EP2976782A1 - Method for doping silicon sheets - Google Patents

Method for doping silicon sheets

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Publication number
EP2976782A1
EP2976782A1 EP14711268.4A EP14711268A EP2976782A1 EP 2976782 A1 EP2976782 A1 EP 2976782A1 EP 14711268 A EP14711268 A EP 14711268A EP 2976782 A1 EP2976782 A1 EP 2976782A1
Authority
EP
European Patent Office
Prior art keywords
doping
oxide layer
silicon
doped
oxide
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP14711268.4A
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German (de)
French (fr)
Inventor
Bernard Bechevet
Johann Jourdan
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Ion Beam Services SA
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Ion Beam Services SA
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Filing date
Publication date
Application filed by Ion Beam Services SA filed Critical Ion Beam Services SA
Publication of EP2976782A1 publication Critical patent/EP2976782A1/en
Withdrawn legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer
    • H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic Table or AIIIBV compounds with or without impurities, e.g. doping materials
    • H01L21/22—Diffusion of impurity materials, e.g. doping materials, electrode materials, into or out of a semiconductor body, or between semiconductor regions; Interactions between two or more impurities; Redistribution of impurities
    • H01L21/223—Diffusion of impurity materials, e.g. doping materials, electrode materials, into or out of a semiconductor body, or between semiconductor regions; Interactions between two or more impurities; Redistribution of impurities using diffusion into or out of a solid from or into a gaseous phase
    • H01L21/2236—Diffusion of impurity materials, e.g. doping materials, electrode materials, into or out of a semiconductor body, or between semiconductor regions; Interactions between two or more impurities; Redistribution of impurities using diffusion into or out of a solid from or into a gaseous phase from or into a plasma phase
    • 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
    • H01L31/04—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices
    • H01L31/06—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices characterised by potential barriers
    • H01L31/068—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices characterised by potential barriers the potential barriers being only of the PN homojunction type, e.g. bulk silicon PN homojunction solar cells or thin film polycrystalline silicon PN homojunction solar cells
    • 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
    • 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
    • H01L31/186—Particular post-treatment for the devices, e.g. annealing, impurity gettering, short-circuit elimination, recrystallisation
    • 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 present invention generally relates to the doping of silicon wafers for forming photovoltaic cells to be mounted on a solar panel.
  • An object of the present invention is to meet the disadvantages of the prior art mentioned above and in particular, first of all, to propose a method of sequentially doping several distinct parts of a silicon wafer which does not require for as much sophisticated equipment or specific location operation to avoid overlap of the doped parts.
  • a first aspect of the invention relates to a doping method of a silicon wafer for manufacturing a photovoltaic cell, the method comprising the steps of:
  • the method according to the present implementation uses a property well known in microelectronics, about the growth rate of oxides on silicon. Indeed, this growth rate of silicon oxide (S1O2) is higher on the first parts of the surface exposed to the first doping. In other words, the oxide layer is thicker on the first doped portions than on the remainder of the surface of the silicon wafer, which presents an additional barrier to the second doping. As a result, the second doping carried out on the entire oxide layer will be effective only on a part of the remainder of the surface of the silicon wafer, because it is made so as to penetrate the small thickness of the layer of silicon.
  • S1O2 silicon oxide
  • the oxide layer acts as a mask for the second doping, and this mask naturally covers the first doped portions.
  • Self-aligned second doped portions are obtained at the first doped portions by virtue of the oxide layer formed on the surface of the silicon wafer prior to the second doping. There is therefore no mask applied to the silicon wafer before the second doping to obtain doped zones of different nature. There is also no stripping or removal of oxides between the first and second doping, which improves the complete manufacturing process and simplifies the production line.
  • the second doping will not penetrate the oxide layer to the right of the first doped portions (because the oxide layer is locally thicker), but will cross the oxide layer formed between the first doped portions (because the oxide layer is locally less thick on undoped silicon), and thus doping the silicon wafer at these locations.
  • Non-masked or intermediate stripping results in second doped portions which are self-aligned lines on the first doped portions.
  • the step of forming an oxide layer is included in an activation annealing step of the first doped portion.
  • the activation annealing of the first doped portions is advantageously combined with the formation of the oxide layer.
  • a single step activates the first doped portion, and form the oxide layer.
  • the step of forming an oxide layer comprises a heating step in an oxygen enriched atmosphere.
  • the formation of the oxide layer is accelerated and better controlled.
  • the step of performing the second doping is a step of doping on a predetermined penetration depth.
  • the step of forming an oxide layer is a step leading to form a first oxide thickness in line with the first doped portion, and a second oxide thickness on the remainder of the surface less than the first oxide thickness, and the depth of penetration is between the first oxide thickness and the second oxide thickness.
  • the present implementation guarantees an optimal process. Indeed, the second doping does not affect the first doped parts, because it does not cross the oxide layer in the thick areas, and reaches the undoped portions of the silicon wafer because it passes through the layer of oxide in thin areas.
  • the step of performing the first doping is performed by plasma immersion.
  • This process step can be performed with simpler equipment than a plasma gun, for example.
  • the step of performing the second doping is performed by plasma immersion.
  • This process step can be performed with simpler equipment than a plasma gun, for example.
  • the step of performing the first doping and / or the step of performing the second doping is performed by plasma immersion.
  • the step of performing the second doping is followed by an activating annealing step of the second doping.
  • the operation of the photovoltaic cell will be optimal.
  • the step of performing the first doping is a silicon doping step with a first species requiring activation annealing at a first temperature
  • the step of performing the second doping is a step doping silicon with a second species requiring activation annealing at a second temperature, lower than the first temperature.
  • Each doping requires activation annealing at a specific temperature.
  • the step of performing the first doping is a step of doping silicon with boron
  • the step of performing the second doping is a step of doping silicon with phosphorus.
  • Each doping requires activation annealing at a specific temperature.
  • the ideal annealing temperature of boron doping is greater than that of phosphorus activation annealing.
  • the temperature of the second activation annealing is lower than that of the first activation annealing, it will not influence the properties of the first doped portions.
  • the step of performing a second doping is followed by a step of removing the oxide layer.
  • This step consists in removing the entire oxide layer at one time, so that the cell is then ready for the following steps of manufacturing the photovoltaic cell.
  • the step of removing the oxide layer is a chemical deoxidation step in a bath comprising hydrofluoric acid.
  • This implementation is fast and simple, the entire layer of silicon oxide is removed at one time, without special precautions.
  • a second aspect of the invention is a photovoltaic cell having a doping produced according to the first aspect of the invention.
  • a final aspect of the invention is a solar panel comprising at least one photovoltaic cell according to the second aspect of the invention.
  • FIG. 1 shows a section of a silicon wafer during a first step of the method according to the invention
  • - Figure 2 shows the section of the silicon plate of Figure 1 during a second step of the method according to the invention
  • FIG. 3 shows the section of the silicon plate of Figure 1 during a third step of the method according to the invention.
