - Physical Vapour Deposition) or liquid phase epitaxy (LPE - Liquid Phase Epitaxy).
  • the silicon thin film can be deposited with a thickness of a few hundred nanometres up to over one hundred micrometres, for example between 500 nm and 100 ⁇ m, preferably between 10 ⁇ m and 30 ⁇ m.
  • a mechanical force can be exerted onto the silicon thin film.
  • the silicon thin film can be adhered onto a carrier substrate, for example made of glass.
  • a method as is used for example in module enclosing, or a sol-gel method can be utilized.
  • the carrier substrate By means of the carrier substrate, the silicon thin film can then be lifted off from the silicon substrate, with the previously produced porous layer serving as a preset breaking point, in particular in the regions with the highest porosity, along which the separating process is carried out.
  • doped regions can be produced in the silicon thin film, which form an emitter or a BSF (Back Surface Field).
  • the doped regions can be produced for example by the diffusing- in of dopants.
  • doped regions can be produced by epitatic application of doped semiconductor layers, so that heterostructures form, in which for example the emitter can be formed by a layer of amorphous silicon, doped and/or intrinsically.
  • electrical contacts can be formed at the surfaces of the silicon thin film, for example in the form of metallizations or by transparent conductive oxides (TCO - Transparent Conductive Oxides).
  • dielectric layers can be formed on the surface, which could serve as surface passivation, antireflex layer or reverse mirror.
  • the currentless chemical etching is carried out in a liquid etching solution which has an oxidizing agent for the partial oxidizing of the surface of the silicon substrate and an etching medium for the etching away of the oxidized silicon.
  • a liquid etching solution which has an oxidizing agent for the partial oxidizing of the surface of the silicon substrate and an etching medium for the etching away of the oxidized silicon.
  • an etching process can be realized which is quick, homogeneous and simple to carry out industrially.
  • any substance can serve as oxidizing agent which is suitable for oxidizing silicon.
  • nitric acid (HNO 3 ) can be used as oxidizing agent.
  • sulphuric acid H 2 S O 4
  • sodium nitrite NaNO 2
  • chromium trioxide CrOs
  • potassium dichromate K 2 Cr 2 Oy
  • potassium bromate KBrOs
  • potassium permanganate KMnO 4
  • Fe(III) iron of the oxidation stage three
  • Mn(VII) manganese in the oxidation stage seven
  • hydrogen peroxide H 2 O 2
  • etching medium Any desired substances which attack and at least partially etch away oxidized silicon (SiO x ) can serve as etching medium.
  • hydrofluoric acid (HF) can be used as etching medium.
  • the etching solution can contain water in order to influence the concentration of the oxidizing agent and etching medium and hence the etching speed.
  • the silicon substrate is moved relative to the etching solution during the etching or, vice versa, the etching solution is moved relative to the substrate.
  • the etching solution can also be moved in relation to the silicon substrate, i.e. a flow can be brought about within the etching solution.
  • the relative movement of silicon substrate and etching solution can lead to small gas bubbles, which can form during the etching process, for example gaseous hydrogen (H 2 ), being flushed away from the surface of the silicon substrate and hence inhomogeneities can be avoided during etching.
  • gaseous hydrogen H 2
  • the silicon substrate is rotated in a vertically inclined position during the etching in the etching solution.
  • the relative movement between the silicon substrate and the etching solution can be brought about in a way which is simple to be realized technically and small gas bubbles which occur can escape along the surface of the inclined silicon substrate.
  • a wetting agent is added to the etching solution.
  • This wetting agent can cause the actual etching substances of the etching solution to be able to wet the surface of the silicon substrate uniformly during the etching process. Furthermore, small gas bubbles can simply disengage from the surface of the silicon substrate due to the wetting agent.
  • Acetic acid C 2 H 4 O 2
  • wetting agent can be used for example as wetting agent.
  • the porous layer is formed with a thickness of at least 0.1 ⁇ m, preferably at least 0.4 ⁇ m, more preferably at least 1.0 ⁇ m.
  • Tests carried out by the inventors have shown that porous layers with a layer thickness which is too small can not serve sufficiently as a preset breaking point.
  • the porous layer has transparent characteristics similar to a dielectric layer, the colour impression brought about by the porous layer changes owing to interference effects.
  • the porous layer becomes increasingly thicker and this changing layer thickness can be observed on the basis of the colour changes involved with this, and can be analysed quantitatively. After the desired number of colour changes has been observed, it can be assumed that the porous layer has the correspondingly desired thickness and the etching process for producing the porous layer can be interrupted.