  • FIG. 1 shows a silicon plate seen in section, during a first step of the method according to the invention.
  • This first step consists of doping the first portions 11 of a surface 10 of the silicon wafer, with a first chemical species.
  • the doping method used is plasma immersion doping P1, as described for example in WO2012168575 A2.
  • the silicon wafer is placed in a plasma chamber 20 and a mask 30 is applied to the face 10 of the silicon wafer.
  • This mask 30 comprises openings 31 and solid portions 32 which are intended to allow the plasma generated in the plasma chamber 20 to bathe only the first portions 11 of the silicon wafer which are opposite openings 31 of the mask 30.
  • the silicon wafer is therefore doped with a first chemical species on the first portions 11 of the silicon wafer.
  • FIG. 2 represents a second step of the method according to the invention, during which an oxide layer 40 is created on the surface 10 of the partially doped silicon plate. Since the surface 10 has doped first portions 11, the properties of this surface 10 are heterogeneous, particularly with respect to reactivity with oxygen. Indeed, the creation of oxides on the first parts 11 is faster than on the rest of the surface 10 of the silicon wafer.
  • the second step of the process comprises exposing the surface 10 to the oxygen 0 2 in a chamber 50, in temperature, to accelerate the growth of silicon dioxide on the surface 10.
  • the growth is therefore faster at the first doped portions 11 than on the rest of the surface 10 of the silicon wafer.
  • the Applicant has found that the thickness of the oxide layer 40 is two to three times greater at the level of the first doped portions 11 than at the remainder of the surface 10, if the first doping is carried out with boron or phosphorus for example.
  • the step of creating the oxide layer 40 is controlled in time, temperature and oxygen flow rate, in order to obtain an oxide layer 40 which has a first thickness E1 ranging from 10 nm to 60 nm at the level of the first doped portions 11, and a second thickness E2 ranging from 4 nm to 20 nm at the remainder of the surface 10.
  • the thickness of the the oxide layer 40 passes progressively from the first substantial thickness to the second low thickness, as shown in FIG.
  • FIG. 3 represents a third step of the method according to the invention.
  • a second doping is performed, directly on the oxidized silicon plate, through the oxide layer 40.
  • a new plasma immersion P2 in the chamber 20 can be performed, but without a mask on the silicon wafer, because the process according to the invention uses the oxide layer 40 as a mask.
  • An electric field is also created in the chamber 20, by applying an electric voltage to the silicon wafer, so that the ions present in the plasma of the plasma chamber 20 are projected onto the silicon wafer, as indicated by the arrows shown. .
  • the parameters of the second doping such as the voltage applied to the silicon wafer, the flow rate of the precursor gases, the ionization current and the pressure that prevails in the plasma chamber 20 are controlled so that the second doping passes through the oxide layer 40 at the level of the small thickness, but not at the level of the thick layer of the oxide layer 40.
  • the control of the mentioned parameters makes it possible to obtain a depth of penetration of the second doping greater than the second thickness of the oxide layer 40, but less than the first thickness of the oxide layer 40.
  • the second doping is therefore:
  • the silicon wafer presents first doped portions 11 during the first doping, and second portions 12 doped during the second doping, which are separated by third undoped portions.
  • the method described above makes it possible to obtain a second doping self aligned with the first doping, without any overlap or overlap of the doped portions.
  • the method according to the invention may then comprise a step consisting in removing the oxide layer 40.
  • This operation may for example be carried out by chemical deoxidation by means of, for example, immersion in a hydrofluoric acid bath (the layer oxide 40 is totally dissolved during the passage in the bath).
  • This passage bath is simple to achieve, cat just let soak the silicon wafer beyond a minimum time of complete dissolution, while ensuring that the acid concentration is sufficient. A simple dripping and drying is then sufficient before proceeding to a later stage of the manufacturing process.
  • an activation annealing of the second doping can be achieved in temperature.
  • the method according to the invention thus makes it possible to dissociate the two activation annealing steps, so that the temperatures chosen will be perfectly adapted to each doping species to be activated.
  • a preferred embodiment of the invention consists in performing the first doping with a first chemical species which requires a first activation annealing at a first temperature, and in performing the second doping with a second chemical species which requires a second annealing of activation at a second temperature, lower than the first temperature.
  • This implementation makes it possible, during the first annealing, to benefit from the highest temperature in order to have a rapid oxide formation, and during the second activation annealing, not to influence the activation of the first doped parts because their temperature activation is not reached.
  • An example of a method for manufacturing a photovoltaic cell is given below:
  • the silicon wafer can be annealed at about 950 ° C, and during this annealing exposure of the 17-minute silicon wafer to oxygen will cause the growth of an oxide layer of about 10 nm. on the undoped portion of the silicon wafer, according to the equations and constants taken from a BE Deal publication "Semiconductor materials and process technology handbook: for very large scale integration (VLSI) and ultra large scale integration (ULSI)" / edited by Gary E. McGuire. (pp 48-57).
  • the oxide layer on the doped portions will be about 20 to 30 nm.
  • Step 2 na doping the rear face can be performed by plasma immersion, with a voltage applied to the silicon wafer of 1 kV to 20kV, a pressure in the chamber comprised between 10 "2 and 10" 7 millibar and an ionization current of 200mA to cross the 10 nm of the oxide layer to the right of undoped portions during 1 doping, and not through the 20 to 30 nm of the oxide layer to the right of the parties doped at 1 doping.
  • the thickness measurements of the SiO 2 oxide layer can be carried out in ellipsometry, or by SIMS analysis, the latter method also being able to obtain the depth of penetration of the doping.
  • an electrical conductivity measurement will make it possible to verify that the second doping has reached the silicon wafer through the oxide layer, and that There is indeed an undoped area between the first doped portions and the second doped portions, which is the purpose of the present invention.

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Abstract

The invention relates to a method for doping a silicon sheet for producing a photovoltaic cell, said method comprising the steps consisting of: carrying out a first doping of at least one first part (11) of a surface (10) of the silicon sheet; forming an oxide layer (40) on the partially doped surface (10); and carrying out a second doping via the oxide layer (40), such that another part (12) of the surface (10) of the silicon sheet is doped.

Description

PROCEDE DE DOPAGE DE PLAQU ES DE SILICI UM  METHOD FOR DOPING PLATES OF SILICI UM
La présente invention concerne de manière générale le dopage de plaques de silicium destinées à former des cellules photovoltaïques pour être montées sur un panneau solaire. The present invention generally relates to the doping of silicon wafers for forming photovoltaic cells to be mounted on a solar panel.
Il est connu dans l'art antérieur de doper séquentiellement les plaques de silicium pour obtenir des cellules photovoltaïques : pour la réalisation de dopages localisés (appelés caissons de dopage) n ou p, les technologies actuelles font appel soit à des technologies de lithographie utilisées en microélectronique soit à des ablations laser, soit par des recuits localisés par laser. En contrepartie, toutes ces techniques sont soit lourdes (nombre de pas de procédé) soit non auto-alignées (c'est-à-dire qu'il faut prévoir de prendre une référence géométrique sur la plaque de silicium avant chaque opération de dopage pour garantir que les parties ultérieurement dopées ne chevaucheront pas celles déjà réalisées et seront bien distinctes). Ensuite il est souvent nécessaire (quand les parties dopées sont réalisées par implantation) de faire un co-recuit d'activation en température, qui est très difficile à mettre au point car les températures d'activation sont différentes entre les parties n (dopé par exemple au Phosphore) ou p (dopé par exemple au Bore). On peut envisager d'effectuer également des dopages avec les espèces suivantes Aluminium, Gallium, Indium, Arsenic ou Antimoine.  It is known in the prior art to dope sequentially the silicon wafers to obtain photovoltaic cells: for the production of localized doping (called doping boxes) n or p, the current technologies use either lithographic technologies used in microelectronics either to laser ablations or by localized laser annealing. In return, all these techniques are either heavy (number of process steps) or not self-aligned (that is to say, it is necessary to provide a geometrical reference on the silicon plate before each doping operation for guarantee that the later doped parts will not overlap with those already realized and will be distinct). Then it is often necessary (when the doped parts are made by implantation) to make a temperature activation co-annealing, which is very difficult to develop because the activation temperatures are different between the parts n (doped by Phosphorus example) or p (doped for example with Boron). One can also consider doping with the following species Aluminum, Gallium, Indium, Arsenic or Antimony.
Un but de la présente invention est de répondre aux inconvénients de l'art antérieur mentionnés ci-dessus et en particulier, tout d'abord, de proposer un procédé de dopage séquentiel de plusieurs parties distinctes d'une plaque de silicium qui ne nécessite pas pour autant d'équipement sophistiqué ou d'opération spécifique de localisation pour éviter le chevauchement des parties dopées. Pour cela un premier aspect de l'invention concerne un procédé de dopage d'une plaque de silicium pour fabriquer une cellule photovoltaïque, le procédé comprenant les étapes consistant à : An object of the present invention is to meet the disadvantages of the prior art mentioned above and in particular, first of all, to propose a method of sequentially doping several distinct parts of a silicon wafer which does not require for as much sophisticated equipment or specific location operation to avoid overlap of the doped parts. For this purpose, a first aspect of the invention relates to a doping method of a silicon wafer for manufacturing a photovoltaic cell, the method comprising the steps of:
- effectuer un premier dopage d'au moins une première partie d'une surface de la plaque de silicium,  to perform a first doping of at least a first part of a surface of the silicon wafer,
- former une couche d'oxyde sur la surface partiellement dopée,  forming an oxide layer on the partially doped surface,
- effectuer un deuxième dopage au travers de la couche d'oxyde, de sorte à doper une autre partie de la surface de la plaque de silicium. Le procédé selon la présente mise en œuvre utilise une propriété bien connue en micro électronique, au sujet de la vitesse de croissance des oxydes sur du silicium. En effet, cette vitesse de croissance d'oxyde de silicium (S1O2) est supérieure sur les premières parties de la surface exposées au premier dopage. En d'autres termes, la couche d'oxyde est plus épaisse sur les premières parties dopées que sur le reste de la surface de la plaque de silicium, ce qui présente une barrière supplémentaire au deuxième dopage. Il en résulte que le deuxième dopage réalisé sur la totalité de la couche d'oxyde ne sera effectif que sur une partie du reste de la surface de la plaque de silicium, car il est réalisé de sorte à pénétrer la faible épaisseur de la couche d'oxyde, et pas la couche épaisse d'oxyde au droit des premières parties dopées. Il en résulte que la couche d'oxyde agit comme un masque pour le deuxième dopage, et ce masque couvre naturellement les premières parties dopées. On obtient des deuxièmes parties dopées auto alignées aux premières parties dopées, grâce à la couche d'oxyde formée sur la surface de la plaque de silicium préalablement au deuxième dopage. Il n'y a donc aucun masque appliqué sur la plaque de silicium préalablement au deuxième dopage pour obtenir des zones dopées de nature différente. Il n'y a également aucun décapage ou retrait d'oxydes entre le premier et le deuxième dopage, ce qui améliore le procédé complet de fabrication et simplifie la chaîne de fabrication.  - Perform a second doping through the oxide layer, so as to dope another part of the surface of the silicon wafer. The method according to the present implementation uses a property well known in microelectronics, about the growth rate of oxides on silicon. Indeed, this growth rate of silicon oxide (S1O2) is higher on the first parts of the surface exposed to the first doping. In other words, the oxide layer is thicker on the first doped portions than on the remainder of the surface of the silicon wafer, which presents an additional barrier to the second doping. As a result, the second doping carried out on the entire oxide layer will be effective only on a part of the remainder of the surface of the silicon wafer, because it is made so as to penetrate the small thickness of the layer of silicon. oxide, and not the thick layer of oxide to the right of the first doped parts. As a result, the oxide layer acts as a mask for the second doping, and this mask naturally covers the first doped portions. Self-aligned second doped portions are obtained at the first doped portions by virtue of the oxide layer formed on the surface of the silicon wafer prior to the second doping. There is therefore no mask applied to the silicon wafer before the second doping to obtain doped zones of different nature. There is also no stripping or removal of oxides between the first and second doping, which improves the complete manufacturing process and simplifies the production line.
Si par exemple le premier dopage consiste à obtenir des lignes dopées espacées, alors le deuxième dopage ne pénétrera pas la couche d'oxydes au droit des premières parties dopées (car la couche d'oxydes est localement plus épaisse), mais traversera cette couche d'oxydes formée entre les première parties dopées (car la couche d'oxydes est localement moins épaisse sur le silicium non dopé), et dopera donc la plaque de silicium à ces endroits. On obtient, sans masque ni décapage intermédiaire, des deuxième parties dopées qui sont des lignes auto alignées sur les premières parties dopées. If, for example, the first doping consists in obtaining spaced doped lines, then the second doping will not penetrate the oxide layer to the right of the first doped portions (because the oxide layer is locally thicker), but will cross the oxide layer formed between the first doped portions (because the oxide layer is locally less thick on undoped silicon), and thus doping the silicon wafer at these locations. Non-masked or intermediate stripping results in second doped portions which are self-aligned lines on the first doped portions.