  • the porous layer is formed with a porosity of between 20 % and 60 %, preferably between 30 % and 50 %. Tests have shown that the porous layer with too low porosity is poor at serving as a preset breaking point in the subsequent separation process. With too high porosity, problems can occur in the formation of the thin silicon layer on the porous layer, because the epitactically deposited silicon can no longer close to a closed silicon thin film owing to possibly too large pores or craters within the porous layer.
  • the porosity is to be defined here as a percentage volume proportion of cavities within the porous layer. It is to be a value averaged over the overall thickness of the porous layer, in which the local porosity can vary along the thickness of the porous layer.
  • the provided silicon substrate has a specific resistance of less than 50 m ⁇ cm (milliohm centimetres), preferably less than 15m ⁇ cm and more preferably less than 5m ⁇ cm.
  • a high temperature step is carried out at temperatures above 850 0 C, preferably above 950 0 C and more preferably above 1,000 0 C.
  • the high temperature step is also designated as "annealing".
  • Such a high temperature step can be carried out over a period of for example 0 to 60 min.
  • the substrate with the porous layer formed thereon can be kept at a high temperature above 950 0 C in a separate annealing step for a specified period of time, for example approximately 30 min, for example in an atmosphere containing hydrogen or argon, and the thin film is only subsequently deposited epitactically in a further process step at even higher temperatures.
  • the temperature can be slowly increased systematically before the epitactic deposition of the thin film, and the gas atmosphere can be selected accordingly, so that in the process step of producing the thin film, a correspondingly high temperature step automatically also occurs with the increasing of the temperature up to the deposition temperature of for example 1100 0 C. It was observed that during such a high temperature step, a transformation of the structure of the porous layer can occur. In order to achieve an optimum surface energy, the pores produced during etching can tend to close on the surface of the porous layer. In this way, the porous layer can form a closed covering layer on its surface, which can serve as an ideal starting layer for the silicon thin film which is later to be deposited.
  • the silicon substrate is flushed in non-etching liquid after the formation of the porous layer and before the deposition of the thin silicon layer.
  • Water (H 2 O) preferably in highly pure, de-ionized form, can be used for this as the non-etching liquid.
  • the silicon substrate is held stationary during the flushing. In other words, no relative movement is to occur between the silicon substrate and the liquid which is used for flushing. It was observed that it can thereby be achieved that in fact excess etching solution is flushed away from the surface of the porous layer, residues of the etching solution, however, remain deeper in the interior in the porous layer and continue to etch there for a certain length of time. It can thereby be achieved that the pore size or the porosity is greater deeper in the interior of the porous layer than on its surface.
  • a similar double layer structure can be achieved as was able to be achieved conventionally with the aid of anodic etching.
  • the high porosity inside the porous layer assists the process of separation of the silicon thin film, whereas owing to the low porosity on the surface of the porous layer, the formation of a qualitatively high-grade silicon thin film can be assisted.
  • Fig. 1 shows a silicon thin film which was deposited on a silicon substrate, according to an embodiment of the production method according to the invention.
  • a porous layer 3 is produced by currentless chemical etching on a monocrystalline silicon wafer serving as silicon substrate 1. After a porous layer 3 with a desired overall layer thickness of for example 1 ⁇ m has been produced, for example by observation of the colour changes brought about by the porous layer 3 owing to the changing layer thickness during etching, the substrate is removed from a HF/HNO3/H2O solution, serving as etching solution. Remaining etching solution is washed off by introduction into a flushing bath of de-ionized, pure water, with the residues of the etching solution being able to remain inside the pores and being able to continue to etch there.
  • the silicon substrate 1 together with the porous layer 3 situated thereon is subjected to a high temperature step at approximately 1000 0 C for a few minutes.
  • the porous layer 3 is partially transformed and preferably forms a closed silicon layer at its outwardly directed surface, which can serve as a starting layer for a silicon thin film 5 which is to be subsequently deposited.
  • Si wafers chemically etched in a suitable solution present a porous silicon layer 0.4 ⁇ m to 1 ⁇ m thick which, in combination with a suitable epitaxy process, allows a monocrystalline closed silicon layer to be separated on surfaces of at least 6" substrates.
  • a thicker or thinner or no compact unetched silicon layer can be seen on the surface of the porous silicon layer, depending on the doping concentration.
  • a porous layer can be situated at the surface under an approximately 50 nm thick compact layer.
  • the porous layer can be approximately 1.5 ⁇ m thick and have a higher porosity than the layer close to the surface.
  • porosity measurements by means of weighing produced a porosity of 20 %. This value is to be regarded as the average value for both layers. Observations on examples have shown that the layer close to the surface has vertical pores a few nanometres in size, through which the etching solution arrives into the lower layers. The layer close to the surface can therefore differ structurally from the underlying porous layer. Even when the sample is not rotated, but is only immersed into the solution, the described layer can form close to the surface.
  • a strongly doped p-type silicon wafer with a size of 6 inch (approximately 15 cm) and with a specific resistance of less than 5 m ⁇ cm is etched in a solution of HF:HN ⁇ 3:H2 ⁇ :acetic acid.
  • HF:HN ⁇ 3:H2 ⁇ :acetic acid is etched in a solution of HF:HN ⁇ 3:H2 ⁇ :acetic acid.
  • more weakly doped p-type silicon wafer with a specific resistance of between 10 - 20 m ⁇ cm is etched in a corresponding solution.
  • the wafer is rotated in an inclined position at 40-80 revolutions per minute. Interferences on the porous surface as a function of the thickness of the porous Si layer and the porosity produce a colour impression.
  • the layer thickness and the porosity can be determined by the number of colour changes or the etching duration, taking into account the refractive index. Typical values here are a few, for example fewer than 10, colour changes and etching durations of 15-25 min.
  • the resulting porosity lies between 40 and 50% for the more strongly doped wafer.
  • the porosity of the more weakly doped wafer lies below this.
  • the thickness of the compact layer is able to be adjusted by the doping concentration of the substrate wafers, the higher the doping, the smaller the thickness of the compact layer.
  • a p-type silicon wafer of between 10 - 20 m ⁇ cm is etched in a solution of HFIHNO S IH 2 O : acetic acid. During the etching process, the wafer is rotated in an inclined position with 40-80 revolutions per minute. Interferences on the porous surface produce a colour impression as a function of the thickness of the porous Si layer and the porosity. Typical values here are etching durations of 15-25 min. The resulting porosity is only 10 - 30%.
  • the thickness of the compact layer is able to be adjusted by the doping concentration of the substrate wafers, the higher the doping, the smaller the thickness of the compact layer.

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Abstract

A method for the production of a semiconductor component, in particular a solar cell, on the basis of a silicon thin film. A method is proposed for the production of a solar cell on the basis of a silicon thin film (5). The method presents: preparing of a silicon substrate (1); forming of a porous layer (3) at a surface of the silicon substrate (1); depositing of a silicon thin film (5) on the porous layer (3); and separating of the thin silicon layer (5) from the silicon substrate (1), with the porous layer (3) serving as a preset breaking point. The porous layer (3) is formed here by currentless chemical etching of the silicon substrate (1). By dispensing with conventionally used anodic etching and replacing with currentless chemical etching, the production process can be simplified considerably.

Description

METHOD FOR THE PRODUCTION OF A SEMICONDUCTOR COMPONENT. IN PARTICULAR A SOLAR CELL. ON THE BASIS OF A THIN SILICON LAYER
FIELD OF THE INVENTION
The invention relates to a method for the production of a semiconductor component, in particular a solar cell, on the basis of a silicon thin film, i.e. a thin silicon layer. In particular, the invention relates to a production method for a silicon solar cell with a layer transfer process according to the introductory clause of Claim 1.
BACKGROUND OF THE INVENTION
Methods are known in the prior art for the production of silicon solar cells, in which firstly a porous silicon layer is produced on a silicon substrate and then a further layer of silicon is deposited over the porous silicon layer, for example epitactically. This further layer can then be separated from the silicon substrate, with the previously produced porous layer serving as a preset breaking point.
The separated further layer can be formed for example with a thickness of a few micrometres and can then serve as a thin film substrate for a solar cell, in which in subsequent process steps essential components of the solar cell, such as for example its emitter and/or its contact metallization, can be formed.
Such a so-called layer transfer method is described for example in an article by R. Brendel in Solar Energy, 77, 2004, 969-982 and in DE 197 30 975 Al. It makes use of the fact that the thin film which is applied onto the porous layer preferably grows with the same crystalline structure as the silicon substrate adjacent therebeneath. When for example a qualitatively high-grade monocrystalline wafer is used as silicon substrate, in this way qualitatively high-grade silicon thin film can be produced, which can then be used as substrates for solar cells with a high efficiency potential. Apart from slight losses through the production of the porous layer, the silicon substrate is scarcely employed and can be used again several times. Conventionally, the porous layer is produced by anodic etching. Here, the silicon substrate is contacted on its rear side by an electrode. The front side of the silicon substrate is brought into contact with an etching solution which usually contains hydrofluoric acid (HF). The etching solution can be electrically contacted with a further electrode, for example a platinum electrode. By applying an electrical voltage to the two electrodes, an electric current can be brought about through the etching solution and the silicon substrate, by which the surface of the silicon substrate is oxidized, wherein the produced silicon oxide is immediately etched away by the etching solution containing HF. In this way, a porous silicon layer can be produced on the surface of the silicon substrate.