D'une manière générale, il n'y a donc pas de gravure ni décapage partiel de la couche d'oxydes formée après le premier dopage, pour effectuer le deuxième dopage sur une partie seulement de la plaque de silicium. C'est la couche d'oxydes qui forme ce masque sans opération spécifique, car la formation d'oxydes est plus importante sur les parties de silicium qui ont reçues le premier dopage. Le procédé est donc caractérisé par son faible nombre d'opérations.  In general, there is therefore no etching or partial etching of the oxide layer formed after the first doping, to perform the second doping on only a portion of the silicon wafer. It is the oxide layer that forms this mask without a specific operation, because the formation of oxides is greater on the silicon parts that received the first doping. The process is therefore characterized by its small number of operations.
Selon un mode de réalisation, l'étape consistant à former une couche d'oxyde est comprise dans une étape de recuit d'activation de la première partie dopée. On combine avantageusement le recuit d'activation des premières parties dopées avec la formation de la couche d'oxyde. Une seule étape permet d'activer la première partie dopée, et de former la couche d'oxydes.  According to one embodiment, the step of forming an oxide layer is included in an activation annealing step of the first doped portion. The activation annealing of the first doped portions is advantageously combined with the formation of the oxide layer. A single step activates the first doped portion, and form the oxide layer.
Selon un mode de réalisation, l'étape consistant à former une couche d'oxyde comprend une étape de chauffage sous atmosphère enrichie en oxygène. La formation de la couche d'oxyde est accélérée et mieux contrôlée.  According to one embodiment, the step of forming an oxide layer comprises a heating step in an oxygen enriched atmosphere. The formation of the oxide layer is accelerated and better controlled.
Selon un mode de réalisation, l'étape consistant à effectuer le deuxième dopage est une étape consistant à effectuer un dopage sur une profondeur de pénétration prédéterminée.  According to one embodiment, the step of performing the second doping is a step of doping on a predetermined penetration depth.
Selon un mode de réalisation, l'étape consistant à former une couche d'oxyde est une étape conduisant à former une première épaisseur d'oxyde au droit de la première partie dopée, et une deuxième épaisseur d'oxyde sur le reste de la surface, inférieure à la première épaisseur d'oxyde, - et la profondeur de pénétration est comprise entre la première épaisseur d'oxyde et la deuxième épaisseur d'oxyde. La présente mise en œuvre garantit un procédé optimal. En effet, le deuxième dopage n'affecte pas les premières parties dopées, car il ne traverse pas la couche d'oxyde dans les zones de forte épaisseur, et atteint les parties non dopées de la plaque de silicium car il traverse la couche d'oxyde dans les zones de faible épaisseur. According to one embodiment, the step of forming an oxide layer is a step leading to form a first oxide thickness in line with the first doped portion, and a second oxide thickness on the remainder of the surface less than the first oxide thickness, and the depth of penetration is between the first oxide thickness and the second oxide thickness. The present implementation guarantees an optimal process. Indeed, the second doping does not affect the first doped parts, because it does not cross the oxide layer in the thick areas, and reaches the undoped portions of the silicon wafer because it passes through the layer of oxide in thin areas.
Selon un mode de réalisation, l'étape consistant à effectuer le premier dopage est réalisée en immersion plasma. Cette étape de procédé peut être réalisée avec des équipements plus simples qu'un canon à plasma par exemple.  According to one embodiment, the step of performing the first doping is performed by plasma immersion. This process step can be performed with simpler equipment than a plasma gun, for example.
Selon un mode de réalisation, l'étape consistant à effectuer le deuxième dopage est réalisée en immersion plasma. Cette étape de procédé peut être réalisée avec des équipements plus simples qu'un canon à plasma par exemple.  According to one embodiment, the step of performing the second doping is performed by plasma immersion. This process step can be performed with simpler equipment than a plasma gun, for example.
Selon un mode de réalisation, l'étape consistant à effectuer le premier dopage et/ou l'étape consistant à effectuer le deuxième dopage est réalisée en immersion plasma.  According to one embodiment, the step of performing the first doping and / or the step of performing the second doping is performed by plasma immersion.
Selon un mode de réalisation, l'étape consistant à effectuer le deuxième dopage est suivie d'une étape de recuit d'activation du deuxième dopage. Le fonctionnement de la cellule photovoltaïque sera optimal.  According to one embodiment, the step of performing the second doping is followed by an activating annealing step of the second doping. The operation of the photovoltaic cell will be optimal.
Selon un mode de réalisation, l'étape consistant à effectuer le premier dopage est une étape de dopage du silicium avec une première espèce nécessitant un recuit d'activation à une première température, et l'étape consistant à effectuer le deuxième dopage est une étape de dopage du silicium avec une deuxième espèce nécessitant un recuit d'activation à une deuxième température, inférieure à la première température. Chaque dopage nécessite un recuit d'activation à une température spécifique. Il résulte de cette mise en œuvre que la température du deuxième recuit d'activation étant plus faible que celle du premier recuit d'activation, elle n'influencera pas les propriété des premières parties dopées. Selon un mode de réalisation, l'étape consistant à effectuer le premier dopage est une étape de dopage du silicium avec du bore, et l'étape consistant à effectuer le deuxième dopage est une étape de dopage du silicium avec du phosphore. Chaque dopage nécessite un recuit d'activation à une température spécifique. La température idéale de recuit d'un dopage au bore est supérieure à celle du recuit d'activation au phosphore. Il résulte de cette mise en œuvre que la température du deuxième recuit d'activation étant plus faible que celle du premier recuit d'activation, elle n'influencera pas les propriétés des premières parties dopées. According to one embodiment, the step of performing the first doping is a silicon doping step with a first species requiring activation annealing at a first temperature, and the step of performing the second doping is a step doping silicon with a second species requiring activation annealing at a second temperature, lower than the first temperature. Each doping requires activation annealing at a specific temperature. As a result of this implementation, since the temperature of the second activation annealing is lower than that of the first activation annealing, it will not influence the properties of the first doped portions. According to one embodiment, the step of performing the first doping is a step of doping silicon with boron, and the step of performing the second doping is a step of doping silicon with phosphorus. Each doping requires activation annealing at a specific temperature. The ideal annealing temperature of boron doping is greater than that of phosphorus activation annealing. As a result of this implementation, since the temperature of the second activation annealing is lower than that of the first activation annealing, it will not influence the properties of the first doped portions.
Selon un mode de réalisation, l'étape consistant à effectuer un deuxième dopage est suivie d'une étape consistant à retirer la couche d'oxyde. Cette étape consiste à retirer toute la couche d'oxyde en une seule fois, de sorte que la cellule est alors prête pour les étapes suivantes de fabrication de la cellule photovoltaïque.  According to one embodiment, the step of performing a second doping is followed by a step of removing the oxide layer. This step consists in removing the entire oxide layer at one time, so that the cell is then ready for the following steps of manufacturing the photovoltaic cell.