The etching rate and hence the structure or porosity of the porous layer can be influenced here, in addition to other factors such as the substrate doping and the composition or temperature of the etching solution, by the choice of the current intensity. In the case of low current intensities, small pores are formed and therefore a low porosity is produced; in the case of greater current intensities, larger pores develop and therefore a greater porosity. Owing to the formation of space charge zones at the surface of the silicon substrate, the etching process continuously advances here in the direction of the interior of the silicon substrate. In other words, through the fact that the silicon substrate is firstly etched at low current intensities, for example less than 100 niA/cm2 for 100 seconds for example and then at greater current intensities, for example more than 200 mA/cm2 for 5 seconds, a porous double layer structure can be produced, in which the pores on the surface of the silicon substrate are smaller than in a layer lying therebeneath. The small-pored layer close to the surface can even close completely due to rearrangement processes during a high temperature step on the surface, so that no more pores at all can be detected on the surface.
Such a porous double layer structure can be advantageous in that on the layer having a low or absent porosity, close to the surface, subsequently a homogeneous, continuous silicon thin film can be deposited in a simple manner and the layer lying therebeneath, with a high porosity, can serve as a preset breaking point on the later separation of this siliconthin film.
However, this process step of anodic etching, which has been known for a long time, for the production of the porous layer requires that each silicon substrate and the etching solution which is used must be contacted electrically by electrodes. The large-scale conversion of the production of solar cells using the layer transfer process was therefore connected hitherto with a considerable expenditure.
SUMMARY OF THE INVENTION
Therefore, a need can exist for a method for the production of a semiconductor component, in particular a solar cell, on the basis of a silicon thin film using a layer transfer method, in which the processing expenditure is reduced compared with conventional methods.
According to one aspect of the present invention, a method is proposed for the production of a semiconductor component, in particular a solar cell, on the basis of a silicon thin film. The method here has at least the following process steps: providing of a silicon substrate; forming of a porous layer on a surface of the silicon substrate; depositing of a silicon thin film on the porous layer; and separating the silicon thin film from the silicon substrate, with the porous layer serving as a preset breaking point. In contrast to conventional layer transfer methods, the porous layer is formed here by currentless (i.e. electroless) chemical etching of the silicon substrate.
The present invention can be regarded as being based on the following perception:
Layer transfer methods hitherto for the formation of thin silicon layers as substrate, e.g. for solar cells, were always carried out using anodic etching. Here, one proceeded from the assumption that a qualitatively high-grade thin silicon layer could only be produced over the porous layer and then separated from the silicon substrate due to the double layer structure, able to be produced by the anodic etching, with low porosity on the surface and greater porosity in layer regions lying therebeneath. In addition, one proceeded hitherto here from the assamption that through currentless chemical etching, neither such a double layer structure nor another porous silicon layer would be able to be produced, which would be suitable for a subsequent depositing and separation of a silicon thin film on this porous layer. This long-held prejudice was supported, inter alia, in that it was assumed that the porous silicon layer produced by currentless chemical etching would always have substantially larger pores on its surface than in regions lying therebeneath. It was therefore assumed that either the size of the pores on the surface of the silicon substrate, produced by the chemical etching, would have to be selected to be so small that a thin silicon layer of suitably high quality could be additionally deposited thereon, with however, a subsequent separation of this silicon thin film from the silicon substrate lying therebeneath being regarded as difficult or impossible, or that on the other hand the chemical etching would have to be carried out so that the pore size is large enough for a subsequent separation of the silicon thin film, but that then, owing to the large pore size on the surface of the silicon substrate, the silicon thin film deposited thereon can not have a sufficiently high quality.
The inventors of the present invention have overcome this long-held prejudice and have recognized that with a suitable carrying out of the process, the currentless chemical etching of a silicon substrate can be used perfectly within the scope of a layer transfer process in order to form the necessary porous layer here.
By replacing the conventionally used anodic etching by a currentless chemical etching of the silicon substrate for the production of the porous layer, the electrical contacting of the silicon substrate and of the etching solution can be dispensed with and therefore the processing for the production of the solar cell can be substantially simplified, so that it can also be converted and used for large-scale use.
Possible features and advantages of embodiments of the production method according to the invention are described in further detail below.
The silicon substrate provided within the framework of the production method according to the invention can have any desired structure and geometry. Preferably, a high-quality silicon wafer, for example of monocrystalline silicon, is used as silicon substrate.
The currentless or electroless chemical etching used for the formation of the porous layer at the surface of the silicon substrate can be characterized in that the silicon substrate does not need to be electrically contacted in any way. Instead, the silicon substrate can be held in any desired, preferably electrically non-conductive holder, whilst it is exposed to an etching solution. No electrical current flows during the etching, in particular through the silicon substrate. In other words, the etching solution which is used for the etching and the silicon substrate can lie at the same electrical potential.
The silicon thin film which is deposited on the porous layer can be produced by means of various epitaxy methods. For example, the layer can be deposited by chemical gas- phase deposition (CVD - Chemical Vapour Deposition), physical gas-phase deposition (PVD - Physical Vapour Deposition) or liquid phase epitaxy (LPE - Liquid Phase Epitaxy). The silicon thin film can be deposited with a thickness of a few hundred nanometres up to over one hundred micrometres, for example between 500 nm and 100 μm, preferably between 10 μm and 30 μm.
In order to separate the silicon thin film from the silicon substrate, for example a mechanical force can be exerted onto the silicon thin film. For example, the silicon thin film can be adhered onto a carrier substrate, for example made of glass. For this purpose, a method as is used for example in module enclosing, or a sol-gel method, can be utilized. By means of the carrier substrate, the silicon thin film can then be lifted off from the silicon substrate, with the previously produced porous layer serving as a preset breaking point, in particular in the regions with the highest porosity, along which the separating process is carried out.
Already before the separating of the thin silicon layer or alternatively after the separating, further process steps can be carried out on the silicon thin film, in order to form components which may be necessary or helpful for the function as semiconductor component, in particular as solar cell. For example, doped regions can be produced in the silicon thin film, which form an emitter or a BSF (Back Surface Field). The doped regions can be produced for example by the diffusing- in of dopants. Alternatively, doped regions can be produced by epitatic application of doped semiconductor layers, so that heterostructures form, in which for example the emitter can be formed by a layer of amorphous silicon, doped and/or intrinsically. In addition, electrical contacts can be formed at the surfaces of the silicon thin film, for example in the form of metallizations or by transparent conductive oxides (TCO - Transparent Conductive Oxides). Furthermore, dielectric layers can be formed on the surface, which could serve as surface passivation, antireflex layer or reverse mirror.
According to one embodiment of the present invention, the currentless chemical etching is carried out in a liquid etching solution which has an oxidizing agent for the partial oxidizing of the surface of the silicon substrate and an etching medium for the etching away of the oxidized silicon. By means of such a liquid etching solution, an etching process can be realized which is quick, homogeneous and simple to carry out industrially. Here, any substance can serve as oxidizing agent which is suitable for oxidizing silicon. For example, nitric acid (HNO3) can be used as oxidizing agent. Alternatively, sulphuric acid (H2 S O4), sodium nitrite (NaNO2), chromium trioxide (CrOs), potassium dichromate (K2Cr2Oy), potassium bromate (KBrOs), potassium permanganate (KMnO4), iron of the oxidation stage three (Fe(III)), manganese in the oxidation stage seven (Mn(VII)) or hydrogen peroxide (H2O2) can be used.
Any desired substances which attack and at least partially etch away oxidized silicon (SiOx) can serve as etching medium. For example, hydrofluoric acid (HF) can be used as etching medium. In addition, the etching solution can contain water in order to influence the concentration of the oxidizing agent and etching medium and hence the etching speed.
According to a further embodiment of the present invention, the silicon substrate is moved relative to the etching solution during the etching or, vice versa, the etching solution is moved relative to the substrate. This can take place in that the silicon substrate is moved within the etching solution, for example in a translatory or rotatory manner. Alternatively, the etching solution can also be moved in relation to the silicon substrate, i.e. a flow can be brought about within the etching solution. The relative movement of silicon substrate and etching solution can lead to small gas bubbles, which can form during the etching process, for example gaseous hydrogen (H2), being flushed away from the surface of the silicon substrate and hence inhomogeneities can be avoided during etching.
According to a further embodiment of the present invention, the silicon substrate is rotated in a vertically inclined position during the etching in the etching solution. In this way, the relative movement between the silicon substrate and the etching solution can be brought about in a way which is simple to be realized technically and small gas bubbles which occur can escape along the surface of the inclined silicon substrate.