Selon un mode de réalisation, l'étape consistant à retirer la couche d'oxyde est une étape de désoxydation chimique dans un bain comprenant de l'acide fluorhydrique. Cette mise en œuvre est rapide et simple, toute la couche d'oxyde de silicium est retirée en une seule fois, sans précautions particulières.  According to one embodiment, the step of removing the oxide layer is a chemical deoxidation step in a bath comprising hydrofluoric acid. This implementation is fast and simple, the entire layer of silicon oxide is removed at one time, without special precautions.
Un second aspect de l'invention est une cellule photovoltaïque présentant un dopage réalisé selon le premier aspect de l'invention.  A second aspect of the invention is a photovoltaic cell having a doping produced according to the first aspect of the invention.
Un dernier aspect de l'invention est un panneau solaire comportant au moins une cellule photovoltaïque selon le deuxième aspect de l'invention.  A final aspect of the invention is a solar panel comprising at least one photovoltaic cell according to the second aspect of the invention.
D'autres caractéristiques et avantages de la présente invention apparaîtront plus clairement à la lecture de la description détaillée qui suit d'un mode de réalisation de l'invention donné à titre d'exemple nullement limitatif et illustré par les dessins annexés, dans lesquels :  Other features and advantages of the present invention will appear more clearly on reading the following detailed description of an embodiment of the invention given by way of non-limiting example and illustrated by the appended drawings, in which:
- la figure 1 représente une coupe d'une plaque de silicium pendant une première étape du procédé selon l'invention ; - la figure 2 représente la coupe de la plaque de silicium de la figure 1 pendant une deuxième étape du procédé selon l'invention ; - Figure 1 shows a section of a silicon wafer during a first step of the method according to the invention; - Figure 2 shows the section of the silicon plate of Figure 1 during a second step of the method according to the invention;
- la figure 3 représente la coupe de la plaque de silicium de la figure 1 pendant une troisième étape du procédé selon l'invention.  - Figure 3 shows the section of the silicon plate of Figure 1 during a third step of the method according to the invention.
La croissance d'oxyde de silicium sur un plaque de silicium partiellement dopée est décrite dans une publication de Biermann, E. : "Silicon Oxidation Rate Dependence on Dopant Pile-up," Solid State Device Research Conférence, 1989. ESSDERC '89. 19th European , vol., no., pp.49,52, 11-14 Sept. 1989  The growth of silicon oxide on a partially doped silicon plate is described in a Biermann, E. publication: "Silicon Oxidation Rate Dependence on Dopant Pile-up," Solid State Device Research Conference, 1989. ESSDERC '89. 19th European, vol., No., Pp.49,52, 11-14 Sept. 1989
L'abrégé peut être trouvé à l'URL:  The abstract can be found at the URL:
http://ieeexplore.ieee. org/stamp/stamp.jsp?tp=&arnumber=5436671&i snumber=5436370  http://ieeexplore.ieee. org / stamp / stamp.jsp? tp = & arnumber = 5436671 & i snumber = 5436370
La figure 1 représente une plaque de silicium vue en coupe, lors d'une première étape du procédé selon l'invention.  FIG. 1 shows a silicon plate seen in section, during a first step of the method according to the invention.
Cette première étape consiste à doper des premières parties 11 d'une surface 10 de la plaque de silicium, avec une première espèce chimique. Le procédé de dopage utilisé est un dopage en immersion plasma P1 , comme décrit par exemple dans le document WO2012168575 A2. Dans le but de créer un premier dopage partiel, la plaque de silicium est placée dans une chambre plasma 20 et un masque 30 est appliqué sur la face 10 de la plaque de silicium. Ce masque 30 comprend des ouvertures 31 et des parties pleines 32 qui ont pour but de ne permettre au plasma généré dans la chambre plasma 20 de ne baigner que les premières parties 11 de la plaque de silicium qui sont en regard des ouvertures 31 du masque 30. Pour implanter la première espèce chimique ionisée dans la chambre 20, une tension électrique est appliquée à la plaque de silicium, de sorte qu'un champ électrique force les ions de la première espèce chimique à s'implanter dans la plaque de silicium, dans les premières parties 11 qui sont laissées libres par les ouvertures 31 de la plaque 30, comme le montrent les flèches représentées. Comme représenté sur la figure 1 , la plaque de silicium est donc dopée avec une première espèce chimique sur les premières parties 11 de la plaque de silicium. This first step consists of doping the first portions 11 of a surface 10 of the silicon wafer, with a first chemical species. The doping method used is plasma immersion doping P1, as described for example in WO2012168575 A2. In order to create a first partial doping, the silicon wafer is placed in a plasma chamber 20 and a mask 30 is applied to the face 10 of the silicon wafer. This mask 30 comprises openings 31 and solid portions 32 which are intended to allow the plasma generated in the plasma chamber 20 to bathe only the first portions 11 of the silicon wafer which are opposite openings 31 of the mask 30. To implant the first ionized chemical species in the chamber 20, an electrical voltage is applied to the silicon wafer, so that an electric field forces the ions of the first chemical species to implant in the silicon wafer, in the first parts 11 which are left free by the openings 31 of the plate 30, as shown by the arrows shown. As shown in FIG. 1, the silicon wafer is therefore doped with a first chemical species on the first portions 11 of the silicon wafer.
La figure 2 représente une deuxième étape du procédé selon l'invention, pendant laquelle une couche d'oxyde 40 est créée sur la surface 10 de la plaque de silicium partiellement dopée. Comme la surface 10 présente des premières parties 11 dopées, les propriétés de cette surface 10 sont hétérogènes, en particulier en ce qui concerne la réactivité avec l'oxygène. En effet, la création d'oxydes sur les premières parties 11 est plus rapide que sur le reste de la surface 10 de la plaque de silicium.  FIG. 2 represents a second step of the method according to the invention, during which an oxide layer 40 is created on the surface 10 of the partially doped silicon plate. Since the surface 10 has doped first portions 11, the properties of this surface 10 are heterogeneous, particularly with respect to reactivity with oxygen. Indeed, the creation of oxides on the first parts 11 is faster than on the rest of the surface 10 of the silicon wafer.
La deuxième étape du procédé comprend une exposition de la surface 10 à l'oxygène 02 dans une enceinte 50, en température, afin d'accélérer la croissance de dioxyde de silicium sur la surface 10. Lors de cette création de couche d'oxyde 40 sur la surface 10 de la plaque de silicium, la croissance est donc plus rapide au niveau des premières parties 11 dopées que sur le reste de la surface 10 de la plaque de silicium. La demanderesse s'est aperçue que l'épaisseur de la couche d'oxyde 40 est deux à trois fois plus importante au niveau des premières parties 11 dopées que sur le reste de la surface 10, si le premier dopage est réalisé avec du bore ou du phosphore par exemple. The second step of the process comprises exposing the surface 10 to the oxygen 0 2 in a chamber 50, in temperature, to accelerate the growth of silicon dioxide on the surface 10. During this creation of oxide layer 40 on the surface 10 of the silicon wafer, the growth is therefore faster at the first doped portions 11 than on the rest of the surface 10 of the silicon wafer. The Applicant has found that the thickness of the oxide layer 40 is two to three times greater at the level of the first doped portions 11 than at the remainder of the surface 10, if the first doping is carried out with boron or phosphorus for example.