According to a further embodiment of the present invention, a wetting agent is added to the etching solution. This wetting agent can cause the actual etching substances of the etching solution to be able to wet the surface of the silicon substrate uniformly during the etching process. Furthermore, small gas bubbles can simply disengage from the surface of the silicon substrate due to the wetting agent. Acetic acid (C2H4O2) can be used for example as wetting agent.
According to a further embodiment of the present invention, the porous layer is formed with a thickness of at least 0.1 μm, preferably at least 0.4 μm, more preferably at least 1.0 μm. Tests carried out by the inventors have shown that porous layers with a layer thickness which is too small can not serve sufficiently as a preset breaking point. As the porous layer has transparent characteristics similar to a dielectric layer, the colour impression brought about by the porous layer changes owing to interference effects. During the etching process, the porous layer becomes increasingly thicker and this changing layer thickness can be observed on the basis of the colour changes involved with this, and can be analysed quantitatively. After the desired number of colour changes has been observed, it can be assumed that the porous layer has the correspondingly desired thickness and the etching process for producing the porous layer can be interrupted.
According to a further embodiment of the present invention, the porous layer is formed with a porosity of between 20 % and 60 %, preferably between 30 % and 50 %. Tests have shown that the porous layer with too low porosity is poor at serving as a preset breaking point in the subsequent separation process. With too high porosity, problems can occur in the formation of the thin silicon layer on the porous layer, because the epitactically deposited silicon can no longer close to a closed silicon thin film owing to possibly too large pores or craters within the porous layer.
The porosity is to be defined here as a percentage volume proportion of cavities within the porous layer. It is to be a value averaged over the overall thickness of the porous layer, in which the local porosity can vary along the thickness of the porous layer.
According to a further embodiment of the present invention, in which the provided silicon substrate has a specific resistance of less than 50 mΩcm (milliohm centimetres), preferably less than 15mΩcm and more preferably less than 5mΩcm.
It was observed that depending on the dopant concentration of the underlying silicon substrate, after etching a thicker or thinner or even no compact quasi unetched layer can remain on the surface of the porous layer. Vertical pores, a few nanometres thick, can run in a manner similar to channels through this quasi unetched layer, these channels being spaced far apart from each other laterally with respect to the diameter of the channels. Etching solution can scarcely attack the silicon substrate on the surface owing to space charge zones, but it can reach deeper into the interior of the substrate locally through the channels and can etch into the porous layer there, underneath the space charge zones.
According to a further embodiment of the present invention, after the formation of the porous layer, in addition a high temperature step is carried out at temperatures above 8500C, preferably above 9500C and more preferably above 1,0000C. The high temperature step is also designated as "annealing". Such a high temperature step can be carried out over a period of for example 0 to 60 min. In other words, the substrate with the porous layer formed thereon can be kept at a high temperature above 9500C in a separate annealing step for a specified period of time, for example approximately 30 min, for example in an atmosphere containing hydrogen or argon, and the thin film is only subsequently deposited epitactically in a further process step at even higher temperatures. Alternatively, the temperature can be slowly increased systematically before the epitactic deposition of the thin film, and the gas atmosphere can be selected accordingly, so that in the process step of producing the thin film, a correspondingly high temperature step automatically also occurs with the increasing of the temperature up to the deposition temperature of for example 11000C. It was observed that during such a high temperature step, a transformation of the structure of the porous layer can occur. In order to achieve an optimum surface energy, the pores produced during etching can tend to close on the surface of the porous layer. In this way, the porous layer can form a closed covering layer on its surface, which can serve as an ideal starting layer for the silicon thin film which is later to be deposited.
According to a further embodiment of the present invention, the silicon substrate is flushed in non-etching liquid after the formation of the porous layer and before the deposition of the thin silicon layer. Water (H2O), preferably in highly pure, de-ionized form, can be used for this as the non-etching liquid. Through the flushing of the silicon substrate, after it has been removed from the etching solution, remaining etching solution can be removed from the surface of the silicon substrate and therefore the etching process on the surface of the silicon substrate can be discontinued.
According to a further embodiment of the present invention, the silicon substrate is held stationary during the flushing. In other words, no relative movement is to occur between the silicon substrate and the liquid which is used for flushing. It was observed that it can thereby be achieved that in fact excess etching solution is flushed away from the surface of the porous layer, residues of the etching solution, however, remain deeper in the interior in the porous layer and continue to etch there for a certain length of time. It can thereby be achieved that the pore size or the porosity is greater deeper in the interior of the porous layer than on its surface. Advantageously, a similar double layer structure can be achieved as was able to be achieved conventionally with the aid of anodic etching. The high porosity inside the porous layer assists the process of separation of the silicon thin film, whereas owing to the low porosity on the surface of the porous layer, the formation of a qualitatively high-grade silicon thin film can be assisted.