L'étape de création de la couche d'oxyde 40 est contrôlée en temps, température et débit d'oxygène, afin d'obtenir une couche d'oxyde 40 qui a une première épaisseur E1 allant de 10nm à 60 nm au niveau des premières parties 11 dopées, et une deuxième épaisseur E2 allant de 4nm à 20nm au niveau du reste de la surface 10. Au niveau du passage entre les premières parties dopées 11 et le reste de la surface 10 de la plaque de silicium, l'épaisseur de la couche d'oxyde 40 passe progressivement de la première épaisseur importante à la deuxième épaisseur faible, comme le montre la figure 2.  The step of creating the oxide layer 40 is controlled in time, temperature and oxygen flow rate, in order to obtain an oxide layer 40 which has a first thickness E1 ranging from 10 nm to 60 nm at the level of the first doped portions 11, and a second thickness E2 ranging from 4 nm to 20 nm at the remainder of the surface 10. At the passage between the first doped portions 11 and the remainder of the surface 10 of the silicon wafer, the thickness of the the oxide layer 40 passes progressively from the first substantial thickness to the second low thickness, as shown in FIG.
Afin d'augmenter l'efficacité de la cellule photovoltaïque qui sera fabriquée avec la plaque de silicium, il faut activer les premières parties 11 dopées avec un recuit d'activation en température, et une mise en œuvre astucieuse consiste à intégrer l'étape de création de la couche d'oxyde 40 lors de l'étape de recuit d'activation en température. In order to increase the efficiency of the photovoltaic cell that will be manufactured with the silicon wafer, it is necessary to activate the first parts 11 doped with a temperature activation annealing, and a clever implementation consists in integrating the step of creating the oxide layer 40 during the temperature activation annealing step.
La figure 3 représente une troisième étape du procédé selon l'invention. Un deuxième dopage est réalisé, directement sur la plaque de silicium oxydée, au travers de la couche d'oxyde 40. A cet effet, une nouvelle immersion plasma P2 dans la chambre 20 peut être réalisée, mais sans masque sur la plaque de silicium, car le procédé selon l'invention utilise la couche d'oxyde 40 comme masque. Un champ électrique est également crée dans la chambre 20, en appliquant une tension électrique à la plaque de silicium, de sorte que les ions présents dans le plasma de la chambre plasma 20 soient projetés sur la plaque de silicium, comme indiqué par les flèches représentées. Il est important de garantir que le deuxième dopage n'atteigne la surface 10 de la plaque de silicium que sur une partie du reste de la surface 10, et sans atteindre les premières parties 11 dopées, ni la partie de la surface 10 immédiatement adjacente aux premières parties 11. A cet effet, les paramètres du deuxième dopage tels que la tension appliquées à la plaque de silicium, le débit des gaz précurseurs, le courant d'ionisation et la pression qui règne dans la chambre plasma 20 sont contrôlés de sorte que le deuxième dopage passe au travers de la couche d'oxyde 40 au niveau de la faible épaisseur, mais pas au niveau de la forte épaisseur de la couche d'oxyde 40. Le contrôle des paramètres mentionnés permet d'obtenir une profondeur de pénétration du deuxième dopage supérieure à la deuxième épaisseur de la couche d'oxyde 40, mais inférieure à la première épaisseur de la couche d'oxyde 40. Le deuxième dopage est donc :  FIG. 3 represents a third step of the method according to the invention. A second doping is performed, directly on the oxidized silicon plate, through the oxide layer 40. For this purpose, a new plasma immersion P2 in the chamber 20 can be performed, but without a mask on the silicon wafer, because the process according to the invention uses the oxide layer 40 as a mask. An electric field is also created in the chamber 20, by applying an electric voltage to the silicon wafer, so that the ions present in the plasma of the plasma chamber 20 are projected onto the silicon wafer, as indicated by the arrows shown. . It is important to ensure that the second doping reaches the surface of the silicon wafer only over a portion of the remainder of the surface 10, and without reaching the first doped portions 11, nor the portion of the surface 10 immediately adjacent to the first parts 11. For this purpose, the parameters of the second doping such as the voltage applied to the silicon wafer, the flow rate of the precursor gases, the ionization current and the pressure that prevails in the plasma chamber 20 are controlled so that the second doping passes through the oxide layer 40 at the level of the small thickness, but not at the level of the thick layer of the oxide layer 40. The control of the mentioned parameters makes it possible to obtain a depth of penetration of the second doping greater than the second thickness of the oxide layer 40, but less than the first thickness of the oxide layer 40. The second doping is therefore:
- strictement limité à la couche d'oxyde 40 au droit des premières parties 11 dopées, ainsi qu'à leur proximité immédiate, - strictly limited to the oxide layer 40 to the right of the first doped parts 11, as well as to their immediate vicinity,
- complètement traversant de la couche d'oxyde 40, et pénètre une partie de la plaque de silicium sur le reste de la surface 10. - completely through the oxide layer 40, and penetrates a portion of the silicon wafer on the rest of the surface 10.
Comme représenté à la figure 3 par le trait en pointillés, à la fin de l'étape de deuxième dopage, la plaque de silicium présente des premières parties 11 dopées iors du premier dopage, et des deuxièmes parties 12 dopées lors du deuxième dopage, qui sont séparées par des troisièmes parties non dopées. Le procédé décrit ci-dessus permet d'obtenir un deuxième dopage auto aligné sur le premier dopage, sans aucun chevauchement ni recouvrement des parties dopées. As represented in FIG. 3 by the dotted line, at the end of the second doping step, the silicon wafer presents first doped portions 11 during the first doping, and second portions 12 doped during the second doping, which are separated by third undoped portions. The method described above makes it possible to obtain a second doping self aligned with the first doping, without any overlap or overlap of the doped portions.
Le procédé selon l'invention peut ensuite comprendre une étape qui consiste à retirer la couche d'oxyde 40. On peut par exemple réaliser cette opération par désoxydation chimique au moyen par exemple d'une immersion dans un bain d'acide fluorhydrique (la couche d'oxyde 40 est totalement dissoute lors du passage dans le bain). Ce passage en bain est simple à réaliser, cat il suffit de laisser tremper la plaque de silicium au-delà d'un temps minimal de dissolution complète, tout en s'assurant que la concentration en acide est suffisante. Un simple égouttage et séchage suffit ensuite avant de passer à une étape ultérieure du procédé de fabrication.  The method according to the invention may then comprise a step consisting in removing the oxide layer 40. This operation may for example be carried out by chemical deoxidation by means of, for example, immersion in a hydrofluoric acid bath (the layer oxide 40 is totally dissolved during the passage in the bath). This passage bath is simple to achieve, cat just let soak the silicon wafer beyond a minimum time of complete dissolution, while ensuring that the acid concentration is sufficient. A simple dripping and drying is then sufficient before proceeding to a later stage of the manufacturing process.
De plus, pour garantir une bonne efficacité à la cellule photovoltaïque qui sera obtenue avec la plaque de silicium, un recuit d'activation du deuxième dopage peut être réalisé en température.  In addition, to ensure good efficiency of the photovoltaic cell that will be obtained with the silicon wafer, an activation annealing of the second doping can be achieved in temperature.
Le procédé selon l'invention permet donc de dissocier les deux étapes de recuit d'activation, de sorte que les températures choisies seront parfaitement adaptées à chaque espèce dopante à activer.  The method according to the invention thus makes it possible to dissociate the two activation annealing steps, so that the temperatures chosen will be perfectly adapted to each doping species to be activated.
Une mise en œuvre préférée de l'invention consiste à effectuer le premier dopage avec une première espèce chimique qui nécessite un premier recuit d'activation à une première température, et à effectuer le deuxième dopage avec une deuxième espèce chimique qui nécessite un deuxième recuit d'activation à une deuxième température, inférieure à la première température.  A preferred embodiment of the invention consists in performing the first doping with a first chemical species which requires a first activation annealing at a first temperature, and in performing the second doping with a second chemical species which requires a second annealing of activation at a second temperature, lower than the first temperature.
Cette mise en œuvre permet, lors du premier recuit de bénéficier de la température la plus haute pour avoir une formation d'oxyde rapide, et lors du deuxième recuit d'activation, de ne pas influencer l'activation des premières parties dopées car leur température d'activation n'est pas atteinte. Un exemple de procédé pour fabriquer une cellule photovoltaïque est donné ci-dessous : This implementation makes it possible, during the first annealing, to benefit from the highest temperature in order to have a rapid oxide formation, and during the second activation annealing, not to influence the activation of the first doped parts because their temperature activation is not reached. An example of a method for manufacturing a photovoltaic cell is given below:
1- texturation/polissage des plaques de silicium (par exemple texturation entre 5pm et 15 pm et pour le polissage entre 5pm et 15pm) ;  1- texturing / polishing of the silicon wafers (for example texturing between 5pm and 15 pm and for polishing between 5pm and 15pm);
2- 1er dopage par implantation masquée de Bore sur la face arrière ;2- 1st doping by masked implantation of Bore on the back face;
3- recuit d'activation du 1er dopage et oxydation de la plaque de Silicium ; 3- activation annealing 1 doping and oxidation of the silicon plate;
Pendant cette étape, on peut recuire la plaque de silicium à environ 950°C, et pendant ce recuit, une exposition de la plaque de silicium de 17 minutes à l'oxygène provoquera la croissance d'une couche d'oxyde de 10 nm environ sur la partie non dopée de la plaque de silicium, selon les équations et constantes tirées d'une publication de B. E. Deal " Semiconductor materials and process technology handbook : for very large scale intégration (VLSI) and ultra large scale intégration (ULSI)" / édité par Gary E. McGuire. (pp. 48-57). La couche d'oxyde sur les parties dopées sera d'environ 20 à 30 nm.  During this step, the silicon wafer can be annealed at about 950 ° C, and during this annealing exposure of the 17-minute silicon wafer to oxygen will cause the growth of an oxide layer of about 10 nm. on the undoped portion of the silicon wafer, according to the equations and constants taken from a BE Deal publication "Semiconductor materials and process technology handbook: for very large scale integration (VLSI) and ultra large scale integration (ULSI)" / edited by Gary E. McGuire. (pp 48-57). The oxide layer on the doped portions will be about 20 to 30 nm.
4- 2nd dopage par implantation pleine tranche face avant et arrière de Phosphore ; 4- 2nd doping by implantation full wafer front and back of Phosphorus;
L'étape de 2nd dopage de la face arrière peut être donc effectuée en immersion plasma, avec une tension appliquée à la plaque de silicium de 1 kV à 20kV, une pression dans la chambre comprise entre 10"2 et 10"7 millibar et un courant d'ionisation de 200mA, pour traverser les 10 nm de la couche d'oxyde au droit des parties non dopées lors du 1er dopage, et pour ne pas traverser les 20 à 30nm de la couche d'oxyde au droit des parties dopées lors du 1er dopage. Step 2 na doping the rear face can be performed by plasma immersion, with a voltage applied to the silicon wafer of 1 kV to 20kV, a pressure in the chamber comprised between 10 "2 and 10" 7 millibar and an ionization current of 200mA to cross the 10 nm of the oxide layer to the right of undoped portions during 1 doping, and not through the 20 to 30 nm of the oxide layer to the right of the parties doped at 1 doping.
5- retrait de la couche d'oxyde dans un bain d'acide fluorhydrique à une concentration de 0,5 à 20% pendant une durée de 1 à 120 s ;  5- removal of the oxide layer in a hydrofluoric acid bath at a concentration of 0.5 to 20% for a period of 1 to 120 s;
6- recuit d'activation/oxydation du 2nd dopage à 850°C environ pendant 10 à 60 minutes ; 7- dépôt d'une couche de passivation/isolation sur la face arrière (par exemple une couche de Si3N4 d'épaisseur allant de 20nm à 220 nm) ; Activation / oxidation annealing of the 2 nd doping at about 850 ° C for 10 to 60 minutes; 7- deposition of a passivation / isolation layer on the rear face (for example a Si3N4 layer with a thickness ranging from 20 nm to 220 nm);
8- dépôt d'une couche de passivation/ anti-réflecteur en face avant (par exemple d'une épaisseur de Si3N4 de 50 à 90 nm) ;  8- depositing a passivation / anti-reflective layer on the front face (for example with a Si3N4 thickness of 50 to 90 nm);
9- prise de contact sur les doigts par sérigraphie et recuit (pâtes d'argent avec frite sur les doigts et sans frite sur les collecteurs, recuit entre 750°C et 950 °C pendant 1s à 60 s).  9- making contact on the fingers by serigraphy and annealing (silver pastes with fries on the fingers and without fries on the collectors, annealing between 750 ° C and 950 ° C for 1s to 60 s).