It is noted that the embodiments, features and advantages of the invention were described partially with regard to the production method according to the invention for a semiconductor component, for example a solar cell, and partially with regard to semiconductor components or solar cells which are able to be produced with the aid of such a method. One skilled in the art will, however, recognize that, in so far as this is not indicated otherwise, the embodiments and features of the invention can also be transferred respectively in an analogous manner to the semiconductor component / the solar cell or to the production method according to the invention, and vice versa. In particular, the features of the various embodiments can also be combined with each other in any desired manner.
BRIEF DESCRIPTION OF THE DRAWINGS
Further features and advantages of the present invention will be evident to one skilled in the art from the following description of example embodiments which, however, is not to be interpreted as restricting the invention, and with reference to the accompanying drawing.
Fig. 1 shows a silicon thin film which was deposited on a silicon substrate, according to an embodiment of the production method according to the invention.
The drawing is merely diagrammatic and is not true to scale.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
A basic principle and specific embodiments of the production method according to the invention are described below with the aid of the silicon layer structure illustrated in Fig. 1.
A porous layer 3 is produced by currentless chemical etching on a monocrystalline silicon wafer serving as silicon substrate 1. After a porous layer 3 with a desired overall layer thickness of for example 1 μm has been produced, for example by observation of the colour changes brought about by the porous layer 3 owing to the changing layer thickness during etching, the substrate is removed from a HF/HNO3/H2O solution, serving as etching solution. Remaining etching solution is washed off by introduction into a flushing bath of de-ionized, pure water, with the residues of the etching solution being able to remain inside the pores and being able to continue to etch there. After a drying process, in which the residues of the etching solution have also been vaporized out of the pores, the silicon substrate 1 together with the porous layer 3 situated thereon is subjected to a high temperature step at approximately 10000C for a few minutes. In so doing, the porous layer 3 is partially transformed and preferably forms a closed silicon layer at its outwardly directed surface, which can serve as a starting layer for a silicon thin film 5 which is to be subsequently deposited.
Si wafers chemically etched in a suitable solution present a porous silicon layer 0.4 μm to 1 μm thick which, in combination with a suitable epitaxy process, allows a monocrystalline closed silicon layer to be separated on surfaces of at least 6" substrates.
A thicker or thinner or no compact unetched silicon layer can be seen on the surface of the porous silicon layer, depending on the doping concentration. For example, a porous layer can be situated at the surface under an approximately 50 nm thick compact layer. The porous layer can be approximately 1.5 μm thick and have a higher porosity than the layer close to the surface. In examples, porosity measurements by means of weighing produced a porosity of 20 %. This value is to be regarded as the average value for both layers. Observations on examples have shown that the layer close to the surface has vertical pores a few nanometres in size, through which the etching solution arrives into the lower layers. The layer close to the surface can therefore differ structurally from the underlying porous layer. Even when the sample is not rotated, but is only immersed into the solution, the described layer can form close to the surface.
A further effect has been found when the sample is simply placed into a flushing glass filled with de-ionized water, instead of flushing with the sprinkler of de-ionized water. After a few minutes, up to hours, small bubbles become visible, adhering to the surface. The etching process presumably proceeds, because etching solution is still to be found in the porous layer. The porosity of the lower layer appears to be greatly increased locally under the layer close to the surface. Measurements showed an increased average porosity of 27 % after 41 hours storage in DI-water. The local porosity directly under the layer close to the surface is presumably much higher. This is supported by the observation that after over four days' storage in de-ionized water, the thin layer close to the surface partially detaches itself. Two actual example embodiments are described below.
Example 1
A strongly doped p-type silicon wafer with a size of 6 inch (approximately 15 cm) and with a specific resistance of less than 5 mΩcm is etched in a solution of HF:HNθ3:H2θ:acetic acid. By comparison, also more weakly doped p-type silicon wafer with a specific resistance of between 10 - 20 mΩcm is etched in a corresponding solution. During the etching process, the wafer is rotated in an inclined position at 40-80 revolutions per minute. Interferences on the porous surface as a function of the thickness of the porous Si layer and the porosity produce a colour impression. The layer thickness and the porosity can be determined by the number of colour changes or the etching duration, taking into account the refractive index. Typical values here are a few, for example fewer than 10, colour changes and etching durations of 15-25 min. The resulting porosity lies between 40 and 50% for the more strongly doped wafer. The porosity of the more weakly doped wafer lies below this. The thickness of the compact layer is able to be adjusted by the doping concentration of the substrate wafers, the higher the doping, the smaller the thickness of the compact layer.
Example 2
A p-type silicon wafer of between 10 - 20 mΩcm is etched in a solution of HFIHNOSIH2O : acetic acid. During the etching process, the wafer is rotated in an inclined position with 40-80 revolutions per minute. Interferences on the porous surface produce a colour impression as a function of the thickness of the porous Si layer and the porosity. Typical values here are etching durations of 15-25 min. The resulting porosity is only 10 - 30%. The thickness of the compact layer is able to be adjusted by the doping concentration of the substrate wafers, the higher the doping, the smaller the thickness of the compact layer. If one now places the etched wafer into a water bath, the porosity under the compact layer increases. Therefore, through correspondingly long storage of the etched sample in the water, a detaching of the compact layer and possibly of a Si layer mounted thereon could be achieved.
Finally, it is pointed out that the expressions "comprise", "have" etc. do not rule out the presence of further elements. The expression "one" also does not rule out the presence of a plurality of objects. The reference numbers in the claims serve merely for better readability and are in no way intended to restrict the scope of protection of the claims.

Claims

1. A method for the production of a semiconductor component, in particular of a solar cell, based on a silicon thin film (5), the method presenting: providing of a silicon substrate (1); forming of a porous layer (3) at a surface of the silicon substrate (1); depositing of a silicon thin film (5) on the porous layer (3); and separating of the silicon thin film (5) from the silicon substrate (1), with the porous layer (3) serving as a preset breaking point,
characterized in that
the porous layer (3) is formed by currentless chemical etching of the silicon substrate (1).
2. The method according to Claim 1, in which the currentless chemical etching is carried out in a liquid etching solution which has an oxidizing agent for the partial oxidizing of the surface of the silicon substrate and an etching medium for etching away the oxidized silicon.
3. The method according to Claim 2, in which the silicon substrate and the etching solution are moved relative to each other during etching.
4. The method according to Claim 3, in which the silicon substrate is rotated during etching in a vertically inclined position in the etching solution.
5. The method according to any of Claims 2 to 4, in which a wetting agent is added to the etching solution.
6. The method according to any of Claims 1 to 5, in which the porous layer is formed with a thickness of at least 0.1 μm, preferably at least 0.4μm.
7. The method according to any of Claims 1 to 6, in which the porous layer is formed with a porosity of between 20% and 60%, preferably between 30% and 50%.
8. The method according to any of Claims 1 to 7, in which the provided silicon substrate has a specific resistance of less than 50 milliohm centimetres.
9. The method according to any of Claims 1 to 8, in which after the formation of the porous layer, in addition a high temperature step is carried out at temperatures above 8500C, preferably above 9500C and more preferably above 10000C.
10. The method according to any of Claims 1 to 9, in which the silicon substrate is flushed in non-etching liquid after the formation of the porous layer and before the depositing of the silicon thin film.
11. The method according to Claim 10, in which the silicon substrate is held stationary during the flushing.
PCT/EP2009/062286 2008-09-23 2009-09-22 Method for the production of a semiconductor component, in particular a solar cell, on the basis of a thin silicon layer WO2010034725A2 (en)

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CN103303904A (en) * 2013-06-13 2013-09-18 中国科学院金属研究所 Method for preferentially growing metallic single-walled carbon nanotube by using non-metallic silicon oxide as catalyst
WO2017136672A1 (en) * 2016-02-05 2017-08-10 Applied Materials, Inc. Porous silicon structures and laser machining methods for semiconductor wafer processing

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DE102014103303A1 (en) 2014-03-12 2015-10-01 Universität Konstanz Process for producing solar cells with simultaneously etched-back doped regions

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2000045426A1 (en) * 1999-01-27 2000-08-03 Interuniversitaire Microelektronicacentrum Vzw Method for fabricating thin film semiconductor devices

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2000045426A1 (en) * 1999-01-27 2000-08-03 Interuniversitaire Microelektronicacentrum Vzw Method for fabricating thin film semiconductor devices

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN103303904A (en) * 2013-06-13 2013-09-18 中国科学院金属研究所 Method for preferentially growing metallic single-walled carbon nanotube by using non-metallic silicon oxide as catalyst
WO2017136672A1 (en) * 2016-02-05 2017-08-10 Applied Materials, Inc. Porous silicon structures and laser machining methods for semiconductor wafer processing

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