Les mesures d'épaisseur de la couche d'oxyde SiO2 peuvent être effectuées en ellipsomètrie, ou par analyse SIMS, cette dernière méthode pouvant également permettre d'obtenir la profondeur de pénétration du dopage. Par contre, pour vérifier qu'une partie de la plaque de silicium est effectivement dopée, une mesure de conductivité électrique permettra de vérifier que le deuxième dopage a bien atteint la plaque de silicium au travers de la couche d'oxyde, et qu'il y a bien une zone non dopée entre les premières parties dopées et les deuxièmes parties dopées, ce qui est le but de la présente invention.. The thickness measurements of the SiO 2 oxide layer can be carried out in ellipsometry, or by SIMS analysis, the latter method also being able to obtain the depth of penetration of the doping. On the other hand, to verify that a portion of the silicon wafer is actually doped, an electrical conductivity measurement will make it possible to verify that the second doping has reached the silicon wafer through the oxide layer, and that There is indeed an undoped area between the first doped portions and the second doped portions, which is the purpose of the present invention.
On comprendra que diverses modifications et/ou améliorations évidentes pour l'homme du métier peuvent être apportées aux différents modes de réalisation de l'invention décrits dans la présente description sans sortir du cadre de l'invention défini par les revendications annexées.  It will be understood that various modifications and / or improvements obvious to those skilled in the art can be made to the various embodiments of the invention described in the present description without departing from the scope of the invention defined by the appended claims.

Claims

REVEN DICATIONS REVEN DICATIONS
1. Procédé de dopage d'une plaque de silicium pour fabriquer une cellule photovoltaïque, le procédé comprenant les étapes consistant à : A method of doping a silicon wafer to make a photovoltaic cell, the method comprising the steps of:
- effectuer un premier dopage d'au moins une première partie (11) d'une surface (10) de la plaque de silicium,  - performing a first doping of at least a first portion (11) of a surface (10) of the silicon wafer,
- former une couche d'oxyde (40) sur la surface (10) partiellement dopée, forming an oxide layer (40) on the partially doped surface (10),
- effectuer un deuxième dopage au travers de la couche d'oxyde (40), de sorte à doper une autre partie (12) de la surface (10) de la plaque de silicium. - Performing a second doping through the oxide layer (40), so as to dope another portion (12) of the surface (10) of the silicon wafer.
2. Procédé de dopage selon la revendication précédente, dans lequel l'étape consistant à former une couche d'oxyde (40) est comprise dans une étape de recuit d'activation de la première partie (11) dopée.  2. Doping process according to the preceding claim, wherein the step of forming an oxide layer (40) is included in an activation annealing step of the first portion (11) doped.
3. Procédé de dopage selon l'une des revendications précédentes, dans lequel l'étape consistant à former une couche d'oxyde (40) comprend une étape de chauffage sous atmosphère enrichie en oxygène.  The doping method according to one of the preceding claims, wherein the step of forming an oxide layer (40) comprises a step of heating in an oxygen enriched atmosphere.
4. Procédé de dopage selon l'une des revendications précédentes, dans lequel l'étape consistant à effectuer le deuxième dopage est une étape consistant à effectuer un dopage sur une profondeur de pénétration (P) prédéterminée.  The doping method according to one of the preceding claims, wherein the step of performing the second doping is a step of doping over a predetermined penetration depth (P).
5. Procédé de dopage selon la revendication précédente,  5. Doping method according to the preceding claim,
- dans lequel l'étape consistant à former une couche d'oxyde (40) est une étape conduisant à former une première épaisseur (E1) d'oxyde au droit de la première partie dopée, et une deuxième épaisseur (E2) d'oxyde sur le reste de la surface (10), inférieure à la première épaisseur (E1) d'oxyde, wherein the step of forming an oxide layer (40) is a step of forming a first oxide (E1) thickness at the first doped portion, and a second oxide (E2) thickness on the remainder of the surface (10), smaller than the first thickness (E1) of oxide,
- et dans lequel la profondeur de pénétration (P) est comprise entre la première épaisseur (E1) d'oxyde et la deuxième épaisseur (E2) d'oxyde. and wherein the penetration depth (P) is between the first oxide thickness (E1) and the second oxide thickness (E2).
6. Procédé de dopage selon l'une des revendications précédentes, dans lequel l'étape consistant à effectuer le premier dopage et/ou l'étape consistant à effectuer le deuxième dopage est réalisée en immersion plasma. 6. Doping method according to one of the preceding claims, wherein the step of performing the first doping and / or the step of performing the second doping is performed by plasma immersion.
7. Procédé de dopage selon l'une des revendications précédentes, dans lequel l'étape consistant à effectuer le deuxième dopage est suivie d'une étape de recuit d'activation du deuxième dopage.  The doping method according to one of the preceding claims, wherein the step of performing the second doping is followed by an activating annealing step of the second doping.
8. Procédé de dopage selon l'une des revendications précédentes, dans lequel :  8. Doping method according to one of the preceding claims, wherein:
- l'étape consistant à effectuer le premier dopage est une étape de dopage du silicium avec une première espèce nécessitant un recuit d'activation à une première température, the step of performing the first doping is a step of doping silicon with a first species requiring activation annealing at a first temperature,
- l'étape consistant à effectuer le deuxième dopage est une étape de dopage du silicium avec une deuxième espèce nécessitant un recuit d'activation à une deuxième température, inférieure à la première température.  the step of performing the second doping is a step of doping silicon with a second species requiring activation annealing at a second temperature, lower than the first temperature.
9. Procédé de dopage selon la revendication précédente, dans lequel :  9. Doping method according to the preceding claim, wherein:
- l'étape consistant à effectuer le premier dopage est une étape de dopage du silicium avec du bore,  the step of performing the first doping is a step of doping silicon with boron,
- l'étape consistant à effectuer le deuxième dopage est une étape de dopage du silicium avec du phosphore. the step of performing the second doping is a step of doping silicon with phosphorus.
10. Procédé de dopage selon l'une des revendications précédentes, dans lequel l'étape consistant à effectuer un deuxième dopage est suivie d'une étape consistant à retirer la couche d'oxyde (40).  The doping method according to one of the preceding claims, wherein the step of performing a second doping is followed by a step of removing the oxide layer (40).
11. Procédé de dopage selon la revendication précédente, dans lequel l'étape consistant à retirer la couche d'oxyde (40) est une étape de désoxydation chimique dans un bain comprenant de l'acide fluorhydrique.  11. Doping process according to the preceding claim, wherein the step of removing the oxide layer (40) is a chemical deoxidation step in a bath comprising hydrofluoric acid.
12. Cellule photovoltaïque présentant un dopage réalisé selon le procédé de l'une des revendications précédentes. Photovoltaic cell having a doping produced according to the method of one of the preceding claims.
13. Panneau solaire comportant au moins une cellule photovoltaïque selon la revendication précédente. 13. Solar panel comprising at least one photovoltaic cell according to the preceding claim.
EP14711268.4A 2013-03-20 2014-03-20 Method for doping silicon sheets Withdrawn EP2976782A1 (en)

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FR1300650A FR3003687B1 (en) 2013-03-20 2013-03-20 METHOD FOR DOPING SILICON PLATES
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